目录
图像
上传图像
DSS Images Other Images
相关文章
Chemodynamics of Compact Stellar Systems in NGC 5128: How Similar are Globular Clusters, Ultra-Compact Dwarfs, and Dwarf Galaxies?
Velocity dispersion measurements are presented for several of the mostluminous globular clusters (GCs) in NGC 5128 (Centaurus A) derived fromhigh-resolution spectra obtained with the UVES echelle spectrograph onthe 8.2 m ESO/Very Large Telescope. The measurements are made utilizinga penalized pixel-fitting method that parametrically recoversline-of-sight velocity dispersions. Combining the measured velocitydispersions with surface photometry and structural parameter data fromthe Hubble Space Telescope enables both dynamical masses andmass-to-light ratios to be derived. The properties of these massivestellar systems are similar to those of both massive GCs containedwithin the Local Group and nuclear star clusters and ultra-compact dwarfgalaxies (UCDs). The fundamental plane relations of these clusters areinvestigated in order to fill the apparent gap between the relations ofLocal Group GCs and more massive early-type galaxies. It is found thatthe properties of these massive stellar systems match those of nuclearclusters in dwarf elliptical galaxies and UCDs better than those ofLocal Group GCs, and that all objects share similarly old (gsim8 Gyr)ages, suggesting a possible link between the formation and evolution ofnuclear star clusters in dwarf elliptical galaxies (dE,Ns), UCDs, andmassive GCs. We find a very steep correlation between dynamicalmass-to-light ratio and dynamical mass of the form \Upsilon_{V}^dyn\!\propto \!{\cal M}_dyn^{0.24\pm 0.02} above {\calM}_dyn\!\approx \!2\times 10^6 M sun. Formation scenarios areinvestigated with a chemical abundance analysis using absorption-linestrengths calibrated to the Lick/IDS index system. The results lendsupport to two scenarios contained within a single general formationscheme. Old, massive, super-solar [?/Fe] systems are formed onshort (lsim100 Myr) timescales through the merging of single-collapseGCs which themselves are formed within single, giant molecular clouds.More intermediate- and old-aged (~3-10 Gyr), solar- to sub-solar[?/Fe] systems are formed on much longer (~Gyr) timescales throughthe stripping of dE,Ns in the 1013-1015 Msun potential wells of massive galaxies and galaxy clusters.Based on observations made with ESO Telescopes at the ParanalObservatories under program 69.D-0094 and 69.D-0196.
| Chemical Abundances of Outer Halo Stars in the Milky Way
We present the chemical abundances of 57 metal-poor ([Fe/H] 5 kpc above andbelow the Galactic plane. High-resolution (R ˜ 50000-55000), highsignal-to-noise (S/N > 100) spectra for the sample stars obtainedwith Subaru/HDS were used to derive the chemical abundances of Na, Mg,Ca, Ti, Cr, Mn, Fe, Ni, Zn, Y, and Ba with an LTE abundance analysiscode. The resulting abundance data were combined with those presented inthe literature that mostly targeted at smaller Zmax stars,and both data were used to investigate any systematic trends in detailedabundance patterns depending on their kinematics. It was shown that, inthe metallicity range of ?2 < [Fe/H] < ?1, the [Mg/Fe]ratios for stars with Zmax > 5 kpc are systematicallylower (˜0.1 dex) than those with a smaller Zmax. Forthis metallicity range, a modest degree of depression in the [Si/Fe] andthe [Ca/Fe] ratios was also observed. This result of lower [?/Fe]for the assumed outer halo stars is consistent with previous studiesthat found a signature of lower [?/Fe] ratios for stars withextreme kinematics. The distribution of the [Mg/Fe] ratios for the outerhalo stars partly overlaps with that for stars belonging to the MilkyWay dwarf satellites in the metallicity interval of ?2 < [Fe/H]< ?1 and spans a range intermediate between the distributionsfor the inner halo stars and the stars belonging to the satellites. Ourresults confirm the inhomogeneous nature of the chemical abundanceswithin the Milky Way stellar halo, depending on the kinematic propertiesof the constituent stars, as suggested by earlier studies. Possibleimplications for the formation of the Milky Way halo and its relevanceto the suggested dual nature of the halo are discussed.
| Chemical Compositions of Kinematically Selected Outer Halo Stars
Chemical abundances of 26 metal-poor dwarfs and giants are determinedfrom high-resolution and high signal-to-noise ratio spectra obtainedwith the Subaru/High Dispersion Spectrograph. The sample is selected sothat most of the objects have outer-halo kinematics. Self-consistentatmospheric parameters were determined by an iterative procedure basedon spectroscopic analysis. Abundances of 13 elements, includingα-elements (Mg, Si, Ca, Ti), odd-Z light elements (Na, Sc),iron-peak elements (Cr, Mn, Fe, Ni, Zn), and neutron-capture elements(Y, Ba), are determined by two independent data reduction and localthermodynamic equillibrium analysis procedures, confirming theconsistency of the stellar parameters and abundances results. We find adecreasing trend of [α/Fe] with increasing [Fe/H] for the range of–3.5< [Fe/H] <–1, as found by Stephens &Boesgaard. [Zn/Fe] values of most objects in our sample are slightlylower than the bulk of halo stars previously studied. These results arediscussed as possible chemical properties of the outer halo in theGalaxy.Based on data collected at the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.
| 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.
| Bright globular clusters in NGC 5128: the missing link between young massive clusters and evolved massive objects
Context: Globular clusters are the simplest stellar systems in whichstructural parameters are found to correlate with their masses andluminosities. Aims: To investigate whether the brightest globularclusters in the giant elliptical galaxies are similar to the lessluminous globular clusters like those found in Local Group galaxies, westudy the velocity dispersion and structural parameter correlations of asample of bright globular clusters in the nearest giant ellipticalgalaxy NGC 5128 (Centaurus A). Methods: The UVES echelle spectrographon the ESO Very Large Telescope (VLT) was used to obtain high-resolutionspectra of 23 bright globular clusters in NGC 5128, and 10 clusters wereobserved with EMMI in echelle mode with the ESO New TechnologyTelescope. The two datasets have 5 clusters in common, while one clusterobserved with UVES had too low a signal-to-noise ratio. Hence the totalnumber of clusters analysed in this work is 27, more than doubling thepreviously known sample. Their spectra were cross-correlated withtemplate spectra to measure the central velocity dispersion for eachtarget. The structural parameters were either taken from the existingliterature, or in cases where this was not available, we derived themfrom our VLT FORS1 images taken under excellent seeing conditions, usingthe ISHAPE software. The velocity dispersion and structural parametermeasurements were used to obtain masses and mass-to-luminosity ratios(M/L_V) for 22 clusters. Results: The masses of the clusters in oursample range from M_vir = 10^5-107 Mȯ, andthe average M/LV is 3 ± 1. The three globular clustersharbouring X-ray point sources are the second, third, and sixth mostmassive in our sample. The most massive cluster, HCH99-18, is also thebrightest and the largest. It has a mass (M_vir =1.4×107 Mȯ) that is an order ofmagnitude higher than the most massive clusters in the Local Group and ahigh M/LV ratio (4.7 ± 1.2). We briefly discusspossible formation scenarios for this object. Conclusions: Thecorrelations of structural parameters, velocity dispersion, masses, andM/LV for the bright globular clusters in NGC 5128 extend theproperties established for the most massive Local Group clusters towardsthose characteristic of dwarf elliptical nuclei and ultra-compact dwarfgalaxies (UCDs). The detection of the mass-radius and themass-M/LV relations for the globular clusters with masseshigher than ~ 2 × 106 Mȯ provides themissing link between “normal” old globular clusters, youngmassive clusters, and evolved objects like UCDs.Based on observations collected at the European Southern Observatory,Paranal, Chile, within the Observing Programmes 63.N-0229 and069.D-0169.
| Redshifts and Velocity Dispersions of Galaxy Clusters in the Horologium-Reticulum Supercluster
We present 118 new optical redshifts for galaxies in 12 clusters in theHorologium-Reticulum supercluster (HRS) of galaxies. For 76 galaxies,the data were obtained with the Dual Beam Spectrograph on the 2.3 mtelescope of the Australian National University at Siding SpringObservatory. After combining 42 previously unpublished redshifts withour new sample, we determine mean redshifts and velocity dispersions for13 clusters in which previous observational data were sparse. In 6 ofthe 13 clusters, the newly determined mean redshifts differ by more than750 km s-1 from the published values. In three clusters,A3047, A3109, and A3120, the redshift data indicate the presence ofmultiple components along the line of sight. The new cluster redshifts,when combined with other reliable mean redshifts for clusters in theHRS, are found to be distinctly bimodal. Furthermore, the two redshiftcomponents are consistent with the bimodal redshift distribution foundfor the intercluster galaxies in the HRS by Fleenor and coworkers.
| 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.
| Spectrophotometry: Revised Standards and Techniques
The telluric features redward of 6700 Å have been removed from theaccurate spectrophotometric standards of Hamuy et al. to permit morereliable relative and absolute spectrophotometry to be obtained from CCDspectra. Smooth fluxes from 3300 to 10500 Å are best determined bydividing the raw spectra of all objects taken in a night by the rawspectrum of a ``smooth'' spectrum star before deriving the instrumentalresponse function using the revised standard star fluxes. In this waythe telluric features and any large instrumental variation withwavelength are removed from the raw data, leaving smooth spectra thatneed only small corrections to place them on an absolute flux scale.These small corrections with wavelength are well described by alow-order polynomial and result in very smooth flux-calibrated spectra.
| 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.
| 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.
| Kinematics and Metallicity of Stars in the Solar Region
Several samples of nearby stars with the most accurate astrometric andphotometric parameters are searched for clues to their evolutionaryhistory. The main samples are (1) the main-sequence stars with b - ybetween 0.29 and 0.59 mag (F3 to K1) in the Yale parallax catalog, (2) agroup of high-velocity subgiants studied spectroscopically by Ryan &Lambert, and (3) high-velocity main-sequence stars in the extensiveinvestigation by Norris, Bessel, & Pickles. The major conclusionsare as follows: (1) The oldest stars (halo), t >= 10-12 Gyr, haveV-velocities (in the direction of Galactic rotation and referred to theSun) in the range from about -50 to -800 km s^-1 and have aheavy-element abundance [Fe/H] of less than about -0.8 dex. The agerange of these objects depends on our knowledge of globular clusterages, but if age is correlated with V-velocity, the youngest may be M22and M28 (V ~ -50 km s^-1) and the oldest NGC 3201 (V ~ -500 km s^-1) andassorted field stars. (2) The old disk population covers the large agerange from about 2 Gyr (Hyades, NGC 752) to 10 or 12 Gyr (Arcturusgroup, 47 Tuc), but the lag (V) velocity is restricted to less thanabout 120 km s^-1 and [Fe/H] >= -0.8 or -0.9 dex. The [Fe/H] ~ -0.8dex division between halo and old disk, near t ~ 10-12 Gyr, is marked bya change in the character of the CN index (C_m) and of the blanketingparameter K of the DDO photometry. (3) The young disk population, t <2 Gyr, is confined exclusively to a well-defined area of the (U, V)velocity plane. The age separating young and old disk stars is also thatseparating giant evolution of the Hyades (near main-sequence luminosity)and M67 (degenerate helium cores and a large luminosity rise) kinds. Thetwo disk populations are also separated by such indexes as the g-indexof Geveva photometry. There appears to be no obvious need to invokeexogeneous influences to understand the motion and heavy-elementabundance distributions of the best-observed stars near the Sun.Individual stars of special interest include the parallax star HD 55575,which may be an equal-component binary, and the high-velocity star HD220127, with a well-determined space velocity near 1000 km s^-1.
| Core velocity dispersions for 25 Galactic and 10 old Magellanic globular clusters.
We present, for 25 Galactic and 10 old Magellanic globular clusters,projected velocity dispersion (σ_p_) measurements obtained byapplying a cross-correlation technique to integrated-light spectra. Inorder to understand and estimate the statistical errors of thesemeasurements due to small numbers of bright stars dominating theintegrated light, we provide an extensive discussion based on detailednumerical simulations. These errors are smaller if the integration areais larger and/or the cluster concentration higher. The simulations showthat measurements are reliable when the integrated light within theintegration area is brighter than a given magnitude. The statisticalerrors on the σ_p_ measurements of Magellanic globular clustersare small because of a physically large integration area, whereas theycan be important for measurements carried out over small central areasin Galactic clusters. The present observational results are used tooutline a few characteristics of the globular cluster fundamental plane.In this respect, the old Magellanic globular clusters appear similar tothe Galactic clusters.
| Internal dynamics of globular clusters
Galactic globular clusters, which are ancient building blocks of ourGalaxy, represent a very interesting family of stellar systems in whichsome fundamental dynamical processes have taken place on time scalesshorter than the age of the universe. In contrast with galaxies, theseclusters represent unique laboratories for learning about two-bodyrelaxation, mass segregation from equipartition of energy, stellarcollisions, stellar mergers, and core collapse. In the present review,we summarize the tremendous developments, as much theoretical asobservational, that have taken place during the last two decades, andwhich have led to a quantum jump in our understanding of these beautifuldynamical systems.
| 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.
| DDO metallicity calibration for metal-deficient red giants and the disk-halo transition
DDO abundance estimates for metal-deficient field red giants from thesurvey by Norris et al., (1985) are compared with high dispersionspectroscopic abundances and recalibrated uvby photometry. The DDOabundances are shown to deviate from the standard system by an amountwhich is metallicity dependent, i.e., a simple offset cannot transformthe DDO data to the spectroscopic system. A recalibration of the DDOphotometry demonstrates that the old DDO calibration provides reliable(Fe/H) estimates near -0.8 and -2.3, but systematically underestimatesthe metallicity of stars near -1.2 by about 0.5 dex. Reanalysis of thered giant sample of Norris et al. leads to a metallicity distributionmuch closer to that of the globular clusters while significantlydecreasing the fracion of metal-weak disk stars. A possible explanationfor origin of the discrepancy is that the clusters of intermediate(Fe/H) used in the DDO calibration are not representative of the fieldstars at the same (Fe/H).
| 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.
| Observations of high-redshift CA II absorption in QSO spectra
A spectroscopic search for Ca II H and K absorption in known QSOabsorption systems is reported, resulting in the detection of this ionin the QSO PKS 0454-22 at z(abs) = 0.4745. Fe II and Mg II absorptionlines in this system have been observed, and it is shown that gaseous CaII is severely underabundant with respect to both Fe II and Mg II. Ifthe observed fraction of Ca II is typical of QSO absorption systems itwould explain why this ion has not been readily seen and why two otherobserved objects, 1101-264 and the BL Lac PKS 0735 + 178, did not givepositive detections. The underabundance of Ca II with respect to Fe IIand Mg II is similar to that in interstellar clouds in the Galaxy,suggesting the selective condensation of elements on to grains.Alternatively, the lack of Ca II may be due to ionization equilibriumconditions, i.e., a lower ratio of the electron density to thephotoionization rate of Ca(+) in the absorbing region than typicallyfound in disk gas in the Galaxy.
| 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).
| Metal-Deficient Giants in the Galactic Field - Catalogue and Some Physical Parameters
Not Available
| Southern subdwarf photometry
UBV photometry and normalized UV excesses are reported for 176 southernmetal-poor stars selected from the objective-prism survey of Bidelmanand MacConnell (1973) as well as 49 other metal-deficient starsidentified in other surveys. Photometry is also presented for 32 otherstars lying near the 225 program stars (although not explicitlyidentified as such in the text, the program stars are apparentlysubdwarfs and subdwarf candidates). Previously determined spectral typesand degrees of line weakening are given for the 225 stars, andmetallicities are estimated on the basis of the degrees of lineweakening. It is noted that 33 F and G stars with extreme meannormalized UV excesses of approximately 0.22 mag have a mean Fe/H valueof -1.4 and probably represent halo subdwarfs, while 82 F and G starswith moderate UV excesses are mostly old disk stars.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
INHABITED SKY
