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Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
While the strong anticorrelation between chromospheric activity and age has led to the common use of the Ca II H and K emission index (R'_(HK) = L_(HK)/L_(bol)) as an empirical age estimator forExpand
A Preliminary Study of the Orion Nebula Cluster Structure and Dynamics
We use optical and near-infrared star counts to explore the structure and dynamics of the Orion Nebula Cluster (ONC). This very young (<1 Myr) cluster is not circularly symmetric in projection but isExpand
Herbig Ae/Be Stars: Intermediate-Mass Stars Surrounded by Massive Circumstellar Accretion Disks
The proposition that Herbig Ae/Be stars are young intermediate mass stars surrounded by optically thick accretion disks is explored. From a study of 47 such objects, a subset of 30 stars isExpand
On the Evolutionary Status of Class I Stars and Herbig-Haro Energy Sources in Taurus-Auriga
We present high-resolution (R ~ 34,000) optical (6330-8750 A) spectra obtained with the HIRES spectrograph on the W. M. Keck I telescope of stars in Taurus-Auriga whose circumstellar environmentExpand
The Stellar Populations of Praesepe and Coma Berenices
We present the results of a stellar membership survey of the nearby open clusters Praesepe and Coma Berenices. We have combined archival survey data from the SDSS, 2MASS, USNOB1.0, and UCAC-2.0Expand
Constraints on the Stellar/Substellar Mass Function in the Inner Orion Nebula Cluster
We present the results of a 0."5-0."9 FWHM imaging survey at K (2.2 μm) and H (1.6 μm) covering ~5.'1 × 5.'1 centered on θ^1C Ori, the most massive star in the Orion Nebula Cluster (ONC). At the ageExpand
UV Excess Measures of Accretion onto Young Very Low Mass Stars and Brown Dwarfs
Low-resolution spectra from 3000 to 9000 A of young low-mass stars and brown dwarfs were obtained with LRIS on Keck I. The excess UV and optical emission arising in the Balmer and Paschen continuaExpand
Evidence for Mass-dependent Circumstellar Disk Evolution in the 5 Myr Old Upper Scorpius OB Association
We present 4.5, 8, and 16 µm photometry from the Spitzer Space Telescope for 204 stars in the Upper Scorpius OB association. The data are used to investigate the frequency and properties ofExpand