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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.
| NGC 3079: X-ray emission from the nuclear super-bubble and halo
We report the results of the spatial and spectral analysis of the ROSATHRI and PSPC observations of the edge-on spiral galaxy NGC 3079. Wedetected several sources in the field of NGC 3079 with both PSPC andHRI, and complex emission from the inner 5' around NGC 3079. We haveidentified possible counterparts for several of the sources outside NGC3079 by comparison with optical plates and catalogues. The X-rayemission from NGC 3079 has a L_X = 3x 10(40) erg s(-1) and can beresolved into the following three components: \begin{itemize} Extendedemission in the innermost region, with L_X = 1x 10(40) erg s(-1) ,coincident with the super-bubble seen in optical images. The activenucleus may contribute to the emission as a point source. Emission fromthe disk of the galaxy, with L_X = 7x 10(39) erg s(-1) , that can bepartly resolved by the HRI in 3 point-like sources with luminosities of~ 6 x 10(38) erg s(-1) each. Very soft X-shaped emission from the halo,with L_X = 6x 10(39) erg s(-1) , extending to a diameter of 27 kpc. TheX-ray luminosity of NGC 3079 is higher by a factor of 10 compared toother galaxies of similar optical luminosity and we argue that this maybe caused by the presence of an AGN rather than by starburst activity.The influence of the AGN on the companion galaxies in the NGC 3079 groupare discussed.
| A Search for Metal-Deficient Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...22..117B&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Orsa Maggiore |
| Ascensione retta: | 10h02m23.08s |
| Declinazione: | +55°34'30.9" |
| Magnitudine apparente: | 9.424 |
| Moto proprio RA: | -19.6 |
| Moto proprio Dec: | 8.3 |
| B-T magnitude: | 9.894 |
| V-T magnitude: | 9.463 |
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