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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 unusual circumstellar environment of the evolved star, U Equulei.
In the course of a spectroscopic survey to identify cold IRAS stars, wediscovered that the evolved star, U Equ, has a very peculiar opticalspectrum indicating an unusual circumstellar environment. The moderateresolution (62A/mm) spectrum has deep, yet unusually thin, molecularabsorption features that must arise in cold gas at a large distance fromthe star. The optical spectrum also has striking molecular emissionlines of TiO, AlO, VO possibly due to a fluorescence mechanism. Althoughthe IRAS 25/12μm colors of U Equ are typical of optically thincircumstellar envelopes, the LRS spectrum displays a strong 10 μmsilicate absorption band, indicating a thick, dusty envelope. Comparingour H_2_O and OH maser observations with profiles in the literaturetaken in 1987 (H_2_O) and 1990 (OH), we have found a variable velocitypattern and profile shape. We suggest that the star is of a warmspectral type, G to early K, and that it has an edge-on dusty disk ortorus and an inner warm molecular circumstellar shell. The luminositycriteria in our moderate-resolution spectra are consistent with that ofan evolved giant. The velocity and Galactic latitude are not consistentwith an early pre-main sequence evolutionary stage; however, theline-of-sight proximity of U Equ and a bright ribbon of IRAS Galacticcirrus suggest further investigation into the interstellar environmentis needed. We present optical spectra, profiles of the H_2_O and OHmasers, and J and K band images and photometry.
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