Astrobites@Austin: Wednesday Afternoon Sessions

This year, Astrobites will be liveblogging AAS. In order to avoid inundating our readers’ RSS feeds, we’ll be updating this post with short paragraphs about the talks we’ve heard and posters we’ve seen. So keep checking back throughout Wednesday afternoon! If you missed them, here are the Monday morning sessions, the Monday afternoon sessions, the Tuesday morning sessions, the Tuesday afternoon sessions, and the Wednesday morning sessions.


4:30 pm – Invited Session: Star Formation in Galaxy Clusters Over the Past 10 Billion Years – Kim-Vy Tran

We now know that structure in the universe form hierarchically, that is, small things like galaxies form first and then large objects like galaxy clusters are some of the most recent to coalesce. Clusters can contain anywhere from hundreds to thousands of bright galaxies with velocity dispersions of around 1000 km/s. Galaxy clusters are interesting as they provide one of the best laboratories to study the effects of dark matter both on the kinematics of the galaxies in the cluster and the lensing of the light from background galaxies.

We can classify galaxies in these environments based on characteristics like color and spectral features which are signatures of star formation or lack there-of. Galaxies in clusters are redder than galaxies in the field indicating older stellar populations and also more likely to be elliptical rather than disk-like in morphology. There is a third very powerful way of tracking star formation and that is the amount of mid-infrared emission. If the galaxy has a lot of dust, the light from new stars will not be able to escape in the optical and will rather escape as infrared radiation.

The first step to studying a cluster is identifying which galaxies are part of the cluster or galaxies that are along the line of sight but not part of the actual cluster itself. What is found is that as you look at clusters at higher redshift, or further back in the history of the universe, there is an increasing fraction of cluster member galaxies that are star forming. Another interesting result is that at redshifts ~ 1.62, there is more star formation  in dense environments like clusters than the field which is opposite of what we observe in the local universe. “A reversal of fortune!” Now Kim-Vy’s team is looking for over-densities in the  K-band with the FourStar instrument on the Magellan telescope to identify high-redshift clusters. Having data from clusters at both high and low redshift will enable careful studies of star formation evolution in clusters and how it differs from galaxies in the field.


3:40 pm – Invited Session: Galaxy Formation Star-by-Star, the View from the Milky Way – Kathryn V. Johnston

When satellite galaxies fall into the tidal radius of a large galaxy like the Milky Way, they form an accreted stellar halo full of stellar streams from the different galaxies. Several streams like this have been observed in the past two decades, the most famous probably being the Sagittarius stream, which is easily detected in the SDSS stellar catalog. This “galactic cannibalism” fits in well with the hierarchical structure formation model of galactic evolution, in which large objects are built up from smaller ones.

Looking at the particular phase-space structure and chemical abundances of various stellar streams in the Milky Way can tell us about the dark matter halo in which the stars were born, as well as the history of baryonic physics in the gas clouds where they were formed. In Dr. Johnston’s words, “Stars remember what gas forgets.” Chemical tagging – measuring the metal content of stars – can tell us about how the Milky Way’s halo formed: was it formed in situ, from stars that were kicked out of the galactic disk, or from accreted stars? Many halo stars have metallicities similar to those of existing satellite galaxies, but there are also some with chemical compositions similar to those in the disk, indicating varied origins for the galactic halo.


3:30 pm – Session 330: Cool Dwarfs, Brown Dwarfs – Part 2

Gregory Mace talked about using WISE to find new late T dwarfs. They’ve used many different follow-up telescopes to identify these faint brown dwarfs. This resulted in a 300% increase in the number of known T9 stars

From the talks in this session (see previous update on Session 330), a listener – or an astrobites  reader – would notice that models of low mass stars are a bit iffy. One way in which they are differ is that observed radii are inflated with respect to model. For his thesis, Waqas Bhatti looked into whether magnetic fields in binaries can explain this.

Sarah Schmidt is exploring the oft-neglected regime of ultra cool dwarfs with spectral types from M7 to L3. She asks us: “which properties of M7-L3 dwarfs correlate well with age?” She looked at activity as a function of spectral type, distance from the galactic plane, kinematics color. She presented so many empirical correlations, some of which can be extended to L dwarfs, that it’s impossible to distill it into a few sentences!


2:45 pm – Session 330: Cool Dwarfs, Brown Dwarfs – Part 1

This session was a three-for-one in understanding the observed physical properties of M dwarfs. It included talks by John Johnson (The Masses and Metallicities of Kepler’s Planet-hosting M Dwarfs), Phil Muirhead (on KOI-961) and Barbara Rojas-Ayala (M-Dwarf Metallicities With K-band Spectra: Testing Calibrations With Observations of 133 Solar Neighborhood M-Dwarfs).

John Johnson talked about characterizing the cool Kepler Objects of Interest (KOIs). Discoveries include a brown dwarf orbiting a binary system, a Jupiter mass object orbiting an M dwarf and the recent announcement of KOI-961. Phil Muirhead talked more in depth about this last discovery of the small planets orbiting the small star KOI-961. Understanding the physical properties of KOI-961 involved the used of Barbara Rojas-Ayala’s method for measuring metallicities.

Barbara Rojas-Ayala gave her thesis talk on using near-infrared lines to measure the metallicities of M dwarfs. These stars are the closest and most abundant stars in our galaxy. She talked about her method, which uses the depth of alkali metal lines and shared some of her results. One result she showed was the metallicity distribution of planet-hosting stars and those that have not shown any sign of hosting planets. The planet hosts are more metal-rich than the non-planet host stars.


2:30 pm – Careers in Media for Scientists

Richard T. Fienberg, American Astronomical Society
David Aguilar, Harvard-Smithsonian Center for Astrophysics
Deborah Byrd, EarthSky: A Clear Voice for Science
James Glanz, The New York Times
Laura Helmuth, Smithsonian Magazine

Rick Feinberg described the panel as a bunch of geeks who don’t work directly with science. To some, this may be very appealing! David Aguilar followed this introduction stating that those who work in science media are real scientists, but missed the calling to devote their lives to one topic and working with only one small group of people, so they bailed. He claims that scientists who work in media are alchemists, who take the science presented by others, molding and shaping scientific charts and graphs into something that the general public can appreciate.A dynamic speaker, he followed with several examples of science stories translated from scientific language into catchy media slogans. A scientist likes to conclude with “More research is needed”, which is not a sufficient conclusion, in Aguilar’s mind. He says that the public wants to know the implications and the conclusions of a story.

The general idea is that scientists are not trained to communicate with the public. The potential we have in astronomy is unique, because the public is fascinated with space and the universe, so we should take advantage and communicate effectively. I regret that I couldn’t report on the presentations by the other panelists, but alas other events at the AAS meeting required my attention. But what I took away from this talk, and from my experience with astrobites, is that science media is a feasible and exciting career.


1:00 pm – Press Conference: Extraordinary Exoplanets

Today at the exoplanet-themed press release, there were three very interesting discoveries announced of three very different systems. There were more questions than the speakers had time to answer!  William Welsh announced Kepler-34b and Kepler-35b, two new circumbinary planets from the Kepler team. John Johnson and Phil Muirhead presented three new sub-Earth sized planets orbiting an M dwarf. Finally, Erik Mamajek showed us the first ever transit of an extrasolar “ring” system. Check back on Astrobites later for more information!

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