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The Michigan/MIKE Fiber System Survey of Stellar Radial Velocities in Dwarf Spheroidal Galaxies: Acquisition and Reduction of Data
We introduce a stellar velocity survey of dwarf spheroidal galaxies,undertaken using the Michigan/MIKE Fiber System (MMFS) at theMagellan/Clay 6.5 m telescope at Las Campanas Observatory. As of 2006November we have used MMFS to collect 6415 high-resolution(R=20,000-25,000) spectra from 5180 stars in four dwarf spheroidalgalaxies: Carina, Fornax, Sculptor, and Sextans. Spectra sample therange 5140-5180 Å, which includes the prominent magnesium tripletabsorption feature. We measure radial velocity (RV) to a medianprecision of 2.0 km s-1 for stars as faint as V~20.5. Fromthe spectra we also are able to measure the strength of iron andmagnesium absorption features using spectral indices that correlate witheffective temperature, surface gravity, and chemical abundance.Measurement of line strength allows us to identify interlopingforeground stars independently of velocity and to examine themetallicity distribution among dSph members. Here we present detaileddescriptions of MMFS, our target selection and spectroscopicobservations, the data reduction procedure, and error analysis. Wecompare our RV results to previously published measurements forindividual stars. In some cases we find evidence for a mild,velocity-dependent offset between the RVs that we measure using themagnesium triplet and previously published RV measurements derived fromthe infrared calcium triplet. In companion papers we will present thecomplete data sets and kinematic analyses of these new observations.This paper includes data obtained with the 6.5 m Magellan Telescopeslocated at Las Campanas Observatory, Chile.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Studies of binary star cluster candidates in the bar of the LMC. I. SL 353 and SL 349
We present a detailed study of the cluster pair SL 353 & SL 349.This candidate binary cluster is located at the northwestern rim of theLMC bar. Based on photometric data we find that both clusters are coevalwith an age of 550+/-100 Myr. We use the Ca II triplet in the spectra ofindividual red giants to derive radial velocities. Both components ofthe binary cluster candidate show very similar mean velocities(~274+/-10 km s-1 for SL 349 and ~279+/-4 km s-1for SL 353) while the field stars show lower velocities (~240+/-19 kms-1). These findings suggest a common origin of the twoclusters from the same GMC. In this sense the cluster pair mayconstitute a true binary cluster. We furthermore investigate the stellardensities in and around the star clusters and compare them withisopleths created from artificial, interacting as well asnon-interacting star clusters. Gravitational interaction leads to adistortion which can also be found in the observed pair. Based onobservations taken at the European Southern Observatory, La Silla,Chile.
| The shape and scale of Galactic rotation from Cepheid kinematics
A catalog of Cepheid variables is used to probe the kinematics of theGalactic disk. Radial velocities are measured for eight distant Cepheidstoward l = 300 deg; these new Cepheids provide a particularly goodconstraint on the distance to the Galactic center, R0. We model the diskwith both an axisymmetric rotation curve and one with a weak ellipticalcomponent, and find evidence for an ellipticity of 0.043 +/- 0.016 nearthe sun. Using these models, we derive R0 = 7.66 +/- 0.32 kpc andv(circ) = 237 +/- 12 km/s. The distance to the Galactic center agreeswell with recent determinations from the distribution of RR Lyraevariables and disfavors most models with large ellipticities at thesolar orbit.
| 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.
| 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.
| Observational data for the kinematics of the local universe. I - Radial velocity measurements
The study of the local velocity field requires the use of a very largesample to describe as accurately as possible some prominent features ofthe local kinematics. The problem of collecting a large sample is mademore difficult because of the Malmquist bias which plagues distancedeterminations. The present program aims at determining bias-freedistances for a complete sample in order to study the local velocityfield. The present paper gives 303 preliminary optical and radioredshifts measured for this program at ESO, OHP and NancayObservatories.
| Gamma velocities of 58 faint Milky Way Cepheids
Using new radial velocity measurements of 47 faint southern hemisphereGalactic Cepheids, together with additional velocity data from Metzgeret al. (1991), gamma velocities are found for 58 low galactic latitudeCepheids. The gamma velocity is determined by using the period of aCepheid to generate a 'typical' velocity curve, then fitting the curveto the velocity measurements using two free parameters, the gammavelocity, and the phase. The velocity curve is generated using a secondorder Fourier series with coefficients determined from the period. Forthe Cepheids with observations that sample the velocity curve over avariety of pulsation phases, gamma velocities are determined to betterthan 1.0 km/s. Good agreement between these gamma velocities andpreviously published values where they exist.
| Progress toward a multiobject radial-velocity spectrometer
It is shown that it is possible to obtain stellar radial velocities ofhigh accuracy using a fiber-fed echelle spectrograph with no crossdisperser. Although the resulting spectrum contains many overlappingorders, the radial-velocity information is still present. Velocities maybe obtained by cross correlation with reference data obtained with thesame instrument. The accuracy is a function of the signal-to-noiseratio, and ranges from + or - 4 km/s to + or - 1 km/s. Velocities areobtained with exposure times just sufficient to obtain the barest traceof a spectrum using the same spectrograph and CCD detector with a crossdisperser. Thus, it appears possible to obtain precision similar to thatobtained with an order separator, but with considerably bettersensitivity, due to a multiplexing gain. Moreover, the overlappingorders of the stellar spectrum only occupy a few rows of the CCD. Usinga multiple-fiber-feed device, many such spectra could be fit on the CCD.This leads to the expectation of obtaining many radial velocitiessimultaneously using a multiobject spectrometer now under constructionat Cerro Tololo.
| Radial velocities of southern stars obtained with the photoelectric scanner CORAVEL. II - Faint southern potential radial-velocity standards
Abstract image available at:http://adsabs.harvard.edu/abs/1984A&AS...57..275M
| Stellar groups, V. Luminosities, motions and masses of the late-type sub-giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1960MNRAS.120..430E&db_key=AST
| Fundamental data for southern stars (Second List)
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1959MNRAS.119..638E&db_key=AST
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | קנטאור |
| התרוממות ימנית: | 12h49m31.81s |
| סירוב: | -45°49'32.8" |
| גודל גלוי: | 8.296 |
| מרחק: | 255.102 פארסק |
| תנועה נכונה: | -49.3 |
| תנועה נכונה: | -38.1 |
| B-T magnitude: | 10.116 |
| V-T magnitude: | 8.447 |
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