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An Overview of the Rotational Behavior of Metal-poor Stars
This paper describes the behavior of the rotational velocity inmetal-poor stars ([Fe/H] <= -0.5 dex) in different evolutionarystages, based on vsin i values from the literature. Our sample iscomprised of stars in the field and some Galactic globular clusters,including stars on the main sequence, the red giant branch (RGB), andthe horizontal branch (HB). The metal-poor stars are, mainly, slowrotators, and their vsin i distribution along the HR diagram is quitehomogeneous. Nevertheless, a few moderate to high values of vsin i arefound in stars located on the main sequence and the HB. We show that theoverall distribution of vsin i values is basically independent ofmetallicity for the stars in our sample. In particular, thefast-rotating main sequence stars in our sample present rotation ratessimilar to their metal-rich counterparts, suggesting that some of themmay actually be fairly young, in spite of their low metallicity, or elsethat at least some of them would be better classified as blue stragglerstars. We do not find significant evidence of evolution in vsin i valuesas a function of position on the RGB; in particular, we do not confirmprevious suggestions that stars close to the RGB tip rotate faster thantheir less-evolved counterparts. While the presence of fast rotatorsamong moderately cool blue HB stars has been suggested to be due toangular momentum transport from a stellar core that has retainedsignificant angular momentum during its prior evolution, we find thatany such transport mechanisms most likely operate very fast as the stararrives on the zero-age HB (ZAHB), since we do not find a link betweenevolution off the ZAHB and vsin i values. We present an extensivetabulation of all quantities discussed in this paper, including rotationvelocities, temperatures, gravities, and metallicities [Fe/H], as wellas broadband magnitudes and colors.
| Line Broadening in Field Metal-Poor Red Giant and Red Horizontal Branch Stars
We report 349 radial velocities for 45 metal-poor field red giant branch(RGB) and red horizontal branch (RHB) stars, with time coverage rangingfrom 1 to 21 years. We have identified one new spectroscopic binary, HD4306, and one possible such system, HD 184711. We also provide 57 radialvelocities for 11 of the 91 stars reported in our previous work. All butone of the 11 stars had been found to have variable radial velocities.New velocities for the long-period spectroscopic binaries BD-1 2582 andHD 108317 have extended the time coverage to 21.7 and 12.5 years,respectively, but in neither case have we yet completed a full orbitalperiod. As was found in the previous study, radial velocity "jitter" ispresent in many of the most luminous stars. Excluding stars showingspectroscopic binary orbital motion, all 7 of the red giants withestimated MV values more luminous than -2.0 display jitter,as well as 3 of the 14 stars with -2.0 < MV <= -1.4. Wehave also measured the line broadening in all the new spectra, usingsynthetic spectra as templates. Comparison with results fromhigh-resolution and higher signal-to-noise (S/N) spectra employed byother workers shows good agreement down to line-broadening levels of 3km s-1, well below our instrumental resolution of 8.5 kms-1. As the previous work demonstrated, the majority of themost luminous red giants show significant line broadening, as do many ofthe red horizontal branch stars, and we briefly discuss possible causes.The line broadening appears related to velocity jitter, in that bothappear primarily among the highest luminosity red giants.
| Halo Star Streams in the Solar Neighborhood
We have assembled a sample of halo stars in the solar neighborhood tolook for halo substructure in velocity and angular momentum space. Oursample (231 stars) includes red giants, RR Lyrae variable stars, and redhorizontal branch stars within 2.5 kpc of the Sun with [Fe/H] less than-1.0. It was chosen to include stars with accurate distances, spacevelocities, and metallicities, as well as well-quantified errors. Withour data set, we confirm the existence of the streams found by Helmi andcoworkers, which we refer to as the H99 streams. These streams have adouble-peaked velocity distribution in the z-direction (out of theGalactic plane). We use the results of modeling of the H99 streams byHelmi and collaborators to test how one might use vz velocityinformation and radial velocity information to detect kinematicsubstructure in the halo. We find that detecting the H99 streams withradial velocities alone would require a large sample (e.g.,approximately 150 stars within 2 kpc of the Sun and within 20° ofthe Galactic poles). In addition, we use the velocity distribution ofthe H99 streams to estimate their age. From our model of the progenitorof the H99 streams, we determine that it was accreted between 6 and 9Gyr ago. The H99 streams have [α/Fe] abundances similar to otherhalo stars in the solar neighborhood, suggesting that the gas thatformed these stars were enriched mostly by Type II supernovae. We havealso discovered in angular momentum space two other possiblesubstructures, which we refer to as the retrograde and progradeoutliers. The retrograde outliers are likely to be halo substructure,but the prograde outliers are most likely part of the smooth halo. Theretrograde outliers have significant structure in the vφdirection and show a range of [α/Fe], with two having low[α/Fe] for their [Fe/H]. The fraction of substructure stars in oursample is between 5% and 7%. The methods presented in this paper can beused to exploit the kinematic information present in future largedatabases like RAVE, SDSS-II/SEGUE, and Gaia.
| A catalog of rotational and radial velocities for evolved stars. IV. Metal-poor stars^
Aims.The present paper describes the first results of an observationalprogram intended to refine and extend the existing v sin i measurementsof metal-poor stars, with an emphasis on field evolved stars.Methods: .The survey was carried out with the FEROS and CORALIEspectrometers. For the v sin i measurements, obtained from spectralsynthesis, we estimate an uncertainty of about 2.0 km s-1. Results: .Precise rotational velocities v sin i are presented for alarge sample of 100 metal-poor stars, most of them evolving off themain-sequence. For the large majority of the stars composing the presentsample, rotational velocities have been measured for the first time.
| Oxygen abundances in metal-poor subgiants as determined from [O I], O I and OH lines
The debate on the oxygen abundances of metal-poor stars has its originin contradictory results obtained using different abundance indicators.To achieve a better understanding of the problem we have acquired highquality spectra with the Ultraviolet and Visual Echelle Spectrograph atVLT, with a signal-to-noise of the order of 100 in the near ultravioletand 500 in the optical and near infrared wavelength range. Threedifferent oxygen abundance indicators, OH ultraviolet lines around 310.0nm, the [O i] line at 630.03 nm and the O i lines at 777.1-5 nm wereobserved in the spectra of 13 metal-poor subgiants with-3.0≤[Fe/H]≤-1.5. Oxygen abundances were obtained from theanalysis of these indicators which was carried out assuming localthermodynamic equilibrium and plane-parallel model atmospheres.Abundances derived from O i were corrected for departures from localthermodynamic equilibrium. Stellar parameters were computed usingT_eff-vs.-color calibrations based on the infrared flux method andBalmer line profiles, Hipparcos parallaxes and Fe II lines. [O/Fe]values derived from the forbidden line at 630.03 nm are consistent withan oxygen/iron ratio that varies linearly with [Fe/H] as[O/Fe]=-0.09(±0.08)[Fe/H]+0.36(±0.15). Values based on theO i triplet are on average 0.19±0.22 dex(s.d.) higher than thevalues based on the forbidden line while the agreement between OHultraviolet lines and the forbidden line is much better with a meandifference of the order of -0.09±0.25 dex(s.d.). In general, ourresults follow the same trend as previously published results with theexception of the ones based on OH ultraviolet lines. In that case ourresults lie below the values which gave rise to the oxygen abundancedebate for metal-poor stars.
| Li and Be depletion in metal-poor subgiants
A sample of metal-poor subgiants has been observed with the UVESspectrograph at the Very Large Telescope and abundances of Li and Behave been determined. Typical signal-to-noise per spectral bin valuesfor the co-added spectra are of the order of 500 for the ion{Li}{i} line(670.78 nm) and 100 for the ion{Be}{ii} doublet lines (313.04 nm). Thespectral analysis of the observations was carried out using the Uppsalasuite of codes and marcs (1D-LTE) model atmospheres with stellarparameters from photometry, parallaxes, isochrones and Fe ii lines.Abundance estimates of the light elements were corrected for departuresfrom local thermodynamic equilibrium in the line formation. Effectivetemperatures and Li abundances seem to be correlated and Be abundancescorrelate with [O/H]. Standard models predict Li and Be abundancesapproximately one order of magnitude lower than main-sequence valueswhich is in general agreement with the observations. On average, ourobserved depletions seem to be 0.1 dex smaller and between 0.2 and 0.4dex larger (depending on which reference is taken) than those predictedfor Li and Be, respectively. This is not surprising since the initial Liabundance, as derived from main-sequence stars on the Spite plateau, maybe systematically in error by 0.1 dex or more, and uncertainties in thespectrum normalisation and continuum drawing may affect our Beabundances systematically.
| IX Ophiuchi: A High-Velocity Star Near a Molecular Cloud
The molecular cloud Barnard 59 is probably an outlier of the UpperSco/ρ Oph complex. B59 contains several T Tauri stars (TTSs), butoutside its northwestern edge are three other Hα-emission objectswhose nature has been unclear: IX, KK, and V359 Oph. This paper is adiscussion of all three and of a nearby Be star (HD 154851), basedlargely on Keck HIRES spectrograms obtained in 2004. KK Oph is a close(1.6") double. The brighter component is an HAeBe star, and the fainteris a K-type TTS. The complex BVR variations of the unresolved pairrequire both components to be variable. V359 Oph is a conventional TTS.Thus, these pre-main-sequence stars continue to be recognizable as suchwell outside the boundary of their parent cloud. IX Oph is quitedifferent. Its absorption spectrum is about type G, with manypeculiarities: all lines are narrow but abnormally weak, with structuresthat depend on ion and excitation level and that vary in detail frommonth to month. It could be a spectroscopic binary of small amplitude.Hα and Hβ are the only prominent emission lines. They arebroad, with variable central reversals. However, the most unusualcharacteristic of IX Oph is the very high (heliocentric) radialvelocity: about -310 km s-1, common to all spectrograms, andvery different from the radial velocity of B59, about -7 kms-1. There is no detectable Li I λ6707 line. There isreason to believe that IX Oph is actually a background object, onlyaligned with B59. Several conceivable interpretations are discussed: (1)It is unlikely that it is a high-velocity ejectee from the Upper Sco orUpper Cen-Lup associations (the lack of detectable λ6707 showsthat it is not the product of a very recent event, and the proper motionpoints in the wrong direction) or that it was born in or ejected fromone of the distant high-velocity CO clouds at this longitude(l=357deg). (2) A stronger possibility is that it is simply ametal-poor high-velocity G- or K-type giant (but such stars are notirregularly variable in light and do not have such strong Balmeremission lines). More likely, (3) IX Oph is a member of thehigh-velocity, low-metallicity SRd class of semiregular variables foundin the field and in some globular clusters. At some phases, those starsshow Hα emission like that found in IX Oph and, in one example,emission lines of neutral metals and double absorption lines as in IXOph.
| Spectroscopic Binaries, Velocity Jitter, and Rotation in Field Metal-poor Red Giant and Red Horizontal-Branch Stars
We summarize 2007 radial velocity measurements of 91 metal-poor fieldred giants. Excluding binary systems with orbital solutions, ourcoverage averages 13.7 yr per star, with a maximum of 18.0 yr. We reportfour significant findings. (1) Sixteen stars are found to bespectroscopic binaries, and we present orbital solutions for 14 of them.The spectroscopic binary frequency of the metal-poor red giants, with[Fe/H]<=-1.4, for periods less than 6000 days, is 16%+/-4%, which isnot significantly different from that of comparable-metallicity fielddwarfs, 17%+/-2%. The two CH stars in our program, BD -1°2582 and HD135148, are both spectroscopic binaries. (2) Velocity jitter is presentamong about 40% of the giants with MV<=-1.4. The twobest-observed cases, HD 3008 and BD +22°2411, showpseudoperiodicities of 172 and 186 days, longer than any knownlong-period variable in metal-poor globular clusters. Photometricvariability seen in HD 3008 and three other stars showing velocityjitter hints that starspots are the cause. However, the phasing of thevelocity data with the photometry data from Hipparcos is not consistentwith a simple starspot model for HD 3008. We argue against orbitalmotion effects and radial pulsation, so rotational modulation remainsthe best explanation. The implied rotational velocities for HD 3008 andBD +22°2411, both with MV<=-1.4 and R~50Rsolar, exceed 12 km s-1. (3) Including HD 3008and BD +22°2411, we have found signs of significant excess linebroadening in eight of the 17 red giants with MV<=-1.4,which we interpret as rotation. In three cases, BD +30°2034, CD-37°14010, and HD 218732, the rotation is probably induced by tidallocking between axial rotation and the observed orbital motion with astellar companion. But this cannot explain the other five stars in oursample that display signs of significant rotation. This high frequencyof elevated rotational velocities does not appear to be caused bystellar mass transfer or mergers: there are too few main-sequencebinaries with short enough periods. We also note that the lack of anynoticeable increase in mean rotation at the magnitude level of the redgiant branch luminosity function ``bump'' argues against the rapidrotation's being caused by the transport of internal angular momentum tothe surface. Capture of a planetary-mass companion as a red giantexpands in radius could explain the high rotational velocities. (4) Wealso find significant rotation in at least six of the roughly 15 (40%)red horizontal-branch stars in our survey. It is likely that theenhanced rotation seen among a significant fraction of both blue and redhorizontal-branch stars arose when these stars were luminous red giants.Rapid rotation alone therefore appears insufficient cause to populatethe blue side of the horizontal branch. While the largest projectedrotational velocities seen among field blue and red horizontal-branchstars are consistent with their different sizes, neither are consistentwith the large values we find for the largest red giants. This suggeststhat some form of angular momentum loss (and possibly mass loss) hasbeen at work. Also puzzling is the apparent absence of rotation seen infield RR Lyrae variables. Angular momentum transfer and conservation inevolved metal-poor field stars thus pose many interesting questions forthe evolution of low-mass stars.
| Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
| Abundances of metal-weak thick-disc candidates
High-resolution spectra of five candidate metal-weak thick-disc starssuggested by Beers & Sommer-Larsen are analysed to determine theirchemical abundances. The low abundance of all the objects has beenconfirmed, with metallicity reaching [Fe/H]=-2.9. However, for threeobjects the astrometric data from the Hipparcos catalogue suggest theyare true halo members. The remaining two, for which proper-motion dataare not available, may have disc-like kinematics. It is therefore clearthat it is useful to address properties of putative metal-weakthick-disc stars only if they possess full kinematic data. For CS22894-19 an abundance pattern similar to those of typical halo stars isfound, suggesting that chemical composition is not a useful discriminantbetween thick-disc and halo stars. CS 29529-12 is found to be C-enhancedwith [C/Fe]=+1.0 other chemical peculiarities involve the s-processelements: [Sr/Fe]=-0.65 and [Ba/Fe]=+0.62, leading to a high [Ba/Sr],considerably larger than that found in more metal-rich carbon-richstars, but similar to those in LP 706-7 and LP 625-44, discussed byNorris et al. Hipparcos data have been used to calculate the spacevelocities of 25 candidate metal-weak thick-disc stars, thus allowing usto identify three bona fide members, which support the existence of ametal-poor tail of the thick disc, at variance with a claim to thecontrary by Ryan & Lambert.
| Early evolution of the Galactic halo revealed from Hipparcos observations of metal-poor stars
The kinematics of 122 red giant and 124 RR Lyrae stars in the solarneighborhood are studied using accurate measurements of their propermotions obtained by the Hipparcos astrometry satellite, combined withtheir published photometric distances, metal abundances, and radialvelocities. A majority of these sample stars have metal abundances of(Fe/H) = -1 or less and thus represent the old stellar populations inthe Galaxy. The halo component, with (Fe/H) = -1.6 or less, ischaracterized by a lack of systemic rotation and a radially elongatedvelocity ellipsoid. About 16 percent of such metal-poor stars have loworbital eccentricities, and we see no evidence of a correlation between(Fe/H) and e. Based on the model for the e-distribution of orbits, weshow that this fraction of low-e stars for (Fe/H) = -1.6 or less isexplained by the halo component alone, without introducing the extradisk component claimed by recent workers. This is also supported by theabsence of a significant change in the e-distribution with height fromthe Galactic plane. In the intermediate-metallicity range, we find thatstars with disklike kinematics have only modest effects on thedistributions of rotational velocities and e for the sample at absolutevalue of z less than 1 kpc. This disk component appears to constituteonly 10 percent for (Fe/H) between -1.6 and -1 and 20 percent for (Fe/H)between -1.4 and -1.
| Distribution and Studies of the Infrared Stellar Population in the Galaxy. VI. The Halo
We present infrared J, H and K observations of 69 local galactic halostars. We produce the two colour (JHK) and the colour magnitude (Kversus (J-K)) diagrams for this stellar sample and compare them with thesame diagrams for the stellar populations in the globular clusters M3,M13, M92 and 47 Tucanae and in the old open cluster M67; we also comparethese diagrams with those for the stellar population in the galacticbulge.
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| Kinematics of metal-poor stars in the galaxy
We discuss the kinematic properties of a sample of 1936 Galactic stars,selected without kinematic bias, and with abundances (Fe/H) is less thanor equal to -0.6. The stars selected for this study all have measuredradial velocities, and the majority have abundances determined fromspectroscopic or narrow-/intermediate-band photometric techniques. Incontrast to previous examinations of the kinematics of the metal-poorstars in the Galaxy, our sample contains large numbers of stars that arelocated at distances in excess of 1 kpc from the Galactic plane. Thus, amuch clearer picture of the nature of the metal-deficient populations inthe Galaxy can now be drawn.
| Reddening estimation for halo red giants using UVBY photometry
Updated uvby observations for a larger sample of metal-deficient redgiants are presented and combined with a select sample of data from theliterature transformed to a common system. Using the reddening maps ofBurstein & Heiles (1982), new absolute magnitudes, distances,metallicities, and reddenings are derived for each star. Themetallicities are determined with a revised calibration of them1, (b-y) diagram based upon comparison to a complilation ofrecent spectrsoscopic abundances transformed to a common system. Thephotometric abundances agree very well with the spectroscopic; thedispersion among the residuals for 58 giants is +/- 0.16 dex. Thedereddened indices are used to show that for red giants with (Fe/H) lessthan -1.5, there is a well-defined relation in the c0,(b-y)0 diagram which exhibits only a weak dependence uponmetallicity. Use of the standard relations allows one to obtainreddening estimates for normal halo field giants and globular clustersin the appropriate metallicity range.
| Photoelectric beta photometry of 118 stars with V in the range 14-15 and B - V not greater than 0.650 at the south galactic pole
Observations of a sample of 118 stars at the south galactic pole arepresented. Diagrams of instrumental vs standard beta values for thestandard stars may indicate that the transformation must be divided intotwo regions with slightly different slopes A and intercepts B. Thenarrow bandpass of the filter set employed has an FWHM of 27 A and iscentered at 4860 A. A radial velocity of 100 km/s will reduce thebeta-index of a sharp beta line with 0.005-0.010 m relative to a zerovelocity star. It is argued that the two transformations are a result ofslightly different bandwidths of the narrow-band filters used for theoriginal measurements of the present secondary standards and in thepresent observing run. The present narrow band's FWHM is smaller by 3 A.
| Spectroscopy of the CA II K line of metal-poor field red giants. I - Southern Hemisphere observations
Spectra of the Ca II K line have been obtained for a sample of fieldmetal-poor red giants. Strong chromospheric emission is found to bequite common among such giants of absolute magnitude brighter than M(v)about -0.3. The behavior of the violet/red asymmetry of the emissionline profile shows no significant difference with that observed amongPopulation I red giants, suggesting that the onset of material outflowis independent of metallicity. The Ca II emission is observed amonggiants more than one magnitude fainter than those which exhibit emissionin the wings of the H-alpha line. One possible interpretation of thisresult is that the transient phenomenon associated with the variableH-alpha emission does not become established until a Population II giantattains luminosities considerably greater than those at whichwell-developed chromospheres are achieved.
| 3883 CN band strengths for 238 metal-poor halo giants - Evidence for chemical differences between globular-cluster and halo field giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1992PASP..104..523L&db_key=AST
| Uvby-beta photometry of high-velocity and metal-poor stars. IV - Distances, kinematics, and galactic orbits for stars with Fe/H equal to or less than -2.0
From the catalog of high-velocity and metal-poor stars of Schuster andNissen 43 stars with Fe/H equal to or less than -2.0 were selected as asample representative of the oldest, most kinematically extremecomponent of the galaxy. For these stars, photometric distances weredetermined. Their galactic orbits were then numerically integrated inthe galactic potential model of Allen and Martos (1986). Of the 40 starswith complete data, 27 are found to be in box-orbits, 2 in orbitsverging on chaotic, 9 in chaotic, and 2 in tube-like orbits. Four starsattaining R(max) greater than 50 kpc and five stars with loweccentricities (e less than 0.4) are present in the sample. No obviouscorrelations of ages and/or metallicities with kinematical parameterswere found. Two mechanisms for hiding chemical gradients in the halo areshown to be of importance.
| Astrometric and astrophysical discontinuities between the galactic old disk and halo stellar populations
Intermediate band, RI, and DDO photometry of the weak-lined stars in thefirst three volumes of the Michigan catalogs of spectral type arediscussed on the basis of luminosity and heavy element abundance. Theinterface between the old disk (Fe/H greater than -0.8 dex) and halo(Fe/H less than -1.2 dex) populations represents discontinuities in boththe stellar motions and the stellar physics. The CN strengths of bothevolved and unevolved halo stars decrease with decreasing temperature,in a mirror image of the increase with decreasing temperature for thedisk objects. The result for the halo giants has been attributed to deepmixing in the stellar atmospheres but the similar result for unevolveddwarfs indicates a difference in formation rather than in evolutionaryprocess of the two populations.
| Estimation of stellar metal abundance. I - Calibration of the CA II K index
A method for estimating the stellar metal abundances is proposed whichcompares measures of the equivalent width of a single feature inmoderate resolution (1 A) optical spectra of stars, the Ca II K line at3933 A, with models of the predicted line strength as a function of thebroadband B-V color and Fe/H. The approach is capable of providingestimates of stellar metallicity over the range -4.5 to -1.0 with ascatter of about 0.15 dex for dwarfs and giants in the color range0.33-0.85. For cooler stars, with B-V in the range 0.85-1.1, the scattermay be as large as 0.19 dex. The calibration of the Ca II K index withFe/H is discussed, and average radial velocities and abundances arepresented for several galactic globular clusters.
| Armchair cartography - A map of the Galactic halo based on observations of local, metal-poor stars
The velocity distribution of metal-poor halo stars in the solarneighborhood is studied to extract data on the global spatial andkinematic properties of the Galactic stellar halo. A global model of thesolar neighborhood stars is constructed from observed positions andthree-dimensional velocity of local, metal-poor halo stars in terms of adiscrete sum of orbits. The characteristics of the reconstructed haloare examined and used to study the evolution of the halo subsystems.
| Ubvy-beta photometry of high-velocity and metal-poor stars. III - Metallicities and ages of the halo stars
The interstellar color excesses, E(b-y) and the metallicities, Fe/Habundance ratio, are determined for the 711 high-velocity and metal-poorstars in the catalog of ubvy-beta photometry compiled by Schuster andNissen (1988). It is found that 220 of these are halo stars and that 15percent of these halo stars have colors that are significantly affectedby interstellar reddening. A minimum age of 18-20 Gyr is determined forthe halo stars. The results suggest that a pressure-supported slowuniform collapse controlled the formation and evolution of the Galaxy.
| Four-color UVBY and H-beta photometry of high-velocity and metal-poor stars. I - The catalogue of observations
A catalog of four-color uvby and H-beta photometry for 711 high-velocityand metal-poor stars is given. The selection of the stars and theobserving and reduction techniques used to obtain these data arediscussed. The photometry has been transformed closely onto the standarduvby-beta system. The errors of the data have been estimated using bothinternal and external comparisons. The data are uniform over the sky;that is, there are no significant north-south differences. For the largemajority of stars the mean errors of V, m1, c1, and beta are less than +or - 0.008 mag, and the error of b-y is less than + or - 0.005 mag.Values of V, b-y and beta and rough photometric classifications aregiven for 63 red and/or evolved stars that fall outside the range of thephotometric transformations.
| Population studies. II - Kinematics as a function of abundance and galactocentric position for (Fe/H) of -0.6 or less
A catalog is presented of some 1200 Galactic objects which have radialvelocities and (Fe/H) abundances of -0.6 or less. These data areanalyzed to yield information on the kinematic properties of the olderpopulations of the Galaxy and on the interdependence between kinematicsand abundance. It is found that the kinematics of the availablekinematically selected stars differ from those of the nonkinematicallyselected objects. No evidence is found for any significant difference inthe kinematic properties of the various halo subgroups, nor for anydependence of kinematics on abundance. While the rotation of the halo issmall at about 37 km/s for (Fe/H) of -1.2 or less, it rises quickly forhigher abundances to a value of about 160 km/s at (Fe/H) = 0.6. Objectsin the abundance range -0.9 to -0.6 appear to belong predominantly to apopulation possessing the kinematic characteristics of a thick disk. Theimplications of these findings for the suggestion that globular clustersbelong to the same population as the noncluster objects, for the originof the thick disk, and for the mass of the Galaxy are discussed.
| The kinematics of halo red giants
The present 337 radial velocities were obtained with typical accuraciesof 0.7 cm km/sec for 85 metal-poor field red giants, selected from thekinematically unbiased samples of Bond (1980) and Bidelman and MacConnel(1973). The multiply-observed stars suggest the field halo binaryfraction exceeds 10 percent. Using these velocities and those publishedby others, a sample of 174 red giants with Fe/H of not more than -1.5 isobtained. Their mean motion with respect to the local standard of restis -206 + or - 23 km/sec, and the velocity dispersions are sigma (R) of154 + or - 18 km/sec, sigma(theta) of 102 + or - 27 km/sec, andsigma(phi) of 107 + or - 15 km/sec. Using photometrically derivedabsolute magnitudes and published proper motions, orbital eccentricitiesare computed for 72 stars not already considered in a similar study ofsouthern stars by Norris et al. (1985). A few stars with e of less than0.4 are found.
| Population studies. I - The Bidelman-MacConnell 'weak-metal' stars
BRVI and DDO photometry are presented for 309 Bidelman-MacConnell'weak-metal' stars. Radial velocities are calculated for most of thestars having Fe/H abundances of no more than -0.8. The photometricobservations were carried out using the 0.6-meter and 1.0-metertelescopes of the Siding Spring Observatory. Photometric taxonomy wasused to classify the stars as dwarfs, giants, red-horizontal branchstars, and ultraviolet-bright stars, respectively. It is found that 35percent of the stars are giants; 50 percent are dwarfs; and 5 percentbelong to the red-horizontal branch group. The role of selection effectsin investigations of the formation of the Galaxy is discussed on thebasis of the photometric observations and the observational constraintsproposed by Eggen et al. (1962).
| VBLUW photometry of some halo field giants
The Walraven VBLUW Photometry for a sample of 43 metal-deficient halogiants and 35 stars with known values for effective temperature (T eff),log g, and FE/H are presented. A calibration of the photometric indicesis determined in terms of the ratios 5040 K/T eff and FE/H. It is shownthat the photometric system has a good metallicity separation, yieldinga metallicity of -2.9 dex for CoD-38 deg 245 which contrasts with theextremely low value (-4.6 dex) obtained by Bessel and Norris (1981). Theimportance of this star as a standard for the calibration of photometricmetallicities is discussed. It is found that spectroscopic abundancemeasurements for stars with Fe/H of less than 2.7 are hampered by thecurrent lack of photometric data. A list of additional halo stars whichmight be suitable for low metallicity observation is presented.
| Metal-Deficient Giants in the Galactic Field - Catalogue and Some Physical Parameters
Not Available
| Extremely metal-deficient red giants. I - A new objective-prism, photometric, and radial-velocity survey
Results of an extensive objective-prism survey to detect extremelymetal-deficient red giants and a subsequent investigation of thephotometric and radial velocity properties of the newly discovered starsare presented. The 132 red giants with Fe/H abundance ratios less thanor equal to -1.5 discovered in the present objective-prism survey on a10-deg prism down to B magnitudes of 11.5, and by previousobjective-prism and other surveys, are listed, together with results ofradial velocity and photometric measurements. Examination of theStromgren m1 index calibrated against high-resolution spectroscopicdeterminations of the Fe-H abundance ratio indicates that population IIIfield giants with abundance ratios less than -3 are extremely rare. TheStromgren c1 index is used as an indicator of surface gravity andanomalous CH strengths, resulting in the identification of field redhorizontal-branch stars, field asymptotic-branch giants and subgiants.Radial velocities obtained for about half the stars reveal thatessentially all of them have halo motions, and that the incidence ofspectroscopic binaries is very low.
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| Sað Açýklýk: | 04h22m55.14s |
| Yükselim: | -37°15'49.2" |
| Görünürdeki Parlaklýk: | 9.565 |
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