Contents
Images
Upload your image
DSS Images Other Images
Related articles
Lithium Isotopes in Population II Dwarfs
We address the evolution of lithium in Population II dwarf stars underthe joint effects of microscopic diffusion and tachocline mixing. Thisprocess relies on analytical developments and is also constrained byhelioseismology observations. It was successfully applied to solaranalogs but never investigated in halo stars. It is induced in the upperradiation zone by rotation and a slight differential rotation inlatitude. Consequently we modeled different possible rotation historiesof halo stars, showing that the initial rotation rate had no impact onlithium in the framework of tachocline mixing. We find a negligibleimpact of pre-main-sequence evolution on 7Li independent ofmetallicity provided that [Fe/H]<-1. On the contrary, microscopicdiffusion and tachocline turbulence act on the long term of mainsequence and shape the current 7Li-Teff patternfrom the turnoff down to 5000 K. The tachocline mixing models fit the7Li-Teff relation better than the pure microscopicdiffusion models. We address the issue of warm 7Li-poor starsand conclude that a moderate mass transfer from a companion couldexplain their composition. Finally, we discuss the lithium lighterisotope. The pre-main-sequence and main-sequence 6Lidepletion we compute seems difficult to reconcile with the currentobservations.
| 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.
| Beryllium in Ultra-Lithium-Deficient Halo Stars: The Blue Straggler Connection
There exists a small group of metal-deficient stars that have Liabundances well below the Li plateau that is defined by over 100unevolved stars with temperatures above 5800 K and values of[Fe/H]<-1.0. Abundances of Be have been determined for most of theseultra-Li-deficient stars in order to investigate the cause of the Lideficiencies. These Li-deficient stars have implications on the value ofprimordial Li. High-resolution and high signal-to-noise ratio spectrahave been obtained in the Be II spectral region near 3130 Å forsix ultra-Li-deficient stars with the Keck I telescope and its newUV-sensitive CCD on the upgraded HIRES. The spectrum synthesis techniquehas been used to determine Be abundances. All six stars are found tohave Be deficiencies also. Two have measurable but reduced Be, and fourhave only upper limits on Be. These results are consistent with the ideathat these Li- and Be-deficient stars are analogous to blue stragglers.The stars have undergone mass transfer events (or mergers) that destroyor dilute both Li and Be. The findings cannot be matched by the modelsthat predict that the deficiencies are due to extramixing in a subset ofhalo stars that were initially rapid rotators, with the possibleexception of one star, G139-8. Because the ultra-Li-deficient stars arealso Be-deficient, they appear to be genuine outliers in the populationof halo stars used to determine the Li plateau in that they no longerhave the Li in their atmospheres that was produced in the big bang.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| Metal-poor Field Blue Stragglers: More Evidence for Mass Transfer
We report radial velocity studies of five candidate metal-poor fieldblue stragglers, all known to be deficient in lithium. Four of the fivestars are single-lined spectroscopic binaries, with periods ranging from302 to 840 days, and low orbital eccentricities, in agreement withsimilar behavior found for other blue straggler candidates by Preston& Sneden and Carney et al. The limited data available for lithiumabundances indicate that all blue straggler binaries have depletedlithium, but that constant velocity stars generally have normal lithiumabundances. This suggests that the ``lithium gap'' for hot metal-poormain-sequence stars may not exist or lies at higher temperatures thanfound in the Hyades. Our results and those of Preston & Sneden showhigher values of vrotsini for the binary stars than those ofcomparable temperature constant velocity stars. The orbital periods aretoo long for tidal effects to be important, implying that spin-up duringmass transfer when the orbital separations and periods were smaller isthe cause of the enhanced rotation. The mass function distribution issteeper for the blue straggler binary stars than that of lower masssingle-lined spectroscopic binaries, indicating a narrower range insecondary masses. We argue that if all secondaries are white dwarfs withthe same mass, it is probably around 0.55 Msolar. The modelsof Rappaport et al., applied to white dwarf secondaries, suggest thatthe orbital elements of all metal-poor binary blue stragglers areconsistent with stable mass transfer, with the possible exception ofG202-65.Some of the results presented here used observations made with theMultiple Mirror Telescope, a joint facility of the SmithsonianInstitution and the University of Arizona.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| Stellar Archaeology: A Keck Pilot Program on Extremely Metal-Poor Stars From the Hamburg/ESO Survey. III. The Lead (Pb) Star HE 0024-2523
We present a detailed abundance analysis, including spectral syntheses,of a very metal-poor ([Fe/H]~=-2.7) peculiar main-sequence star (HE0024-2523) detected during the course of the Keck Pilot Program. Radialvelocities of this star were obtained during four different observingruns over a time span of 1.1 yr and demonstrate that it is clearly ashort-period spectroscopic binary. An orbital solution was obtained, andorbital parameters were determined with high precision. The rotationalvelocity was also measured (vrotsini=9.7+/-1.5 kms-1) rotation appears likely to be synchronous with theorbit. The abundance analysis and spectral syntheses indicate that theobject is a CH star characterized by extreme s-process enrichment,likely due to mass accretion from an evolved companion that has nowprobably become a white dwarf. The lead (Pb) abundance of (HE 0024-2523)is very high, the same as that of the recently discovered lead-rich,metal-poor star CS 29526-110, [Pb/Fe]=+3.3. The abundance ratio of theheavy to light s-elements, as characterized by Pb and Ba, [Pb/Ba]=+1.9,is the highest yet found for any metal-poor star and is about 0.7 dexhigher than that of CS 29526-110. On the basis of the measured isotopicratio of carbon (C12/C13~6) we argue that the massdonor must have had an original mass of at least ~3 Msolar.The unusually short period of this CH star suggests that it underwent apast common-envelope phase with its evolved companion. Our results arecompared with the latest available models for asymptotic giant branchyields and s-process nucleosynthesis. We also discuss the possibleconnection between HE 0024-2523, the lithium depletion of halo stars,and halo blue straggler formation.Based in part on observations obtained at the W. M. Keck Observatory,which is operated jointly by the California Institute of Technology, theUniversity of California, and NASA.
| 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.
| Rapid Rotation of Ultra-Li-depleted Halo Stars and Their Association with Blue Stragglers
Observations of 18 halo main-sequence turnoff stars, four of which areextremely deficient in Li, show that three of the Li-poor ones havesubstantial line broadening. We attribute this to stellar rotation.Despite the great ages of halo stars, for G202-65, BD +51°1817, andWolf 550 we infer vsini=8.3+/-0.4, 7.6+/-0.3, and 5.5+/-0.6 kms-1, respectively. The stated errors are 3 σ. For CD-31°19466 we derive a 3 σ upper limit vsini<2.2 kms-1. The three rotating stars are known spectroscopicbinaries. We explain the high rotation velocities in terms of mass andangular momentum transfer onto the surface of the turnoff star from aninitially more massive donor. Estimates of the specific angular momentumof accreted material indicate that quite small transfer masses couldhave been involved, although the unknown subsequent spin-down of theaccretor prevents us from assigning definitive values for each star. Theaccretor is now seen as an ultra-Li-deficient star whose origin makes ita low-mass counterpart of field blue stragglers. The Li could have beendestroyed before or during the mass transfer episode. Such objects mustbe avoided in studies of the primordial Li abundance and ininvestigations into the way normal single stars process their initialLi. Based on observations obtained with the University College Londonechelle spectrograph (UCLES) on the Anglo-Australian Telescope (AAT) andwith the Utrecht echelle spectrograph (UES) on the William HerschelTelescope (WHT).
| A Survey of Proper-Motion Stars. XIV. Spectroscopic Binaries among Metal-poor Field Blue Stragglers
We summarize the results from a program of monitoring the radialvelocities of 10 metal-poor, high-velocity field stars whose colors are0.01 to 0.13 mag bluer than main-sequence turnoffs ofcomparable-metallicity globular clusters. Two of the candidate halo bluestragglers (BD +72 94 and BD +40 1166) show no signs of velocityvariability, one (HD 84937) shows only weak signs of variability, one(BD +25 1981) appears to be a very long-period binary, and six (BD -122669, HD 97916, HD 106516, BD +51 1817, G66-30, and G202-65) aresingle-lined spectroscopic binaries, with periods ranging from 167 to844 days. Velocity coverage for the four candidates without orbitalsolutions ranges from 15.9 to 19.0 years. The orbital eccentricities areall low, e<0.30 and =0.11. Five of the six binary orbitshave very low eccentricities, with =0.07. We have reanalyzedthe velocity data from Preston & Sneden and have derived orbitalsolutions similar to theirs for 10 of the spectroscopic binaries amongtheir ``blue metal-poor'' stars with [Fe/H]<=-0.6. We confirm theirconclusion that the binary frequency is high; we find 47+/-10% if weinclude only the definite binaries with [Fe/H]<=-0.6. Our orbitalsolutions for the seven binaries with periods longer than 20 days allhave low eccentricities, with e<=0.26 and =0.11. Theseorbital characteristics are very similar to the Ba II, CH, subgiant CH,and dwarf carbon stars, suggesting that mass transfer has been involvedin their formation. Of the five binary stars in our program withpublished abundances of lithium, all have been found to be deficient(and one in beryllium as well). In contrast, two of the three apparentlysingle stars have published lithium abundances and show no deficiency.The mass functions for the six binaries in our program and seven similarsystems studied by Preston & Sneden are consistent with their unseencompanions all being white dwarfs with M~0.55 Msolar andrandom orbital inclinations. Taking all of our observations and those ofothers together, we argue that the results are consistent with all fieldblue stragglers being binary systems with long periods and loweccentricities, the primary stars being deficient in lithium and thesecondary stars being normal-mass white dwarfs. All these properties aresuggestive of a blue-straggler formation model that involves masstransfer. For six of the 13 stars in the two programs for whichs-process elemental abundances are available, no signs of enhancementare discernible, suggesting that the donor star was a first-ascent redgiant. For the star with the longest orbital period (1307 days), CS22956-028, s-process abundance enhancements have been reported. Thisstar may be a precursor to the subgiant CH class, as suggested by Luck& Bond. Some of the results presented here used observations madewith the Multiple Mirror Telescope, a joint facility of the SmithsonianInstitution and the University of Arizona.
| Abundances and Evolution of Lithium in the Galactic Halo and Disk
We have measured the Li abundance of 18 stars with -2<~[Fe/H]<~-1and 6000<~Teff<~6400 K, a parameter range that waspoorly represented in previous studies. We examine the Galactic chemicalevolution (GCE) of this element, combining these data with previoussamples of turnoff stars over the full range of halo metallicities. Wefind that A(Li) increases from a level of ~2.10 at [Fe/H]=-3.5 to ~2.40at [Fe/H]=-1.0, where A(Li)=log10(n(Li)/n(H))+12.00. We comparethe observations with several GCE calculations, including existingone-zone models and a new model developed in the framework ofinhomogeneous evolution of the Galactic halo. We show that Li evolved ata constant rate relative to iron throughout the halo and old disk epochsbut that during the formation of young disk stars, the production of Lirelative to iron increased significantly. These observations can beunderstood in the context of models in which postprimordial Li evolutionduring the halo and old disk epochs is dominated by Galactic cosmic-rayfusion and spallation reactions, with some contribution from theν-process in supernovae. The onset of more efficient Li production(relative to iron) in the young disk coincides with the appearance of Lifrom novae and asymptotic giant branch (AGB) stars. The major challengefacing the models is to reconcile the mild evolution of Li during thehalo and old disk phases with the more efficient production (relative toiron) at [Fe/H]>-0.5. We speculate that cool-bottom processing(production) of Li in low-mass stars may provide an importantlate-appearing source of Li, without attendant Fe production, that mightexplain the Li production in the young disk. Based on observationsobtained with the University College London échelle spectrograph(UCLES) on the Anglo-Australian Telescope (AAT) and the Utrechtéchelle spectrograph (UES) on the William Herschel Telescope(WHT).
| Ultra-Lithium-deficient Halo Stars and Blue Stragglers: A Common Origin?
We present data for four ultra-Li-deficient, warm, halo stars. The Lideficiency of two of these is a new discovery. Three of the four starshave effective temperatures Teff~6300 K, in contrast topreviously known Li-deficient halo stars, which spanned the temperaturerange of the Spite plateau. In this paper we propose that these andpreviously known ultra-Li-deficient halo stars may have had theirsurface lithium abundances reduced by the same mechanism as produceshalo field blue stragglers. Even though these stars have yet to revealthemselves as blue stragglers, they might be regarded as``blue-stragglers-to-be.'' In our proposed scenario, the surfaceabundance of Li in these stars could be destroyed (1) during the normalpre-main-sequence single-star evolution of their low-mass precursors,(2) during the post-main-sequence evolution of an evolved mass donor,and/or (3) via mixing during a mass-transfer event or stellar merger.The warmest Li-deficient stars at the turnoff would be regarded asemerging ``canonical'' blue stragglers, whereas cooler ones representsub-turnoff-mass blue-stragglers-to-be. The latter are presently hiddenon the main sequence, Li depletion being possibly the clearest signatureof their past history and future significance. Eventually, themain-sequence turnoff will reach down to their mass, exposing thoseLi-depleted stars as canonical blue stragglers when normal stars of thatmass evolve away. Arguing against this unified view is the observationthat the three Li-depleted stars at Teff~=6300 K are allbinaries, whereas very few of the cooler systems show evidence forbinarity; it is thus possible that two separate mechanisms areresponsible for the production of Li-deficient main-sequence halo stars.Based on observations obtained with the University College Londonéchelle spectrograph (UCLES) on the Anglo-Australian Telescope(AAT) and the Utrecht échelle spectrograph (UES) on the WilliamHerschel Telescope (WHT).
| Estimation of Stellar Metal Abundance. II. A Recalibration of the Ca II K Technique, and the Autocorrelation Function Method
We have recalibrated a method for the estimation of stellar metalabundance, parameterized as [Fe/H], based on medium-resolution (1-2Å) optical spectra (the majority of which cover the wavelengthrange 3700-4500 Å). The equivalent width of the Ca II K line (3933Å) as a function of [Fe/H] and broadband B-V color, as predictedfrom spectrum synthesis and model atmosphere calculations, is comparedwith observations of 551 stars with high-resolution abundances availablefrom the literature (a sevenfold increase in the number of calibrationstars that were previously available). A second method, based on theFourier autocorrelation function technique first described by Ratnatunga& Freeman, is used to provide an independent estimate of [Fe/H], ascalibrated by comparison with 405 standard-star abundances.Metallicities based on a combination of the two techniques for dwarfsand giants in the color range 0.30<=(B-V)_0<=1.2 exhibit anexternal 1 sigma scatter of approximately 0.10-0.20 dex over theabundance range -4.0<=[Fe/H]<=0.5. Particular attention has beengiven to the determination of abundance estimates at the metal-rich endof the calibration, where our previous attempt suffered from aconsiderable zero-point offset. Radial velocities, accurate toapproximately 10 km s^-1, are reported for all 551 calibration stars.
| A Survey of Proper Motion Stars. XIII. The Halo Population
Based on our expanded sample of metallicities and kinematics for a largesample of stars selected from the Lowell Proper Motion Catalog, we studyseveral questions relating to the halo stellar population(s) in ourGalaxy. For [m/H]≤-1.4, there does not seem to be any variation with[m/H] in the mean values of the V velocity (i.e., angular momentumrelated to that in the disk) or the Galactic orbital eccentricities. Further, in spite of the strong kinematical biases in our sample, starswith very low metallicities are found that have small V velocities (highorbital angular momenta) and low orbital eccentricities. These resultscontradict the model that the metal-poor stars are a single populationthat is only the relic of the earliest stages of the Galaxy's collapse. There are signs that some of the metal-poor stars in the solarneighborhood are due to accretion events and, perhaps, also to theearliest stages of the formation of the Galactic disk. Regardingaccretion, we confirm Majewski's [ApJS, 78, 87 (1992)] finding of aretrograde rotation among stars that reach S kpc or more from the plane. These stars do not show any radial metallicity gradient, and may beyounger on average than dynamically hot, metal-poor stars closer to theplane. These latter stars show net prograde rotation and a radialmetallicity gradient, suggestive of a dissipative process in theearliest stages of disk formation. The correlation between metallicityand perigalacticon found by Ryan & Norris [AJ, 101, 1835 (1991a)]disappears when care is taken to exclude the stars that may have beenaccreted by our Galaxy. The field star results complement those forglobular clusters found by other workers, notably Zinn (1993), whoargued for two populations of metal-poor clusters, one apparently inretrograde rotation with no radial metallicity gradient and slightlyyounger ages, and the other with prograde rotation, a weak radialmetallicity gradient, and slightly older ages. The field stars andglobular clusters do differ slightly, however. Their metallicitydistributions differ, with the field stars showing a larger fraction ofthe most metal-poor stars. This could be caused by accretion of Dracodwarf galaxy-like objects, with very low metallicities and no globularclusters. We see in our data, particularly in the V vs>Rapo< plane, possible signs of large-scale kinematicsubstructure suggestive of specific accretion events. We also see signsfor the Preston et al. [AJ, 108, 538 (1994)] low-metallicity,intermediate kinematics, and younger age stellar population. However,the strength of the signal in our data suggests that a fairly largefraction of its stars may be old. On the other hand, the "away" versus"toward" mystery of Croswell et al. [Al, 93, 1445 (1987)] hasdisappeared: the numbers of stars approaching and receding from theplane agree with expectations. Finally, we point out that the model ofNorris [ApJ, 431, 645 (1994)] for a proto-disk population that is hotterdynamically than the accreted halo components does not agree with ourexpanded data sample. We suggest that the proto-disk component wasdynamically cooler when the mean metallicity was very low.
| A survey of proper motion stars. 12: an expanded sample
We report new photometry and radial velocities for almost 500 stars fromthe Lowell Proper Motion Catalog. We combine these results with ourprior sample and rederive stellar temperatures based on the photometry,reddening, metallicities (using chi squared matching of our 22,500 lowSignal to Noise (S/N) high resolution echelle spectra with a grid ofsynthetic spectra), distances, space motions, and Galactic orbitalparameters for 1269 (kinematics) and 1261 (metallicity) of the 1464stars in the complete survey. The frequency of spectroscopic binariesfor the metal-poor ((m/H) less than or equal to -1.2) stars with periodsshorter than 3000 days is at least 15%. The spectroscopic binaryfrequency for metal-rich stars ((m/H) greater than -0.5) appears to belower, about 9%, but this may be a selection effect. We also discussspecial classes of stars, including treatment of the double-linedspectroscopic binaries, and identification of subgiants. Four possiblenew members of the class of field blue stragglers are noted. We pointout the detection of three possible new white dwarfs, six broad-lined(binary) systems, and discuss briefly the three already knownnitrogen-rich halo dwarfs. The primary result of this paper will beavailable on CD-ROM, in the form of a much larger table.
| High-tangential-velocity stars
Two lists of high tangential velocity (greater than 100 km/s) starscontained in the Lowell Northern Hemisphere proper motion surveycatalogue have been compiled, the stellar distances being inferred fromeither trigonometric or spectroscopic parallaxes. The information givenincludes equatorial coordinates, corrected photographic magnitudes,proper motions, trigonometric or spectroscopic parallaxes, and spectraltypes.
| Spectral classification of high-proper-motion stars
Spectral types have been found for about 900 stars of high proper motioncontained in the Lowell Observatory Northern Hemisphere proper-motionstar survey using all blue-region objective prism plates. The spectralclassification criteria are given. About eighty stars of largetangential velocity have been classified using slit spectrograms takenwith a 36-in. reflector. A new calibration of Luyten's absolutemagnitude vs reduced proper motion relation is made, and its dependenceon spectral type is investigated.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
