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

326

M Dwarfs, Brown Dwarfs, White Dwarfs

Poster Session

Essex Ballroom

326.01

8:00 AM - 7:00 PM

Determining distances to celestial objects is one of the fundamental challenges in astronomy. In particular, distance determinations to nearby objects are of vital importance, as our solar neighbors set the standard for the primary rung in the cosmic distance ladder. The optimal tool for accomplishing this seemingly simple task is trigonometric parallax. However, because measuring parallaxes is time-intensive, photometric distance estimates are useful in deciding which targets are good candidates for the limited slots available in traditional parallax programs --- or in the near future, which stars are worthy of special attention. In 1999, RECONS (Research Consortium on Nearby Stars) began gathering

326.02

We present results of an analysis of public infrared sky surveys including 2MASS and AKARI to identify young, low-mass stars with excesses. The results include new T Tauri stars in young associations and debris disk candidates. We also discuss a search for new very high proper motion stars in the solar neighborhood.

326.03

M Dwarf Photometric Variability In The Optical And NIR

James R. A. Davenport¹, A. C. Becker¹, A. F. Kowalski¹, S. L. Hawley¹, E. J. Hilton^1
1University of Washington.

8:00 AM - 7:00 PM

We present limits on the observability of stochastic flare events from M dwarfs in SDSS and 2MASS filters. We have studied 30,000 M dwarfs from the SDSS Stripe 82 time-domain catalog, and 4300 M dwarfs from the 2MASS Calibration Scan Point Source Working Database which overlap the SDSS DR7 single-epoch data. M dwarfs are chosen based on their SDSS r,i,z colors. Stripe 82 stars each have 50-100 epochs of data, while 2MASS Calibration stars have 2000-3000. An M dwarf continuum spectral model is used to predict observed flare signatures in each band. From these data we estimate the observed rates and theoretical detection thresholds for flares in eight photometric bands as a function of spectral type. The structure function of the variability for each spectral type bin is also calculated for all eight bands. These rates of flares and photometric variations at longer wavelengths will be important for predicting the impact of M dwarf variability in next-generation instruments such as JWST.

326.04

The First Detection of Time-Variable Infrared Line Emission During M Dwarf Flares

Sarah J. Schmidt¹, E. J. Hilton¹, B. Tofflemire¹, J. P. Wisniewski¹, A. F. Kowalski¹, J. Holtzman², S. L. Hawley^1
1University of Washington, ²New Mexico State University.

8:00 AM - 7:00 PM

M dwarfs are notorious for their active chromospheres, characterized by quiescent line emission at optical wavelengths in addition to dramatic flare events. These flares have been well-studied at X-ray, radio, UV, and optical wavelengths, but so far there is only one single-epoch detection of high-order Paschen emission lines in a red optical spectrum (Schmidt et al. 2007). In order to investigate infrared line emission during flares, we have conducted a monitoring campaign totaling about 60 hours on 5 active M dwarfs. We have obtained infrared (0.9 to 2.4 micron) spectroscopy using the TripleSpec instrument on the Apache Point Observatory 3.5-m, simultaneous optical/UV photometry on the NMSU 1-m and ARC 0.8-m, and optical spectroscopy on the DAO 1.8-m for one run. During the three brightest flares observed on EV Lac and YZ CMi (> 2 magnitudes in U), we observed emission from Hydrogen Paschen beta, gamma, and delta; Brackett gamma, and Helium 10830A. We characterize the strength and time variation of these lines and investigate the heating needed to produce infrared emission during flares.

326.05

Hα Variability in Active M Dwarf Spectra on Intermediate Timescales

Keaton Bell¹, E. J. Hilton¹, S. L. Hawley¹, A. B. Rogel^2
1University of Washington, ²Bowling Green State University.

8:00 AM - 7:00 PM

The strength of Hα emission in magnetically active M dwarfs has been observed to increase on very short (seconds) timescales during flares, and to decrease on very long (millions-billions of years) timescales with stellar aging. We utilize a set of ~13,000 time-resolved active M dwarf spectra taken on several-minute intervals from the Sloan Digital Sky Survey and an independent set of 312 Hydra spectra taken hourly with the WIYN 3.5-meter telescope to study Hα variability on intermediate timescales. With several observations per target, and with many targets observed on multiple nights, we are able to probe variability in the equivalent width measurements of Hα on timescales from minutes to weeks. We will present the variability structure function and discuss it in the context of previous results.

326.06

8:00 AM - 7:00 PM

We present a preliminary analysis of M dwarfs identified in both the Sloan Digital Sky Survey (SDSS) and the Very Large Array's (VLA) Faint Images of the Radio Sky at Twenty-centimeters survey (FIRST). The presence of magnetic fields is often associated with indirect magnetic activity measurements, such as H-alpha or X-ray emission. Radio emission, in contrast, is directly proportional to the magnetic field strength in addition to being another measure of activity. We search for stellar radio emission by cross-matching the SDSS DR7 M dwarf sample with the FIRST catalog. The SDSS data allow us to examine the spectra of our objects and correlate the magnetic activity (H-alpha) with the magnetic field strength (radio emission). Accurate positions and proper motions are important for obtaining a complete list of overlapping targets. Positions in FIRST and SDSS need to be proper motion corrected in order to ensure unique target matches since nearby M dwarfs can have significant proper motions (up to ~ 1'' per year). Some previous studies have neglected the significance of proper motions in identifying overlapping targets between SDSS and FIRST; we correct for some of these previous oversights. In addition the FIRST data were taken in multiple epochs; individual images need to be proper motion corrected before the images can be co-added. Our cross-match catalog puts important constraints on models of magnetic field generation in low-mass stars in addition to the true habitability of attending planets.

326.07

The Effect of Close Companions on the Magnetic Activity of M Dwarfs

Dylan Morgan¹, A. A. West¹, N. M. Silvestri^2
1Boston University, ²University of Washington.

8:00 AM - 7:00 PM

We used close white dwarf and M dwarf (WD+dM) binary systems as a method to understand the effect that close companions have on magnetic field generation in M dwarfs. We used a base sample of 1602 white dwarf - main sequence (WDMS) binaries from Rebassa-Mansergas et al. (2010) to aid in determining a set of color cuts using GALEX, SDSS, 2MASS, and UKIDSS colors. Using the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8) we constructed a sample of ~1800 WD+dM pairs. We separated the dM and WD from each combined spectrum using an iterative technique that compares the WD and dM components to best-fit templates. Using the absolute height above the Galactic plane as a proxy for age and the Hα emission line as an indicator for magnetic activity, we investigated the age-activity relation for our sample. Our results show that M dwarfs in close binary systems have increased magnetic activity in both magnitude and duration compared to their field counterparts.

326.08

8:00 AM - 7:00 PM

M dwarfs are the most promising candidates around which to find habitable, Earth-sized planets amenable to detailed spectroscopic study of their atmospheres by transmission or occultation methods. A correlation between stellar metallicity and planet occurrence has been demonstrated for F, G and K stars, with exoplanet detections rising sharply above solar metallicity. Recent results indicate that this relation holds for M-type stars; if correct, we would be able to increase the yield of planet surveys by targeting metal-rich stars. The MEarth Project is a transiting planet survey that is photometrically monitoring 2000 of the nearest M dwarfs in the Northern sky and which will expand in the next year to include an additional 2000 stars in the southern hemisphere. We will present the first results of a campaign to measure the metallicities of M dwarfs in the MEarth sample. We are using and refining a new method for measuring M dwarf metallicities pioneered by Rojas-Ayala et al. (2010) that uses moderate resolution mid-infrared spectra. Unlike other empirical methods for measuring M dwarf metallicities, it does not rely on parallaxes or accurate V-band magnitudes; thus, it may be applied to less luminous and more distant stars than can photometric methods. Our results will inform the MEarth target list and is an important element in the census of our nearest and most abundant neighbors.

326.09

8:00 AM - 7:00 PM

We present FIRE spectroscopic observations of the ultracool (T ∼ 520 K) brown dwarf, UGPS 0722-05, obtained during instrument commissioning on the 6.5m Baade Magellan Telescope at Las Campanas Observatory. At a distance of 4.1 pc, this cool brown dwarf is well-suited for detailed followup, and represents a keystone at the transition between the lowest-mass brown dwarfs and exoplanets. Our spectrum of UGPS 0722-05 covers the 0.8-2.5 micron bandpasses at a resolution of R ∼ 6,000, and is measured to high signal-to-noise, peaking at 80 near 1.27 microns. We derive radial and rotational velocities for the isolated brown dwarf, and examine its space motion and Galactic orbit. The spectrum of UGPS 0722-05 is also compared to theoretical spectral models to constrain its atmospheric parameters. Finally, we comment on the presence of unidentified absorption features reported in the discovery spectrum of Lucas et al. (2010).

326.10

8:00 AM - 7:00 PM

We present a sample of 364 M subdwarfs from the 7th Data Release of the Sloan Digital Sky Survey (DR7; SDSS). This catalog contains stellar coordinates, SDSS magnitudes, spectral classes, radial velocities, proper motions, absolute magnitudes and estimated distances. We discuss the selection criteria, the spectral classification and radial velocity determination processes. We calculate 3D space motions (U,V,W) in the standard Galactic system and place each star in its proper subdwarf subclass (as efined by Lepine et al.). We show that the metal poor populations are moving faster than metal rich stars on average,

326.11

8:00 AM - 7:00 PM

Multiple star systems aid in constraining star formation models and understanding Galactic history. The focus of this poster is on wide multiple star systems detected through a cross-correlation of the Lepine-Shara Proper Motion North and South (LSPM-N,S) catalogs with themselves and with the Hipparcos catalog. Of the 1,987 systems detected, 937 were previously unidentified in the literature. The spectral types of the primaries range from B stars to M stars with a vast majority having spectral type F or G. Moreover, a large percentage of the new systems are higher order multiples. In this poster we discuss characteristics of the multiple systems including age and metallicity estimates as well as wide binary and hierarchichal system fractions in the field.

326.12

An Investigation into the Periodic Optical Variability of Radio Detected Ultracool Dwarfs using the GUFI Photometer

Richard P. Boyle¹, L. K. Harding², G. Hallinan³, R. F. Butler², A. Golden^2
1Vatican Observatory, ²National University of Ireland Galway, Ireland, ³UC Berkeley.

8:00 AM - 7:00 PM

In the past ten years or so, radio observations of ultracool dwarfs have yielded the detection of both quiescent and time-variable radio emission in the late-M and L dwarf regime. Four of these dwarfs have been found to produce periodic pulses, determined to be associated with the dwarf's rotation. More recently, two of these radio pulsing dwarfs have been shown to be periodically variable in broadband optical photometry, where the detected periods match the periods of the radio pulses. For one of these dwarfs in particular, it has been established that the mechanism which is driving the optical and radio periodic variability are possibly linked, being a consequence of a magnetically-driven auroral process. We therefore undertook a campaign to investigate the ubiquity of optical periodicity for known radio detected ultracool dwarfs, via multi-color photometric monitoring. To facilitate this research, the GUFI instrument (Galway Ultra Fast Imager) was commissioned on the 1.8m VATT observatory, on Mt. Graham, Arizona. We present the recently published results from this observation campaign, where we have confirmed periodic variability for five of these dwarfs, three of which have been detected for the first time by GUFI. These data provide an insight into the cause of this optical emission, its connection to the radio processes, and most importantly determine whether optical periodic signals are present only in radio pulsing dwarfs.

326.13

The ELM Survey: A Successful Targeted Survey for Extremely Low Mass White Dwarfs

Warren R. Brown¹, M. Kilic¹, C. Allende Prieto², S. J. Kenyon^1
1Smithsonian Astrophysical Observatory, ²Instituto de Astrofisica de Canarias, Spain.

8:00 AM - 7:00 PM

We present the first targeted survey for Extremely Low Mass (ELM) white dwarfs (WDs), helium core WDs with masses <0.3 M ⊙. Such low mass WDs are the signature of extreme mass-loss stellar evolution. We have discovered over a dozen new ELM WDs, most of which are compact binary systems with <1 day orbital periods. We predict that at least one of the systems is an eclipsing double-WD system that we can use to place fundamental mass-radius constraints on helium-core WD models. Intriguingly, the observed ELM WD systems are merging due to gravitational wave radiation and will become gravitational wave sources. We use our well-defined, non-kinematically-selected sample to measure the space density of ELM WD systems; their merger rate is comparable to the rate ofunderluminous supernovae, one model for which is the detonation of ~0.3 M ⊙ worth of helium.