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Chemical Abundance Patterns in the Inner Galaxy: The Scutum Red Supergiant Clusters
The location of the Scutum Red Supergiant (RSG) clusters at the end ofthe Galactic Bar makes them an excellent probe of the Galaxy's secularevolution, while the clusters themselves are ideal testbeds in which tostudy the predictions of stellar evolutionary theory. To this end, wepresent a study of the RSG's surface abundances using a combination ofhigh-resolution Keck/NIRSPEC H-band spectroscopy and spectral synthesisanalysis. We provide abundance measurements for elements C, O, Si, Mg,Ti, and Fe. We find that the surface abundances of the stars studied areconsistent with CNO burning and deep, rotationally enhanced mixing. Theaverage ?/Fe ratios of the clusters are solar, consistent with athin-disk population. However, we find significantly subsolar Fe/Hratios for each cluster, a result which strongly contradicts a simpleextrapolation of the Galactic metallicity gradient to lowerGalactocentric distances. We suggest that a simple one-dimensionalparameterization of the Galaxy's abundance patterns is insufficient atlow Galactocentric distances, as large azimuthal variations may bepresent. Indeed, we show that the abundances of O, Si, and Mg areconsistent with independent measurements of objects in similar locationsin the Galaxy. In combining our results with other data in theliterature, we present evidence for large-scale (~ kpc) azimuthalvariations in abundances at Galactocentric distances of 3-5 kpc.While we cannot rule out that this observed behavior is due tosystematic offsets between different measurement techniques, we do findevidence for similar behavior in a study of the barred spiral galaxy NGC4736 which uses homogeneous methodology. We suggest that these azimuthalabundance variations could result from the intense but patchy starformation driven by the potential of the central bar.
| The Cool Supergiant Population of the Massive Young Star Cluster RSGC1
We present new high-resolution near-IR spectroscopy and OH maserobservations to investigate the population of cool luminous stars of theyoung massive Galactic cluster RSGC1. Using the 2.293 ?m CO band-headfeature, we make high-precision radial velocity measurements of 16 ofthe 17 candidate red supergiants (RSGs) identified by Figer et al. Weshow that F16 and F17 are foreground stars, while we confirm that therest are indeed physically associated RSGs. We determine that star F15,also associated with the cluster, is a yellow hypergiant based on itsluminosity and spectroscopic similarity to ? Cas. Using thecluster's radial velocity, we have derived the kinematic distance to thecluster and revisited the stars' temperatures and luminosities. We finda larger spread of luminosities than in the discovery paper, consistentwith a cluster age 30% older than previously thought (12+/-2 Myr), and atotal initial mass of (3+/-1)×104 Msolar.The spatial coincidence of the OH maser with F13, combined with similarradial velocities, is compelling evidence that the two are related.Combining our results with recent SiO and H2O maserobservations, we find that those stars with maser emission are the mostluminous in the cluster. From this we suggest that the maser activephase is associated with the end of the RSG stage, when theluminosity-mass ratios are at their highest.
| β Cephei stars in the ASAS-3 data. II. 103 new β Cephei stars and a discussion of low-frequency modes
Context: The β Cephei stars have been studied for over a hundredyears. Despite this, many interesting problems related to this class ofvariable stars remain unsolved. Fortunately, these stars seem to bewell-suited to asteroseismology. Hence, the results of seismic analysisof β Cephei stars should help us to better understand pulsationsand the main sequence evolution of massive stars, particularly theeffect of rotation on mode excitation and internal structure. It istherefore extremely important to increase the sample of known βCephei stars and select targets that are useful for asteroseismology. Aims: We analysed ASAS-3 photometry of bright early-type stars with thegoal of finding new β Cephei stars. We were particularly interestedin β Cephei stars that would be good for seismic analysis, i.e.,stars that (i) have a large number of excited modes; (ii) showrotationally split modes; (iii) are components of eclipsing binarysystems; (iv) have low-frequency modes, that is, are hybrid βCephei/SPB stars. Methods: Our study was made with a homogeneous sampleof over 4100 stars having MK spectral type B5 or earlier. For thesestars, the ASAS-3 photometry was analysed by means of a Fourierperiodogram. Results: We have discovered 103 β Cephei stars,nearly doubling the number of previously known stars of this type. Amongthese stars, four are components of eclipsing binaries, seven have modesequidistant or nearly equidistant in frequency. In addition, we foundfive β Cephei stars that show low-frequency periodic variations,very likely due to pulsations. We therefore regard them as candidatehybrid β Cephei/SPB pulsators. All these stars are potentially veryuseful for seismic modeling. Moreover, we found β Cephei-typepulsations in three late O-type stars and fast period changes in one, HD168050.Table 2 and Figs. 2-14 are only available in electronic form athttp://www.aanda.org The V photometry for all 103 stars is available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/477/917
| A Massive Cluster of Red Supergiants at the Base of the Scutum-Crux Arm
We report on the unprecedented red supergiant (RSG) population of amassive young cluster, located at the base of the Scutum-Crux Galacticarm. We identify candidate cluster RSGs based on 2MASS photometry andmedium-resolution spectroscopy. With follow-up high-resolutionspectroscopy, we use CO band-head equivalent width and high-precisionradial velocity measurements to identify a core grouping of 26physically associated RSGs-the largest such cluster known to date. Usingthe stars' velocity dispersion and their inferred luminosities inconjunction with evolutionary models, we argue that the cluster has aninitial mass of ~40,000 Msolar and is therefore among themost massive in the galaxy. Further, the cluster is only a few hundredparsecs away from the cluster of 14 RSGs recently reported by Figer atal.. These two RSG clusters represent 20% of all known RSGs in theGalaxy, and now offer the unique opportunity to study the presupernovaevolution of massive stars, and the blue- to red-supergiant ratio atuniform metallicity. We use GLIMPSE, MIPSGAL, and MAGPIS survey data toidentify several objects in the field of the larger cluster which seemto be indicative of recent regionwide starburst activity at the pointwhere the Scutum-Crux arm intercepts the Galactic bulge. Futureabundance studies of these clusters will therefore permit the study ofthe chemical evolution and metallicity gradient of the Galaxy in theregion where the disk meets the bulge.
| A photometric study of Be stars located in the seismology fields of COROT
Context: In preparation for the COROT mission, an exhaustive photometricstudy of Be stars located in the seismology fields of the mission hasbeen performed. The very precise and long-time-spanned photometricobservations gathered by the COROT satellite will give important clueson the origin of the Be phenomenon. Aims: The aim of this work is tofind short-period variable Be stars located in the seismology fields ofCOROT, and to study and characterise their pulsational properties. Methods: Light curves obtained at the Observatorio de Sierra Nevada,together with data from Hipparcos and ASAS-3 for a total of 84 Be stars,were analysed in order to search for short-term variations. We appliedstandard Fourier techniques and non-linear least-square fitting to thetime series. Results: We found 7 multiperiodic, 21 mono-periodic and 26non-variable Be stars. Short-term variability was detected in 74% ofearly-type Be stars and in 31% of mid- to late-type Be stars. We showthat non-radial pulsations are more frequent among Be stars than inslow-rotating B stars of the same spectral range.Appendix A is only available in electronic form at http://www.aanda.org
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Photoelectric Photometry of Herbig Ae/be and Related Stars in the Vilnius Photometric System
A catalog of photoelectric photometry of 62 Herbig Ae/Be and relatedstars in the Vilnius system is presented. It contains stars down to V =12 mag located mainly in the northern hemisphere and observed in theperiod of 1994--1996.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Studies in Galactic STRUCTURE.II.LUMINOSITY Classification for 1270 Blue Giant Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJS....2...41M&db_key=AST
| A Finding List of O and B Stars of High Luminosity.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1951ApJ...113..141N&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Scudo |
| Ascensione retta: | 18h34m15.84s |
| Declinazione: | -04°48'48.9" |
| Magnitudine apparente: | 8.726 |
| Distanza: | 10000000 parsec |
| Moto proprio RA: | 0.3 |
| Moto proprio Dec: | -0.3 |
| B-T magnitude: | 9.229 |
| V-T magnitude: | 8.768 |
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