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.
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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.
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Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
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Cepheiden: was wird beobachtet - was nicht ?
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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.
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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.
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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.
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Spectroscopic survey of field Type II Cepheids
A sample of relatively bright, short- and intermediate-period (P=1-10d)Type II Cepheids in the Galactic field have been observedspectroscopically with an intermediate-resolution(lambda/Deltalambda=11000) spectrograph. The wavelength region was6500-6700A, including the Hα line and some photospheric ironlines. The signal-to-noise ratio (S/N) was usually between 50 and 100,depending on weather conditions and the brightness of target stars.Radial velocities were determined by cross-correlating the Cepheidspectra with those of selected IAU velocity standard stars having F-Gspectral types. The internal error of the velocity determination processwas calculated to be about 1 km s^-1. Hα emission and strong linesplitting were observed in BL Her during the expansion phase, but nosimilar phenomenon was detected in any other stars in this programme,except for AU Peg which has an unusual Hα line showing a PCygni-like profile. The velocity curve agrees well with recent CORAVELmeasurements. The velocity gradients in Cepheid atmospheres are studiedusing the Hα minus metallic velocities. Similar data are collectedfrom the literature. It seems that having large velocity differences(v_Hα-v_metal>40 km s^-1) is a characteristic feature of thevery short-period (P<1.5d) and longer period (P>10d) Cepheids.Between these period regions the Cepheid atmospheres exhibit smallervelocity differences. Most of the Type II Cepheids observed in thepresent study fall into this latter category. There might be a tendencyfor classical Cepheids of intermediate period to have larger maximumvelocity differences.
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UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
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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.
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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.
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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.
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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
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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.
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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.
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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.
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Period changes of Cepheid variables. I - Secular period changes
Secular period changes of one hundred northern Cepheids are investigatedwith the help of O-C diagrams. With the classical Cepheids the rate ofobserved period changes is in good agreement with that determined fromstellar evolution theory. The period noise cannot mask the evolutionaryperiod changes especially in longer period Cepheids for which theoccurrence of parabolic O-C graphs is unusually frequent.
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Variable Stars in the Northern Luminous Stars Catalogues
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Photometric abundances of Type II Cepheid variables
Washington-system colors and V magnitudes of 63 Type II Cepheids areused to investigate the distribution of metal abundances in these starsand correlations of their abundances with position in the Galaxy. Only asmall fraction of Cepheids in the field represent a true halopopulation; most have characteristics of a transition population betweenthe halo and the disk. The origin of the metal-rich stars and theirrelation to the metal-rich RR Lyraes is discussed. The abundancedistribution of all Type II Cepheids shows no strong dependence ondistance from the galactic center.
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Photoelectric UBV Photometry of Northern Cepheids, III
New UBV photoelectric observational data on 25 northern Cepheids withperiods longer than 10 days are presented. The period changes and thevariations in the light curve of the observed Cepheids are investigated.Almost half of the programme stars show continuous period change(parabolic O-C curve). Among the Cepheids in binary systems YZ Aur, SVPer and perhaps AN Aur show a period jump and a subsequent rejump to theearlier value of the period. The apparent period changes due to orbitalmotion around the common centre of gravity can be seen in RW Cam, X Cyg,SZ Cyg and T Mon. The orbital period of RW Cam is about 6600 Days. Theonly new case of secular light curve variation is observed in AN Aur.
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The structure of the Cepheid instability strip
The properties of Cepheids in the Galaxy, LMC, and SMC are analyzed tocompare them with theoretical models. The PLC relationships of the LMCand SMC agree with theoretically derived PLC relationships when fittingof data is done by the maximum likelihood method. Differences in the tworelationships can be ascribed to abundance differences. Empirical blueedges in the period-color plane agree with models for log P not greaterthan 1.1, but have significantly steeper slopes at longer periods; theredoes not seem to be any satisfactory explanation of this.
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One More Criterion for Distinguishing Between W Virginis Stars (CW) and Classical Cepheids (Cdelta)
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The frequency of Cepheids with companions: a photoelectric approach.
Abstract image available at:http://adsabs.harvard.edu/abs/1977MNRAS.178..505M
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The light curve parameters of photoelectrically observed galactic Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&AS....4..265S&db_key=AST
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The Phase Shift between the Radius and Temperature Variations in Cepheids
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Investigations on Population II Cepheids.IV. Colours and luminosities
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Investigations on Population II Cepheids. III. Light-curves and two-colour diagrams
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Investigations on Population II Cepheids. II. Epochs and periods
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Investigations on Population II Cepheids. I. New photoelectric observations
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Metal-to-H ratios in the Galaxy as indicated by narrow-band photometry of Cepheids.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..615W&db_key=AST
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INHABITED SKY
