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Ýlgili Makaleler
Shapes of Spectral Line Bisectors for Cool Stars
The shape of the line bisector for the prototype spectral line Fe Iλ6253 was measured for an array of 54 stars on the cool half ofthe HR diagram. These bisectors are given in tables along with theirerrors. The classic C shape is shown by only a rather restricted rangein effective temperature and luminosity. The detailed change in bisectorshape with effective temperature and luminosity is documented moreprecisely than in previous work. The most blueward point on the bisectorchanges its height systematically with luminosity and can be used as aluminosity or gravity discriminant. The wide range of bisector shapescontains significant information about the velocity fields in theatmospheres of these stars, but extracting that information may requireextensive modeling.
| An Improved Infrared Passband System for Ground-based Photometry: Realization
We describe new simulations and field trials of the new infraredpassband system developed and discussed by Young, Milone, & Stagg,who discussed and illustrated the state of infrared photometry andsuggested ways in which it could be improved. In particular, theypresented a new set of passbands that minimize the dependence of thephotometry on the water vapor bands of the atmospheric windows, whichdefined the edges of many previous infrared passbands, especially whenused at sites and under conditions for which they were not designed. Inthis paper, we present numerical simulations for three atmosphericmodels, demonstrate a measure of the signal-to-noise ratio in the newpassbands for these models, and present observational data obtained at arelatively low-elevation site. The latter demonstrate the utility ofthis system for most astronomical sites where photometry can beperformed, and permit the transformation of observations to this system.Publications of the Rothney Astrophysical Observatory, No. 74.
| Analysis of the Na, Mg, Al, and Si Abundances in the Atmospheres of Red Giants of Different Spectral Subgroups
We analyze the Na, Mg, Al, and Si abundances in the atmospheres of morethan 40 stars, includingred giants of different spectral subgroups(normal red giants, mild and classical barium stars) and severalsupergiants. All these elements exhibit abundance excesses, with theoverabundance increasing with the star’s luminosity. Thedependence of the overabundances for each of these elements on theluminosity (or log g) is the same for all the spectral subgroups,testifying to a common origin: they are all products of hydrogen burningin the NeNa and MgAl cycles that have been dredged up from the stellarinteriors to the outer atmospheric layers by convection that graduallydevelops during the star’s evolution from the main sequence to thered-giant stage. The sodium abundances derived for several stars arelower than for other stars with similar atmospheric parameters. The agesand kinematic characteristics of these two groups of stars suggest thatthey probably belong to different stellar generations.
| HST STIS Spectroscopy of the Triple Nucleus of M31: Two Nested Disks in Keplerian Rotation around a Supermassive Black Hole
We present Hubble Space Telescope (HST) spectroscopy of the nucleus ofM31 obtained with the Space Telescope Imaging Spectrograph (STIS).Spectra that include the Ca II infrared triplet (λ~=8500 Å)see only the red giant stars in the double brightness peaks P1 and P2.In contrast, spectra taken at λ~=3600-5100 Å are sensitiveto the tiny blue nucleus embedded in P2, the lower surface brightnessnucleus of the galaxy. P2 has a K-type spectrum, but we find that theblue nucleus has an A-type spectrum: it shows strong Balmer absorptionlines. Hence, the blue nucleus is blue not because of AGN light butrather because it is dominated by hot stars. We show that the spectrumis well described by A0 giant stars, A0 dwarf stars, or a 200 Myr old,single-burst stellar population. White dwarfs, in contrast, cannot fitthe blue nucleus spectrum. Given the small likelihood for stellarcollisions, recent star formation appears to be the most plausibleorigin of the blue nucleus. In stellar population, size, and velocitydispersion, the blue nucleus is so different from P1 and P2 that we callit P3 and refer to the nucleus of M31 as triple.Because P2 and P3 have very different spectra, we can make a cleandecomposition of the red and blue stars and hence measure the lightdistribution and kinematics of each uncontaminated by the other. Theline-of-sight velocity distributions of the red stars near P2 strengthenthe support for Tremaine's eccentric disk model. Their wings indicatethe presence of stars with velocities of up to 1000 km s-1 onthe anti-P1 side of P2.The kinematics of P3 are consistent with a circular stellar disk inKeplerian rotation around a supermassive black hole. If the P3 disk isperfectly thin, then the inclination angle i~=55deg isidentical within the errors to the inclination of the eccentric diskmodels for P1+P2 by Peiris & Tremaine and by Salow & Statler.Both disks rotate in the same sense and are almost coplanar. Theobserved velocity dispersion of P3 is largely caused by blurred rotationand has a maximum value of σ=1183+/-201 km s-1. This ismuch larger than the dispersion σ~=250 km s-1 of thered stars along the same line of sight and is the largest integratedvelocity dispersion observed in any galaxy. The rotation curve of P3 issymmetric around its center. It reaches an observed velocity ofV=618+/-81 km s-1 at radius 0.05"=0.19 pc, where the observedvelocity dispersion is σ=674+/-95 km s-1. Thecorresponding circular rotation velocity at this radius is ~1700 kms-1. We therefore confirm earlier suggestions that thecentral dark object interpreted as a supermassive black hole is locatedin P3.Thin-disk and Schwarzschild models with intrinsic axial ratiosb/a<~0.26 corresponding to inclinations between 55° and 58°match the P3 observations very well. Among these models, the best fitand the lowest black hole mass are obtained for a thin-disk model withM•=1.4×108 Msolar. AllowingP3 to have some intrinsic thickness and considering possible systematicerrors, the 1 σ confidence range becomes(1.1-2.3)×108 Msolar. The black hole massdetermined from P3 is independent of but consistent with Peiris &Tremaine's mass estimate based on the eccentric disk model for P1+P2. Itis ~2 times larger than the prediction by the correlation betweenM• and bulge velocity dispersionσbulge. Taken together with other reliable black holemass determinations in nearby galaxies, notably the Milky Way and M32,this strengthens the evidence that theM•-σbulge relation has significantintrinsic scatter, at least at low black hole masses.We show that any dark star cluster alternative to a black hole must havea half-mass radius <~0.03"=0.11 pc in order to match theobservations. Based on this, M31 becomes the third galaxy (after NGC4258 and our Galaxy) in which clusters of brown dwarf stars or deadstars can be excluded on astrophysical grounds.
| 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}
| Formation and evolution of S0 galaxies: a SAURON case study of NGC 7332
We present SAURON integral-field observations of the S0 galaxy NGC7332. Existing broad-band ground-based and Hubble Space Telescope (HST)photometry reveals a double-disc structure and a boxy bulge interpretedas a bar viewed close to edge-on. The SAURON two-dimensional stellarkinematic maps confirm the existence of the bar and inner disc but alsouncover the presence of a cold counter-rotating stellar component withinthe central 250 pc. The Hβ and [O III] emission line maps show thatthe ionized gas has a complex morphology and kinematics, including botha component counter-rotating with respect to the stars and a faintercorotating one. Analysis of the absorption line-strength maps show thatNGC 7332 is young everywhere. The presence of a large-scale bar canexplain most of those properties, but the fact that we see a significantamount of unsettled gas, together with a few peculiar features in themaps, suggests that NGC 7332 is still evolving. Interactions as well asbar-driven processes must thus have played an important role in theformation and evolution of NGC 7332, and presumably of S0 galaxies ingeneral.
| 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.
| Hubble Space Telescope Observations of NGC 6240: A Case Study of an Ultraluminous Infrared Galaxy with Obscured Activity
We present results from a Hubble Space Telescope (HST) study of themorphology and kinematics of NGC 6240. This merging galaxy with a doublenucleus is one of the nearest and best-studied ultraluminous infraredgalaxies. HST resolves both nuclei into separate components. Thedistance between the northern and southern optical/near-infraredcomponents is greater than that observed in radio and X-ray studies,arguing that even in K band we may not be seeing all the way through thedust to the true nuclei. The ionized gas does not display rotationaround either of the nuclei, or equilibrium motion in general. There isa strong velocity gradient between the nuclei, similar to what is seenin CO data. There is no such gradient in our stellar kinematics. Thevelocity dispersion of the gas is larger than expected for a cold disk.We also map and model the emission-line velocity field at an off-nuclearposition where a steep velocity gradient was previously detected inground-based data. Overall, the data indicate that line-of-sightprojection effects, dust absorption, nonequilibrium merger dynamics, andthe possible influence of a wind may be playing an important role in theobserved kinematics. Chandra observations of hard X-rays have shown thatboth of the nuclei contain an active galactic nucleus (AGN). The HSTdata show no clear sign of the two AGNs: neither continuum nornarrowband imaging shows evidence for unresolved components in thenuclei, and there are no increased emission line widths or rapidrotation near the nuclei. This underscores the importance of X-ray datafor identifying AGNs in highly dust-enshrouded environments.
| The Compact H II Region S88B: Excitation and Extinction
We have undertaken an investigation into the excitation of, and dustextinction to, the massive star formation region S88B. Studying stellarproperties of the wide-field Two Micron All Sky Survey (2MASS) J (1.23μm), H (1.65 μm), and Ks (2.16 μm) images, we havedetermined the extent of, and extinction to, the molecular cloudassociated with the ultracompact H II regions S88B-1 and S88B-2 and witha newly described infrared H II region. Infrared observations ofBrγ and Brα hydrogen recombination lines provide extinctionmaps to the infrared H II region, and 3.3 and 3.4 μm images show thepolycyclic aromatic hydrocarbon (PAH) emission distribution. We alsoreport the detection of an infrared counterpart to S88B-2.
| High-Precision Near-Infrared Photometry of a Large Sample of Bright Stars Visible from the Northern Hemisphere
We present the results of 8 yr of infrared photometric monitoring of alarge sample of stars visible from Teide Observatory (Tenerife, CanaryIslands). The final archive is made up of 10,949 photometric measuresthrough a standard InSb single-channel photometer system, principally inJHK, although some stars have measures in L'. The core of this list ofstars is the standard-star list developed for the Carlos SánchezTelescope. A total of 298 stars have been observed on at least twooccasions on a system carefully linked to the zero point defined byVega. We present high-precision photometry for these stars. The medianuncertainty in magnitude for stars with a minimum of four observationsand thus reliable statistics ranges from 0.0038 mag in J to 0.0033 magin K. Many of these stars are faint enough to be observable with arraydetectors (42 are K>8) and thus to permit a linkage of the bright andfaint infrared photometric systems. We also present photometry of anadditional 25 stars for which the original measures are no longeravailable, plus photometry in L' and/or M of 36 stars from the mainlist. We calculate the mean infrared colors of main-sequence stars fromA0 V to K5 V and show that the locus of the H-K color is linearlycorrelated with J-H. The rms dispersion in the correlation between J-Hand H-K is 0.0073 mag. We use the relationship to interpolate colors forall subclasses from A0 V to K5 V. We find that K and M main-sequence andgiant stars can be separated on the color-color diagram withhigh-precision near-infrared photometry and thus that photometry canallow us to identify potential mistakes in luminosity classclassification.
| 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.
| JHK Standards for Small Telescopes
The AAVSO Futures meeting, held in Madison, WI, in May 2001, proposedthat the AAVSO support near-infrared research with small telescopes. Aphotometer, the SSP-4, has been developed to provide J- and H-bandcapability for a reasonable cost. However, proper calibrated photometryrequires a set of standard stars. This paper describes such a set ofstars, suitable for small telescopes, and with accurate coordinates,proper motions, and high-quality magnitudes.
| 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.
| 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.
| Absolute spectrophotometry of late-type stars.
Not Available
| The chemical composition of the red giant η Ser
The paper presents the results of an analysis of elemental abundances inthe atmosphere of η Sera red giant of spectral typeK2IIIabCN1, according to Hoffleit and Jaschek [4]. The resultingatmospheric parameters correspond to a K0 giant, and the peculiaritiesof the star’s chemical composition provide evidence that theassignment of η Ser to the class of CN stars was erroneous.
| A Comparative Analysis of Chemical Abundances in the Atmospheres of Red Giants of Different Age Groups
We analyze previously published chemical abundances in the atmospheresof red giants. Excess abundances are observed not only for Na, but alsofor Al and Si, with the overabundances increasing with the stars’luminosity. The observed anomalies provide evidence that, in addition tothe CNO hydrogen-burning cycle, the Mg-Al and Ne-Na cycles operate inthe interiors of main-sequence stars; their products are brought to thestellar atmospheres by convection after the transition to the red-giantphase. The abundance anomalies for s-process elements, also observed inthe atmospheres of field stars, testify to the presence of a substantialnumber of neutrons. The s-process abundance anomalies are absent fromgiants of the young Hyades cluster.
| The Nuclear Dynamics of M32. I. Data and Stellar Kinematics
We have obtained optical long-slit spectroscopy of the nucleus of M32using the Space Telescope Imaging Spectrograph aboard the Hubble SpaceTelescope. The stellar rotation velocity and velocity dispersion, aswell as the full line-of-sight velocity distribution (LOSVD), weredetermined as a function of position along the slit using twoindependent spectral deconvolution algorithms. We see three clearkinematical signatures of the nuclear black hole: a sudden upturn, at~0.3" from the center, in the stellar velocity dispersions; a flat orrising rotation curve into the center; and strong, non-Gaussian wings onthe central LOSVD. The central velocity dispersion is ~130 kms-1 (Gaussian fit) or >~175 km s-1 (correctedfor the wings). The central kinematics are consistent with the presenceof a supermassive compact object in M32 with a mass in the range(2-4)×106 Msolar. Based on observations withthe NASA/ESA Hubble Space Telescope, obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.
| Evidence of a Supermassive Black Hole in the Galaxy NGC 1023 from the Nuclear Stellar Dynamics
We analyze the nuclear stellar dynamics of the SB0 galaxy NGC 1023,utilizing observational data both from the Space Telescope ImagingSpectrograph aboard the Hubble Space Telescope and from the ground. Thestellar kinematics measured from these long-slit spectra show rapidrotation (V~70 km s-1 at a distance of 0.1"=4.9 pc from thenucleus) and increasing velocity dispersion toward the nucleus (whereσ=295+/-30 km s-1). We model the observed stellarkinematics assuming an axisymmetric mass distribution with both two andthree integrals of motion. Both modeling techniques point to thepresence of a central dark compact mass (which presumably is asupermassive black hole) with confidence greater than 99%. The isotropictwo-integral models yield a best-fitting black hole mass of(6.0+/-1.4)×107 Msolar and mass-to-lightratio (M/LV) of 5.38+/-0.08, and the goodness of fit(χ2) is insensitive to reasonable values for the galaxy'sinclination. The three-integral models, which nonparametrically fit theobserved line-of-sight velocity distribution as a function of positionin the galaxy, suggest a black hole mass of(3.9+/-0.4)×107 Msolar and M/LVof 5.56+/-0.02 (internal errors), and the edge-on models are vastlysuperior fits over models at other inclinations. The internal dynamicsin NGC 1023 as suggested by our best-fit three-integral model shows thatthe velocity distribution function at the nucleus is tangentiallyanisotropic, suggesting the presence of a nuclear stellar disk. Thenuclear line-of-sight velocity distribution has enhanced wings atvelocities >=600 km s-1 from systemic, suggesting thatperhaps we have detected a group of stars very close to the central darkmass. Based on observations with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc. (AURA),under NASA contract NAS 5-26555.
| M33: A Galaxy with No Supermassive Black Hole
Galaxies that contain bulges appear to contain central black holes whosemasses correlate with the velocity dispersion of the bulge. We show thatno corresponding relationship applies in the pure disk galaxy M33.Three-integral dynamical models fit Hubble Space Telescope WFPC2photometry and Space Telescope Imaging Spectrograph spectroscopy best ifthe central black hole mass is zero. The upper limit is 1500Msolar. This is significantly below the mass expected fromthe velocity dispersion of the nucleus and far below any mass predictedfrom the disk kinematics. Our results suggest that supermassive blackholes are associated only with galaxy bulges and not with their disks.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| 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.
| The M 31 double nucleus probed with OASIS. A natural vec m = 1 mode?
We present observations with the adaptive optics assisted integral fieldspectrograph OASIS of the M 31 double nucleus in the spectral domainaround the Calcium triplet at a spatial resolution better than 0farcs5FWHM. These data are used to derive the two-dimensional stellarkinematics within the central 2 arcsec. Archival WFPC2/HST images in theF300W, F555W and F814W bands are revisited to perform a photometricdecomposition of the nuclear region. We also present STIS/HST kinematicsobtained from the archive. The luminosity distribution of the centralregion is well separated into the respective contributions of the bulge,the nucleus including P1 and P2, and the so-called UV peak. We thenshow, using the OASIS kinematical maps, that the axis joining P1 and P2,the two local surface brightness maxima, does not coincide with thekinematic major-axis, which is also the major-axis of the nuclearisophotes (excluding P1). We also confirm that the velocity dispersionpeak is offset by ~ 0farcs2 from the UV peak, assumed to mark thelocation of the supermassive black hole. The newly reduced STIS/HSTvelocity and dispersion profiles are then compared to OASIS and otherpublished kinematics. We find significant offsets with previouslypublished data. Simple parametric models are then built to successfullyreconcile all the available kinematics. We finally interpret theobservations using new N-body simulations. The nearly Keplerian nucleardisk of M 31 is subject to a natural m=1 mode, with a very slow patternspeed (3 km s-1/pc for MBH = 7 107Msun), that can be maintained during more than a thousanddynamical times. The resulting morphology and kinematics of the mode canreproduce the M 31 nuclear-disk photometry and mean stellar velocity,including the observed asymmetries. It requires a central massconcentration and a cold disk system representing between 20 and 40% ofits mass. Such a slow mode could be excited when interstellar cloudsfrom the more external gaseous disk infall towards the centre. Nucleardisks formed from accreted gas are possible candidates for theprecursors of these types of structures, and may be common in centralregions of galaxies. Based on observations collected at theCanada-France-Hawaii Telescope, operated by the National ResearchCouncil of Canada, the Centre National de la Recherche Scientifique ofFrance, and the University of Hawaii.} and HST
| 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
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is 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/367/297
| 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
| Cyclic variations in the angular diameter of χ Cygni
We report the direct detection of cyclic diameter variations in the Miravariable χ Cygni. Interferometric observations made between 1997July and 1999 September, using the Cambridge Optical Aperture SynthesisTelescope (COAST) and the William Herschel Telescope (WHT), indicateperiodic changes in the apparent angular diameter at a wavelength of905nm, with amplitude 45per cent of the smallest value. The star appearslargest at minimum light. Measurements made at a wavelength of 1.3μmover the same period suggest much smaller size changes. This behaviouris consistent with a model in which most of the apparent diametervariation at 905nm is caused by a large increase in the opacity of theouter atmospheric layers (which is mostly owing to titanium oxide) nearminimum light, rather than by physical motions of the photosphere. The1.3-μm waveband is relatively uncontaminated by TiO, and so muchsmaller size changes would be expected in this band. The latestnon-linear pulsational models predict maximum physical size close tomaximum light, and increases in opacity near minimum light that are toosmall to reproduce the diameter variation seen at 905nm. This suggestseither that the phase-dependence of the model pulsation is incorrect, orthat the opacities in the models are underestimated. Futureinterferometric monitoring in uncontaminated near-infrared wavebandsshould resolve this question.
| K-Band Calibration of the Red Clump Luminosity
The average near-infrared (K-band) luminosity of 238 Hipparcos red clumpgiants is derived and then used to measure the distance to the Galacticcenter. These Hipparcos red clump giants have been previously employedas I-band standard candles. The advantage of the K-band is a decreasedsensitivity to reddening and perhaps a reduced systematic dependence onmetallicity. In order to investigate the latter, and also to refer ourcalibration to a known metallicity zero point, we restrict our sample ofred clump calibrators to those with abundances derived fromhigh-resolution spectroscopic data. The mean metallicity of the sampleis [Fe/H]=-0.18 dex (σ=0.17 dex). The data are consistent with nocorrelation between MK and [Fe/H] and only weakly constrainthe slope of this relation. The luminosity function of the sample peaksat MK=-1.61+/-0.03 mag. Next, we assemble published opticaland near-infrared photometry for ~20 red clump giants in a Baade'swindow field with a mean metallicity of [Fe/H]=-0.17+/-0.09 dex, whichis nearly identical to that of the Hipparcos red clump. Assuming thatthe average (V-I)0 and (V-K)0 colors of these twored clumps are the same, the extinctions in the Baade's window field arefound to be AV=1.56, AI=0.87, andAK=0.15, in agreement with previous estimates. We derive thedistance to the Galactic center: (m-M)0=14.58+/-0.11 mag, orR=8.24+/-0.42 kpc. The uncertainty in this distance measurement isdominated by the small number of Baade's window red clump giantsexamined here.
| Rotation and lithium in single giant stars
In the present work, we study the link between rotation and lithiumabundance in giant stars of luminosity class III, on the basis of alarge sample of 309 single stars of spectral type F, G and K. We havefound a trend for a link between the discontinuity in rotation at thespectral type G0III and the behavior of lithium abundances around thesame spectral type. The present work also shows that giant starspresenting the highest lithium contents, typically stars earlier thanG0III, are those with the highest rotation rates, pointing for adependence of lithium content on rotation, as observed for otherluminosity classes. Giant stars later than G0III present, as a rule, thelowest rotation rates and lithium contents. A large spread of about fivemagnitudes in lithium abundance is observed for the slow rotators.Finally, single giant stars with masses 1.5 < M/Msun<=2.5 show a clearest trend for a correlation between rotational velocityand lithium abundance. Based on observations collected at theObservatoire de Haute -- Provence (France) and at the European SouthernObservatory, La Silla (Chile). Table 2 is only available electronicallywith the On-Line publication athttp://link.springer.de/link/service/00230/
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| Takýmyýldýz: | Kugu |
| Sað Açýklýk: | 19h56m18.40s |
| Yükselim: | +35°05'00.0" |
| Görünürdeki Parlaklýk: | 3.89 |
| Uzaklýk: | 42.735 parsek |
| özdevim Sað Açýklýk: | -33.9 |
| özdevim Yükselim: | -27.7 |
| B-T magnitude: | 5.189 |
| V-T magnitude: | 4.008 |
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