5 research outputs found
The Elusive Majority of Young Moving Groups. I. Young Binaries and Lithium-rich Stars in the Solar Neighborhood
Young stars in the solar neighborhood serve as nearby probes of stellar evolution and represent promising targets to directly image self-luminous giant planets. We have carried out an all-sky search for late-type (≈K7-M5) stars within 100 pc selected primarily on the basis of activity indicators from the Galaxy Evolution Explorer and ROSAT. Approximately 2000 active and potentially young stars are identified, of which we have followed up over 600 with low-resolution optical spectroscopy and over 1000 with diffraction-limited imaging using Robo-AO at the Palomar 1.5 m telescope. Strong lithium is present in 58 stars, implying ages spanning ≈10-200 Myr. Most of these lithium-rich stars are new or previously known members of young moving groups including TWA, β Pic, Tuc-Hor, Carina, Columba, Argus, AB Dor, Upper Centaurus Lupus, and Lower Centaurus Crux; the rest appear to be young low-mass stars without connections to established kinematic groups. Over 200 close binaries are identified down to 0.″2 - the vast majority of which are new - and will be valuable for dynamical mass measurements of young stars with continued orbit monitoring in the future
Observational diagnostics of gas in protoplanetary disks
Protoplanetary disks are composed primarily of gas (99% of the mass).
Nevertheless, relatively few observational constraints exist for the gas in
disks. In this review, I discuss several observational diagnostics in the UV,
optical, near-IR, mid-IR, and (sub)-mm wavelengths that have been employed to
study the gas in the disks of young stellar objects. I concentrate in
diagnostics that probe the inner 20 AU of the disk, the region where planets
are expected to form. I discuss the potential and limitations of each gas
tracer and present prospects for future research.Comment: Review written for the proceedings of the conference "Origin and
Evolution of Planets 2008", Ascona, Switzerland, June 29 - July 4, 2008. Date
manuscript: October 2008. 17 Pages, 6 graphics, 134 reference
What works in preventing unintentional injuries in children and young adolescents? An updated systematic review
Over the past year, we have conducted a multi-faceted program to investigate
the origin and early evolution of brown dwarfs. Using high-resolution Keck
optical spectra of ~30 objects near and below the sub-stellar boundary in
several star-forming regions, we present compelling evidence for a T Tauri-like
accretion phase in young brown dwarfs. Our systematic study of infrared L'-band
(3.8-micron) disk excess in ~50 spectroscopically confirmed young very low mass
objects reveal that a significant fraction of brown dwarfs harbor disks at a
very young age. Their inner disk lifetimes do not appear to be vastly different
from those of disks around T Tauri stars. Taken together, our findings are
consistent with a common origin for most low-mass stars, brown dwarfs and
isolated planetary mass objects.Comment: to appear in proceedings of the conference on "Open Issues in Local
Star Formation and Early Stellar Evolution" held in Ouro Preto, Brazil, 2003
April 5-1