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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.
| Spectroscopy of the type Ia supernova SN 2002er: Days -11 to +215
We present an extensive set of optical spectroscopy of the nearby typeIa supernova, SN 2002er, with 24 epochs spanning -11 to +34 days. Itsspectral evolution is fairly typical of a type Ia supernova although itsuffers high extinction. Nevertheless, there are differences in thespectral evolution when compared to coeval spectra of other normal typeIa supernova with comparable decline-rate parameters. Modelling of thephotospheric phase spectra using a homogeneous abundance distribution inthe atmosphere provides a fair match to the observations, but only bypushing the adopted distance and risetime close to the observationallimits. Future improvements here will require models with a morerealistic stratified abundance distribution. From simple modelling of anebular spectrum obtained at +215 d, we infer a 56Ni mass of0.69 M_ȯ, consistent with that derived from the light curve.
| Study of the Largest Multiwavelength Campaign of the Microquasar GRS 1915+105
We present the results from a multiwavelength campaign of GRS 1915+105performed from 2000 April 16 to April 25. This is one of the largestcoordinated set of observations ever performed for this source, coveringthe wide energy band in radio (13.3-0.3 cm), near-infrared (J, H, and Kbands), X-rays, and gamma rays (from 1 keV to 10 MeV). During thecampaign GRS 1915+105 was predominantly in the ``plateau'' (or low/hard)state but sometimes showed soft X-ray oscillations: before April 20.3,rapid, quasi-periodic (~=45 minutes) flare-dip cycles were observed. Inthe spectral energy distribution in the plateau state, optically thicksynchrotron emission and Comptonization is dominant in the radio and X-to gamma-ray bands, respectively. The small luminosity in the radio bandrelative to that in X-rays indicates that GRS 1915+105 falls in theregime of ``radio-quiet'' microquasars. In three epochs we detectedfaint flares in the radio or infrared bands with amplitudes of 10-20mJy. The radio flares observed on April 17 shows frequency-dependentpeak delay, consistent with an expansion of synchrotron-emitting regionstarting at the transition from the hard-dip to the soft-flare states inX-rays. On the other hand, infrared flares on April 20 appear to follow(or precede) the beginning of X-ray oscillations with an inconstant timedelay of ~=5-30 minutes. This implies that the infrared-emitting regionis located far from the black hole by >~1013 cm, while itssize is <~1012 cm constrained from the time variability.We find a good correlation between the quasi-steady flux level in thenear-infrared band and in the X-ray band. From this we estimate that thereprocessing of X-rays, probably occurring in the outer parts of theaccretion disk, accounts for about 20%-30% of the observed K magnitudein the plateau state. The OSSE spectrum in the 0.05-10 MeV band isrepresented by a single power law with a photon index of 3.1 extendingto ~1 MeV with no cutoff. We can model the combined GIS-PCA-HEXTEspectra covering 1-200 keV by a sum of the multicolor disk model, abroken power law modified with a high-energy cutoff, and a reflectioncomponent. The power-law slope above ~30 keV is found to be very similarbetween different states in spite of large flux variations in softX-rays, implying that the electron energy distribution is not affectedby the change of the state in the accretion disk.
| Photoelectric Vilnius Photometry of Hipparcos Turn-Off Region Stars
Seven-color photometry in the Vilnius system and photometricclassification in terms of spectral type, absolute magnitude andmetallicity are presented for 145 Hipparcos stars of the turn-offregion, most of which have parallaxes determined to an accuracy of atleast 15%. The stars selected for the observing program included thoseidentified kinematically as intermediate between the thin disk and halo,plus a number of weak-lined stars discovered previously from objectiveprism surveys. The metallicity distribution we find for a kinematicallydefined sample of possible members of the thick disk has a meanabundance [Fe/H]= --0.3 dex and a dispersion of 0.3 dex. Our data seemto suggest a large age for this intermediate population.
| 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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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Aquila |
| Ascensió Recta: | 19h26m06.10s |
| Declinació: | +03°46'43.0" |
| Magnitud Aparent: | 8.884 |
| Distancia: | 273.224 parsecs |
| Moviment propi RA: | 17.1 |
| Moviment propi Dec: | -9 |
| B-T magnitude: | 9.522 |
| V-T magnitude: | 8.937 |
Catàlegs i designacions:
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