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Obscured AGB stars in the Magellanic Clouds. I. IRAS candidates
We have selected 198 IRAS sources in the Large Magellanic Cloud, and 11in the Small Magellanic Cloud, which are the best candidates to bemass--loosing AGB stars (or possibly post--AGB stars). We used thecatalogues of \cite[Schwering \& Israel (1990)]{ref42} and\cite[Reid et al. (1990)]{ref36}. They are based on the IRAS pointedobservations and have lower detection limits than the Point SourceCatalogue. We also made cross-identifications between IRAS sources andoptical catalogues. Our resulting catalogue is divided in 7 tables.Table \ref{tab1} lists optically known red supergiants and AGB stars forwhich we found an IRAS counterpart (7 and 52 stars in the SMC and LMC,respectively). Table \ref{tab2} lists ``obscured'' (or ``cocoon'') AGBstars or late-type supergiants which have been identified as such inprevious works through their IRAS counterpart and JHKLM photometry (2SMC and 34 LMC sources; no optical counterparts). Table \ref{tab3} listsknown planetary nebulae with an IRAS counterpart (4 SMC and 19 LMC PNe).Table \ref{tab4} lists unidentified IRAS sources that we believe to begood AGB or post--AGB or PNe candidates (11 SMC and 198 LMC sources).Table~\ref{tab5} lists unidentified IRAS sources which could be any typeof object (23 SMC and 121 LMC sources). Table \ref{tab6} lists IRASsources associated with foreground stars (29 SMC and 135 LMC stars).Table \ref{tab7} lists ruled out IRAS sources associated with HIIregions, hot stars, etc... We show that the sample of IRAS AGB stars inthe Magellanic Clouds is very incomplete. Only AGB stars more luminousthan typically 10^4 L_\odot and with a mass-loss rate larger thantypically 5 10^{-6} M_\odot/yr could be detected by the IRAS satellite.As a consequence, one expects to find very few carbon stars in the IRASsample. We also expect that most AGB stars with intermediate mass--lossrates have not been discovered yet, neither in optical surveys, nor inthe IRAS survey. Tables 1 to 8 are also available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A large, complete, volume-limited sample of G-type dwarfs. I. Completion of Stroemgren UVBY photometry
Four-colour photometry of potential dwarf stars of types G0 to K2,selected from the Michigan Spectral Catalogues (Vol. 1-3), has beencarried out. The results are presented in a catalogue containing 4247uvby observations of 3900 stars, all south of δ = -26deg. Theoverall internal rms errors of one observation (transformed to thestandard system) of a program star in the interval 8.5 < V < 10.5are 0.0044, 0.0021, 0.0039, and 0.0059, respectively, in V, b-y, m_1_ ,and c_1_. The purpose of the catalogue, combined with earliercatalogues, is to allow selection of a large, complete, volume-limitedsample of G- and K-type dwarfs, investigate their metallicitydistribution, and compare it to predictions of various models ofgalactic chemical evolution. Future papers in this series will discussthese subjects.
| Reddening estimation for halo red giants using UVBY photometry
Updated uvby observations for a larger sample of metal-deficient redgiants are presented and combined with a select sample of data from theliterature transformed to a common system. Using the reddening maps ofBurstein & Heiles (1982), new absolute magnitudes, distances,metallicities, and reddenings are derived for each star. Themetallicities are determined with a revised calibration of them1, (b-y) diagram based upon comparison to a complilation ofrecent spectrsoscopic abundances transformed to a common system. Thephotometric abundances agree very well with the spectroscopic; thedispersion among the residuals for 58 giants is +/- 0.16 dex. Thedereddened indices are used to show that for red giants with (Fe/H) lessthan -1.5, there is a well-defined relation in the c0,(b-y)0 diagram which exhibits only a weak dependence uponmetallicity. Use of the standard relations allows one to obtainreddening estimates for normal halo field giants and globular clustersin the appropriate metallicity range.
| Evolved GK stars near the sun. I - The old disk population
A sample of nearly two thousand GK giants with intermediate band, (R,I),DDO and Geneva photometry has been assembled. Astrometric data is alsoavailable for most of the stars. The some 800 members of the old diskpopulation in the sample yield accurate luminosities (from two sources),reddening values and chemical abundances from calibrations of thephotometric parameters. Less than one percent of the objects arepeculiar in the sense that the flux distribution is abnormal. Thepeculiarity is signaled by strong CH (and Ba II) and weak CH. The CH+stars are all spectroscopic binaries, probably with white dwarfcompanions, whereas the CH- stars are not. A broad absorption band,centered near 3500 A, is found in the CH+ stars whereas the CH- objectshave a broad emission feature in the same region. The intensity of theseabsorptions and emissions are independent of the intensity of abnormalspectral features. Ten percent of the old disk sample have a heavyelement abundance from one and a half to three times the solar value.The distribution of the heavy element abundances is nearly a normal onewith a peak near solar abundance and ranges three times to one sixthsolar. The distribution of the (U, V) velocities is independent of theheavy element abundance and does not appear to be random. Ten percent ofthe old disk stars show a CN anomaly, equally divided between CN strongand CN weak. Several stars of individual astrometric or astrophysicalimportance are isolated.
| Astrometric and astrophysical discontinuities between the galactic old disk and halo stellar populations
Intermediate band, RI, and DDO photometry of the weak-lined stars in thefirst three volumes of the Michigan catalogs of spectral type arediscussed on the basis of luminosity and heavy element abundance. Theinterface between the old disk (Fe/H greater than -0.8 dex) and halo(Fe/H less than -1.2 dex) populations represents discontinuities in boththe stellar motions and the stellar physics. The CN strengths of bothevolved and unevolved halo stars decrease with decreasing temperature,in a mirror image of the increase with decreasing temperature for thedisk objects. The result for the halo giants has been attributed to deepmixing in the stellar atmospheres but the similar result for unevolveddwarfs indicates a difference in formation rather than in evolutionaryprocess of the two populations.
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