Spacebuzz

Blog posts tagged with spectroscopy

Posts in the past four weeks

Wednesday
Aug 26 2015
03:59 UTC

color maps, stellar ages, stellar multiples

At breakfast I told Morgan Fouesneau (MPIA) my desiderata for a set of matplotlib color maps: I want a map that indicates intensity (dark to bright, say), a map that indicates a sequential value (mass or metallicty or age, say), a map that indicates residuals away from zero that de-emphasizes the near-zero values, and a map that is the same but that emphasizes the near-zero values. I want the diverging maps to never hit pure white or pure black (indeed none of these maps should) because we alw

Posted by Hogg's Research

Thursday
Aug 20 2015
03:59 UTC

stars on a train

[I caught a train to London today. What a civilized world we live in!] I started to write up my ideas about pairs of pairs of spectral twins.

Posted by Hogg's Research

Wednesday
Aug 19 2015
03:59 UTC

taking numerical derivatives; spectroscopic tagging

... of models of stellar spectroscopy, taken by Yuan-Sen Ting (Harvard). When you numerically differentiate someone else's computer code, you have to be careful! If you take a step size that is too large, the behavior won't be linear. If you take a step size that is too small, the differences won't be trustable (because the code has unknown convergence precision). So there should be a “sweet spot”. Ting's analysis doesn't clearl

Posted by Hogg's Research

Tuesday
Aug 18 2015
03:59 UTC

information theory and stellar spectroscopy

[I am supposed to still be on vacation but we came back a day early.]At the end of the day, Rix and I met with Yuan-Sen Ting (Harvard) and Ness to discuss the state of projects. Ting is modeling stellar spectra with linear combinations of model derivatives and has some extremely promising results (and some small bugs). We worked on diagnosis. One great thing about his project is that many of the results (on fake data, anyway) can be predicted exactly by methods of information theory. That is

Posted by Hogg's Research

Friday
Aug 14 2015
03:59 UTC

confusion in angle-spectrum space, and search

... MUSE integral-field spectroscopy instrument. They extract spectra using spatial priors based on HST imaging, which is not unlike the forced photometry we did with WISE. This is obviously a good idea in confused fields. That led to a bus conversation with Mendel about the confusion limit as applied to spectroscopic (or multi-band imaging data). The confusion limit is a function (in this ca

Posted by Hogg's Research

Wednesday
Aug 12 2015
16:23 UTC

the star-formation history, stream-finding, and more

[Off the grid for the last few days.]In Milky Way group meeting, Xue (MPIA) talked about our Kinematic Consensus project, which is starting to show promise: We look for sets of stars with observable properties consistent with having the same orbital integrals of motion. It appears to group stars even when the trial potential (we use for orbit construction) is significantly different from the true potential. At that same meeting, I described my hopes for modeling or measuring the Milky Way star-

Posted by Hogg's Research

Friday
Aug 07 2015
03:59 UTC

Galaxy Coffee

At MPIA Galaxy Coffee, Rix talked about mono-abundance populations in the Milky Way, and Dan Weisz talked about combining photometric and spectroscopic observations to constrain the properties of distant, compact star clusters. In the first talk, Rix showed that at low abundances, the stellar populations want negative scale lengths: This is because they are like "donuts" or "rings" around the Milky Way: Low-abundance stars in the disk appear to form far out. In the discussion, we argued abou

Posted by Hogg's Research

Wednesday
Aug 05 2015
03:59 UTC

model derivatives

Today Yuan-Sen Ting (Harvard) gave Ness and me derivatives of Kurucz-like models of APOGEE spectral data with respect to individual element abundances and effective temperature and gravity. Ness and I plotted these theoretical derivatives against “beliefs” obtained by The Cannon sbout these same dependencies. They agree remarkably well! But in detail they disagree; it remains to figure out what parts of the disagreement are noise or real results. We also showed (based on the der

Posted by Hogg's Research

Friday
Jul 31 2015
03:59 UTC

Milky Way disk kinematics

At MPIA Galaxy coffee, there were great talks about the Milky Way disk by Gail Zasowski (JHU) and Jonathan Bird (Vanderbilt). Zasowski showed results on the kinematics of the MW disk ISM based on diffuse interstellar bands. She used the three-d dust map from Schlafly et al to figure out the mean distance to each absorber, and sees a consistent story. Bird showed that the age–metallicity relationship in the disk (briefly, that older stars have higher velocity dispersion) is a product not

Posted by Hogg's Research

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