내용
사진
사진 업로드
DSS Images Other Images
관련 글
Fluorine Abundances of Galactic Low-metallicity Giants
With abundances and 2σ upper limits of fluorine (F) in sevenmetal-poor field giants, nucleosynthesis of stellar F at low metallicityis discussed. The measurements are derived from the HF(1-0) R9 line at23358 Å using near-infrared K-band high-resolution spectraobtained with CRIRES at the Very Large Telescope. The sample reacheslower metallicities than previous studies on F of field giants, rangingfrom [Fe/H] = -1.56 down to –2.13. Effects of three-dimensionalmodel atmospheres on the derived F and O abundances are quantitativelyestimated and shown to be insignificant for the program stars. Theobserved F yield in the form of [F/O] is compared with two sets ofGalactic chemical evolution models, which quantitatively demonstrate thecontribution of Type II supernova (SN II) ν-process and asymptoticgiant branch/Wolf-Rayet stars. It is found that at this low-metallicityregion, models cannot well predict the observed distribution of [F/O],while the observations are better fit by models considering an SN IIν-process with a neutrino energy of E ν = 3 ×1053 erg. Our sample contains HD 110281, a retrogradeorbiting low-α halo star, showing a similar F evolution asglobular clusters. This supports the theory that such halo stars arepossibly accreted from dwarf galaxy progenitors of globular clusters inthe halo.
| 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.
| Strömgren Photometry of Galactic Globular Clusters. I. New Calibrations of the Metallicity Index
We present a new calibration of the Strömgren metallicity indexm1 using red giant (RG) stars in four globular clusters (GCs:M92, M13, NGC 1851, 47 Tuc) with metallicity ranging from -2.2 to -0.7,marginally affected by reddening [E(B-V)<=0.04] and with accurate(u,v,b,y) photometry. The main difference between the newmetallicity-index-color (MIC) relations and similar relations availablein the literature is that we have adopted the u-y and v-y colors insteadof b-y. These colors present a stronger sensitivity to effectivetemperature, and the MIC relations show a linear slope. The differencebetween photometric estimates and spectroscopic measurements for RGs inM71, NGC 288, NGC 362, NGC 6397, and NGC 6752 is 0.04+/-0.03 dex(σ=0.11 dex). We also apply the new MIC relations to 85 field RGswith metallicity ranging from -2.4 to -0.5 and accurate reddeningestimates. We find that the difference between photometric estimates andspectroscopic measurements is -0.14+/-0.01 dex (σ=0.17 dex). Wealso provide two sets of MIC relations based on evolutionary models thathave been transformed into the observational plane by adopting eithersemiempirical or theoretical color-temperature relations. We apply thesemiempirical relations to the nine GCs and find that the differencebetween photometric and spectroscopic metallicities is 0.04+/-0.03 dex(σ=0.10 dex). A similar agreement is found for the sample of fieldRGs, with a difference of -0.09+/-0.03 dex (with σ=0.19 dex). Thedifference between metallicity estimates based on theoretical relationsand spectroscopic measurements is -0.11+/-0.03 dex (σ=0.14 dex)for the nine GCs and -0.24+/-0.03 dex (σ=0.15 dex) for the fieldRGs. Current evidence indicates that new MIC relations providemetallicities with an intrinsic accuracy better than 0.2 dex.Based in part on observations collected with the 1.54 m Danish Telescopeoperated at ESO (La Silla, Chile) and with the Nordic Optical Telescope(NOT) operated at La Palma (Spain).
| Catalogue of [Fe/H] determinations for FGK stars: 2001 edition
The catalogue presented here is a compilation of published atmosphericparameters (Teff, log g, [Fe/H]) obtained from highresolution, high signal-to-noise spectroscopic observations. This newedition has changed compared to the five previous versions. It is nowrestricted to intermediate and low mass stars (F, G and K stars). Itcontains 6354 determinations of (Teff, log g, [Fe/H]) for3356 stars, including 909 stars in 79 stellar systems. The literature iscomplete between January 1980 and December 2000 and includes 378references. The catalogue is made up of two tables, one for field starsand one for stars in galactic associations, open and globular clustersand external galaxies. The catalogue is distributed through the CDSdatabase. Access to the catalogue with cross-identification to othersets of data is also possible with VizieR (Ochsenbein et al.\cite{och00}). The catalogue (Tables 1 and 2) is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/373/159 and VizieRhttp://vizier.u-strasbg.fr/.
| Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
| Ca II H and K Photometry on the UVBY System. III. The Metallicity Calibration for the Red Giants
New photometry on the uvby Ca system is presented for over 300 stars.When combined with previous data, the sample is used to calibrate themetallicity dependence of the hk index for cooler, evolved stars. Themetallicity scale is based upon the standardized merger of spectroscopicabundances from 38 studies since 1983, providing an overlap of 122evolved stars with the photometric catalog. The hk index producesreliable abundances for stars in the [Fe/H] range from -0.8 to -3.4,losing sensitivity among cooler stars due to saturation effects athigher [Fe/H], as expected.
| Al, Mg and Eu Abundances in Globular Cluster Giants. I. Tests of Deep Mixing
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.1517S&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.
| Where does the disk stop and the halo begin? Kinematics in a rotation field
A sample of G and K giants, approximately 4 kpc away from the sun,covering the abundance range from disk to halo in a field chosen tomeasure rotational kinematics, is discussed. To study the disk to halotransition, the sample has been enlarged with similar samples of starsin the solar neighborhood to include almost 200 giants and the conceptof 'thick disk' has been introduced. For selected giants, abundances,distances, and reddenings are derived, and velocity dispersion isestimated. From the data presented, it is concluded that the disk andhalo abundance distributions overlap and that their kinematics arediscontinuous. The kinematics of the metal-weak red giants, withabundances extended as low as Fe/H = -1.6, is compared with thekinematics of the halo objects, and the data are interpreted withrespect to the thick disk, the halo kinematics, and the theories ofgalaxy formation.
| Probable new halo stars toward L = 360 deg, B = +30 deg
The Stock objective-prism radial-velocity survey catalog has beensearched for probable halo giants at intermediate Galactic longitude. Atotal of 83 objects were found. The sample yielded a velocity dispersionof 98 + or - 8 km/sec and a frequency of 0.15 halo giants brighter thanm(pg) = 11.5/sq deg.
| Southern stars of high radial velocity
First, it has been shown that the Stock Velocity Survey is a usefulsource of velocity information on 8-13th mag southern stars. Theparticular use has been to identify stars of very large velocity.Thackeray (1975) has tabulated those galactic objects with heliocentricradial velocities over 250 km/s; his list contains 69 objects, of which59 are stellar. The authors have found twelve more stars. Second, theslit spectra of a sample of high-velocity stars in the Stock Surveyrevealed several extremely metal-weak stars. Abundance analysis forthese objects would be worthwhile. Finally, among the high-velocityobjects are a surprising number of late B and early A stars. In mostinstances, these objects appear to be spectroscopically normal,main-sequence stars, but three are definite A + G spectrum binaries.High-velocity binaries are rare.
| Metal-Deficient Giants in the Galactic Field - Catalogue and Some Physical Parameters
Not Available
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
INHABITED SKY
