Calendar

Apr
6
Fri
Colloquium PhD Thesis Defense: Sten Hasselquist
Apr 6 @ 3:15 pm – 4:15 pm
Colloquium PhD Thesis Defense: Sten Hasselquist @ BX102

Colloquium Title

Sten Hasselquist, NMSU

Abstract

Oct
5
Fri
Colloquium: David Nataf (Host: Jason Jackiewicz)
Oct 5 @ 3:15 pm – 4:15 pm
Colloquium: David Nataf (Host: Jason Jackiewicz) @ BX102

Clues to Globular Cluster Formation

David Nataf, Johns Hopkins University

Globular clusters are now well-established to host “Second-generation” stars, which show anomalous abundances in some or all of He, C, N, O, Na, Al, Mg, etc.  The simplest explanations for these phenomena typically require the globular clusters to have been ~20x more massive at birth, and to have been enriched by processes which are not consistent with the theoretical predictions of massive star chemical synthesis models. The library of observations is now a vast one, yet there has been comparatively little progress in understanding how globular clusters could have formed and evolved. In this talk I discuss two new insights into the matter. First, I report on a meta-analysis of globular cluster abundances that combined APOGEE and literature data for 28 globular clusters, new trends with globular cluster mass are identified. I discuss the chemical properties of former globular cluster stars that are now part of the field population, and what can be learned.

Oct
8
Mon
Pizza lunch: Patrick Gaulme
Oct 8 @ 12:30 pm – 1:30 pm
Pizza lunch: Patrick Gaulme @ AY 119

Red giants, eclipsing binaries, and asteroseismology.

Patrick Gaulme, Max Planck Institute for Solar System Research

Nov
15
Fri
Colloquium: Phil Judge (Host James McAteer)
Nov 15 @ 3:15 pm – 4:15 pm
Colloquium: Phil Judge (Host James McAteer) @ BX102

Using every photon to learn about the physics of solar plasmas

Phil Judge, High Altitude Observatory, Boulder CO.

The Sun has traditionally been the Rosetta Stone that can overcome the gap in regimes between laboratory and astronomical plasmas.   Theories applicable in the laboratory may not readily apply to solar plasmas, and vice-versa. Yet we still face challenges in understanding how the observable plasmas are produced, and why the magnetic field threading and energizing them must globally reverse every 11 years. I will give a general overview of currently pressing problems in solar physics, followed by two specific examples: one concerning the physics of flares through infrared spectroscopy and polarimetry, the other concerning how we might wring every last ounce of information from the emitted photons. Along the way I will introduce the NMSU-operated Dunn Solar Telescope, the new DKIST, Parker Solar Probe and Solar Orbiter, and suggest how we might take advantage of these new facilities to make lasting progress.

May
29
Fri
Remote Colloquium Thesis Defense: Drew Chojnowski
May 29 @ 2:30 pm – 3:30 pm
Remote Colloquium Thesis Defense: Drew Chojnowski @ Online

H-Band Spectroscopy of Exotic, Massive Stars

Drew Chojnowski, NMSU

We report on spectroscopy of exotic B-type emission line (Be) stars and chemically peculiar (CP) stars in the near-infrared (NIR) H-band, using data provided by the Apache Point Observatory Galactic Evolution Experiment, one of the sub-surveys of the Sloan Digital Sky Survey (SDSS). Between 2011-2020, SDSS/APOGEE has observed more than a million stars in the Milky Way Galaxy (MW), with roughly 10% of the targets being hot, blue stars that serve as telluric absorption standard stars (TSS). The TSS are selected mostly on the basis of having blue raw J-K color indices with no preference for any particular spectral type that might be known from optical spectroscopy. This targeting strategy has led to the TSS being a mixed bag, with those observed in the MW Halo typically being F-type stars that are only slightly more massive than the Sun, and with those observed in the MW Disk and Bulge being OBA-type stars of a few up to 20 times the mass of the Sun. While the vast majority of the TSS are superficially normal main sequence stars, the inclusion of large numbers of Be and CP stars has serendipitously resulted in the largest ever homogeneous spectroscopic surveys of these stellar classes, both of which present observational anomalies that remain very poorly understand despite more than a hundred years of research. Prior to SDSS/APOGEE, the H-band spectra of Be and CP stars had only been discussed in a handful of studies, all of which used small numbers of spectra of considerably lower resolution than the R=22,500 of the APOGEE instruments. The material presented in this thesis therefore represents the first ever detailed studies of Be and CP stars in the H-band, while also greatly expanding the known samples through discovery of many hundreds of new examples.