Astrobites@Austin: Thursday 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 Thursday! If you missed them, here are the Monday morning sessions, the Monday afternoon sessions, the Tuesday morning sessions, the Tuesday afternoon sessions, the Wednesday morning sessions, and the Wednesday afternoon sessions.


3:00 pm – Session 414: Understanding the Kepler candidates

As Tim Morton reminded us, Kepler is above all else a statistical mission, which aims to answer the question of how many Earth-like planets are out there. (Kepler is a transiting planet survey, you can read more about it in this introductory astrobite). Understanding the overall statistics of the Kepler Mission requires understanding each of the individual candidates, which are of different sizes and orbit stars with different radii and noise levels. Kepler has produced a large number of candidates and here has been much speculation as to the false positive rate: how many of these planet candidates aren’t really planets? Three of the talks in this Kepler-themed session looked into this question.

Jean-Michel Desert investigated the Kepler false positive rate observationally. He and his collaborators used Spitzer, an infrared telescope, to follow up 34 of the Kepler candidates. The depth of a planet transit doesn’t depend on wavelength and so should have the same depth whether they are observed with Kepler or with Spitzer. On the other hand, blends, the most likely false positive, would have different depths. Desert finds excellent agreement between the Spitzer and Kepler transit depths, implying that the candidates are bona fide planets. Combining the Kepler and Spitzer transits with adaptive optics and Kepler centeroiding, they measure the false positive rates for the objects they observed to be between 0.1 and 10%.

The Kepler field is crowded and a single pixel can have more than one star in it. In addition, as Tim Morton pointed out, 40% of stars are binaries; since Kepler didn’t make a selection based on binarity, 40% of the Kepler Objects of Interest are probably binaries. How do you know your planet is orbiting the star you think it is? Steve Bryson looked into quantifying the probability that a planet candidate is transiting a background star. Tim Morton investigated a similar idea. He started with the case of KOI 284, a binary star that has transiting planets around both companions. Morton calls systems like these “coincidental multiples.” By simulating a population of stars, his preliminary results indicate that (I’m simplifying substantially here) 20-40% of stars could be coincidental multiples.


11:15 pm – Session 405: Chemical abundances of stars and planets

Natalie Hinkel compiled spectroscopic abundance measurements of main sequence stars within 150pc into the Hypatia Catalogue (named after the first female Greek astronomer). When synthesizing this much data from 49 literature sources over 25 years, there were of course a lot of issues that needed to be dealt with. Natalie identified 1200 solar-like stars in their catalog with abundances similar to the Sun as good targets around which to look for habitable planets. She also identified stars which had enhanced abundances of the elements required for life. Finally, she looked at the abundances of known planet-hosting stars.

Nikku Madhusudhan talked about a related issue: the chemical abundances of the exoplanets themselves. He focused on the carbon to oxygen ratio (C/O), a topic well explored in planetary science. In a planetesimal, if C/O < 1, you get lots of H2O, but if C/O > 1, you replace essentially all water with CO. Thus the C/O ratio has a dramatic effect of an exoplanet’s interior composition. A similar effect is seen in atmospheres. He reports on measurements he and collaborators made of Wasp-12b, finding it to be enhanced in C/O. He also argues that several other planet atmospheres can be explained by a C/O ratio greater than 1 rather than the atmospheric inversion typically turned to. There are currently two theories that can explain how to get a carbon rich planet.

Drake Deming discussed grism spectroscopy of hot Jupiters, using the WFC3 instrument aboard Hubble. They have a spectrum of hot Jupiter XO-1, in which they see that water absorption is consistent with that of a solar abundance, although it is a factor of two less strong than a previously published result.

10:15 am – Session 405: Lessons learned from planet occurrence in Kepler – Andrew Howard

Andrew Howard taught us four lessons learned from his work on understanding planet occurrence in Kepler:

1. Population synthesis models incorrectly predict a desert at close in 3-15 Earth masses. This occurs because in the models, planets don’t grow so large in or they migrate out of this region.
2. Planet radius distribution is a power law, a generic prediction of the core accretion theory. This agrees with results from Kepler. The predicted mass distribution should have bumps in it, which isn’t seen – but this could simply be because the Kepler stars are poorly characterized.
3. The period distribution of planets increases with increasing orbital period but there is then a break, the location of which depends on the size of the planet. Could this be because of resonances set up during planet migration?
4. The planet distribution of super earths is opposite to that of larger planets: smaller planets prefer smaller stars.


8:30 am – Invited Session: The Evolving Context of Science and Society – Alan Leshner

This session began with a surprise appearance by Congressman Lamar Smith of Texas. Congressman Smith is on the Science, Space, and Technology Committee of the House of Representatives. Following his brief remarks about the importance of continuing support for astronomy in Washington (including support for the James Webb Space Telescope), the invited speaker, Alan Leshner, took the stage. Leshner is the CEO of the AAAS, the world’s largest science and engineering society. Leshner, who is not an astronomer, spent the majority of his talk discussing major trends that affect the American scientific enterprise, specifically the societal climate and public perception of science. Quoting Abraham Lincoln, Leshner said, “Public sentiment is everything. With public sentiment, nothing can fail. Without it, nothing can succeed.”

Though people generally like science and technology (according to studies of the general public, scientists and engineers are the second-most prestigious career, ranking just after firefighters), people don’t necessarily understand what science is. Astrology, ESP, and other pseudo-science topics are often given just as much credence as genuine scientific enterprises. In addition, scientific discoveries that raise issues in the current political climate or abut against people’s core values tend to be particularly problematic, for example, global warming and stem-cell research. As scientists, we often think that the solution to these problems is just a better-educated public. But Leshner stresses that there is more to it than that.

We, as scientists, need to try to find common ground with the public – enhancing understanding, but also trying to engage with the public, listening to public concerns about THEIR priorities, as well as ours. This is not easy, of course, and involves things like public policy discussions on topics like scientific ethics, as well as the general goals of the NSF’s “broader impacts” criterion. When engaging with the public, we as scientists need to remain the “fact people” – leaving our personal values behind. In-person engagement works best, says Leshner, stressing the importance of lab visits, public tours, science fairs, and other opportunities for scientists to connect with the public on a local level. As astronomers in particular, we have an important opportunity, given that our science seems to be the most interesting to the public.

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1 Comment

  1. The Lamar Smith comments were important given the political climate (and general Republican party science “denial”)today.


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