Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Elemental Abundance Ratios in Stars of the Outer Galactic Disk. I. Open Clusters
We summarize radial velocity studies of selected stars in the old,distant clusters Berkeley 20, Berkeley 21, NGC 2141, Berkeley 29, andBerkeley 31. Cluster members are identified using optical and infraredcolor-magnitude diagrams, as well as radial velocities derived fromhigh-resolution echelle spectra. Three members of M67 were observedsimilarly, and those velocities compare extremely well with priormeasures. Mean cluster radial velocities are determined. We also employthe highest quality spectra to analyze the chemical compositions of allsix clusters for [Fe/H], as well as abundances of α-elements,iron-peak elements, and those synthesized in either the s-process or ther-process. In Be 21 our observed star is found to be rotating rapidlyand overabundant in lithium, the second Li-rich star found in thissparse cluster.We confirm the lack of correlation between abundance and age. For theouter disk, the abundance gradient for [Fe/H] deviates from the trenddefined near the solar neighborhood. Rather than declining withincreasing galactocentric distance, [Fe/H] appears to reach a``basement'' at [Fe/H]~-0.5 beyond RGC~10-12 kpc. Our radialabundance distribution for [Fe/H] is not inconsistent with the radialabundance discontinuity exhibited by Cepheids. We find enhanced [O/Fe],[α/Fe], and [Eu/Fe] in the outer disk, revealing a rapid starformation history. The outer disk also exhibits enhancements fors-process elements. We compare the open cluster compositions with thoseof the thin disk, thick disk, halo, bulge, and dwarf spheroidalgalaxies. None of these stellar populations perfectly matches theabundance ratios of the outer disk open clusters. Several key pointsarise from these comparisons: (1) [O/Fe] and [α/Fe] resemble thoseof the thick disk. (2) [Na/Fe] and [Al/Fe] are enhanced relative tothose of the thin disk. (3) [Ni/Fe] and [Mn/Fe] are in accord with thoseof the thin disk, while [Co/Fe] may be slightly enhanced. (4) Theneutron-capture elements indicate different ratios of s-process tor-process material, with no cluster showing a pure r-processdistribution. (5) An unusual pattern exists among the α-elements,with [/Fe] enhanced while [/Fe] is normal.Similar abundance ratios have been reported for Galactic bulge giantsand indicate a common but not necessarily shared nucleosynthetic historybetween the bulge and the outer disk. Enhanced ratios of [Al/Fe] and[Co/Fe] offer another possible similarity between the bulge and theouter disk.An intriguing but tentative conclusion is that the outer disk opencluster abundance ratios are consistent with the outer disk being formedvia a merger event or series of merger events. The basement in [Fe/H]and enhanced [α/Fe] suggest that the outer disk formed from areservoir of gas with a star formation history distinct from the solarneighborhood. That the open clusters may be associated with an accreteddwarf galaxy or galaxies is appealing, since the clusters are young andhave [α/Fe] ratios indicating a rapid star formation history.However, the high [α/Fe] ratios are unlike those seen in anycurrent dwarf galaxies at the same [Fe/H]. Therefore, the open clustersmay have formed as a result of star formation triggered by a mergerevent or series of mergers in the outer disk. The ages of the outer diskopen clusters would then be a measure of when the merger(s) occurred.However, Be 29 is a candidate merger member, while Be 31 is not. Oneproblem with the merger scenario is that open clusters with presumablyvery different origins have similar and unusual compositions.This paper makes use of observations obtained at the National OpticalAstronomy Observatory, which is operated by the Association ofUniversities for Research in Astronomy (AURA), Inc., under contract fromthe National Science Foundation. We also employ data products from theTwo Micron All Sky Survey, which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center,California Institute of Technology, funded by the National Aeronauticsand Space Administration and the National Science Foundation.
| The Evolution of Massive Stars. I. Red Supergiants in the Magellanic Clouds
We investigate the red supergiant (RSG) content of the SMC and LMC usingmultiobject spectroscopy on a sample of red stars previously identifiedby BVR CCD photometry. We obtained high-accuracy (<1 kms-1) radial velocities for 118 red stars seen toward the SMCand 167 red stars seen toward the LMC, confirming most of these (89% and95%, respectively) as red supergiants. Spectral types were alsodetermined for most of these RSGs. We find that the distribution ofspectral types is skewed toward earlier type at lower metallicities: theaverage (median) spectral type is K5-K7 I in the SMC, M1 I in the LMC,and M2 I in the Milky Way. Our examination of the Kurucz ATLAS9 modelatmospheres suggests that the effect that metallicity has on theappearance on the TiO lines is probably sufficient to account for thiseffect, and we argue that RSGs in the Magellanic Clouds are 100 K (LMC)and 300 K (SMC) cooler than Galactic stars of the same spectral types.The colors of the Kurucz models are not consistent with thisinterpretation for the SMC, although other models (e.g., Bessell et al.)show good agreement. A finer grid of higher resolution synthetic spectraappropriate to cool supergiants is needed to better determine theeffective temperature scale. We compare the distribution of RSGs in theH-R diagram to that of various stellar evolutionary models; we find thatnone of the models produce RSGs as cool and luminous as what is actuallyobserved. This result is much larger than any uncertainty in theeffective temperature scale. We note that, were we to simply adopt theuncorrected Galactic effective scale for RSGs and apply this to oursample, then the SMC's RSGs would be underluminous compared with theLMC's, contrary to what we expect from stellar evolution considerations.In all of our H-R diagrams, however, there is an elegant sequence ofdecreasing effective temperatures with increasing luminosities;explaining this will be an important test of future stellar evolutionarymodels. Finally, we compute the blue-to-red supergiant ratio in the SMCand LMC, finding that the values are indistinguishable (~15) for the twoClouds. We emphasize that ``observed'' B/R values must be carefullydetermined if a comparison with that predicted by stellar models is tobe meaningful. The nonrotation Geneva models overestimate the number ofblue to red supergiants for the SMC, but underestimate it for the LMC;however, given the inability to produce high-luminosity RSGs in themodels that match what is observed in the H-R diagram, such adisagreement is not surprising.
| The mass of the neutron star in Vela X-1 and tidally induced non-radial oscillations in GP Vel
We report new radial velocity observations of GP Vel / HD 77581, theoptical companion to the eclipsing X-ray pulsar Vela X-1. Using dataspanning more than two complete orbits of the system, we detect evidencefor tidally induced non-radial oscillations on the surface of GP Vel,apparent as peaks in the power spectrum of the residuals to the radialvelocity curve fit. By removing the effect of these oscillations (tofirst order) and binning the radial velocities, we have determined thesemi-amplitude of the radial velocity curve of GP Vel to beKo = 22.6 +/- 1.5 km s-1. Given the accuratelymeasured semi-amplitude of the pulsar's orbit, the mass ratio of thesystem is 0.081 +/- 0.005. We are able to set upper and lower limits onthe masses of the component stars as follows. Assuming GP Vel fills itsRoche lobe then the inclination angle of the system, i, is70.1deg +/- 2.6deg. In this case we obtain themasses of the two stars as Mx = 2.27 +/- 0.17 Msunfor the neutron star and Mo = 27.9 +/- 1.3 Msunfor GP Vel. Conversely, assuming the inclination angle isi=90deg, the ratio of the radius of GP Vel to the radius ofits Roche lobe is beta = 0.89 +/- 0.03 and the masses of the two starsare Mx = 1.88 +/- 0.13 Msun and Mo =23.1 +/- 0.2 Msun. A range of solutions between these twosets of limits is also possible, corresponding to other combinations ofi and beta . In addition, we note that if the zero phase of the radialvelocity curve is allowed as a free parameter, rather than constrainedby the X-ray ephemeris, a significantly improved fit is obtained with anamplitude of 21.2 +/- 0.7 km s-1 and a phase shift of 0.033+/- 0.007 in true anomaly. The apparent shift in the zero phase of theradial velocity curve may indicate the presence of an additional radialvelocity component at the orbital period. This may be anothermanifestation of the tidally induced non-radial oscillations andprovides an additional source of uncertainty in the determination of theorbital radial velocity amplitude.
| 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.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Spectroscopy of Giant Stars in the Pyxis Globular Cluster
The Pyxis globular cluster is a recently discovered globular clusterthat lies in the outer halo (Rgc~40 kpc) of the Milky Way.Pyxis lies along one of the proposed orbital planes of the LargeMagellanic Cloud (LMC), and it has been proposed to be a detached LMCglobular cluster captured by the Milky Way. We present the firstmeasurement of the radial velocity of the Pyxis globular cluster basedon spectra of six Pyxis giant stars. The mean heliocentric radialvelocity is ~36 km s-1, and the corresponding velocity ofPyxis with respect to a stationary observer at the position of the Sunis ~-191 km s-1. This radial velocity is a large enoughfraction of the cluster's expected total space velocity-assuming that itis bound to the Milky Way-that it allows strict limits to be placed onthe range of permissible transverse velocities that Pyxis could have inthe case that it still shares or nearly shares an orbital pole with theLMC. We can rule out that Pyxis is on a near circular orbit if it isMagellanic debris, but we cannot rule out an eccentric orbit associatedwith the LMC. We have calculated the range of allowed proper motions forthe Pyxis globular cluster that result in the cluster having an orbitalpole within 15° of the present orbital pole of the LMC and that areconsistent with our measured radial velocity, but verification of thetidal capture hypothesis must await proper motion measurement from theSpace Interferometry Mission or Hubble Space Telescope. A spectroscopicmetallicity estimate of [Fe/H]=-1.4+/-0.1 is determined for Pyxis fromseveral spectra of its brightest giant; this is consistent withphotometric determinations of the cluster metallicity from isochronefitting.
| 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.
| Chemical abundances in seven red giants of NGC 2360 and NGC 2447
Chemical abundances of about fifteen elements from oxygen to europiumare measured in seven red giants of the two open clusters NGC 2360 andNGC 2447. The effective temperatures of the giants are determinedspectroscopically by taking advantage of their known masses (~ 2Msolar in NGC 2360 and ~ 3 Msolar in NGC 2447) andbolometric magnitudes. The average iron abundances we obtain for the twoclusters are [Fe/H]=0.07 for NGC 2360 and [Fe/H]=0.03 for NGC 2447.Evolutionary stellar model calculations are performed in the mass range1 - 4 Msolar in order to analyze the surface Na and Oabundances predicted after the first dredge-up. The sodium abundanceshows a well defined correlation with stellar mass in the 2 - 3Msolar range. The agreement between our Na abundancedeterminations in NGC 2360 and our model predictions at 2Msolar is very good. In contrast, the overabundance in one ofthe three stars in NGC 2447 exceeds that predicted at 3Msolar by ~ 0.08 dex, which is significant compared to theobservational error bars. The effects of core overshooting, convectionprescription, metallicity and nuclear reaction rates on the Na surfacepredictions of our models are investigated. An oxygen deficiencyrelative to iron by 0.2 dex is measured in our stars, in disagreementwith our model predictions. Assuming that the Sun is 0.1-0.3 dexenriched in oxygen relative to neighbor stars could explain thediscrepancy. Based on observations collected at the European SouthernObservatory, La Silla, Chile (period 56) Table 3 is available only inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Properties of Hot White Dwarfs in Extreme-Ultraviolet/Soft X-Ray Surveys
Intermediate-dispersion spectroscopy (Δ~6 Å) of 38 ultrasoftX-ray sources (ROSAT PSPC/WFC and EUVE)-27 H-rich white dwarfs (DA), onemagnetic white dwarf (DAp), eight active galactic nuclei, a newcataclysmic variable, and an active late-type star-is presented.Atmospheric (Teff, log g) and stellar (age, mass) parametersof the DA white dwarfs are determined, for the first time in the case of12 objects. Adding the present sample to the EUV-selected sample ofprevious studies by Vennes et al., I define an enlarged population of141 hot white dwarfs and redetermine the DA white dwarf massdistribution taking into account improved mass measurements forultramassive white dwarfs. High-dispersion spectroscopy (Δ~1.0-1.4Å) of the Hα line core in a representative collection ofwhite dwarfs (the ultramassive DA GD 50, two hot DAs, and the low-massDA EUVE J0512-006) indicate low projected rotation velocityvrot sin i<=30-65 km s-1 and no perceptibleradial velocity variations in the low-mass white dwarf EUVE J0512-006.Questions on the origin and evolution of hot white dwarf stars areexamined in light of these results.
| Lithium in population I subgiants
We present a lithium survey for a sample of 91 Pop. I stars. JHKLphotometry was also obtained for 61 stars in the sample. Besides Liabundances, [Fe/H] values were derived. Thanks to Hipparcos parallaxes,we could infer absolute V magnitudes for our sample stars and were ableto place them on the color-magnitude diagram, which allowed us toconstrain their evolutionary status. Masses and ages were derived formost of the stars by comparison with evolutionary tracks. The sample wasoriginally selected so to include class IV stars later thanspectral-type F0, but, based on the location on the color-magnitudediagram, we found a posteriori that a fraction of the stars (about 20%)are either main sequence stars or evolved giants. As it is the case fordwarfs and giants, a large spread in lithium abundance is present amongthe subgiants in our sample. As expected, the average lithium decreasesas the stars evolve along the subgiant branch; however, there is not aone-to-one relationship between the position on the color-magnitudediagram and lithium abundance, and the observed dispersion is onlypartially explainable as due to a dispersion in mass, metallicity, andage. In particular, a dispersion in lithium is seen among slightlyevolved subgiants with masses close to solar but in the sameevolutionary stage as the G2 IV star beta Hyi. The comparison of thebeta Hyi-like sample with a sample of non evolved solar-like starsindeed suggests that beta Hyi has most likely evolved from a mainsequence Li-rich star, rather than from a Li-poor star (like the Sun)that has dredged-up previously stored lithium. Our sample includesseveral stars that have completed the first-dredge up lithium dilution,but that have not yet evolved to the evolutionary point whereextra-mixing in the giant phase is thought to occur. A large number ofthem have Li abundances considerably below the theoretical predictionsof first dredge-up dilution. We confirm that this is due to the factthat the progenitors of these stars are most likely stars that havedepleted lithium while on the main sequence; the fraction of post-dredgeup Li rich/poor stars, in fact, is consistent with the observeddistribution of Li abundances among stars that have just left the mainsequence. The signature of the second mixing (or RGB extra-mixing)episode is evident in the log n(Li) vs. B-V and log n(Li) vs. M_boldistributions of the stars in the sample; it seems however that theextra-mixing occurs at luminosities lower than predicted by the modelsof Charbonnel (1994). Finally, a few evolved giants are found thatshould have passed the second mixing episode, but that do not show signsof it. At least half of them are spectroscopic binaries. Based onobservations carried out at the European Southern Observatory, La Silla,Chile
| The Henize sample of S stars. I. The technetium dichotomy
This paper is the first one in a series investigating the properties ofthe S stars belonging to the Henize sample (205 S stars with delta<-25(deg) and R<10.5) in order to derive the respective properties(like galactic distribution and relative frequencies) of intrinsic (i.e.genuine asymptotic giant branch) S stars and extrinsic (i.e. postmass-transfer binary) S stars. High-resolution (R=30 000 to 60 000)spectra covering the range lambda lambda4230 -4270 Angstroms have beenobtained for 76 S stars, 8 M stars and 2 symbiotic stars. The lambda4262Angstroms and lambda4238 Angstroms blends involving a Tc I line wereanalysed separately and yield consistent conclusions regarding thepresence or absence of technetium. Only one `transition' case (Hen 140 =HD 120179, a star where only weak lines of technetium are detectable) isfound in our sample. A resolution greater than R =30 000 is clearlyrequired in order to derive unambiguous conclusions concerning thepresence or absence of technetium. The Tc/no Tc dichotomy will becorrelated with radial velocity and photometric data in a forthcomingpaper. Based on observations carried out at the European SouthernObservatory (ESO, La Silla, Chile)
| A study of the Chamaeleon star-forming region from the ROSAT all-sky survey. III. High resolution spectroscopic study
We present the results of a high-resolution spectroscopic study on some70 stars, discovered recently on the basis of the ROSAT all-sky surveyspread over a wide area in the Chamaeleon star forming region andclassified as new weak-line T Tauri stars. We refine the previousspectral type classification, based on low-resolution spectra, andcharacterize each star in the sample according to the Hα lineprofile. We use the strength of Li I 6708, compared to Pleiades stars ofthe same spectral type, as a youth discriminator in order to recognizebona-fide pre-main sequence stars. According to the adopted ``lithiumcriterion'', more than 50% of the stars in our sample are confirmed tobe truly young, PMS stars (most having age less than 5x 10(6) yr), whilethe remaining part seems mostly composed by active, young, foregroundmain-sequence stars (possibly Pleiades-like), which contaminate theoriginal sample. We confirm the existence of some very young stars farfrom the main Chamaeleon clouds, while we do not find clear evidence forthe presence of post-T Tauri stars in our sample. We find that 5 starsin the sample are spectroscopic binaries and 1 is a spectroscopic triplesystem. We derive radial and rotational velocities for all the stars insample and analyse their distributions for different spectral typeintervals. The radial velocity distribution shows a clear peak at about15 km s(-1) , which coincides with the radial velocity of stars and gasin the Cha I cloud. However, the velocity dispersion of the weak-line TTauri stars appears much broader and, possibly, a second peak is presentaround 16-18 km s(-1) . A clear segregation in radial velocity isobserved between the strong-lithium and the weak-lithium stars, with theformer showing radial velocities which, in most cases, fall in theinterval 12
| On the reflection effect in three sdOB binary stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.279.1380H&db_key=AST
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| 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.
| Lucifers, a photoelectric radial-velocity spectrometer
A spectrometer dedicated to the measurement of stellar radial velocitieshas been developed at the University of Canterbury and the Mt JohnUniversity Observatory. The spectrometer scans a spectrum from theObservatory's 1-meter McLellan reflecting telescope and fiber-fedechelle with an oscillating mask having 2447 rectangular slotsrepresenting absorption lines in the spectrum of the star Alpha CentauriA covered by the wavelength range 397 to 570 nm in orders 40 to 58 ofthe spectrograph and measures the light passing through the mask as afunction of mask position. A dedicated computer constructs across-correlation function to which a Gaussian distribution function isfitted. The difference between the radial velocities of a star and azero-velocity reference spectrum provided by a hollow-cathode ironemission lamp is calculated from the Gaussian parameters. The sources ofrandom error in the system are discussed and its magnitude for stars ofspectral types F0 to M3.5 is estimated. Systematic errors in the systemare also discussed.
| Evolved GK stars near the Sun. 2: The young disk population
From a sample of nearly 2000 GK giants a group of young disk stars withwell determined space motions has been selected. The zero point of theluminosity calibrations, both from the ultraviolet flux (modifiedStroemgren system) and that in the region of 4200 to 4900 A (DDOsystem), show a discontinuity of about a half magnitude at the border ofthe young disk and old disk domains. The population separation is basedon the space velocity components, which are also an age discriminant,with the population interface near 2 x 109 yr, based onmodels with convective overshoot at the core. This age corresponds togiant masses near 1.7 solar mass, near the critical mass separating theyoung stars that do not burn helium in degenerate cores from older starsthat do. Ten percent of both populations show CN anomalies in that thederived value of P(Fe/H) from CN (Cm) and fromFe(M1) differ by more than 0.1 dex and the weak and strong CNstars occur equally in the old disk but the weak CN stars predominate inthe young disk. Peculiar stars, where flux distortions affect theluminosity calibrations, are of the CH+(Ba II) and CH-(weak G band)variety and represent less than 1% of the stars in both populations. Theyoung disk giants are restricted to ages greater than about109 yr, because younger stars are bright giants orsupergiants (luminosity class 2 or 1), and younger than about 2 x109 yr, because the old disk-young disk boundary occurs near1.7 solar mass. The distribution of heavy element abundances, P(Fe/H),for young disk giants is both more limited in range (+/- 0.4 dex) and isskewed toward higher abundances, compared with the nearly normaldistribution for old disk giants. The distribution of (U,V) velocityvectors gives (U,V,W) and their dispersions = (+17.6 +/- 18.4, -14.8 +/-8.4, -6.9 +/- 13.0) and (+3.6 +/- 38.4, -20.7 +/- 27.5, -6.7 +/-17.3)km/s for young and old disk giants, respectively.
| Large and Kinematically Unbiased Samples of G- and K-Type Stars. III. Evolved Young Disk Stars in the Bright Star Sample
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989PASP..101...54E&db_key=AST
| Large and kinematically unbiased samples of G- and K-type stars. II - Observations of evolved stars in the Bright Star sample. III - Evolved young disk stars in the Bright Star sample
Four color and RI observations were obtained for a large sample ofG-type and K-type stars in the Bright Star Catalogue. Data are firstpresented for 110 evolved stars. Photometry of evolved young diskpopulation stars have then been calibrated for luminosity, reddening,and metallicity on the basis of results for members of the Hyades andSirius superclusters. New DDO results are given for 120 stars.
| The stellar dynamics of NGC 1399
The dynamical properties of NGC 1399 as revealed through new CCD surfacephotometry and measurements of the velocity dispersion profile out toalmost 6 kpc are considered. The data reveal no unusual features in thesurface brightness profile of this galaxy, but the velocity dispersionprofile is quite striking. It is approximately constant through theregion 10-86 arcsec from the core but within 10 arcsec increasessignificantly from about 200 km/s to a central value of 365 km/s.Alternative interpretations of the velocity dispersion data involvingeither anisotropic stellar orbits or a black hole are considered. It isconcluded that a black hole in NGC 1399 is unlikely and that mildanisotropy in the stellar distribution is adequate to explain the data.
| Radial velocities in three fields along the southern galactic equator
A list of radial velocities for 764 stars is given for three fields inthe Vela-Carina region of the galaxy. They were obtained from GPO-platestaken at La Silla and reduced following Fehrenbach's method.Slit-spectra were collected with the 152 cm-spectrographic telescope atLa Silla, to derive an accurate radial velocity for a sufficient numberof calibration stars: out of the 29 stars, 26 had no formerly publishedvalue. The global motions of 10 to 14 km/s can be considered as normalon the basis of galactic rotation. Some stars, however, show highvelocities, and are therefore marked with one or two asterisks in thetable.
| Radial velocities of bright southern stars. VI - Standard and reference stars 1983-1986
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...68..347A&db_key=AST
| Radial velocities of CaII emission stars - Photographic data
Photographically determined radial velocities are given for eighteenstars selected from lists of G, K and M stars with strong CaII emissionreversals. The results of observations of radial velocity standards arealso given.
| About the stability of the spectrograph of the 1-m Yale telescope at Cerro Tololo.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1986RMxAA..13....3L&db_key=AST
| An analysis of the radial-velocity performance of the image-tube spectrograph on the CTIO 1-meter telescope
An analysis of the radial-velocity performance of the 120 A/mmconfiguration of the image-tube spectrograph on the CTIO/Yale 1-metertelescope is presented. The instrument is found to be stable within agiven run but to be susceptible to small changes from run to run. Theremay be systematic changes in velocity residual with declination; noneare found with zenith angle or hour angle. A typical precision of plusor minus 10 km/sec for a single spectrum of a Population I star isachieved for the spectrograph configuration. Rest wavelengths derivedfor F0-K4 Population I stars observed with this spectrograph/image-tubeconfiguration are presented. A table of radial velocities and residualsfor IAU radial-velocity standard stars, as well as some other brightstars, is also presented.
| Systematic Errors in Radial Velocities Measured on Image Tube Spectra from the CTIO 1-METER Telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1984RMxAA...9..165B&db_key=AST
| The radial velocities of 116 southern red stars
Using a photoelectric speedometer based on the radial velocityspectrometer of Griffin (1967), radial velocities of 116 southern redstars, many of them semi-regular variables, were measured. Theinstrument was placed at the Newtonian focus of the 130-inch (4.2-m)camera of the Coude spectrograph of the Mount Stromlo 74-inch (1.88-m)reflector. The stellar spectrum was focused on a mask 50 mm in length,designed to match the spectrum of the M-giant Beta Pegasi. The inversedispersion was 2.5 angstroms per millimeter in the second order. Thewavelength range used (5338-5449 angstroms) was chosen because it isbetween two TiO bands and so suffers less blanketing in M stars. Resultsare tabulated and compared with standard values.
| Observations of Standard Velocity Stars
Not Available
| Standard Velocity Stars
Not Available
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Vele |
| Ascensione retta: | 09h16m57.20s |
| Declinazione: | -39°24'05.0" |
| Magnitudine apparente: | 5.33 |
| Distanza: | 108.932 parsec |
| Moto proprio RA: | -30.5 |
| Moto proprio Dec: | -35.3 |
| B-T magnitude: | 6.808 |
| V-T magnitude: | 5.434 |
Cataloghi e designazioni:
|
