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 Wednesday afternoon!
-The Astrobites Team
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PREVIEW: Stay tuned from 2:00-3:30 pm today for another round of Astrobites One-liners from session 332: Star Formation – Cores, Clouds, and the IMF!
Image courtesy of the University of Maryland Department of Physics
12:45 PM: Press Conference on Particle Astrophysics and Precision Cosmology
This press conference covered five presentations on the intersection between astronomical observations and fundamental physics.
Robert Nemiroff (Michigan Technical University) spoke first on using gamma ray bursts to search for evidence of discretization in space and time. Some theories of quantum gravity explore the idea that space and time themselves might be quantized – that there is a minimum quantum “second” and quantum “length”, so that at a very fine level the universe appears essentially pixelated. In this framework spacetime is often described as a “foam.” Nemiroff’s group looked for evidence of this foamy spacetime in the behavior of very high energy photons from GRB 090510A as observed by the Fermi-LAT. Based on the bunched arrival times of the photons, they placed a limit on the resolution of a foam that’s much smaller than the Planck length.
Jonathan Whitmore (Swinburne University of Technology) spoke next on measurements of the fine structure constant over cosmic time using absorption lines in QSO spectra. Because the ratios of certain absorption lines are a function of the fine structure constant, any change in that constant would appear as a long-term variation in the appearance of those lines. They measured 15 quasar lines of sight with the VLT-UVES spectrograph, cataloguing 45 absorption line systems at redshifts out to z = 1.69, or back as far as 10 billion years. They found no evidence for a change in the fine structure constant over cosmic time.
Rodger Thompson (University of Arizona) continued the theme of searching for changes in fundamental constants over cosmic time by speaking about the search for variations in the electron-proton mass ratio. The two current leading theories for explaining the acceleration of the universe are a cosmological constant, which predicts no change in fundamental constants over time but the value of which we cannot correctly calculate at the moment, and a rolling field changing over cosmic time, which has the right values but which would also cause changes in fundamental constants like alpha and the e-p mass ratio. Thompson spoke about the Bagdonaite et al. paper of 2012 in which they published evidence that the e-p mass ratio has remained constant to 1 part in 10 million since z = 0.88582, placing strong constraints on a possible rolling field model and bolstering the cosmological constant.
Ryan Cooke (UC-Santa Cruz) next spoke about the observation of the primordial deuterium/hydrogen abundance in near-pristine clouds of gas. Deuterium is a “primordial” element because it is only made during Big Bang Nucleosynthesis, so studying the ratio of deuterium to hydrogen in gas clouds that have undergone very little processing since the Big Bang can give us an idea of what happened in the chaotic minutes afterwards. Cooke found the gas cloud in absorption near a quasar at z = 3.08, and extracted a deuterium/hydrogen abundance from it that, combined with the observed baryonic matter density of the universe, constrains the number of interacting neutrino species at 3 +/- 0.5.
Douglas Finkbeiner (Harvard-Smithsonian CfA) spoke last about the status of the 130 GeV line potentially seen in the Fermi-LAT gamma ray data, a candidate for a dark matter annihilation signal. In 8 months of additional data, Finkbeiner said, they have only seen a photon signal consistent with the background, which, although it does not disprove the initial detection, is less than heartening news. The upcoming Pass 8 reprocessing and data release from Fermi should provide more information, and the HESS 2 array now coming online could also search for a line. Sadly there is little hope for re-examining the dwarf satellites to search for a signal, as the flux expected from them in this model would be on the order of 1 photon a year.
Although many of the results in this press conference related to negative detections or confirmations of existing, well-regarded models, all five speakers were anything but discouraged; the process of testing existing models and searching for new physics with ever-increasing accuracy still has great promise to produce interesting new results.
2:00 PM: Surveys and Catalogs of Extrasolar Planet Hosts
There were several simultaneous exoplanet sessions this afternoon, so many astronomers traveled back and forth between multiple sessions. This particular exoplanet session began with a talk by Solange Ramirez (Caltech) about the NASA Exoplanet Archive, a fantastic resource for exoplanet enthusiasts. The new Kepler planet candidate list is already available on the archive if you’d like to learn more about the 817 new planet candidates announced at AAS this week. The second talk of the session was a dissertation talk by Tim Morton (Caltech). Morton is conducting a statistical analysis of the false positive probability of Kepler planet candidates and excited the audience by displaying a plot of the false positive probabilities for the new planet candidates announced on Tuesday. In the third talk, Steve Bryson (NASA Ames) presented a new method to quantify the likelihood that a transit signal observed in the Kepler data is due to a transit of a star or a transit of a background object. Next, Philip Muirhead (Caltech) discussed the interesting case of KOI 256.01, a Kepler planet candidate that turned out to be a white dwarf orbiting an M dwarf.
In the second half of the session, Andrew Mann (University of Hawaii) delivered a dissertation talk about his work using near-infrared and optical spectra to refine the radius, metallicity, and temperature estimates of the cool Kepler target stars. After Mann, Nicholas Law (University of Toronto) discussed the Robo-AO project to automatically acquire high-resolution adaptive optics images of stars using a laser guide star. As the name of the system suggests, Robo-AO is entirely robotic and runs without the need for a human operator. The Robo-AO system is incredibly efficient and can observe 25 Kepler target stars in a single hour. The final talk was by Michael Pagano (Arizona State University). Pagano discussed his work to measure the elemental abundances of nearby exoplanet host stars using spectra acquired by Paul Butler (Carnegie Institute of Washington).
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