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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
| Internal Kinematics of the Fornax Dwarf Spheroidal Galaxy
We present new radial velocity results for 176 stars in the Fornax dwarfspheroidal galaxy, of which at least 156 are probable Fornax members. Wecombine with previously published data to obtain a radial velocitysample with 206 stars, of which at least 176 are probable Fornaxmembers. We detect the hint of rotation about an axis near Fornax'smorphological minor axis, although the significance of the rotationsignal in the galactic rest frame is sensitive to the adopted value ofFornax's proper motion. Regardless, the observed stellar kinematics isdominated by random motions, and we do not find kinematic evidence oftidal disruption. The projected velocity dispersion profile of thebinned data set remains flat over the sampled region, which reaches amaximum angular radius of 65'. Single-component King models in whichmass follows light fail to reproduce the observed flatness of thevelocity dispersion profile. Two-component (luminous plus dark matter)models can reproduce the data, provided that the dark component extendssufficiently beyond the luminous component and the central dark matterdensity is of the same order as the central luminous density. Theserequirements suggest a more massive, darker Fornax than standardcore-fitting analyses have previously concluded, with M/LVover the sampled region reaching 10-40 times the M/LV of theluminous component. We also apply a nonparametric mass estimationtechnique, introduced in a companion paper. Although it is designed tooperate on data sets containing velocities for >1000 stars, theestimation yields preliminary results suggesting M/LV~15inside r<1.5 kpc.
| 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 search for binaries in the globular cluster NGC 3201
We present BV charge coupled devices (CCD) and Automated Plate Measuring(APM) photometry, accurate astrometry and 1859 radial velocities for1318 stars within approximately 36 min. of the Galactic globular clusterNGC 3201. The field and cluster populations separate unambiguously intwo distinct samples since the systemic radial velocity of NGC 3201 is494.2 km/sec. After removal of the 19 known NGC 3201 photometricvariables in our sample, we have a database of 930 radial velocities for420 member giants (276 of which have multiple velocity measurements)with which to identify spectroscopic binaries on the basis of radialvelocity variations. The mean time span of the observations is 1.7 yr,with coverage up to approximately 6 yr for our best-studied stars. MonteCarlo simulations of the observed velocity variations have providedupper limits to the cluster binary fraction (for binaries with 0.1 lessthan or equal to P less than or equal to 5 to 10 yr and mass ratios inthe range 0.1 to 1 of 0.06 to 0.10 (circular orbits) and 0.15 to 0.18(eccentric orbits). These results suggest an incidence of binarism forNGC 3201 consistent with the corresponding incidence among nearbysolar-type stars having similar periods and mass ratios (0.04 to 0.08)and that for a small sample of other globular clusters (0.05-0.12)studied by Hut et al. (1992).
| Dynamics of the young binary LMC cluster NGC 1850
BV CCD images and echelle spectra of 52 supergiants are used to examinethe age and internal dynamics of the young binary LMC cluster NGC 1850.A color-magnitude diagram was constructed and found to contain threedistinct populations of stars. Using star-subtracted, median filtered BVimages, attempts were made to determine ellipticity parameters, BVluminosity profiles were constructed to project radii greater than 40. Apower law model was applied to test for the presence of a tidal cutoffin the luminosity profile. Of the 52 stars with echelle spectra, asubset of 36 were used to study the cluster dynamics. A rotationalsignal in the radial velocities has been detected at the 93-percentconfidence level, implying a rotation axis at a position angle of 100+/- 40 deg. Values for the slope of the mass function were determinedusing mass luminosity relationships and different forms for the IMF. Thecurrent cluster age is similar to its central relaxation time.
| Spectroscopy of giants in LMC clusters. I - Velocities, abundances, and the age-metallicity relation
Velocities and equivalent widths are presented for a large sample of LMCclusters. The calcium abundance is found to be a sensitive abundanceindicator over a very wide range of (Fe/H) between 0.0 and -2.2. Theage-metallicity relation is constructed for the inner and outer parts ofthe LMC. This relationsip can be characterized by a simple one-zoneenrichment model. The abundances for the inner and outer clusters at anage of 2 Gyr are nearly identical, so that little radial abundancegradient is evident in the cluster system.
| The radial velocity, velocity dispersion, and mass-to-light ratio of the Sculptor dwarf galaxy
Radial velocities for 16 K giants in the Sculptor dwarf spheroidalgalaxy are presented. The velocities have been determined viacross-correlation techniques from spectra obtained at the calciuminfrared triplet. They have a single-observation accuracy of 4.7 km/s.The mean velocity of the Sculptor stars is +107.4±2.0 km/s, avalue that supports the adoption of a large mass for the Galaxy. Theone-dimensional velocity dispersion of this sample is 6.3 (+1.1, -1.3)km/s, a value which, when combined with a new estimate of the coreradius of the galaxy and the observed central surface brightness, yieldsa visual mass-to-light ratio of 6.0 in solar units. This value is morethan twice current estimates of global mass-to-light ratios of globularclusters, and thus, if interpreted literally, indicates that Sculptorcontains a substantial amount of additional mass not found in globularclusters.
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Osservazione e dati astrometrici
| Costellazione: | Fornace |
| Ascensione retta: | 03h42m09.16s |
| Declinazione: | -34°25'15.9" |
| Magnitudine apparente: | 8.968 |
| Distanza: | 751.88 parsec |
| Moto proprio RA: | -0.7 |
| Moto proprio Dec: | 1.6 |
| B-T magnitude: | 10.461 |
| V-T magnitude: | 9.092 |
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