Astrobites is again 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 Tuesday afternoon!
-The Astrobites Team
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An image of "Nessie", the dark filaments which are begin called the bones of the Milky Way.
12:45 pm Press Conference: “Journey to the Center of the Galaxy”
This session focused on studies of the structure of our Milky Way galaxy, with four out of the five presentations discussing the extreme conditions found near the very center.
Alyssa Goodman (Harvard-CfA) began by presenting the discovery of what she called one of the “bones” of the Milky Way: an extremely thin (300:1 aspect ratio or more), dense, filamentary dark cloud extending along one of the spiral arms. This structure, dubbed “Nessie” due to its extended snake-like appearance, is now estimated to be much longer than previously thought. Furthermore, Goodman showed that the origin of the Galactic coordinate system is NOT actually at the Galactic center – the Sun is 20 or so parsecs above the line along b=0 (b is Galactic latitude), while the center of the Galaxy is actually below that line. There may be several more of these “bones” that, if detected, could help with the challenging problem of trying to map the Galaxy from the inside-out.
Jens Kauffman (Caltech) continued the discussion of infrared dark clouds with the presentation of a study of a cloud near the center of the galaxy, called G0.253+0.016. This object has the highest average density amongst known clouds but almost no star formation. The observations presented here resolved for the first time small, sub-parsec scales and measured the density structure within the cloud, showing that while the average density was high, there were no very strong density peaks within the cloud – densities are quite low locally. Furthermore, the velocity dispersion of the gas is as high as 10 km/s – enough to resist gravity’s pull and further suppress star formation.
Farhad Yusef-Zadeh (Northwestern Univ.) showed examples of a surprising result: “dark” patches observed at radio wavelengths (typically, radio waves pass unimpeded through medium of basically any density). The radio observations taken here probe free-free emission, or emission caused by collisions of free electrons, and thus are a measure of ionized gas. Molecular clouds are dense enough that ionizing radiation cannot penetrate them, and thus no free-free emission is found within them. In other words, molecular gas and ionized gas are spatially anticorrelated in regions around molecular clouds.
The last two presentations discussed new results on the Galactic center region from the SOFIA observatory, a repurposed 747sp aircraft outfitted with a 2.5m telescope. It flies at 40,000 ft – well above most of the atmosphere that blocks most mid-infrared emission – and thus allows unprecedented study of the Galactic center, which is normally quite difficult to observe due to the large amount of dust in the Galactic plane. Matthew Hankins (Univ. of Central Arkansas) discussed the Quintuplet Cluster, a massive star cluster. SOFIA observations show that the five dust-enshrouded sources for which the cluster is named are likely Wolf-Rayet + massive star binaries having different separations and orientations. Ryan Lau (Cornell Univ.) then presented observations of the circumnuclear ring, a dusty ring-like structure surrounding the supermassive black hole at the center of the Galaxy at a distance of only a few parsecs. The SOFIA results show that the ring is tilted at about 70 degrees to our line-of-sight, is centrally heated (presumably by the star cluster at the Galactic center), and is very clumpy.
2:00pm: Exoplanet Atmospheres
This Exoplanet Atmospheres session was composed mostly of thesis talks—in essence, summarizing the last 3-6 years of the speaker’s research in 15 minutes! This session really focused on the challenges of observing and characterizing super Earths. Ian Crossfield, a postdoc at Max Planck in Heidelberg, kicked it off talking about ground based observations of exoplanet atmospheres. Among other things, he discussed their current efforts to observe the super Earth GJ 3470b, which will be an interesting addition to our super Earth studies. Laura Kreidberg, a grad student at UChicago, showed early results from a very exciting HST program to detect features in GJ 1214b’s atmospheres. Mike Line and Bjoern Benneke, grad students at Caltech and MIT, discussed their theoretical models developed to retrieve the abundances of molecules in planets from observations and use that information to see if atmospheres are in or out of chemical equilibrium. Renyu Hu finished the session with his new code which can determine potential good and bad biosignatures, to find evidence of life on exoplanets; he finds that some potential biosignatures like hydrogen sulfide can occur in abundance without life.
3:40 pm Plenary Session: Newton Lacy Pierce Prize: “Hot on the trail of Warm Planets Orbiting Cool M Dwarfs”
The first plenary talk this afternoon was delivered by Professor John Johnson (Caltech), this year’s winner of the Newton Lacy Pierce Prize, which is an award granted by the AAS to an astronomer under the age of 36 who has completed outstanding achievements in observational science. Professor Johnson received this award “for major contributions to understanding fundamental relationships between extrasolar planets and their parent stars, including finding a variety of orientations between planetary orbital planes and the spin axes of their stars, developing a rigorous understanding of planet detection rates in transit and direct imaging experiments, and examining possible correlations between planet frequency and the mass and metallicity of host stars.” Some of our regular readers may recall that Professor Johnson is also a frequent astrobites contributor.
Professor Johnson began his talk by presenting three reasons to study exoplanets: 1) understanding our origins; 2) putting the solar system into a broader galactic context; and 3) discovering life elsewhere in the galaxy. Regarding the second point, Professor Johnson joked that basing our understanding of planets on only the planets in the solar system “is like trying to do sociology on yourself.” Fortunately, planetary astronomers now have a sample of more than 3000 planets and planet candidates that we can study to address those three goals.
Although many of those planets and planet candidates orbit stars similar to the Sun, Professor Johnson focused his talk on the advantages of studying planets orbiting M dwarfs (cool stars). His ExoLab research group consists of 7 graduate students, 4 undergraduates, and 3 postdocs is pursuing an impressive array of projects to study planets around M dwarfs. The projects range from validating Kepler planet candidates to revising the parameters of planet host stars and they combine to present a revised picture of planet formation and occurrence around M dwarfs. The main conclusions of the talk were that understanding the properties of planet host stars is crucial to understanding planets and that most M stars (and therefore most stars!) have planets. If you’d like to learn more about the ExoLab, check out their webpage and this astrobite. For our readers attending the AAS, a complete list of talks and posters by ExoLab members is here.
I’d like to point out John Johnson’s shout-out to Courtney Dressing, one of our astrobites authors, in his talk. John Johnson praised Courtney for leap-frogging his results “as good graduate students should.” In her Tuesday morning talk, Courtney presented an independent analysis finding that 87% of M dwarfs harbor a small planet, and that there is a 95% chance of an Earth-size planet in the habitable zone transiting an M dwarf within 31 parsecs. The great odds of finding an Earth analog around an M dwarf close to home bolster the exoplanet community’s push to launch a satellite mission that will search for nearby transiting planets. Congratulations, Courtney!