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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.
| Observations of fuors. FU Orionis during 1984-1990 - Notable variation in the brightness decline rate
Results of FU Ori photometry on Mt. Maidanak during 1984-1990 areanalyzed. In December 1987, the fuor exhibited a stepwise decrease inbrightness by 0.1 mag, after which the decrease rate of FU Oribrightness grew threefold (0.07 mag/yr compared to 0.02 mag/yr during1961-1980), while the U-B color parameter decreased to +0.82 mag. Adistance modulus of 8.1 +/- 0.2 mag is confirmed on the basis ofphotometry of 65 stars in the neighborhood of FU Ori. UBVR magnitudes ofvariable and emission-line stars in the FU Ori field are also presented;brightness variations are suspected for seven stars.
| FUOR observations III. FU Orionis during 1984-1990. A remarkable change in the brightness decrease rate.
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Osservazione e dati astrometrici
| Costellazione: | Orione |
| Ascensione retta: | 05h43m32.35s |
| Declinazione: | +08°45'30.3" |
| Magnitudine apparente: | 8.017 |
| Distanza: | 215.054 parsec |
| Moto proprio RA: | 9.6 |
| Moto proprio Dec: | 1.8 |
| B-T magnitude: | 8.346 |
| V-T magnitude: | 8.045 |
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