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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.
| A Moving Cluster Distance to the Exoplanet 2M1207b in the TW Hydrae Association
A candidate extrasolar planet companion to the young brown dwarf 2MASSWJ1207334-393254 (hereafter 2M1207) was recently discovered by Chauvin etal. They find that the temperature and luminosity of 2M1207b areconsistent with a young, ~5MJ planet. The 2M1207 system ispurported to be a member of the TW Hya association (TWA) and situated~70 pc away. Using a revised space motion vector for TWA and improvedproper motion for 2M1207, I use the moving cluster method to estimatethe distance to the 2M1207 system and other TWA members. The deriveddistance for 2M1207 (53+/-6 pc) forces the brown dwarf and planet to behalf as luminous as previously thought. The inferred masses for 2M1207Aand 2M1207b decrease to ~21 and ~3-4MJ, respectively, withthe mass of 2M1207b well below the observed tip of the planetary massfunction and the theoretical deuterium-burning limit. After removingprobable Lower Centaurus Crux (LCC) members from the TWA sample, as wellas the probable nonmember TWA 22, the remaining TWA membership is foundto have distances of 49+/-3 (s.e.m.)+/-12 (1 σ) pc and an internalone-dimensional velocity dispersion of 0.8+0.3-0.2km s-1. There is weak evidence that the TWA is expanding, andthe data are consistent with a lower limit on the expansion age of 10Myr (95% confidence).
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Osservazione e dati astrometrici
| Costellazione: | Vele |
| Ascensione retta: | 10h56m29.49s |
| Declinazione: | -48°19'55.2" |
| Magnitudine apparente: | 7.96 |
| Distanza: | 91.158 parsec |
| Moto proprio RA: | -34.5 |
| Moto proprio Dec: | -2.2 |
| B-T magnitude: | 8.291 |
| V-T magnitude: | 7.988 |
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