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.
Magnetic Influences on Coronal Heating and the Solar Wind
Lauren Woolsey, Harvard University
The physical mechanism(s) that generate and accelerate the solar wind have not been conclusively determined after decades of study, though not for lack of possibilities. The long list of proposed processes can be grouped into two main paradigms: 1) models that require the rearranging of magnetic topology through magnetic reconnection in order to release energy and accelerate the wind and 2) models that require the launching of magnetoacoustic and Alfvén waves to propagate along the magnetic field and generate turbulence to heat the corona and accelerate the emanating wind. After a short overview of these paradigms, I will present my ongoing dissertation work that seeks to investigate the latter category of theoretical models and the role that different magnetic field profiles play in the resulting solar wind properties with Alfvén-wave-driven turbulent heating. I will describe the computer modeling in 1D and 3D that I have done of bundles of magnetic field (flux tubes) that are open to the heliosphere, and what our results can tell us about the influences of magnetic field on the solar wind in these flux tubes, including the latest time-dependent modeling that produces bursty, nanoflare-like heating. Additionally, I will present the latest results of our study of chromospheric network jets and the magnetic thresholds we are finding in magnetogram data.
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.
Do star formation laws break in the center of the Galaxy?
Betsy Mills, University of Arizona
I will review our understanding of molecular gas conditions in the central 500 parsecs of the Milky Way, and summarize recent studies that find that the Galactic center deviates from universal star formation relations. It is suggested that the amount of star formation in the Galactic center is less than expected, given the quantity of dense gas in this region. However, in order to conclude that the Galactic center truly breaks these ‘laws’ of star formation, two possibilities must be ruled out: that our indicators in this region could underestimate the amount of star formation, and that prior observations could have overestimated the amount of dense gas. I will analyze new evidence for ongoing star formation in the Galactic center and present new measurements of the gas densities in the Galactic center that show it to be less dense than originally thought. However, I will ultimately argue that the average density of the gas is less relevant to explaining the dearth of star formation than the fraction of gas at each density.
Asteroseismology of Red Giants: The Detailed Modeling of Red Giants in Eclipsing Binary Systems
Jean McKeever, NMSU
Asteroseismology is an invaluable tool that allows one to peer into the inside of a star and know its fundamental stellar properties with relative ease. There has been much exploration of solar-like oscillations within red giants with recent advances in technology, leading to new innovations in observing. The Kepler mission, with its 4-year observations of a single patch of sky, has opened the floodgates on asteroseismic studies. Binary star systems are also an invaluable tool for their ability to provide independent constraints on fundamental stellar parameters such as mass and radius. The asteroseismic scaling laws link observables in the light curves of stars to the physical parameters in the star, providing a unique tool to study large populations of stars quite easily. In this work we present our 4-year radial velocity observing program to provide accurate dynamical masses for 16 red giants in eclipsing binary systems. From this we find that asteroseismology overestimates the mass and radius of red giants by 15% and 5% respectively. We further attempt to model the pulsations of a few of these stars using stellar evolution and oscillation codes. The goal is to determine which masses are correct and if there is a physical cause for the discrepancy in asteroseismic masses. We find there are many challenges to modeling evolved stars such as red giants and we address a few of the major concerns. These systems are some of the best studied systems to date and further exploration of their asteroseismic mysteries is inevitable.
Fresh Perspectives on Star
Formation from LEGUS, the Legacy ExtraGalactic Ultraviolet Survey
David Thilker, Johns Hopkins University
The Legacy ExtraGalactic Ultraviolet Survey (LEGUS) was a Cycle 21 Large Treasury HST program which obtained ~parsec resolution NUV- to I-band WFC3 imaging for 50 nearby, representative star-forming Local Volume galaxies, with a primary goal of linking the scales of star formation from the limit of individual stars, to clusters and associations, eventually up through the hierarchy to giant star forming complexes and galaxy-scale morphological features.
I will review the basics of the survey, public data products and science team results pertaining to clusters and the field star hierarchy. I will then describe work to optimize photometric selection methods for massive main sequence O star candidates and LBV candidates, in the former case establishing a means to statistically constrain the fraction of O stars in very isolated locales. I will introduce new ideas on how to quantify the complex spatio-temporal nature of hierarchical star formation using multi-scale clustering methods. The first steps of this work have yielded a landmark OB association database for 36 LEGUS target fields (in 28 of the nearest available galaxies), with tracer stellar populations selected and interpreted uniformly. I will finish with discussion of a pilot HST program to demonstrate remarkably increased survey efficiency of WFC3 UV imaging enabled by use of extra-wide (X) filter bandpasses. Such efficiency is required as we move beyond LEGUS and begin to rigorously explore low surface brightness star-forming environments where canonical results for the IMF and cluster formation efficiency are increasingly called into question.
The SPLASH Survey of the Andromeda Galaxy
Raja Guhathurkurta, University of California, Santa Cruz
Our nearest large spiral galaxy neighbor, the Andromeda galaxy (M31),
and its dwarf satellites, offer a panoramic yet detailed view of
galaxy formation and evolution in our astronomical backyard. This
system also serves as an excellent laboratory for the study of stellar
populations because the stars are all practically at the same distance
from us. I will present results from the SPLASH (Spectroscopic and
Photometric Landscape of Andromeda’s Stellar Halo) survey, the
backbone of which was a large Keck DEIMOS spectroscopic survey of
evolved stars in M31. Most of the SPLASH spectroscopic targets in
M31’s disk were selected from the PHAT (Panchromatic Hubble Andromeda
Treasury) survey, a wide-field 6-filter Hubble Space Telescope mosaic
image of a portion of the disk of M31. The talk will cover a range of
science topics including: Local Group dynamics, structure/substructure
and metallicity of M31’s stellar halo, satellite tidal interactions,
disk/halo interface, dynamical heating of the disk, and rare stellar