arXiv subjects

C. G. Tinney

Publications and source records attributed to C. G. Tinney.

150 records · Page 9Linked to original sources

arXiv1998

Searching for Weather in Brown Dwarfs

We have used an innovative tuneable filter technique to carry out a search for the variability signatures of meterological processes in the atmospheres of two nearby brown dwarfs. We find no evidence for variability in the L-type brown dwarf DENIS-PJ1228-1547 in an observations spanning approximately half a rotation period (3 hours), and evidence for variability in the M-type brown dwarf LP 944-20 in multiple observations spanning approximately one third of a rotation period (1.5 hours).

astro-ph↗

arXiv1998

High-resolution Spectra of Very Low-Mass Stars

We present the results of high-resolution (1-0.4A) optical spectroscopy of a sample of very low-mass stars. These data are used to examine the kinematics of the stars at the bottom of the hydrogen-burning main sequence. No evidence is found for a significant difference between the kinematics of the stars in our sample with I-K > 3.5 (MBol > 12.8) and those of more massive M-dwarfs (MBol = 7-10). A spectral atlas at high (0.4A) resolution for M8-M9+ stars is provided, and the equivalent widths of CsI, RbI and Halpha lines present in our spectra are examined. We analyse our data to search for the presence of rapid rotation, and find that the brown dwarf LP 944-20 is a member of the class of ``inactive, rapid rotators''. Such objects seem to be common at and below the hydrogen burning main sequence. It seems that in low-mass/low-temperature dwarf objects either the mechanism which heats the chromosphere, or the mechanism which generates magnetic fields, is greatly suppressed.

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arXiv1998

Optical Spectroscopy of DENIS Mini-survey Brown Dwarf Candidates

We present optical (6500-9200A) spectroscopy of eight cool dwarfs detected in a 231 square degree ``Mini-survey'' of the Deep NEar Infrared Survey (DENIS) data. We are able to confirm that the spectral types derived from the Mini-survey infrared spectroscopy are meaningful. We provide a spectral sequence which extends beyond the M-dwarf range and into the proposed ``L'' class of dwarfs. The dominant spectral features in the optical for these L-type dwarfs are resonance lines of Cs I and molecular band heads of CrH and FeH. The other dominant feature in these L-type spectra is a broad 600A absorption dip centered on 7700A, which we identify with extremely strong (equivalent width $\sim$ several hundred A) absorption associated with the 7664,7698A resonance doublet of K I. We find that model atmospheres which include the effects of molecular condensation without dust opacity (to simulate rapid gravitational settling of dust grains) produce significantly better agreement with observed optical spectra for L-type dwarfs, than models including dust opacity. This suggests gravitational settling of dust grains plays an important role in L-dwarf photospheres. The extreme strength of the K I resonance doublet, and disappearance of TiO and VO, and the consequent dominance of CrH and FeH in L-dwarf spectra offer considerable prospects as sensitive effective temperature diagnostics, even at low spectral resolution.

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arXiv1998

The Intermediate Age Brown Dwarf LP 944-20

Observations are presented which show that LiI 6708A is detected with equivalent width of 0.53+-0.05A in the proper-motion object LP 944-20 (which is also known as BRI 0337-3535). This Li detection implies that LP 944-20 is a brown dwarf with mass between 0.057 and 0.063Mo and age between 475 and 650Myr, making it the first brown dwarf to have its mass and age precisely determined.

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arXiv1997

DENIS-P J1228.2-1547 -- A New Benchmark Brown Dwarf

We present optical spectroscopy of three brown dwarf candidates identified in the first 1% of the DENIS sky survey. Low resolution spectra from 6430 - 9150A show these objects to have similar spectra to the brown dwarf candidate GD 165B. High resolution spectroscopy shows that one of the objects -- DENIS-P J1228.2-1547 -- has a strong 2.3+-0.05A equivalent width absorption line of Li I 6708A, and is therefore a brown dwarf with mass below 0.065Msol, and age < 1.5 Gyr. DENIS-P J1228.2-1547 can now be considered a proto-type for brown dwarfs closer to the hydrogen burning limit than Gl 229B.

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arXiv1995

HE 3-1475 AND ITS JETS

We present spectra and high-resolution images taken with HST, the NTT, the VLA, and the MPIA/ESO 2.2m of the emission-line star He 3-1475 which we suggest is a post-AGB star. The star is at the origin of a 15-arcsec-long structure containing symmetrically opposing bright knots. The knots have radial velocities of about 500 km/s from the center of He 3-1475 to the ends of the jets. HST snapshots show that the core of He 3-1475 is unipolar with a star at the SE end and the nebula fanning out toward the NW. VLA observations show the presence of OH masers, which are positioned parallel to the optical jets. A model is proposed that accounts for all of the observational data. This unusual object may link the OH/IR stars having extreme outflow velocities with highly bipolar planetary nebulae.

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