Садржај
Слике
| - Није пронађена ниједна слика - |
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
Carbon-rich giants in the HR diagram and their luminosity function
The luminosity function (LF) of nearly 300 Galactic carbon giants isderived. Adding BaII giants and various related objects, about 370objects are located in the RGB and AGB portions of the theoretical HRdiagram. As intermediate steps, (1) bolometric corrections arecalibrated against selected intrinsic color indices; (2) the diagram ofphotometric coefficients 1/2 vs. astrometric trueparallaxes varpi are interpreted in terms of ranges of photosphericradii for every photometric group; (3) coefficients CR andCL for bias-free evaluation of mean photospheric radii andmean luminosities are computed. The LF of Galactic carbon giantsexhibits two maxima corresponding to the HC-stars of the thick disk andto the CV-stars of the old thin disk respectively. It is discussed andcompared to those of carbon stars in the Magellanic Clouds and Galacticbulge. The HC-part is similar to the LF of the Galactic bulge,reinforcing the idea that the Bulge and the thick disk are part of thesame dynamical component. The CV-part looks similar to the LF of theLarge Magellanic Cloud (LMC), but the former is wider due to thesubstantial errors on HIPPARCOS parallaxes. The obtained meanluminosities increase with increasing radii and decreasing effectivetemperatures, along the HC-CV sequence of photometric groups, except forHC0, the earliest one. This trend illustrates the RGB- and AGB-tracks oflow- and intermediate-mass stars for a range in metallicities. From acomparison with theoretical tracks in the HR diagram, the initial massesMi range from about 0.8 to 4.0 Msun for carbongiants, with possibly larger masses for a few extreme objects. A largerange of metallicities is likely, from metal-poor HC-stars classified asCH stars on the grounds of their spectra (a spheroidal component), tonear-solar compositions of many CV-stars. Technetium-rich carbon giantsare brighter than the lower limit Mbol =~ -3.6+/- 0.4 andcentered at =~-4.7+0.6-0.9 at about =~(2935+/-200) K or CV3-CV4 in our classification. Much like the resultsof Van Eck et al. (\cite{vaneck98}) for S stars, this confirms theTDU-model of those TP-AGB stars. This is not the case of the HC-stars inthe thick disk, with >~ 3400 K and>~ -3.4. The faint HC1 and HC2-stars( =~ -1.1+0.7-1.0) arefound slightly brighter than the BaII giants ( =~-0.3+/-1.3) on average. Most RCB variables and HdC stars range fromMbol =~ -1 to -4 against -0.2 to -2.4 for those of the threepopulation II Cepheids in the sample. The former stars show the largestluminosities ( <~ -4 at the highest effectivetemperatures (6500-7500 K), close to the Mbol =~ -5 value forthe hot LMC RCB-stars (W Men and HV 5637). A full discussion of theresults is postponed to a companion paper on pulsation modes andpulsation masses of carbon-rich long period variables (LPVs; Paper IV,present issue). This research has made use of the Simbad databaseoperated at CDS, Strasbourg, France. Partially based on data from theESA HIPPARCOS astrometry satellite. Table 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/390/967
| The Cepheids of Population II and Related Stars
The Type II Cepheids include most intrinsic variables with periodsbetween 1 and about 50 days, except for the classical Cepheids and theshortest semiregular variables of type M. The Type II Cepheids may bedivided in groups by period, such that the stars with periods beween 1and 5 days (BL Her class), 10-20 days (W Vir class), and greater than 20days (RV Tau class) have differing evolutionary histories. The chemicalcomposition of Type II Cepheids reflects the material they were madefrom as modified by their internal nuclear evolution and mixing.Finally, RV Tau stars are affected by mass loss by dust and speciesattached to the dust. The populations to which the various classes ofType II Cepheids are assigned constitute important clues to the originand evolution of the halo of our Galaxy and the dwarf spheroidal systemsfrom which at least part of the halo seems to have been accreted.
| Coordinates and Identifications of Harvard Variables
Coordinates and identifications are presented for 726 Harvard Variablestars and suspected variables, discovered or studied by D. Hoffleit andannounced in Harvard Bulletins 874, 884, 887, 901, and 902; plus 141others, previously known, lying in the same fields.
| The effective temperatures of carbon-rich stars
We evaluate effective temperatures of 390 carbon-rich stars. Theinterstellar extinction on their lines of sights was determined andcircumstellar contributions derived. The intrinsic (dereddened) spectralenergy distributions (SEDs) are classified into 14 photometric groups(HCi, CVj and SCV with i=0,5 and j=1,7). The newscale of effective temperatures proposed here is calibrated on the 54angular diameters (measured on 52 stars) available at present from lunaroccultations and interferometry. The brightness distribution on stellardiscs and its influence on diameter evaluations are discussed. Theeffective temperatures directly deduced from those diameters correlatewith the classification into photometric groups, despite the large errorbars on diameters. The main parameter of our photometric classificationis thus effective temperature. Our photometric < k right >1/2 coefficients are shown to be angular diameters on arelative scale for a given photometric group, (more precisely for agiven effective temperature). The angular diameters are consistent withthe photometric data previously shown to be consistent with the trueparallaxes from HIPPARCOS observations (Knapik, et al. \cite{knapik98},Sect. 6). Provisional effective temperatures, as constrained by asuccessful comparison of dereddened SEDs from observations to modelatmosphere predictions, are in good agreement with the values directlycalculated from the observed angular diameters and with those deducedfrom five selected intrinsic color indices. These three approaches wereused to calibrate a reference angular diameter Phi 0 and theassociated coefficient CT_eff. The effective temperatureproposed for each star is the arithmetic mean of two estimates, one(``bolometric'') from a reference integrated flux F0, theother (``spectral'') from calibrated color indices which arerepresentative of SED shapes. Effective temperatures for about 390carbon stars are provided on this new homogeneous scale, together withvalues for some stars classified with oxygen-type SEDs with a total of438 SEDs (410 stars) studied. Apparent bolometric magnitudes are given.Objects with strong infrared excesses and optically thick circumstellardust shells are discussed separately. The new effective temperaturescale is shown to be compatible and (statistically) consistent with thesample of direct values from the observed angular diameters. Theeffective temperatures are confirmed to be higher than the mean colortemperatures (from 140 to 440 K). They are in good agreement with thepublished estimates from the infrared flux method forTeff>= 3170 K, while an increasing discrepancy is observedtoward lower temperatures. As an illustration of the efficiency of thephotometric classification and effective temperature scale, the C/Oratios and the Merrill-Sanford (M-S) band intensities are investigated.It is shown that the maximum value, mean value and dispersion of C/Oincrease along the photometric CV-sequence, i.e. with decreasingeffective temperature. The M-S bands of SiC2 are shown tohave a transition from ``none'' to ``strong'' at Teff =~(2800+/- 150right ) K. Simultaneously, with decreasing effectivetemperature, the mean C/O ratio increases from 1.04 to 1.36, thetransition in SiC2 strength occurring while 1.07<= C/O<= 1.18. This research has made use of the Simbad database operatedat CDS, Strasbourg, France. Table 10 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)}or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/369/178
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| 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.
| General Catalog of Galactic Carbon Stars by C. B. Stephenson. Third Edition
The catalog is an updated and revised version of Stephenson's Catalogueof Galactic Cool Carbon Stars (2nd edition). It includes 6891 entries.For each star the following information is given: equatorial (2000.0)and galactic coordinates, blue, visual and infrared magnitudes, spectralclassification, references, designations in the most significantcatalogs and coordinate precision classes. The main catalog issupplemented by remarks containing information for which there was noplace in entries of the main part, as well as some occasional notesabout the peculiarities of specific stars.
| Fourier Analysis of Hipparcos Photometry of Cepheid Variables
Fourier parameters have been computed for 240 field Cepheids observed bythe Hipparcos satellite. We have identified three new PopulationIovertone Cepheids: V411Lac, V898 Cen and V572 Aql. We have comparedFourier progressions of Population I and Population II Cepheids. Thepossibility of using Fourier parameters to distinguish between the twotypes is discussed.
| The carbon Cepheid RT Trianguli Australis: additional evidence of triple-α and CNO cycling
We have used echelle spectra of resolving power 35000 to derive chemicalabundances and the 12C/13C ratio in the 1.9-dcarbon Cepheid RT TrA and the Cepheid U TrA, employed as a comparisonstar. We confirm that RT TrA is very metal-rich with [Fe/H]=+0.4. Inaddition, C and N are substantially in excess, and a small deficiency inO is present. We interpret these anomalies as resulting from theappearance on the stellar surface of material enriched in 12Cby the 3-α process, followed by CNO cycling to convert12C to 13C and 14N. In addition, some16O has been processed to 14N. The partialprocessing of 16O to 14N indicates thatsubstantial 17O may be present. Proton capture seems to haveenhanced 23Na from the Ne isotopes.
| Period Changes in Population II Cepheids: TX Del and W Vir
We have used the Hipparcos database of epoch photometry to study thevariability of two Population II Cepheids: TX Del and W Vir. We haveconstructed (O-c) diagrams for these stars, using the new data and datafrom the literature. The period of TX Del is decreasing, at a ratewhich is consistent with evolutionary predictions. THe periodchange ofW Vir is uncertain because of the many recent gaps in the data of thisstar. We urge AAVSO visual and photoelectric observers to monitorPopulation II Cepheids more systematically, since amny of these starshave unstable periods, and at least one has an unstable amplitude.
| Photometric Parameters for Short-Period Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1313E&db_key=AST
| A New Version of the Catalog of CH and Related Stars (CH95 Catalog)
A new version of the catalog of CH and related stars contains 244 fieldstars and 17 globular cluster stars. Here a list of these stars withtheir coordinates, their positions in the HR diagram and somestatistical diagrams is presented. The catalog will soon be available inthe printed and computerized versions.
| Physical parameters of pulsating variables with periods between one and three days. II - Fundamental parameters
On the basis of the Walraven VBLUW photometry data reported by Diethelm(1986) on 57 pulsating variables with periods between one and threedays, primary parameters (metallicity, log g, Teff, and the amount ofreddening) were deduced for 11 of these stars, using a semiempiricalapproach based on model atmosphere calculations. Results indicate thatboth the C-delta and the SA-class of the pulsating variables are youngstars of the disc-population pulsating either in the fundamental(C-delta) or in the first overtone mode (SA). The AHB1 stars, whichshowed a marked deficiency in metal abundance, are members of the halopopulaton. The stars of the AHB2 and AHB3 groups, which show anintermediate metallicity, must be considered as members of anintermediate stellar population.
| Color Excesses on a Uniform Scale for 328 Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990ApJS...72..153F&db_key=AST
| Catalogue of CH and metal-deficient barium stars
Not Available
| Studies of Cepheid-type variability. V - The Fourier phases of type II Cepheids with periods of 1-3 days
Fourier phases of type II Cepheids with periods 1-3 d are reanalyzed andcompared with similar data for classical Cepheids, using a new phasedefinition recently proposed by Stellingwerf and Donohoe (1986). It isfound that this definition allows an improved analysis, mainly due tothe possibility of comparison with a standard case. It is shown that theavailable data for the type II Cepheids are in good agreement with theassumption of a resonance at a period of about 1.5 d.
| On the short-period type II Cepheid field stars
The most accurate recent photoelectric light curve observations of theshort-period type II Cepheids are used here to plot Fourier diagrams andmake comparisons with both the classical type I Cepheids and with themodels of Hodson, Cox, and King (1982), also subjected to Fourierdecomposition. It is found that the resonance sequence among the type IIstars differs in significant ways from its Population I counterpart, butthat hydrodynamic models of the type II Cepheids are amazinglysuccessful in depicting the light curve progression for these stars. Theproblems posed for theories of stellar and galactic evolution by theexistence of disk, halo, and cluster pulsators with very similar lightcurves are discussed.
| Physical parameters of pulsating variables with periods between one and three days. I - Photometry and metallicities
Based on a new set of observations in the Walraven VBLUW system,obtained at the European Southern Observatory, La Silla, Chile,Fe/H(VBLU) values of 57 pulsating variables, mostly with periods betweenone and three days,. are determined. The distribution of the metalabundances is shown to be essentially bimodal. All the variables withFe/H ratios of less than -0.4 were classified by Diethelm (1983) as RRdstars. They are identified as the galactic field counterpart of theCepheids in the same period range found in globular clusters.
| Studies of Cepheid-type variability. III - Fourier description of light curves of Type II Cepheids of periods 1-3 days
Abstract image available at:http://adsabs.harvard.edu/abs/1986A&A...156..337P
| Intermediate-band and H-beta observations of short-period Cepheids
Intermediate-band and H-beta observations along with light and colorcurves for short-period Cepheids are presented. Although mainlysouthern, a few northern variables are included. Two of the variablesare briefly discussed.
| The period-luminosity-abundance relations for galactic Cepheids
The median photometric parameters from intermediate and H-betaphotometry of 106 Cepheids are used to test the Sandage-Tammann resultthat dispersions in the PL and PC relations are correlated with theamplitude of the light curves, as measured by the amplitude defect F(B).The correlation of both color and luminosity dispersions from mean PLand PC relations with F(B) are found to be the result of a correlationbetween abundance and amplitude. The short-period Cepheids (SPC) aredistinctly divided between type C and normal Cepheids, with type Cvariables defined by F(B). The C-type and normal SPC are separated by0.65 mag at a given period and abundance, or about 300 K at a givenluminosity, with the C-type Cepheids being fainter and bluer,respectively. The light curves of nine-day Cepheids with strong humpsmay be misinterpreted in that the hump has mistakenly been taken formaximum light.
| A catalogue of field Type II Cepheids
A catalogue of field Type II Cepheids is presented. The primary listconsists of 152 Cepheids sufficiently far from the galactic plane to bevery probably Type II stars. A second list contains 56 additional starsthat are likely, but less certain, Type II Cepheids, including bothstars estimated to be at large distances from the galactic plane butwith uncertain distances and stars close to the galactic plane believedto be Type II for independent reasons.
| UBV photometry of short period cepheids
613 UBV observations of 15 pulsating variables collected on the 1 mreflector at ESO, La Silla, Chile are reported. The variables observedhave periods between one and three days.
| Carbon stars among the type II Cepheids
Not Available
| A photometric classification of pulsating variables with periods between one and three days
Available photometric (2000 UBV measurements) data were employed toestablish standard classifications of Cepheid variables. The datacovered pulsating variables in the Galaxy with periods between 1-3 days.The V lightcurves revealed that the 28 variables in the surveys could beclassified into four groups. The RR Lyrae stars have a smooth Vlightcurve, a short rise time, and a large amplitude in B(AB). The WVirginis stars exhibit a pronounced brightness hump on the ascendingbranch 0.2 h before brightness maximum, while BL Herculis stars have ahump on the descending branch, with rise times decreasing withincreasing periods. Finally, classical Cepheids have a smooth variationwith a gradual rise to maximum. All lie within 3 deg of the galacticequator. The UBV measurements are concluded to be suitable for a coarseseparation of populations of stars.
| The Catalogue of Distances and Light Absorption for Cepheids
Not Available
| Photoelectric Photometry of Cepheid Variables with Periods Between One and Three Days
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982A&AS...47..335D&db_key=AST
| Linear and nonlinear studies of BL Herculis variables
Linear and nonlinear nonadiabatic calculations for BL Herculis variableshave been made to study the occurrence of bumps in light and velocitycurves. Lines of constant period and constant linear theory for thesecond overtone to fundamental period ratio are plotted in the radialpulsation instability strip on the Hertzsprung-Russell diagram.Nonlinear calculations show that if the ratio is roughly between 0.47and 0.53, bumps do occur on the light and velocity curves, just as forthe classical Cepheids discussed by Simon and Schmidt. These bumps seemto be global but not necessarily echoes of surface disturbances from thecenter. Other bumps in light curves may be only photospheric shock wavesand not related to the ratio period resonance. Some comparisons withobservations are made.
| BVI Photometry of Southern Cepheids
Not Available
| VBI photometry of some southern cepheid and RR Lyrae variables
Not Available
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
Каталог и designations:
|
