Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
The Spectra of Type II Cepheids. III. The Hα Line and Helium Emission in Long-Period Stars
We have obtained Hα profiles from 175 spectra of 37 Cepheids withperiods longer than 8 days. About two-thirds of the stars are likelytype II Cepheids. In contrast to the situation among short-period stars,the velocity of Hα relative to the metal-line spectrum is not auseful parameter for distinguishing type I and type II Cepheids. On theother hand, at periods longer than 11 days and shorter than 34 daysstrong emission is observed in many stars and appears to be a gooddiscriminator of type. On this basis we identify one probable type ICepheid at a large distance from the Galactic plane. We have found Heλ5876 emission in seven Cepheids among the long-period starsdiscussed here and in one star with a short period, bringing to nine thenumber of type II Cepheids known to exhibit He emission.Based in part on observations obtained with the Apache Point Observatory3.5 m telescope, which is owned and operated by the AstrophysicalResearch Consortium.
| Photometry of Type II Cepheids. I. The Long-Period Stars
We present 1256 new photometric observations of 36 Cepheids with periodslonger than 8 days. The majority are likely type II Cepheids, but wehave included about a dozen classical Cepheids for comparison purposes,a few stars of uncertain type, and one putative RV Tauri star. Wediscuss the appearance of the light curves, the Fourier parameters, andthe light-curve stability in terms of differentiation between type I andtype II Cepheids. Although we encounter the same difficulties asprevious investigators in using these parameters for this purpose, weare able to identify some stars of particular interest, includingseveral likely type I Cepheids at large distances from the Galacticplane. Six stars with especially large period changes are identified anddiscussed.
| String/Rope length methods using the Lafler-Kinman statistic
The original Lafler-Kinman statistic for exploring any auto-correlationwithin a set of measurements relative to their underlying variance hasbeen regularized so that its determination is independent of the datasample size. In its new form, the power of its application toString-Length period searches (SLLK) has been assessed in terms ofestablishing confidence levels to point value detections within anygenerated periodogram and to confidence levels of not missing thedetection when an underlying period is present. These estimations dependonly on the amplitude of the variation relative to the measurement noiseand are independent of the signal-to-noise ratio of the measurements andof their number. Examples of the behaviour of periodograms based on SLLKas produced from computer generated data and real data are discussed. Itis also demonstrated that the principle can be readily extended tomultivariate data in the form of Rope-Length period searches (RLLK),with the measurements of each parameter not necessarily being takensimultaneously nor with equal number. Using simulated data it is shownthat the power of period detection improves slightly if the underlyingmodulations in each parameter are out of phase with each other. Examplesof the RLLK principle are given for computer simulated data and forstellar multi-colour photometric and polarimetric measurements.
| Polarimetry of 167 Cool Variable Stars: Data
Multicolor photoelectric polarimetry is presented for 167 stars, most ofwhich are variable stars. The observations constitute a data set thatfor some stars covers a time span of 35 yr. Complex variations are foundover time and wavelength and in both the amount of polarization and itsposition angle, providing constraints for understanding the polarizingenvironments in and around these cool stars.
| 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.
| The intermediate-band approach to the surface-brightness method for Cepheid radii and distance determination
The surface-brightness parameter Fν is calibrated in termsof the Strömgren intermediate-band colour b-y. The relationFν-(b-y)o valid for Cepheids is calibratedusing accurate near-infrared radii and distances for selected Cepheids.We have obtained uvby photometry for non-Cepheid giant and supergiantstars with known angular diameters and compared the slope and zero-pointof their Fν-(b-y)o relation with the Cepheidcalibration. We found that the two calibrations are significantlydifferent. The theoretical models lie in between the two calibrations.It is remarked that Fν-colour relations derived fromnon-Cepheids and involving blue colours (e.g. B-V or b-y) are notapplicable to Cepheids, while those involving redder colours (e.g. V-R,V-K or V-J) also produce good radii for Cepheids. Selected Cepheids ascalibrators lead to the accurate relationFν=3.898(+/-0.003)-0.378(+/-0.006)(b-y)o, whichallowed the calculation of radii and distances for a sample of 59Galactic Cepheids. The uncertainties in the zero-point and slope of theabove relation are similar to those obtained from near-infrared colours,and determine the accuracies in radii and distance calculations. Whileinfrared light and colour curves for Cepheids may be superior inprecision, the intermediate-band b-y colour allows the recovery of meanradii with an accuracy comparable to those obtained from the infraredsolutions. The derived distances are consistent within the uncertaintieswith those predicted by a widely accepted period-luminosityrelationship. Likewise, the resulting period-radius relation from theintermediate-band approach is in better agreement with infrared versionsthan with optical versions of this law. It is highlighted that theintermediate-band calibration of the surface-brightness method in thiswork is of comparable accuracy to the near-infrared calibrations. Thepresent results stress the virtues of uvby in determining the physicalparameters of supergiant stars of intermediate temperature.
| 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.
| 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.
| Using BV Photometry to Distinguish between Type I and Type II Cepheids
We use Johnson BV photometry of Galactic type I and type II Cepheids ina variety of diagrams to see whether the two populations can beadequately separated. The diagrams include the Fourier parametersphi_21, phi_31, phi_41, R_21, R_31, R_41, the loop width in the V-(B-V)plane, the relative phasing of V and B-V extrema, and the amplituderatios of B-V to V, all versus period. We found the R_i1 diagramsuseless in this regard, while a plot of the phasing parameter versusamplitude ratio was best, closely followed by the phi_i1 diagrams. Amajor difficulty was arriving at a sample of Cepheids that could bereliably taken to be definitely type II. We found it necessary to useonly stars that would have been more than 2 kpc from the Galactic planehad they been type I for this sample, and even then it is uncertainwhether such overlap between types as we find in our diagrams is due toinadequacy of the tests or is due to type I stars' having contaminatedour type II sample. We point out evidence strongly suggesting that typeI stars can be found at least up to 2 kpc from the plane. Selectioneffects in our sample of type II Cepheids resulted in only one BLHerculis star (short-period type II) being included, so our conclusionsbasically apply only to W Virginis stars.
| UVBY beta Photometric Data and Fourier Coefficients for Galactic Population I and Population II Cepheids
Photometric data in the uvby beta system are presented for a sample of98 Population I Cepheids and seven W Virginis or Population II Cepheids.The importance of the Fourier decomposition technique in the study ofthe structure of pulsating stars is stressed. Mean values and Fourierdecomposition coefficients for the V, b - y, m1, and c1 variations arecalculated. Also, mean values of H beta are provided. New times ofmaximum V light are reported for the majority of the stars in thesample. Significant shifts of the light and color curves were found insome Cepheids; these are explained by their period variations. Thesestars are highlighted in the text.
| A catalog of Cepheid radial velocities measured in 1995-1998 with the correlation spectrometer.
Not Available
| Baade-Wesselink Radius Determination of Type II Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113.1833B&db_key=AST
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Structural Properties of Pulsating Star Light Curves Through Fuzzy Divisive Hierarchical Clustering
Not Available
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| 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.
| A new approach to the surface brightness method for cepheid radii determination.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994RMxAA..29..148R&db_key=AST
| Period variation of selected cepheids
The aim of the present paper is to study the period as well asgamma-velocity changes of 12 cepheid-type variable stars in order tofind possible evidence for duplicity. Light-time effect was found in theO-C diagram of RY CMa, the orbital period being about 5200 days.Furthermore, especially spectroscopic observations are needed to confirmthe duplicity or render the accurate orbital solution possible.
| Stromgren photometry of short period population II Cepheids
Observations of the v, b, and y bands of the Stromgren system arepresented for 13 Cepheids of the disk and halo populations. Data forfour additional stars in the literature are included. Values of (M/H)are derived for each star using theoretical v, b, y colors. The (M/H)values agree quite well with high dispersion investigations of threestars. A range of (M/H) values from -2.3 to +0.5 and greater is found.At least nine of the 17 Cepheids are found to have (M/H) values that aregreater than found in any globular cluster that contains Cepheids. Thehighest M/H values may be due to uncertainties in circumstellarreddening of AU Peg and in the case of HR Aur, the likely presence ofcarbon bands in the spectrum. For the other stars whose (M/H) value isnear zero it is possible that their atmospheres have been polluted byhydrogen-depleted material due to mass loss or mass transfer in a binarysystem.
| 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
| Observational studies of Cepheids. VII - Radial velocities of faint Cepheids
Abstract image available at:http://adsabs.harvard.edu/abs/1988ApJS...66...43B
| 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.
| 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.
| Observational studies of Cepheids. III - Catalog of light curve parameters
The BVRI light curve parameters of 104 Cepheids are determined byFourier analysis from over 4000 photoelectric observations. A catalog ofthe light and color curve parameters and of the Fourier coefficients forthe V light curves is presented. The results are in good agreement withearlier catalogs except for (B-V) quantities. Possible photometricproblems with the (B-V) colors of Cepheids are discussed.
| 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.
| MG 2 emission of Pop. 2 long-period Cepheids
The population II Cepheid pulsational variables AL Vir (P = 10.3 days)and W Vir (P = 17.3 days) were observed with IUE at two phases each.Only low dispersion mid-UV exposures were feasible, but were sufficientto show a great range in Mg II emission behavior. The relationship tophase variation of emission in classical (Pop. I) Cepheids of longperiod is unclear.
| Observational studies of Cepheids. II - BVRI photometry of 112 Cepheids
Over 4000 differentially determined photoelectric BVRI observations andthe resulting light curves are presented for 112 Cepheids accessiblefrom Northern Hemisphere observatories. The internal precision of thesedata is better than + or - 0.01 mag, and the accuracy of transformationto the Johnson BVRI system is nearly as good.
| Kinematics of field Type II Cepheid variables
The spectra of 49 field Type II Cepheids have been assembled andcombined with 14 additional stars with previously published radialvelocities in order to investigate the kinematics and spectralcharacteristics of these stars. Many of the stars have low peculiarvelocities consistent with circular rotation around the galaxy, whilesome are high-velocity stars. Outside the nuclear bulge, the velocitiesare correlated with photometric metallicities in the sense thatmetal-rich stars show a nearly normal, disklike rotation velocity and alow velocity dispersion. This correlation shows that the low-velocity,metal-rich stars have an old-disk origin. Fewer Cepheids are found inthe field than expected relative to clusters, suggesting a differencebetween the populations of the halo field and clusters. The kinematicproperties of Cepheids in the nuclear bulge appear to be different inthat both metal-poor and metal-rich Cepheids have a high velocitydispersion and show little systematic galactic rotation.
| The Classical Cepheid Program JD 2442000 - 2443000
AAVSO Observations of the long period Cepheid variables RW Cas, VX Per,SZ Cas, RW Cam, SV Per, AN Aur, SY Aur, SV Mon, T Mon, ST Pup, ΖGem, RU Cam, SS CMa, X Pup, AQ Pup, RS Pup, W Vir, AL Vir, RX Lib, YOph, RU Sct, Z Sct, SZ Aql, TT Aql, SV Vul, SZ Cyg, X Cyg, TX Cyg, ZLac, and RY Cas have been compiled for the interval JD 2442000 - 2443000(November 13, 1973 - August 9, 1976), and are presented as mean lightcurves, with accompanying comments. Also presented is a list ofcontributing observers and their observational totals.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Дева |
| Прямое восхождение: | 14h11m09.05s |
| Склонение: | -13°18'38.4" |
| Видимая звёздная величина: | 9.676 |
| Собственное движение RA: | -4.8 |
| Собственное движение Dec: | -0.4 |
| B-T magnitude: | 10.296 |
| V-T magnitude: | 9.728 |
Каталоги и обозначения:
|
