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Публикации по объекту
Identification of blue high proper motion objects in the Tycho-2 and 2MASS catalogues using Virtual Observatory tools
Aims: With available Virtual Observatory tools, we looked for newbright blue high proper motion objects in the entire sky: white dwarfs,hot subdwarfs, runaway OB stars, and early-type stars in nearby youngmoving groups. Methods: We performed an all-sky cross-matchbetween the optical Tycho-2 and near-infrared 2MASS catalogues withAladin, and selected objects with proper motions ? > 50 masyr-1 and colours VT - Ks < -0.5 magwith TOPCAT. We also collected multi-wavelength photometry, constructedthe spectral energy distributions and estimated effective temperaturesfrom fits to atmospheric models with VOSA for the most interestingtargets. Results: We assembled a sample of 32 bright blue highproper motion objects, including ten sdO/B subdwarfs, nine DA whitedwarfs, five young early-type stars (two of which are runaway stars),two blue horizontal branch stars, one star with poor information, andfive objects reported for the first time in this work. These last fiveobjects have magnitudes BT ? 11.0-11.6 mag, effectivetemperatures Teff ? 24 000-30 000 K, and are located inthe region of known white dwarfs and hot subdwarfs in a reduced propermotion-colour diagram. We confirmed the hot subdwarf nature of one ofthe new objects, Albus 5, with public far-ultraviolet spectroscopic dataobtained with FUSE.
| Stratification and isotope separation in CP stars
We investigate the elemental and isotopic stratification in theatmospheres of selected chemically peculiar (CP) stars of the upper mainsequence. Reconfiguration of the UV-Visual Echelle Spectrograph in 2004has made it possible to examine all three lines of the CaII infrared(IR) triplet. Much of the material analysed was obtained in 2008. Wesupport the claim of Ryabchikova, Kochukhov & Bagnulo (RKB) that thecalcium isotopes have distinct stratification profiles for the stars 10Aql, HR 1217 and HD 122970, with the heavy isotope concentrated towardsthe higher layers. Better observations are needed to learn the extent towhich 40Ca dominates in the deepest layers of all or most CPstars that show the presence of 48Ca. There is littleevidence for 40Ca in the spectra of some HgMn stars, and theinfrared (IR) triplet in the magnetic star HD 101065 is well fit by pure48Ca. In HR 5623 (HD 133792) and HD 217522, it is likely thatthe heavy isotope dominates, though models are possible where this isnot the case. While elemental stratification is surely needed in manycases, we point out the importance of including adjustments in theassumed Teff and log(g) values, in attempts to modelstratification. We recommend emphasis on profiles of the strongestlines, where the influence of stratification is most evident. Isotopicmixtures, involving the four stable calcium nuclides with masses between40 and 48 are plausible, but are not emphasized.Based on observations obtained at the European Southern Observatory,Paranal and La Silla, Chile - ESO programmes 65.L-0316(a), 68.D-0254(A),076.D-0169(A) and 081.D-0498(A).E-mail: cowley@umich.ed
| A high-resolution study of isotopic composition and chemical abundances of blue horizontal branch stars in the globular clusters NGC 6397 and NGC 6752
Aims: Large abundance anomalies have been previously detected inHorizontal Branch B-type stars. It has been suggested that at T_eff >11 000 K the stellar atmospheres become susceptible to diffusion effectsand thus develop surface abundances similar to those that appear in themain-sequence, chemically peculiar group of A and B-type stars. Wepresent the first high-resolution study of isotopic anomalies andchemical abundances in six Horizontal Branch B-type stars in globularclusters NGC 6397 and NGC 6752 and compare them to those observed inHgMn stars. Methods: We obtained high-resolution (up to R ~ 115000) UVES spectra of a representative sample of six B-type stars (T183,T191, T193, B652, B2151, B2206) with sharp spectral lines (v sin i ?10 km s-1). The stars T183 and B2151 were observed on twoconsecutive nights to examine potential spectrum variability. A detailedspectrum analysis was done relying on Kurucz ATLAS9 and ATLAS12 models.The spectra were analysed using the SYNTHE code to generate syntheticspectra. Results: It is the first time an abundance analysis isperformed for all elements for which spectral lines were detected inUVES spectra of Horizontal Branch B-type stars. Our study of these starsrevealed no signs of He isotopic anomalies, which would produce a3He/4He ratio different from the solar one. Theisotopic anomaly of Ca is detected in all six studied stars. Thechemical abundance analysis reveals an overabundance over the solarvalues of P, Ti, Mn, Fe, and Y and an overabundance over the clustermetallicity of Mg, Ca, and Cr. This behaviour is very similar in all sixstars of both clusters with a few exceptions: the Na abundance is largerby more than 1.4 dex than the cluster metallicity in B652, and by morethan 0.8 dex greater than the cluster metallicity in B2206; the Coabundance is 1.0 dex over the solar abundance for T191, while Zr isoverabundant over the solar abundance by 0.4 dex in B2206. No lines ofHg or other heavy elements were observed in the spectra. Weak emissionlines of Ti II, similar to those frequently observed in HgMn stars havebeen discovered in one Horizontal Branch B-type star T191. Furthermore,we detected a radial velocity change of 0.9 km s-1 from onenight to the next for T183 and 0.4 km s-1 for B2151. Furtherhigh-resolution observations are needed to examine whether both starsare spectroscopic binaries.Based on observations obtained at the European Southern Observatory,Paranal, Chile (ESO programmes 076.D-0169(A) and 081.D-0498(A)).
| Search for vertical stratification of metals in atmospheres of blue horizontal-branch stars
Context: The observed abundance peculiarities of many chemical speciesrelative to the expected cluster metallicity in blue horizontal-branch(BHB) stars presumably appear as a result of atomic diffusion in thephotosphere. The slow rotation (typically v sin{i} < 10 kms-1) of BHB stars with effective temperatures T_eff > 11500 K supports this idea since the diffusion mechanism is only effectivein a stable stellar atmosphere. Aims: In this work we search forobservational evidence of vertical chemical stratification in theatmospheres of six hot BHB stars: B84, B267 and B279 in M 15 andWF2-2541, WF4-3085 and WF4-3485 in M 13. Methods: We undertake anabundance stratification analysis of the stellar atmospheres of theaforementioned stars, based on acquired Keck HIRES spectra. Results: We have found from our numerical simulations that three stars(B267, B279 and WF2-2541) show clear signatures of the verticalstratification of iron whose abundance increases toward the loweratmosphere, while the other two stars (B84 and WF4-3485) do not. ForWF4-3085 the iron stratification results are inconclusive. B267 alsoshows a signature of titanium stratification. Our estimates for radialvelocity, v sin{i} and overall iron, titanium and phosphorus abundancesagree with previously published data for these stars after taking themeasurement errors into account. The results support the hypothesisregarding the efficiency of atomic diffusion in the stellar atmospheresof BHB stars with T_eff > 11 500 K.Full Table [see full textsee full textsee full text] is only availablein electronic form at http://www.aanda.org
| A refined analysis of the remarkable Bp star HR 6000
Aims:UVES spectra of the very young (˜ 107 years)peculiar B-type star HR 6000 were analyzed in the near-UV and visualspectral regions (3050-9460 Å) with the aim of extending to otherspectral ranges the study made previously in the UV using IUE spectra.Methods: Stellar parameters T_eff = 12 850 K, log g = 4.10, and?=0 km s-1, as determined from H?, H?, H?Balmer profiles and from the Fe I, Fe II ionization equilibrium, wereused to compute an individual abundances ATLAS12 model. We identifiedspectral peculiarities and obtained final stellar abundances bycomparing observed and computed equivalent widths and line profiles. Results: The adopted model fails to reproduce the (b-y) and c colorindices. The spectral analysis revealed: the presence of emission linesfor Mn II, Cr II, and Fe II; isotopic anomalies for Hg, Ca; the presenceof interstellar lines of Na I at ?? 3302.3, 3302.9, 5890,5896 Å, and of K I at 7665, 7699 Å; the presence of a hugequantity of unidentified lines, which we presume to be mostly due to FeII transitions owing to the large Fe overabundance amounting to [+0.7].The main chemical peculiarities are an extreme overabundance of Xe,followed by those of Hg, P, Y, Mn, Fe, Be, and Ti. The mostunderabundant element is Si, followed by C, N, Al, S, Mg, V, Sr, Co, Cl,Sc, and Ni. The silicon underabundance [ -2.9] is the lowest value forSi ever observed in any HgMn star. The observed lines of He I cannot bereproduced by a single value of the He abundance, but they requirevalues ranging from [ -0.8] to [ -1.6] . Furthermore, when the observedand computed wings of He I lines are fitted, the observed line cores aremuch weaker than the computed ones. From the present analysis we inferthe presence of vertical abundance stratification for He, Mn, andpossibly also Fe and P.Based on observations collected at the European Southern Observatory,Paranal, Chile (ESO programme 076.D-0169(A)). Table 6 is only availablein electronic form at http://www.aanda.org
| Heavy calcium in CP stars
Large wavelength shifts of infrared triplet lines of CaII have beenobserved in the spectra of HgMn and magnetic Ap stars. They have beenattributed to the heavy calcium isotopes, including 48Ca. Onemember of the triplet, ?8542, had been either unavailable, or ofpoor quality in earlier spectra. The present material shows conclusivelythat the stellar ?8542 shifts are consistent with aninterpretation in terms of 48Ca. We find no relation betweenisotopic shifts of the CaII triplet lines, and those of HgII?3984. There is a marginal indication that the shifts areanticorrelated with the surface field strengths of the magnetic stars.We see sparse evidence for 48Ca in other chemically peculiarstars, for example, Am stars, metal-poor stars or chemically peculiarred giants. However, the sample is still very small, and the wavelengthsof all three triplet lines, including those in the Sun, show slightpositive shifts with respect to terrestrial positions.Some profiles of the CaII infrared triplet in the magnetic stars showextensive wings beyond a well-defined core. We can obtain reasonablefits to these profiles using a stratified calcium abundance similar tothat used by previous workers. There is no indication that either thestratification or the Zeeman effect significantly disturbs themeasurement of isotope shifts.Based on observations obtained at the European Southern Observatory,Paranal and La Silla, Chile [ESO programmes 076.D-0169(A) and076.C-0172(A)].E-mail: cowley@umich.edu (CRC); shubrig@eso.org (SH);castelli@ts.astro.it (FC); fgonzalez@casleo.gov.ar (JFG); bwolff@eso.org(BW)
| Detection of variable Si II, Mn II, and Fe II emission lines in the magnetic Bp star a Centauri
Context: The nature of non-variable high-excitation emission linesdetected in the optical spectra of normal late-B type and chemicallypeculiar HgMn and PGa stars is still poorly understood. Aims: Tobetter understand the origin of the weak emission lines in B type starsit is especially important to investigate the spectra of a variety ofstars to search for correlations between the emergence of these linesand fundamental stellar parameters. Methods: We have acquiredhigh resolution UVES spectra for the sharp-lined magnetichelium-variable star a Cen over the rotation period of 8.82 d to searchfor the presence of weak emission lines. Results: For the firsttime we present observational evidence for the appearance of variablehigh-excitation Si II, Mn II and Fe II emission lines in a magnetic Bpstar. Si II emissions are the strongest at the phase corresponding tothe maximum strength of He I lines. Mn II and Fe II emissions vary inantiphase to the He I lines. A correlation is found between the probablelocation of Mn and Fe surface spots and the strength of the emissionlines. On the basis of the currently available data it seems possiblethat the same kind of selective excitation process is working in theatmospheres of objects within a broad parameter space which could bedefined by age, effective temperature, chemical composition, rotationalvelocity, and magnetic field. Neutral iron lines previously reported toappear broad and shallow at certain phases are not detected in ourspectra, although two of them are identified as He I forbidden lines,showing maximum strength at the phase of the passage of the He richregion across the visible disk.Based on observations collected at the European Southern Observatory,Paranal, Chile (ESO programmes 65.L-0316(A) and 073.D-0504(A)).
| Vertical abundance stratification in the blue horizontal branch star HD 135485
Context: It is commonly believed that the observed overabundances ofmany chemical species relative to the expected cluster metallicity inblue horizontal branch (BHB) stars appear as a result of atomicdiffusion in the photosphere. The slow rotation of BHB stars (with T_eff> 11 500 K), typically v sin{i} < 10 km s-1, isconsistent with this idea. Aims: In this work we search forobservational evidence of vertical chemical stratification in theatmosphere of HD 135485. If this evidence exists, it will demonstratethe importance of atomic diffusion processes in the atmospheres of BHBstars. Methods: We undertake an extensive abundance stratificationanalysis of the atmosphere of HD 135485, based on recently acquired highresolution and S/N CFHT ESPaDOnS spectra and a McDonald-CE spectrum. Results: Our numerical simulations show that nitrogen and sulfur revealsignatures of vertical abundance stratification in the stellaratmosphere. It appears that the abundances of these elements increasetoward the upper atmosphere. This fact cannot be explained by theinfluence of microturbulent velocity, because oxygen, carbon, neon,argon, titanium and chromium do not show similar behavior and theirabundances remain constant throughout the atmosphere. It seems that theiron abundance may increase marginally toward the lower atmosphere. Thisis the first demonstration of vertical abundance stratification ofmetals in a BHB star.Based on observations made with ESPaDOnS at the Canada-France-HawaiiTelescope (CFHT) operated by the National Research Council (NRC) ofCanada, the Institut des Sciences de l'Univers of the Centre National dela Recherche Scientifique (CNRS) and the University of Hawaii and onobservations made with Echelle Spectrograph on the McDonald Observatory2.1-m Otto Struve Telescope. Full Table 2 is only available inelectronic form at http://www.aanda.org
| 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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| Abundance anomalies in hot horizontal branch stars of the galactic globular cluster NGC 1904
We present abundance measurements, based on high-resolution opticalspectroscopic data obtained with the Ultraviolet and Visual EchelleSpectrograph mounted on Kueyen (Very Large Telescope UT2), for ten starsin the extended blue horizontal branch of the Galactic globular clusterNGC 1904 (M79). In agreement with previous findings for other clusters,we obtain normal abundances for stars cooler than T_eff 11 000 K,and largely anomalous abundances for hotter stars: large He depletions,and overabundances of Fe, Ti, Cr, P and Mn. The abundances of Mg, Si andCa are roughly normal, in the hot stars as well as in the cooler ones.This abundance pattern can be attributed to the onset of diffusion andto radiation pressure in the stable atmospheres of hot horizontal branchstars.
| 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.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| A peculiar metal-rich star, HD 135485
Local thermodynamic equilibrium (LTE) absolute and differentialabundances are presented for a peculiar metal-rich B-type star, HD135485. These suggest that HD 135485 has a general enrichment of ~0.5dexin all the metals observed (C, N, O, Ne, Mg, Al, Si, P, S, Cl, Ar, Sc,Ti, Cr, Mn, Fe and Sr), except for nickel. The helium enhancement andhence hydrogen deficiency can account for <=0.2dex of thisenhancement of metals, with the additional enhancement probably beingrepresentative of the progenitor gas. However, some of the metals appearto have greater enhancements, which may have occurred during the star'sevolution. The significantly larger nitrogen abundance coupled with amodest helium enhancement observed in HD 135485 indicates thatcarbon-nitrogen (CN) processed material has possibly contaminated thestellar surface. Neon and carbon enhancements may indicate that heliumcore flashes have also occurred in HD 135485. Some of the iron-groupelements (viz. Mn and Ni) appear to have similar abundance patterns tothat of silicon Ap stars, but it is uncertain how these abundancepatterns formed if they were not present in the progenitor gas. From akinematical investigation it is unclear whether this star formed in ametal-rich region as implied by its chemical composition. From itsposition in the Hertzsprung-Russell diagram, HD 135485 would appear tobe an evolved star lying close to or on the horizontal branch.
| 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
| The First 50 Years at Palomar, 1949-1999 Another View: Instruments, Spectroscopy and Spectrophotometry and the Infrared
We review the research on a wide variety of topics using data obtainedwith the 200-inch Hale telescope. Using state-of-the-art spectrographs,photometers, spectrometers and infrared detectors, the Palomarastronomers investigated the spectra of stars, interstellar matter, AGNsand quasars in great detail. Spectral resolutions ranged from 1000 A forbroad-band photometry to 0.04 A using interferometric techniques.
| Orbital elements and abundance analyses of the double-lined spectroscopic binary alpha Andromedae
We performed a spectroscopic study of the SB2 Mercury-Manganese staralpha And with Reticon and CCD spectra obtained at the Crimean and theDominion Astrophysical Observatories. Our measurements particularly ofthe secondary's radial velocities resulted in improved orbital elementswith a spectroscopic mass ratio m_B/m_A = 0.50 +/- 0.03 which is in goodagreement with the mass-luminosity solution for this system. Elementalabundance analyses using synthetic spectra show that the primary haselemental abundances somewhat similar to those of other HgMn stars whilethe cooler secondary probably is a metallic-line star. The possiblevariability of Hg II lambda 3984 is discussed.
| Hot Horizontal-Branch Stars: The Ubiquitous Nature of the ``Jump'' in Strömgren u, Low Gravities, and the Role of Radiative Levitation of Metals
A ``jump'' in the blue horizontal-branch (HB) distribution in the (V,u-y) color-magnitude diagram has recently been detected in the globularcluster (GC) M13 (NGC 6205) by Grundahl and coworkers. Such an effect ismorphologically best characterized as a discontinuity in the (u, u-y)locus, with stars in the range 11,500 K<~T_eff<~20,000 K deviatingsystematically from (in the sense of appearing brighter and/or hotterthan) canonical zero-age HB models. In this article, we presentStrömgren u, y photometry of 14 GCs obtained with three differenttelescopes (ESO Danish, Nordic Optical Telescope, and the Hubble SpaceTelescope) and demonstrate that the jump in Strömgren u is presentin every GC whose HB extends beyond T_eff>~11,500 K, irrespective ofmetallicity, mixing history on the red giant branch (RGB), or any knownparameter characterizing our sample of GCs. We thus suggest that the ujump is a ubiquitous feature, intrinsic to all HB stars hotter thanT_eff~=11,500 K. We draw a parallel between the ubiquitous nature of theu jump and the well-known problem of low measured gravities among blueHB stars in GCs and in the field. We note that the ``gravity jump''occurs over the same temperature range as the u jump and also that itoccurs in every metal-poor cluster for which gravities have beendetermined-again irrespective of metallicity, mixing history on the RGB,or any known parameter characterizing the surveyed GCs. Furthermore, wedemonstrate that the u jump and the gravity jump are connected on astar-by-star basis. We thus suggest that the two most likely aredifferent manifestations of one and the same physical phenomenon. Wepresent an interpretative framework which may be capable ofsimultaneously accounting for both the u jump and the gravity jump.Reviewing spectroscopic data for several field blue HB stars, as well astwo blue HB stars in NGC 6752, we find evidence that radiativelevitation of elements heavier than carbon and nitrogen takes place atT_eff>~11,500 K, dramatically enhancing the abundances of such heavyelements in the atmospheres of blue HB stars in the ``critical''temperature region. We argue that model atmospheres which take diffusioneffects into account are badly needed and will likely lead to betteroverall agreement between canonical evolutionary theory and theobservations for these stars. Based on observations made with the NOT,operated on the island of La Palma jointly by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.
| On the gap in horizontal branches at B - V about zero
It is proposed that the gap observed in the horizontal branch sequenceof many globular clusters at B-V about zero is due to a surfacephenomenon. Stars on the hotter side of the gap - T_eff gtrsim 10000 K -have an atmospheric chemical composition altered as in peculiar A and Bstars. The appearance of a convective regime in the surface layers atthe temperature and gravity of the gap cancel the peculiarities: it isproposed that the ensuing changes in surface physical conditions giveorigin to the observed gap.
| UV observations of B to F-type stars.
Not Available
| Identification of lambda Bootis stars using IUE spectra. I. Low resolution data
An analysis of the stars included in the catalogue of lambda Bootisstars by Paunzen et al. (1997) and which also have IUE observations ispresented here. Population I A-F type stars as well as field horizontalbranch stars were also included in the analysis. Using line-ratios ofcarbon to heavier elements (Al and Ni) allows us to establishunambiguous membership criteria for the lambda Bootis group. Tables 1-3are only available in electronic form at CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| Abundances of the ^3^He star 3 CEN A (B5 IIIp) from ultraviolet IUE spectra.
High resolution (0.010-0.025nm) IUE ultraviolet spectra of the peculiar^3^He star 3 Cen A were analyzed in the whole 120-320nm region.Abundances were derived from the comparison of the observed and computedspectra. For computing spectra a Kurucz ATLAS9 model with parametersT_eff_=17500K, logg=3.8, and microturbulent velocity ?=0km/s wasadopted. A rotational velocity vsini=0km/s was assumed. Colour indices,flux distribution, ultraviolet Si lines, and Balmer profiles were usedto fix the model parameters. The observed spectra are reproduced at bestwith the following abundances: He [-0.55], B [-1.0], C [-0.75], N[-0.5], Mg [-0.5], Al [-1.5] underabundant, P [+1.6], Sc [+1.0], Mn[+1.4], Cu [+2.0] overabundant, Ga [+3.25], Kr [+3.3], Hg [+4.5]extremely overabundant. The comparison of the ultraviolet spectrum andof the abundances of 3 Cen A with those of the normal B-type star ?Her and of the Pop II peculiar B-type star Feige 86 has shown that thesame elements contribute to the line spectrum of ? Her and 3 Cen Aeven if with different abundances, so that the spectra can be compared.In the case of Feige 86, the overabundance of heavy elements which arenot observed in 3 Cen A (i.e. Pt II, Pt III, Au II, Au III, probably MoIII), the lower overabundance of Ga [+1.0], and the largerunderabundance of the light elements C [-2.5] and N [-2.0] make theultraviolet line spectra of Feige 86 somewhat different from those ofboth ? Her and 3 Cen A. Also the He I lines have different profilesin the two peculiar stars, although He is underabundant in both. Withthe specific abundances of 3 Cen A we computed an opacity samplingATLAS12 model having the same parameters as the ATLAS9 model. We foundthat the energy distribution from the ATLAS9 model and solar abundancesis not very different from that derived from the ATLAS12 model, thesynthetic spectrum approach, and the specific abundances of 3 Cen A.
| Interstellar polarization at high galactic latitudes from distant stars. II. Evidence for depolarization starting at Z=~600pc.
We have measured linear polarization for 20 distant high latitude A andF stars, as a first step to extend our previous study (Berdyugin et al.1995A&A...294..568B: Paper I) of the North Galactic polar cap todistances larger than 600pc. The results give tentative evidence fordepolarization starting to be seen around Z=~500pc, possibly indicatingthat there is a significant change in the magnetic field direction.Depolarization requires that there is still light-polarizing dust in theZ range 500-1000pc and the lower limit to extinction inferred in Paper I(A_B_>0.11mag) must be increased by a yet undetermined amount.
| 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.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| A search for stars with strong magnetic fields among horizontal-branch stars and hot subdwarfs
Not Available
| The field horizontal-branch B-type star Feige 86.
IUE and visible high resolution spectra of the halo B-type star Feige 86are analyzed with the aim to get further insight into the atmosphericparameters and surface chemical composition of this Pop II star. Theanalysis is mostly based on the comparison of photometric,spectrophotometric, and spectroscopic observations with color indices,fluxes, and spectra computed by using Kurucz (1993a,b) codes, Kurucz(1993a) LTE ATLAS9 model atmospheres, and Kurucz (1993b) line lists. Theatmospheric parameters T_eff_=16430+/-250K and logg=4.20+/-0.02 aredetermined from the Stroemgren photometry, visual energy distribution,and Balmer profiles. A colour excess E(B-V) between 0.02 and 0.08mag isdeduced on the basis of both photometric and spectrophotometric data.Although the star's kinematics implies that it is a Pop II object (henceon the HB, given its spectral type) we find that its chemicalcomposition is peculiar and unlike that of Pop II stars. We find thatlight elements (up to S) are underabundant, with the exception of P;iron-peak elements are solar or slightly overabundant; heavy elements,with the exception of Ge, are overabundant. In particular, we identifylines of Pt II, Au III, and Hg II consistent with overabundances from3.5 to 4.0dex. Several Mo III lines are also identified. He I lines arecarefully analyzed and the detection of the ^3^He line at 667.8nm isdiscussed. Some ultraviolet lines arising from a lower level with energyclose to 0eV are affected by an additional slightly red-shiftedabsorption, probably of interstellar or circumstellar origin. We comparethe spectra of Feige 86 with those of the normal Pop I B-type star? Her and with those of the peculiar Pop I B-type star 3 Cen A, towhich Feige 86 has always been associated. We show that the similaritywith 3 Cen A is marginal, because, although nearly all the same elementsare affected by abundance anomalies, these occur in a different degreein the two stars, except for He, P, and Cu. No Mo, Pt, and Au lines havebeen identified in 3 Cen A. To what extent the different abundances ofthe two stars can be explained in terms of the different evolutionaryhistory or of different atmospheric phenomena, such as diffusion, isstill an open question.
| The metallicities and kinematics of RR Lyrae variables, 1: New observations of local stars
In order to study the structure and formation history of the galaxy, wehave obtained low-to-moderate dispersion spectra of 302 nearby RR Lyraevariables of Bailey type 'ab'. We derived abundances, typically accurateto 0.15-0.20 dex and calibrated to the Zinn & West (1984) globularcluster metallicity scale, from the pseudoequivalent widths of the Ca IIK, H delta, H gamma, and H beta lines. Radial velocities accurate tobetween 2 and 30 km/s were obtained from the spectra and from theliterature. Distances accurate to between 5% and 20% were derived frompublished apparent magnitudes and Burstein & Heiles (1982)reddenings. The metallicity distribution of the RR Lyrae stars peaks at(Fe/H)K approximately equals -1.5, and is narrower than thatof the Ryan & Norris (1991) subdwarfs, as expected since the mostmetal-rich and metal-poor progenitors preferentially appear as stablered and blue horizontal branch stars, rather than as RR Lyrae. Themetal-rich tail of the RR Lyrae distribution extends to(Fe/H)K approximately equals 0, and a qualitative analysis ofthe distribution of distances from the galactic plane shows that thestars in this tail (i.e., (Fe/H)K greater than -1.0) are moreconcentrated to the plane than the more metal-poor stars. The abundancedistribution of the local RR Lyrae stars is in excellent agreement withthe changing abundance distributions of distant RR Lyrae stars as afunction of galactocentric distance, as derived by Suntzeff et al.(1991), who ascribed this change to systematic variation in horizontalbranch morphology (probably age variations) with galactocentricdistance. The abundance distribution of the local RR Lyrae stars alsoagrees well with those of the distant RR Lyrae stars as a function ofdistance from the galactic plane. There is no evidence for an abundancegradient in this direction, suggesting that gaseous dissipation did notplay a major role in the formation of the outer halo.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Гончие Псы |
| Прямое восхождение: | 13h38m24.76s |
| Склонение: | +29°21'56.0" |
| Видимая звёздная величина: | 10.009 |
| Собственное движение RA: | -14.8 |
| Собственное движение Dec: | -110 |
| B-T magnitude: | 9.868 |
| V-T magnitude: | 9.998 |
Каталоги и обозначения:
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