Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
On the Connection Between CWA and RVA Stars
Phase plots of ASAS-3 data of a large number of CWA and RVA variablestars reveal that there is no clear distinction in period or light curveshape between these two types of stars.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Metal Abundances and Kinematics of Bright Metal-poor Giants Selected from the LSE Survey: Implications for the Metal-weak Thick Disk
We report medium-resolution (1-2 Å) spectroscopy and broadband(UBV) photometry for a sample of 39 bright stars (the majority of whichare likely to be giants) selected as metal-deficient candidates from anobjective-prism survey concentrating on Galactic latitudes below|b|=30°, the Luminous Stars Extension (LSE) survey of Drilling &Bergeron. Although the primary purpose of the LSE survey was to selectOB stars (hence the concentration on low latitudes), the small number ofbright metal-deficient giant candidates noted during this survey provideinteresting information on the metal-weak thick disk (MWTD) population.Metal abundance estimates are obtained from several different techniquesand calibrations, including some that make use of the availablephotometry and spectroscopy and others that use only the spectroscopy;these methods produce abundance estimates that are consistent with oneanother and should be secure. All of the targets in our study haveavailable high-quality proper motions from the Hipparcos or Tycho IIcatalogs, or both, that we combine with radial velocities from ourspectroscopy to obtain full space motions for the entire sample. Therotational (Vφ) velocities of the LSE giants indicatethe presence of a rapidly rotating population, even at quite lowmetallicity. We consider the distribution of orbital eccentricity of theLSE giants as a function of [Fe/H] and conclude that the local fraction(i.e., within 1 kpc from the Sun) of metal-poor stars that might beassociated with the MWTD is on the order of 30%-40% at abundances below[Fe/H]=-1.0. Contrary to recent analyses of previous (much larger)samples of nonkinematically selected metal-poor stars (assembledprimarily from prism surveys that concentrated on latitudes above|b|=30°), we find that this relatively high fraction of localmetal-poor stars associated with the MWTD may extend to metallicitiesbelow [Fe/H]=-1.6, much lower than had been considered before. Weidentify a subsample of 11 LSE stars that are very likely to be membersof the MWTD, based on their derived kinematics; the lowest metallicityamong these stars is [Fe/H]=-2.35. Implications of these results for theorigin of the MWTD and for the formation of the Galaxy are considered.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| The Milton Bureau Revisited
Under the direction of Cecilia Payne-Gaposchkin and Sergei Gaposchkin, aprogram was subsidized by the Milton Fund of Harvard Observatory in 1937for the study of all variable stars then known to be brighter than tenthphotographic magnitude at maximum. This included some 1512 stars forwhich a grand total of 1,263,562 estimates of magnitude were made,ranging from a low of 16 (except for a few novae) to 4084 observationsper star. The sky had been divided into 54 fields, and the results ofthe measurements presented field by field in two volumes of the Annalsof Harvard Observatory. Then, in another volume, the results werediscussed in four sections, each dealing with a particular class ofvariable: 1, those of RV Tauri type; 2, the eclipsing variables; 3,Cepheids and RR Lyrae variables, and 4, the red variables, especiallyMira-type and semiregular variables.For the present paper, many of these results have been compared withmodern determinations in the 1985-87 version of the "General Catalogueof Variable Stars (GCVS)". In particular, there are numerous instancesof disagreement as to whether a star should be classified RV or SR.Although there are many instances where the Milton Bureau determinationsof types of variability differ from the types given in moderncatalogues, the reasons for the differences are generallyunderstandable.For 17 RV Tauri type stars in this survey multiple periods have now beendetermined. Many of these still deserve continued observations in orderto ascertain the constance of the periods and improve the accuracy oftheir longest reported periods.
| 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.
| 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.
| Atmospheric conditions in yellow and red variables
Pulsation occurs in late-type giant and supergiant stars under a widerange of atmospheric conditions and evolutionary stages. Longobservational baselines are necessary to distinguish pulsationbehaviors. Spectrographic and photometric observations of a variety oflate-type pulsators are considered in the context of light-curvetaxonomy and changing atmospheric conditions.
| RV Tauri stars - II. A spectroscopic study
A long-term photometric and spectroscopic survey of eleven RV Tauristars has been undertaken with a view to obtaining a betterunderstanding of the nature of these pulsating variables. Pollard et al.presented the results from the long-term multicolour photometric survey.This paper presents the contemporaneous moderate- to high-resolutionspectroscopy of these stars. All the RV Tauri stars in our sampledisplay, or are consistent with, two shock waves propagating in theiratmospheres per `formal' period (the time between successive deepminima). This is consistent with the few previous high-resolutionspectroscopic studies of the three brightest RV Tauri stars: R Sct, UMon and AC Her. Specifically, the Hα profiles exhibit twoenhancements of emission per cycle following the passage of the primaryand secondary shock waves through the photosphere around phases 0.1 and0.6. Metallic lines showed `doubled' profiles characteristic of anatmospheric shock wave around these phases, with evidence of two radialvelocity cycles per formal period. In the RVb-type stars, an additionalcontribution to the Hα emission is seen and this appears to becorrelated with the long-term period. Two stars, AI Sco and IW Car,display extended blueward Hα absorption which may arise from massoutflow. Evidence of long-term radial velocity variations is also seenin a number of the RVb stars.
| RV Tauri stars - I. A long-term photometric survey.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.279..949P&db_key=AST
| An Extension of the Case-Hamburg OB Star Surveys
We have extended the Case-Hamburg OB star surveys to b = +- 30 degreesfor l = +- 60 degres using the Curtis Schmidt telescope and 4 degreeobjective prism at the Cerro Tololo Inter-American Observatory. Acatalog of 234 OB stars and other objects with peculiar spectra ispresented along with finding charts for those objects too faint to beincluded on the BD or CD charts. (SECTION: Stars)
| 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
| 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.
| Pseudocepheids. III - The low-mass stars
Light and color curves in four-color, H-beta, and (RI) photometricsystems are presented for 20 low-mass pseudocepheids. Members of theWolf 630 group and the cluster M67 are used to establish the positionsof both variable and nonvariable giants with near solar abundance in theluminosity-temperature plane for old disk population stars, whilemembers of Omega Cen and of Kapteyn's Star Group are used for the lowmetal abundance halo giants. The low-mass pseudocepheids discussed aredivided into two main categories, based on the amplitude of lightvariation. The smaller amplitude stars, characterized by R CrB and RYSgr in the old disk population, show the R CrB syndrome of occasionaldeep light minima, as does UW Cen. The small amplitude variables in thehalo population, BL Tel and LN Hya, do not show the R CrB syndrome andtheir periods are longer than those of old disk stars. Large amplitudevariables, with periods ranging from 10 to 150 days, are all haloobjects with stability of period and form of light curve an obviousfunction of the period. Cen and BL Tel are members of Kapteyn's StarGroup, and the spectroscopic orbital elements of the latter indicate amass near 0.5 solar mass for the pseudocepheid and 1 solar mass for thelate-type giant companion. Far-infrared observations are important inexploring the correlations between the presence and character ofcircumstellar dust shells and other post-AGB star parameters.
| Metal-Deficient Giants in the Galactic Field - Catalogue and Some Physical Parameters
Not Available
| 65th Name-List of Variable Stars
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.
| Light Variation of CoD -37 9248
Not Available
| Mitteilungen uber Veranderliche der Bamberger Liste.
Not Available
| A test of accuracy of low-dispersion objective-prism spectral classification of late-type stars using DDO photometry.
Abstract image available at:http://adsabs.harvard.edu/abs/1976PASP...88..463C
| CPD -37 6004: a fast moving star with Hbeta emission.
Abstract image available at:http://adsabs.harvard.edu/abs/1976A&A....50..133H
| Observations of southern emission-line stars
A catalog of 1929 stars showing H-alpha emission on photographic platesis presented which covers the entire southern sky south of declination-25 deg to a red limiting magnitude of about 11.0. The catalog providesprevious designations of known emission-line stars equatorial (1900) andgalactic coordinates, visual and photographic magnitudes, H-alphaemission parameters, spectral types, and notes on unusual spectralfeatures. The objects listed include 16 M stars, 25 S stars, 37 carbonstars, 20 symbiotic stars, 40 confirmed or suspected T Tauri stars, 16novae, 14 planetary nebulae, 11 P Cygni stars, 9 Bep stars, 87 confirmedor suspected Wolf-Rayet stars, and 26 'peculiar' stars. Two new Tassociations are discovered, one in Lupus and one in Chamaeleon. Objectswith variations in continuum or H-alpha intensity are noted, and thedistribution by spectral type is analyzed. It is found that the skydistribution of these emission-line stars shows significantconcentrations in the region of the small Sagittarius cloud and in theCarina region.
| CD -37 9248, a metal-poor star of high radial velocity
Not Available
| Discoveries on southern objective-prism plates. III. Three hydrogen-deficient stars and a bright B-type subdwarf
Abstract image available at:http://adsabs.harvard.edu/abs/1972PASP...84..388M
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Кентаур |
| Ректацензија: | 14h13m56.35s |
| Deклинација: | -38°05'46.6" |
| Apparent магнитуда: | 9.072 |
| Proper motion RA: | -15.8 |
| Proper motion Dec: | -15 |
| B-T magnitude: | 10.5 |
| V-T magnitude: | 9.19 |
Каталог и designations:
|
