Contents
Images
Upload your image
DSS Images Other Images
Related articles
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 Evolution of Massive Stars. I. Red Supergiants in the Magellanic Clouds
We investigate the red supergiant (RSG) content of the SMC and LMC usingmultiobject spectroscopy on a sample of red stars previously identifiedby BVR CCD photometry. We obtained high-accuracy (<1 kms-1) radial velocities for 118 red stars seen toward the SMCand 167 red stars seen toward the LMC, confirming most of these (89% and95%, respectively) as red supergiants. Spectral types were alsodetermined for most of these RSGs. We find that the distribution ofspectral types is skewed toward earlier type at lower metallicities: theaverage (median) spectral type is K5-K7 I in the SMC, M1 I in the LMC,and M2 I in the Milky Way. Our examination of the Kurucz ATLAS9 modelatmospheres suggests that the effect that metallicity has on theappearance on the TiO lines is probably sufficient to account for thiseffect, and we argue that RSGs in the Magellanic Clouds are 100 K (LMC)and 300 K (SMC) cooler than Galactic stars of the same spectral types.The colors of the Kurucz models are not consistent with thisinterpretation for the SMC, although other models (e.g., Bessell et al.)show good agreement. A finer grid of higher resolution synthetic spectraappropriate to cool supergiants is needed to better determine theeffective temperature scale. We compare the distribution of RSGs in theH-R diagram to that of various stellar evolutionary models; we find thatnone of the models produce RSGs as cool and luminous as what is actuallyobserved. This result is much larger than any uncertainty in theeffective temperature scale. We note that, were we to simply adopt theuncorrected Galactic effective scale for RSGs and apply this to oursample, then the SMC's RSGs would be underluminous compared with theLMC's, contrary to what we expect from stellar evolution considerations.In all of our H-R diagrams, however, there is an elegant sequence ofdecreasing effective temperatures with increasing luminosities;explaining this will be an important test of future stellar evolutionarymodels. Finally, we compute the blue-to-red supergiant ratio in the SMCand LMC, finding that the values are indistinguishable (~15) for the twoClouds. We emphasize that ``observed'' B/R values must be carefullydetermined if a comparison with that predicted by stellar models is tobe meaningful. The nonrotation Geneva models overestimate the number ofblue to red supergiants for the SMC, but underestimate it for the LMC;however, given the inability to produce high-luminosity RSGs in themodels that match what is observed in the H-R diagram, such adisagreement is not surprising.
| The discovery of low-mass pre-main-sequence stars in Cepheus OB3b
We report the discovery of a low-mass pre-main-sequence (PMS) stellarpopulation in the younger subgroup of the Cepheus OB3 association, CepOB3b, using UBVI CCD photometry and follow-up spectroscopy. The opticalsurvey covers approximately 1300 arcmin2 on the sky and givesa global photometric and astrometric catalogue for more than 7000objects. The location of a PMS population is well defined in a V versus(V-I) colour-magnitude diagram.Multifibre spectroscopic results for optically selected PMS candidatesconfirm the T Tauri nature for 10 objects, with equal numbers ofclassical TTS (CTTS) and weak-line TTS (WTTS). There are six otherobjects that we classify as possible PMS stars. The newly discovered TTSstars have masses in the range ~0.9-3.0 Msolar and ages from<1 to nearly 10 Myr, based on the Siess, Dufour & Forestiniisochrones. Their location close to the O and B stars of the association(especially the O7n star) demonstrates that low-mass star formation isindeed possible in such an apparently hostile environment dominated byearly-type stars and that the latter must have been less effective ineroding the circumstellar discs of their lower-mass siblings comparedwith other OB associations (e.g. λ-Ori). We attribute this to thenature of the local environment, speculating that the bulk of molecularmaterial, which shielded low-mass stars from the ionizing radiation oftheir early-type siblings, has only recently been removed.
| Lensing in the Hercules Supercluster
We report Keck LRIS observations of an arclike background galaxy nearthe center of Abell 2152 (z=0.043), one of the three clusters comprisingthe Hercules supercluster. The background object has a redshift z=0.1423and is situated 25" north of the primary component of the A2152brightest cluster galaxy (BCG). The object is about 15" in total lengthand has a reddening-corrected R-band magnitude ofmR=18.55+/-0.03. Its spectrum shows numerous strong emissionlines, as well as absorption features. The strength of the Hαemission would imply a star formation rate SFR~3 h-2Msolar yr-1 in the absence of any lensing.However, the curved shaped of this object and its tangential orientationalong the major axis of the BCG suggest lensing. We model the A2152 coremass distribution including the two BCG components and the clusterpotential. We present velocity and velocity dispersion profilemeasurements for the two BCG components and use these to help constrainthe potential. The lens modeling indicates a likely magnification factorof ~1.9 for the lensed galaxy, making A2152 the nearest cluster in whichsuch significant lensing of a background source has been observed.Finally, we see evidence for a concentration of early-type galaxies atz=0.13 near the centroid of the X-ray emission previously attributed toA2152. We suggest that emission from this background concentration isthe cause of the offset of the X-ray center from the A2152 BCG. Thebackground concentration and the dispersed mass of the Herculessupercluster could add further to the lensing strength of the A2152cluster. Based on observations obtained at the W. M. Keck Observatory,which is jointly operated by the California Institute of Technology, theUniversity of California, and the National Aeronautics and SpaceAdministration.
| 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.
| 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.
| 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).
| The Stellar and Gaseous Kinematics in NGC 253
This paper presents observations made at intermediate spectral andspatial resolutions along the major and minor axes of the starburstgalaxy NGC 253. The spectral ranges analyzed are in the region of thestellar Mg I b (~5175 Angstroms) line, in the near-IR Ca II triplet(~8550 Angstroms) absorption features, and in the region of the H alphaemission line. We compare the shape of the stellar features with thoseof reference stars and determine the line-of-sight velocity distributionof the stellar component by using a two-dimensional Gaussiandecomposition algorithm, and we show for the first time the rotationcurve of the stellar component in NGC 253. Comparing the recessionvelocity curves of the gas and stars, we show that the stellar componenthas a decoupled kinematics with respect to the gas, displaying ashallower velocity gradient and larger velocity dispersion than the gasin the inner regions. The minor-axis kinematics, together with thekinematics across the central 40" along the major axis, suggest thepresence of a rotating body with a kinematically misaligned axis withrespect to the main disk of the galaxy. The asymmetries in the LOSvelocity distribution along the minor axis, together with the steepvelocity gradient of the gaseous component, suggest a merger scenario asthe source of these kinematic signatures. The enclosed mass in thecentral regions is computed to be (2.4 +/- 0.5) x 107 Mȯ for aradius of r = 0."7 (10 pc). A double gaseous component in the central 6"is detected from the [S III] lambda 9069 Angstroms data along the minoraxis; this seems to be the signature of a superbubble, due to asupernova rate of 0.05 yr-1.
| Extended Broad Balmer Emission in the Seyfert 1 Galaxy Markarian 509
We present two-dimensional spectroscopic observations of thecircumnuclear region of Mrk 509. The spectra show extended (off-nuclear)broad Balmer emission ( {FWZI}>1 5,000 km s-1) in a region of about8" in diameter (8 kpc if H0=50 km s-1 Mpc-1). These featuresare interpreted as reflected radiation coming from the unresolved activenucleus. The nearly isotropic appearance of the scattering region can beexplained within the framework of the unified picture for activegalactic nuclei, if the scatterers lie outside the galaxy's disk;otherwise, the present observations would not support simple anisotropicmodels for the Seyfert nucleus in Mrk 509.
| A Study of the Chromospherically Active, Short-Period Binary VZ PISCIUM
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...455..300H&db_key=AST
| 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.
| MK classification and photometry of stars used for time and latitude observations at Mizusawa and Washington
MK spectral classifications are given for 591 stars which are used fortime and latitude observations at Mizusawa and Washington. Theclassifications in the MK system were made by slit spectrograms ofdispersion 73 A/mm at H-gamma which were taken with the 91 cm reflectorat the Okayama Astrophysical Observatory. Photometric observations in UBV were made with the 1-meter reflector at the Flagstaff Station of U.S.Naval Observatory. The spectrum of HD 139216 was found to show a strongabsorption line of H-beta. The following new Am stars were found:HD9550, 25271, 32784, 57245, 71494, and 219109. The following new Apstars were found: HD6116, 143806, 166894, 185171, and 209260. The threestars, HD80492, 116204, and 211376, were found to show the emission inCaII H and K lines.
| Stellar Spectrum Processing - Part Two
Not Available
| 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.
| Time-resolved spectroscopy of SS Cygni at minimum and maximum light
Double-line spectra were obtained of the dwarf nova SS Cygni in Augustand October 1981 to examine the effects of eruption on the radialvelocity curve of the cataclysmic variable. The data covered the4000-5300 A interval and all phases from maximum to minimum light.Calculations were performed for the absorption line and Balmer emissionline radial velocities. An orbital period close to 0.2751297 d wasfound, along with an effective temperature close to 2,444,842 K and aradial velocity of -16 to -14 km/sec. Since the system, a binaryconsisting of a white dwarf and a late-type star, is not eclipsing nodeterminations of the masses or orbital inclinations of the componentswere possible. It was noted that the velocity of the late-type starapparently increases to 195 km/sec during an outburst.
| Standard Velocity Stars
Not Available
| 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
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Pégase |
| Right ascension: | 22h34m36.54s |
| Declination: | +26°35'53.6" |
| Apparent magnitude: | 6.871 |
| Distance: | 366.3 parsecs |
| Proper motion RA: | -8.4 |
| Proper motion Dec: | 0.3 |
| B-T magnitude: | 8.804 |
| V-T magnitude: | 7.031 |
Catalogs and designations:
|
INHABITED SKY
