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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.
| Flaring vs. self-shadowed disks: The SEDs of Herbig Ae/Be stars
Isolated Herbig Ae stars can be divided into two groups (Meeus et al.\citeyear{meeuswatersbouw:2001}): those with an almost flat spectralenergy distribution in the mid-infrared (``group I''), and those with astrong decline towards the far-infrared (``group II''). In this paper weshow that the group I vs. II distinction can be understood as arisingfrom flaring vs. self-shadowed disks. We show that these two types ofdisks are natural solutions of the 2D radiation-hydrostatic structureequations. Disks with high optical depth turn out to be flaring and havea strong far-IR emission, while disks with an optical depth below acertain threshold drop into the shadow of their own puffed-up inner rimand are weak in the far-IR. In spite of not having a directly irradiatedsurface layer, self-shadowed disks still display dust features inemission, in agreement with observations of group II sources. We proposean evolutionary scenario in which a disk starts out with a flaring shape(group I source), and then goes through the process of grain growth,causing the optical depth of the disk to drop and the disk to becomeself-shadowed (group II source). We show that this scenario predictsthat the (sub-)millimeter slope of the disk changes from steep (smallgrains) to Rayleigh-Jeans-like (large grains) in the early stages ofevolution, so that all group II sources are expected to haveRayleigh-Jeans-like slopes, while some group I sources may still havesteep (sub-)millimeter slopes.
| 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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Osservazione e dati astrometrici
| Costellazione: | Orione |
| Ascensione retta: | 05h29m05.89s |
| Declinazione: | -07°46'38.7" |
| Magnitudine apparente: | 8.986 |
| Moto proprio RA: | 3 |
| Moto proprio Dec: | 5.4 |
| B-T magnitude: | 9.321 |
| V-T magnitude: | 9.014 |
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