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|Dynamical mass estimates for two luminous young stellar clusters in Messier 83|
Using new data from the UVES spectrograph on the ESO Very LargeTelescope and archive images from the Hubble Space Telescope, we havemeasured projected velocity dispersions and structural parameters fortwo bright young star clusters in the nearby spiral galaxy NGC5236. One cluster is located near the nuclear starburst of NGC5236, at a projected distance of 440 pc from the centre, while the otheris located in the disk of the galaxy at a projected galactocentricdistance of 2.3 kpc. We estimate virial masses for the two clusters of(4.2±0.7)×105 Mȯ and(5.2±0.8)×105 Mȯ and ages (frombroad-band photometry) of 107.1±0.2 years and108.0±0.1 years, respectively. Comparing the observedmass-to-light (M/L) ratios with simple stellar population models, wefind that the data for both clusters are consistent with a Kroupa-typestellar mass function (MF). In particular, we rule out any MF with asignificantly lower M/L ratio than the Kroupa MF, such as aSalpeter-like MF truncated at a mass of 1 Mȯ or higher.These clusters provide a good illustration of the fact that massive,globular cluster-like objects (``super star clusters'') can form at thepresent epoch even in the disks of seemingly normal, undisturbed spiralgalaxies.Based on observations collected at the European Southern Observatory,Chile under programme 71.B-0303A, and on observations obtained with theNASA/ESA Hubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
|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.
|Near-infrared spectroscopy of the circumnuclear star formation regions in M100: evidence for sequential triggering|
We present low-resolution (R~450) K-band spectroscopy for 16 of the 43circumnuclear star-forming knots in M100 identified by Ryder &Knapen. We compare our measurements of equivalent widths for theBrγ emission line and CO 2.29-μm absorption band in each knotwith the predictions of starburst models from the literature, and deriveages and burst parameters for the knots. The majority of these knots arebest explained by the result of short, localized bursts of starformation between 8 and 10Myr ago. By examining both radial andazimuthal trends in the age distribution, we present a case forsequential triggering of star formation, most likely resulting from theaction of a large-scale shock. In an appendix, we draw attention to thefact that the growth in the CO spectroscopic index with decreasingtemperature in supergiant stars is not as regular as is commonlyassumed.
|Silicate and hydrocarbon emission from Galactic M supergiants|
Following our discovery of unidentified infrared (UIR) band emission ina number of M supergiants in h and chi Per, we have obtained 10-μmspectra of a sample of 60 galactic M supergiants. Only three newsources, V1749 Cyg, UW Aql and IRC+40 427, appear to show the UIR bands;the others show the expected silicate emission or a featurelesscontinuum. The occurrence of UIR-band emission in M supergiants istherefore much higher in the h and chi Per cluster than in the Galaxy asa whole. Possible explanations for the origin and distribution of UIRbands in oxygen-rich supergiants are discussed. We use our spectra toderive mass-loss rates ranging from 10^-8 to 10^-4 M_solar yr^-1 for thenew sample, based on the power emitted in the silicate feature. Therelationship between mass-loss rate and luminosity for M supergiants isdiscussed, and correlations are explored between their mid-infraredemission properties.
|Classification and Identification of IRAS Sources with Low-Resolution Spectra|
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
|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.
|The 1.5-1.7 micrometer spectrum of cool stars: Line identifications, indices for spectral classification and the stellar content of the Seyfert galaxy NGC 1068|
The first aim of this paper is to determine which lines or narrowmolecular bands in the H-band spectra of cool stars could be of interestfor the classification of K-M stars. For this purpose we present highquality, medium resolution (R approximates 1500) spectra of field stars(mostly K-M giants and supergiants) and compare them with detailedsynthetic spectra computed on the basis of existing model atmospheresfor red giants. The agreement between theoretical and observed spectrais good and virtually all the observed features can be accounted for bylines of (12)CO, (13)CO, OH, Mg, Al, Si, Ca and Fe. We analyze in detailthe relative contribution of these and other species and conclude thatthe feature at 1.62 micrometers which is weak in early K but very strongin late M stars, is mainly due to the CO(6-3) band-head, while that at1.59 micrometers, which is prominent in all stars later than G, isprimarily attributable to silicon up to early M types, while in late Mstars this feature is strongly contaminated by OH lines. We choose thesetwo features as 'spectral classificators' and measure their equivalentwidths in more than 40 G, K, M giants and supergiants. From these datait is found that CO 1.62 in giants increases rapidly and with arelatively small scatter going to later spectral types. Supergiants havedeeper CO(6-3) and display a larger scatter. The (1.62)/(2.29) ratiosteadily increases going to cooler stars but does not vary significantlywith luminosity class. A very useful ratio is (1.62)/(1.59) whichincreases by a large factor from early K to late M stars and couldtherefore be a powerful tool to identify and estimate the averagespectral type of cool stars in complex objects like active galaxynuclei. To demonstrate such a possibility we also present long slitspectra of the Seyfert galaxy NGC 1068 where the equivalent widths ofall stellar features are found to decrease in the central 4 arcsecaround the nucleus but the (1.62)/(1.59) ratio, and hence the averagestellar temperature, does not change significantly. The estimatedaverage spectral type is late-K which is compatible with either an oldand very metallic bulge population or a younger one associated with arecent starburst. These data also show that the non-stellar continuumaccounts for approximately 30% and approximately equal to or greaterthan 80% of the flux at 1.62 and 2.3 micrometers respectively in thecentral 4.4 arcsec. The features around 1.6 micrometers are thus muchless diluted than CO(2, 0) and hence offer advantages for studies of thestellar content in such objects. The non-stellar nuclear emission isvery red and most probably associated with a hot (T approximately equalor greater than 800 K) dust component.
|New features of IRSPEC.|
|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.
|Walraven photometry of nearby southern OB associations|
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
|A list of MK standard stars|
|The Perkins catalog of revised MK types for the cooler stars|
A catalog is presented listing the spectral types of the G, K, M, and Sstars that have been classified at the Perkins Observatory in therevised MK system. Extensive comparisons have been made to ensureconsistency between the MK spectral types of stars in the Northern andSouthern Hemispheres. Different classification spectrograms have beengradually improved in spite of some inherent limitations. In thecatalog, the full subclasses used are the following: G0, G5, G8, K0, K1,K2, K3, K4, K5, M0, M1, M2, M3, M4, M5, M6, M7, and M8. Theirregularities are the price paid for keeping the general scheme of theoriginal Henry Draper classification.
|Ionization of the mass-loss wind of the M supergiant IRS 7 by the ultraviolet flux in the Galactic center|
The Br-alpha hydrogen recombination line is detected from the Msupergiant IRS 7 in the Galactic center. The line strength appears to bestronger than expected for normal stellar processes. If the star lieswithin 0.6 pc of the Galactic center, the ionization can be explained asthe effect of the ambient field of UV photons on the mass-loss wind ofthe star. This model requires that massive stars formed in the Galacticcenter in the last 10 Myr; it is then likely that they account for asignificant portion of the luminosity and excitation of the central pcof the Galaxy.
|A multifrequency study of circumstellar envelopes of cool giants and supergiants|
A multifrequency study of all parts of circumstellar envelopes of coolgiants and supergiants is presented. In order to investigate theinfluence of stellar parameters on spectral features of these envelopes,a sample of 77 cool giants and supergiants that occupies a horizontalstrip in the Hertzsprung-Russell diagram was observed. Spectroscopic andphotometric observations at optical, infrared and radio wavelengths ledto the following results: (1) for giants there exists a strongcorrelation between H-alpha emission and SiO masers, which led to thesuggestion that SiO masers are triggered by shock-waves and can bepumped by collisions, (2) the SiO expansion velocity was found to besystematically lower by 2 km/s compared to the CO expansion velocity,and (3) a relation between the asymmetry of the light curve and theintensity of the dust emission at 9.7 microns has been confirmed for awide range of periods. Rather than luminosity alone, pulsationalproperties of the variable play a dominant role for the structure ofcircumstellar envelopes of cool giants and supergiants.
|1988 Revised MK Spectral Standards for Stars GO and Later|
|UBV Photoelectric Photometry Catalogue (1986). III Errors and Problems on DM and HD Stars|
|The dwarf star content of elliptical and lenticular galaxies|
Near-IR spectra of 14 galaxies are analyzed to determine accurate lowermain-sequence dwarf light contributions and to set limits on themass-to-light (M/L) ratios. While dwarf light contributes 30-50 percentof the total at 8200 A, low measured FeH indices preclude contributionsof more than 15 percent to the integrated light at 9900 A from late Mdwarfs. M/L ratios of about 6 are found, consistent with dynamicalestimates. The brighter galaxies exhibit substantial gradients in theequivalent width of the Na I feature. This is at least partly due tometal abundance gradients also reflected in the TiO index, but there issome evidence for concentrations of metal-rich dwarfs toward the centersof giant galaxies.
|IRAS catalogues and atlases - Atlas of low-resolution spectra|
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
|The MK classification and its calibration|
The system of spectral classification is described as it has developedfrom the original Yerkes Atlas (Morgan, Keenan, Kelman 1943) untiltoday. The word 'developed' is used because any system that is to remainuseful must be flexible enough to adapt not only to improved techniquesof measurement but also to new theoretical insights into the variablesthat actually determine the energy spectrum of a star in all itsfascinating but sometimes frustrating detail. The discussion does notconsider the criteria of classification but is confined to the resultingset of temperature types and luminosity classes. Chemical composition isexamined as a third variable. Tabulated and plotted informationincludes: MK temperature subclasses; lists of MK types of fainter stars;published calibrations of luminosity classes for early-type stars;calibration of MK luminosity classes for types later than F8; thedistribution among groups of the 426 stars in the author's current listof best types; and the effects of metal deficiencies on spectra of KOIII stars. The revised MK classification can be applied to all but a fewpercent of the stars later in type than GO. For the two-thirds of thesethat have approximately solar composition no abundance index is needed;for most of the remainder one abundance index suffices.
|1985 revised MK spectral standards : stars GO and later|
|Visual measurements of southern double stars|
A double-star observing program is described which has been started atCordoba with a 30 cm refractor. Usually neglected Index Catalog ofVisual Double Stars (IDS) pairs south of -60 deg are selected forobservation, most of them having been measured only one or two timespreviously. A total of 174 micrometric observations of 78 wide pairs arepresented together with a few measurements of 9 double stars not foundin the IDS. Also reported is a list of 135 additional measurements of 26test stars. By comparison with all earlier observations, an estimate forthe personal equation has been made, which is applied in combinationwith catalogue proper motions to investigate the nature of many of thesepairs.
|Carbon monoxide band intensities in M giants|
The strength of CO (2.3 micron) bands was measured using the photometercomponent of the Kitt Peak 1.3-m telescope in an attempt to identifyextremely carbon-poor M giants. Magnitudes for about 200 bright M starswere obtained through a J filter, and narrow filters were centered on2.17 and 2.40 microns, respectively. No M giants were found with COindices indicative of extremely low carbon abundances. The correlationof CO index to effective temperature did not extend to the extremelylate and variable M giants. The dependence of CO index upon carbonabundance, 12-C/13-C ratio, surface gravity, effective temperature, andmicroturbulent velocity indices were also investigated. It is found thatthe predicted and observed CO indices are in good agreement for starswith spectroscopically determined carbon abundance.
|Close visual binaries. I - MK classifications|
Each component of 170 close visual binaries has been classified with newprocedures for controlling contamination problems. These classificationsare presented and are shown to be on the MK system. Two sources of areascanner UBV photometry were compared in order to establish homogeneousphotometric as well as spectroscopic data. From a consideration ofsystematic errors in the V magnitude difference (Delta V) betweencomponents the photometry of Hurly and Warner (1983) is to be preferred.Absolute magnitudes for each binary are derived from Delta V via atested MK - M(v) map.
|Area Scanner Observations of Close Visual Double Stars - Part Two - Results for 153 Southern Stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983MNRAS.202..761H&db_key=AST
|Revised MK Spectral Standard Stars Later than G0|
|New UBVRI photometry for 900 supergiants|
A description is presented of the results obtained in connection with asystematic program of supergiant photometry on the Johnson UBVRI system.During the eight years after the start of the program, almost 1000 starshave been observed, about 400 three or more times each. The originalselection of stars used the spectral type catalog of Jaschek et al.(1964) to choose supergiants. Since observations were possible from bothChile and Canada, no declination limits were imposed, and no particularselection criteria were imposed other than to eliminate carbon stars.These are so red as to require enormous extrapolations of thetransformation equations.
|Radial velocities of southern HR stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980PASP...92..713B&db_key=AST
|Erratum - Discordances Between SAO and HD Numbers for Bright Stars|
|Revised MK spectral types for G, K, and M stars|
A catalog of spectral types of 552 G, K, and M stars is presented, whichis classified on the revised MK system. Stellar representatives of thehalo, disk, and arm populations in all parts of the sky are included.Photoelectric V magnitudes are given, as are intensity estimates of anyfeatures which make the spectrum appear peculiar as compared to thespectrum of a similar normal star. Abundance indices are also providedin the following lines or bands: CN, barium, Fe, calcium, and CH.
|Photoelectric two-dimensional spectral classification of M supergiants|
A photoelectric system defined by eight narrow bands between 0.7 and 1.1microns has been used to measure nearly all M supergiants that have beenclassified on the MK system. The photometric TiO and CN indicesreproduce the two-dimensional MK classifications to the accuracy of theMK types themselves. Mean fluxes and spectral classifications arepresented for 128 stars.
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