Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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 Vertical Stellar Kinematics in Face-On Barred Galaxies: Estimating the Ages of Bars
In order to perform a detailed study of the stellar kinematics in thevertical axis of bars, we obtained high signal-to-noise spectra alongthe major and minor axes of the bars in a sample of 14 face-on galaxiesand used them to determine the line-of-sight stellar velocitydistribution, parameterized as a Gauss-Hermite series. With these data,we developed a diagnostic tool that allows one to distinguish betweenrecently formed and evolved bars, as well as to estimate their ages,assuming that bars form in vertically thin disks that are recognizableby low values for the vertical velocity dispersion σz.Through N-body realizations of bar unstable disk galaxies we were alsoable to check the timescales involved in the processes that give bars animportant vertical structure. We show that σz inevolved bars is roughly 100 km s-1, which translates to aheight scale of about 1.4 kpc, giving support to scenarios in whichbulges form through disk material. Furthermore, the bars in ournumerical simulations have values for σz generallysmaller than 50 km s-1, even after evolving for 2 Gyr,suggesting that a slow process is responsible for making bars asvertically thick as we observe. We verify theoretically that theSpitzer-Schwarzschild mechanism is quantitatively able to explain theseobservations if we assume that giant molecular clouds are twice asconcentrated along the bar as in the rest of the disk.
| 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.
| 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}
| 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.
| A Photometric and Spectroscopic Study of Dwarf and Giant Galaxies in the Coma Cluster. II. Spectroscopic Observations
This is the second paper in a series studying the photometric andspectroscopic properties of galaxies of different luminosities in theComa Cluster. We present the sample selection, spectroscopicobservations, and completeness functions. To study the spectralproperties of galaxies as a function of their local environment, twofields were selected for spectroscopic observations to cover both thecore (Coma 1) and outskirts (i.e., southwest of the core and centered onNGC 4839; Coma 3) of the cluster. To maximize the efficiency ofspectroscopic observations, two subsamples were defined, consisting of``bright'' and ``faint'' galaxies, both drawn from magnitude-limitedparent samples. Medium-resolution spectroscopy (6-9 Å) was thencarried out for a total of 490 galaxies in both fields (302 in Coma 1and 188 in Coma 3), using the WYFFOS multifiber spectrograph on theWilliam Herschel Telescope. The galaxies cover a range of 122. The completeness functions for our sampleare calculated. These show that the bright sample is 65% complete atR<17 mag, becoming increasingly incomplete toward fainter magnitudes,while the faint sample follows a monotonically decreasing completenessfunction at R>19 mag. Based on observations made with the WilliamHerschel Telescope, operated on the island of La Palma by the IsaacNewton Group in the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.
| A Large-Scale Jet and FR I Radio Source in a Spiral Galaxy: The Host Properties and External Environment
We have identified a large (~200 h-175 kpc),powerful double radio source whose host galaxy is clearly a disk andmost likely a spiral. This FR I-like radio galaxy is located very nearthe center of the richness class 0 cluster A428. The existence of suchan object violates a fundamental paradigm for radio-loud active galacticnuclei (AGNs). In our first paper, we showed that this object was mostconsistent with a spiral host classification with optical emission-lineratios and colors suggestive of an active nucleus. However, we were notable to confirm actual radio jet emission based on the maps available atthat time. In this paper, we present new, higher resolution radioimaging, a radio/millimeter continuum spectrum for the nucleus, adetection of H I absorption against the bright radio core, an upperlimit to CO emission and the gas mass, and 70 (68 new) optical redshiftsmeasured in the direction of A428. We confirm the existence of a radiojet at 20 cm, extending 42 h-175 into the southernlobe. At 3.6 cm, we also detect a nuclear jet similar in length to thatin M87, although 10 times weaker. We believe that this is the firstdetection of a radio jet on these scales in a disk/spiral host galaxy.The nuclear radio spectrum is similar to many blazar- or quasar-likeobjects, suggesting that the galaxy harbors an imbedded and obscuredAGN. We model a turnover in the spectrum at low frequencies as a resultof free-free absorption. We detect very strong and narrow H Iabsorption, with nearly the entire 20 cm continuum flux of the corebeing absorbed, implying an unusually large optical depth (τ~1). Themost consistent model is that we are viewing the nucleus through adisklike distribution of gas in the interstellar medium, possiblythrough a spiral arm or a warp to account for the above-average columndensity. From the radial velocity distribution, we find that A428 is infact made up of at least two clumps of galaxies separated by ~3300 kms-1, which themselves appear to be imbedded in a nearlycontinuous distribution of galaxies over 13,000 km s-1 invelocity space. Thus, the environment around this unusual radio sourceis more like that of a poor galaxy group imbedded in a filament-likestructure viewed end-on.
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Seeing Galaxies through Thick and Thin. II. Direct Measures of Extinction in Spiral Disks through Spectroscopy of Overlapping Galaxies
We use slit spectroscopy of overlapping pairs of galaxies to directlydetermine the extinction in disks of foreground spiral galaxies. TheDoppler shifts of pair members are determined via cross-correlation, andtheir relative correlation amplitudes are used to separate theircontributions to the combined spectra in regions of overlap. Thisspectroscopic approach is less subject to stringent symmetry constraintsthan our previous, purely photometric analyses. Extinctions offoreground members were obtained for six of the candidates in our sampleof 18 mostly spiral/spiral pairs, when the signal-to-noise-ratio andvelocity differences were suitable. In agreement with our previousimaging results, we find that the extinction in interarm regions is verymodest, typically AB~0.1 mag (corrected to face-on), whilespiral arms exhibit higher extinctions of ~0.3 mag.
| 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.
| 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).
| Kinematics of the Galactic Globular Cluster System: New Radial Velocities for Clusters in the Direction of the Inner Galaxy
The High-Resolution Echelle Spectrometer (HIRES) on the Keck I telescopehas been used to measure the first radial velocities for stars belongingto 11 heavily reddened globular clusters in the direction of the innerGalaxy. The sample consists of the clusters Terzan 3, NGC 6256, IC 1257,NGC 6380 (=Ton 1), Ton 2 (=Pismis 26), Djorg 1, NGC 6540 (=Djorg 3), IC1276 (=Pal 7), Terzan 12, NGC 6749, and Pal 10. Candidate clustermembers were selected from a combination of previously publishedcolor-magnitude diagrams (CMDs) and new instrumental CMDs obtained withthe Palomar 1.5 m telescope. The systemic velocities of Djorg 1 and Pal10 should be considered provisional, since velocities are available foronly two stars. For the remaining nine clusters, we have measured radialvelocities for three to nine member stars. Using our HIRES spectra, weestimate metallicities of [Fe/H]~=-0.75 for both Terzan 3 and IC 1276,two clusters lacking previous metallicity estimates. The question ofkinematic substructuring among the Galactic globular clusters isinvestigated using an updated catalog of globular cluster distances,metallicities, and velocities. It is found that the population ofmetal-rich globular clusters shows significant rotation at allGalactocentric radii. For the metal-rich clusters within 4 kpc of theGalactic center, the measured rotation velocity and line-of-sightvelocity dispersion are similar to those of bulge field stars. Weinvestigate claims that the metal-rich clusters are associated with thecentral Galactic bar by comparing the kinematics of the innermostclusters to that of the atomic hydrogen in the inner Galaxy. Thelongitude-velocity diagram of both metal-rich and metal-poor clustersbears a remarkable similarity to that of the gas, including the samenoncircular motions that have traditionally been interpreted as evidencefor a Galactic bar, or, alternatively, a nonaxisymmetric bulge. However,uncertainties in the existing three-dimensional Galactocentric positionsfor most of the clusters do not yet allow an unambiguous discriminationbetween the competing scenarios of membership in a rigidly rotating baror in a bulge that is an oblate isotropic rotator. We conclude that themajority of metal-rich clusters within the central ~4 kpc of the Galaxyare probably associated with the bulge/bar, and not the thick disk.
| Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and 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,199 of the stars in Part I 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(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
| Systematic Errors in the FK5 Catalog as Derived from CCD Observations in the Extragalactic Reference Frame.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..850S&db_key=AST
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| 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.
| Nine Seasons of Velocity Measurements in the Draco and Ursa Minor Dwarf Spheroidal Galaxies with the MMT Echelle
We have used the Multiple Mirror Telescope echelle spectrograph tomeasure 112 velocities of 42 stars in the Draco and Ursa Minor dwarfspheroidal galaxies and three velocities of three foreground starsbetween 1982 April and 1990 September. We used 11 A resolution spectraobtained with the MX multifiber spectrograph at the Steward 90" to findadditional giant candidates; 5 UMi and 13 Draco stars were then observedat the MMT and added to the original sample of velocity members. Inaddition, the MX spectra were used to eliminate 74 stars in thedirection of UMI and 59 stars in Draco as likely foreground dwarfs. Wedetected 7 velocity variables, defined as those stars whose probabilityof exceeding the measured X^2^ by chance is less than 1.5%. Three ofthese stars are Carbon (C) stars (UMi K and VA 335 and Draco C1); twohave emission lines (Draco CI and UMi M). We show that the C star DracoC4, with a proper motion membership probability of 7%, has a velocityconsistent with membership. It is not surprising that these C (mostlikely CH) stars are binaries because McClure has shown that mostGalactic CH stars are in binary systems. Of the remaining 35 stars, only4 are velocity variables, with measured velocity extrema of 29.1 kms^-1^ (UMi M), 7.2 km s^-1^ (Draco XI-2), 9.0 km s^-1^ (Draco 24), and8.3 km s^-1^ (Draco 473). The velocity dispersions are 10.1 +/- 1.7 kms^-1^ for UMi, and 9.9 +/- 1.4 km s^-1^ for Draco. These dispersionschange to 10.5 +/- 2.0 for UMi, and 8.2 +?- 1.3 for Draco if weeliminate the velocity variables. Our dispersion for UMi differs fromthat of Hargreaves et al. [MNRAS, 271,693 (1994b)] by 1.3σ of thecombined errors. These velocities are combined with the one-componentKing models of Pryor & Kormendy [AJ, 100,127 (1990)] to give M/L =73 for UMi, and 77 for Draco.
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
| Santiago Fundamental Catalogue - A catalogue of 1105 FK5 stars (equinox J2000.0)
The positions in right ascension and declination of 1105 FK5 stars,observed with a Meridian Circle during the period 1979 to 1991, aregiven. The average mean square error of a position, for the wholecatalog, is +/- 0.009 s in right ascension and +/- 0.10 arcsec indeclination. The mean epoch of the catalog is 1983.148.
| Einstein Observatory magnitude-limited X-ray survey of late-type giant and supergiant stars
Results are presented of an extensive X-ray survey of 380 giant andsupergiant stars of spectral types from F to M, carried out with theEinstein Observatory. It was found that the observed F giants orsubgiants (slightly evolved stars with a mass M less than about 2 solarmasses) are X-ray emitters at the same level of main-sequence stars ofsimilar spectral type. The G giants show a range of emissions more than3 orders of magnitude wide; some single G giants exist with X-rayluminosities comparable to RS CVn systems, while some nearby large Ggiants have upper limits on the X-ray emission below typical solarvalues. The K giants have an observed X-ray emission level significantlylower than F and F giants. None of the 29 M giants were detected, exceptfor one spectroscopic binary.
| Physical data of the fundamental stars.
Not Available
| A catalogue of right ascensions and declinations of FK4 stars
The position parameters of 578 stars from the fundamental catalog FK4are determined on the basis of 3-4-h meridian-circle observationsobtained by the differential method at Belgrade Astronomical Observatoryduring 1981-1987. The observation method and data-reduction proceduresare explained, and the results are compiled in extensive tables. Theaverage mean-square errors per observation are found to beepsilon(alpha) cos delta = + or - 0.022 sec and epsilon(delta) = + or -0.32 arcsec.
| 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).
| Spectroscopic orbits of eclipsing binaries - AA UMa
High dispersion and time resolution spectra for the eclipsing binary AAUMa, obtained using an intensified Reticon, were measured bycross-correlation techniques. The spectra of the two components arefound to be very similar, and AA UMa is shown to belong to Subtype W ofW UMa binaries. The orbital elements of the system are determined andcompared with other W UMa binaries. It is found that the orbital periodis 0.48171 days and that the estimated mean mass center velocity for thesystem is -34.8 km/s. The mass ratio between the components isdetermined to be 0.54 and the magnitude difference in the wavelengthobserved is estimated to be 0.36.
| 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.
| New measurements of radial velocities in clusters of galaxies
Redshifts for 100 galaxies in 10 clusters of galaxies are presentedbased on data obtained between March 1984 and March 1985 from CalarAlto, La Palma, and ESO, and on data from Mauna Kea. Data for individualgalaxies are given, and the accuracy of the velocities of the fourinstruments is discussed. Comparison with published data shows thepresent velocities to be shifted by + 4.0 km/s on average, with astandard deviation in the difference of 89.7 km/s, consistent with therms of redshift measurements which range from 50-100 km/s.
| Standard Velocity Stars
Not Available
| The fourth meridian catalog of Besancon Observatory
The catalog presented gives differential meridian positions for 670F-type stars between plus 15 and plus 45 deg declination. The positionsare reduced to the equinox of 1950.0 without proper motions; 333 FK4stars were used as reference stars. A minimum of three and an average offive transits of each program star were observed photoelectrically usinga Gautier transit circle and a Hog grid. The internal accuracy ofindividual measurements is shown to range from 0.013 sec in rightascension and 0.30 arcsec in declination for brighter stars under betterobserving conditions to 0.020 sec in right ascension and 0.38 arcsec indeclination for fainter stars under worse conditions. The standarderrors were applied to compute weighted mean positions, mean epochs, andunweighted means for the program stars. Mean corrections for 283 FK4stars are also provided.
| 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.
| Spectroscopy of five faint M dwarf stars near the north galactic pole
Radial velocities and estimates of absolute magnitudes are presented forfive M dwarfs selected from a proper-motion study of M stars near thenorth galactic pole by Murray and Sanduleak (1972). The derived meandistance and velocity dispersion are significantly larger than thecorresponding quantities found by Murray and Sanduleak, but only a smallsample limited to the earlier-type stars on their list was used in thepresent study.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kucuk Aslan |
| Sað Açýklýk: | 10h29m53.69s |
| Yükselim: | +28°34'52.4" |
| Görünürdeki Parlaklýk: | 6.896 |
| Uzaklýk: | 168.634 parsek |
| özdevim Sað Açýklýk: | 4.7 |
| özdevim Yükselim: | -0.8 |
| B-T magnitude: | 8.328 |
| V-T magnitude: | 7.015 |
Kataloglar ve belirtme:
|
