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A catalog of rotational and radial velocities for evolved stars. IV. Metal-poor stars^
Aims.The present paper describes the first results of an observationalprogram intended to refine and extend the existing v sin i measurementsof metal-poor stars, with an emphasis on field evolved stars.Methods: .The survey was carried out with the FEROS and CORALIEspectrometers. For the v sin i measurements, obtained from spectralsynthesis, we estimate an uncertainty of about 2.0 km s-1. Results: .Precise rotational velocities v sin i are presented for alarge sample of 100 metal-poor stars, most of them evolving off themain-sequence. For the large majority of the stars composing the presentsample, rotational velocities have been measured for the first time.
| Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesismodelling is presented. The library consists of 985 stars spanning alarge range in atmospheric parameters. The spectra were obtained at the2.5-m Isaac Newton Telescope and cover the range λλ3525-7500 Å at 2.3 Å (full width at half-maximum) spectralresolution. The spectral resolution, spectral-type coverage,flux-calibration accuracy and number of stars represent a substantialimprovement over previous libraries used in population-synthesis models.
| The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. I. Composition and Spectral Features
The existence of faint blue stars far above the Galactic plane that havespectra that are similar to nearby Population I B stars presents severalinteresting questions. Among them are the following: Can a Population IB star travel from the disk to a position many kiloparsecs above theplane in a relatively short main-sequence lifetime? Is it possible thatsingle massive star formation is occurring far from the Galactic plane?Are these objects something else masquerading as main-sequence B stars?This paper (the first of two) analyzes the abundances of a sample ofthese stars and reveals several that are chemically similar to nearbyPopulation I B stars, whereas others clearly have abundance patternsmore like those expected in blue horizontal-branch (BHB) orpost-asymptotic giant branch stars. Several of those with old evolvedstar abundances also have interesting features of note in their spectra.We also consider why this sample does not have any classical Be starsand identify at least two nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory operated by the University of Texas at Austin.
| 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.
| Rotation Velocities of Red and Blue Field Horizontal-Branch Stars
We present measurements of the projected stellar rotation velocities(vsini) of a sample of 45 candidate field horizontal-branch (HB) starsspanning a wide range of effective temperatures, from red HB stars withTeff~=5000K to blue HB stars with Teff of 17,000K.Among the cooler blue HB stars (Teff=7500-11500 K), weconfirm prior studies showing that, although a majority of stars rotateat vsini<15kms-1, there exists a subset of ``fastrotators'' with vsini as high as 30-35 km s-1. All but one ofthe red HB stars in our sample have vsini<10kms-1, and noanalogous rotation bimodality is evident. We also identify anarrow-lined hot star (Teff~=16,000K) with enhancedphotospheric metal abundances and helium depletion, similar to theabundance patterns found among hot BHB stars in globular clusters, andfour other stars that may also belong in this category. We discussdetails of the spectral line fitting procedure that we use to deducevsini and explore how measurements of field HB star rotation may shedlight on the issue of HB star rotation in globular clusters.
| The Century Survey Galactic Halo Project. I. Stellar Spectral Analysis
The Century Survey Galactic Halo Project is a photometric andspectroscopic survey from which we select relatively blue stars(V-R<0.30 mag) as probes of the Milky Way halo. The survey stripspans the range of Galactic latitude 35°
| Hα+[N II] Observations of the H II Regions in M81
In a first of a series of studies of the Hα+[N II] emission fromnearby spiral galaxies, we present measurements of Hα+[N II]emission from H II regions in M81. Our method uses large-field CCDimages and long-slit spectra and is part of the ongoingBeijing-Arizona-Taipei-Connecticut Sky Survey (the BATC survey). The CCDimages are taken with the National Astronomical Observatories of China(NAOC) 0.6/0.9 m f/3 Schmidt telescope at the Xinglong ObservingStation, using a multicolor filter set. Spectra of 10 of the brightest HII regions are obtained using the NAOC 2.16 m telescope with a Tek1024×1024 CCD. The continua of the spectra are calibrated byflux-calibrated images taken from the Schmidt observations. We determinethe continuum component of our Hα+[N II] image via interpolationfrom the more accurately measured backgrounds (M81 starlight) obtainedfrom the two neighboring (in wavelength) BATC filter images. We use thecalibrated fluxes of Hα+[N II] emission from the spectra tonormalize this interpolated, continuum-subtracted Hα+[N II] image.We estimate the zero-point uncertainty of the measured Hα+[N II]emission flux to be ~8%. A catalog of Hα+[N II] fluxes for 456 HII regions is provided, with those fluxes being on a more consistentlinear scale than previously available. The logarithmically binnedHα+[N II] luminosity function of H II regions is found to haveslope α=-0.70, consistent with previous results (which allowedα=-0.5 to -0.8). From the overall Hα+[N II] luminosity ofthe H II regions, the star formation rate of M81 is found to be ~0.68Msolar yr-1, modulo uncertainty with extinctioncorrections.
| Is HCG 31 undergoing a merger or a fly-by interaction?
We present Fabry-Perot and multi-object spectroscopy of the galaxies inHickson compact group 31 (HCG 31). Based upon our Hα data cubes,galaxies A and C are a single entity, showing no discontinuity in theirkinematics. Kinematically, galaxy E is probably a component of the A+Ccomplex; otherwise it is a recently detached fragment. Galaxy F appears,both kinematically and chemically, to have formed from material tidallyremoved from the A+C complex. Galaxies B and G are kinematicallydistinct from this complex. Galaxy Q also has a radial velocitycompatible with group membership. Galaxies A, B, C, and F have nearlyidentical oxygen abundances, despite spanning a luminosity range of 5mag. Galaxy B's oxygen abundance is normal for its luminosity, whilegalaxy F's abundance is that expected given its origin as a tidalfragment of the A+C complex. The oxygen abundances in galaxies A and Care also understandable if the A+C complex is a late-type spiralsuffering strong gas inflow and star formation as a result of a tidalinteraction. Given the kinematics of both the galaxies and the H I gas,the oxygen abundances, and the position of galaxy G, we propose that aninteraction of galaxy G with the A+C complex, rather than a merger ofgalaxies A and C, is a more complete explanation for the tidal featuresand other properties of HCG 31. In this case, the A+C complex need notbe a merger in progress, though this is not ruled out.
| Distant field blue horizontal branch stars and the mass of the Galaxy - I. Classification of halo A-type stars
This is the first in a series of three papers presenting a newcalculation of the mass of the Galaxy based on radial velocities anddistances measured for a sample of some 100 faint 16 < B < 20field blue horizontal branch (BHB) stars. This study aims to reduce theuncertainty in the measured mass of the Galaxy by increasing the numberof halo objects at Galactocentric distances r > 30 kpc with measuredradial velocities by a factor of 5. Faint A-type stars in the Galactichalo have been identified from ubjr photometry in six UKSchmidt fields. These samples include field BHB stars as well as lessluminous stars of main-sequence surface gravity, which are predominantlyfield blue stragglers. We obtain accurate charge-coupled devicephotometry and spectra to classify these stars. This paper describes ourmethods for separating out clean samples of BHB stars in a way that isefficient in terms of telescope time required. We use the highsignal-to-noise (S/N) ratio spectra of A-type stars of Kinman, Suntzeff& Kraft (published in 1994), and their definitive spectrophotometricΛ classifications, to assess the reliability of two methods, andto quantify the S/N ratio requirements. First we revisit, refine andextend the hydrogen linewidth versus colour relation as a classifier(here called the D0.15-colour method). The second method isnew and compares the shapes of the Balmer lines. With this method (herecalled the scale-width-shape method) there is no need for colours orspectrophotometry. Using the equivalent width of the CaII K line as anadditional filter we find we can reproduce Kinman, Suntzeff &Kraft's Λ classifications with both methods. In a sample of starswith strong Balmer lines, equivalent width Hγ > 13Å[equivalent to the colour range 0 <= (B-V)0<=0.2], halo BHB stars can be separated from halo blue stragglersreliably. For the spectroscopy (i.e. both classification methods) theminimum required continuum S/N ratio is 15 Å-1. For theD0.15-colour method (B-V)0 colours accurate to0.03 mag are needed.
| The determination of Teff for metal-poor A-type stars using V and 2MASS J, H and K magnitudes
Effective temperatures (T_eff) can be determined from (V-J)_0, (V-H)_0and (V-K)_0 colours that are derived from 2MASS magnitudes. This givesanother way to estimate the T_eff of faint blue halo stars (V la 15)whose temperatures are now usually deduced from bo.Transformations (adapted from Carpenter \cite{carp01b}) are used tochange colours derived from the 2MASS data to the Johnson system. T_effis then derived from these colours using an updated Kurucz model. Tablesare given to derive T_eff as a function of (V-J)_0, (V-H)_0 and (V-K)_0for a variety of metallicities and log g suitable for blue horizontalbranch and main sequence stars. The temperatures obtained in this wayare compared with those in the recent literature for various stars with5 <= V <= 15 and T_eff in the range 6500 to 9500 K; systematicdifferences are ~ 100 K. An exception is the sample of BHB starsobserved by Wilhelm et al. (\cite{wbsl99}) whose T_eff are significantlycooler than those we derive by an amount that increases with increasingtemperature. NOAO is operated by the Association of Universities forresearch in Astronomy, Inc., under contract with the National ScienceFoundation. Tables 2 and 3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http:/ /cdsweb.u-strasbg.fr/cgi-bin/ qcat?J/ A+A/391/1039
| Rotation of Hot Horizontal-Branch Stars in the Globular Clusters NGC 1904, NGC 2808, NGC 6093, and NGC 7078
We present high-resolution Very Large Telescope/Ultraviolet VisualEchelle Spectrograph observations of 56 stars in the extendedhorizontal-branch (EHB) of the Galactic globular clusters NGC 1904, NGC2808, NGC 6093, and NGC 7078. Our data reveal for the first time thepresence in NGC 1904 of a sizable population of fast (vsini>=20 kms-1) horizontal-branch (HB) rotators, confined to the coolend of the EHB, similar to that found in M13. We also confirm the fastrotators already observed in NGC 7078. The cooler stars(Teff<11,500 K) in these three clusters show a range ofrotation rates, with a group of stars rotating at ~15 km s-1or less and a fast rotating group at ~30 km s-1. Apparently,the fast rotators are relatively more abundant in NGC 1904 and M13 thanin NGC 7078. No fast rotators have been identified in NGC 2808 and NGC6093. All the stars hotter than Teff~11,500 K have projectedrotational velocities of vsini<12 km s-1, but less than20% have vsini<2 km s-1. The connection betweenphotometric gaps in the HB and the change in the projected rotationalvelocities is not confirmed by the new data. However, our data areconsistent with a relation between this discontinuity and the HB jump.We discuss a number of possibilities for the origin of the stellarrotation distribution along the HB. We conclude that none of them canyet provide a satisfactory explanation of the observations. Based onobservations with the ESO Very Large Telescope Ultraviolet VisualEchelle Spectrograph at the Paranal Observatory, Chile.
| Kurucz Model Energy Distributions: A Comparison With Real Stars. II. Metal-Deficient Stars
Energy distributions of synthetic spectra for Kurucz model atmospheresare compared with observed energy distributions of metal-deficient starsof the blue horizontal-branch (BHB), F--G--K subdwarf (SD) and G--Kgiant (MDG) types. The best coincidence of the synthetic and observedenergy curves is found for BHB stars. The largest differences are foundin the ultraviolet wavelengths for subdwarfs and cool MDGs. Theinfluence of errors of effective temperatures, gravities andmetallicities is estimated.
| Stellar parameters for Pop II A-type stars from IUE spectra and new-ODF ATLAS9 model atmospheres
Stellar parameters for twenty-seven field horizontal branch A-typestars, a post-AGB star (BD +32 2188), and a possible cool sdB star (BD+00 0145) were obtained by fitting the whole IUE energy distributionstaken from the IUE-INES archive to the ultraviolet energy distributionspredicted by new-ODF ATLAS9 model atmospheres, which include theLyman-alpha H-H+ and H-H quasi-molecular absorptions near1400 Å and 1600 Å. The sample of stars was extensivelystudied by Kinman et al. (2000), who derived stellar parameters for themby using visual observations and also an ultraviolet color index. Theeffective temperatures obtained by fitting the IUE spectra to thenew-ODF models agree with T_eff derived by Kinman et al. (2000) for mostof the stars in the sample. The gravities from UV agree with those fromKinman et al. (2000) for stars hotter than about 8700 K, while they arelower, on average, by 0.3 dex for the cooler stars. The same discrepancyis present when log g from the ultraviolet energy distribution iscompared with log g from the visible energy distribution. The differenceis insensitive to reddening, microturbulent velocity, metallicity, ormixing-length parameter for the treatment of the convection. Figures A.1to A.15 are only available in electronic form athttp://www.edpsciences.org
| IC 10: More evidence that it is a blue compact dwarf
We present optical spectroscopy of H Ii regions in the Local Groupgalaxy IC 10 and UBVR photometry of foreground stars in three fieldstowards this galaxy. From these data, we find that the foregroundreddening due to the Milky Way is E(B-V)=0.77+/- 0.07 mag. We find thatIC 10 contains considerable internal dust, which qualitatively explainsthe variety of reddening values found by studies of its differentstellar populations. Based upon our foreground reddening, IC 10 hasintrinsic photometric properties like those of a blue compact dwarfgalaxy, and not those of a dwarf irregular. This result is consistentwith much evidence that IC 10 is in the throes of a starburst that beganat least 10 Myr ago. We also report the discovery of a new WR star inthe H Ii region HL111c.
| 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
| A spectroscopic study of field BHB star candidates
New spectroscopic observations are presented for a sample of thirty-oneblue horizontal branch (BHB) star candidates that are sufficientlynearby to have reliable proper motions. Comments are given on a furthertwenty-five stars that have previously been suggested as BHB starcandidates but which were not included in our sample. Moderatelyhigh-resolution spectra (lambda /Delta lambda ~ 15 000) of twenty fiveof our program stars were taken with the coudé feed spectrographat Kitt Peak. Twelve of the program stars were also observed with theCAT spectrograph at ESO. Six of these program stars were observed fromboth hemispheres. IUE low-resolution spectra are available for most ofour candidates and were used, in addition to other methods, in thedetermination of their Teff and reddening. A compilation ofthe visual photometry for these stars (including new photometry obtainedat Kitt Peak) is also given. Abundances were obtained from these spectrausing models computed by Castelli with an updated version of the ATLAS9code (Kurucz 1993a). All thirty one candidates are halo stars. Of these,twenty eight are classified as BHB stars because: [(1)]they lie close tothe ZAHB (in a similar position to the BHB stars in globular clusters)in the Teff versus log g plot. For all but one of thesestars, far-UV data were available which were consistent with other data(Strömgren photometry, energy distributions, Hγ profiles) forderiving Teff and log g. [(2)]they have a distribution of kms-1i (<=40 km s-1) that is similar to thatfound for the BHB in globular clusters. Peterson et al. (1995) and Cohen& McCarthy (1997) have shown that the BHB stars in the globularclusters M13 and M92 have a higher km s-1i (<= 40 kms-1) than those in M3 and NGC 288 (<=20 kms-1). The mean deprojected rotational velocity (/line{v}) wascalculated for both the two globular clusters and the nearby BHB starsamples. A comparison of these suggests that both globular cluster kms-1i types are present in our nearby sample. No obvious trendis seen between km s-1i and either (B-V)o or [Fe/H].[(3)]they have -0.99>=[Fe/H]>=-2.95 (mean [Fe/H] -1.67; dispersion0.42 dex), which is similar to that found for field halo RR Lyrae andred HB stars. These local halo field stars appear (on average) to bemore metal-poor than the halo globular clusters. The local sample of redgiant stars given by Chiba & Yoshii (1998) contains a greaterfraction of metal-poor stars than either our halo samples or the haloglobular clusters. The stars in our sample that have a Teffthat exceeds about 8 500 K show the He i (lambda 4471) line with astrength that corresponds to the solar helium abundance. [(4)]they showa similar enhancement of the alpha -elements (< [Mg/Fe]right > =+0.43+/-0.04 and also < [Ti/Fe]right > = +0.44+/-0.02) to thatfound for other halo field stars of similar metallicity. Based onobservations obtained at KPNO, operated by the Association ofUniversities for Research in Astronomy, Inc., under contract with theNational Science Foundation, and the European Southern Observatory,Chile. Tables 4 and 5 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr
| Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
| Kinematical trends among the field horizontal branch stars
Horizontal branch (HB) stars in the field of the Milky Way can be usedas tracers for the study of early stages of the evolution of our galaxy.Since the age of individual HB stars is not known a priori, we havestudied the kinematics of a sample of field HB stars measured withHipparcos to look for signs of age and population nature. Our samplecomprises 14 HBA, 2 HBB and 5 sdB/O stars. We found that the kinematicsof the HBA stars is very different from that of the sdB/O stars(including those from an earlier study). The HBA stars have low orbitalvelocities, some are even on retrograde orbits. Their orbits have largeeccentricities and in many cases reach large distances above thegalactic plane. In contrast, the sdB/O stars show disk-like orbitalcharacteristics. The few HBB stars (with T_eff> 10,000 K) in oursample seem to have kinematics similar to that of the sdB/O stars. Inorder to see if there is a trend among the HB stars in their kinematics,we investigated also RR Lyrae stars measured with Hipparcos. Here wefound a mixed kinematical behaviour, which was already known fromprevious studies. Some RR Lyrae stars have disk-like orbits (most ofthese being metal rich) but the majority has halo-like orbits, verysimilar to those of our HBA stars. Since the atmospheres of most typesof HB stars do not reflect original metallicities any more thekinematics is the only aspect left to study the origin and populationmembership of these stars. Thus, the clear trend found in kinematics ofstars along the HB, which is also a sequence in stellar mass, shows thatthe different kinds of field HB stars arose from stars having differentorigins in age and, e.g., metallicity or mass loss rate. Based in parton HIPPARCOS data
| Non-LTE analyses of strontium abundances in stars. A stars
Not Available
| Spectroscopy of Hot Stars in the Galactic Halo. II. The Identification and Classification of Horizontal-Branch and Other A-Type Stars
We discuss a spectroscopic and photometric technique that enables theidentification and classification of field horizontal-branch (FHB) andother A-type stars, even from relatively low signal-to-noise ratiomedium-resolution spectra. This technique makes use of broadband UBVcolors predicted from model atmosphere calculations and Balmer lineprofiles and Ca II K equivalent widths determined from synthetic spectrato estimate the physical parameters T_eff, log g, and [Fe/H] for starsin the effective temperature range 6000-10,000 K. A comparison of ourmethod with high signal-to-noise ratio spectra of standard starsindicates a scatter in the derived parameters of sigma(T_eff)=+/-250 K,sigma(log g)=+/-0.14 dex, and sigma([Fe/H])=+/-0.12 dex. This precisionallows for a separation of low surface gravity FHB and other, generallyhigher surface gravity, A-type (and somewhat later) stars. We alsodevelop a synthetic-template comparison technique, which is veryeffective in the identification of metallic-line and peculiar A-typestars. A detailed investigation of the influence of noise in the spectraon the determination of physical parameters shows that, for spectra withsignal-to-noise ratios in the range 10
| Multiwavelength Observations of Collisional Ring Galaxies. III. Oxygen/Nitrogen Abundances and Star Formation Properties of Ring Knots
This is the third paper in a series examining the multiwavelengthproperties of a sample of northern ring galaxies, in which we presentoptical long-slit spectra and broadband BVR and JHK colors of individualstar-forming knots embedded in the ring. We present the oxygen andnitrogen abundances of the starburst knots and compare thereddening-corrected colors of individual star clusters with recentmodels of stellar evolution. We also present kinematic data for onesystem, LT 41. The star-forming knots in the rings have very similarcolors, which implies similar ages in the range 4-80 Myr. These ages areless than the dynamical ages of the rings, which are typically 100-300Myr. The fact that the implied ages of knots within individual ringgalaxies cluster around the same age argues that their formation isrecently triggered by a coherent event all around the ring. Thisstrongly supports the triggering of the star formation as being due tothe propagation of a radial density wave, as in the classical picture.The ring galaxies are found to have subsolar metallicities in the rangeone-half to one-fifth solar in [O/H] and [N/H] ratios. There is asuggestion of an increase in the mean nitrogen abundance for the ringsof larger linear size, but oxygen abundances show no trend with ringdiameter. The uniformity of the oxygen abundances over the sample isconsistent with their rather narrow range of K-band luminosities, whichsuggests that even in strongly disturbed galaxies, when prompt localenrichment is expected to be important, the primary factor governingoxygen metallicity is total luminosity.
| Ca II H and K Photometry on the UVBY System. III. The Metallicity Calibration for the Red Giants
New photometry on the uvby Ca system is presented for over 300 stars.When combined with previous data, the sample is used to calibrate themetallicity dependence of the hk index for cooler, evolved stars. Themetallicity scale is based upon the standardized merger of spectroscopicabundances from 38 studies since 1983, providing an overlap of 122evolved stars with the photometric catalog. The hk index producesreliable abundances for stars in the [Fe/H] range from -0.8 to -3.4,losing sensitivity among cooler stars due to saturation effects athigher [Fe/H], as expected.
| The absolute magnitude of field metal-poor horizontal branch stars
Hipparcos satellite parallaxes for 22 metal-poor field horizontal branchstars with V_0<9 are used to derive their absolute magnitude. Theweighted mean value is M_V=+0.69+/-0.10 for an average metallicity of[Fe/H]=-1.41 a somewhat brighter average magnitude of M_V=+0.60+/-0.12for an average metallicity of [Fe/H]=-1.51 is obtained by eliminating HD17072, which might be on the first ascent of the giant branch ratherthan on the horizontal branch. The present values agree with thedeterminations based on proper motions and application of theBaade-Wesselink method to field RR Lyraes; they are 0.1-0.2 mag fainterthan those based on calibration of cluster distances obtained by usinglocal subdwarfs and on alternative distance calibrators for the LargeMagellanic Cloud (LMC). The possibility that there is a real differencebetween the luminosity of the horizontal branch for clusters and thefield is briefly commented on.
| A search for magnetic stars in late stages of stellar evolution
No abstract submitted
| The physical structure of the Herbig Haro object HH 29
We have obtained Echelle spectra covering a number of important shockdiagnostic emission lines, mapping out the full extent of theHerbig-Haro object HH 29. Through this, the velocity field, the level ofexcitation and the electron density have all been determined with aspatial resolution of 1({') '} - 2({') '} and a spectral resolution of10 kms(-1) - 20 kms(-1) respectively. Our observations of shockdiagnostic lines allow us to produce an empirical 3D description(velocity is the third dimension) of F(Hα ), the level ofexcitation and the electron density. Our results indicate that HH 29 isamong the Herbig-Haro objects with the highest level of excitation. Wederive electron densities of between a few thousand cm(-3) and 10(4)cm(-3) in `clumps' interspersed in an `inter-clump medium' of density ~300 cm(-3) . The spatial scale of the clumps is <_{ ~ } 2({') '}, andthe velocity dispersion of individual clumps is on the order of 30kms(-1) - 50 km s(-1) , implying that the `knotty' structure obvious inhigh spatial resolution images also exist in 3 dimensions. Based on themorphological and spectroscopical data, HH 29 appears to consist of anumber of HH-knots where the shock is located on the side of the objectoriented towards the originating source in some and on the opposite sidein others. We find that HH 29 is best explained as an aggregate ofclumps interacting with ambient material on the side away from theoriginating source, and also being shocked by a faster wind on the sidetowards the originating source. Based on observations collected at theEuropean Southern Observatory, La Silla, Chile
| 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
| The Fundamental Parameters of Field Horizontal-Branch Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2291G&db_key=AST
| Spectral Characteristics of Field Horizontal-Branch Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2286C&db_key=AST
| The Poststarburst Galactic Nucleus of NGC 4736
We present optical spectroscopic analysis of the nuclear region of thenearby Sab galaxy NGC 4736 in which the strong Balmer absorption linesare observed, providing evidence for a past starburst event. In order tostudy both the present-day stellar populations and the emission-lineactivity in the nucleus, we have made the stellar population synthesisand found that a luminous starburst occurred 1 x 10^9^ years ago in thenuclear region. Correcting for the effect of the underlying stellarabsorption features, we find that the ionized gas in the nuclear regionshows the very marginal nature between an ordinary H II region and alow- ionization nuclear emission-line region (LINER). Theabsorption-corrected Hα luminosity amounts only to 1.3 x 10^38^ergs s^-1^, which is lower than that of the Galactic H II region W49. Ifwe consider a case of the photoionization by massive stars, only six O6stars are responsible for the ionization in the central 37 pc x 60 pcregion. We also study the emission-line ratio properties of theclassical LINERs in the literature. The LINERs tend to show a sequencein the excitation diagram: the positive correlation between log [O III]λ5007/Hβ and log [N II] λ6583/Hα. Thiscorrelation may be attributed to a scatter of the relative strength ofstellar Balmer absorption to nebular Balmer emission among the sample.Therefore, we call attention to the possibility that some LINERs may infact be poststarburst galaxies rather than genuine active galacticnuclei.
| Elemental abundances of field horizontal branch stars - IV. HD 74721, 86986 and 93329
Studies of 200-A-long regions recently obtained with a 3000-pixel-longCCD at the coude feed telescope of the Kitt Peak National Observatory(KPNO) are used to extend fine analyses of the field horizontal branch Astars HD 74721, 86986 and 93329. Spectra of other stars obtained both atKPNO and at the Dominion Astrophysical Observatory show that previouslyfound wavelength-dependent equivalent width systematics are probably dueto how the spectra were measured as well as to resolution differences.The derived He/H ratios agree with the Buzzoni et al. value of 0.075,within measurement errors. Some derived elemental abundances are foundto be correlated with one another.
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Datos observacionales y astrométricos
| Constelación: | Cangrejo |
| Ascensión Recta: | 08h45m59.26s |
| Declinación: | +13°15'48.6" |
| Magnitud Aparente: | 8.699 |
| Distancia: | 2941.176 parsecs |
| Movimiento Propio en Ascensión Recta: | -41.8 |
| Movimiento Propio en Declinación: | -115.2 |
| B-T magnitude: | 8.759 |
| V-T magnitude: | 8.704 |
Catálogos y designaciones:
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