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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.
| An XMM-Newton look at the Wolf-Rayet star WR 40. The star itself, its nebula and its neighbours
We present the results of an XMM-Newton observation of the field of theWolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the highsensitivity of the satellite, the star itself is not detected: we thusderive an upper limit on its X-ray flux and luminosity. Joining thisresult to recent reports of a non-detection of some WC stars, we suggestthat the X-ray emission from single normal Wolf-Rayet stars could oftenbe insignificant despite remarkable instabilities in the wind. On thebasis of a simple modelling of the opacity of the Wolf-Rayet wind of WR40, we show that any X-ray emission generated in the particular zonewhere the shocks are supposed to be numerous will indeed have littlechance to emerge from the dense wind of the Wolf-Rayet star. We alsoreport the non-detection of the ejecta nebula RCW 58 surrounding WR 40.Concerning the field around these objects, we detected 33 X-ray sources,most of them previously unknown: we establish a catalog of these sourcesand cross-correlate it with catalogs of optical/infrared sources.Based on observations with XMM-Newton, an ESA Science Mission withinstruments and contributions directly funded by ESA Member States andthe USA (NASA).
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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