62 research outputs found
Resolved Spectroscopy of M Dwarf/L Dwarf Binaries. III. The "Wide" L3.5/L4 Dwarf Binary 2MASS J15500845+1455180AB
We report the identification of 2MASS J15500845+1455180 as a 0"9 L dwarf
visual binary. This source is resolved in Sloan Digital Sky Survey (SDSS)
images and in near-infrared imaging with the IRTF SpeX imager/spectrometer. The
two components, oriented along a north-south axis, have similar brightnesses in
the near-infrared (Delta{K} ~ 0.2 mag), although the fainter northern component
is redder in J-K color. Resolved near-infrared spectroscopy indicates spectral
types of L3.5 and L4, consistent with its L3 combined-light optical
classification based on SDSS data. Physical association is confirmed through
common proper motion, common spectrophotometric distances and low probability
of chance alignment. The projected physical separation of 2MASS J1550+1455AB,
30+/-3 AU at an estimated distance of 33+/-3 pc, makes it the widest L dwarf-L
dwarf pair identified to date, although such a separation is not unusual among
very low-mass field binaries. The angular separation and spectral composition
of this system makes it an excellent target for obtaining a precise lithium
depletion age, and a potential age standard for low-temperature atmosphere
studies.Comment: 8 pages, 4 figures, accepted for publication to A
Periodic Accretion From A Circumbinary Disk In The Young Binary UZ Tau E
Close pre-main-sequence binary stars are expected to clear central holes in their protoplanetary disks, but the extent to which material can flow from the circumbinary disk across the gap onto the individual circumstellar disks has been unclear. In binaries with eccentric orbits, periodic perturbation of the outer disk is predicted to induce mass flow across the gap, resulting in accretion that varies with the binary period. This accretion may manifest itself observationally as periodic changes in luminosity. Here we present a search for such periodic accretion in the pre-main-sequence spectroscopic binary UZ Tau E. We present BVRI photometry spanning 3 years; we find that the brightness of UZ Tau E is clearly periodic, with a best-fit period of 19.16 +/- 0.04 days. This is consistent with the spectroscopic binary period of 19.13 days, refined here from analysis of new and existing radial velocity data. The brightness of UZ Tau E shows significant random variability, but the overall periodic pattern is a broad peak in enhanced brightness, spanning more than half the binary orbital period. The variability of the H alpha line is not as clearly periodic, but given the sparseness of the data, some periodic component is not ruled out. The photometric variations are in good agreement with predictions from simulations of binaries with orbital parameters similar to those of UZ Tau E, suggesting that periodic accretion does occur from circumbinary disks, replenishing the inner circumstellar disks and possibly extending the timescale over which they might form planets
Common Proper-motion Wide White Dwarf Binaries Selected From the Sloan Digital Sky Survey
Wide binaries made up of two white dwarfs (WDs) receive far less attention than their tight counterparts. However, our tests using the binary population synthesis code StarTrack indicate that, for any set of reasonable initial conditions, there exists a significant observable population of double white dwarfs (WDWDs) with orbital separations of 102-105 AU. We adapt the technique of Dhital et al. to search for candidate common proper-motion WD companions separated by 12,000 spectroscopically confirmed hydrogen-atmosphere WDs recently identified in the Sloan Digital Sky Survey. Using two techniques to separate random alignments from high-confidence pairs, we find nine new high-probability wide WDWDs and confirm three previously identified candidate wide WDWDs. This brings the number of known wide WDWDs to 45; our new pairs are a significant addition to the sample, especially at small proper motions (10''). Spectroscopic follow-up and an extension of this method to a larger, photometrically selected set of SDSS WDs may eventually produce a large enough dataset for WDWDs to realize their full potential as testbeds for theories of stellar evolution
A Gyrochronology and Microvariability Survey of the Milky Way's Older Stars Using Kepler's Two-Wheels Program
Even with the diminished precision possible with only two reaction wheels,
the Kepler spacecraft can obtain mmag level, time-resolved photometry of tens
of thousands of sources. The presence of such a rich, large data set could be
transformative for stellar astronomy. In this white paper, we discuss how
rotation periods for a large ensemble of single and binary main- sequence
dwarfs can yield a quantitative understanding of the evolution of stellar
spin-down over time. This will allow us to calibrate rotation-based ages beyond
~1 Gyr, which is the oldest benchmark that exists today apart from the Sun.
Measurement of rotation periods of M dwarfs past the fully-convective boundary
will enable extension of gyrochronology to the end of the stellar
main-sequence, yielding precise ages ({\sigma} ~10%) for the vast majority of
nearby stars. It will also help set constraints on the angular momentum
evolution and magnetic field generation in these stars. Our Kepler-based study
would be supported by a suite of ongoing and future ground-based observations.
Finally, we briefly discuss two ancillary science cases, detection of
long-period low-mass eclipsing binaries and microvariability in white dwarfs
and hot subdwarf B stars that the Kepler Two-Wheels Program would facilitate.Comment: Kepler white pape
The Effects of Close Companions (and Rotation) on the Magnetic Activity of M Dwarfs
We present a study of close white dwarf and M dwarf (WD+dM) binary systems
and examine the effect that a close companion has on the magnetic field
generation in M dwarfs. We use a base sample of 1602 white dwarf -- main
sequence binaries from Rebassa et al. to develop a set of color cuts in GALEX,
SDSS, UKIDSS, and 2MASS color space to construct a sample of 1756 WD+dM
high-quality pairs from the SDSS DR8 spectroscopic database. We separate the
individual WD and dM from each 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 H{\alpha} emission
line as an indicator for magnetic activity, we investigate the age-activity
relation for our sample for spectral types \leqM7. Our results show that
early-type M dwarfs (\leqM4) in close binary systems are more likely to be
active and have longer activity lifetimes compared to their field counterparts.
However, at a spectral type of M5 (just past the onset of full convection in M
dwarfs), the activity fraction and lifetimes of WD+dM binary systems becomes
more comparable to that of the field M dwarfs. One of the implications of
having a close binary companion is presumed to be increased stellar rotation
through disk-disruption, tidal effects, or angular momentum exchange. Thus, we
interpret the similarity in activity behavior between late-type dMs in WD+dM
pairs and late-type field dMs to be due to a decrease in sensitivity in close
binary companions (or stellar rotation), which has implications for the nature
of magnetic activity in fully-convective stars. (Abridged)Comment: 21 pages, 19 figures, emulateapj style, accepted to Astronomical
Journal June 28, 201
- …