Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Atlas and Catalog of Dark Clouds Based on Digitized Sky Survey I
We present a quantitative atlas and catalog of dark clouds derived byusing the optical database ``Digitized Sky Survey I''. Applying atraditional star-count technique to 1043 plates contained in thedatabase, we produced an AV map covering the entire region inthe galactic latitude range |b| ≤ 40°. The map was drawn at twodifferent angular resolutions of 6' and 18', and is shown in detail in aseries of figures in this paper. Based on the AV map, weidentified 2448 dark clouds and 2841 clumps located inside them. Somephysical parameters, such as the position, extent, and opticalextinction, were measured for each of the clouds and clumps. We alsosearched for counterparts among already known dark clouds in theliterature. The catalog of dark clouds presented in this paper lists thecloud parameters as well as the counterparts.
| The sub-arcsecond dusty environment of Eta Carinae
The core of the nebula surrounding Eta Carinae has been observed withthe VLT Adaptive Optics system NACO and with the interferometerVLTI/MIDI to constrain spatially and spectrally the warm dustyenvironment and the central object. In particular, narrow-band images at3.74 μm and 4.05 μm reveal the butterfly shaped dusty environmentclose to the central star with unprecedented spatial resolution. A voidwhose radius corresponds to the expected sublimation radius has beendiscovered around the central source. Fringes have been obtained in theMid-IR which reveal a correlated flux of about 100 Jy situated 0.3arcsec south-east of the photocenter of the nebula at 8.7 μm, whichcorresponds with the location of the star as seen in other wavelengths.This correlated flux is partly attributed to the central object, andthese observations provide an upper limit for the SED of the centralsource from 2.2 μm to 13.5 μm. Moreover, we have been able tospectrally disperse the signal from the nebula itself at PA = 318degree, i.e. in the direction of the bipolar nebula (~310°) withinthe MIDI field of view of 3 arcsec. A large amount of corundum (Al2O3)is discovered, peaking at 0.6 arcsec-1.2 arcsec south-east from thestar, whereas the dust content of the Weigelt blobs is dominated bysilicates. We discuss the mechanisms of dust formation which are closelyrelated to the geometry of this Butterfly nebulae.
| The mid-IR spatially resolved environment of OH 26.5+0.6 at maximum luminosity
We present observations of the famous OH/IR star OH 26.5+0.6 obtainedusing the Mid-Infrared Interferometric Instrument MIDI at the EuropeanSouthern Observatory (ESO) Very Large Telescope Interferometer VLTI.Emission of the dusty envelope, spectrally dispersed at a resolution of30 from 8 μm to 13.5 μm, appears resolved by a single dish UTtelescope. In particular the angular diameter increases strongly withinthe silicate absorption band. Moreover an acquisition image taken at 8.7μm exhibits, after deconvolution, a strong asymmetry. The axis ratiois 0.75±0.07 with the FWHM of the major and minor axis which are286 mas and 214 mas respectively. The measured PA angle, 95°±6°, is reminiscent of the asymmetry in the OH maser emissiondetected at 1612 MHz. In interferometric mode the UT1-UT3 102 m baselinewas employed to detect the presence of the star. No fringes were foundwith a detection threshold estimated to be about 1% of the total flux ofthe source, i.e. 5-8 Jy. These observations were carried out during themaximum luminosity phase of the star, when the dust shell is morediluted and therefore the chance to detect the central source maximized.We modeled the dusty environment based on the work of Justtanont et al.(1996). In particular, the failure to detect fringes provides strongconstraints on the opacities in the inner regions of the dust shell orin the close vicinity of the star.
| First VLTI/MIDI observations of a Be star: Alpha Arae
We present the first VLTI/MIDI observations of the Be star alpha Ara (HD158 427), showing a nearly unresolved circumstellar disk in the N band.The interferometric measurements made use of the UT1 and UT3 telescopes.The projected baselines were 102 and 74 meters with position angles of 7° and 55°, respectively. These measurements put an upper limiton the envelope size in the N band under the uniform disk approximationof φmax= 4±1.5 mas, corresponding to 14R*, assuming R*=4.8 Rȯ and theHipparcos distance of 74 pc. On the other hand the disk density must belarge enough to produce the observed strong Balmer line emission. Inorder to estimate the possible circumstellar and stellar parameters wehave used the SIMECA code developed by Stee et al. (1995, A&A, 300,219) and Stee & Bittar (2001, A&A, 367, 532). Optical spectrataken with the échelle instrument Heros and the ESO-50 cmtelescope, as well as infrared ones from the 1.6m Brazilian telescopewere used together with the MIDI spectra and visibilities. Theseobservations place complementary constraints on the density and geometryof the alpha Ara circumstellar disk. We discuss the potential truncationof the disk by a companion and we present spectroscopic indications of aperiodic perturbation of some Balmer lines.
| First results from the ESO VLTI calibrators program
The ESO Very Large Telescope Interferometer (VLTI) is one of the leadinginterferometric facilities. It is equipped with several 8.2 and 1.8 mtelescopes, a large number of baselines up to 200 m, and with severalsubsystems designed to enable high quality measurements and to improvesignificantly the limits of sensitivities currently available tolong-baseline interferometry. The full scientific potential of the VLTIcan be exploited only if a consistent set of good quality calibrators isavailable. For this, a large number of observations of potentialcalibrators have been obtained during the commissioning phase of theVLTI. These data are publicly available. We briefly describe theinterferometer, the VINCI instrument used for the observations, the dataflow from acquisition to processed results, and we present and commenton the volume of observations gathered and scrutinized. The result is alist of 191 calibrator candidates, for which a total of 12 066observations can be deemed of satisfactory quality. We present a generalstatistical analysis of this sample, using as a starting point theangular diameters previously available in the literature. We derive thegeneral characteristics of the VLTI transfer function, and its trendwith time in the period 2001 through mid-2004. A second paper will bedevoted to a detailed investigation of a selected sample, aimed atestablishing a VLTI-based homogeneous system of calibrators.
| Mid-infrared interferometry of the Mira variable RR Sco with the VLTI MIDI instrument
We present the results of the first mid-infrared interferometricobservations of the Mira variable RR Sco with the MID-infraredInterferometer (MIDI) coupled to the European Southern Observatory's(ESO) Very Large Telescope Interferometer (VLTI), together with K-bandobservations using VLTI VINCI. The observations were carried out in June2003, when the variability phase of the object was 0.6, using two unittelescopes (UT1 and UT3), as part of the Science Demonstration Time(SDT) program of the instrument. Projected baseline lengths ranged from73 to 102 m, and a spectral resolution of 30 was employed in theobservations, which enabled us to obtain the wavelength dependence ofthe visibility in the region between 8 and 13 μm. The uniform-diskdiameter was found to be 18 mas between 8 and 10 μm, while itgradually increases at wavelengths longer than 10 μm to reach 24 masat 13 μm. The uniform-disk diameter between 8 and 13 μm issignificantly larger than the K-band uniform-disk diameter of 10.2± 0.5 mas measured using VLTI VINCI with projected baselinelengths of 15-16 m, three weeks after the MIDI observations. Our modelcalculations show that optically thick emission from a warm molecularenvelope consisting of H2O and SiO can cause the apparent mid-infrared diameter to be much larger than the continuum diameter. Wefind that the warm molecular envelope model extending to 2.3R\star with a temperature of 1400 K and column densitiesof H2O and SiO of 3 × 1021 cm-2and 1 × 1020 cm-2, respectively, canreproduce the observed uniform-disk diameters between 8 and 10 μm.The observed increase of the uniform-disk diameter longward of 10 μmcan be explained by an optically thin dust shell consisting of silicateand corundum grains. The inner radius of the optically thin dust shellis derived to be 7-8 R\star with a temperature of 700 K,and the optical depth at 10 μm is found to be 0.025.Based on observations made with the Very Large Telescope Interferometerof the European Southern Observatory.
| High-Resolution Imaging of Dust Shells by Using Keck Aperture Masking and the IOTA Interferometer
We present first results of an experiment to combine data from Keckaperture masking and the Infrared-Optical Telescope Array to image thecircumstellar environments of evolved stars with ~20 mas resolution. Theunique combination of excellent Fourier coverage at short baselines andhigh-quality long-baseline fringe data allows us to determine thelocation and clumpiness of the innermost hot dust in the envelopes andto measure the diameters of the underlying stars themselves. We findevidence for large-scale inhomogeneities in some dust shells and alsosignificant deviations from uniform brightness for the photospheres ofthe most evolved M stars. Deviations from spherically symmetric massloss in the red supergiant NML Cyg could be related to recent evidencefor dynamically important magnetic fields and/or stellar rotation. Wepoint out that dust shell asymmetries, like those observed here, canqualitatively explain the difficulty recent workers have had insimultaneously fitting the broadband spectral energy distributions andhigh-resolution spatial information, without invoking unusual dustproperties or multiple distinct shells (from hypothetical``superwinds''). This paper is the first to combine opticalinterferometry data from multiple facilities for imaging, and we discussthe challenges and potential for the future of this method, givencurrent calibration and software limitations.
| Mid-infrared sizes of circumstellar disks around Herbig Ae/Be stars measured with MIDI on the VLTI
We present the first long baseline mid-infrared interferometricobservations of the circumstellar disks surrounding Herbig Ae/Be stars.The observations were obtained using the mid-infrared interferometricinstrument MIDI at the European Southern Observatory (ESO) Very LargeTelescope Interferometer VLTI on Cerro Paranal. The 102 m baseline givenby the telescopes UT1 and UT3 was employed, which provides a maximumfull spatial resolution of 20 milli-arcsec (mas) at a wavelength of 10μm. The interferometric signal was spectrally dispersed at aresolution of 30, giving spectrally resolved visibility information from8 μm to 13.5 μm. We observed seven nearby Herbig Ae/Be stars andresolved all objects. The warm dust disk of HD 100546 could even beresolved in single-telescope imaging. Characteristic dimensions of theemitting regions at 10 μm are found to be from 1 AU to 10 AU. The 10μm sizes of our sample stars correlate with the slope of the 10-25μm infrared spectrum in the sense that the reddest objects are thelargest ones. Such a correlation would be consistent with a differentgeometry in terms of flaring or flat (self-shadowed) disks for sourceswith strong or moderate mid-infrared excess, respectively. We comparethe observed spectrally resolved visibilities with predictions based onexisting models of passive centrally irradiated hydrostatic disks madeto fit the SEDs of the observed stars. We find broad qualitativeagreement of the spectral shape of visibilities corresponding to thesemodels with our observations. Quantitatively, there are discrepanciesthat show the need for a next step in modelling of circumstellar disks,satisfying both the spatial constraints such as are now available fromthe MIDI observations and the flux constraints from the SEDs in aconsistent way.Based on observations made with the Very Large Telescope Interferometerat Paranal Observatory.
| 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
| High-Precision Radial Velocity Measurements of Some Southern Stars
Precise absolute radial velocities have been obtained at Mount JohnUniversity Observatory for a number of southern stars, using the 1 mtelescope and fiber-fed echelle spectrograph. Only the stars that havebeen observed three or more times are presented, including 14 IAUstandards and 11 program stars. Six echelle orders in the green(5000-5600 Å) are used. Many delicate steps have been undertakenin order to maintain the same conditions in both recording and reducingthe spectra over a period of 27 months. The Th-Ar lamp has been used forthe wavelength calibration. The absolute radial velocities have beendetermined by cross-correlation with synthetic spectra computed by R. L.Kurucz. The zero point has been adjusted using blue-sky spectra. Anadditional strong correlation, between the measured velocities andphoton counts in stellar and Th-Ar spectra, has been detected for thePM3000 CCD camera and has been eliminated. A resulting precision ofabout 20-30 m s-1 has been obtained. The overall uncertaintyof the absolute radial velocities was estimated to be about 100-200 ms-1. The present paper is a continuation of our recentprevious work, including more details on the reduction process and thepresentation of the radial velocities for more stars.
| Magnitudes absolues des étoiles standards MK des types G à M à partir des parallaxes Hipparcos. The absolute magnitudes of the G to M type MK standards from the Hipparcos parallaxes
We analyse a sample of about 500 MK standards of cool spectral types (Gto M) for to compare the visual absolute magnitudes obtained from bothHipparcos data and Schmidt-Kaler calibrations. Our purpose is tovalidate our spectroscopic work \cite[(Ginestet et al. 1997, 1999)]{G97}on stars with composite spectra with the help of Hipparcos data.Contrary to what is claimed in other papers, the absolute magnitudedomain devoted to the giant stars does not overlap the domain of dwarfs.We find that the discrepancies between absolute magnitudes fromHipparcos data and absolute magnitudes deduced from Schmidt-Kalercalibrations increase with the relative error sigma (pi )/pi on theparallaxes. So, for sigma (pi )/pi <= 0.05 only 3% of the starspresent a discrepancy of one luminosity class, while this percentagereaches 54% for 0.25 < sigma (pi )/pi <= 0.50. Curiously, theluminosity of the giants seems to increase with the distance of thestars, whereas the supergiants of the sample appear underluminous atleast for d < 600 pc! We point out a list of 14 MK standards whoseluminosity classes may be erroneous and need a new spectralclassification, in the near infrared. The case of composite-spectrumbinaries is also discussed. Most of these are too distant for accurateparallaxes even with Hipparcos: only sixteen stars have sigma (pi )/pi<= 0.10; for these, we give new spectral classifications in agreementwith both our classifications in the near infrared of the coolcomponents and Hipparcos data. Finally, for stars having high-precisionparallaxes (sigma (pi )/pi <= 5%) there is no serious problem forSchmidt-Kaler calibrations whith respect to Hipparcos data. The datacorresponding to parallaxes of lower precisions should be used withcaution and only for statistical analyses.
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Wilson-Bappu effect of the MgII K line - dependence on stellar temperature, activity and metallicity
The Wilson-Bappu effect is investigated using accurate absolutemagnitudes of 65 stars obtained through early release of data from theHipparcos satellite together with MgII k line widths determined fromhigh resolution spectra observed with the International UltravioletExplorer (IUE) observatory. Stars of spectral classes F, G, K and M andluminosity classes I-V are represented in the sample. Wilson-Bappurelations for the Mg II k line for stars of different temperatures i.e.spectral classes are determined. The relation varies with spectral classand there is a significant scatter of the line widths around theregression lines. The sample contains slowly rotating stars of differentactivity levels and is suitable for investigations of a possiblerelation between line width and stellar activity. A difference inbehavior between dwarfs and giants (and supergiants) of spectral class Kseems to be present. Magnetic activity affects the width of the Mg II kline in dwarfs. Metallicity is found to influence the Mg II k line widthin giants and supergiants. Possible interpretations of the new resultsare briefly discussed.
| Recalibration of the Wilson-Bappu Effect Using the Singly Ionized Magnesium K Line
A new calibration of the Wilson-Bappu effect is presented using datafrom a survey of the singly ionized magnesium (Mg ii) h and k lines(near 280 nm) taken from the archives of the International UltravioletExplorer satellite. Our sample consisted of 94 stars with absolutemagnitudes derived from parallaxes reported from Hipparcos. We describethe dependencies of the base widths, peak widths, and full widths athalf-maximum (FWHM) on the fundamental stellar parameters T_eff,metallicity, log g, and activity.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| RV Tauri stars - II. A spectroscopic study
A long-term photometric and spectroscopic survey of eleven RV Tauristars has been undertaken with a view to obtaining a betterunderstanding of the nature of these pulsating variables. Pollard et al.presented the results from the long-term multicolour photometric survey.This paper presents the contemporaneous moderate- to high-resolutionspectroscopy of these stars. All the RV Tauri stars in our sampledisplay, or are consistent with, two shock waves propagating in theiratmospheres per `formal' period (the time between successive deepminima). This is consistent with the few previous high-resolutionspectroscopic studies of the three brightest RV Tauri stars: R Sct, UMon and AC Her. Specifically, the Hα profiles exhibit twoenhancements of emission per cycle following the passage of the primaryand secondary shock waves through the photosphere around phases 0.1 and0.6. Metallic lines showed `doubled' profiles characteristic of anatmospheric shock wave around these phases, with evidence of two radialvelocity cycles per formal period. In the RVb-type stars, an additionalcontribution to the Hα emission is seen and this appears to becorrelated with the long-term period. Two stars, AI Sco and IW Car,display extended blueward Hα absorption which may arise from massoutflow. Evidence of long-term radial velocity variations is also seenin a number of the RVb stars.
| The radial velocity variations of cool hydrogen-deficient carbon stars
We have obtained a series of radial velocities for many of the brightgalactic R Coronae Borealis (RCB) and hydrogen-deficient carbon (HdC)stars, in order to characterize the pulsations of these types of coolhydrogen-deficient carbon stars. By comparing these velocities with theresults of long-term photometric monitoring, we investigate thepulsation properties of these objects, the link between pulsations andmass loss, and the relationship between these stars and the higher-T_effhydrogen-deficient stars, the extreme helium (eHe) stars. We find thatmost of the RCB stars have radial velocity and V light amplitudes of10-20kms^-1 and 0.2-0.3 mag, respectively. Pulsationally more-activestars such as RY Sgr are rare. Only one other RCB star, RT Nor, has asimilar photometric amplitude to RY Sgr, but this star has a much lowerradial velocity amplitude. With only one exception, HD 175893, all ofthe HdC stars have a lower pulsation amplitude than the RCB stars. Sincethe RCB and HdC stars appear to be distinguished by the large-amplitudedeclines and infrared excesses of the RCB stars, we suggest that thepulsation amplitude dictates whether significant mass loss occurs inthese objects. The radial velocity-to-light amplitude (RV/V) ratioappears to be temperature dependent, but we suspect that this is not anintrinsic effect. The 7000-K group of RCB stars haveRV/V~50kms^-1mag^-1, which is similar to radially pulsating Cepheids.The similar pulsation properties of the RCB and HdC stars and the coolereHe stars provide further evidence that these types of stars are closelyrelated.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Barium stars, galactic populations and evolution.
In this paper HIPPARCOS astrometric and kinematical data together withradial velocities from other sources are used to calibrate bothluminosity and kinematics parameters of Ba stars and to classify them.We confirm the results of our previous paper (where we used data fromthe HIPPARCOS Input Catalogue), and show that Ba stars are aninhomogeneous group. Five distinct classes have been found i.e. somehalo stars and four groups belonging to disk population: roughlysuper-giants, two groups of giants (one on the giant branch, the otherat the clump location) and dwarfs, with a few subgiants mixed with them.The confirmed or suspected duplicity, the variability and the range ofknown orbital periods found in each group give coherent resultssupporting the scenario for Ba stars that are not too highly massivebinary stars in any evolutionary stages but that all were previouslyenriched with Ba from a more evolved companion. The presence in thesample of a certain number of ``false'' Ba stars is confirmed. Theestimates of age and mass are compatible with models for stars with astrong Ba anomaly. The mild Ba stars with an estimated mass higher than3Msun_ may be either stars Ba enriched by themselves or``true'' Ba stars, which imposes new constraints on models.
| Stellar activity and the Wilson-Bappu relation.
The MgII h and k lines of 78 single stars observed with theInternational Ultraviolet Explorer (IUE) observatory have been analyzed.Stars of spectral classes F, G, K and M and luminosity classes I-V arerepresented in the sample. From these data it is shown that theWilson-Bappu relation for the Mg II h and k lines is fulfilled over arange of 18 magnitudes, i.e. from M_v_=+12 to M_v_=-6. The samplecontains slowly rotating stars of different activity levels and issuitable for investigations of a possible relation between line widthand stellar activity. It is found that active stars have broader linesand show a larger variation in line widths than quiet stars.Observations of the active RS CVn binary σ Gem taken at epochswhen it shows different levels of activity, clearly demonstrate linebroadening following higher activity. Possible implications of the newresults for the interpretation of the Wilson-Bappu relation are brieflydiscussed.
| Absolute magnitudes and kinematics of barium stars.
The absolute magnitude of barium stars has been obtained fromkinematical data using a new algorithm based on the maximum-likelihoodprinciple. The method allows to separate a sample into groupscharacterized by different mean absolute magnitudes, kinematics andz-scale heights. It also takes into account, simultaneously, thecensorship in the sample and the errors on the observables. The methodhas been applied to a sample of 318 barium stars. Four groups have beendetected. Three of them show a kinematical behaviour corresponding todisk population stars. The fourth group contains stars with halokinematics. The luminosities of the disk population groups spread alarge range. The intrinsically brightest one (M_v_=-1.5mag,σ_M_=0.5mag) seems to be an inhomogeneous group containing bariumbinaries as well as AGB single stars. The most numerous group (about 150stars) has a mean absolute magnitude corresponding to stars in the redgiant branch (M_v_=0.9mag, σ_M_=0.8mag). The third group containsbarium dwarfs, the obtained mean absolute magnitude is characteristic ofstars on the main sequence or on the subgiant branch (M_v_=3.3mag,σ_M_=0.5mag). The obtained mean luminosities as well as thekinematical results are compatible with an evolutionary link betweenbarium dwarfs and classical barium giants. The highly luminous group isnot linked with these last two groups. More high-resolutionspectroscopic data will be necessary in order to better discriminatebetween barium and non-barium stars.
| The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NM
A spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%.
| The Stromlo-APM Redshift Survey. IV. The Redshift Catalog
The Stromlo-APM Redshift Survey consists of 1797 galaxies with b_J_ <17.15 selected randomly at a rate of 1 in 20 from automated platemeasurement (APM) scans. The survey covers a solid angle of 1.3 sr (4300deg^2^) in the south Galactic cap. Redshifts have been measured for 1790(99.6%) of the galaxies. The median galaxy recession velocity is 15,300km s^-1^, and so the volume probed is V ~ 1.38 x 10^6^ h^-3^ Mpc^3^. Inthis paper we describe the construction of the redshift catalog andpresent the survey data.
| K Giants in 47 Tucanae: Detection of a New Class of Variable Stars
We report the discovery of variability among K giants in the globularcluster 47 Tucanae, using a time series of U exposures with the HubbleSpace Telescope. The variables lie along a narrow band in thecolor-magnitude diagram, joining the faint end of the asymptotic giantbranch to the red giant branch. The variations, if coherent, mostly haveperiods between ~2 and ~4 days, consistent with low-overtone radialpulsation or nonradial pulsation, and V amplitudes in the range 5--15mmag, which explains their nondetection so far in clusters. One of thevariables may have a period of 1.1 days and a V amplitude of 5.3 mmag.These stars define a new class of variable stars and probably containvariable field K giants such as alpha Boo as members. An understandingof their variations may have significant ramifications for theories ofstellar structure and stellar evolution.
| Hybrid stars and the reality of "dividing lines" among G to K bright giants and supergiants.
We present results of pointed ROSAT PSPC observations of 15 hybridstars/candidates, which have been analyzed in a homogenous way. 7 ofthese stars were observed in X-rays for the first time. 12 out of 15hybrid stars have been detected as X-ray sources, some of them close tothe detection limit. We conclude that essentially all hybrid stars asdefined by the simultaneous presence of transition region line emissionand cool stellar winds are X-ray sources if exposed sufficiently deep.The X-ray luminosities of hybrid stars cover a range between 2x10^27^and ~10^30^erg/s. Their X-ray surface fluxes can be as low as =~20erg/cm^2^/s and thus considerably lower than those of normal luminosityclass (LC) III giants. X-ray spectra of hybrid stars tend to be harderthan that of normal LC III giants, moreover, the X-ray brightest starshave the hardest spectra. We find that for K II giants the normalizedX-ray flux versus C IV flux obeys a power law with an exponent a=2.9,steeper than among normal giants (1.5). Hybrid K II stars are X-rayunderluminous by a factor of 5 to 20 compared to LC III giants at thesame level of normalized CIV flux f_CIV_/f_bol_; hybrid G supergiantsare even more X-ray deficient. We reanalyze the CaII wind dividing lineand find it vertical at B-V=1.45 for LC III giants. It is nearlyhorizontal between B-V=1.45 and 1.0 (at M_bol_=~-2...-3), and not welldefined for supergiants with B-V<1.0. We therefore suggest thatpossibly all LC II and Ib G and K giants are hybrid stars and that the"dividing line" concept in its simplest form is not valid for G/K giantsbrighter than M_bol_=~-2. Hybrid stars are supposed to be evolvedintermediate mass stars and their coronal activity may in principle bedetermined by the individual history of each star.
| ROSAT X-ray observations of a complete, volume-limited sample of late-type giants.
We have investigated a complete sample of the nearest 39 late typegiants (d<=25pc) for which we have probed the X-ray luminosityfunction with unprecedented sensitivity by deep (3...18ksec) ROSATPSPC-observations in the pointed mode, together with ROSAT All-Skysurvey (RASS) data. We confirm the X-ray dividing line for luminosityclass III giants as proposed by Haisch et al. (1991, 1992) and we findevidence, that essentially all luminosity class III giants withB-V<1.2 or spectral type
| Intriguing, Low-amplitude Periodicity in the Radial Velocities of delta Sagittarrii
We present the initial results of the analysis of the precise radialvelocities of the relatively little-studied star delta Sagittarii, K2.5IIIa, HR 6859. The data were obtained at the Canada-France-HawaiiTelescope using the hydrogen fluoride absorption cell technique. Theperiodogram shows significant peaks at 2.8 days (K=104 m s(-1) ), 63days (K=85 m s(-1) ), and 295 days (K=72 m s(-1) ). Because of ourlimited data the true period cannot be distinguished from thesepossibilities due to aliasing. This giant is an interesting example of astar having a radial velocity periodicity which may be attributed tointrinsic variability, rotational modulation, or the presence of a lowM_2 sin i companion (see A. Walker et al., this conference). Moreobservations are urgently required to determine the true period and todiscover the underlying origin for this star's radial velocityvariability.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Nyilas |
| Rektaszcenzió: | 18h20m59.70s |
| Deklináció: | -29°49'41.0" |
| Vizuális fényesség: | 2.7 |
| Távolság: | 93.721 parszek |
| RA sajátmozgás: | 30.1 |
| Dec sajátmozgás: | -26.4 |
| B-T magnitude: | 4.502 |
| V-T magnitude: | 2.83 |
Katalógusok és elnevezések:
|
