Michael F. Skrutskie

A sensitive 10-micron search for emission arising from circumstellar dust associated with solar-type pre-main-sequence stars

The presence and evolutionary timescales of circumstellar disks surrounding solar-type premain-sequence stars are studied using excess IR radiation above photospheric levels. The analysis is based on optical photometry, published near-IR fluxes, IRAS fluxes, and 10-micron flux measurements of 20 stars in Taurus-Auriga obtained with the NASA IR telescope facility. About half of the stars with ages less than 3 Myr show excess 2.2 and 10 micron emission, consistent with emission from optically thick disks extending inward to the stellar surface. At ages of about 10 Myr, less than 10 percent of the sample stars show evidence of dust emission from optically thick disks. It is concluded that the timescale over which disks survive as IR-luminous, optically thick structures is less than 10 Myr. Also, evidence for inner holes in premain-sequence stars surrounded by optically thick disks is discussed. 18 refs.

Correlations of optical and infrared excesses in T Tauri stars

The results of a survey of excess optical continuum emission (veiling) in a sample of 35 K7-M1 pre-main-sequence stars in Taurus-Auriga are reported. Stars with detectable veiling emission always show significant near-infrared K-L excesses. This result agrees with the prediction of a simple accretion disk model, where a boundary layer produces the veiling and the infrared excess comes from the disk. The K-N colors of T Tauri stars fall into two distinct groups: stars in the group with small or absent K-N excesses have no detectable veiling emission, while objects with large K-N excesses usually have detectable veiling. This result also agrees with the prediction of the disk model, where a large K-N excess indicates an optically thick disk, and an optically thick disk is required to generate a mass accretion rate large enough to produce detectable veiling. 27 refs.

2MASS Observations of the Large Magellanic Cloud

The Two Micron All Sky Survey (2MASS) has observed a portion of the Large Magellanic Cloud (LMC) at J (1.25 μm), H (1.65 μm), and K s (2.17 μm), as part of its routine nightly operations with an automated 1.3-m telescope at CTIO, Chile. The camera observes the sky in the three channels simultaneously, using 256 × 256 HgCdTe detector arrays. The survey samples the sky in 6° x 8.′3 scans. The 2MASS Production Processing System provides final atlas images and source extractions with precise photometric calibration and astrometric positions. The surveys 10σ sensitivity is 15.8 mag at J , 15.1 at H , and 14.3 at K s . 2MASS will ultimately detect ~10 7 point sources in the LMC and will support analyses of the ages, luminosity and mass functions, and metallicities of the red stellar populations and a census of AGB and carbon stars, as well as extinction maps, across the LMC. This work presents an initial analysis of ~20 square degrees.