Gizis Daily Astronomy Research

A color-magnitude diagram for brown dwarfs. This choice of color (J from the ground, W2 from WISE satellite) gives a clean diagram. You can see here how dramatic the L/T transition is! WISE0855, the coolest known brown dwarf, is in the bottom right. The plotted data is from a huge number of astronomers, compiled in the Ultracool Sheet on Google:

News on the Rubin Observatory LSST: Today we (the Science Collaboration Chairs) had a meeting with the new Survey Cadence Optimization Committee (SCOC). The next step will be a workshop in early December; over the next year SCOC will develop recommendations for the survey strategy or cadence. The big picture, I think, is that none of the four main science goals will be sacrificed: For example, a proposal to increase the supernovae yield by 50% that dropped the asteroid yield by 50% would likely be unacceptable. Anyway, first they will make the big decisions (rolling cadence or not, sky coverage, etc.) then later continue to work to optimize the details. 

Labor Day Weekend 2020 was spent on re-visiting standard brown dwarf models in MESA. You can see that the stars (such as 0.090 solar masses) achieve long-term hydrogen burning, with a constant central temperature and luminosity. The brown dwarf models reach a peak and cool. The early evolution at around one million years is flat in luminosity for a little while as the deuterium burns. The 0.011 model doesn’t even fuse deuterium.

It was a really interesting research day, as a large group of “massive star” researchers were visiting Profs. Petit and Owocki, and a small group of Philadelphia-area Vera C. Rubin Observatory LSST experts were visiting Prof. Bianco. Class and other obligations kept me away for more time than I would have liked, but we had a discussion of LSST and stars,. Sadly, the ~16th magnitude saturation limit (or is it 17?) limits the direct connection to LSST. They’re cleaning up with TESS though! 

Today is Day 3 of the joint TVS-SMWLV LSST workshop and hackathon, held here at University of Delaware using support from the LSST Corporation. The first two days were mainly talks, and now a lot is getting done....

TVS= Transients and Variable Stars

SMWLV = Stars, Milky Way and Local Volume

I submitted an abstract for the January 2020 AAS meeting on our HST/K2 Uranus observations.

The undergraduate students are all making progress.

My new copy of Principles of Planetary Climate arrived today. I spent the day thinking about brown dwarf atmospheres... looking through the new book, Mihalas’s classic Stellar Atmospheres, and some other sources. It’s nice to be able to sketch diagrams on my iPad Pro knowing that I can find them again someday. (Unlike paper, which I inevitably lose.)

I really enjoyed closely reading the new preprint on brown dwarf retrieval with a new open source package. They apply it to some standard brown dwarfs but also the new Sonora models. One interesting result is that because they use a different model of how much the K atomic line is broadened, they can have some large discrepancies with the Sonora models in the Y band region. Mark Marley pointed out another issue on Twitter: only the Sonora models correctly model “rain out” chemistry; the retrieval model’s chemistry is therefore off.

I asked Kevin Luhman for young IMFs and he recommended sources for Taurus and IC348. I read some nice papers on Upper Sco from his group too.

There was a nice preprint today comparing free floating Upper Sco brown dwarfs to the companions. Wouldn’t it be great to see signatures of differing formation processes?

I noticed today that this blog says I’m an associate professor... sadly I have no idea how to update it. Well, it’s not as if I actually post daily.

Jinbaio Ji showed me a detailed outline of his new paper. I worked a bit on the upcoming LSST TVS-SMWLV joint Hackathon. Sally told me about some interesting research ideas -- but she’s finishing her book. 

Did I mention I’m thinking of writing a book? 

This is a 0.050 solar mass brown dwarf with an effective temperature of 600K and log g = 4.75 from MESA. The circles show the pre-computed boundary conditions in the deep atmosphere (tau=100) which I believe are from the COND (Allard et al.) models for 600K and log g = 5.0 and 4.5. The interior model runs between them as you’d expect for an interpolation.  I’ve also plotted two atmosphere models from the Sonora 2018 family; these are also 600K.Here it’s the log g = 5.0 model that seems to line up perfectly with the interior model. So there’s a slight offset, but with different physics and newer opacities I don’t think that’s surprising. A wise astronomer would read the papers to understand this better; I’ve posted this and will read later.