Contents
Images
Upload your image
DSS Images Other Images
Related articles
The first observation of optical pulsations from a soft gamma repeater: SGR 0501+4516
We present high-speed optical photometry of the soft gamma repeater SGR0501+4516, obtained with ULTRACAM on two consecutive nightsapproximately 4 months after the source was discovered via its gamma-raybursts. We detect SGR 0501+4516 at a magnitude of i'= 24.4 ± 0.1.We present the first measurement of optical pulsations from a SGR,deriving a period of 5.7622 ± 0.0003 s, in excellent agreementwith the X-ray spin period of the neutron star. We compare themorphologies of the optical pulse profile with the X-ray and infraredpulse profiles; we find that the optical, infrared and harder X-raysshare similar double-peaked morphologies, but the softer X-rays exhibitonly a single-peaked morphology, indicative of a different origin. Theoptical pulsations appear to be in phase with the X-ray pulsations andexhibit a root-mean-square pulsed fraction of 52 ± 7 per cent,approximately a factor of 2 greater than in the X-rays. Our results finda natural explanation within the context of the magnetar model for SGRs.
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| Chemical composition of high proper-motion stars based on short-wavelength optical spectra
The results of spectroscopic observations made with the NES echellespectrograph of the 6-m BTA telescope of the Special AstrophysicalObservatory of the Russian Academy of Sciences in the wavelengthinterval of 3550-5100 Å with a spectral resolution of R≥50000are used to determine the fundamental parameters and atmosphericabundances of more than 20 chemical elements including heavy s- andr-process elements from Sr to Dy for a total of 14 metal-poor G-K-typestars. The abundances of Mg, Al, Sr, and Ba were calculated with non-LTEline-formation effects accounted for. The inferred overabundance ofeuropium with respect to iron agrees with the results obtained for thestars of similar metallicity. The chemical composition of the starBD+80°245 located far from the Galactic plane is typical of stars ofthe accreted halo: this star exhibits, in addition to theover-deficiency of α-process elements, also the over-deficiency ofthe γ-process element Ba: [Ba/Fe]= -1.46. The kinematicalparameters and chemical composition imply that the stars studied belongto different Galactic populations. The abundance of the long-livingelement Th relative to that of the r-process element Eu is determinedfor six stars using the synthetic-spectrum method.
| The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
| An absolutely calibrated Teff scale from the infrared flux method. Dwarfs and subgiants
Various effective temperature scales have been proposed over the years.Despite much work and the high internal precision usually achieved,systematic differences of order 100 K (or more) among various scales arestill present. We present an investigation based on the infrared fluxmethod aimed at assessing the source of such discrepancies and pin downtheir origin. We break the impasse among different scales by using alarge set of solar twins, stars which are spectroscopically andphotometrically identical to the Sun, to set the absolute zero point ofthe effective temperature scale to within few degrees. Our newlycalibrated, accurate and precise temperature scale applies to dwarfs andsubgiants, from super-solar metallicities to the most metal-poor starscurrently known. At solar metallicities our results validatespectroscopic effective temperature scales, whereas for [Fe/H]? -2.5our temperatures are roughly 100 K hotter than those determined frommodel fits to the Balmer lines and 200 K hotter than those obtained fromthe excitation equilibrium of Fe lines. Empirical bolometric correctionsand useful relations linking photometric indices to effectivetemperatures and angular diameters have been derived. Our results takefull advantage of the high accuracy reached in absolute calibration inrecent years and are further validated by interferometric angulardiameters and space based spectrophotometry over a wide range ofeffective temperatures and metallicities.Table 8 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/512/A54
| Kinematics of high proper motion stars determined from high resolution spectra in ground-based ultraviolet
Radial velocities for 15 stars with high proper motions were measured asa result of spectral observations, conducted with the NES echellespectrograph of the 6-m BTA telescope in the wavelength range of3550-5100 Å with a spectral resolution of R=60000. Thestandard deviation of the measured velocity does not exceed ? ?0.9 km/s for the stars with metallicity [Fe/H]? ?1, and? ? 1.1 km/s for [Fe/H]? ?1. The heliocentricvelocities measured with high accuracy in combination withtrigonometrical parallaxes and proper motions from the HIPPARCOS catalogallowed us to determine the distances and parameters of the galacticorbits of the stars under study. In general they are located within 100pc; the binarity of several program stars is confirmed.
| Binarity of transit host stars. Implications for planetary parameters
Context: Straight-forward derivation of planetary parameters can only beachieved in transiting planetary systems. However, planetary attributessuch as radius and mass strongly depend on stellar host parameters.Discovering a transit host star to be multiple leads to a necessaryrevision of the derived stellar and planetary parameters. Aims:Based on our observations of 14 transiting exoplanet hosts, we deriveparameters of the individual components of three transit host stars(WASP-2, TrES-2, andTrES-4) which we detected to be binaries. Two ofthese have not been known to be multiple before. Parameters of thecorresponding exoplanets are revised. Methods: High-resolution“Lucky Imaging” with AstraLux at the 2.2 m Calar Altotelescope provided near diffraction limited images in i' and z'passbands. These results have been combined with existing planetary datain order to recalibrate planetary attributes. Results: Despitethe faintness (Δmag ~ 4) of the discovered stellar companions toTrES-2, TrES-4, and WASP-2, light-curve deduced parameters change by upto more than 1σ. We discuss a possible relation between binaryseparation and planetary properties, which - if confirmed - could hintat the influence of binarity on the planet formation process.Based on observations collected at the Centro AstronómicoHispano Alemán (CAHA) at Calar Alto, operated jointly by theMax-Planck-Institut für Astronomie and the Instituto deAstrofísica de Andalucía (CSIC).
| Searching for the metal-weak thick disc in the solar neighbourhood
An abundance analysis is presented of 60 metal-poor stars drawn fromcatalogues of nearby stars provided by Arifyanto et al. and Schuster etal. In an attempt to isolate a sample of metal-weak thick disc stars, weapplied the kinematic criteria Vrot >=100kms-1,|ULSR| <= 140kms-1 (LSR -local standard of rest) and |WLSR| <= 100kms-1.14 stars satisfying these criteria and having [Fe/H] <= -1.0 areincluded in the sample of 60 stars. Eight of the 14 have [Fe/H] >=-1.3 and may be simply thick disc stars of slightly lower than average[Fe/H]. The other six have [Fe/H] from -1.3 to -2.3 and are eithermetal-weak thick disc stars or halo stars with kinematics mimickingthose of the thick disc. The sample of 60 stars is completed by eightthick disc stars, 20 stars of a hybrid nature (halo or thick disc stars)and 18 stars with kinematics distinctive of the halo.
| Speckle interferometry of metal-poor stars in the solar neighborhood. II
The results of speckle interferometric observations of 115 metal-poorstars ([m/H] < ‑1) within 250 pc from the Sun and with propermotions µ ≳ 0.2″/yr, made with the 6-m telescope of theSpecial Astrophysical Observatory of the Russian Academy of Sciences,are reported. Close companions with separations ranging from0.034″ to 1″ were observed for 12 objects—G76-21,G59-1, G63-46, G135-16, G168-42, G141-47, G142-44, G190-10, G28-43,G217-8, G130-7, and G89-14—eight of them are astrometricallyresolved for the first time. The newly resolved systems include onetriple star—G190-10. If combined with spectroscopic and visualdata, our results imply a single:binary:triple:quadruple star ratio of147:64:9:1 for a sample of 221 primary components of halo and thick-diskstars.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Fourier Analysis of Hubble Space Telescope Fine Guidance Sensor Data of Binary Stars and Application to the Multiple System HD 157948
A Fourier-based method is presented for the analysis of binary andmultiple star data taken with the Hubble Space Telescope Fine GuidanceSensors (FGSs). Relative astrometry and magnitude differences areobtained as with standard FGS analysis techniques, and although the FGSsystem is essentially unfiltered, this method also permits thecharacterization of color differences between components of binary ormultiple star systems based on the wavelength dependence of theinterference fringes produced by the instrument. Using the multiplesystem HD 157948, we show that the method produces astrometric andphotometric measurements that are consistent with previous FGS analysisfor the three components that lie within the field of view of FGS andgives color differences relative to the primary for two of the threeknown companions. Speckle observations of the system with the WIYN 3.5 mtelescope at Kitt Peak National Observatory are also presented, which,in combination with the FGS results and other data available in theliterature, permit B-V colors and absolute V magnitudes to be obtainedof all four components in the system. Their colors and magnitudes areplotted on the H-R diagram, and a comparison with theoretical isochronesindicates that the results are consistent with theory for a relativelyyoung, somewhat metal-poor system.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Chemical abundances of very metal-poor stars
High-resolution and high signal-to-noise ratio spectra of 32 verymetal-poor stars were obtained with the Coudé echellespectrograph mounted on the 2.16-m telescope at the NationalAstronomical Observatories (Xinglong, China). Equivalent widths of FeI,FeII, OI, NaI, MgI, AlI, SiI, SiII, KI, CaI, ScII, TiI, VI, CrI, MnI,NiI, CuI and BaII lines were measured. Stellar effective temperatureswere determined by colour indices. Stellar surface gravities werecalculated from Hipparcos parallaxes and stellar evolutionary tracks.Photospheric abundances of 16 elements were derived by localthermodynamical equilibrium analysis. Stellar space motions (U, V, W)and Galactic orbital parameters were calculated. Based on kinematics,sample stars were separated into dissipative collapse and accretioncomponents of halo population. The global kinematics of the twocomponents were analysed. Element abundances were discussed as functionsof metallicities. The results of oxygen and α-elements abundanceconfirmed the previous works. The [K/Fe] shows a gradual systematicincrease toward a lower metallicity, such as in the case ofα-elements. The [Ba/Fe] trend suggests that the s-processdominated Ba production at least for the metal-poor stars with[Fe/H]> -2.0.
| The lithium content of the Galactic Halo stars
Thanks to the accurate determination of the baryon density of theuniverse by the recent cosmic microwave background experiments, updatedpredictions of the standard model of Big Bang nucleosynthesis now yieldthe initial abundance of the primordial light elements withunprecedented precision. In the case of ^7Li, the CMB+SBBN value issignificantly higher than the generally reported abundances for Pop IIstars along the so-called Spite plateau. In view of the crucialimportance of this disagreement, which has cosmological, galactic andstellar implications, we decided to tackle the most critical issues ofthe problem by revisiting a large sample of literature Li data in halostars that we assembled following some strict selection criteria on thequality of the original analyses. In the first part of the paper wefocus on the systematic uncertainties affecting the determination of theLi abundances, one of our main goal being to look for the "highestobservational accuracy achievable" for one of the largest sets of Liabundances ever assembled. We explore in great detail the temperaturescale issue with a special emphasis on reddening. We derive four sets ofeffective temperatures by applying the same colour {T}_eff calibrationbut making four different assumptions about reddening and determine theLTE lithium values for each of them. We compute the NLTE corrections andapply them to the LTE lithium abundances. We then focus on our "best"(i.e. most consistent) set of temperatures in order to discuss theinferred mean Li value and dispersion in several {T}_eff and metallicityintervals. The resulting mean Li values along the plateau for [Fe/H]≤ 1.5 are A(Li)_NLTE = 2.214±0.093 and 2.224±0.075when the lowest effective temperature considered is taken equal to 5700K and 6000 K respectively. This is a factor of 2.48 to 2.81 (dependingon the adopted SBBN model and on the effective temperature range chosento delimit the plateau) lower than the CMB+SBBN determination. We findno evidence of intrinsic dispersion. Assuming the correctness of theCMB+SBBN prediction, we are then left with the conclusion that the Liabundance along the plateau is not the pristine one, but that halo starshave undergone surface depletion during their evolution. In the secondpart of the paper we further dissect our sample in search of newconstraints on Li depletion in halo stars. By means of the Hipparcosparallaxes, we derive the evolutionary status of each of our samplestars, and re-discuss our derived Li abundances. A very surprisingresult emerges for the first time from this examination. Namely, themean Li value as well as the dispersion appear to be lower (althoughfully compatible within the errors) for the dwarfs than for the turnoffand subgiant stars. For our most homogeneous dwarfs-only sample with[Fe/H] ≤ 1.5, the mean Li abundances are A(L)_NLTE = 2.177±0.071 and 2.215±0.074 when the lowest effective temperatureconsidered is taken equal to 5700 K and 6000 K respectively. This is afactor of 2.52 to 3.06 (depending on the selected range in {T}_eff forthe plateau and on the SBBN predictions we compare to) lower than theCMB+SBBN primordial value. Instead, for the post-main sequence stars thecorresponding values are 2.260±0.1 and 2.235±0.077, whichcorrespond to a depletion factor of 2.28 to 2.52. These results,together with the finding that all the stars with Li abnormalities(strong deficiency or high content) lie on or originate from the hotside of the plateau, lead us to suggest that the most massive of thehalo stars have had a slightly different Li history than their lessmassive contemporaries. In turn, this puts strong new constraints on thepossible depletion mechanisms and reinforces Li as a stellartomographer.
| A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)
The LSPM catalog is a comprehensive list of 61,977 stars north of theJ2000 celestial equator that have proper motions larger than 0.15"yr-1 (local-background-stars frame). The catalog has beengenerated primarily as a result of our systematic search for high propermotion stars in the Digitized Sky Surveys using our SUPERBLINK software.At brighter magnitudes, the catalog incorporates stars and data from theTycho-2 Catalogue and also, to a lesser extent, from the All-SkyCompiled Catalogue of 2.5 million stars. The LSPM catalog considerablyexpands over the old Luyten (Luyten Half-Second [LHS] and New LuytenTwo-Tenths [NLTT]) catalogs, superseding them for northern declinations.Positions are given with an accuracy of <~100 mas at the 2000.0epoch, and absolute proper motions are given with an accuracy of ~8 masyr-1. Corrections to the local-background-stars propermotions have been calculated, and absolute proper motions in theextragalactic frame are given. Whenever available, we also give opticalBT and VT magnitudes (from Tycho-2, ASCC-2.5),photographic BJ, RF, and IN magnitudes(from USNO-B1 catalog), and infrared J, H, and Ks magnitudes(from 2MASS). We also provide an estimated V magnitude and V-J color fornearly all catalog entries, useful for initial classification of thestars. The catalog is estimated to be over 99% complete at high Galacticlatitudes (|b|>15deg) and over 90% complete at lowGalactic latitudes (|b|>15deg), down to a magnitudeV=19.0, and has a limiting magnitude V=21.0. All the northern starslisted in the LHS and NLTT catalogs have been reidentified, and theirpositions, proper motions, and magnitudes reevaluated. The catalog alsolists a large number of completely new objects, which promise to expandvery significantly the census of red dwarfs, subdwarfs, and white dwarfsin the vicinity of the Sun.Based on data mining of the Digitized Sky Surveys (DSSs), developed andoperated by the Catalogs and Surveys Branch of the Space TelescopeScience Institute (STScI), Baltimore.Developed with support from the National Science Foundation (NSF), aspart of the NASA/NSF NStars program.
| Reappraising the Spite Lithium Plateau: Extremely Thin and Marginally Consistent with WMAP Data
The lithium abundance in 62 halo dwarfs is determined from accurateequivalent widths reported in the literature and an improved infraredflux method temperature scale. The Li abundance of 41 plateau stars(those with Teff>6000 K) is found to be independent oftemperature and metallicity, with a star-to-star scatter of only 0.06dex over a broad range of temperatures (6000K
| A CCD imaging search for wide metal-poor binaries
We explored the regions within a radius of 25 arcsec around 473 nearby,low-metallicity G- to M-type stars using (VR)I optical filters andsmall-aperture telescopes. About 10% of the sample was searched up toangular separations of 90 arcsec. We applied photometric and astrometrictechniques to detect true physical companions to the targets. The greatmajority of the sample stars was drawn from the Carney-Latham surveys;their metallicities range from roughly solar to [Fe/H] = -3.5 dex. OurI-band photometric survey detected objects that are between 0 and 5 magfainter (completeness) than the target stars; the maximum dynamicalrange of our exploration is 9 mag. We also investigated the literature,and inspected images from the Digitized Sky Surveys to complete oursearch. By combining photometric and proper motion measurements, weretrieved 29 previously known companions, and identified 13 new propermotion companions. Near-infrared 2MASS photometry is provided for thegreat majority of them. Low-resolution optical spectroscopy (386-1000nm) was obtained for eight of the new companion stars. Thesespectroscopic data confirm them as cool, late-type, metal-depleteddwarfs, with spectral classes from esdK7 to sdM3. After comparison withlow-metallicity evolutionary models, we estimate the masses of theproper motion companion stars to be in the range 0.5-0.1Mȯ. They are moving around their primary stars atprojected separations between 32 and 57 000 AU. These orbitalsizes are very similar to those of solar-metallicity stars of the samespectral types. Our results indicate that about 15% of the metal-poorstars have stellar companions in wide orbits, which is in agreement withthe binary fraction observed among main sequence G- to M-type stars andT Tauri stars.Based on observations made with the IAC80 telescope operated on theisland of Tenerife by the Instituto de Astrofísica de Canarias inthe Spanish Observatorio del Teide; also based on observations made withthe 2.2 m telescope of the German-Spanish Calar Alto Observatory(Almería, Spain), the William Herschel Telescope (WHT) operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos (ORM) of the Instituto deAstrofísica de Canarias; and the Telescopio Nazionale Galileo(TNG) at the ORM.The complete Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/419/167
| Empirically Constrained Color-Temperature Relations. II. uvby
A new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our ``final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile.
| Lithium Abundance of Metal-poor Stars
High-resolution, high signal-to-noise ratio spectra have been obtainedfor 32 metal-poor stars. The equivalent widths of Li λ6708Åwere measured and the lithium abundances were derived. The averagelithium abundance of 21 stars on the lithium plateau is 2.33±0.02dex. The Lithium plateau exhibits a marginal trend along metallicity,dA(Li)/d[Fe/H] = 0.12±0.06, and no clear trend with the effectivetemperature. The trend indicates that the abundance of lithium plateaumay not be primordial and that a part of the lithium was produced inGalactic Chemical Evolution (GCE).
| IRFM temperature calibrations for the Vilnius, Geneva, RI(C) and DDO photometric systems
We have used the infrared flux method (IRFM) temperatures of a largesample of late type dwarfs given by Alonso et al. (\cite{alonso:irfm})to calibrate empirically the relations Teff=f (colour,[Fe/H]) for the Vilnius, Geneva, RI(C) (Cousins) and DDOphotometric systems. The resulting temperature scale and intrinsiccolour-colour diagrams for these systems are also obtained. From thisscale, the solar colours are derived and compared with those of thesolar twin 18 Sco. Since our work is based on the same Teffand [Fe/H] values used by Alonso et al. (\cite{alonso:escala}) tocalibrate other colours, we now have an homogeneous calibration for alarge set of photometric systems.Based on data from the GCPD.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| A Survey of Proper-Motion Stars. XVI. Orbital Solutions for 171 Single-lined Spectroscopic Binaries
We report 25,563 radial velocity measurements for 1359 single-linedstars in the Carney-Latham sample of 1464 stars selected for high propermotion. For 171 of these, we present spectroscopic orbital solutions. Wefind no obvious difference between the binary characteristics in thehalo and the disk populations. The observed frequency is the same, andthe period distributions are consistent with the hypothesis that the twosets of binaries were drawn from the same parent population. Thissuggests that metallicity in general, and radiative opacities inparticular, have little influence over the fragmentation process thatleads to short-period binaries. All the binaries with periods shorterthan 10 days have nearly circular orbits, while the binaries withperiods longer than 20 days exhibit a wide range of eccentricities and amedian value of 0.37. For the metal-poor high-velocity halo binaries inour sample, the transition from circular to eccentric orbits appears tooccur at about 20 days, supporting the conclusion that tidalcircularization on the main sequence is important for the oldestbinaries in the Galaxy. Some of the results presented here usedobservations made with the Multiple Mirror Telescope, a joint facilityof the Smithsonian Institution and the University of Arizona.
| The u'g'r'i'z' Standard-Star System
We present the 158 standard stars that define the u'g'r'i'z' photometricsystem. These stars form the basis for the photometric calibration ofthe Sloan Digital Sky Survey. The defining instrument system andfilters, the observing process, the reduction techniques, and thesoftware used to create the stellar network are all described. Webriefly discuss the history of the star selection process, thederivation of a set of transformation equations for theUBVRCIC system, and plans for future work.
| Models for Old, Metal-Poor Stars with Enhanced α-Element Abundances. II. Their Implications for the Ages of the Galaxy's Globular Clusters and Field Halo Stars
The ages of globular clusters (GCs) and post-turnoff field stars in theGalactic halo are derived using new stellar evolutionary models thatexplicitly take into account the observed abundances of theα-elements. Whereas the distances of the field subgiantsconsidered in this study are based on Hipparcos parallax measurements,theoretical zero-age horizontal-branch (ZAHB) loci have been used to setthe GC distance scale. (As reported in Paper I, the latter imply RRLyrae luminosities that are within 0.1-0.15 mag, on the high side, ofthose found for field variables from Baade-Wesselink, trignometicparallax, and statistical parallax studies.) Both the field and clusterobservations indicate that the most metal-deficient stars are >~14Gyr old while those with [Fe/H] <~-1.3 are 2-3 Gyr younger. Unlessthe O/Fe (or, more generally, the α/Fe) number abundance ratiorises quite steeply with decreasing [Fe/H], it seems unlikely that asignificant age-metallicity relation can be avoided. Using what iseffectively the ΔVHBTO method of determiningrelative cluster ages, we find that the dispersion in age at any [Fe/H]less than ~-1.0 is small (<~10%-15%). Even Arp 2 and IC 4499, whichhad been previously categorized as ``young GCs,'' probably havenear-normal ages for their metallicities-though a more definitiveconclusion must await improved photometry for these systems. Ruprecht106 appears no more than 1-1.5 Gyr younger than M3, as opposed to the ~4Gyr age difference that others have found. However, Palomar 12 andTerzan 7 are undoubtedly young, and they provide strong evidence that,at [Fe/H] >~-1.0, the ages of GCs differ by as much as 4 Gyr (or~25%). (A much larger sample of metal-rich clusters must be studied toascertain whether the distribution of ages at higher metallicities isbroad or narrow: Pal 12 and Ter 7 could well be atypical and representthe tail of a distribution that is strongly peaked near 12 Gyr.)Importantly, for the best-observed systems, there is no obvious conflictbetween the relative age estimates based on theΔVHBTO method, on the one hand, and theΔ(B-V)TO,RGB technique, on the other. However, thereare some exceptions, like M68, M53, M13, and NGC 288 for which the twoapproaches give slightly different results, indicating that something inaddition to, or besides, age must be playing a role. From isochrone/ZAHBfits to the C-M diagrams (CMDs) of the outer-halo GCs Pal 3, Pal 4, andEridanus, we conclude that there is no more than a small dependence ofage on Galactocentric distance. Pal 4 seems to have very close to thesame age as NGC 362, NGC 1261, and NGC 1851, while Eridanus and Pal 3appear to be <~1 Gyr younger than most inner-halo systems of the samemetallicity. Unless our understanding of the HB phase of evolution isseriously in error, cluster-to-cluster age differences (at a givenmetallicity) are much too small for age to be the most important of thepossible second parameters in determining the morphology of thehorizontal branch (the first parameter being [Fe/H]). Finally, wesuggest that the GC distance scale as inferred from studies of nearby RRLyraes is not necessarily in conflict with that based on localsubdwarfs. A reconciliation of the two approaches is possible simply byadopting a particular metallicity scale for the globular clusters-onethat is much closer to the Zinn-West scale than to that recentlyproposed by Carretta & Gratton. Indeed, such a simple way ofachieving consistency between subdwarf-based distances and thoseinferred from RR Lyraes seems compelling. If this suggestion is correct,then the ``long'' distance scale and low estimates of GC ages are nottenable. In fact, the adoption of the ``short'' distance scale, implyingages >~15 Gyr for the most metal-poor GCs (and <~18.30 for thetrue distance modulus of the Large Magellanic Cloud), leads to muchimproved agreement between synthetic and observed CMDs in the vicinityof the turnoff. It does cause a mismatch between predicted and observedHB luminosities, in the sense that the models are too bright by~0.1-0.15 mag, but this may simply be an indication that currentconductive opacities or the assumed chemical abundance parameters (Y,[O/Fe], and/or [α/Fe]) are not quite right.
| Younger and Brighter - New Distances to Globular Clusters Based on HIPPARCOS Parallax Measurements of Local Subdwarfs
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..161R&db_key=AST
| The primordial lithium abundance
Lithium abundances in a selected sample of halo stars have been revisedby using the new accurate infrared flux method (IRFM) effectivetemperatures by Alonso, Arribas & Martinez-Roger. From 41 plateaustars (T_eff>5700 and [Fe/H]<=-1.5) we found no evidence forintrinsic dispersion, a tiny trend with T_eff and no trend with [Fe/H].The trend with the T_eff is fully consistent with the standard Liisochrones of Deliyannis, Demarque & Kawaler, implying a primordialvalue for Li of A(Li)=2.238+/-0.012_1sigma+/-0.05_sys. The presentresults argue against any kind of depletion predicted by diffusion,rotational mixing or stellar winds. Therefore the Li observed inPopulation II stars provides a direct and reliable estimate of thebaryonic density which can rival other baryonic indicators such as thedeuterium in high-redshift systems. The present upwards revision ofprimordial Li in the framework of standard big bang nucleosynthesis(SBBN) gives, at 1sigma, two solutions for the baryonic density:Omega_Bh^2=0.0062^+0.0018_-0.0011 or Omega_Bh^2=0.0146^+0.0029_-0.0033.
| Determination of effective temperatures for an extended sample of dwarfs and subdwarfs (F0-K5).
We have applied the InfraRed Flux Method (IRFM) to a sample of 475dwarfs and subdwarfs in order to derive their effective temperatureswith a mean accuracy of about 1.5%. We have used the new homogeneousgrid of theoretical model atmosphere flux distributions developed byKurucz (1991, 1993) for the application of the IRFM. The atmosphericparameters of the stars cover, roughly, the ranges:3500K<=T_eff_<=8000K -3.5<=[Fe/H]<=+0.53.5<=log(g)<=5. The monocromatic infrared fluxes at the continuum,and the bolometric fluxes are derived using recent results, whichsatisfy the accuracy requeriments of the work. Photometric calibrationshave been revised and applied to estimate metallicities, although directspectroscopic determinations were preferred when available. The adoptedinfrared absolute flux calibration, based on direct optical measurementsof angular stellar diameters, sets the effective temperatures determinedusing the IRFM on the same scale than those obtained by direct methods.We derive three temperatures, T_J_, T_H_ and T_K_, for each star usingthe monochromatic fluxes at different infrared wavelengths in thephotometric bands J, H, and K. They show good consistency over 4000 K,and no trend with wavelength may be appreciated. We provide a detaileddescription of the steps followed for the application of the IRFM, aswell as the sources of the errors associated to the different inputs ofthe method, and their transmission into the final temperatures. We alsoprovide comparison with previous works.
| Lithium Processing in Halo Dwarfs, and T eff, [Fe/H] Correlations on the Spite Plateau
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...458..543R&db_key=AST
| 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.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Cassiopeia |
| Right ascension: | 00h43m44.34s |
| Declination: | +72°10'43.1" |
| Apparent magnitude: | 10.208 |
| Proper motion RA: | 321.5 |
| Proper motion Dec: | 90.7 |
| B-T magnitude: | 10.619 |
| V-T magnitude: | 10.242 |
Catalogs and designations:
|
