On the Edge: Exoplanets with Orbital Periods Shorter Than a Peter Jackson Movie
Brian Jackson, Boise State Univeristy
From wispy gas giants to tiny rocky bodies, exoplanets with orbital periods of several days and less challenge theories of planet formation and evolution. Recent searches have found small rocky planets with orbits reaching almost down to their host stars’ surfaces, including an iron-rich Mars-sized body with an orbital period of only four hours. So close to their host stars that some of them are actively disintegrating, these objects’ origins remain unclear, and even formation models that allow significant migration have trouble accounting for their very short periods. Some are members of multi-planet system and may have been driven inward via secular excitation and tidal damping by their sibling planets. Others may be the fossil cores of former gas giants whose atmospheres were stripped by tides.
In this presentation, I’ll discuss the work of our Short-Period Planets Group (SuPerPiG), focused on finding and understanding this surprising new class of exoplanets. We are sifting data from the reincarnated Kepler Mission, K2, to search for additional short-period planets and have found several new candidates. We are also modeling the tidal decay and disruption of close-in gaseous planets to determine how we could identify their remnants, and preliminary results suggest the cores have a distinctive mass-period relationship that may be apparent in the observed population. Whatever their origins, short-period planets are particularly amenable to discovery and detailed follow-up by ongoing and future surveys, including the TESS mission.
New Tools for Galactic Archaeology from the Milky Way
Gail Zasowski, John Hopkins University
One of the critical components for understanding galaxy evolution is understanding the Milky Way Galaxy itself — its detailed structure and chemodynamical properties, as well as fundamental stellar physics, which we can only study in great detail locally. This field is currently undergoing a dramatic expansion towards the kinds of large-scale statistical analyses long used by the extragalactic and other communities, thanks in part to an enormous influx of data from space- and ground-based surveys. I will describe the Milky Way and Local Group in the context of general galaxy evolution and highlight some recent developments in Galactic astrophysics that take advantage of these big data sets and analysis techniques. In particular, I will focus on two diverse approaches: one to characterize the distribution and dynamics of the carbon-rich, dusty diffuse ISM, and one to map the resolved bulk stellar properties of the inner disk and bulge. The rapid progress in these areas promises to continue, with the arrival of data sets from missions like SDSS, Gaia, LSST, and WFIRST.
Utilizing Planetary Oscillations to Constrain the Interior Structure of the Jovian Planets
Seismology has been the premier tool of study for understanding the
interior structure of the Earth, the Sun, and even other stars. Yet in this
thesis proposal, we wish to utilize these tools to understand the interior
structure of the Jovian planets, Saturn in particular. Recent observations
of spiral density structures in Saturn’s rings caused by its oscillations
have provided insight into which modes exist within Saturn and at what
frequencies. Utilizing these frequencies to compare to probable mode can-
didates calculated from Saturn models will also us to ascertain the interior
profiles of state variables such as density, sound speed, rotation, etc. Using
these profiles in a Saturn model, coupled with tweaking the interior struc-
ture of the model, i.e. the inclusion of stably stratified regions, should
allow us to explain which modes are responsible for the density structures
in the rings, as well as predict where to look to find more such structures.
In doing so, we will not only have a much greater understanding of Sat-
urn’s interior structure, but will have constructed a method that can also
be applied to Jupiter once observations of its mode frequencies become
available. In addition, we seek to explain if moist convection on Jupiter is
responsible for exciting its modes. We aim to do this by modeling Jupiter
as a 2D harmonic oscillator. By creating a resonance between moist con-
vective storms and Jovian modes, we hope to match the expected mode
energies and surface displacements of Jupiter’s oscillations.
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.