Volume-limited sample of cool dwarfs. I. L0-T8 dwarfs
Short Name:
J/AJ/161/42
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new volume-limited sample of L0-T8 dwarfs out to 25pc defined entirely by parallaxes, using our recent measurements from UKIRT/WFCAM along with Gaia DR2 and literature parallaxes. With 369 members, our sample is the largest parallax-defined volume-limited sample of L and T dwarfs to date, yielding the most precise space densities for such objects. We find the local L0-T8 dwarf population includes 5.5%{+/-}1.2% young objects (<~200Myr) and 2.6%{+/-}1.6% subdwarfs, as expected from recent studies favoring representative ages <~4Gyr for the ultracool field population. This is also the first volume-limited sample to comprehensively map the transition from L to T dwarfs (spectral types ~L8-T4). After removing binaries, we identify a previously unrecognized, statistically significant (>4.4{sigma}) gap ~0.5mag wide in (J-K)_MKO_ colors in the L/T transition, i.e., a lack of such objects in our volume-limited sample, implying a rapid phase of atmospheric evolution. In contrast, the most successful models of the L/T transition to date-the "hybrid" models of Saumon & Marley-predict a pileup of objects at the same colors where we find a deficit, demonstrating the challenge of modeling the atmospheres of cooling brown dwarfs. Our sample illustrates the insights to come from even larger parallax-selected samples from the upcoming Legacy Survey of Space and Time by the Vera Rubin Obsevatory.
In a volume-limited sample of 63 ultracool dwarfs of spectral type M7-M9.5, we have obtained high-resolution spectroscopy with UVES at the Very Large Telescope and HIRES at Keck Observatory. In this first paper we introduce our volume-complete sample from DENIS and 2MASS targets, and we derive radial velocities and space motion. Kinematics of our sample are consistent with the stars being predominantly members of the young disk. The kinematic age of the sample is 3.1Gyr. We find that six of our targets show strong Li lines implying that they are brown dwarfs younger than several hundred million years. Five of the young brown dwarfs were unrecognized before. Comparing the fraction of Li detections to later spectral types, we see a hint of an unexpected local maximum of this fraction at spectral type M9. It is not yet clear whether this maximum is due to insufficient statistics, or to a combination of physical effects including spectral appearance of young brown dwarfs, Li line formation, and the star formation rate at low masses.
VOPSAT is a set of southern sky digital surveys based on ESO-R, SRC-J and POSS1-E atlases. The plates have been digitized with the MAMA microdensitometer with a resolution of 0.7 arc-sec. Pixel resampling will allow mosaicing neighbouring Schmidt fields up to hundreds of square degrees.
VOResource: an XML Encoding Schema for Resource Metadata
Short Name:
VOResource
Date:
02 Apr 2013 11:19:48
Publisher:
International Virtual Observatory Alliance
Description:
This document describes an XML encoding standard for IVOA
Resource Metadata, referred to as VOResource. This schema is
primarily intended to support interoperable registries used
for discovering resources; however, any application that needs
to describe resources may use this schema. In this document,
we define the types and elements that make up the schema as
representations of metadata terms defined in the IVOA
standard, Resource Metadata for the Virtual Observatory
[Hanisch et al. 2004]. We also describe the general model for
the schema and explain how it may be extended to add new
metadata terms and describe more specific types of resources.
VOResource: an XML Encoding Schema for Resource Metadata
Short Name:
VOResource
Date:
16 Apr 2025 09:07:32
Publisher:
International Virtual Observatory Alliance
Description:
This document describes an XML encoding standard for IVOA Resource
Metadata, referred to as VOResource. This schema is primarily intended
to support metadata exchange between interoperable registries and
resource discovery within them. However, any application that needs to
describe resources may use this schema. In this document, we define the
types and elements that make up the schema in close alignment to the
metadata terms defined in Resource Metadata for the Virtual Observatory
(Hanisch 2007), but also taking into account other metadata standards as
well as experiences from the operation of the VO Registry. We also
describe the general model for the schema and explain how it is extended
to add new metadata terms and describe more specific types of resources.
One of the greatest uncertainties in modelling the mass-exchange phases during the evolution of a binary system is the amount of mass and angular momentum that has been lost from the system. In order to constrain this problem, a favourable, evolved and detached real binary system is valuable as an example of the end result of this process. We study the 52-day post-mass-exchange eclipsing binary V643 Ori from complete uvby light curves and high-resolution spectra. V643 Ori is double-lined and shows total primary eclipses. The orbit is accurately circular and the rotation of both stars synchronised with the orbit, but the photometry from a single year (1993) shows signs of weak spot activity (0.02mag) around the primary eclipse. We determine accurate masses of 3.3 and 1.9M_{sun}_ from the spectroscopic orbit and solve the four light curves to determine radii of 16 and 21R_{sun}_, using the Wilson-Devinney photometric code. The rotational velocities from the cross-correlation profiles agree well with those computed from the known radii and orbital parameters. All observable parameters are thus very precisely determined, but the masses and radii of V643 Ori are incompatible with undisturbed post-main-sequence evolution. We have attempted to simulate the past evolutionary history of V643 Ori under both conservative and non-conservative Case B mass transfer scenarios. In the non-conservative case we varied the amounts of mass and angular momentum loss needed to arrive at the present masses in a circular 52-day orbit, keeping the two stars detached and synchronized as now observed, but without following the evolution of other stellar properties in any detail. Multiple possible solutions were found. Further attempts were made using both the BSE formalism and the binary MESA code in order to track stellar evolution more closely, and make use of the measured radii and temperatures as important additional constraints. Those efforts did not yield satisfactory solutions, possibly due to limitations in handling mass transfer in evolved stars such as these. We remain hopeful that future theoreticians can more fully model the system under realistic conditions.
Table 3 presents the emission line spectrum of V380 Ori in the optical region observed at OHP in January 1995 with a mean resolution of 10000. For the line blends the wavelength and flux (not reddening corrected) of each contributor are given. For the P-Cygni profiles the equivalent widths of the absorption component are also reported. We estimate an error of less than 10% for the strongest lines, 10% to 40% for the weakest lines.
