104 research outputs found
Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs
We present medium resolution optical and NIR spectral data for components of
the newly discovered WISE J104915.57-531906.1AB (Luhman 16AB) brown dwarf
binary. The optical spectra reveal strong 6708 A Li I absorption in both Luhman
16A (8.0+/-0.4 A) and Luhman 16B (3.8+/-0.4 A). Interestingly, this is the
first detection of Li I absorption in a T dwarf. Combined with the lack of
surface gravity features, the Li I detection constrains the system age to 0.1 -
3 Gyr. In the NIR data, we find strong KI absorption at 1.168, 1.177, 1.243,
and 1.254 {\mu}m in both components. Compared to the strength of KI line
absorption in equivalent spectral subtype brown dwarfs, Luhman 16A is weaker
while Luhman 16B is stronger. Analyzing the spectral region around each doublet
in distance scaled flux units and comparing the two sources, we confirm the J
band flux reversal and find that Luhman 16B has a brighter continuum in the
1.17 {\mu}m and 1.25 {\mu}m regions than Luhman 16A. Converting flux units to a
brightness temperature we interpret this to mean that the secondary is ~ 50 K
warmer than the primary in regions dominated by condensate grain scattering.
One plausible explanation for this difference is that Luhman 16B has thinner
clouds or patchy holes in its atmosphere allowing us to see to deeper, hotter
regions. We also detect comparably strong FeH in the 0.9896 {\mu}m Wing-Ford
band for both components. Traditionally, a signpost of changing atmosphere
conditions from late-type L to early T dwarfs, the persistence and similarity
of FeH at 0.9896 {\mu}m in both Luhman 16A and Luhman 16B is an indication of
homogenous atmosphere conditions. We calculate bolometric luminosities from
observed data supplemented with best fit models for longer wavelengths and find
the components are consistent within 1{\sigma} with resultant Teffs of
1310+/-30 K and 1280+/-75 K for Luhman 16AB respectively.Comment: 17 pages, 11 figures, 4 tables. Submitted to ApJ and revised after
referee repor
A Chandra Study: Are Dwarf Carbon Stars Spun Up and Rejuvenated by Mass Transfer?
Carbon stars (with C/O> 1) were long assumed to all be giants, because only
AGB stars dredge up significant carbon into their atmospheres. The case is
nearly iron-clad now that the formerly mysterious dwarf carbon (dC) stars are
actually far more common than C giants, and have accreted carbon-rich material
from a former AGB companion, yielding a white dwarf and a dC star that has
gained both significant mass and angular momentum. Some such dC systems have
undergone a planetary nebula phase, and some may evolve to become CH, CEMP, or
Ba giants. Recent studies indicate that most dCs are likely from older,
metal-poor kinematic populations. Given the well-known anti-correlation of age
and activity, dCs would not be expected to show significant X-ray emission
related to coronal activity. However, accretion spin-up might be expected to
rejuvenate magnetic dynamos in these post mass-transfer binary systems. We
describe our Chandra pilot study of six dCs selected from the SDSS for Halpha
emission and/or a hot white dwarf companion, to test whether their X-ray
emission strength and spectral properties are consistent with a rejuvenated
dynamo. We detect all 6 dCs in the sample, which have X-ray luminosities
ranging from logLx= 28.5 - 29.7, preliminary evidence that dCs may be active at
a level consistent with stars that have short rotation periods of several days
or less. More definitive results require a sample of typical dCs with deeper
X-ray observations to better constrain their plasma temperatures.Comment: 13 pages, 5 figures. Revised and resubmitted June 20, accepted June
21, 2019 to Ap
The First Brown Dwarf Discovered by the Backyard Worlds: Planet 9 Citizen Science Project
The Wide-field Infrared Survey Explorer (WISE) is a powerful tool for finding
nearby brown dwarfs and searching for new planets in the outer solar system,
especially with the incorporation of NEOWISE and NEOWISE-Reactivation data. So
far, searches for brown dwarfs in WISE data have yet to take advantage of the
full depth of the WISE images. To efficiently search this unexplored space via
visual inspection, we have launched a new citizen science project, called
"Backyard Worlds: Planet 9," which asks volunteers to examine short animations
composed of difference images constructed from time-resolved WISE coadds. We
report the discovery of the first new substellar object found by this project,
WISEA J110125.95+540052.8, a T5.5 brown dwarf located approximately 34 pc from
the Sun with a total proper motion of 0.7 as yr. WISEA
J110125.95+540052.8 has a WISE magnitude of , this
discovery demonstrates the ability of citizen scientists to identify moving
objects via visual inspection that are 0.9 magnitudes fainter than the
single-exposure sensitivity, a threshold that has limited prior motion-based
brown dwarf searches with WISE.Comment: 9 pages, 4 figures, 1 table. Accepted for publication in the
Astrophysical Journal Letter
Touchstone Stars: Highlights from the Cool Stars 18 Splinter Session
We present a summary of the splinter session on "touchstone stars" -- stars
with directly measured parameters -- that was organized as part of the Cool
Stars 18 conference. We discuss several methods to precisely determine cool
star properties such as masses and radii from eclipsing binaries, and radii and
effective temperatures from interferometry. We highlight recent results in
identifying and measuring parameters for touchstone stars, and ongoing efforts
to use touchstone stars to determine parameters for other stars. We conclude by
comparing the results of touchstone stars with cool star models, noting some
unusual patterns in the differences.Comment: Proceedings of the 18th Cambridge Workshop on Cool Stars, Stellar
Systems, and the Sun, Eds G. van Belle & H. Harri
A nearby young M dwarf with a wide, possibly planetary-mass companion
We present the identification of two previously known young objects in the solar neighbourhood as a likely very wide binary. TYC 9486-927-1, an active, rapidly rotating early-M dwarf, and 2MASS J21265040-8140293, a low-gravity L3 dwarf previously identified as candidate members of the 45 Myr old Tucana Horologium association (TucHor). An updated proper motion measurement of the L3 secondary, and a detailed analysis of the pair's kinematics in the context of known nearby, young stars, reveals that they share common proper motion and are likely bound. New observations and analyses reveal the primary exhibits Li 6708~\AA~absorption consistent with M dwarfs younger than TucHor but older than the 10 Myr TW Hydra association yielding an age range of 10-45 Myr. A revised kinematic analysis suggests the space motions and positions of the pair are closer to, but not entirely in agreement with, the 24 Myr old Pictoris moving group. This revised 10-45 Myr age range yields a mass range of 11.6--15 M for the secondary. It is thus likely 2MASS J21265040-8140293short is the widest orbit planetary mass object known (4500AU) and its estimated mass, age, spectral type, and are similar to the well-studied planet Pictoris b. Because of their extreme separation and youth, this low-mass pair provide an interesting case study for very wide binary formation and evolution.Peer reviewedFinal Accepted Versio
Individual dynamical masses of DENIS J063001.4−184014AB reveal a likely young brown dwarf triple
The binary nature of the M8.5 dwarf DENIS J063001.4184014AB (DE063018)
was discovered with astrometric monitoring from the ground, which determined
the unresolved photocentric orbit and the trigonometric parallax of the system.
Here we present radial-velocity monitoring and resolved observations in the
near-infrared with Keck aperture masking that allow us to measure the system's
relative separation and brightness. By combining all available information, we
determine the individual dynamical masses of the binary components to be and , both firmly in the substellar regime. These masses are
surprising given the object's M8.5 optical spectral type and equivalent
absolute magnitude, and the significant difference in brightness between the
components ( = 1.740.06 mag). Our results suggest that
DE063018 is a relatively young system (200 Myr) with a secondary
component that is itself a potentially unresolved binary.Comment: 10 pages, 8 figures, accepted for publication in MNRA
Primeval very low-mass stars and brown dwarfs - III. The halo transitional brown dwarfs
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We report the discovery of an esdL3 subdwarf, ULAS J020858.62+020657.0 and a usdL4.5 subdwarf, ULAS J230711.01+014447.1. They were identified as L subdwarfs by optical spectra obtained with the Gran Telescopio Canarias, and followed up by optical to near infrared spectroscopy with the Very Large Telescope. We also obtained an optical to near infrared spectrum of a previously known L subdwarf, ULAS J135058.85+081506.8, and re-classified it as a usdL3 subdwarf. These three objects all have typical halo kinematics. They have around 2050-2250 K, 1.8 [Fe/H] 1.5, and mass around 0.0822-0.0833 M, according to model spectral fitting and evolutionary models. These sources are likely halo transitional brown dwarfs with unsteady hydrogen fusions, as their masses are just below the hydrogen-burning minimum mass, which is 0.0845 M at [Fe/H] = 1.6 and 0.0855 M at [Fe/H] = 1.8. Including these, there are now nine objects in the `halo brown dwarf transition zone', which is a `substellar subdwarf gap' spans a wide temperature range within a narrow mass range of the substellar population.Peer reviewedFinal Accepted Versio
Primeval very low-mass stars and brown dwarfs. I. Six new L subdwarfs, classification and atmospheric properties
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reservedWe have conducted a search for L subdwarf candidates within the photometric catalogues of the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey. Six of our candidates are confirmed as L subdwarfs spectroscopically at optical and/or near infrared wavelengths. We also present new optical spectra of three previously known L subdwarfs (WISEA J001450.17-083823.4, 2MASS J00412179+3547133, ULAS J124425.75+102439.3). We examined the spectral types and metallicity subclasses classification of known L subdwarfs. We summarised the spectroscopic properties of L subdwarfs with different spectral types and subclasses. We classify these new L subdwarfs by comparing their spectra to known L subdwarfs and L dwarf standards. We estimate temperatures and metallicities of 22 late type M and L subdwarfs by comparing their spectra to BT-Settl models. We find that L subdwarfs have temperatures between 1500 K and 2700 K, which are higher than similarly-typed L dwarfs by around 100-400 K depending on different subclasses and subtypes. We constrained the metallicity ranges of subclasses of M, L and T subdwarfs. We also discussed the spectral type and absolute magnitude relationships for L and T subdwarfs.Peer reviewedFinal Published versio
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