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AAS Publishing

Editor’s Note: There’s a lot of discussion in the scientific community right now about topics like open access, preprint servers, and the role of scientific journals in the evolving academic publishing landscape. The following article, which is reproduced here from the new AAS journals website, explores the AAS journals business model in the context of these conversations.

The American Astronomical Society is a nonprofit professional society for astronomers that is somewhat unusual in owning and having complete editorial control over its own journals. The AAS prides itself on the fact that these journals — The Astronomical Journal, The Astrophysical Journal, The Astrophysical Journal Letters, and The Astrophysical Journal Supplement Series — are run by scientists, for scientists. But in the age of the internet, when anything can be posted online and viewed around the world, what is the value and role of a scientific journal?

We recently sent out a survey asking authors for feedback on the AAS journals. We’re carefully studying the thousands of responses we received with an eye to improving the journal offerings — but in the meantime, we thought this would be a good opportunity to clarify the AAS journals business model.

Our Business Model

Realistically speaking, it’s not possible to publish a journal without money. As the AAS is not a commercial publisher, it has no source of external funding for its journals. Money within the AAS is generally divided into separate pools: dues and meeting fees are fed back into the Society, whereas the journal operating costs and development are supported by journal revenue. As a result, there are only two potential revenue streams that the AAS journals can use to meet operating costs: author fees and subscription fees.

To completely eliminate author fees (free to publish), the entire operating cost must be shouldered by subscribing institutes — which can be a significant hardship, particularly for smaller institutes whose libraries may not have a large budget. Because the AAS is committed to providing broad access to our authors’ work, dramatically increasing subscription fees to eliminate author fees is not currently an option.

Instead, the AAS has had a combination revenue stream for decades, meeting part of the journal operating costs via author fees and the other part through subscription fees. With such a model, the Society is able to adapt to fluctuating economic times both nationally and internationally, adjusting its fee scale as the scientific funding landscape changes.

journal revenue

History of annual institutional subscription rates for AJ and the ApJ family (ApJ, ApJS, and ApJL). The 2017 institutional subscription rate for Monthly Notices of the Royal Astronomical Society, an example of a journal that does not charge author fees, is shown for comparison (source). Bottom: History of author fees per page published in AJ, ApJ, and ApJS.

The Role of Open Access

What does this mean in the age of open-access journals and preprint servers? Again, it comes down to a choice: for a journal to be fully open-access, its revenue can’t come from subscription fees. With no subscription fees, nor author fees, nor external funding (even the arXiv needs nearly $2 million of external funding annually to run!), the journal cannot exist — so a compromise is necessary.

The AAS believes that broad access to astronomical research work is crucial for open scientific dialog and for communication with the larger community that funds the research. Toward this end, the Society has instituted three policies for its journals:

  1. All articles published in AAS journals are made freely available twelve months after publication.
  2. For authors who would like to make their work publicly available immediately upon publication, the AAS journals offer authors the option of Gold Open Access: for a fee (set at a level that offsets the lost subscription revenue), an article can be published under a CC-BY license and will be available for any reader to download or read for free immediately.
  3. Under the AAS journal copyright, authors who publish in AAS journals may also post their preprint to the astronomy preprint server arXiv, to another repository, or even to their own personal website, thus ensuring that a version is immediately available to the public for free.

With this model, the AAS hopes to both support broad access to scientific research while still generating enough revenue to meet journal operating costs.

What the AAS Journals Offer

interactive figure

An example of an interactive figure within an ApJ manuscript. Visit the article, “Evolution of a Pulsar Wind Nebula within a Composite Supernova Remnant” by Kolb et al. 2017, to experience the interactivity yourself.

So why bother having an official journal if everyone can post for free on the arXiv instead?

As scientists ourselves, we at the AAS journals don’t see our role as simply republishing our authors’ work with better typesetting. Instead, we feel that the critical mission of the AAS journals is to increase the scientific integrity of the field. To us, achieving this means not only providing the obvious services — such as acting as gatekeepers for pseudoscience, facilitating peer review for manuscripts, and providing long-term preservation of articles and data — but also the less obvious services that improve the quality and reach of manuscripts published with us.

As astronomy is driven more and more by big data and statistics, ensuring that these aspects are correctly handled in manuscripts will systematically improve the quality of research published in the field. For this reason, the AAS journals employ two full-time data editors, Drs. Greg Schwarz and Gus Muench, who review submitted manuscripts and edit the data, figures, and software citations for those articles that contain significant tabular or other data material. Our data editors provide many forms of author support, including developing and supporting AASTeX and documenting best practices for using online repositories and data linking. They also set up and maintain new initiatives for the journals, such as interactive and animated figures, and they work with in collaboration with community archives and science platforms to improve data linking.

AAS Nova

The homepage of AAS Nova, a website through which summaries of recent AAS journal articles are shared with the community.

Additionally, the AAS journals have a dedicated statistics editor: astrostatistician Dr. Eric Feigelson, professor at Pennsylvania State University. The statistics editor reviews all AAS journal manuscripts that include a significant statistical component, offering authors recommendations on how to strengthen the statistics of their studies in accordance with current best practices in the field.

In the interest of broadening the reach of articles published in our journals, the Society developed AAS Nova, a website designed to help disseminate our authors’ work to the larger astronomical community and the broader public. AAS Nova editor Dr. Susanna Kohler produces and edits summaries of research articles that appear on AAS Nova, ensuring that this work is shared with other astronomy researchers, science journalists, and the general public.

We’re Your Journals

AAS journals are produced by the astronomy community, for the astronomy community — which sets us apart from commercially published journals. We pride ourselves on our work with and support for existing community structures (like databases, repositories, and archives). The development and operations within AAS publishing are all pursued under the oversight of a Publications Committee, which is comprised of astronomers seeking to advance the broader community goals.

The intent of the AAS journals has always been to add value to the astronomy community, and to improve the quality and reach of the research work produced by astronomers. That said, we also acknowledge that there’s always something we can improve — and the fact of the matter is, we’re your journals. Please don’t hesitate to let us know if there’s something we can do to better serve your needs. Our team of more than 30 journal editors — astronomers across a broad range of subfields — would love to chat with you at future scientific meetings. By listening to you, we hope that we can continue to evolve and to play a meaningful part in today’s academic publishing landscape.

RNAAS

Editor’s note: This week, we celebrate one year since we first launched Research Notes of the American Astronomical Society (RNAAS) — a non-peer-reviewed, indexed, and secure record of brief works in astronomy and astrophysics. Editor Chris Lintott shares his thoughts on one year of RNAAS below.

Launched in October 2017, Research Notes of the AAS (RNAAS) has now reached its first birthday. The idea behind RNAAS was to provide a venue for quick and easy publishing of things that otherwise might not enter the formal record, like negative results, one-off observations, or student projects. We knew what the format was — one figure or table, 1,000 words — but the truth is, I don’t think any of us knew quite what to expect.

A year on, it seems evident that RNAAS is an enormous success. 243 notes have been accepted, and the diversity has been astounding. There have been flurries of activity around exciting events, like the passage of ‘Oumuamua through our solar system or the release of Gaia data, but there have also been conference reports, theoretical notes, comments on statistical techniques, reports of observations by students, (polite) quibbles with published results, suggestions for classroom activities, and even people using Research Notes to record predictions. I’m also excited to see people using RNAAS to publicise the release of catalogues and data online, rather than allowing the need for a full paper be a reason to delay or not to document such a release. 

We’ve highlighted just a few of my favourites below, but it’s the variety that strikes me. It turns out that all sorts of people wanted an open, slightly formal (indexed in ADS!), but not peer-reviewed way of recording their thoughts and efforts, and my mornings are enlivened by reading them as part of the moderation process. Another pleasant surprise has been the degree to which RNAAS has entered the mainstream of astronomical work; nearly 70 Notes have already been cited. 

My thanks to the Journals team, and to my fellow editors who help keep an eye on things. We’ve all worked to keep to our goals of being fast and keepingNotes both free to publish and free to read without being too rough around the edges. If you have any suggestions, do get in touch. 

I hope you’ll keep Research Notes in mind for pretty much anything, and drop me an email if you have questions about what might be suitable. The odds are we’d love to publish your thoughts. 

Chris Lintott
Editor, Research Notes of the AAS

 

Highlights from a Year of RNAAS

Want a taste of the research that’s been published in the first year of RNAAS? Check out these ten suggestions from RNAAS Editor Chris Lintott.

'Oumuamua galactic velocity

‘Oumuamua’s galactic velocities don’t match those of any nearby star systems. [Mamajek 2017]

“Kinematics of the Interstellar Vagabond 1I/‘Oumuamua (A/2017 U1),” Eric Mamajek 2017 Res. Notes AAS 1 21. doi:10.3847/2515-5172/aa9bdc

Calculations in this Note support a picture in which the asteroid 1I/’Oumuamua (A/2017 U1) originated from outside of our solar system, but did not come from any of the dozen star systems nearest to us. This is currently the most-cited Research Note and has been downloaded more than 1,300 times.

“The Third Workshop on Extremely Precise Radial Velocities: The New Instruments,” Jason T. Wright and Paul Robertson 2017 Res. Notes AAS 1 51. doi:10.3847/2515-5172/aaa12e

This Note provides a very brief overview of events during the Third Workshop on Extremely Precise Radial Velocities, held in Pennsylvania in August 2016. The Note includes a link to a table produced during the workshop that summarizes nearly all of the next-generation extremely precise Doppler velocimeters being designed, built, or commissioned today.

“Strong Hydrogen Absorption at Cosmic Dawn: The Signature of a Baryonic Universe,” Stacy S. McGaugh 2018 Res. Notes AAS 2 37. doi:10.3847/2515-5172/aab497

After the groundbreaking discovery of the signature of light from the very first stars in the universe, first announced in February 2018, this Note rapidly followed on its heels with a theoretical explanation for the signal’s unexpected strength.

“Another unWISE Update: The Deepest Ever Full-sky Maps at 3-5 μm,” A. M. Meisner et al 2018 Res. Notes AAS 2 1. doi:10.3847/2515-5172/aaa4bc

This Note presents the deepest ever fully-sky maps at 3.4 and 4.6 µm, built by reprocessing ~140 terabytes of infared images from the Wide-field Infrared Survey Explorer (WISE) and Near-Earth Object Wide-field Survey Explorer (NEOWISE) missions.

NGC1052-DF2

The backwards “S” shape faintly visible in the true-color image of NGC1052-DF2 (background) and zoomed insets may be a cold stellar stream. [Abraham et al. 2018]

“The Maybe Stream: A Possible Cold Stellar Stream in the Ultra-diffuse Galaxy NGC1052-DF2,” Roberto Abraham et al 2018 Res. Notes AAS 2 16. doi:10.3847/2515-5172/aac087

Remember the controversial NGC1052-DF2, the ultra-diffuse galaxy reported to be strangely lacking dark matter? This Note reports on the provisional detection of a cold stellar stream within this galaxy, cautiously referred to as “The Maybe Stream”. If confirmed, this would be located 500 times further away than the current most-distant cold stellar stream known.

“No Bursts Detected from FRB121102 in Two 5 hr Observing Campaigns with the Robert C. Byrd Green Bank Telescope,” Danny C. Price et al 2018 Res. Notes AAS 2 30. doi:10.3847/2515-5172/aaaf69

This Note is an excellent example of a helpfully documented null result. The repeating fast radio burst FRB 121102 was observed over two 5-hour observation sessions on the 100-m Green Bank Telescope, and no bursts were detected during that time. These are among the longest published contiguous observations of FRB 121102, and support the notion that FRB 121102 bursts are episodic.

“The Spectroscopic Classification of Seven Cataclysmic Variables with the Liverpool Telescope,” E. W. Upsdell et al 2018 Res. Notes AAS 2 161. doi:10.3847/2515-5172/aadee7

This Note presents a student project in which the spectra of seven cataclysmic variables — observed using the 2-m Liverpool Telescope in the UK — are analyzed. The objects are shown to be consistent with dwarf novae.

“Predicting The Orbit of TRAPPIST-1i,” David Kipping 2018 Res. Notes AAS 2 136. doi:10.3847/2515-5172/aad6e8

What would the period be for a hypothetical eighth planet in TRAPPIST-1, an exoplanetary system currently known to host seven planets that share near mean motion resonances with their neighbors? This Note presents a prediction that we can hope to test, should we discover TRAPPIST-1i in the future.

North Celestial Pole path

Path, in green, of the apparent position of the North Celestial Pole (i.e., the center of star trails) as a function of time. [Wright 2018]

“Proving Heliocentrism and Measuring the Astronomical Unit in a Laboratory Astronomy Class Via the Aberration of Starlight,” Jason T. Wright 2018 Res. Notes AAS 2 119. doi:10.3847/2515-5172/aad0f5

For professors looking for an interesting class project, check out this Note, which describes a student project to measure the aberration of starlight caused by the motion of the Earth. With just a small telescope and camera, students can directly prove that the Earth travels around the Sun.

“Unbiased Inference of the Masses of Transiting Planets from Radial Velocity Follow-up,” Benjamin T. Montet 2018 Res. Notes AAS 2 28. doi:10.3847/2515-5172/aac2c1

This Note reveals an overlooked observational bias toward artificially high mass values estimated for planets discovered via the radial velocity method. The author proposes a means for avoiding this bias in the future.

 

NGC 2623

Editor’s Note: This week we’re at the 232nd AAS Meeting in Denver, CO. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume next week.

Wednesday, 6 Jun

Plenary Lecture: George Ellery Hale Prize, Amazing Journeys to the Hearts of Stars (by Kerry Hensley)

The first talk of the day was given by Dr. Sarbani Basu (Yale University), who was awarded the George Ellery Hale Prize for “outstanding contributions to the field of solar astronomy.” Dr. Basu is an expert in helioseismology — the study of tremors and vibrations of the Sun. While stars in certain mass ranges undergo huge, regular oscillations (so-called variable stars, like Cepheid or RR Lyrae variables), Sun-like stars experience smaller-amplitude pulsations generated at the top of their convective zones.

These subtle pulsations hold the key to understanding the interior structure of the Sun and other stars — a problem that renowned astronomer Arthur Eddington thought would never be solved, commenting that although telescopes enable us to peer at more and more distant stars, no instrument could help us look into the interiors of stars. Luckily, that’s not the case! The Sun oscillates in millions of different modes, which we can tease apart using helioseismology. Helioseismology can help us determine the true metallicity of the Sun (a long-standing problem that has huge implications for virtually all of astronomy!), how the solar interior rotates, and the degree of diffusion and settling of different elements within the Sun.

One of the huge triumphs of helioseismology came in the midst of the solar neutrino controversy — the realization that the number of solar neutrinos received by Earth-based neutrino detectors was too small by a factor of three. By using the absurdly good helioseismology data (Dr. Basu showed a plot of data where the 1,000-sigma error bars were smaller than the plotting symbols!), solar physicists showed that their models of the solar interior were right and the error must lie in the standard model. As it turns out, they were absolutely right — neutrinos, which were initially thought to be massless, instead possessed a tiny amount of mass, which allowed them to oscillate into any of three “flavors” (only one of which was easily detectable) as they traveled from the Sun to the detector.

red giants

Different types of red giants fall in distinct areas of parameter space. Another win for asteroseismology!

In the case of stars outside our solar system, asteroseismology can help us infer the fundamental properties of stars, since the maximum frequency of stellar oscillations scales with the stellar mass and the square root of the temperature. Also very exciting is the potential to distinguish between red giant branch and red clump stars — two types of stars that fall in the same area of the HR diagram but represent different stages of stellar evolution. Although they have similar temperatures and luminosities, their internal structure is different — and we can probe that structure with asteroseismology. Expect big discoveries from this field in the future!

Press Conference: Erupting Stars & Dissolving Stars (by Gourav Khullar)

corona

Layers of a total solar eclipse. [Inside: SDO/LMSAL/NASA GSFC;
Middle: Jay Pasachoff/Ron Dantowitz/Williams College Solar Eclipse Expedition/NSF/National Geographic;
Outside: LASCO/NRL/SOHO/ESA]

For this morning’s press conference, Kerry Hensley began the proceedings, supported by AAS media officer, Rick Feinberg, and Gourav Khullar.

The conference opened with Jay Pasachoff (Williams College & Carnegie-Hopkins Observatories), who discussed observations of the solar corona during the 2017 total solar eclipse. Salem, Oregon was the observing site for the project, where Pasachoff and collaborators constructed composite images of the eclipse to highlight the corona. Coronal streamers were also studied, along with polar plumes. Pasachoff also showed some observations from the International Space Station, clearly exhibiting a shadow of totality!

This was a great opportunity to study active regions in the Sun, especially from composites from multiple sites around the US. Pasachoff ended with a pitch about future total and annular eclipses across the US in the next 5 years.

This was followed by Thomas Ayres (University of Colorado Boulder), who described his project characterizing the habitability of planets around our nearest interstellar neighbour, the Alpha Centauri star system. Two of the stars have Sun-like environments, but Alpha Cen C is what Ayres likes to call a ‘weather hell’, due to its extreme X-ray flux capable of stripping away atmospheres and frying unprotected life. Ayres and collaborators used the Chandra X-ray Observatory to track the X-ray emission from the Alpha Cen system over the past 13 years. Chandra observations are the only ones capable of resolving stars A and B — B is seen to have stronger X-ray flux than A. According to Ayres, it so happens that Alpha Cen A is great for potential habitability prospects (its X-ray hazard is much lower than that of the Sun). Cen B is not too bad either, whereas Cen C is literal death!

Sofia Moschou (Harvard-Smithsonian Center for Astrophysics) was to follow, with her work on studying coronal mass ejections (CMEs) in the star Algol. Moschou’s recent paper in The Astrophysical Journal described indirect observations of monstrous CMEs in Algol. This work also characterized Algol’s place on the well-known proportionality between CMEs and flare intensities in the Sun (known as the solar CME–flare relation). The objective here, according to Moschou, is to see whether the proportionality of strength of the flares with CME activity continue with more active stars like Algol. The answer? It probably does. Stellar CME observations via Doppler shift measurements and X-ray absorption characterization enabled Moschou and collaborators to demonstrate Algol’s properties in the context of the relation, within the bounds of systematic uncertainties in observations of the Sun and Algol.

The final presentation of the press conference was by Andrea Kunder (Saint Martin’s University), talking about dissolving globular-cluster stars! Globular clusters are the oldest stars in a galaxy, akin to fossils. Kunder and collaborators are interested in seeing the interplay of globular clusters and the Milky Way bulge, especially since the bulge is the site of exciting activities! Kunder studied NGC 6441, the 5th most massive cluster in the Milky Way, which lies in a crowded bulge field with many field stars, and affected by massive amounts of gas and dust. This study used RR Lyrae stars as distance and velocity indicators on a velocity-radius diagram to isolate stars in the globular cluster from RR Lyrae stars outside the cluster. Kunder showed the results, which remarkably point to the idea that there are groups of RR Lyrae stars on the outskirts of the current form of NGC 6441, and the trajectory of the cluster indicates that these are ex-cluster members. In other words, stars in this globular cluster are dissolving away as we write this!

Plenary Lecture: Supermassive Black Hole Fueling and Feedback in Galaxies (by Mia de los Reyes)

Dr. Julie Comerford’s plenary talk at lunch time was — appropriately — on hungry galaxies. Comerford, a professor from University of Colorado Boulder, started by describing how nearly every massive galaxy hosts a supermassive black hole (SMBH). Sometimes, the black hole is actively accreting and spitting out energetic jets; this is called an active galactic nucleus or AGN. (Comerford has a great explanation of supermassive black holes and AGN in this feature by PhD Comics.)

The properties of an AGN are intimately linked with the properties of its host galaxy; the SMBH mass is correlated with the galaxy’s halo mass, and its accretion rate is proportional to the star formation rate of the galaxy. These black holes are truly behemoths, with masses equivalent to millions or billions of suns — but they’re not that big compared to their host galaxies. Yet SMBHs still manage to influence their galaxies on such large scales. As Comerford noted, the scale difference between a galaxy and its SMBH is equivalent to the difference between a grain of rice and the size of the Earth!

Comerford’s talk focused on two major ways that AGN can influence their host galaxy: fueling (the SMBH accretes matter) and feedback (the SMBH launches energetic jets and outflows, which can help turn off star formation in a galaxy). If you want to read more about these, check out my interview with Julie Comerford here!

Both fueling and feedback can be traced using pairs of supermassive black holes. These pairs can either be observed as dual AGN, in which both SMBHs are active, or offset AGN, in which one SMBH is quiescent so the active one looks off-center.

How do we actually find these dual and offset AGN? As Comerford explained, we can search for galaxies with narrow emission lines that have two peaks. These double peaks can be caused either by dual AGN, by disk rotation, or by AGN outflows; spectroscopy and images from radio and X-ray data can then be used to identify the dual AGN. We can also look for offset AGN by carefully comparing the positions of SMBHs (in X-ray images) and galactic centers (in optical images).

Comerford then listed several science questions that we can answer with these AGN:

  • Are the most luminous AGN triggered by galaxy mergers? Simulations have suggested this is the case, but observations were unclear… until now! Using dual AGN, it seems that the major mergers do trigger the most luminous AGN. (Contrast with some earlier Astrobites posts!)
  • Where in a galaxy merger does AGN fueling occur? The fraction of AGN increases as the two SMBHs get closer together, and new observations show that the AGN fraction is highest in the inner ~1 kpc.
  • Can outflows from moderate luminosity AGN contribute to feedback? The most powerful outflows seem to be driven by the most luminous AGN, But it turns out that about 90% of moderate-luminosity AGN outflows that have double-peaked narrow emission lines do have enough energy to turn off star formation in the galaxy!

Finally, Comerford talked about ways to connect fueling and feeding. Her group recently discovered a dual AGN that showed two discrete accretion events — a flickering AGN! Each event caused an outflow event, leading to a signature of asymmetric outflows. In the future, integral field spectroscopy on other interesting systems like this will help us further our understanding of these hungry galaxies.

Press Conference: The Milky Way & Active Galactic Nuclei (by Susanna Kohler)

This afternoon’s press conference explored distant, active galaxies — and also a quieter galaxy much closer to home: our own Milky Way.

William Reach (SOFIA/Universities Space Research Association) opened the conference by presenting work exploring where cosmic rays — highly energetic particles — originate and how they’re accelerated to their incredible speeds. Recent research has localized the source of some energetic cosmic rays and suggested that they may be originating in interactions between supernovae and molecular clouds. At these interaction sites, dense shocks occur, which can accelerate particles to their high speeds.

Ekta Patel (University of Arizona) followed next, presenting her efforts with her advisor, Gurtina Besla, to obtain a precise estimate of the mass of the Milky Way. Finding the mass of our galaxy is tricky, since we’re stuck in the middle of it — values in the literature range from 700 billion to 2 trillion solar masses! Patel has developed a new approach to weighing our galaxy, by comparing observations of nine of the Milky Way’s satellite galaxies’ full three-dimensional motions with the motions of tens of thousands of simulated galaxies. From these comparisons, she estimates the mass of the Milky Way to be 0.96 trillion solar masses. We can look forward to even more precise estimates using this technique in a few years, after simulations increase in resolution and we get Gaia’s measurements for even more of the Milky Way’s satellites! (Press release)

Next up, Randall Campbell (W. M. Keck Observatory) & Anna Ciurlo (University of California, Los Angeles) tag-teamed a presentation on Keck observations of the galactic center over the past 12 years. The center of the Milky Way hosts a supermassive black hole, Sgr A* — and we can learn a lot by watching close-in objects orbit around it! In particular, Campbell and Ciurlo have tracked several G-objects — objects in the same class as the exciting G2 that passed close to Sgr A* in 2014. Observations of these objects suggest that they are likely puffed-up stars shrouded by their thick outer layers of dust and gas. They may have originated from binary mergers, and it’s possible that they’re the progenitors of future S-stars: young, bright and very massive stars.

The press conference rounded out with results for which Julie Comerford had provided us with a quick teaser during her earlier plenary. Scott Barrows (University of Colorado, Boulder) presented efforts to hunt for offset active galactic nuclei (AGN): accreting supermassive black holes that don’t reside at the center of a galaxy. These objects are generally signs of a recent galaxy merger that left an AGN stranded away from the center of the newly formed galaxy, and they often mean that a second AGN that hasn’t yet turned on may be lurking nearby. Barrows found that single offset AGN were most commonly hosted in lopsided mergers — those in which one galaxy was more than four times the size of the other — whereas mergers hosting two active black holes at the center were more commonly equal-mass collisions. (Press release)

Plenary Lecture: Status of the Daniel K. Inouye Solar Telescope: Unraveling the Mysteries of the Sun (by Kerry Hensley)

The final talk of the day was an update on the status of the Daniel K. Inouye Solar Telescope (DKIST) given by Dr. Valentin Martínez Pillet (National Solar Observatory; NSO). DKIST is a 4-meter solar telescope currently under construction at Haleakala Observatory on the island of Maui in Hawai’i. After 8.5 years, DKIST (formerly known as the Advanced Technology Solar Telescope) is 83% complete, with first light planned for 2019 and the beginning of science operations following in 2020. DKIST aims to answer persistent questions about the Sun — in particular understanding the physical driver for coronal mass ejections. The 4-meter aperture translates to a resolution of 25 kilometers and a signal-to-noise ratio of 10,000 — so it’s no surprise that Dr. Martínez Pillet called it “a microscope on the Sun”!

DKIST promises to transform solar physics with its multiwavelength (0.38 – 28 microns) observing capabilities, coronagraph, and polarimetry. Some of the most exciting possibilities for DKIST involve the potential to combine its observations with those from Parker Solar Probe (which will fly to within 9 solar radii of the Sun’s surface and make detailed measurements of plasma properties there), Solar Orbiter (which will orbit the Sun at about the distance of Mercury’s orbit and carry both plasma instruments and a telescope), and the Atacama Large Millimeter/submillimeter Array (ALMA; a ground-based radio telescope array). This signals the beginning of a true multimessenger era for solar physics — get excited for first light in 2019!

Thursday, 7 Jun

Plenary Lecture: Gaia: Mapping the Milky Way: The Scientific Promise of Gaia DR2 (by Gourav Khullar)

The final plenary session of AAS232 is upon us, and what better to talk about than one of the greatest set of observations taken this century — the Gaia Data Release 2 (DR2)! Nicholas Walton (University of Cambridge, and Gaia), began by crediting the European Space Agency, the Gaia Collaboration, the Data Processing and Analysis Consortium (DPAC), and the massive efforts put in by industry and member universities of the collaboration. Read more about Nick Walton here!

This talk was both an overview of the Gaia mission and a brief description of science currently being done with this ginormous new dataset released a month ago! Gaia was launched in December 2013 and traveled all the way up to the 2nd Lagrangian point (L2 orbit) between the Earth and the Moon. Its first data release occurred in September 2016, and DR2 came out last month — with 1.7 billion objects in the catalog, recording photometry, spectrometry, and astrometry. This dataset is being used to characterize dust in the Milky Way, as well as the luminosity, proper motion, position, color, and surface temperature of stars around us!

Gaia maps the sky with a 1-arcsecond resolution, showing the Large and Small Magellanic Clouds, and the Sagittarius stellar stream in all their glory! The talk described the Gaia focal plane (106 CCDs, a billion pixels!), data-processing effort (pan-European, 450 specialists in 24 countries!), and DR1, which did not utilize the entire processing flow that allowed DR2 to obtain its microarcsecond-level astrometry, milli-magnitude level photometry, and 1 km/s-level radial velocities. This blows my mind! Read more Astrobites coverage of this mission here.

This was followed by a discussion of the completeness and sky coverage of the mission, which is significantly better for nearby astrophysical objects than ground-based surveys. While the astrophysical parameters (which we call second-order parameters here, derived from primary observations) need to be interpreted with care, Walton (and we at Astrobites!) would urge you to check out all the 70 arXiv papers in the last month or so based on DR2. These papers characterize the Milky Way disk kinematics, discover new stellar streams, construct magnificent HR diagrams for 4 billion stars, survey asteroids in the solar system, measure dynamics of globular clusters in the Milky Way, and so much more!

Walton also cautioned the audience to treat DR2 and DR1 as independent datasets, since the systematics are different, as well as the photometric processing pipeline. The future is bright, since Gaia is scheduled to make extended observations over the next five years, and release datasets beyond DR4 (Data Release 4)! Accessing DR2 data is as easy as googling the Gaia Collaboration website, which lets you parse any sub-dataset with ease. Log on and get to science, people!

Sculptor dwarf galaxy

Editor’s Note: This week we’re at the 232nd AAS Meeting in Denver, CO. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume next week.

Plenary Lecture: Small Interstellar Molecules and What They Tell Us (by Kerry Hensley)

The first talk of the day was the Laboratory Astrophysics Division plenary given by Dr. David Neufeld (Johns Hopkins University). While biologists and chemists can poke and prod some of the substances they study, astrophysicists aren’t so lucky. Other than rocks from the Moon and a puff of cometary dust captured in aerogel, we get most of our information about the universe from photons and gravitational waves (other than solar system missions, through which we can directly probe magnetic fields and plasma — but we don’t get to bring those home with us!). Laboratory astrophysics is a powerful tool to help us interpret the messages those photons are sending, giving us a better idea of the physics at work in the universe.

Dr. Neufeld specializes in laboratory studies of small molecules, the kind that might be found in the interstellar medium or the material surrounding young stars. In particular, Dr. Neufeld studies a class of small molecules called hydrides — molecules made up of just one heavy element (typically one that is happy to donate electrons) and any number of hydrogen atoms. So, for example, ammonia is a hydride since it contains only one “heavy” element (nitrogen).

These tiny molecules are particularly helpful in three situations:

  1. Tracing cold molecular hydrogen gas
    Take hydrogen fluoride (HF) as an example. Laboratory studies showed that HF should form readily in cold environments from molecular hydrogen and fluorine, so even though fluorine isn’t extremely abundant in the universe, it should form HF whenever it’s in a cold environment with abundant molecular hydrogen — like the interstellar medium. Observations of diffuse interstellar clouds showed that HF was present — and could be used to trace more diffuse clouds than carbon monoxide could. Just one example of how laboratory astrophysics can guide observational astrophysics!
  2. Tracing gas that has been warmed by shocks or turbulence
    Warm interstellar gas can also be traced by hydrides, in this case SH, SH+, and CH+. These molecules react endothermically with H2, and the amount of heat needed for the reaction differs between the three molecules. Determining the amount of each of the three compounds in an interstellar cloud can help us figure out the temperature of the cloud.
  3. Helping to measure the cosmic ray ionization rate in the galaxy
    Cosmic rays, which aren’t “rays” at all but instead extremely relativistic particles, ionize gas everywhere from Earth’s atmosphere to the most distant interstellar clouds. Dr. Neufeld highlighted two ways in which interstellar molecules can be used to measure cosmic ray ionization rates: observing H3+ ions in diffuse molecular gas and observing ArH+ in diffuse atomic gas.
    In order to use molecules to infer the properties of interstellar gas, we need to know how those molecules behave under different conditions (temperature, density, etc.). That’s where laboratory astrophysics is hugely helpful! In the future, expect to see astronomers pair more laboratory determinations of molecular properties with observations to learn more about the interstellar medium.

Press Conference: Stars that Make You Say “WTF?” (by Mara Zimmerman, Gourav Khullar, and Susanna Kohler)

What’s the latest news regarding the mysterious Boyajian’s star? This strange object and another odd star, Epsilon Aurigae, were the subject of the talks at today’s morning press conference.

The first presentation was given by two high school students, Yao Yin and Alejandro Wilcox of the Thacher School! These intrepid students presented their research monitoring Boyajian’s star since April of 2017 using the Thatcher Observatory. Yin and Wilcox found that Boyajian’s star’s bizarre flux dips have a dependence on the wavelength of light observed, suggesting that the dimming may be due to dust that differs in composition or size distribution.

Boyajian's star

Bizarre recent dips in the light curve of Boyajian’s star. [Boyajian et al. 2018]

Eva Bodman, a postdoc at Arizona State University, backed these findings with the results from a Kickstarter-backed study of Boyajian’s star using LCOGT. An endearing quality of this campaign is that funders get to vote on the names of the weird dips in Boyajian’s star’s light curves! Bodman’s work focused on four dips in particular: Elsie, Celeste, Skara Brae, and Angkor. This study agrees that dust is the most likely conclusion for the dips — and it appears to be an extremely complex dust cloud that is likely clumpy and amorphous, with ephemeral fine grains and longer-lasting large grains. We still have a lot to learn about this strange star!

Switching up the topic, Dr. Robert Stencel from the University of Denver presented work completed with his graduate student Justus Gibson on Epsilon Aurigae, which belongs to a class of ‘disk-eclipsed’ binary stars. This is a very bright star, often associated with a hidden companion that is grabbing material and creating an accretion disk that produces irregular variability in its flux. When given the opportunity to interferometrically image the disk, observers found an opaque accretion disk, with the data characterizing the star as a pre-asymptotic giant branch star that may be obstructed by this disk.

A question raised during the Q&A led to interesting discussions — what can comparing these two stars tell us? The participants felt that any oddities in stellar observations can help provide us with more insight in the science of stars, pushing the limit of what is possible with the observations of stellar-type objects.

The Dynamics of the Local Group in the Era of Precision Astrometry (by Mia de los Reyes)

Dr. Gurtina Besla from the University of Arizona started today’s lunch plenary talk with a reminder: although textbooks might suggest that we’ve known everything about the Local Group for a long time, it’s only over the last decade or so that we’ve gotten precise positions and motions of these nearby systems! This has led to a lot of new and exciting science; as Besla said, “With every measurement, we have challenged conventional wisdom.”

The “Local Group” refers to the Milky Way, M31 (the Andromeda Galaxy), and about 50 nearby dwarf satellites. By studying the kinematics of these satellites, we can better understand all kinds of science. The recent data release from the European Space Agency’s Gaia mission has revolutionized our ability to do this by measuring the proper motions of over a billion stars to incredible precision — the accuracy involved in these measurements is equivalent to measuring the speed of human hair growth at the distance of the moon!

Besla gave us the run-down on several of the exciting results made possible with data from Gaia and the Hubble Space Telescope:

  • The orbits of Milky Way satellites: Besla started by noting the historical importance of the Magellanic Clouds to indigenous cultures around the world (see the figure below). The new Gaia data can tell us about how these galaxies, which are the Milky Way’s nearest satellites, orbit the Milky Way. It suggests that these satellites are “new neighbors” that only recently fell into the Milky Way’s gravitational potential for the first time!

  • The Large Magellanic Cloud (LMC): The LMC seems to be moving much faster and is about 10 times more massive than was previously thought. In fact, the LMC is so massive that it dragged five other satellite galaxies along with it when it fell into the Milky Way. It’s even massive enough to perturb the Milky Way’s halo and change its shape!
  • Andromeda and its satellites: In 2012, the Hubble Space Telescope delivered a (very) early collision warning: in a few billion years, the Andromeda galaxy (M31) will irrevocably change our view of the night sky. It’ll collide with our Milky Way, destroying the galactic disk and leaving us sitting in a giant elliptical galaxy (see the figure below).

Now, with Gaia DR2, we can look directly at internal motions of M31 and its largest satellite M33! We can confirm the earlier result that Andromeda will in fact collide with our galaxy — but beyond that, we can watch how M31 and M33 are rotating and interacting with each other. Besla’s group has found that, like the LMC in our Milky Way, M33 may be on its first infall into Andromeda now! The James Webb Space Telescope will look more at M31’s satellites in the future.

Besla concluded by noting that we still haven’t fully understood the dynamics of the Local Group. She also spoke to the young people in the room, reminding them that the gut reaction to a new and exciting result is often “no.” “But look at what the new data is telling you,” she said, “and continue onwards.”

Talk: Astrobites as a Pedagogical Tool in Classrooms (by Susanna Kohler)

Astrobiter Gourav Khullar presented today in the “College-Level Astronomy Education: Research and Resources” session. At two past AAS meetings (AAS229 and AAS231), Astrobites hosted workshops on how to introduce modern research into undergraduate and graduate classrooms using astrobites.com as a resource. Today, Khullar provided a speed-introduction to the idea for educators and outreach practitioners who may not yet have considered the idea, or who may not know where to start!

astrobites in the classroom talk

Gourav Khullar presents on using Astrobites to bring current astronomy research into the classroom.

Khullar opened his talk with a brief overview of the site. Astrobites recently celebrated publishing its 2,000th article (!), so the site, at this point, provides an extensive archive of brief summaries of astronomy research conducted over the past 7 years. Have a topic in mind that you’d like your students to learn about? We’ve almost certainly covered it!

Khullar then briefly introduced the three full lesson plans that we’ve written up as suggestions of how to use Astrobites in the classroom — which come complete with student handouts, online form templates for collecting student work, grading rubrics, adaptations for different learning levels, and more.

He rounded out the talk by introducing the research study we are currently conducting — with the aid of an AAS Education & Professional Development (EPD) mini-grant — to explore how Astrobites has been used in classes and the impacts that it has had. If you’ve used Astrobites in your class or journal club or plan to in the future, and you’d be interested in being a part of our study, please don’t hesitate to reach out! Email us at astrobites@gmail.com.

Press Conference: Metal-Poor Stars & Dwarf Galaxies (by Susanna Kohler and Mia de los Reyes)

The second press conference of #AAS232 started off with Timothy Beers, a professor from the University of Notre Dame. Beers explained that while we may never directly see the first generation of stars, we can see their “fingerprints.” This is because the first stars distributed their nucleosynthetic products when they died, and these elements were then incorporated into the second generation of stars. These second-gen stars have a characteristic abundance pattern: lots of carbon, and not much of any other heavy elements (“metals”). They probably formed in ultra-faint dwarf galaxies and were then accreted onto the Milky Way halo, so we can actually look for these stars in our own galaxy! (Press release)

galaxy accretion simulation

A simulation showing the process of galaxy accretion. It’s a messy business! [J. Helly, A. Cooper, S. Cole and C. Frenk (ICC)]

Kris Youakim from the Leibniz Institute for Astrophysics in Germany then continued on this theme. He started with some beautiful simulation videos of dwarf galaxies being accreted onto the Milky Way, and then showed that we can actually use stars with very low metal abundances to trace this accretion. In particular, he found that the most metal-poor stars are the most strongly clustered. This implies that not only are there a lot of small metal-poor dwarf galaxies, but also that these satellites haven’t yet been tidally disrupted by the Milky Way.

Next up, Gina Duggan from Caltech spoke about using the metal abundances to track how elements were produced in dwarf galaxies over time. In particular, she uses barium as a proxy for elements that are produced by a nucleosynthetic mechanism called the r-process (see our summary of Enrico Ramirez-Ruiz’s talk yesterday for more details). It’s not clear where the r-process happens; it could occur either in a special class of supernovae or in neutron star mergers. The pattern of barium abundances that Duggan observes suggests that neutron star mergers are the culprit in dwarf galaxies! (Press release)

JWST

One of the goals of the James Webb Space Telescope is to explore the most distant objects in the universe, including the first stars and galaxies. [NASA]

Aparna Venkatesan (University of San Francisco) next discussed how we might be able to use nearby galaxies as a tool to answer questions about much more distant objects, such as the very first stars in the universe. She argues that nearby low-mass, star-forming galaxies are ideal analogs for the first galaxies that formed in the universe. Studying these convenient nearby dwarfs can therefore advance our understanding of early star clusters and the physical conditions of early galaxies, providing context for when we start to get results from JWST’s planned observations of distant galaxies in the universe.

The final presentation of the conference was by Mustapha Ishak-Boushaki (University of Texas, Dallas), who introduced an intriguing prospect: discrepancies between data sets (normal a source of concern for astronomers!) may actually be useful for informing our understanding of the universe. Ishak-Boushaki’s work addresses an age-old problem: what happens when different missions take measurements that imply different values for cosmological parameters — for instance, the age of the universe, or how quickly it’s expanding? There are two possible resolutions: either there are errors in one or more of the data sets, or the models we’re using are missing new physics! Ishak-Boushaki and collaborators developed a new mathematical tool to quantify these inconsistencies between different data sets. The goal of this tool is to help us better explore issues like tensions between local and large-scale measurements, to evaluate whether we need to reconsider our models (Press release)

Plenary Lecture: An Era of Precision Astrophysics for Exoplanets, Stars, and the Milky Way (by Kerry Hensley)

It’s a great time to be an astronomer! In the final plenary session of the day, Dr. Keivan Stassun (Vanderbilt University) highlighted the many (many!) exciting advances in the field of high-precision astrophysics. In this talk, Dr. Stassun focused on the importance of precisely determining the properties of stars. After all, you need to first understand stars in order to understand the planets that orbit them, the galaxies that are composed of them, and how those galaxies have evolved over time.

Dr. Stassun focused on three categories of advances in high-precision astrophysics: astrometry, photometry, and spectroscopy. He covered a lot of cool techniques, but here I’ll summarize just a few.

Astrometry
Astrometry is one of the oldest astronomical techniques, but this simple act of plotting the positions of stars and tracing their motions is still valid today. Highly precise parallaxes (the kind you might get from Gaia or Hubble) enable a technique that Dr. Stassun calls “pseudo-interferometry,” which allow us to make careful measurements of stellar radii. Advances in astrometry may soon allow us to determine stellar radii to within a few percent at a distance of three hundred light-years! Precisely measuring the radii of stars is critical for studying exoplanets (since uncertainty in the radius of the star translates to uncertainty in the radius of the planet… and its density, composition, surface gravity…) and can also help us better understand stellar activity and stellar structure.

Photometry
One of the coolest techniques that Dr. Stassun covered in his talk was the use of highly precise photometry (measuring the light from an object in wide wavelength ranges) to obtain stellar masses. This technique works by analyzing the change in the light emitted by the star due to granulation — the motion of individual convective cells bubbling up to the surface of the star. The amplitude of the modulation tells us about the surface gravity of the star. If you know the radius of the star (say, from some precise astrometry), this gives you the mass. The most exciting part of this technique is that it works for individual isolated stars, which have long been a challenge to weigh! Dr. Stassun estimated that this technique will yield masses to within 10% accuracy for hundreds of thousands of stars.

Spectroscopy
While highly precise spectroscopy is exciting in and of itself, it’s best when paired with machine learning. Using machine learning, we can amass thousands of stellar spectra and extract temperatures, gravities, bulk metallicities, and abundances of individual chemical elements for the individual stars. This means large-scale chemical forensics, allowing us to piece together the formation histories of everything from galaxies to planetary systems and track down the Sun’s long-lost siblings!

While astronomers have already achieved amazing advances with the help of precise astrophysical techniques, more discoveries are headed our way. So sit back, relax, and enjoy the show (or get some data and get crunching!).

Sedna

Editor’s Note: This week we’re at the 232nd AAS Meeting in Denver, CO. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume next week.

 Sunday, 3 June

Using Python to Search NASA’s Astrophysics Archives (by Gourav Khullar)

The sessions for this AAS meeting began with a workshop on using python to parse NASA data archives, organized by Vandana Desai (IPAC/Caltech) and the team at NASA Astronomical Virtual Observatory (NAVO).

To quote the workshop organizers, “NASA missions have collected a huge amount of data spanning a large range in wavelengths. These data are housed in four different archives: the HEASARC, MAST, IRSA, NED…..The archives have been working together…to assemble the data you need to get your research done. We’ve done this by standardizing the way that programs can access the data we house. Since Python is a very popular programming language, we are going to use it to show you how you can take advantage of this standardization..”

The resources are available at the following link: “https://github.com/NASA-NAVO/aas_workshop_2018_summer”. We would like to encourage all our readers to start retrieving multi-wavelength information from these rich exquisite datasets!

Using Anchored Inquiry to Teach Astronomy and Physics (by Gourav Khullar)

This session, organized by Zoe Buck Bracey, PhD (BSCS Science Learning), focused around pedagogical techniques to be used in classrooms about concepts. This 4-hour workshop was full of mini-experiments, tasks and group work (along the ideas of “Think, Pair, Share!”), to encourage instructors towards building classes around concept “anchors”. The example studied throughout this amazing workshop attempted to teach the model of the Earth-Sun system and encourage understanding of seasons on our planet. We used average planetary temperature datasets as anchors, which allowed us participants to put student engagement at the forefront, encouraging students to come up with a model that explains why seasons occur. Throughout the activities, the emphasis was on students bringing prior knowledge into a class and how an instructor can enable them cross the bridge from having a partial idea of concepts to a complete understanding.

Monday, 4 June

poster sessions

Don’t forget to check out poster sessions at AAS 232 and talk with presenters!

Plenary Lecture: Welcome Address (by Susanna Kohler)

AAS President Christine Jones opened the day with a brief session welcoming attendees to this meeting and outlining some of the highlights that we can look forward to at AAS 232 in the coming week. She especially drew attention to the plenary sessions (don’t forget to check out our interviews with keynote speakers!), the town halls, and a few special sessions such as this morning’s AAS Taskforce on Diversity and Inclusion in Astronomy Graduate Education, which Gourav reported on below. She also pointed out the value of visiting posters and talking with presenters — we appreciated the photos of students presenting their work at past meetings!

Kavli Foundation Lecture: From Extrasolar Planets to Exo-Earths (by Susanna Kohler)

Dr. Debra Fischer (Yale University) kicked off the plenary talks of this meeting by giving the Kavli Foundation Plenary Lectureship, an invited talk on “recent research of great importance.” Fischer’s opening comment — “It’s tough to give a lecture on exoplanets these days, because I know there are so many experts in the audience!” — acknowledged the huge boom that exoplanet research has undergone since its inception. Fischer, however, is a highly qualified expert herself: she’s spent more than two decades in the field, developing techniques for detecting exoplanets.

Fischer gave a broad overview of the past and current state of exoplanetary studies, discussing the types of planets we’ve discovered and how we’ve found them. There are several approaches that have been used to discover and characterize the ~4,000 exoplanets known at this time:

  1. Transits, in which a dip in a star’s light reveals the presence of a planet passing in front of its host;
  2. Direct detection, in which exoplanets are actually imaged directly by telescopes;
  3. Gravitational microlensing, in which the planet is never seen, but its gravitational pull bends light from a background star in a telltale way, indicating the planet’s presence;
  4. Astrometry, in which the visible wobbling motion of a star reveals the gravitational tug of an orbiting planet; and
  5. Radial velocity, in which such a stellar wobble is seen in the star’s spectrum, as its spectral lines shift back and forth due to the approaching and receding star.

This last technique, radial velocity, is the approach that Fischer has been working to improve. Thus far, the smallest radial-velocity wobble we’ve been able to detect is around 1–2 m/s, or roughly walking speed; Fischer hopes that in the future we can push this precision down to just 10 cm/s, a signal akin to the wobble that Earth induces in the Sun. This requires remarkable advancements in both technology of spectrographs and modeling of things like contamination of stellar spectra by Earth’s atmosphere — but Fischer and other members of the field are making significant progress in these directions!

Fischer concluded by mentioning the many new and upcoming missions that will advance the field of exoplanet studies — like Gaia, TESS, CHEOPS, JWST, and WFIRST — and she threw in a sales pitch for the Large Ultraviolet/Optical/Infrared Surveyor (LUVOIR), a space telescope under consideration as a future NASA project. She also pointed out the broad community and general-public support of exoplanet science. The future of this field is bright!

You can check out Stephanie Hamilton’s interview of Fischer here.

HST vs. LUVOIR

A simulated view of the same part of the sky as observed by Hubble Space Telescope (left) vs. the proposed LUVOIR (right). [G. Snyder, STScI /M. Postman, STScI]

Press Conference: Minor Planets, Dwarf Planets & Exoplanets (by Susanna Kohler)

Sedna

Artist’s rendering of the minor planet Sedna, a distant body in the outer solar system. [NASA/JPL-Caltech]

The first press conference of the meeting kicked off (a little late, due to some technical difficulties) with a presentation by undergrad Jacob Fleisig of University of Colorado Boulder. Fleisig and his advisor, Ann-Marie Madigan, have a proposal that may be disappointing to the many fans of the Planet Nine theory: they argue that the population of detached trans-Neptunian objects (TNOs) — icy bodies like the minor planet Sedna in the outer reaches of our solar system — can be explained by a different theory than Planet Nine, a hypothetical massive planet orbiting beyond Neptune. Fleisig and Madigan instead suggest that the collective gravity of objects like Sedna and other space debris in the outer solar system could explain how the detached TNOs reached their odd orbits. Press release

press conference 1 of aas232

Panelists prepare for the first press conference of AAS 232.

Next up, University of Virginia graduate student Jake Turner presented his and collaborators’ work in the search for exoplanets with magnetic fields. Magnetic fields are of interest in the context of exoplanets and habitability because they can protect their planets from stellar winds and help them to retain their atmospheres. Turner and collaborators hope to be able to use the Low-Frequency Array (LOFAR) to find exoplanet radio signals that would indicate the presence of magnetic fields. To improve their ability to extract such radio signals from background radio noise, the team simulated the expected signals using a real planetary signal — Jupiter’s radio waves, as seen by LOFAR. They hope to soon use these methods to discover magnetic fields of planets beyond our solar system. Press release

Intrigued by Tattooine? In the final presentation of the press conference, graduate student Franco Busetti (University of the Witwatersrand, South Africa) one-ups this sci-fi binary by discussing how planets might orbit around triple star systems. By running a series of orbital integrations — over 45,000 of them! — Busetti and collaborators showed that exoplanets can exist on stable orbits in substantial regions around triple systems. While only 40 or so planets have been found around triple systems thus far, we can hope that the Gaia and TESS missions will find many more.

AAS Taskforce on Diversity and Inclusion in Astronomy Graduate Education (by Gourav Khullar)

This AAS special session aimed to disseminate updates of the AAS Taskforce on Diversity and Inclusion to the membership. Kelle Cruz and Alex Rudolph began the proceedings with a description of the Taskforce, which was empaneled in November 2018, and is in the process of putting together a report on their findings via several of their initiatives.

A description of the Taskforce’s charge is as follows:

  1. To look into retention and recruitment practices along all axes of identity.
  2. To build consensus on evidence-based practices across the community.
  3. To create and collaborate on a statement of best practices.
  4. To develop guidelines that help astro grad programs towards implementation of suggestions coming out of the Taskforce initiatives.
  5. To develop recommendations for ongoing data collection from astro grad programs.

The Taskforce has 3 working groups:

  • Recruiting & Admission
  • Mentoring & Retention
  • Data Collection & Dissemination

Some of the working-group recommendations were discussed, after which we broke out in smaller sessions for direct engagement with the working-group members:

Recruiting and admission

  1. Inclusive Astronomy & Nashville Recommendations were brought up (read more about this here: https://astrobites.org/2017/12/25/building-an-inclusive-astronomy-community/).
  2. Partnering with institutions producing PhD-ready under-represented minorities could go a long way in bringing diversity and representation to departments.
  3. There is a need for implementing evidence-based, holistic approaches to admissions.
  4. Coordinating with campus offices regarding fee waivers, fellowship opportunities, GRE policies, and application contents is a priority.

Mentoring and retention

  1. One of the priorities was facilitating an accessible and welcoming environment, ending harassment in and around astro workplaces, and supporting effective, evidence-based mentorship at all levels of astrophysics research.
  2. The working group is also involved in engaging departments in conversations, conducting assessments in your local environment, incentivizing professional development, taking actions, and monitoring progress on these actions.

Data Collection & Dissemination

  1. This working group’s priorities are built on baselines and progress in demographics and climate, as well as initiatives that provide accountability.
  2. There is a proposal to conduct climate surveys every 2 years, collect and report demographic data, and create a platform to collect data, analysis and decentralize information as soon as is feasible.

Plenary Lecture: Heavy Element Synthesis in the Universe (by Kerry Hensley)

What do gold, krypton, plutonium, and europium have in common? They’re all r-process elements, of course! Elements heavier than iron form through neutron-capture processes; when an atom captures a free-roaming neutron, the neutron will often change into a proton by emitting a beta particle (an electron, in this case). This leads to atoms bulking up into heavier and heavier elements over time. There are two neutron-capture processes: rapid (r-process) and slow (s-process), where the speed refers to the rate of neutron capture compared to the rate of beta decay. While all elements heavier than iron can be formed through both pathways, some elements (like gold and europium) are almost exclusively formed through the r-process.

In today’s lunchtime plenary, Dr. Enrico Ramirez-Ruiz (University of California, Santa Cruz) described the importance of understanding r-process nucleosynthesis in the universe. While the basic understanding of how heavy elements form has long been known, the details are still unclear — especially in terms of what astrophysical objects produce them and in what amounts. In this talk, Dr. Ramirez-Ruiz focused on neutron star mergers as a source of r-process elements. Although neutron star mergers are rare, each collision can produce about a Jupiter-mass worth of gold — equivalent to the gold abundance of a million stars!

R-process enrichment by Type II supernovae (left) and neutron star mergers (right). Cookies are now scientifically relevant! [brandeating.com and handletheheat.com]

Dr. Ramirez-Ruiz used a tasty metaphor to explain the relative contributions of Type II supernovae and neutron star mergers to the cosmic r-process abundance: while Type II supernovae spread a thin layer of r-process elements fairly evenly across a galaxy like a layer of chocolate coating on a cookie, neutron star mergers generate huge amounts of these elements in random locations — like the chocolate chips in a chocolate chip cookie.

This unevenness in heavy-element production helps to explain the huge variation in europium abundance (europium is almost exclusively made through the r-process) relative to iron in old stars. While we still need to know more about how heavy elements get mixed throughout a galaxy, studying and modeling neutron star mergers can help us understand the origins of very heavy elements in the universe.

Be sure to check out Mia de los Reyes’ interview with Dr. Ramirez-Ruiz here!

Plenary Lecture: The Relationship Between Galaxies and the Large-Scale Structure of the Universe (Mia de los Reyes, Mara Zimmerman, and Gourav Khullar)

Dr. Alison Coil (UC San Diego) started off the last plenary lecture of the day with a map of bright galaxies in the sky — a snapshot of the large-scale structure of the universe (see tweet below). This beautiful filamentary structure comes from the evolution of the universe, which is largely driven by what Coil described as a “tug of war between different cosmological parameters.”

These cosmological parameters more or less describe the ingredients that make up our universe:

  • Quantum fluctuations in the early universe produced density perturbations, which collapse into dark matter halos
  • Baryonic matter (that is, “normal” observable matter) then fell into these halos, eventually producing the galaxies we see today
  • At later times in the universe, dark energy became important, pushing apart galaxies and increasing the space between them

This led us to Coil’s main topic: the connection between galaxies and dark-matter halos, and what this can tell us about these cosmological parameters.

The way galaxies cluster can help us do precision cosmology to constrain these parameters. This is because galaxies trace the underlying dark-matter distribution of the universe, sometimes called the “cosmic web” (see tweet below). The challenge is then connecting our observations of galaxies (especially from galaxy surveys like DEEP2, which mapped out the positions of galaxies out to a redshift of z~2) with our theoretical understanding of the cosmic web (particularly cosmological simulations like the Millennium Simulation).

As Coil described, one way we can bridge this theory-observational gap is by using the halo model. This model reasonably assumes that more massive halos host more massive galaxies, so that we can use a technique called abundance matching to match halos with their associated galaxies. “This is a very, very successful model,” Coil pointed out.

We can also figure out what other parameters affect the clustering of galaxies. It turns out that the clustering of galaxies depends on several parameters: more luminous/massive galaxies and redder galaxies are both more strongly clustered than less luminous or bluer galaxies. Also, older halos are more strongly clustered in a phenomenon called assembly bias, which might be required to explain an effect called galactic conformity (how galaxies at the center of a halo appear to influence the star formation rates of galaxies in another halo).

Understanding all of these effects is vital for understanding the close connection between galaxies and halos. Coil concluded that in order to do this, theorists and observers need to work together to do precision cosmology and interpret the results!

aas232

Greetings from the 232nd American Astronomical Society meeting in Denver, Colorado! This week, AAS Media Fellow Kerry Hensley and I will be joined by a team of talented Astrobites authors — Gourav Khullar, Mia de los Reyes, and Mara Zimmerman — writing updates on selected events at the meeting. We’ll post the summary of the day’s events at the end of each day, and you can follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume next week.

Want to get a head start before the #AAS232 plenaries begin? Astrobites has been conducting brief interviews with the plenary speakers; you can read about them as they come out over at Astrobites.

We hope to see you around at Denver! Drop by to visit AAS, AAS Journals, and Astrobites at the AAS booth in the exhibit hall to learn more about AAS’s new publishing endeavors, pick up some Astrobites swag, or grab a badge pin to represent your AAS journals corridor!

corridors

InSight

Atlas-V

JPL’s Stephanie Smith introduces the InSight prelaunch press briefing next to a model of the Atlas-V rocket. [AAS Nova]

Were you awake at 4 am PDT today? If so, you were in good company — a lot of anxious and excited scientists, engineers, media, and others were wide awake at Vandenberg Air Force Base at 4:05 am PDT, when the NASA InSight spacecraft was lifted on its way to Mars on board an Atlas-V rocket.

A Unique Journey

Today’s launch marked the first interplanetary launch to take off from the west coast. Usually, launches to other planets occur from the east coast; this is because the Earth’s spin gives the rocket an extra boost when it launches east.

But rocket launchpads are crowded, and the wait to get in on the east coast can be extremely inconvenient for an interplanetary mission with a specific timeline for when it needs to launch. InSight had an alternative, however: the Atlas-V rocket was still plenty powerful — even with the southward launch from Vandenberg — to hoist InSight and send it on its way into a parking orbit. After launch, the second stage then boosted InSight out of Earth’s orbit and on its way to Mars.

What Happens Next?

InSight model

The guest of honor at the pre-launch briefing: a model of the InSight lander. [AAS Nova]

205 days from now, in November of this year, InSight will arrive at Mars and proceed to enter the planet’s atmosphere at more than 13,000 mph. A parachute will then slow it to around ~130 mph before the lander separates and lowers itself to Mars’s surface using 12 descent engines.

So once InSight touches down, it can start doing science, right? Not so fast! The placement of the lander’s instruments on the ground will take 10 weeks after it lands; sinking the heat probe will then take another 7 weeks after that. Impatient? Do try to remember that we’re operating a robot on Mars.

Experiencing InSight’s Launch Firsthand

I had the good fortune of being able to catch the InSight launch in person today, as well as the lead-up to it. At Thursday’s press briefing, the media gathered at the NASA building on Vandenberg AFB to hear from people representing multiple facets of the mission — from those who built it, to those who would be launching it, to those who will manage the science that comes from it.

press in the fog

Reporters ready to photograph the InSight launch to Mars, should Vandenberg’s marine layer clear out in time for a view. [AAS Nova]

Seeing the faces behind the mission makes the excitement and tension surrounding launch very real, and occasional comments reminded us that cockiness is never a good attitude for a mission being blasted off into space. Stu Spath, the InSight program manager at Lockheed Martin — a veteran company that has been involved with 20 Mars missions in the past — summed up the sentiment nicely: “There’s nothing ‘routine’ about going to Mars.”

Fortunately, you wouldn’t have known it from the launch itself! Liftoff occurred right on schedule at the start of the first launch window, and the Atlas-V took off without a hitch. For those of us in the press viewing area at Vandenberg, a typical blanket of marine-layer fog enveloped us, hiding the launch from view. But the roar of the engines and tremble of the ground is unmistakable, and we could hear cheers echoing in the distance around us through the fog, alerting us to the success of the first step in InSight’s journey to Mars. Sometimes, being awake at 4 am can be pretty awesome.

Christopher Conselice and M51

We’ve recently welcomed a new face to our team of Lead Editors for the AAS journals: Christopher Conselice. Chris, who joined the AAS journal team in 2010 as a Scientific Editor, is taking over the role of Lead Editor for the Galaxies and Cosmology corridor from AAS Editor in Chief Ethan Vishniac.

Chris is a professor at the University of Nottingham in the United Kingdom, specializing in the formation and evolution of galaxies. Read on to learn more about Chris’s background, his current work, and what he thinks is important in scientific articles.

Getting Started

Chris discovered astrophysics during his undergraduate studies. He originally wanted to be a physicist, but in his first year at University of Chicago, he applied for summer jobs at Fermilab and at the Yerkes Observatory. He got the job at Yerkes Observatory — “and the rest is history.”

M51

M51 (the Whirlpool Galaxy shown above), as imaged from the Yerkes Observatory in 1902. [G.W. Ritchey]

His first real research project was in galaxies, and he’s continued in that field ever since. “I thought of some ideas based on that project, and one thing has led to another, and 20 or so years later I’m still looking into those questions and follow up ones. There’s so much to learn that it is easy to spend a career on even a few questions or mastering a few techniques.”

What Can We Learn From Galaxies?

Chris’s current research focuses on observations of distant galaxies; he uses systems at different redshifts to try to infer how galaxy evolution has occurred. He also studies how the reionization of the universe occurred and examines other basic properties of galaxies such as their number densities, mass functions, and the total number of galaxies in the universe. Looking to the future, Chris is preparing for the James Webb Space Telescope and Euclid space missions, which should both launch in the next few years.

When asked about the biggest open questions in the field of galaxies and cosmology today, Chris goes deep: “Cosmological questions are the biggest questions we have in astronomy. Did inflation occur, and if so how? Is gravity modified in any way? What is the nature of dark energy and dark matter? Very fundamental stuff, but very difficult questions to answer, which many brilliant people have grappled with for decades. Galaxies themselves can tell us quite a bit about these questions, and in many ways they are the ultimate experimental subjects, as they are sensitive to everything — the nature, makeup, and geometry of the universe, dark matter, black hole assembly and feedback, and baryonic gas physics and dynamics.”

An Editor’s Insight into Publishing

Chris argues that a “good, solid paper” is easy to identify. In his view, well-authored papers have clear, specific aims and goals, thorough analyses that include detailed accounting of errors and systematics, and well-made figures.

He offers two additional tips for authors:

  1. Avoid vague, general titles; these type of titles aren’t cited as much as they could be.
  2. Be sure to avoid repeating (and failing to cite) previous work. “Always be sure you know the latest work in a field you are writing a paper in. This is easy to do with ADS searches, but some papers miss some significant work and don’t put their results into the current, up-to-date context.”
Hubble Ultra Deep Field

This Hubble Ultra Deep Field image contains approximately 10,000 galaxies, extending back in time to within a few hundred million years of the big bang. [NASA/ESA/H. Teplitz and M. Rafelski (IPAC/Caltech)/A. Koekemoer (STScI)/R. Windhorst (Arizona State University)/Z. Levay (STScI)]

Chris also emphasizes the importance of referees to the publishing process. “If I can communicate anything to the astronomical community about the publication process, it’s that if you are asked to referee a paper and can’t or don’t want to do it, please let the editor know as soon as you can. There is no judgment here, and keeping communication open is important.” Unsurprisingly, this coordination between multiple people can be one of the slowest parts of the publishing process, and timely referee responses can significantly reduce the turnaround time for article publication.

Go Forth and Create New Knowledge

We hope you enjoyed this opportunity to learn more about Chris Conselice! You can expect hear from him if you submit to the Galaxies and Cosmology corridor in the future.

We’ll leave you with one final thought from Chris, which nicely sums up why we do what we do: “I was always impressed with my professors as an undergraduate, and I can recall seeing research papers being produced and thinking that was the most magical thing possible — creating new knowledge. That seemed like the most amazing thing one could do.”

AAS Nova

Today’s post marks the 500th highlight published on AAS Nova since our launch in August 2015. To celebrate, we’re taking a moment today to look back at what we’ve published during this time.

What Does AAS Nova Cover?

AAS Nova topics

Breakdown of AAS Nova Highlights by topic, including the seven journal corridors and two AAS-related topics. Click for a closer look.

Journal articles featured in AAS Nova Highlights are selected by the lead and scientific editors of the AAS journals in collaboration with the AAS Nova editor, with the goal of identifying research that is of particular importance or of potential interest to a broad community.

Highlighted articles are selected from across all five AAS journals —The Astronomical Journal (AJ), The Astrophysical Journal (ApJ), The Astrophysical Journal Letters (ApJL), The Astrophysical Journal Supplements (ApJS), and Research Notes of the AAS (RNAAS) — and they span all seven journal corridors.

Observation-based AAS Nova Highlights are twice as common as theory-based Highlights.

The first 500 Highlights published on AAS Nova since launch have been distributed across corridor topics; the four most commonly featured corridors are Planets and Solar System, Stars and Stellar, Galaxies and Cosmology, and High Energy.

The breakdown between theory-based and observation-based articles highlighted on AAS Nova is roughly two-thirds observation, one-third theory.

Who Reads What?

AAS Nova readers come from nearly everywhere in the world, representing over 200 countries and territories. Roughly half of our readers are located in the United States.

AAS Nova readers come from over 200 different countries. [Google Analytics]

Our normal Features posts (i.e., summaries of AAS journal articles) are the most commonly read Highlights.

Do readers go on to explore the original scientific papers that the Highlights summarize? We can’t determine that with certainty, but we have found that articles that have been featured on AAS Nova are, on average, downloaded more than four times more often than typical journal articles.

What Have You Missed?

Wondering what you’ve missed since we first launched? Here’s a list of the ten most popular Highlights published on AAS Nova in the last 500 posts.

  1. An Update on Planet Nine
  2. An Explanation for Saturn’s Hexagon
  3. LIGO Discovers the Merger of Two Black Holes
  4. Update On the Puzzling Boyajian’s Star
  5. A Ninth Planet in Our Solar System?
  6. What Do You Get When Two Neutron Stars Merge?
  7. Featured Image: The Q Continuum Simulation
  8. How Normal is Our Solar System?
  9. Another Possibility for Boyajian’s Star
  10. Explaining the Birth of the Martian Moons

We’ve very much enjoyed covering the amazing work AAS journal authors are producing, and we look forward to seeing the exciting ideas and discoveries that we get to feature on AAS Nova in the coming years!

cocoon

Editor’s Note: This week we’re at the 231st AAS Meeting in National Harbor, MD. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume next week.

Plenary Talk: Illuminating Gravitational Waves (by Caroline Huang)

Professor Mansi Kasliwal [Mario de Lopez]

The past few months have been exciting ones for Mansi Kasliwal, a professor at the California Institute of Technology (Caltech). She has spent countless sleepless nights working with a team of astronomers (many of them graduate students and postdocs, which she took the time to acknowledge in her talk) that discovered and analyzed the first electromagnetic (EM) counterpart to a gravitational wave (GW) event, GW170817. Details about the GW event itself were a major component of Gabriela González’s talk on Wednesday. In the plenary talk this morning, Kasliwal focused on what we can take away from its EM counterpart.

Kasliwal began by discussing the bright outlook on multi-messenger astronomy — in which we study and coordinate observations between different messenger signals (GW, EM radiation, neutrinos, and cosmic rays). She then gave us an outline of the timeline for the EM detections. A burst of gamma-rays was the first EM counterpart, detected 1.7 seconds after the merger, and after cross-matching galaxy catalogs with the region identified from the two LIGO detectors and VIRGO, infrared telescopes were able to pinpoint the location of the merger.

So what does the EM counterpart tell us? As Kasliwal pointed out, when the neutron star-neutron star (NS-NS) merger was first announced, 84 papers appeared on arXiv — and that number has climbed steadily since. For one, the NS merger has given us insight into where r-process elements are formed. People had theorized that perhaps NS-NS mergers or NS-black hole mergers produced many of the elements heavier than hydrogen, but we had never actually seen one of these events before LIGO, let alone been able to take spectra of the remnant, as they have done with GW170817. The spectra give us a wealth of information about what elements are present and were created after the merger, but a full analysis won’t be finished for months or years from. Still, they have shown us that some r-process elements can be formed in this kind of merger.

cocoon

An artist’s rendition of a “cocoon” surrounding a burst of gamma rays. [NRAO/AUI/NSF: D. Berry]

Secondly, the event has also given us new insight into jet physics. While GW170817 was often characterized as a short gamma-ray burst, Kasliwal was careful to refer to it only as a “burst of gamma-rays.” This event hasn’t quite fit the profile of a short, hard-gamma-ray object, in part because its was 10,000 times wimpier than others in this class have been. Our basic picture of an off-axis short, hard gamma-ray burst fails to explain the event and the afterglow, nor does it explain how bright and blue it was for a long time afterwards. It is also what Kasliwal calls “mildly relativistic”, with a Lorentz factor of 2–3 (still ~0.9 the speed of light) instead of 100 (~0.99995 the speed of light!), as we would normally have seen. Instead, Kasliwal discussed the application of the “cocoon” model to explain this burst. In the cocoon model, the merging neutron stars rip off a few hundredths of a solar mass of material from each other as they spiral in, causing the jet to break out into a messy ejecta and creating a wide angle instead of a narrow, 10-degree beam that we might otherwise have expected. This explains the wimpy burst and the bright blue appearance (due to the accelerated ejecta).

Even with all of this new information however, some things — like the ultimate fate of the jet — still remain to be seen. What we can take away from Kasliwal’s talk is that analysis of GW170817 is far from over — there is still much more we can learn from it and other events like it in the bright, multi-messenger astronomy future.

Plenary Talk: The Fate of Exploding White Dwarfs (by Kerry Hensley)

detonation channels

Detonation channels for Type Ia supernovae.

Robert Fisher of the University of Massachusetts at Dartmouth is an expert in complex explosions and uses supercomputers to study how Type Ia supernovae detonate. Dr. Fisher tells a story of competing explanations for the thermonuclear explosions of Type Ia supernovae: single-degenerate and double-degenerate pathways. The single-degenerate pathway is the textbook Type Ia supernova: a white dwarf siphons mass off of its main-sequence or red-giant companion until it exceeds the Chandrasekhar mass and explodes. The double-degenerate pathway requires either a degenerate or helium-rich companion. Dr. Fisher commented that both pathways likely exist in nature, but we need a better understanding of the outcomes of each scenario to fully grasp the observed diversity of supernova light curves.

single-degenerate pathway

Simulations showing that the single-degenerate pathway can lead to a variety of outcomes.

There are many outstanding questions in supernova science: Do all “normal” Ia supernovae detonate the same way, or is it possible to get a typical result through different pathways? What about the atypical (abnormally bright or dim) supernovae — are they just extreme cases or the typical supernovae or do they arise from a different pathway? Most importantly, how can we distinguish between these scenarios?

Simulations are an excellent tool for understanding how supernovae detonate and how the resultant light curves will look. Dr. Fisher outlined the shortcomings and successes of supernova simulations. Simulations have been successful in showing that the single-degenerate pathway produces diverse explosions, but there are theorized detonation methods that still haven’t been modeled, such as the “deflagration to detonation” method. Modeling unusual supernovae like SNR 3C 397, which is asymmetrical, could lead to a better understanding of how Type Ia supernovae explode.

length scales

The variety of important length scales in supernovae. The recent advances in modeling will help capture the small-scale physics that can have a big effect on the outcome of a supernova.

For the double-degenerate channel, current simulations fail to capture small-scale physics like turbulence or the size of the carbon flame. This leads to poor agreement between the modeled and observed light curves, which is an ongoing issue. Advances in supernova modeling will capture turbulence-driven detonation, which should help the modeled light curves match the observations more closely.

Observed supernova light curves, when used in tandem with simulations, can also yield information about the origins of the supernova. Looking at the light curves of supernovae well after peak brightness (late-time light curves) can help distinguish between the scenarios. The ratio between iron-55 and cobalt-57, for example, is predicted to be different in the single-degenerate and double-degenerate pathways. The ratio should be reflected in how quickly the luminosity declines since the different isotopes have different half-lives, providing an observational constraint on supernova detonation mechanisms.

Plenary Talk: The Politics of Science Funding: Is the Fault in Our Stars (by Kerry Hensley)

David Goldston of MIT got real with the assembled astronomers about their federal budget woes. He explained that what astronomers sometimes fail to do is put things in context; when the budget numbers are released (and science inevitably gets a disappointingly small piece of the pie), scientists can be quick to attach sinister meaning. Not so fast, said Goldston. Interpreting the budget numbers without first considering the context can be misleading. The single largest determining factor for the annual science budget is the total size of the federal budget. While the amount allocated each year to science varies, the percentage of the budget distributed to science has remained nearly the same for decades.

David Goldston

David Goldston

While this can seem discouraging — what control do individuals have over the federal budget?! — Goldston thinks that this shows that a major fear of scientists is unfounded; if science’s slice of the pie has remained the same for decades, the insidious threat of anti-science sentiment must not have taken hold as firmly as many scientists fear. (A clear exception to this is climate science, where views tend to fall along political lines, with some lawmakers complaining that climate science is carried out by “politicians in lab coats” and pushing for cuts to funding.) He cited yearly polling that shows that scientists consistently rank first or second on the list of people who act most in the public interest and are highly-respected. Plus, people are attracted to the idea of discovery, of having “Wow!” moments, of learning new things. And luckily for astronomers, the appeal of discovery can override the desire for practicality; when lawmakers attempted to surreptitiously slash funding for Hubble, public outcry saved the beloved telescope.

So, what does that mean for scientists? What, if anything, can individuals and organizations like the AAS do to improve budget prospects for science? Goldston reminded the audience that politics begins at home, and small changes can have a big effect. He emphasized the potential impact of higher education institutions and encouraged universities to host government representatives and show them what federal funding pays for — especially the “Gee whiz!” stuff — because they may not know. He added that introducing the representatives to students is especially important, saying, “Education is the most politically attractive aspect of science research.” He shared some advice for conversations with lawmakers: Remember that they’re people — people who are awed and inspired by images from Hubble — but people with a great responsibility that scientists do not have. Connect with them as people and show them that your work is in the public interest — because big changes won’t happen without people committed to bringing them about.

Lancelot M. Berkeley Prize: The Instruments that Launched Gravitational-Wave Astronomy (by Caroline Huang)

Peter Fritschel

Peter Fritschel

The final plenary talk of AAS 231 was given by MIT professor Peter Fritschel, who received the 2017 Lancelot M. Berkeley Prize. His talk was the instrumentional counterpart to Gabriela González’s Wednesday presentation, focusing on the aspects of the LIGO design that allowed them to make their amazing discoveries. Most of the talk was accompanied by pictures of the various parts of the experiment that was being discussed.

LIGO’s basic design can be thought of as an enhanced Michelson interferometer. However the LIGO interferometers have several changes that make them much more powerful than standard Michelson interferometers. To effectively increase the arm length of the interferometer, they add Fabry Perot “cavities” to the arms. Mirrors are placed near the beam splitter to allow the laser light to bounce back and forth 280 times before the light is merged again. For gravitational-wave (GW) experiments, the larger the experiment the better, so this increases LIGO’s effective arm length from 4 km to 1120 km, making it far easier to detect any GW passing through. LIGO also uses power-recycling mirrors to build up the power of the laser and is able to boost the power by 3750 times, ultimately generating an output 750 kW beam. This allows the instrument to produce a sharper interference pattern to make it easier to detect any GWs passing through.

LIGO test masses

Two of LIGO’s test masses. [LIGO]

The LIGO interferometer has four test masses that must be very well isolated from the surrounding environment in order to measure the incredibly tiny distortions from a gravitational wave. They use a combination of both active and passive damping to achieve this. The active damping senses vibrations in the surrounding environment and acts in a way to counteract them. The passive damping holds the test masses still using a four-stage pendulum. These test masses are 40 kg of fused silica, which they chose to minimize infrared absorption. Since LIGO uses an infrared laser, this is especially important. Astonishingly, only one out of every 3.3 million photons is absorbed by their mirrors. The others are all reflected or transmitted.

LIGO is also built in such a way that allows (and anticipates) that it will be upgraded, which includes having space for bigger and newer components. It has already been upgraded several times and they are continuing to increase the sensitivity. By design, it is currently limited by quantum and thermal noise. They plan to decrease the quantum noise by using squeezed light. The thermal noise largely comes from the Brownian motion of the optical coatings, so finding new low-thermal-noise coatings with high reflectivity will help LIGO achieve even better sensitivity in the future.

Fritschel concluded his talk by discussing the future of gravitational-wave astronomy as a whole. With Virgo interferometer now online and Kagra and and LIGO India joining in the future, the study of gravitational waves is just getting started.

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