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Dynamical masses of young star clusters in NGC 4038/4039
In order to estimate the masses of the compact, young star clusters inthe merging galaxy pair, NGC 4038/4039 (``the Antennae''), we haveobtained medium and high resolution spectroscopy using ISAAC on VLT-UT1and UVES on VLT-UT2 of five such clusters. The velocity dispersions wereestimated using the stellar absorption features of CO at 2.29 mu m andmetal absorption lines at around 8500 Å, including lines of theCalcium Triplet. The size scales and light profiles were measured fromHST images. From these data and assuming Virial equilibrium, weestimated the masses of five clusters. The resulting masses range from6.5 x 105 to 4.7 x 106 Msun. Thesemasses are large, a factor of a few to more than 10 larger than thetypical mass of a globular cluster in the Milky Way. The mass-to-lightratios for these clusters in the V- and K-bands in comparison withstellar synthesis models suggest that to first order the IMF slopes areapproximately consistent with Salpeter for a mass range of 0.1 to 100Msun. However, the clusters show a significant range ofpossible IMF slopes or lower mass cut-offs and that these variations maycorrelate with the interstellar environment of the cluster. Comparisonwith the results of Fokker-Planck simulations of compact clusters withproperties similar to the clusters studied here suggest that they arelikely to be long-lived and may lose a substantial fraction of theirtotal mass. This mass loss would make the star clusters obtain masseswhich are comparable to the typical mass of a globular cluster. Based onobservations collected at the European Southern Observatory, Chile.
| Mass-losing M supergiants in the solar neighborhood
A list of the 21 mass-losing red supergiants (20 M type, one G type; Lgreater than 100,000 solar luminosities) within 2.5 kpc of the sun iscompiled. These supergiants are highly evolved descendants ofmain-sequence stars with initial masses larger than 20 solar masses. Thesurface density is between about 1 and 2/sq kpc. As found previously,these stars are much less concentrated toward the Galactic center thanW-R stars, which are also highly evolved massive stars. Although withconsiderable uncertainty, it is estimated that the mass return by the Msupergiants is somewhere between 0.00001 and 0.00003 solar mass/sq kpcyr. In the hemisphere facing the Galactic center there is much less massloss from M supergiants than from W-R stars, but, in the anticenterdirection, the M supergiants return more mass than do the W-R stars. Theduration of the M supergiant phase appears to be between 200,000 and400,000 yr. During this phase, a star of initially at least 20 solarmasses returns perhaps 3-10 solar masses into the interstellar medium.
| Supergiants and the Galactic metallicity gradient. II - Spectroscopic abundances for 64 distant F- to M-type supergiants
The metallicity gradient in the Galactic disk from in situ stars withvisual magnitude ranging from 6 to 10 is analyzed. Atmosphericparameters and detailed chemical abundances for 64 Population Isupergiants of spectral types F through M and luminosity classes Iathrough II have been determined. The derived Fe/H ratios ranging from-0.5 to + 0.7 show a mean value of +0.13 with an estimated uncertaintyof + or - 0.2. A subset of 25 supergiants fainter than 7th magnitudelying in the direction of the Galactic center shows a Fe/H mean of +0.18+ or - 0.04, while a similar sample of 15 faint supergiants lying in thedirection of the Galactic anticenter shows a lower Fe/H mean of +0.07 +or - 0.06. For a sample of bright supergiants analyzed by Luck andLambert (1985), the mean abundance pattern for all 64 stars showed thefollowing: deficient C and O along with enhancement of N, indicatingmixing of CNO-cycled material to the stellar surfaces; an apparent Srenhancement attributed to departures from LTE; and an essentially solarpattern of other chemical elements.
| Finding list and spectral classifications for southern luminous stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976AJ.....81..225M&db_key=AST
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