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Ursa Major: A Missing Low-Mass CDM Halo?
The recently discovered Ursa Major dwarf spheroidal (dSph) galaxycandidate is about 5-8 times less luminous than the faintest previouslyknown dSphs, And IX, Draco, and Ursa Minor. In this Letter, we presentvelocity measurements of seven color-magnitude-selected Ursa Majorcandidate stars. Two of them are apparent nonmembers based onmetallicity and velocity, and the remaining five stars yield a systemicheliocentric velocity of v¯=-52.45+/-4.27 km s-1 and acentral line-of-sight velocity dispersion of1/2=9.3+11.7-1.2km s-1, with 95% confidence that1/2>6.5 km s-1. Assumingthat UMa is in dynamical equilibrium, it is clearly darkmatter-dominated and cannot be a purely stellar system like a globularcluster. It has an inferred central mass-to-light ratio of M/L~500Msolar/Lsolar and, based on our studies of otherdSphs, may possess a much larger total mass-to-light ratio. UMa isunexpectedly massive for its low luminosity-indeed, UMa appears to bethe most dark matter-dominated galaxy yet discovered. The presence of somuch dark matter in UMa immediately suggests that it may be a member ofthe missing population of low-mass galaxies predicted by the cold darkmatter (CDM) paradigm. Given the weak correlation between dSph mass andluminosity, it is entirely likely that a population of dark dwarfssurrounds our Galaxy.
| 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.
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| The Dynamics of A2125
We present 371 galaxy velocities in the field of the very rich clusterA2125 (z~0.25). These were determined using optical spectroscopycollected over several years from both the WIYN 3.5 m telescope and NOAOMayall 4 m telescope. Prior studies at a variety of wavelengths (radio,optical, and X-ray) have indicated that A2125 is a likelycluster-cluster merger, a scenario that we are able to test using ourlarge velocity database. We identified 224 cluster galaxies, which weresubjected to a broad range of statistical tests using both positionaland velocity information to evaluate the cluster dynamics andsubstructure. The tests confirmed the presence of substructures withinthe A2125 system at high significance, demonstrating that A2125 is acomplex dynamical system. Comparison of the test results with existingsimulations strengthens the merger hypothesis and provides clues aboutthe merger geometry and stage. The merger model for the system canreconcile A2125's low X-ray temperature and luminosity with itsapparently high richness and might also explain A2125's high fraction ofactive galaxies identified in prior radio and optical studies.
| Rotationally Supported Virgo Cluster Dwarf Elliptical Galaxies: Stripped Dwarf Irregular Galaxies?
New observations of 16 dwarf elliptical galaxies (dEs) in the VirgoCluster indicate that at least seven dEs have significant velocitygradients along their optical major axis, with typical rotationamplitudes of 20-30 km s-1. Of the remaining nine galaxies inthis sample, six have velocity gradients of less than 20 kms-1 kpc-1, while the other three observations hadtoo low a signal-to-noise ratio to determine an accurate velocitygradient. Typical velocity dispersions for these galaxies are ~44+/-5 kms-1, indicating that rotation can be a significant componentof the stellar dynamics of Virgo dEs. When corrected for the limitedspatial extent of the spectral data, the rotation amplitudes of therotating dEs are comparable to those of similar-brightness dwarfirregular galaxies (dIs). Evidence of a relationship between therotation amplitude and galaxy luminosity is found and, in fact, agreeswell with the Tully-Fisher relation. The similarity in the scalingrelations of dIs and dEs implies that it is unlikely that dEs evolvefrom significantly more luminous galaxies. These observations reaffirmthe possibility that some cluster dEs may be formed when the neutralgaseous medium is stripped from dIs in the cluster environment. Wehypothesize that several different mechanisms are involved in thecreation of the overall population of dEs and that stripping ofinfalling dIs may be the dominant process in the creation of dEs inclusters like Virgo.
| The Fundamental Plane at z=1.27: First Calibration of the Mass Scale of Red Galaxies at Redshifts z>1
We present results on the fundamental plane of early-type galaxies inthe cluster RDCS J0848+4453 at z=1.27. Internal velocity dispersions ofthree K-selected early-type galaxies are determined from deep Keckspectra, using absorption lines in the rest-frame wavelength range3400-4000 Å. Structural parameters are determined from HubbleSpace Telescope NICMOS images. The galaxies show substantial offsetsfrom the fundamental plane of the nearby Coma Cluster, as expected frompassive evolution of their stellar populations. The offsets from thefundamental plane can be expressed as offsets in mass-to-light (M/L)ratio. The M/L ratios of the two most massive galaxies are consistentwith an extrapolation of results obtained for clusters at0.023 and R-K>5, and ourresults show that it is hazardous to use simple models for convertingluminosity to mass for these objects. The work presented here, andprevious mass measurements at lower redshift, can be considered firststeps to empirically disentangle luminosity and mass evolution at thehigh-mass end of the galaxy population, lifting an important degeneracyin the interpretation of evolution of the luminosity function.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the California Institute of Technology and theUniversity of California.
| The early-type galaxy population in Abell 2218
We present high signal-to-noise, moderate-resolution spectroscopy of 48early-type members of the rich cluster Abell 2218 at z=0.18, taken withthe LDSS2 spectrograph on the 4.2-m William Herschel Telescope. Thissample both is larger and spans a wider galaxy luminosity range, down toMB*+1, than previous studies. In addition to the relatively large sizeof the sample, we have detailed morphological information from archivalHubble Space Telescope imaging for 20 of the galaxies. We combine themorphological, photometric, kinematic and line-strength information tocompare A2218 with similar samples drawn from local clusters and toidentify evolutionary changes between the samples which have occurredover the last ~3Gyr. The overall picture is one of little or noevolution in nearly all of the galaxy parameters. Zero-point offsets inthe Faber-Jackson, Mgb-σ and Fundamental Planerelations are all consistent with passively evolving stellarpopulations. The slopes of these relations have not changedsignificantly in the 3Gyr between A2218 and today. We do however find asignificant spread in the estimated luminosity-weighted ages of thestellar populations in the galaxies, based on line diagnostic diagrams.This age spread is seen in both the discy early-type galaxies (S0) andalso the ellipticals. We observe both ellipticals with a strongcontribution from a young stellar population and lenticulars dominatedby old stellar populations. On average, we find no evidence forsystematic differences between the populations of ellipticals andlenticulars. In both cases there appears to be little evidence fordifferences between the stellar populations of the two samples. Thispoints to a common formation epoch for the bulk of the stars in most ofthe early-type galaxies in A2218. This result can be reconciled with theclaims of rapid morphological evolution in distant clusters if thesuggested transformation from spirals to lenticulars does not involvesignificant new star formation.
| On the Accuracy of GAIA Radial Velocities
We have obtained 782 real spectra and used them as inputs for 6700automatic cross-correlation runs to investigate the GAIA potential interms of radial velocity accuracy. We have explored the dispersions0.25, 0.5, 1 and 2 Å/pix over the 8490--8740 Å GAIA range.We have investigated late-F to early-M stars (constituting the vastmajority of GAIA targets), slowly rotating ( = 4 km/s), of solar metallicity (<[Fe/H]> = --0.07) and notbinary. The results are accurately described by the simple law: {logsigma = 0.6 (log S/N)2 -- 2.4 log S/N + 1.75 log D + 3, wheresigma is the cross-correlation standard error (in km/s) and D is thespectral dispersion (in Å/pix). The spectral dispersion has turnedout to be the dominant factor, with S/N being less important and thespectral mis-match being a weak player at the lowest S/N. Our resultsshow that mission-averaged radial velocities of faint GAIA targets (V ~15 mag) can match the ~ 0.5 km/s accuracy of tangential motions,provided the observations are performed at a dispersion not less than0.5 Å/pix.
| Ages and metallicities of globular clusters in NGC 4472
We have derived ages and metallicities from co-added spectra of 131globular clusters associated with the giant elliptical galaxy NGC 4472.Based upon a calibration with Galactic globular clusters, we find thatour sample of globular clusters in NGC 4472 span a metallicity range ofapproximately -1.6<=[Fe/H]<=0dex. There is evidence of a radialmetallicity gradient in the globular cluster system which is steeperthan that seen in the underlying starlight. Determination of theabsolute ages of the globular clusters is uncertain, but formally, themetal-poor population of globular clusters has an age of 14.5+/-4Gyr andthe metal-rich population is 13.8+/-6Gyr old. Monte Carlo simulationsindicate that the globular cluster populations present in these data areolder than 6Gyr at the 95per cent confidence level. We find that withinthe uncertainties, the globular clusters are old and coeval, implyingthat the bimodality seen in the broadband colours primarily reflectsmetallicity and not age differences.
| Circumnuclear structure and kinematics in the active galaxy NGC 6951
A study is presented of the central structure and kinematics of thegalaxy NGC 6951, by means of broad band B{\arcminIJK} images and highresolution high dispersion longslit spectroscopy, together with archivalHST WFPC2 V and NICMOS2 J and H images. We find that there is littleongoing star formation inside the bar dominated region of the galaxy,except for the circumnuclear ring at 5 arcsec radius. There is someevidence that this star formation occurs in two modes, in bursts andcontinuously, along the ring and inwards, towards the nucleus. Theequivalent width of the Ca Ii triplet absorption lines show that, in themetal rich central region, the continuum is dominated by a population ofred supergiants, while red giants dominate outside. The gaseouskinematics along three slit position angles, and the comparison with thestellar kinematics, suggest the existence of a hierarchy of disks withindisks, whose dynamics are decoupled at the two inner Linblad resonances(ILR), that we find to be located at 180 pc and at 1100 pc. This issupported by the structure seen in the high resolution HST images. Thenucleus is spatially resolved in the emission line ratio [N Ii]/Hα, and in the FWHM of the emission lines, within a radius of1.5{\arcsec}, just inside the innermost ILR. Outside the iILR, thestellar CaT velocity profile is resolved into two different components,associated with the bar and the disk. Several results indicate that thisis a dynamically old system: the little ongoing star formation insidethe bar dominated part of the galaxy, the very large relative amount ofmolecular to total mass within the inner 6 arcsec radius, ~ 25%, and thegeometry of the circumnuclear ring that leads the stellar bar at aposition angle greater than 90°. It is thus possible that a nuclearbar has existed in NGC 6951 that drove the gas towards the nucleus, asin the bars within bars scenario, but that this bar has alreadydissolved by the gas accumulated within the circumnuclear region. Wediscuss the possibility that the kinematical component inside the iILRcould be due to a nuclear outflow produced by the combined effects of SNand SN remnants, or to a nuclear disk, as in the disk within diskscenario that we propose for the fueling of the AGN in NGC 6951. Basedon observations made with the 4.2m William Herschel Telescope operatedby the Isaac Newton Group, and the 2.6m Nordic Optical Telescopeoperated jointly by Denmark, Finland, Iceland, Norway, and Sweden, onthe island of La Palma in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofísica de Canarias. Also basedon observations made with the NASA/ESA Hubble Space Telescope, obtainedfrom the data archive at the ESA Space Telescope European CoordinatingFacility.
| Fundamental plane distances to early-type field galaxies in the South Equatorial Strip. I. The spectroscopic data
Radial velocities and central velocity dispersions are derived for 238E/S0 galaxies from medium-resolution spectroscopy. New spectroscopicdata have been obtained as part of a study of the Fundamental Planedistances and peculiar motions of early-type galaxies in three selecteddirections of the South Equatorial Strip, undertaken in order toinvestigate the reality of large-scale streaming motion; results of thisstudy have been reported in Müller et al. (1998). The new APM SouthEquatorial Strip Catalog (-17fdg 5 < delta < +2fdg 5) was used toselect the sample of field galaxies in three directions: (1) 15h10 -16h10; (2) 20h30 - 21h50; (3) 00h10 - 01h30. The spectra obtained have amedian S/N per Å of 23, an instrumental resolution (FWHM) of ~ 4Å, and the spectrograph resolution (dispersion) is ~ 100 kms-1. The Fourier cross-correlation method was used to derivethe radial velocities and velocity dispersions. The velocity dispersionshave been corrected for the size of the aperture and for the galaxyeffective radius. Comparisons of the derived radial velocities with datafrom the literature show that our values are accurate to 40 kms-1. A comparison with results from Jo rgensen et al. (1995)shows that the derived central velocity dispersion have an rms scatterof 0.036 in log sigma . There is no offset relative to the velocitydispersions of Davies et al. (1987).
| Optical spectroscopy of X-ray sources in the old open cluster M 67
We have obtained optical spectra of seven stars in the old galacticcluster M 67 that are unusual sources of X-rays, andinvestigate whether the X-ray emission is due to magnetic activity or tomass transfer. The two binaries below the giant branch S 1063 and S1113, the giant with the white dwarf companion S 1040 and the eccentricbinary on the subgiant branch S 1242 show magnetic activity in the formof Ca Ii H&K emission and Hα emission, suggesting that theirX-rays are coronal. The reason for the enhanced activity level in S 1040is not clear. The two wide, eccentric binaries S 1072 and S 1237 and theblue straggler S 1082 do not show evidence for Ca Ii H&K emission. Asecond spectral component is found in the spectrum of S 1082, mostclearly in the variable Hα absorption profile. We interpret thisas a signature of the proposed hot subluminous companion. Based onobservations made with the William Herschel Telescope operated on theisland of La Palma by the Isaac Newton Group in the Spanish Observatoriodel Roque de los Muchachos of the Instituto de Astrofisica de Canarias
| The 3D structure of the Virgo cluster from H-band Fundamental Plane and Tully-Fisher distance determinations
We undertook a surface photometry survey of 200 galaxies in the Virgocluster (complete to B<14.0 mag) carried out in the near-infrared(NIR) H band. Combining velocity dispersion measurements from theliterature with new spectroscopic data for 11 galaxies, we derivedistances of 59 early-type galaxies using the Fundamental Plane (FP)method. The distances of another 75 late-type galaxies are determinedusing the Tully-Fisher (TF) method. For this purpose we use the maximumrotational velocity, as derived from HI spectra from the literature,complemented with new Hα rotation curves of eight highlyHI-deficient galaxies. The zero-points of the FP and TF templaterelations are calibrated assuming the distance modulus of Virgomu_0=31.0, as determined with the Cepheids method. Using these 134distance determinations (with individual uncertainties of 0.35 mag (TF)and 0.45 mag (FP)) we find that the distance of cluster A, associatedwith M87, is mu_0=30.84 +/- 0.06. Cluster B, offset to the south, isfound at mu_0=31.84 +/- 0.10. This subcluster is falling on to A atabout 750 km s^-1. Clouds W and M are at twice the distance of A.Galaxies on the north-west and south-east of the main cluster A belongto two clouds composed almost exclusively of spiral galaxies withdistances consistent with A, but with significantly different velocitydistributions, suggesting that they are falling on to cluster A atapproximately 770 km s^-1 from the far side and at 200 km s^-1 from thenear side respectively. The mass of Virgo inferred from the peculiarmotions induced on its vicinity is consistent with the virialexpectation.
| Velocity Dispersion of the Gravitational Lens 0957+561
The lens system 0957+561 is the first gravitational lens system to bediscovered and the first for which a time delay was measured. Becausethe system is unusually rich in observables such as image positions,fluxes, VLBI structure, and polarization it has been modeled quiteextensively. However, since it resides in a cluster providingsubstantial convergence, the velocity dispersion of the lensing galaxyis an important component to models. We have measured this dispersion tobe 288+/-9 km s^-1 (1 sigma), which implies a Hubble constant of 72+/-7km s^-1 Mpc^-1 (1 sigma) according to the preferred fine guidancesensors model of Grogin and Narayan and 70+/-7 km s^-1 Mpc^-1 (1 sigma)using the softened power-law sphere model. The unknown velocitydispersion anisotropy of the central galaxy produces an additionaluncertainty of perhaps 15% or more. We see no variation in dispersionwith position to a radius of +/-3". In addition to a galaxy from thebackground cluster at z=0.5, our slit serendipitously picked up a galaxyat z=0.448 and two galaxies that may be part of a background cluster ata redshift of z=0.91.
| The Starburst-Active Galactic Nucleus Connection in Active Galaxies: The MassiveNuclear Star-Forming Disk in NGC 4303
Two-dimensional spectroscopy of the low-redshift active galaxy NGC 4303obtained with the Two-Dimensional Fiber ISIS System is presented. Theionization structure and velocity field of the nuclear region of thisgalaxy, where a compact UV-bright spiral structure connected with theUV-bright core has been detected with the Hubble Space Telescope (HST;Colina et al. 1997a), are investigated in detail. The ionized gas showsa structure similar to that observed in the high spatial resolution HSTUV-continuum image. The Hβ and Hα emission is dominated bythe nuclear star-forming regions, while the core of the galaxy is thebrightest region in the [O III] lambda5007 and [N II] lambda6584emission lines. The optical emission line ratios of the nuclearstar-forming regions are characteristic of young (ages 2-3 Myr)star-forming regions, while the core of the galaxy shows theemission-line ratios of a low-luminosity AGN in between an [O I]-weakLINER and a low-excitation Seyfert 2. The nature of the ionizing sourcelocated at the core of the galaxy is still unsolved. Its luminosity andoptical emission line ratios are compatible with the presence of a young(~3.5 Myr) massive (~8x10^4 M_solar) cluster of stars, but are alsoconsistent with the existence of a power-law nonthermal ionizing source.Whatever the nature of this ionizing source, the nuclear star-formingspiral dominates the ionizing radiation, contributing about 90% of thetotal ionizing flux. The velocity field of the ionized gas, as measuredby the Hβ emission line, is consistent with that of a massiverotating disk characterized by a radius of 300 pc, a rotation velocityof 85 km s^-1, an inclination of 45 deg with respect to the line ofsight, and a kinematic major axis oriented along P.A. 130 deg. Theinferred dynamical mass inside a radius of 300 pc is 5.0x10^8 M_solar.The mass and size of this nuclear rotating disk is similar to thoserecently detected in ultraluminous infrared galaxies like Mrk 231 andArp 220. The observed line profiles of the high-excitation [OIII]-emitting gas show the presence of two kinematically distinctgaseous components. The main component follows the velocity pattern ofthe massive rotating disk. The secondary component has an amplitude of+/-350 km s^-1, and a minor axis oriented, in projection, almostperpendicular to the minor axis of the low-ionization gas. This second[OIII] velocity component could represent gas located in a nuclearionizing cone, i.e., gas flowing outward outside the plane of thelow-excitation gas disk, and being ionized by the UV-bright sourcelocated at the core of the galaxy. The proximity of NGC 4303 togetherwith the detection of (1) an AGN-like nucleus, (2) a compact nuclearstar-forming spiral structure connected to the nucleus, (3) a massiverotating nuclear disk, and (4) radially flowing high-excitation gasmakes this galaxy an ideal candidate for the study of the fueling ofactive galaxies and the starburst-AGN connection.
| Spectroscopy of Globular Clusters in NGC 4472
Optical multislit spectra have been obtained for 47 globular clusterssurrounding the brightest Virgo elliptical galaxy, NGC 4472 (M49).Including data from the literature, we analyze velocities for a totalsample of 57 clusters and present the first tentative evidence forkinematic differences between the red and blue cluster populations thatmake up the bimodal color distribution of this galaxy. The redderclusters are more centrally concentrated and have a velocity dispersionof 240 km s^-1, compared with 320 km s^-1 for the blue clusters. Theorigin of this difference appears to be a larger component of systematicrotation in the blue cluster system. The larger rotation in the moreextended blue cluster system is indicative of efficient angular momentumtransport, as provided by galaxy mergers. Masses estimated from theglobular cluster velocities are consistent with the mass distributionestimated from X-ray data and indicate that the M/L_B rises to 50(M/L)_ȯ at 2.5R_e.
| Redshifts of the gravitational lenses B1422+231 and PG 1115+080
B1422+231 and PG 1115+080 are gravitational lens systems that producequadruple QSO images. In each, there is real promise that time delayscan constrain the Hubble constant, and both belong to systems that canplay an important role in modeling the lens potential. This articlereports redshifts for the lensing galaxies and three neighboringgalaxies in each of the two systems. B1422+231 comprises a group at z =0.339 with a dispersion of 733 km/s, and PG 1115+080 comprises a groupat z = 0.311 with a dispersion of 326 km/s. One of the neighboringgalaxies in the B1422+231 system turned out to be an emission-linegalaxy at z = 0.536, suggesting that QSO light passing through B1422+231may have been subjected to lensing by a cluster at this more distantredshift. The velocity dispersion of the lensing galaxy in PG 1115+080is determined to be 281 +/- 25 km/s, which is surprisingly large giventhe image splittings of 1.2 arcsec in that system.
| The Norris Survey of the Corona Borealis Supercluster. I. Observations and Catalog Construction
We have conducted a redshift survey of a 6 deg x 6 deg region in thecore of the Corona Borealis Supercluster using the 176 fiber NorrisSpectrograph on the Hale 5 m telescope. The input catalog from which weselected objects is based on machine scans of Schmidt plates andconsists of over 5 x 105 objects. As it was impractical for us to obtainspectroscopy of such an enormous number of objects, we chose to observe36 20' diameter fields arranged in a 6 x 6 grid across the core of thesupercluster. We have completed observations of 23 of these fields, aswell as an additional nine fields that were closely spaced along theridge of galaxies between Abell 2061 and Abell 2067. We have measuredredshifts for 1491 extragalactic objects, 420 with ~8 A resolution andthe remainder with ~4 A resolution. Our newly measured redshifts wereaugmented with 163 redshifts from the literature, yielding 1654redshifts for the entire survey. The faintest galaxies in the surveyhave magnitudes of g ~ 23 mag, and the most distant galaxies haveredshifts of z ~ 0.7. This survey will be used to explore the dynamicsof the Corona Borealis Supercluster and, since 1060 of the galaxies aremore distant than the Corona Borealis Supercluster, to study large-scalestructure and galaxy evolution to z ~ 0.5. In this paper, we describethe selection of targets, the multifiber spectroscopy, and the datareduction. We also present the redshift catalog and an analysis ofpossible selection biases in apparent magnitude, surface brightness,color, and angular separation of pairs on the sky.
| An Estimate of H 0 from Keck Spectroscopy of the Gravitational Lens System 0957+561
We present long-slit LRIS/Keck spectroscopic observations of thegravitational lens system 0957+561. Averaged over all of our data, therest-frame velocity dispersion sigma v of the central lens galaxy G1 issigma v = 279 +/- 12 km s-1. However, there appears to be a significantdecrease in sigma v as a function of distance from the center of G1 thatis not typical of the brightest cluster galaxies. Within 0."2 of thecenter of G1, we find the average sigma v = 316 +/- 14 km s-1, whereasfor positions greater than 0."2 from the center of G1, we find theaverage sigma v = 266 +/- 12 km s-1. A plausible explanation is that G1contains a central massive dark object of mass MMDO ~ 4 x 109h^{-1}100 Mȯ (h100 = H0/100 km s-1 Mpc-1), whichcontributes to the central velocity dispersion, and that the outer valueof sigma v is the appropriate measure of the depth of the potential wellof G1. The determination of a luminosity-weighted estimate of sigma v isessential for a determination of H0 from Q0957+561; our accuratemeasurements remove one of the chief uncertainties in the assumed formof the mass distribution of the lens. Thus, with the recent apparentreduction in the uncertainty in the measurement of the time delay forthe images A and B of Q0957+561, Delta tau BA = 417 +/- 3 days (Kundicet al.), we obtain an estimate for the Hubble constant: H0 = 62 +/- 7 kms-1 Mpc-1. If for some reason the trend of sigma v with slit position isspurious and we should use the dispersion averaged along the slit, thenthe estimate of H0 increases to 67 +/- 8 km s-1 Mpc-1. These standarderrors, however, do not include any contribution from any errors in theassumed form of the mass distribution of the lens. In particular, weused the mass model described by Falco, Gorenstein, & Shapiro, asupdated by Grogin & Narayan. The reduced chi 2 of model fits to theavailable position and magnification data for this system is relativelyhigh (~4), indicating that the estimate of H0 may have a significantcontribution from model errors. Further observations, discussed herein,should allow such errors to be estimated reliably.
| 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.
| Radial velocities of 26 northern Milky Way Cepheids
Spectra taken with the Palomar 60 inch echelle spectrograph are used toobtain 231 radial velocity measurements of 26 northern hemisphere MilkyWay Cepheids with latitude between 15 and 140 deg and b below 5 deg. Thetypical accuracy of the Cepheid velocities is 0.8 km/s. Radialvelocities of standard stars with accuracies of 0.6 km/s are alsoreported, and zero points determined from several systems are compared.The adopted zero point agrees with those of several other systems to +or - 0.1 km/s.
| Spectroscopy of V471 Tau. I - Review of basic properties
Spectroscopic observations of the eclipsing binary V471 Tau are reportedand analyzed. Data obtained mainly in the red band at Mt. WilsonObservatory and KPNO during the period 1975-1983 are compiled inextensive tables and graphs, and the radial velocity of the K dwarfcomponent is determined using a Griffin-mask technique. Resultsdiscussed include: (1) distance 44 + or - 6 pc, (consistent withmembership in the Hyades), (2) apparent period variation consistent witha third component, (3) emissionlike features affecting theradial-velocity determination, (4) transient features consistent withthe presence of flares, and (5) phase-coherent variation in H-alpha(attributed to the action of the white-dwarf Lyman continuum emission onthe K dwarf).
| 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.
| An interstellar contribution of NA I D from the arm of M 51 toward the nucleus of NGC 5195
The paper reports on evidence for interstellar absorption due to theforeground spiral arm of NGC 5194 (M 51) in the spectrum of the nucleusof NGC 5195. The presence of such absorption was hinted at by Spinrad(1973) but not confirmed. The Na I D lines in the spectrum areanomalously strong and might be accounted for by interstellar dust inthe arm projected against the nucleus of NGC 5195.
| Velocity measurements in the Coma filament of galaxies
58 new velocity measurements of galaxies located in the Coma filamentcarried out with the 2.5-m Issac Newton telescope at La Palma arepresented. These optical observations complete a sample of 21-cm lineobservations in the same region up to the 15.0th magnitude.
| Standard Velocity Stars
Not Available
| C1 - A white-dwarf-red-dwarf spectroscopic binary
Emission lines in the spectrum of the DA white dwarf star C1 indicatedthe existence of an unresolved companion, whose spectral type wasdetermined to be approximately dM2. A radial-velocity curve for eachstar was obtained by observing the H-alpha emission line of itscompanion, and by considering the average difference between measuredand standard velocities for each star. The proper motion of C1 issimilar in magnitude to that of the Ursa Major cluster but in the wrongdirection. A lower limit for the mass of the white dwarf component iscomputed by assuming that the M dwarf is a normal main sequence star.The system shows similarities to post-common-envelope binaries.
| Accuracy of two-dimensional spectral classes derived through DDO photometry.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977AJ.....82..832Y&db_key=AST
| Photoelectric radial velocities, paper 6 Heard's IAU standard stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975MNRAS.171..407G&db_key=AST
| The establishment of 21 new ninth magnitude IAU standard radial velocity stars
Not Available
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | שומר הדובים |
| התרוממות ימנית: | 14h59m52.39s |
| סירוב: | +27°09'37.0" |
| גודל גלוי: | 7.633 |
| מרחק: | 390.625 פארסק |
| תנועה נכונה: | -39.2 |
| תנועה נכונה: | 48.4 |
| B-T magnitude: | 8.932 |
| V-T magnitude: | 7.741 |
קטלוגים וכינוים:
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