Contents
Images
Upload your image
DSS Images Other Images
Related articles
SparsePak: A Formatted Fiber Field Unit for The WIYN Telescope Bench Spectrograph. II. On-Sky Performance
We present a performance analysis of SparsePak and the WIYN BenchSpectrograph for precision studies of stellar and ionized gas kinematicsof external galaxies. We focus on spectrograph configurations withechelle and low-order gratings yielding spectral resolutions of ~10,000between 500 and 900 nm. These configurations are of general relevance tothe spectrograph performance. Benchmarks include spectral resolution,sampling, vignetting, scattered light, and an estimate of the systemabsolute throughput. Comparisons are made to other, existing, fiberfeeds on the WIYN Bench Spectrograph. Vignetting and relative throughputare found to agree with a geometric model of the optical system. Anaperture-correction protocol for spectrophotometric standard-starcalibrations has been established using independent WIYN imaging dataand the unique capabilities of the SparsePak fiber array. The WIYNpoint-spread function is well fitted by a Moffat profile with a constantpower-law outer slope of index -4.4. We use SparsePak commissioning datato debunk a long-standing myth concerning sky-subtraction with fibers:by properly treating the multifiber data as a ``long-slit'' it ispossible to achieve precision sky-subtraction with a signal-to-noiseperformance as good or better than conventional long-slit spectroscopy.No beam-switching is required, and hence the method is efficient.Finally, we give several examples of science measurements that SparsePaknow makes routine. These include Hα velocity fields of low surfacebrightness disks, gas and stellar velocity-fields of nearly face-ondisks, and stellar absorption-line profiles of galaxy disks at spectralresolutions of ~24,000.
| 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.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| 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}
| A near-infrared stellar spectral library: I. H-band spectra.
This paper presents the H band near-infrared (NIR) spectral library of135 solar type stars covering spectral types O5-M3 and luminosityclasses I-V as per MK classification. The observations were carried outwith 1.2 meter Gurushikhar Infrared Telescope (GIRT), at Mt. Abu, Indiausing a NICMOS3 HgCdTe 256 x 256 NIR array based spectrometer. Thespectra have a moderate resolution of 1000 (about 16 A) at the H bandand have been continuum shape corrected to their respective effectivetemperatures. This library and the remaining ones in J and K bands oncereleased will serve as an important database for stellar populationsynthesis and other applications in conjunction with the newly formedlarge optical coude feed stellar spectral library of Valdes et al.(2004). The complete H-Band library is available online at: http://vo.iucaa.ernet.in/~voi/NIR_Header.html
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Empirically Constrained Color-Temperature Relations. II. uvby
A new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our ``final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile.
| VLTI near-IR interferometric observations of Vega-like stars. Radius and age of α PsA, β Leo, β Pic, ɛ Eri and τ Cet
We report in this paper the direct interferometric measurement of theangular diameter of five nearby Vega-like stars: α PsA, βLeo, β Pic, ɛ Eri and τ Cet. The near-infrared (K and Hbands) observations were conducted at the VLTI during the commissioningperiod with the VINCI instrument and three different baselines rangingfrom 66 m to 140 m. The five stellar photospheres are resolved and wederive their angular diameters with a 1 to 2% accuracy, except forβ Pic (14%). We discuss the detectability and the influence of apossible small amount of warm circumstellar dust on our measurements. Inaddition, we have used the stellar evolution code CESAM (Morel\cite{m97}) to compare the computed fundamental parameters to theobserved values (linear diameter, luminosity, temperature and chemicalabundance). As a result of the simulation, the age of the stars isinferred and found to be in good agreement with previous estimates fromvarious other methods.
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/413/1037
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Oxygen line formation in late-F through early-K disk/halo stars. Infrared O I triplet and [O I] lines
In order to investigate the formation of O I 7771-5 and [O I] 6300/6363lines, extensive non-LTE calculations for neutral atomic oxygen werecarried out for wide ranges of model atmosphere parameters, which areapplicable to early-K through late-F halo/disk stars of variousevolutionary stages.The formation of the triplet O I lines was found to be well described bythe classical two-level-atom scattering model, and the non-LTEcorrection is practically determined by the parameters of theline-transition itself without any significant relevance to the detailsof the oxygen atomic model. This simplifies the problem in the sensethat the non-LTE abundance correction is essentially determined only bythe line-strength (Wlambda ), if the atmospheric parametersof Teff, log g, and xi are given, without any explicitdependence of the metallicity; thus allowing a useful analytical formulawith tabulated numerical coefficients. On the other hand, ourcalculations lead to the robust conclusion that LTE is totally valid forthe forbidden [O I] lines.An extensive reanalysis of published equivalent-width data of O I 7771-5and [O I] 6300/6363 taken from various literature resulted in theconclusion that, while a reasonable consistency of O I and [O I]abundances was observed for disk stars (-1 <~ [Fe/H] <~ 0), theexistence of a systematic abundance discrepancy was confirmed between OI and [O I] lines in conspicuously metal-poor halo stars (-3 <~[Fe/H] <~ -1) without being removed by our non-LTE corrections, i.e.,the former being larger by ~ 0.3 dex at -3 <~ [Fe/H] <~ -2.An inspection of the parameter-dependence of this discordance indicatesthat the extent of the discrepancy tends to be comparatively lessenedfor higher Teff/log g stars, suggesting the preference ofdwarf (or subgiant) stars for studying the oxygen abundances ofmetal-poor stars.Tables 2, 5, and 7 are only available in electronic form, at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/343 and Table\ref{tab3} is only available in electronic form athttp://www.edpsciences.org
| Line Absorption as a Metallicity Index for Giant Stars
The fraction of light removed from a star's spectrum by the spectrallines, the line absorption, is shown to be a precise empirical indicatorof metallicity. We measured the line absorption in 89 class III giantstars in a 42.5 Å window between 6219.0 and 6261.5 Å andthen calibrated these values against published metallicities. We showthat the line absorption can be measured precisely enough to improve themetallicity precision about fivefold over the original calibrationmetallicities, reaching a precision of 0.01 dex in favorable cases.
| On the Abundance of Potassium in Metal-Poor Stars
Based on extensive statistical-equilibrium calculations, we performed anon-LTE analysis of the K I 7699 equivalent-width data ofmetal-deficient stars for the purpose of clarifying the behavior of thephotospheric potassium abundance in disk/halo stars. While the resultingnon-LTE abundance corrections turned out to be considerably large,amounting to 0.2-0.7dex, their effect on the [K/Fe] vs. [Fe/H] relationis not very important, since these corrections do not show anysignificant dependence on the metallicity. Hence, we again confirmed theresults of previous LTE studies, that [K/Fe] shows a gradual systematicincrease toward a lowered metallicity up to [K/Fe] ~ 0.3 - 0.5 at[Fe/H]} ~ -1 to -2, such as in the case of αelements.
| An optical velocity for the Phoenix dwarf galaxy
We present the results of a Very Large Telescope observing programmecarried out in service mode using FORS1 on ANTU in long-slit mode todetermine the optical velocities of nearby low surface brightnessgalaxies. As part of our programme of service observations we obtainedlong-slit spectra of several members of the Phoenix dwarf galaxy fromwhich we derive an optical heliocentric radial velocity of -13 +/- 9 kms-1. This agrees very well with the velocity of the mostpromising of the H I clouds seen around Phoenix, which has aheliocentric velocity of -23 km s-1, but is significantlydifferent from the recently published optical heliocentric velocity ofPhoenix of -52 +/- 6km s-1 by Gallart et al.
| New nearby stars among bright APM high proper motion stars
As part of a new southern sky survey for faint high proper motion starsbased on Automatic Plate Measuring (APM) measurements of UK SchmidtTelescope plates, we have found a large number of previously unknownbrighter objects. Spectroscopic follow-up observations with the EuropeanSouthern Observatory New Technology Telescope of 15 of these new,relatively bright (120.45arcsecyr-1) show one-third of them to be nearby(d<25pc). Among the nearby stars is an M6 dwarf with strong emissionlines at a spectroscopic distance of about 11pc and an M4 dwarf at about13pc. Coupled with earlier South African Astronomical Observatoryspectroscopic observations of three similar bright high proper motionstars, the success rate of finding nearby stars (d<25pc) is about 45per cent. All newly discovered nearby stars have disc kinematicsconfirmed by radial velocity measurements from our spectra. In additionthere are several high-velocity stars with halo kinematics in thesample, mainly subdwarfs, at about 60 to 110pc distance. Thesehigh-velocity stars are interesting targets for further study of theGalactic escape velocity. One of the detected nearby high proper motionstars was formerly thought to be an M giant in the Small MagellanicCloud. The spectrum of one M3 star shows a strong blue continuum, whichis likely to signify the presence of a hot companion. Spectroscopicfollow-up observations of high proper motion stars are shown to be aneffective tool in the search for the missing stars in the Solarneighbourhood. Candidates for more extensive trigonometric parallaxdetermination can be selected on the basis of the spectroscopic distanceestimates.
| The Stellar and Gas Kinematics of Several Irregular Galaxies
We present long-slit spectra of three irregular galaxies from which wedetermine the stellar kinematics in two of the galaxies (NGC 1156 andNGC 4449) and ionized gas kinematics in all three (including NGC 2366).We compare this to the optical morphology and H I kinematics of thegalaxies. In the ionized gas, we see a linear velocity gradient in allthree galaxies. In NGC 1156 we also detect a weak linear velocitygradient in the stars of (5+/-1/sini) km s-1 kpc-1to a radius of 1.6 kpc. The stars and gas are rotating about the sameaxis, but this is different from the major axis of the stellar bar,which dominates the optical light of the galaxy. In NGC 4449 we do notdetect organized rotation of the stars and place an upper limit of(3/sini) km s-1 kpc-1 to a radius of 1.2 kpc. ForNGC 4449, which has signs of a past interaction with another galaxy, wedevelop a model to fit the observed kinematics of the stars and gas. Inthis model the stellar component is in a rotating disk seen nearlyface-on, while the gas is in a tilted disk with orbits whose planesprecess in the gravitational potential. This model reproduces theapparent counterrotation of the inner gas of the galaxy. The peculiarorbits of the gas are presumed as a result of acquisition of gas in thepast interaction.
| Rotation and Activity in the Solar-Metallicity Open Cluster NGC 2516
We report new measures of radial velocities and rotation rates (vsini)for 51 F and early G stars in the open cluster NGC 2516 and combinethese with previously published data. From high signal-to-noise ratiospectra of two stars, we show that NGC 2516 has a relative ironabundance with respect to the Pleiades of Δ[Fe/H]=+0.04+/-0.07 atthe canonical reddening of E(B-V)=0.12, in contrast to previousphotometric studies that placed the cluster 0.2-0.4 dex below solar. Weconstruct a color-magnitude diagram based on radial velocity members andexplore the sensitivity of photometric determinations of the metallicityand distance to assumed values of the reddening. For a metal abundancenear solar, the Hipparcos distance to NGC 2516 is probablyunderestimated. Finally, we show that the distribution of rotation ratesand X-ray emission does not differ greatly from that of the Pleiades,when allowance is made for the somewhat older age of NGC 2516. Based onobservations obtained at the Anglo-Australian Telescope and onobservations obtained at the Cerro Tololo Inter-American Observatory,NOAO, which is operated by the Associated Universities for Research inAstronomy (AURA), Inc., under cooperative agreement with the NationalScience Foundation.
| Kinematic Study of the Disrupting Globular Cluster Palomar 5 Using VLT Spectra
Wide-field photometric data from the Sloan Digital Sky Survey haverecently revealed that the Galactic globular cluster Palomar 5 is in theprocess of being tidally disrupted. Here we investigate the kinematicsof this sparse remote star cluster using high-resolution spectra fromthe Very Large Telescope (VLT). Twenty candidate cluster giants locatedwithin 6' of the cluster center have been observed with the UV-VisualEchelle Spectrograph on VLT-UT2. The spectra provide radial velocitieswith a typical accuracy of 0.15 km s-1. We find that thesample contains 17 certain cluster members with very coherentkinematics, two unrelated field dwarfs, and one giant with a deviantvelocity, which is most likely a cluster binary showing fast orbitalmotion. From the confirmed members we determine the heliocentricvelocity of the cluster as -58.7+/-0.2 km s-1. The totalline-of-sight velocity dispersion of the cluster stars is 1.1+/-0.2 kms-1 (all members) or 0.9+/-0.2 km s-1 (stars onthe red giant branch only). This is the lowest velocity dispersion thathas so far been measured for a stellar system classified as a globularcluster. The shape of the velocity distribution suggests that there is asignificant contribution from orbital motions of binaries and that thedynamical part of the velocity dispersion is therefore stillsubstantially smaller than the total dispersion. Comparing theobservations with the results of Monte Carlo simulations of binaries wefind that the frequency of binaries in Pal 5 is most likely between 24%and 63% and that the dynamical line-of-sight velocity dispersion of thecluster must be smaller than 0.7 km s-1 (90% confidence upperlimit). The most probable values of the dynamical dispersion lie in therange 0.12<=σ/km s-1<=0.41 (68% confidence). Pal5 thus turns out to be a dynamically very cold system. Our results arecompatible with an equilibrium system. We find that the luminosity ofthe cluster implies a total mass of only 4.5 to 6.0×103Msolar. We further show that a dynamical line-of-sightvelocity dispersion of 0.32 to 0.37 km s-1 admits a Kingmodel that fits the observed surface density profile of Pal 5 (withW0=2.9 and rt=16.1′) and its mass. Based onobservations obtained at the European Southern Observatory, Paranal,Chile (program 67.D-0298A).
| Chromospherically Active Stars. XXI. The Giant, Single-lined Binaries HD 89546 And HD 113816
We have obtained spectroscopy and photometry of the chromosphericallyactive, single-lined spectroscopic binaries HD 89546 and HD 113816. HD89546 has a circular orbit with a period of 21.3596 days. Its primaryhas a spectral type of G9 III and is somewhat metal-poor with[Fe/H]~-0.5. HD 113816 has an orbit with a period of 23.6546 and a loweccentricity of 0.022. Its mass function is extremely small, 0.0007Msolar, consistent with a very low inclination. The primaryis a slightly metal-poor K2 III. A decade or more of photometricmonitoring with an automatic telescope demonstrates that both systemsdisplay brightness variations due to rotational modulation of thevisibility of photospheric star spots, as well as light-curve changesresulting from the redistribution of star spots by differential rotationand long-term changes in the filling factor of the spots. We determinedrotation periods for each season when the observations were numerousenough. Our mean rotation periods of 21.3 and 24.1 days for HD 89546 andHD 113816, respectively, confirm that the giants in each system aresynchronously rotating. The orbital elements and properties of the giantcomponents of these two systems, including levels of surface magneticactivity, are quite similar. However, the two rotational inclinationsare rather different, 57° for HD 89546 and 13° for HD 113816.Thus the latter giant is seen nearly pole on. We analyzed the lightcurves for similarities and differences that result from viewing thesetwo systems from quite different inclinations.
| A catalogue of calibrator stars for long baseline stellar interferometry
Long baseline stellar interferometry shares with other techniques theneed for calibrator stars in order to correct for instrumental andatmospheric effects. We present a catalogue of 374 stars carefullyselected to be used for that purpose in the near infrared. Owing toseveral convergent criteria with the work of Cohen et al.(\cite{cohen99}), this catalogue is in essence a subset of theirself-consistent all-sky network of spectro-photometric calibrator stars.For every star, we provide the angular limb-darkened diameter, uniformdisc angular diameters in the J, H and K bands, the Johnson photometryand other useful parameters. Most stars are type III giants withspectral types K or M0, magnitudes V=3-7 and K=0-3. Their angularlimb-darkened diameters range from 1 to 3 mas with a median uncertaintyas low as 1.2%. The median distance from a given point on the sky to theclosest reference is 5.2degr , whereas this distance never exceeds16.4degr for any celestial location. The catalogue is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/183
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/492, and from theauthors on CD-Rom.
| New algorithms for reducing cross-dispersed echelle spectra
We describe advanced image processing algorithms, implemented in a dataanalysis package for conventional and cross-dispersed echelle spectra.Comparisons with results from other packages illustrate the outstandingquality of the new REDUCE package, particularly in terms of resultingnoise level and treatment of CCD defects and cosmic ray spikes. REDUCEcan be adapted relatively easily to handle a variety of instrumenttypes, including spectrographs with prism or grating cross-dispersers,possibly fed by a fiber or image slicer, etc. In addition to reducedspectra, an accurate spatial profile is recovered, providing valuableinformation about the spectrograph PSF and simplifying scattered lightcorrections. Based on data obtained with the VLT UVES and SAAO Giraffespectrometers.
| Line-Depth Ratios: Temperature Indices for Giant Stars
Ratios of the depths of appropriately chosen spectral lines are shown tobe excellent indicators of stellar temperatures for giant stars in theG3 to K3 spectral type range. We calibrate five line-depth ratiosagainst B-V and R-I color indices and then translate these intotemperatures. Our goal is to set up line-depth ratios to (1) accuratelymonitor any temperature variations of a few degrees or less that mayoccur during magnetic cycles or oscillations and (2) rank giantsprecisely on a temperature coordinate. This is not an absolutecalibration of stellar temperatures. We show how giant spectra can bemisleading because of the complex dependences of spectral lines onmetallicity and absolute magnitude as well as temperature, and it isessential to make corrections to accommodate these complications. Thefive line-depth ratios we use yield precision for monitoring, i.e.,detecting temperature variations, of 4 K from a single exposure. Rankinggiants by temperature can be done with errors of ~25 K but could beimproved with better determinations of the metallicity andabsolute-magnitude corrections.
| 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.
| On the Wilson-Bappu relationship in the Mg II k line
An investigation is carried out on the Wilson-Bappu effect in the Mg Iik line at 2796.34 Å. The work is based on a selection of 230 starsobserved by both the IUE and HIPPARCOS satellites, covering a wide rangeof spectral types (F to M) and absolute visual magnitudes (-5.4<=MV <=9.0). A semi-automatic procedure is used to measurethe line widths, which applies also in the presence of strong centralabsorption reversal. The Wilson-Bappu relationship here provided isconsidered to represent an improvement over previous recent results forthe considerably larger data sample used, as well as for a properconsideration of the measurement errors. No evidence has been found fora possible dependence of the WB effect on stellar metallicity andeffective temperature.
| Doppler imaging of stellar surface structure. XV. A possible detection of differential rotation and local meridional flows on the rapidly-rotating giant HD 218153 = KU Pegasi
Time-resolved Doppler images of the rapidly rotating, but long-period(25 days), giant KU Pegasi show several cool low-to-medium latitudespots as well as an asymmetric polar feature. The average spottemperature is about 700 K below the photospheric temperature of 4700 K.KU Peg is one of the most massive, and currently the most evolved,late-type star with a Doppler image. We obtained two independent imagesfrom two consecutive stellar rotations covering 50 nights with a totalof 43 spectra. From a cross-correlation analysis of the two maps, wedetect systematic longitudinal and latitudinal shifts that wetentatively interpret as latitude-dependent differential rotation andlocal meridional flows, respectively. The differential-rotation patternis more complex than on the Sun, but on average in the sense that thepoles rotate slower than the stellar equator, i.e. in the same directionand also of the same order than on the Sun. The latitudinal shifts areof the order of 0.4° day-1 towards the stellar pole andoccur at longitudes of around 40° and 330°. The residual{Hα } profiles show a stationary emission component at restwavelength and a blue-shifted absorption. The latter suggests an outwardpointed velocity field with a flow velocity of approximately 35 kms-1.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| 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
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | おとめ座 |
| Right ascension: | 12h20m21.00s |
| Declination: | +03°18'45.0" |
| Apparent magnitude: | 4.96 |
| Distance: | 87.489 parsecs |
| Proper motion RA: | -293.8 |
| Proper motion Dec: | -63.2 |
| B-T magnitude: | 6.471 |
| V-T magnitude: | 5.093 |
Catalogs and designations:
|
