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Infrared Spectroscopy of the Ultra-Low-Mass Binary Oph 162225-240515
Binary properties are an important diagnostic of the star and browndwarf formation processes. While wide binaries appear to be rare in thesubstellar regime, recent observations have revealed Ophiuchus162225-240515 (2MASS J16222521-2405139) as a likely young ultra-low-massbinary with an apparent separation of ~240 AU. Here we presentlow-resolution near-infrared spectra of the pair from NTT/SOFI (R~600)and VLT/ISAAC (R~1400), covering the 1.0-2.5 ?m spectral region. Bycomparing them to model atmospheres from Chabrier & Baraffe andBurrows et al., we confirm the surface temperatures to beTA=2350+/-150 K and TB=2100+/-100 K for the twocomponents of the binary, consistent with earlier estimates from opticalspectra. Using gravity-sensitive K I features, we find the surfacegravity to be significantly lower than field dwarfs of the same spectraltype, providing the best evidence so far that these objects are indeedyoung. However, we find that models are not sufficiently reliable toinfer accurate ages/masses from surface gravity. Instead, we derivemasses of MA=13+8-4MJ andMB=10+5-4MJ for the twoobjects using the well-constrained temperatures and assuming an age of1-10 Myr, consistent with the full range of ages reported for the Ophregion.
| Far-Ultraviolet Stellar Photometry: Fields Centered on rho Ophiuchi and the Galactic Center
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..104..101S&db_key=AST
| Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
| UVBY H-beta photometry of UV-bright stars
uvby H-beta photometry is presented for 90 stars taken from an earlyversion of the Carnochan and Wilson (1983) catalogue of stars that havevery negative UV colors. Two have definite UV excesses (HD 36629, and HD81307). Four early-B stars have UV colors too positive for their visibleclassification, and beta-indices that indicate higher luminosities thanappear possible on galactic distribution grounds. Six late-B starsappear to have discordant flux distributions for which there are noobvious explanations. It is suggested that the high population ofsubluminous stars derived by Carnochan and Wilson is the product of thestatistical treatment used and the extreme patchiness in theinterstellar absorption, which gives rise to large numbers oflittle-reddened stars.
| Investigations of a Milky Way field in Scorpius. VI. Radial velocities of bright O and B stars
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