Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
Improvement of Hipparcos Proper Motions in Declination
More than a decade elapsed after the HIPPARCOS ESA mission (ESA 1997)observations have been collected. This first astronomical satellitemission was less than 4 years long so that 1991.25 is the epoch of theHIPPARCOS Catalogue. Many other projects have checked or improvedHIPPARCOS data. Also, a long series of ground - based opticalobservations of some stars included in HIPPARCOS Catalogue, made withPhotographic Zenith Tubes (PZT) are useful for the task of improving theproper motions of these stars. The ARIHIP Catalogue (after ACT, TYCHO -2, FK6, GC+HIP, TYC2+HIP) is a combination of the HIPPARCOS and someground - based data, and the ARIHIP proper motions are more accuratethan the HIPPARCOS ones. Here we present a new step of our procedure ofcalculation; between PZT data we added the HIPPARCOS position withsuitable weight - the point with the coordinates (1991.25, 0ŭ0)in our case. The method was applied to 202 stars observed at RichmondPZTs in the course of a few decades. The result is better proper motionsin declination for these HIPPARCOS stars, and a good agreement withARIHIP proper motions (we found 128 common Richmond and ARIHIP stars tocheck our result). Also, we present the result for other 74 Richmondstars which are not found in ARIHIP.
| A Dozen New γ Doradus Stars
We use new high-dispersion spectroscopic and precise photometricobservations to identify 12 new γ Doradus stars. Two of the 12systems are double-lined binaries that show obvious velocityvariability. Five other stars have metallic lines with compositeprofiles characterized by a narrow feature near the center of each broadcomponent. Spectrograms of the Hα line indicate that all fivestars are binaries rather than shell stars. The remaining five stars inour sample are probably single. All 12 stars are photometricallyvariable with amplitudes between 6 and 87 mmag in Johnson B and periodsbetween 0.3 and 1.2 days. Four stars are monoperiodic; the rest havebetween two and five independent periods. The variability at all periodsapproximates a sinusoid. Although many of the stars lie within theδ Scuti instability strip, none exhibit the higher frequencyvariability seen in δ Scuti stars. We have increased the sample ofknown γ Doradus stars by 40% and revised the positions of a numberof variables in the H-R diagram by accounting for duplicity. Our list of42 confirmed γ Doradus variables gives some of their properties.All are dwarfs or subgiants and lie within a well-defined region of theH-R diagram that overlaps the cool edge of the δ Scuti instabilitystrip. We compare the observed location of the γ Doradus variableswith a recently published theoretical γ Doradus instability stripand find good agreement.
| Stellar Archaeology: A Keck Pilot Program on Extremely Metal-Poor Stars From the Hamburg/ESO Survey. III. The Lead (Pb) Star HE 0024-2523
We present a detailed abundance analysis, including spectral syntheses,of a very metal-poor ([Fe/H]~=-2.7) peculiar main-sequence star (HE0024-2523) detected during the course of the Keck Pilot Program. Radialvelocities of this star were obtained during four different observingruns over a time span of 1.1 yr and demonstrate that it is clearly ashort-period spectroscopic binary. An orbital solution was obtained, andorbital parameters were determined with high precision. The rotationalvelocity was also measured (vrotsini=9.7+/-1.5 kms-1) rotation appears likely to be synchronous with theorbit. The abundance analysis and spectral syntheses indicate that theobject is a CH star characterized by extreme s-process enrichment,likely due to mass accretion from an evolved companion that has nowprobably become a white dwarf. The lead (Pb) abundance of (HE 0024-2523)is very high, the same as that of the recently discovered lead-rich,metal-poor star CS 29526-110, [Pb/Fe]=+3.3. The abundance ratio of theheavy to light s-elements, as characterized by Pb and Ba, [Pb/Ba]=+1.9,is the highest yet found for any metal-poor star and is about 0.7 dexhigher than that of CS 29526-110. On the basis of the measured isotopicratio of carbon (C12/C13~6) we argue that the massdonor must have had an original mass of at least ~3 Msolar.The unusually short period of this CH star suggests that it underwent apast common-envelope phase with its evolved companion. Our results arecompared with the latest available models for asymptotic giant branchyields and s-process nucleosynthesis. We also discuss the possibleconnection between HE 0024-2523, the lithium depletion of halo stars,and halo blue straggler formation.Based in part on observations obtained at the W. M. Keck Observatory,which is operated jointly by the California Institute of Technology, theUniversity of California, and NASA.
| 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
| Low-Luminosity Early-Type Galaxies in the Coma Cluster: Variations in Spectral Properties
We present spectra of nine low-luminosity early-type galaxies (M_B >-17.5) in the Coma Cluster. The spectra, which were obtained with theMultiple Mirror Telescope and cover the spectral region 3300-5350Å, exhibit a large variation in Balmer line strengths. In fact,the line-strength variation among the Coma low-luminosity galaxies is aslarge as that found among a sample of low-luminosity elliptical galaxiesin the Virgo Cluster and lower density environments. When compared withdetailed population synthesis models, the variation in Balmer linestrengths among the Coma galaxies indicates a range inluminosity-weighted mean age from ~1 to ~12 Gyr. The two youngestgalaxies are shown to be in a poststarburst state, i.e., they are notsimply former spirals whose star formation was recently terminated.Moreover, the ~1 Gyr ages of these two youngest low-luminosity galaxiesare similar to those of the brighter poststarburst galaxies in the ComaCluster.
| 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.
| A sample of galaxy clusters to study the fundamental plane: Redshift measurements
We present the results of spectroscopic observations of galaxies in asample of nearby clusters. We measured galaxy redshifts and estimatedcluster velocity dispersions. These observations were carried out at theObservatoire de Haute Provence as part of a program aiming at a moredetailed study of the Cluster Fundamental Plane. Based on observationsmade at Haute-Provence Observatory, CNRS, France.
| 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.
| The Mass-To-Light Ratios of the Draco and Ursa Minor Dwarf Spheroidal Galaxies.I. Radial Velocities from Multifiber Spectroscopy
We have measured 206 radial velocities for 94 probable members in theUrsa Minor dwarf spheroidal galaxy and 167 velocities for 91 probablemembers in the Draco dwarf spheroidal galaxy. These velocities wereobtained using the KPNO 4 m telescope with the Hydra multifiberpositioner and bench spectrograph in 1992,1993, and 1994. Bothsimulations and repeated measurements show that the median uncertaintyin these velocities is 4.0 km/s. Our velocities are compared with theother major datasets for Draco and Ursa Minor. Aside from a smallzero-point difference, there is excellent agreement between the Hydravelocities and the Olszewski et al. MMT echelle velocities. Comparisonwith the Hargreaves et al. Ursa Minor velocities reveals inconsistencieswhich we ascribe to underestimated errors in the Hargreaves et al. data,After correcting for zero-point differences, we combine the three majorsets of velocities. Our spectra recovered all of the known Carbon (C)stars in Draco and Ursa Minor and revealed one new C star in Draco andtwo in Ursa Minor. In addition, one star whose velocity is consistentwith membership in Ursa Minor has a deep and wide Hβ absorptionline in its spectrum. An initial discussion of the kinematics of the twogalaxies is presented. The systemic velocities of Draco and Ursa Minorare -293.3 +/- 1.0 and -247.4 +/- 1.0 km s^-1^, respectively. Ursa Minorshows apparent rotation about a position angle of 75^deg^ with anamplitude of about 3 km s^-1^; the morphological major axis is 53^deg^+/-5^deg^. No such rotation is found in Draco. We find a velocitydispersion of 10.4 +/- 0.9 km s^-1^ for Ursa Minor including all starsand 8.8 +/- 0.8 km s^-1^ excluding the star with the most extremevelocity. In Draco we find 10.7 +/- 0.9 km s^-1^ including all stars and8.5 +/- 0.7 km s^-1^ excluding the three stars with the most extremevelocities. These dispersions are consistent with the dispersionsmeasured in the other two studies and confirm that Draco and Ursa Minorhave the largest mass-to-light ratios of any of the dwarf spheroidals.
| 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.
| Abundances and velocities for open and globular cluster giants: The data.
We present a large dataset consisting of giants in the field, and inopen and globular clusters. A total of 122 giants were observed in thefields of 8 open clusters. A total of 342 giants were observed in thefields of 25 globular clusters. A total of 36 field stars with wellknown abundances and luminosities were also observed. Radial velocitiesare determined for most giants, some of which have no photometryavailable. We have analyzed several spectral features in order to definea grid that will allow the determination of metal abundances for haloand bulge giants. The errors involved in the determination of radialvelocities and [Fe/H] are carefully examined. We find that field andopen cluster stars on one side, and globular cluster giants on the otherside, do not follow the same calibration. This is possibly due toenhanced [α/Fe] abundances in globular clusters. Therefore, wehave defined a calibration based only on globular cluster giants, validfrom [Fe/H]=-2.0 to +0.5. This calibration is carried out with thepurpose of measuring metallicities for bulge and halo giants, with theunderlying assumption that the abundance ratios of the relevant elementsrelative to iron are similar to the calibrating stars. Adopting asstandards the globular clusters NGC 288, NGC 362, NGC 1851, NGC 6356,NGC 6624, 47 Tuc, M 4 , M 3, and M 22 we derive metallicities forglobular clusters with less well known compositions, like M 28, and NGC6637. In particular, we confirm a low metallicity for M 28([Fe/H]=-1.35+/-0.2), a cluster that has a disk orbit.
| Internal kinematics of the Leo II dwarf spherodial galaxy
We have obtained radial velocities of 31 red giants in the Leo II dwarfspheroidal (dSph) galaxy using the HIRES echelle spectrograph of theKeck 10 m telescope. These stars were selected using CCD photometryobtained with the Palomar 1.5 m telescope. The radial velocity of errorswere determined from repeat measurements of Leo II giants and faintradial velocity standards; the average error for the Leo II giants is2.4 km/s. The systemic velocity of Leo II is 76.0 +/- 1.3 km/s, and thevelocity dispersion is 6.7 +/- 1.1 km/s. Adopting the standardassumptions (mass follows light, isotropy, and equilibrium) we derive aglobal V-band mass-to-light ratio (Msub tot)/Ltot = 11.1 +/-3.8, and a central value rho0/I0 = 11.6 +/- 3.2(both in solar units). These values are larger than the M/L ratiosmeasured for local stellar populations (star clusters or the solarneighborhood). Monte Carlo simulations show that a large population ofbinaries probably has not inflated a small intrinsic velocity dispersionto the observed value. A model-independent lower limit of the centralmass density of Leo II yeilds rho0,min = solar masspc-3, larger than the central luminous mass density in Leo IIfor (M/L)lum = 2.2. This demands an extensive dark halo inthe outer regions of the galaxy to account for the observed dispersion.We conclude that Leo II contains a significant dark matter component.The total mass of the dark halo is 0.9X177 solar mass,consistent with the masses inferred in all well-studied dSph galaxies.Because it is remote from the Galaxy, tide cannot plausibly affect thevelocity dispersion of Leo II. However, we cannot use these results torule out the possibility that tides may influence the kinematics ofother dSph galaxies found closer to the Milky Way.
| Spectral-line broadening functions of W UMa-type binaries. II - AH VIR
Twenty-four 10 A/mm spectra of the W UMa binary AH Vir have beenanalyzed for radial velocities and for geometrical parameters of thesystem components by the method of spectral-line broadening functions.It is shown that the broadening functions determined through the linearrestoration process are much better defined than cross-correlationfunctions, even in the presence of broad spectral features. A newspectroscopic orbit for AH Vir has been determined on the basis ofradial velocity information contained in the broadening functions. Acombination of this orbit with a parallel solution for the geometricelements gave a new set of absolute elements of the system: a = 2.80solar radii, M1 = 1.36 solar mass, M2 = 0.41 solar mass, R1 = 1.40 solarradius, and R2 = 0.83 solar radius. The absolute bolometric magnitude ofthe system was found to be 4.07 m and the distance about 94 pc. AH Virbelongs to the OO Aq1 subclass of contact binaries which ischaracterized by the unusually low effective temperature for theobserved large dimensions. The radius of the primary is close to whatwould be expected if it obeyed the Main-Sequence mass-radius relation,but the luminosity of the system (most likely produced solely by theprimary component) is lower than that for the ZAMS. The underluminosityof the system is due to the abnormally low effective temperature whichremains significantly low after the energy transfer between componentsis taken into account.
| 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.
| UBV photometry of stars whose positions are accurately known. IV
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...68..211O&db_key=AST
| Standard Velocity Stars
Not Available
| UBV Photoelectric Photometry of 259 PZT Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980PASP...92..215G&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
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Херкулес |
| Ректацензија: | 18h32m35.94s |
| Deклинација: | +25°29'22.1" |
| Apparent магнитуда: | 7.436 |
| Даљина: | 289.855 parsecs |
| Proper motion RA: | 4.9 |
| Proper motion Dec: | 15 |
| B-T magnitude: | 8.561 |
| V-T magnitude: | 7.529 |
Каталог и designations:
|
