Aavso paper Session I sunday Sunday, May 22, 2011, 9: 30 am – 12: 00 pm

325

Low-Mass Stellar Science

Poster Session

Essex Ballroom

325.01

8:00 AM - 7:00 PM

We use stellar spectra from the Sloan Digital Sky Survey (SDSS) to create a high- latitude extinction map of the local Galaxy. Our technique compares spectra from SDSS stars in low-extinction lines of sight, as determined by Schlegel, Finkbeiner, & Davis, to other SDSS spectra in order to derive improved distance estimates and accurate line-of-sight extinctions. Unlike most previous studies, which have used a two-color method to determine extinction, we fit extinction curves to fluxes across a large spectral range. We apply this method to SDSS K dwarfs, nearby L dwarfs, and stars in the DR7 M dwarf sample. Our result is an extinction map that extends from tens of pc to several kpc away from the sun. We also use a similar technique to create a map of R_V values within approximately 1 kpc of the sun, and find they are consistent with the widely accepted diffuse interstellar medium value of 3.1. Using our extinction data, we derive a dust scale height for the local galaxy of 119 ± 15 parsecs and find evidence for a local dust cavity.

325.02

8:00 AM - 7:00 PM

The magnetic reconnection events that power stellar flares lead to a wide variety of light curve shapes, hinting at the complex underlying magnetic field topologies. Using our quantitative definition of a flare event, we find more than 100 flares during 600 hours of photometric monitoring of two dozen stars. The sample includes both active and inactive M dwarfs with a range of spectral type. We fit models for the light curve evolution to our photometric flare catalogue and present an analysis of the rise and decay times as well as flare colors. We additionally present the distribution of flare rates as a function of energy and equivalent duration. The flare frequency distribution is used to characterize the impact of M dwarf flares seen in time domain surveys, and is also necessary to model the effect of flares on the atmospheres of exoplanets orbiting an M dwarf host.

325.03
The Living with a Red Dwarf Program: dM Star Evolution and the Usefulness of Rotation as an Age Indicator

Scott G. Engle¹, E. Guinan¹, S. Kafka², S. Messina³, T. Oswalt⁴, J. Bochanski^5
1Villanova University, ²Carnegie Institution - DTM, ³INAF-Catania Astrophysical Observatory, Italy, ⁴Florida Institute of Technology, ⁵The Pennsylvania State University.

8:00 AM - 7:00 PM

The ability to accurately estimate the age of a dM stars is of critical importance. However, due to their long lifetimes, and very slow nuclear evolution, the best method for determining ages would seem to be through “magnetic tracers” such as X-UV activity levels and stellar rotation rates. The Living with a Red Dwarf Program’s database of dM stars with photometrically determined rotation rates (from starspot modulations) is becoming substantial, and has recently been expanded to include dM stars with well-detached WD companions - through which reliable ages can be determined. When combined with dM stars possessing cluster/population memberships, or specific kinematics, a full range of Main Sequence ages is being realized. We report on our continuing efforts to build reliable Age-Activity-Rotation relationships for dM stars. Such relationships have broad impacts on not only the studies of Magnetic Dynamo Theory and Angular Momentum Loss on low-mass stars with deep convective zones, but also the suitability of planets around red dwarfs to sustain life. We hope that, after proper calibration, the relationships will also permit the age of a field red dwarf to be determined through measures of either its rotation period or X-UV activity level.

325.04

8:00 AM - 7:00 PM

We present preliminary results from a study of M dwarf magnetic activity in clusters of known ages with the ultimate goal of constraining the age-activity relation. The age-activity relation provides clues to the mechanisms generating magnetic dynamos, especially in late-type dwarfs where their stellar interiors become fully convective. Broadband griz photometry was obtained for four clusters with ages ranging from 150 Myrs to 4 Gyrs. Narrowband images of each cluster were acquired with the Maryland Magellan Tunable Filter, tuned to the frequency of H-alpha (including a correction for each cluster’s radial velocity) and a nearby, similarly sized bandpass sampling the stellar pseudo-continuum. This permits a “photometric” measurement of the H-alpha emission for each star, and thus a measure of activity. Cluster membership is determined from broadband photometry and comparison to stellar positions from previous studies. We report on our findings for the clusters NGC 2516 and M67. H-alpha measurements are stronger for cluster stars than for field stars of the same magnitude. In NGC 2516, a clear correlation is seen between our H-alpha strengths measured by narrowband imaging and previous spectroscopic activity measurements in stars for which spectra have been obtained. J.M.A. acknowledges support through an NSF Graduate Research Fellowship.

325.05

8:00 AM - 7:00 PM

The Folded-port Infrared Echellette (FIRE) spectrograph has recently been commissioned on 6.5m Baade Telescope, enabling high-throughput, low- and moderate-resolution spectroscopy of faint infrared sources. As part of science verification observations, we have observed a sample of ~35 mid- and late-type T dwarfs in the southern hemisphere down to J ~ 17 at a resolution of 6000 (Δv = 50 km/s), spanning the full 0.85-2.4 micron near-infrared window. We present the results of these observations, including radial velocity measurements based on both spectral fitting and comparison to radial velocity standards, and 3D kinematics for sources with proper motions and parallaxes from the Brown Dwarf Kinematics Program. We also present preliminary rotational velocities down to the pixel-sampling limit (12.5 km/s), made possible by the dozens of molecular transitions resolved by FIRE echelle data. Finally, we present limits on radial velocity variability for two sources suspected of being unresolved (a < 10 AU) spectral binaries.