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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.
| The distance to the high-velocity clouds - Mass infall and galactic disk formation
The high-velocity neutral hydrogen complex C in optical (Ca K)absorption against stars at distances of 1-2 kpc has been detected,confirming a previous tentative detection and placing an upper limit onthe distance to this complex. A similar (though as yet more uncertain)limit is placed to the distance to complex A. No complex is detected inabsorption against any nearby star, effectively ruling out models inwhich the clouds are formed by supershells in the local disk. If thesedistances are representative of the bulk of the high-velocity clouds,the local mass infall rate is 6 x 10 to the -9th solar mass/sq pc/yr,which would supply the disk column density in 10 billion yr. The cloudslie above the bulk of the disk, and it is shown how they may be used tomeasure the pressure of the halo and to place an upper bound on themetagalactic UV flux.
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| Сазвежђа: | Змај |
| Ректацензија: | 16h18m37.31s |
| Deклинација: | +59°41'37.1" |
| Apparent магнитуда: | 8.569 |
| Даљина: | 233.1 parsecs |
| Proper motion RA: | 14.2 |
| Proper motion Dec: | -7.4 |
| B-T magnitude: | 8.944 |
| V-T magnitude: | 8.6 |
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