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Keck Interferometer Observations of Classical and Weak-line T Tauri Stars
We present observations of the T Tauri stars BP Tau, DG Tau, DI Tau, GMAur, LkCa 15, RW Aur, and V830 Tau, using long baseline infraredinterferometry at K band (2.2 μm) from the Keck Interferometer. Thetarget sources have a range of mass accretion rates and excessnear-infrared emission. The interferometer is most sensitive to extendedemission on characteristic size scales of 1-5 mas. All sources showevidence for resolved K-band emission on these scales, although a few ofthe sources are marginally consistent with being unresolved. Wecalculate the infrared excess based on fitting stellar photospheremodels to the optical photometry and estimate the physical size of theemission region using simple geometric models for the sources with asignificant infrared excess. Assuming that the K-band-resolved emissiontraces the inner edge of the dust disk, we compare the measuredcharacteristic sizes to predicted dust sublimation radii and find thatthe models require a range of dust sublimation temperatures and possiblyoptical depths within the inner rim to match the measured radii.
| Observations of DG Tauri with the Keck Interferometer
We present the first science results from the Keck Interferometer, adirect-detection infrared interferometer utilizing the two 10 m Kecktelescopes. The instrument and system components are briefly described.We then present observations of the T Tauri object DG Tau, which isresolved by the interferometer. The resolved component has a radius of0.12-0.24 AU, depending on the assumed stellar and extended componentfluxes and the model geometry used. Possible origins and implications ofthe resolved emission are discussed.
| Finding Cool Subdwarfs Using a V-J Reduced Proper-Motion Diagram: Stellar Parameters for 91 Candidates
We present the results of a search for cool subdwarfs for which ourcandidates were drawn from a V-J reduced proper-motion diagramconstructed by Salim & Gould. Kinematic (U, V, and W) andself-consistent stellar parameters (Teff, logg, [Fe/H], andξt) are derived for 91 candidate subdwarfs based onhigh-resolution spectra. The observed stars span 3900K
| Radial velocity measurements. IV - Ground-based accompaniment to the HIPPARCOS observation program
The paper presents 396 radial velocities of stars distributed in 19fields of 4 x 4 degrees. The study employs the Fehrenbach objectiveprism method and the same measuring technique used in a previous paper(Fehrenbach et al., 1987).
| Photoelectric observations of lunar occultations. XV
The last (or possibly penultimate) paper in a series on lunaroccultations presents observations of 404 phenomena, preceded by somegeneral remarks of a retrospective nature. The series of observationsbegan in 1968. Data for 20 doubles or suspected doubles are presented,ranked in order of certainty, with designation 3 representing thesurest. Thirteen of the cases refer to stars not previously noted asdoubles. Seven determinations of angular diameters are presented, ofwhich three have been previously observed.
| A library of stellar spectra
Spectra for 161 stars having spectral classes O-M and luminosity classesV, III, and I have been incorporated into a library available onmagnetic tape. The spectra extend from 3510 to 7427 A at a resolution ofabout 4.5 A. The typical photometric uncertainty of each resolutionelement in the spectra is on the order of 1 percent while broad-bandvariations are smaller than 3 percent. Potential uses for the libraryinclude population synthesis of galaxies and clusters, tests of stellaratmosphere models, spectral classification, and the generation of colorindices having arbitrary wavelength and bandpass.
| Magnetic field structure in the Taurus dark cloud
Optical and infrared polarimetry of sources in the direction of theTaurus cloud are obtained in order to study the magnetic field in thiscloud and its possible role in the cloud's evolution. Most of the starsare background giant stars whose light shines through the cloud and ispolarized by the cloud material. The transverse component of themagnetic field, as delineated by the polarization vectors, is generallyperpendicular to the galactic plane, and the stratified structure of thecloud could be due to the effect of the magnetic field during the earlystages of collapse. Three of the 13 embedded stars are stronglypolarized with position angles nearly perpendicular to those of nearbyfield stars. The polarization of these stars is most likely intrinsic,and the direction of polarization indicates that the materialsurrounding these stars may be magnetic i.e., that the magnetic field isfrozen in this material.
| U, B, V, R, I stellar photometry in the field of the Taurus dark clouds
A program of photoelectric stellar photometry has been carried out inthe field of the Taurus dark clouds with a view to establishing thedistance of the clouds and the absorption law in that region of the sky.It is found that the distance of the dark clouds accompanying the Tau T1and Tau T3 associations is 132 plus or minus 10 pc. Within theabsorption region 0-4 m, the Taurus dark clouds are characterized by anearly normal absorption law (to within 5-10%). In the field of the darkclouds a group of F0-G0 stars close to the main sequence is found whosespace density is three to eight times that in the solar neighborhood.
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