Contents
Images
Upload your image
DSS Images Other Images
Related articles
Do the Nearby Blue Horizontal Branch Stars Belong to the Thick Disk or the Halo?
We study the Milky Way region (|Z|< 3.0 kpc) where the thickdisk and inner halo overlap by using the kinematics of local bluehorizontal branch (BHB) stars (within 1 kpc) and new samples of BHBstars and A-type stars from the Century Survey. We derive Galactic U, V,and W velocities for these BHB and A-type star samples using propermotions from the NOMAD catalog. The mean velocities and the velocitydispersions of the BHB samples (|Z| < 3 kpc) are characteristicof the halo, while those of the Century Survey A-type stars arecharacteristic of the thick disk. There is no evidence from our samplesthat the BHB stars rotate with the thick disk in the region |Z| <3 kpc. Nearly a third of the nearby local RR Lyrae stars have diskkinematics and are more metal rich than [Fe/H] ~ –1. Only a fewpercent of the Century Survey BHB (CBHB) stars have these properties.Only one nearby BHB star (HD 130201) is likely to be such a disk starbut selection based on high proper motions will have tended to excludesuch stars from the local sample. The scale height derived from a sampleof local RR Lyrae stars agrees with that of the CBHB stars. The localsamples of BHB stars and metal-weak red giants are too incomplete for asimilar comparison.
| Observations towards early-type stars in the ESO-POP Survey - II. Searches for intermediate- and high-velocity clouds
We present CaII K and TiII optical spectra of early-type stars takenmainly from the ultraviolet and visual echelle spectrograph (UVES)Paranal Observatory Project, plus HI 21-cm spectra, from the Vila-Elisaand Leiden-Dwingeloo Surveys, which are employed to obtain distances tointermediate- and high-velocity clouds (IHVCs). HI emission at avelocity of -117 kms-1 towards the sightline HD30677 () withcolumn density ~1.7 × 1019 cm-2 has nocorresponding CaII K absorption in the UVES spectrum, which has asignal-to-noise ratio (S/N) of 610 per resolution element. The star hasa spectroscopically determined distance of 2.7 kpc, and hence sets thisas a firm lower distance limit towards Anti-Centre cloud ACII. Towardsanother sightline (HD46185 with ), HI at a velocity of +122kms-1 and column density of 1.2 × 1019cm-2 is seen. The corresponding CaII K spectrum has a S/N of780, although no absorption is observed at the cloud velocity. Thissimilarly places a firm lower distance limit of 2.9 kpc towards thisparcel of gas that may be an intermediate-velocity (IV) cloud. The lackof IV CaII absorption towards HD196426 () at a S/N of 500 reinforces alower distance limit of ~700 pc towards this part of complex gp, wherethe HI column density is 1.1 × 1019 cm-2 andvelocity is +78 kms-1. Additionally, no IV CaII is seen inabsorption in the spectrum of HD19445, which is strong in HI with acolumn density of 8 × 1019 cm-2 at avelocity of ~ -42 kms-1, placing a firm althoughuninteresting lower distance limit of 39 pc to this part of IV South.Finally, no high-velocity CaII K absorption is seen towards HD115363 ()at a S/N of 410, placing a lower distance of ~3.2 kpc towards the HVCgas at velocity of ~ +224 kms-1 and HI column density of 5.2× 1019 cm-2. This gas is in the same regionof the sky as complex WE (Wakker 2001), but at higher velocities. Thenon-detection of CaII K absorption sets a lower distance of ~3.2 kpctowards the HVC, which is unsurprising if this feature is indeed relatedto the Magellanic System.
| Measuring the Balmer Jump and the Effective Gravity in FGK Stars
It is difficult to accurately measure the effective gravity (logg) inlate-type stars using broadband (e.g., UBV or SDSS) or intermediate-band(uvby) photometric systems, especially when the stars can cover a rangeof metallicities and reddenings. However, simple spectroscopicobservational and data reduction techniques can yield accurate valuesfor logg through comparison of the Balmer jumps of low-resolutionspectra with recent grids of synthetic flux spectra.
| Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for MILES, a new spectral stellarlibrary covering the range λλ 3525-7500Å at2.3Å (FWHM) spectral resolution. The library consists of 985 starsspanning a large range in atmospheric parameters, from super-metal-rich,cool stars to hot, metal-poor stars. The spectral resolution, spectraltype coverage and number of stars represent a substantial improvementover previous libraries used in population synthesis models. Theatmospheric parameters that we present here are the result of aprevious, extensive compilation from the literature. In order toconstruct a homogeneous data set of atmospheric parameters we have takenthe sample of stars of Soubiran, Katz & Cayrel, which has very welldetermined fundamental parameters, as the standard reference system forour field stars, and have calibrated and bootstrapped the data fromother papers against it. The atmospheric parameters for our clusterstars have also been revised and updated according to recent metallicityscales, colour-temperature relations and improved set of isochrones.
| 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.
| A Periodicity Analysis of the Light Curve of 3C 454.3
We analyzed the radio light curves of 3C 454.3 at frequencies 22 and 37GHz taken from the database of Metsähovi Radio Observatory, andfound evidence of quasi-periodic activity. The light curves show greatactivity with very complicated non-sinusoidal variations. Two possibleperiods, a very weak one of 1.57+/-0.12 yr and a very strong one of6.15+/-0.50 yr were consistently identified by two methods, theJurkevich method and power spectrum estimation. The period of6.15+/-0.50 yr is consistent with results previously reported byCiaramella et al. and Webb et al. Applying the binary black hole modelto the central structure we found black hole masses of1.53×109Modot and1.86×108Modot, and predicted that the nextradio outburst is to take place in 2006 March and April.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| STELIB: A library of stellar spectra at R ~ 2000
We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃsica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433
| 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
| 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
| 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
| Empirical calibration of the lambda 4000 Å break
Empirical fitting functions, describing the behaviour of the lambda 4000Ä break, D4000, in terms of effective temperature,metallicity and surface gravity, are presented. For this purpose, thebreak has been measured in 392 stars from the Lick/IDS Library. We havefollowed a very detailed error treatment in the reduction and fittingprocedures, allowing for a reliable estimation of the breakuncertainties. This calibration can be easily incorporated into stellarpopulation models to provide accurate predictions of the break amplitudefor, relatively old, composite systems. Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Sub-arcsecond morphology and kinematics of the DG Tauri jet in the [O I]λ6300 line.
We present the first 3D spectro-imaging observations of the [OI]λ6300 line in an active T Tauri star: DG Tau. The morphologicalstructure of the mass outflow is revealed with unprecedented spatialresolution (0.35''). It consists of an unresolved inner peak containingtwo thirds of the total line flux, followed by a collimated jet-likebody extending out to ~1.5" from the star, and two resolved knots atdistances of 2.7" and 4''. One of the outer knots possesses a curvedmorphology and transverse velocity gradient strongly suggestive of aresolved bowshock. Time variability in the ejection velocity (withtimescale {DELTA}t=~8.5yr) could explain the presence of such abowshock, the spacing of knots at distances >=1'' from the star, andthe strong velocity gradients along the jet observed closer to the star.The unresolved inner peak, centered at ~20AU of the star, is apparentlystationary and possibly linked to the initial jet collimation. Our sizelimit and absolute photometry for this peak set new constraints on thejet mass loss rate (between 1.3x10^-8^ and6.5x10^-6^Msun_/yr), lowering previous estimates by a factor5 to 25. Finally, our high sensitivity combined with velocityinformation allows us to detect unambiguously the counterjet of thesystem (v=~+230km/s), and to establish the existence of a diffuse haloof low-velocity [O I] emission, which might trace a wider flow or anextended scattering nebula.
| H gamma and H delta Absorption Features in Stars and Stellar Populations
The H gamma and H delta absorption features are measured in a sample of455 (out of an original 460) Lick/IDS stars with pseudo--equivalentwidth indices. For each Balmer feature, two definitions, involving anarrow (~20 Angstroms) and a wide (~40 Angstroms) central bandpass, aremeasured. These four new Balmer indices augment 21 indices previouslydetermined by Worthey et al., and polynomial fitting functions that giveindex strengths as a function of stellar temperature, gravity, and[Fe/H] are provided. The new indices are folded into models for theintegrated light of stellar populations, and predictions are given forsingle-burst stellar populations of a variety of ages and metallicities.Contrary to our initial hopes, the indices cannot break a degeneracybetween burst age and burst strength in post-starburst objects, but theyare successful mean-age indicators when used with sensitive metallicityindicators. An appendix gives data, advice, and examples of how totransform new spectra to the 25-index Lick/IDS system.
| 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
| High Velocity Outflow in the Extended Emission-Line Region of the Seyfert Galaxy NGC 7319
We found a high velocity and large-scale outflow in the extendedemission-line region (EELR) of the Seyfert 2 galaxy NGC 7319 withoptical long-slit spectroscopy. The EELR elongates ~10" towardsouth-southwest direction whose position and direction is coincidentwith those of the radio emission. The velocity of the outflow comes upto 500 km s^-1^, and its extent is 4 kpc. The outflow which we found inNGC 7319 is one of the largest outflowing phenomenon that have ever beenfound in Seyfert galaxies. Comparing observed line intensity ratios withthe photoionization models and the shock ionization models, it isindicated that the outflow gas is predominantly photoionized by theionizing radiation from the nucleus. The electron density of the nucleusand that of the outflowing gas are estimated from [S II] doublet ratioas 300 and 600 cm^-3^, respectively. The electron density of theoutflowing gas is very high, and it is a rare case that the electrondensity of the EELR is higher than that of the nucleus. The volumefilling factor of the EELR/outflow of NGC 7319 was found to be verysmall, 10^-4^-10^-5^. This small volume filling factor and relativelyhigh electron density suggest that the outflowing gas would comprisemany small filaments or blobs which are compressed by interaction of theoutflow with interstellar matter. We have compared the number ofionizing photons which is required to ionize the EELR to that towardsthe line-of-sight direction. It is shown that the number of ionizingphotons which is required to ionize the EELR is larger than that towardsthe line-of-sight direction by at least one order of magnitude. Thisindicates a strong anisotropic nuclear ionizing radiation which could beproduced by a obscuring torus.
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| Kinematics of metal-poor stars in the galaxy
We discuss the kinematic properties of a sample of 1936 Galactic stars,selected without kinematic bias, and with abundances (Fe/H) is less thanor equal to -0.6. The stars selected for this study all have measuredradial velocities, and the majority have abundances determined fromspectroscopic or narrow-/intermediate-band photometric techniques. Incontrast to previous examinations of the kinematics of the metal-poorstars in the Galaxy, our sample contains large numbers of stars that arelocated at distances in excess of 1 kpc from the Galactic plane. Thus, amuch clearer picture of the nature of the metal-deficient populations inthe Galaxy can now be drawn.
| Heisse Horizontalaststerne im Feld der Milchstrasse und in Kugelsternhaufen.
Not Available
| The structure of the galactic halo outside the solar circle as traced by the blue horizontal branch stars
A complete sample of blue horizontal branch (BHB) stars in the magnituderange 13.0 less than or equal to V less than or equal to 16.5 isisolated in two Galactic fields that have previously been searched forRR Lyrae variables: SA 57 in the Northern Polar Cap and the LickAstrograph field RR 7 in the Anticenter (l = 183 deg, b = +37 deg).These BHB stars are a subset of the AF stars found in the CaseLow-Dispersion Northern Survey; lists of these AF stars were madeavailable by the late Nick Sanduleak. In the color range 0.00 less thanor equal to (B - V)0 less than or equal to +0.20, we candistinguish the BHB stars among these AF stars by comparing them bothwith well known local field horizontal branch (FHB) stars and also theBHB members of the halo globular clusters M3 and M92. The criteria forthis comparison include (1) a (u - B)K color index (derivedfrom photoelectric observations using the Stroemgren u filter and theJohnson B and V filters) that measures the size of the Balmer jump, (2)a spectrophotometric index lambda that measures the steepness of theBalmer jump, and (3) a parameter D0.2 that is the mean widthof the H-delta and H-gamma Balmer lines measured at 20 percent of thecontinuum level. These criteria give consistent results in separatingBHB stars from higher gravity main sequence AF stars in the color range0.00 less than or equal to (B - V)0 less than or equal to+0.20. All three photometric and spectrophotometric criteria weremeasured for 35 stars in the SA 57 field and 37 stars in the RR 7 fieldthat are in the color range (B - V)0 less than or equal to+0.23 and in the magnitude range 13.0 less than or equal to V less thanor equal to 16.5. For a small number of additional stars only (u -B)K was obtained. Among the AF stars that are fainter than B= 13 and bluer than (B - V)0 = +0.23, about half of those inthe SA 57 field and about one third of those in the lower latitude RR 7field are BHB stars. Isoabundance contours were located empirically inplots of the pseudoequivalent width versus (B - V)0 for thelines of Mg II lambda-4481 A, Ca II lambda-3933 A, and Fe I lambda-4272A. Solar abundances were defined by the data from main sequence stars inthe Pleiades and Coma open clusters. Data from the BHB stars in M3 andM92 defined the (Fe/H) = -1.5 and -2.2 isoabundance contours,respectively. Metallicities of all stars were estimated by interpolatingthe measured pseudoequivalent widths in these diagrams at the observed(B - V)0. The distribution of (Fe/H) found for the BHB starsin this way is very similar to that which we found for the RR Lyraestars in the same fields using the Preston Delta-S method. The spacedensities of these BHB stars were analyzed both separately and togetherwith earlier observations of field BHB stars. This analysis supports atwo-component model for the halo of our Galaxy that is similar in manyrespects to that proposed by Hartwick although our discussion refersonly to the region outside the solar circle.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Cetus |
| Right ascension: | 00h31m53.79s |
| Declination: | -05°15'42.9" |
| Apparent magnitude: | 9.888 |
| Proper motion RA: | -9.7 |
| Proper motion Dec: | -65.5 |
| B-T magnitude: | 10.156 |
| V-T magnitude: | 9.911 |
Catalogs and designations:
|
