AAS 228: Day 4


Editor’s Note: Last week we were at the 228th AAS Meeting in San Diego, CA. Here is a final post about selected events on the last day of the meeting, written by authors from astrobites.com, a grad-student collaborative project with which we recently announced a new partnership! Starting in July, keep an eye out for astrobites posts at AAS Nova in between Highlights (i.e., on Tuesdays and Thursdays). We’re excited to be working together to bring you more recent astronomy research from AAS journals!

Extrasolar Planets: Detection (by Leonardo dos Santos)

Thursday’s first session on exoplanets was about detecting these distant worlds, and the opening talk was given by Robert Siverd (Las Cumbres Observatory). He describes the NRES, a network of spectrographs that will look for exoplanets using the radial velocity method. One of the coolest aspects of this instrument is that it will feature an “on the fly” scheduling system that will perform observations as efficiently as possible. The spectrograph is still being tested, but a unit will be deployed at CTIO later this year.

Measuring the depths of transits and eclipses in Spitzer has been problematic in the past, since the Spitzer instrument IRAC (InfraRed Array Camera) has a non-uniform response in its detector’s pixels. But, as reported by James Ingalls (Spitzer Science Center, Caltech), observers are circumventing this issue by using what they call the staring mode (avoiding large pointing jumps) and an algorithm to pick “sweet spot” pixels. Moreover, the results from the IRAC Data Challenge are helping to better understand its behavior. Giuseppe Morello (University College London), on the other hand, explained how his research group gets rid of instrumental effects from IRAC using machine learning. This method removes systematics from exoplanet transit data no matter if the noise source is from an instrument or a star. Speaking of transits, Kepler was one of the shining stars of this meeting. The original mission observed 150,000 stars continually for months during its first run, as it was designed to be a statistical mission. But can its findings be considered fully complete in planet radii and orbital periods? Joseph Catanzarite (SETI Institute) aims to answer this question by performing numerous simulations (“injections”) in order to validate our estimations of planet occurrence rates from transit data.

During Kepler’s primary mission, it was relatively easy to identify eclipsing binaries — which are a common type of false positive in exoplanet detection — owing to the spacecraft’s stability. Fergal Mullally (Kepler Science Office) points out that this is not true for K2, due to its continual drift from the pressure of sunlight. They are currently developing dave, a Python program that aims to find and vet planets from K2 data.


Another tool being developed for K2 data analysis is Robovetter, which was introduced by Susan Thompson (SETI Institute, NASA Ames). This new software will allow astronomers to fully and uniformly automate the creation of the final KOI (Kepler Object of Interest) catalog. And what about the science being done by K2? Jessie Christiansen (NASA Exoplanet Science Institute, Caltech) explains that it will not look for Earth-like exoplanets, but will instead be more flexible in the types of targets and their positions on the sky, allowing us to build a census of planets in the galactic plane.

Black Holes and Supernovae (by Ashley Villar)

There are still many open questions about supernovae and their progeny, black holes. Some of these questions will hopefully be answered by LIGO, though many will be solved using the electromagnetic radiation we detect from these sources.

Anthony Piro began the session by explaining his new models which trace the diffusive cooling of an initial supernova shock. His team has created an open source code, the SuperNova Explosion Code or SNEC, to allow others to explore a variety of explosion properties. Janie De La Rosa then spoke about her work on observing Type IIn supernovae (those with narrow emission lines in their spectra) at ultraviolet and optical wavelengths. These wavelengths are sensitive to progenitor models and the geometry of the surrounding material.

Cas A

Composite image of the supernova remnant Cassiopeia A, using data from the Chandra X-ray telescope, NASA’s Spitzer Space Telescope, and ground-based facilities. [NASA/CXC/SAO]

Following the exploration of progenitor geometry, Douglas C. Leonard spoke about his work in hunting for polarization in type IIP supernovae (those with long, plateaued light curves). A high degree of polarization implies asymmetry in the explosion itself, and he has been able to find such asymmetry in a number of type IIP supernovae. He pointed out that “bubble”-like structure (like what we see in the beautiful supernova remnant Cassiopeia A) might explain the polarization as well.

Switching gears, Karri Kolijonen spoke about an interesting X-ray binary (a binary consistent of a compact object and star that emits strongly in X-rays) known as GS 1354-64. This pair has an extremely short orbital period of just two and a half days! He explained how an instability in the black hole’s accretion disk might explain a recent outburst in the system.
Thomas Pannuti explained the basic morphologies of supernova remnants: shell, composite, and mixed. He has taken extensive, multiwavelength images of a mixed remnant known as W28 from radio through X-ray wavelengths. He notes that the radio masers in the remnant are offset from the X-ray light, although the significance of this is still an open question.
Finally, Maria Dainotti wrapped up the session with a discussion of long duration GRBs as standard candles. She finds that, like type Ia supernovae, the light curves of GRBs can be renormalized and standardized with a small scatter in their diversity. Because GRBs are so much brighter than type Ia supernova, these objects could be used as standard candles at much larger distances, and therefore probe the expansion of the universe at much earlier times.