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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.
| Detailed Analysis of Nearby Bulgelike Dwarf Stars. III. α-Element and Heavy-Element Abundances
The present sample of nearby bulgelike dwarf stars has kinematics andmetallicities characteristic of a probable inner disk or bulge origin.Ages derived by using isochrones give 10-11 Gyr for these stars, andmetallicities are in the range -0.80<=[Fe/H]<=+0.40. We calculatestellar parameters from spectroscopic data, and chemical abundances ofMg, Si, Ca, Ti, La, Ba, Y, Zr, and Eu are derived by using spectrumsynthesis. We found that [α-elements/Fe] show different patterns,depending on the element. Si/Fe, Ca/Fe, and Ti/Fe ratios declinesmoothly for increasing metallicities and essentially follow the diskpattern. O and Mg, products of massive supernovae, and also ther-process element Eu are overabundant relative to disk stars, showing asteeper decline for metallicities [Fe/H]>-0.3 dex, and[s-elements/Fe] roughly track the solar values, with no apparent trendwith metallicity for [Fe/H]<0, showing subsolar values for the metalrich stars. Both kinematical and chemical properties of the bulgelikestars indicate a distinct identity of this population when compared withdisk stars.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Detailed Analysis of Nearby Bulgelike Dwarf Stars. II. Lithium Abundances
Li abundances are derived for a sample of bulgelike stars withisochronal ages of 10-11 Gyr. These stars have orbits with pericentricdistances, Rp, as small as 2-3 kpc and Zmax<1kpc. The sample comprises G and K dwarf stars in the metallicity range-0.80<=[Fe/H]<=+0.40. Few data on Li abundances in old turnoffstars (>=4.5 Gyr) within the present metallicity range are available.M67 (4.7 Gyr) and NGC 188 (6 Gyr) are the oldest studied metal-rich openclusters with late-type stars. Li abundances have also been studied fora few samples of old metal-rich field stars. In the present work, a highdispersion in Li abundances is found for bulgelike stars with allmetallicity ranges, comparable with values in M67. The role ofmetallicity and age on a Li depletion pattern is discussed. The possibleconnection between Li depletion and oxygen abundance due to atmosphericopacity effects is investigated.
| Detailed Analysis of Nearby Bulgelike Dwarf Stars. I. Stellar Parameters, Kinematics, and Oxygen Abundances
High-resolution échelle spectra were obtained with the Fiber-fedExtended Range Optical Spectrograph at the 1.5 m ESO telescope for 35nearby bulgelike stars with metallicities in the range-0.8<=[Fe/H]<=+0.4. Geneva photometry, astrometric data fromHipparcos, and radial velocities from CORAVEL are available for thesestars. From Hipparcos data, it appears that the turnoff of thispopulation indicates an age of 10-11 Gyr (as stated by Grenon in 1999).Detailed analysis of the sample stars is carried out, and atmosphericparameters derived from spectroscopic and photometric determinations arepresented. Oxygen abundances are derived based on the forbidden [O I]6300.3 Å line. The results show an oxygen overabundance patternfor most of the sample stars when compared to their disk counterparts.Based on observations carried out at the European Southern Observatory,La Silla.
| Oxygen Abundances in Bulge-like Dwarf Stars
High resolution échelle spectra were obtained with the FEROSspectrograph at the 1.5m ESO telescope for 35 nearby bulge-like stars.From Hipparcos data it appears that the turn-off of this populationindicates an age of 10--11 Gyr (Grenon 2000). Oxygen abundances arecalculated using the [O I] line at 6300.3 Å. The derived resultsshow an oxygen overabundance for most of our sample stars when comparedto their disk counterparts.
| Early type high-velocity stars in the solar neighborhood. IV - Four-color and H-beta photometry
Results are presented from photometric obaservations in the Stromgrenuvby four-color and H-beta systems of early-type high-velocity stars inthe solar neighborhood. Several types of photometrically peculiar starsare selected on the basis of their Stromgren indices and areprovisionally identified as peculiar A stars, field horizontal-branchstars, metal-poor stars near the Population II and old-disk turnoffs,metal-poor blue stragglers, or metallic-line A stars. Numerousphotometrically normal stars were also found.
| Early-type high-velocity stars in the solar neighborhood. I - List of candidates
Suspected nearby high-velocity stars of spectral types B and A areidentified by their proper motions, which are generally too small forthe stars to have been included in previous catalogs of high-velocitystars. The same selection process is then extended to spectral type Fstars, in order to both provide a companion sample and investigatewhether the hypothetical high-velocity, metal-rich population continuesto later spectral types. Of the presented list of 371 stars withconfirmed proper motions, 168 are of A and B spectral types. Photometricand spectroscopic observations of these stars are required to eliminatethose with misclassified spectra and convert proper motions into spacevelocities. The identification of type of stars is important forunderstanding apparent exceptions to the correlation between stellarages, metal abundances, and kinematic properties.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Южная Гидра |
| Прямое восхождение: | 01h40m32.24s |
| Склонение: | -69°59'13.1" |
| Видимая звёздная величина: | 8.511 |
| Расстояние: | 85.763 парсек |
| Собственное движение RA: | 234.6 |
| Собственное движение Dec: | -5 |
| B-T magnitude: | 9.201 |
| V-T magnitude: | 8.568 |
Каталоги и обозначения:
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