Contents
Images
Upload your image
DSS Images Other Images
Related articles
Dynamical mass estimates for two luminous star clusters in galactic merger remnants
We present high-dispersion spectra of two extremely massive starclusters in galactic merger remnants, obtained using the UVESspectrograph mounted on the ESO Very Large Telescope. One cluster, W30,is located in the ~500 Myr old merger remnant NGC 7252 and has avelocity dispersion and effective radius of σ=27.5±2.5 kms-1 and Reff=9.3±1.7 pc, respectively. Theother cluster, G114, located in the ~3 Gyr old merger remnant NGC 1316,is much more compact, Reff=4.08±0.55 pc, and has avelocity dispersion of σ=42.1±2.8 km s-1. Thesemeasurements allow an estimate of the virial mass of the two clusters,yielding Mdyn(W30)=1.59(±0.26)× 10^7Mȯ and Mdyn(G114)=1.64(±0.13)×10^7 Mȯ. Both clusters are extremely massive, being morethan three times heavier than the most massive globular clusters in theGalaxy. For both clusters we measure light-to-mass ratios, which whencompared to simple stellar population (SSP) models of the appropriateage, are consistent with a Kroupa-type stellar mass function. Usingmeasurements from the literature we find a strong age dependence on howwell SSP models (with underlying Kroupa or Salpeter-type stellar massfunctions) fit the light-to-mass ratio of clusters. Based on this resultwe suggest that the large scatter in the light-to-mass ratio of theyoungest clusters is not due to variations in the underlying stellarmass function, but instead to the rapidly changing internal dynamics ofyoung clusters. Based on sampling statistics we argue that while W30 andG114 are extremely massive, they are consistent with being the mostmassive clusters formed in a continuous power-law cluster massdistribution. Finally, based on the positions of old globular clusters,young massive clusters (YMCs), ultra-compact dwarf galaxies (UCDs) anddwarf-globular transition objects (DGTOs) in κ-space we concludethat 1) UCDs and DGTOs are consistent with the high mass end of starclusters and 2) YMCs occupy a much larger parameter space than oldglobular clusters, consistent with the idea of preferential disruptionof star clusters.
| The ACS Virgo Cluster Survey. VII. Resolving the Connection between Globular Clusters and Ultracompact Dwarf Galaxies
NO>1Based on observations with the NASA/ESA Hubble Space Telescopeobtained at the Space Telescope Science Institute, which is operated bythe association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555.
| Differential rotation and star-spot evolution on HK Aqr in 2001 and 2002
We present images of the rapidly rotating (Prot= 0.431 d)M1.5Ve dwarf HK Aqr, from data obtained during 2001 and 2002. Star-spotsare found distributed at a range of latitudes during both observingseasons, but unlike other solar-type rapid rotators of higher mass, HKAqr does not show a strong polar cap at either epoch. In addition to thesurface brightness images, we make use of the four-night time-base overwhich the 2002 observations were made, in order to derive an estimate ofthe latitudinal dependent rotation on HK Aqr. We find that theequator-lap-pole time lies in the range -1449 to +448 d. Although verysmall, we are therefore unable to determine whether the degree ofdifferential rotation is in the solar or anti-solar sense.
| The orbits of southern binary Cepheids
High-resolution spectroscopic observations have been made of a number ofsouthern Cepheids. The stars studied were part of a long-term programmeto observe southern variable stars and to complete a data base of radialvelocities over a long time interval. The radial velocities have aprecision of ~300 m s-1, allowing the detection of velocitydifferences of ~1 km s-1 with confidence. Our new dataprovide a consistent set of data against which other sources of data canbe compared.Masses were determined for two systems, the 9-d Cepheid S Mus (6.2 +/-0.2 Msolar) and the 5-d Cepheid V350 Sgr (6.0 +/- 0.9Msolar). For another seven Cepheids (Y Car, YZ Car, AX Cir,BP Cir, V636 Sco, W Sgr and T Mon), new or improved orbital solutionswere found.New results presented here include the first orbital solution for AXCir, a completely revised orbital solution for YZ Car, which establishedits eccentricity and orbital motion, and a new pulsation period (2.39819 d) for BP Cir. The pulsational mass determinations provide furtherconfirmation of the convergence of mass determinations between dynamicaland evolutionary methods.
| An optical velocity for the Phoenix dwarf galaxy
We present the results of a Very Large Telescope observing programmecarried out in service mode using FORS1 on ANTU in long-slit mode todetermine the optical velocities of nearby low surface brightnessgalaxies. As part of our programme of service observations we obtainedlong-slit spectra of several members of the Phoenix dwarf galaxy fromwhich we derive an optical heliocentric radial velocity of -13 +/- 9 kms-1. This agrees very well with the velocity of the mostpromising of the H I clouds seen around Phoenix, which has aheliocentric velocity of -23 km s-1, but is significantlydifferent from the recently published optical heliocentric velocity ofPhoenix of -52 +/- 6km s-1 by Gallart et al.
| Testing stellar population models with star clusters in the Large Magellanic Cloud
We present high signal-to-noise ratio integrated spectra of 24 starclusters in the Large Magellanic Cloud (LMC), obtained using the FLAIRspectrograph at the UK Schmidt telescope. The spectra have been placedon to the Lick/IDS system in order to test the calibration of SimpleStellar Population (SSP) models. We have compared the SSP-predictedmetallicities of the clusters with those from the literature,predominantly taken from the Ca-triplet spectroscopy of Olszewski et al.(1991). We find that there is good agreement between the metallicitiesin the range -2.10 <=[Fe/H]<= 0. However, the Mg2 index(and to a lesser degree Mg b) systematically predict highermetallicities (up to +0.5 dex higher) than . Among thepossible explanations for this are that the LMC clusters possess[α/Fe] > 0. Metallicities are presented for eleven LMC clusterswhich have no previous measurements. We compare SSP ages for theclusters, derived from the Hβ, Hγ and Hδ Lick/IDSindices, with the available literature data, and find good agreement forthe vast majority. This includes six old globular clusters in oursample, which have ages consistent with their HST colour-magnitudediagram (CMD) ages and/or integrated colours. However, two globularclusters, NGC 1754 and NGC 2005, identified as old (~15 Gyr) on thebasis of HST CMDs, have Hβ line-strengths which lead ages that aretoo low (~8 and ~6 Gyr respectively). These findings are inconsistentwith their CMD-derived values at the 3σ level. Comparison betweenthe horizontal branch morphology and the Balmer line strengths of theseclusters suggests that the presence of blue horizontal branch stars hasincreased their Balmer indices by up to ~1.0 Å. We conclude thatthe Lick/IDS indices, used in conjunction with contemporary SSP models,are able to reproduce the ages and metallicities of the LMC clustersreassuringly well. The required extrapolations of the fitting functionsand stellar libraries in the models to lower ages and low metallicitiesdo not lead to serious systematic errors. However, owing to thesignificant contribution of horizontal branch stars to Balmer indices,SSP model ages derived for metal-poor globular clusters are ambiguouswithout a priori knowledge of horizontal branch morphology.
| Adaptive Optics Near-Infrared Spectroscopy of the Sagittarius A* Cluster
We present K-band λ/Δλ~2600 spectroscopy of fivestars (K~14-16 mag) within 0.5" of Sgr A*, the radio source associatedwith the compact massive object suspected to be a2.6×106Msolar black hole at the center ofour Galaxy. High spatial resolution of ~0.09" and good Strehl ratios of~0.2 achieved with adaptive optics on the 10 m Keck telescope make itpossible to measure moderate-resolution spectra of these starsindividually for the first time. Two stars (S0-17 and S0-18) areidentified as late-type stars by the detection of CO band headabsorption in their spectra. Their absolute K magnitudes and CO bandhead absorption strengths are consistent with early K giants. Threestars (S0-1, S0-2, and S0-16) with rproj<0.0075 pc (~0.2")from Sgr A* lack CO band head absorption, confirming the results ofearlier lower spectral and lower spatial resolution observations thatthe majority of the stars in the Sgr A* cluster are early-type stars.The absolute K magnitudes of the early-type stars suggest that they arelate O, early B main-sequence stars of ages less than 20 Myr. Thepresence of young stars in the Sgr A* cluster so close to the centralsupermassive black hole poses the intriguing problem of how these starscould have formed or could have been brought within its strong tidalfield.
| Cyclic and secular variation in the temperatures and radii of extreme helium stars
The ultraviolet properties of 17 extreme helium stars have been examinedusing 150 IUE spectra. Combining short-wave and long-wave image pairsand using a grid of hydrogen-deficient model atmospheres and aχ2 minimization procedure, 70 measurements of effectivetemperature (Teff), angular diameters (θ) andinterstellar extinction (EB_V) were obtained. In most cases,these were in good agreement with previous measurements, but there aresome ambiguities in the case of the hotter stars, where the solutionsfor Teff and EB_V become degenerate, and in thecase of the cooler stars with large EB_V, where the totalflux is no longer dominated by the ultraviolet. The behaviour of 12helium stars was examined over an interval exceeding 10yr. The surfacesof four stars (HD 168476, HD 160641, BD -9°4395 and BD -1°3438)were found to be heating at rates between 20 and 120Kyr-1, inremarkable agreement with theoretical predictions. This result providesthe first direct evidence that extreme helium stars are heliumshell-burning stars of up to ~0.9Msolar contracting towardsthe white dwarf sequence. Low-luminosity helium stars do not show adetectable contraction, also in agreement with theory, although one, BD+10°2179, may be expanding. The short-term behaviour of threevariable helium stars (PV Tel variables: HD 168476, BD +1°4381, LSIV-1°2) was examined over a short interval in 1995. All three showedchanges in Teff and θ on periods consistent withprevious observations. Near-simultaneous radial velocity (v)measurements were used to establish the total change in radius, withsome reservations concerning the adopted periods. Subsequently,measurements of the stellar radii and distances could be derived. WithTeff and surface gravities established previously, stellarluminosities and masses were thus obtained directly from observation. Inthe case of HD 168476, the mass is 0.94 ± 0.68 M\odot.Assuming a similar gravity for LSIV -1°2 based on its neutral heliumline profiles, its mass becomes 0.79 ± 0.46 M\odot.The θ amplitude for BD +1°4381 appears to be overestimated bythe IUE measurements and leads to a nonsensical result. These firstdirect measurements of luminous extreme helium star masses agree wellwith previous estimates from stellar structure and pulsation theory.
| Radial Velocity of the Phoenix Dwarf Galaxy: Linking Stars and H I Gas
We present the first radial velocity measurement of the stellarcomponent of the Local Group dwarf galaxy Phoenix, using the FORS1instrument at the VLT's Unit Telescope 1 (Antu). From the spectra of 31red giant branch stars, we derive a heliocentric optical radial velocityfor Phoenix of Vsolar=-52+/-6 km s-1. On the basisof this velocity, and taking into account the results of a series ofsemianalytical and numerical simulations, we discuss the possibleassociation of the H I clouds observed in the Phoenix vicinity. Weconclude that the characteristics of the H I cloud with heliocentricvelocity -23 km s-1 are consistent with this gas having beenassociated with Phoenix in the past and being lost by the galaxy afterthe last event of star formation in the galaxy, about 100 Myr ago. Twopossible scenarios are discussed: the ejection of the gas by the energyreleased by the supernovae (SNe) produced in that last event of starformation and a ram pressure stripping scenario. We derive that thekinetic energy necessary to eject the gas isESNe~2×1051 ergs and that the number of SNenecessary to transfer this amount of kinetic energy to the gas cloud is~20. This is consistent with the number of SNe expected for the lastevent of star formation in Phoenix, according to the star formationhistory derived by Martínez-Delgado, Gallart, & Aparicio. Thedrawback of this scenario is the regular appearance of the H I cloud andits anisotropic distribution with respect to the stellar component.Another possibility is that the H I gas was stripped as a consequence ofram pressure by the intergalactic medium. In our simulations, thestructure of the gas remains quite smooth as it is stripped fromPhoenix, keeping a distribution similar to that of the observed H Icloud. Both in the SNe ejection case and in the ram pressure sweepingscenario, the distances and relative velocities imply that the H I cloudis not gravitationally bound to Phoenix, since this would require aPhoenix total mass about an order of magnitude larger than its totalestimated mass. Finally, we discuss the possibility that Phoenix may bea bound Milky Way satellite. The minimum required mass of the Milky Wayfor Phoenix to be bound is MMW(<450kpc)>=1.2×1012 Msolar, which comfortablyfits within most current estimates. Based on observations collected invisitor mode with the VLT UT1, Antu, at the European SouthernObservatory, Chile.
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/367/297
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| The optical velocity of the Antlia dwarf galaxy
We present the results of a Very Large Telescope observing programmecarried out in service mode using fors1 on ANTU (UT1) in long slit modeto determine the optical velocities of nearby low surface brightnessgalaxies. Outlying Local Group galaxies are of paramount importance inplacing constraints on the dynamics and thus on both the age and thetotal mass of the Local Group. Optical velocities are also necessary todetermine if the observations of Hi gas in and around these systems arethe result of gas associated with these galaxies or a chancesuperposition with high-velocity Hi clouds or the Magellanic Stream. Thedata were of a sufficient signal-to-noise ration to enable us to obtaina reliable result in one of the galaxies we observed - Antlia - forwhich we have found an optical heliocentric radial velocity of351+/-15kms-1.
| Estimation of Stellar Metal Abundance. II. A Recalibration of the Ca II K Technique, and the Autocorrelation Function Method
We have recalibrated a method for the estimation of stellar metalabundance, parameterized as [Fe/H], based on medium-resolution (1-2Å) optical spectra (the majority of which cover the wavelengthrange 3700-4500 Å). The equivalent width of the Ca II K line (3933Å) as a function of [Fe/H] and broadband B-V color, as predictedfrom spectrum synthesis and model atmosphere calculations, is comparedwith observations of 551 stars with high-resolution abundances availablefrom the literature (a sevenfold increase in the number of calibrationstars that were previously available). A second method, based on theFourier autocorrelation function technique first described by Ratnatunga& Freeman, is used to provide an independent estimate of [Fe/H], ascalibrated by comparison with 405 standard-star abundances.Metallicities based on a combination of the two techniques for dwarfsand giants in the color range 0.30<=(B-V)_0<=1.2 exhibit anexternal 1 sigma scatter of approximately 0.10-0.20 dex over theabundance range -4.0<=[Fe/H]<=0.5. Particular attention has beengiven to the determination of abundance estimates at the metal-rich endof the calibration, where our previous attempt suffered from aconsiderable zero-point offset. Radial velocities, accurate toapproximately 10 km s^-1, are reported for all 551 calibration stars.
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Spectroscopy of the optical Einstein ring 0047-2808
We present optical and near-infrared spectroscopic observations of theoptical Einstein ring 0047-2808. We detect both [O III] lineslambdalambda4959, 5007 near ~2.3mum, confirming the redshift of thelensed source as z=3.595. The Lyalpha line is redshifted relative to the[O III] line by 140+/-20kms^-1. Similar velocity shifts have been seenin nearby starburst galaxies. The [O III] line is very narrow, 130kms^-1FWHM. If the ring is the image of the centre of a galaxy, theone-dimensional stellar velocity dispersion sigma=55kms^-1 isconsiderably smaller than the value predicted by Baugh et al. for thesomewhat brighter Lyman-break galaxies. The Lyalpha line issignificantly broader than the [O III] line, probably due to resonantscattering. The stellar central velocity dispersion of the early-typedeflector galaxy at z=0.485 is 250+/-30kms^-1. This value is in goodagreement both with the value predicted from the radius of the Einsteinring (and a singular isothermal sphere model for the deflector), andwith the value estimated from the D_n-sigma relation.
| Rotation, activity and lithium in NGC 6475
Radial and rotational velocities, chromospheric activity, and lithiumabundances are presented for an X-ray-selected sample of stars in theyoung (220 Myr) open cluster NGC 6475. Low-mass members of the clusterhave been identified on the basis of photometric and spectroscopiccriteria. The observations show that the rapid spindown seen amongsolar-type stars in the Pleiades is incomplete at 220 Myr, as there areF, G, and K stars in NGC 6475 with v sin i greater than 10 km/s. Peakrotation rates for G stars are 12-14 km/s, and are robust to uncertaininclination angles, because the magnetic activity of these stars is lessthan the saturation value observed for fast rotators in the Pleiades.Two mid-K stars are found with v sin i about 25 km/s and with saturatedmagnetic activity levels, indicating that spindown time-scales aremass-dependent, increasing from about 20 Myr for early-G stars togreater than 75 Myr for mid-K stars.
| Circumstellar Gas in the Wide Binary HD 188037
We report radio, optical, and ultraviolet studies of the wide binary HD188037 (=IRC +20439). We detect the CO (2--1) and (1--0) rotationallines from the circumstellar envelope in this system, which consists ofa luminous (~7000 Lȯ) mass-losing M-type star and, at a separationof 0."75, a main-sequence A-type star. The strong (2--1) line has a veryunusual skewed shape with a width at zero intensity of about 30 km s-1,which we explain with a model wherein the gas ejected by the M-type staris preferentially photodissociated on one side of the outflow byultraviolet light from the A-type companion. We infer that the wind fromthe M giant expands at 15 km s-1 and, for an estimated distance of 300pc, carries ~3 x 10-7 Mȯ yr-1. Our simplified model for CO in awind being photodissociated by ultraviolet from a companion explains whyCO can be detected around Mira yet not around alpha Sco.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Core velocity dispersions for 25 Galactic and 10 old Magellanic globular clusters.
We present, for 25 Galactic and 10 old Magellanic globular clusters,projected velocity dispersion (σ_p_) measurements obtained byapplying a cross-correlation technique to integrated-light spectra. Inorder to understand and estimate the statistical errors of thesemeasurements due to small numbers of bright stars dominating theintegrated light, we provide an extensive discussion based on detailednumerical simulations. These errors are smaller if the integration areais larger and/or the cluster concentration higher. The simulations showthat measurements are reliable when the integrated light within theintegration area is brighter than a given magnitude. The statisticalerrors on the σ_p_ measurements of Magellanic globular clustersare small because of a physically large integration area, whereas theycan be important for measurements carried out over small central areasin Galactic clusters. The present observational results are used tooutline a few characteristics of the globular cluster fundamental plane.In this respect, the old Magellanic globular clusters appear similar tothe Galactic clusters.
| The Stromlo-APM Redshift Survey. IV. The Redshift Catalog
The Stromlo-APM Redshift Survey consists of 1797 galaxies with b_J_ <17.15 selected randomly at a rate of 1 in 20 from automated platemeasurement (APM) scans. The survey covers a solid angle of 1.3 sr (4300deg^2^) in the south Galactic cap. Redshifts have been measured for 1790(99.6%) of the galaxies. The median galaxy recession velocity is 15,300km s^-1^, and so the volume probed is V ~ 1.38 x 10^6^ h^-3^ Mpc^3^. Inthis paper we describe the construction of the redshift catalog andpresent the survey data.
| K Giants in Baade's Window. I. Velocity and Line-Strength Measurements
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1774T&db_key=AST
| H-alpha measurements for cool giants
The H-alpha line in a cool star is usually an indication of theconditions in its chromosphere. I have collected H-alpha spectra of manynorthern G-M stars, which show how the strength and shape of the H-alphaline change with spectral type. These observations detect surprisinglittle variation in absoption-line depth (Rc approximately0.23 +/- 0.08), linewidth (FWHD approximately 1.44 +/- 0.22 A), orequivalent width (EW approximately 1.12 +/- 0.17 A) among G5-M5 IIIgiants. Lines in the more luminous stars tend to be broader and strongerby 30%-40% than in the Class III giants, while the H-alpha absorptiontends to weaken among the cooler M giants. Velocities of H-alpha andnearby photospheric lines are the same to within 1.4 +/- 4.4 km/s forthe whole group. To interpret these observations, I have calculatedH-alpha profiles, Ly-alpha strengths, and (C II) strengths for a seriesof model chromospheres representing a cool giant star like alpha Tau.Results are sensitive to the mass of the chromosphere, to chromospherictemperature, to clumping of the gas, and to the assumed physics of lineformation. The ubiquitous nature of H-alpha in cool giants and the greatdepth of observed lines argue that chromospheres of giants cover theirstellar disks uniformly and are homogeneous on a large scale. This isquite different from conditions on a small scale: To obtain a highenough electron density with the theoretical models, both to explain theexitation of hydrogen and possibly also to give the observed C IImultiplet ratios, the gas is probably clumped. The 6540-6580 A spectraof 240 stars are plotted in an Appendix, which identifies the date ofobservation and marks positions of strong telluric lines on eachspectrum. I assess the effects of telluric lines and estimates that thestrength of scattered light is approximately 5% of the continuum inthese spectra. I give the measurements of H-alpha as well as equivalentwidths of two prominent photospheric lines, Fe I lambda 6546 and Ca Ilambda 6572, which strengthen with advancing spectral type.
| 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.
| A kinematic study of the Sculptor dwarf spheroidal galaxy.
We derive new, accurate radial velocity (V_r_) measurements for 23Sculptor K-giant stars from high-resolution echelle spectra made withthe ESO NTT and 3.6-m telescopes. Comparing our velocities with previousmeasurements (Armandroff & Da Costa 1986) for 15 stars, we show thatthe V_r_ measurements are reliable, and discover two V_r_ variable starswith large amplitudes (>17km/s). These variations are best explainedby binary orbital motions. As our sample is likely to contain manyadditional undetected binaries with smaller velocity amplitudes (due toless favorable orbit inclinations, smaller mass ratios, or longerperiods), the observations suggest a large binary fraction in Sculptor,possibly larger than ~20% within the period limits ~0.5 to ~20yrs. Thisresult is consistent with the recent discoveries of 2-3 large-amplitudevariable stars in Ursa Minor and Sextant. Previous kinematic studies ofdSph galaxies based on single-epoch measurements are consequently notfully reliable. Radial velocity-variable stars artificially inflate thevelocity dispersion and the mass-to-light (M/L) ratio estimates. Thisweakens the case for dark matter, at least in some of the dSph galaxies.In the case of Sculptor, a velocity dispersion of 6.2+/-1.1km/s and aM/L ratio of 13+/-6(M/L_V_)sun_ are derived from our sample.These results do not provide unambiguous evidence for a dominant darkmatter component in Sculptor, mainly because our sample is likely tocontain additional undetected V_r_ variables of lower amplitude.
| Metallicity Calibration for Super-Solar Stars
Not Available
| On the velocity dispersion in the core of the globular cluster M15
A projected velocity dispersion sigmap of 0 = 14.0 km/s isderived from an integrated light spectrum obtained at the EuropeanSouthern Observatory (ESO) at La Silla, Chile, over a central 6 sec x 6sec area in the core of the globular cluster M15. Extensive numericalsimulations of velocity dispersion determinations from integrated lightspectra show that all the velocity dispersions obtained from integratedlight measurements over small central areas suffer from largestatistical errors due to the small numbers of bright stars present inthe integration area. These simulations, over our area of integration of6 sec x 6 sec, give sigmap = 15(+6/-4) km/s as the mostprobable values for the central velocity dispersion and its statisticalerror. The observational result differs from the challenging highcentral velocity dispersion sigmap of 0 = 25 km/s derived byPeterson, Seitzer, & Cudworth (1989) are consistent with ours. In asimilar way, all the above velocity dispersion values obtained fromintegrated light measurements are consistent with the velocitydispersion sigmap = 14.2 +/- 1.9 km/s obtained by Peterson etal. (1989) from the radial velocities of 27 stars within 20 sec of thecenter. Given the large statistical errors on the integrated lightmeasurements, there is no significant observational evidence that thecentral value of the velocity dispersion is much larger than about 15km/s. All observed values are consistent with the predictions fromvarious theoretical dynamical models of M15: sigmap of 0 =12-17 km/s from Illingworth & King (1977), sigma p of 0 =13-15 km/s from Phinney & Sigurdsson (1991) and Phinney (1993), andsigmap of 0 = 14 km/s from Grabhorn et al. (1992). Althoughit cannot be ruled out, the presence of a massive black hole or somenonthermal dynamics in the core of M15 is not required by the presentobservations.
| Metal enrichment in elliptical galaxies and globular clusters through the study of iron and H-Beta spectral indices
Chemical evolution of elliptical galaxies and globular clusters isaddressed through a combined study of the iron indices at 5270 and 5335A, and of the H-Beta line strength. The observational database of 74standard stars (both dwarfs and giants) referred to in a previous paper(Buzzoni et al. (1992)) complemented with the data of Faber et al.(1985) and Gorgas et al. (1993) allowed us to explore here Fe and H-Betaindex dependence on stellar temperature, gravity, and metallicity. Thederived fitting functions were then included into Buzzoni's (1989) codefor population synthesis in order to derive expected integrated indicesfor simple stellar populations and compare with observations. Partitionof metals in the current chemical mix of galaxies and globulars has beenconstrained supporting the claim that light alpha elements might beenhanced in the globular cluster metal-poor population. An alternativeconclusion resting on the standard framework with (alpha/Fe) = 0 wouldrequire a systematically larger age, about 18-20 Gyr. Iron and magnesiumin ellipticals are found in average solar but a systematic trend of(Mg/Fe) vs global metallicity does exist with iron more deficient withrespect to magnesium at high Z. We conclude that this effect mightindicate that Fe abundance per unit mass in the galaxies is constant(suggesting a constant rate per unit mass of SN I events) while lightmetals supplied by SNe II should have been more effectively enrichedwith increasing galactic total mass.
| High-resolution kinematical mapping of the core of the globular cluster M15=NGC7078
Using the ESO New Technology Telescope, we have obtained fivehigh-resolution integrated-light echelle spectra over the core of theglobular cluster M15=NGC7078. We used a 1"x8" slit, with a 1" offsetbetween each exposure in order to cover a total central area of 5"x8".By taking advantage of the spatial resolution along the slit, weextracted spectra at 120 different locations over apertures ~1" square.The Doppler velocity broadening of the cross-correlation functions(CCFs) of these integrated-light spectra is always <=17km/s, at alllocations in the 5"x8" area. Our measurements therefore provide noevidence for the velocity dispersion cusp observed by Peterson et al.(1989). These new observations confirm the predictions of our recentnumerical simulations (Dubath et al. 1994a): the CCFs of integratedlight spectra taken over such small apertures are mostly dominated bythe contribution of one or two bright stars, leading to unreliableestimates of the velocity dispersion. This bias can be reduced by takingthe average of all 120 CCFs, normalized in intensity, over the whole5"x8" central area. This gives equal weight to spatially independentdominant stars of different brightness. The mean CCF derived in this waygives a velocity dispersion σ_p_=11.7+/-2.6km/s. This value isindependently confirmed by comparing our observations with numericalsimulations. The individual radial velocities of the 14 best-resolved(spatially or spectroscopically) bright stars are also determined; theygive σ_p_=14.2+/-2.7km/s, a value consistent with the abovedetermination. Two of the brightest central stars, separated by 2.5",have radial-velocity values differing by 45.2km/s. These stars may bethe origin of previous reports in the literature of large rotation orstreaming motion across the centre of M15. Our study complements therecent work by Gebhardt et al. (1994), who measured the radialvelocities of 216 stars located within 1.5' of the cluster centre. From0.1' to 0.4,' their data suggest a constant velocity dispersion of aboutσ_p_=11km/s consistent with our result obtained inside 0.1.'
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | やぎ座 |
| Right ascension: | 21h24m09.60s |
| Declination: | -20°51'07.0" |
| Apparent magnitude: | 5.41 |
| Distance: | 69.881 parsecs |
| Proper motion RA: | -7.8 |
| Proper motion Dec: | -127.3 |
| B-T magnitude: | 6.869 |
| V-T magnitude: | 5.496 |
Catalogs and designations:
|
INHABITED SKY
