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Spectroscopic Detection of Carbon Monoxide in Two Late-Type T Dwarfs
M-band spectra of two late-type T dwarfs, 2MASS J09373487+2931409, andGliese 570D, confirm evidence from photometry that photospheric carbonmonoxide (CO) is present at abundance levels far in excess of thosepredicted from chemical equilibrium. These new and unambiguousdetections of CO, together with an earlier spectroscopic detection of COin Gliese 229B and existing M-band photometry of a large selection of Tdwarfs, suggest that vertical mixing in the photosphere drives the COabundance out of chemical equilibrium and is a common, and likelyuniversal feature of mid-to-late-type T dwarfs. The M-band spectra allowdeterminations of the timescale of vertical mixing in the radiativeregion of the atmosphere of each object, the first such measurements ofthis important parameter in late T dwarfs. A detailed analysis of thespectral energy distribution of 2MASS J09373487+2931409 results in thefollowing values for metallicity, temperature, surface gravity, andluminosity: [M/H] ~-0.3, T eff = 925-975 K, log g= 5.20-5.47, and log L/L sun = -5.308 ± 0.027.The age is 3-10 Gyr and the mass is in the range 45-69 M Jup.
| Starlight polarization and CO observations towards the Lupus clouds
We performed an observational study of the dark filaments Lupus 1 andLupus 4 using both polarimetric observations of 190 stars and a sampleof 72 ^12CO profiles towards these clouds. We have estimated lowerlimits to the distances of Lupus 1 and Lupus 4 (>~ 140 and >~ 125pc, respectively). The observational strategy of the survey allows us tocompare the projected magnetic field in an extended area around eachcloud with the magnetic field direction observed to prevail along theclouds. Lupus 4 could have collapsed along the magnetic field lines,while in Lupus 1 the magnetic field appears to be less ordered, havingthe major axis of the filaments parallel to the large-scale projectedmagnetic field. These differences would imply that both filaments havedifferent pattern evolutions. From the CO observations we have probedthe velocity fields of the filaments and the spatial extension of themolecular gas with respect to the dust.
| The nature of the Yale Common Proper Motion groups of stars
Attention is given to a large group of approximately 90 stars, twogroups of 20-30 stars, and 12 groups of a few stars each, taken from DDOsystem image tube spectral classification and intermediate bandphotometry for the Yale Common Proper Motion groups of 180 southernstars. Spectroscopic and photometric analyses of these groups haveindicated a very scattered Pop I main sequence in their color-magnitudediagrams. Distance moduli of 5 or less were derived from the averagespectroscopic parallaxes, in keeping with the proper motion amplitude of0.1 arcsec/year. The main sequence of each group shows scatter whenplotted in an HR diagram, indicating that they are probably nothomogeneous groups of stars sharing common physical origins.
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