How to Take Pictures of Baby Planets
Kate Follette, Amherst College
Of the thousands of known extrasolar planets, why are the dozen or so directly imaged exoplanets among the most important despite their apparently anomalous properties within the general exoplanet population (>10 astronomical units, >2x the mass of Jupiter)? What are the prospects for (and recent successes in) detecting younger, lower-mass and/or closer-in planets via direct imaging? I will discuss the current state of the art in the field of high-contrast imaging of extrasolar planets and the disks of gas and dust from which planets form (“circumstellar disks”). I will place particular emphasis on a subset of objects that host both disks and (likely) planets – the so-called “transitional disks”. These young circumstellar disks are almost certainly actively undergoing planet formation, and yet the presence of disk material complicates our ability to isolate light from planets and/or protoplanets embedded within them. I will end by discussing recent results from the Giant Accreting Protoplanet Survey (GAPplanetS) of 15 southern-hemisphere transition disks. The GAPlanetS survey aims to find protoplanets embedded in transitional disks through a distinctive signature at hydrogen wavelengths, and has so far discovered: 2-3 planets, 1 accreting M-dwarf stellar companion, and 1 disk feature masquerading as a planet.
Rethinking the Fundamentals of Classical Nova Explosions
Laura Chomiuk, MSU
Over the past few years, a revolution has been taking place in our understanding of classical novae, largely driven by the discovery of GeV gamma-rays emanating from these garden-variety explosions. These gamma-rays hint that shocks are energetically important—perhaps even dominant—in novae. I will present our burgeoning understanding of shocks in novae, from both multi-wavelength observational and theoretical perspectives, and illustrate how novae can be used as testbeds to understand other shock-powered explosions.
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.