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The Planetary Mass Companion 2MASS 1207-3932B: Temperature, Mass, and Evidence for an Edge-on Disk
We present J-band imaging and H+K-band low-resolution spectroscopy of2MASS 1207-3932AB, obtained with VLT NACO. For the putative planetarymass secondary, we find J=20.0+/-0.2 mag. The HK spectra of bothcomponents imply low gravity and a dusty atmosphere for the secondary.Comparisons to synthetic spectra yield Teff,A~2550+/-150 Kand Teff,B~1600+/-100 K, consistent with their late-M andmid- to late-L types. For these Teff and an age of 5-10 Myr,evolutionary models imply MA~24+/-6 MJup andMB~8+/-2 MJup. Independent comparisons of thesemodels to the observed colors, spanning ~I to L', also yield the samemasses and temperatures. Our primary mass agrees with other recentanalyses; however, our secondary mass, while still in the planetaryregime, is 2-3 times larger than claimed previously. This discrepancycan be traced to the luminosities: while the absolute photometry andMbol of the primary agree with theoretical predictions, thesecondary is ~2.5+/-0.5 mag fainter than expected in all bands from I toL' and in Mbol. This accounts for the much lower secondarymass (and temperature) derived earlier. We argue that this effect ishighly unlikely to result from a variety of model-related problems andis instead real. This conclusion is bolstered by the absence of anyluminosity problems in either the primary or AB Pic B, which we alsoanalyze. We therefore suggest gray extinction in 2M1207B, due toocclusion by an edge-on circumsecondary disk. This is consistent withthe observed properties of edge-on disks around T Tauri stars and withthe known presence of a high-inclination evolved disk around theprimary. Finally, the system's implied mass ratio of ~0.3 suggests abinary-like formation scenario.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| 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.
| New Faint Southern Variable Stars
Not Available
| New faint southern variable stars.
Not Available
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Pozíciós és asztrometriai adatok
| Csillagkép: | Mérleg |
| Rektaszcenzió: | 14h56m02.54s |
| Deklináció: | -15°39'23.5" |
| Vizuális fényesség: | 8.006 |
| Távolság: | 130.89 parszek |
| RA sajátmozgás: | 1.6 |
| Dec sajátmozgás: | 11 |
| B-T magnitude: | 8.723 |
| V-T magnitude: | 8.066 |
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