Period-colour and amplitude-colour relations in classical Cepheid variables - IV. The multiphase relations
The superb phase resolution and quality of the Optical GravitationalLensing Experiment (OGLE) data on the Large Magellanic Cloud (LMC) andSmall Magellanic Cloud (SMC) Cepheids, together with existing data onGalactic Cepheids, are combined to study the period-colour (PC) andamplitude-colour (AC) relations as a function of pulsation phase. Ourresults confirm earlier work that the LMC PC relation (at mean light) ismore consistent with two lines of differing slopes, separated at aperiod of 10 d. However, our multiphase PC relations reveal much newstructure which can potentially increase our understanding of Cepheidvariables. These multiphase PC relations provide insight into why theGalactic PC relation is linear but the LMC PC relation is non-linear.This is because the LMC PC relation is shallower for short (logP < 1)and steeper for long (logP > 1) period Cepheids than thecorresponding Galactic PC relation. Both of the short- and long-periodCepheids in all three galaxies exhibit the steepest and shallowestslopes at phases around 0.75-0.85, respectively. A consequence is thatthe PC relation at phase ~ 0.8 is highly non-linear. Further, theGalactic and LMC Cepheids with logP > 1 display a flat slope in thePC plane at phases close to the maximum light. When the LMCperiod-luminosity (PL) relation is studied as a function of phase, weconfirm that it changes with the PC relation. The LMC PL relation in Vand I band near the phase of 0.8 provides compelling evidence that thisrelation is also consistent with two lines of differing slopes joined ata period close to 10 d.
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Mean Angular Diameters and Angular Diameter Amplitudes of Bright Cepheids
We predict mean angular diameters and amplitudes of angular diametervariations for all monoperiodic PopulationI Cepheids brighter than=8.0 mag. The catalog is intended to aid selecting mostpromising Cepheid targets for future interferometric observations.
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New Period-Luminosity and Period-Color relations of classical Cepheids: I. Cepheids in the Galaxy
321 Galactic fundamental-mode Cepheids with good B, V, and (in mostcases) I photometry by Berdnikov et al. (\cite{Berdnikov:etal:00}) andwith homogenized color excesses E(B-V) based on Fernie et al.(\cite{Fernie:etal:95}) are used to determine their period-color (P-C)relation in the range 0.4~ 1.4). The latter effect is enhanced by asuggestive break of the P-L relation of LMC and SMC at log P = 1.0towards still shallower values as shown in a forthcoming paper.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/423
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Photoelectric Observations of Southern Cepheids in 2001
A total of 2097 photometric observations in the BVIc systemare presented for 117 Cepheids located in the southern hemisphere. Themain purpose of the photometry is to provide new epochs of maximumbrightness for studying Cepheid period changes, as well as to establishcurrent light elements for the Cepheids.
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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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Galactic Cepheids. Catalogue of light-curve parameters and distances
We report a new version of the catalogue of distances and light-curveparameters for Galactic classical Cepheids. The catalogue listsamplitudes, magnitudes at maximum light, and intensity means for 455stars in BVRI filters of the Johnson system and (RI)_C filters of theCron-Cousins system. The distances are based on our new multicolour setof PL relations and on our Cepheid-based solution for interstellarextinction law parameters and are referred to an LMC distance modulus of18.25. The catalogue is only available in electronic form at the CDS viaanonymous ftp (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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Multi-colour PL-relations of Cepheids in the bt HIPPARCOS catalogue and the distance to the LMC
We analyse a sample of 236 Cepheids from the hipparcos catalog, usingthe method of ``reduced parallaxes'' in V, I, K and the reddening-free``Wesenheit-index''. We compare our sample to those considered by Feast& Catchpole (1997) and Lanoix et al. (1999), and argue that oursample is the most carefully selected one with respect to completeness,the flagging of overtone pulsators, and the removal of Cepheids that mayinfluence the analyses for various reasons (double-mode Cepheids,unreliable hipparcos solutions, possible contaminated photometry due tobinary companions). From numerical simulations, and confirmed by theobserved parallax distribution, we derive a (vertical) scale height ofCepheids of 70 pc, as expected for a population of 3-10 Msunstars. This has consequences for Malmquist- and Lutz-Kelker (Lutz &Kelker 1973, Oudmaijer et al. 1998) type corrections which are smallerfor a disk population than for a spherical population. The V and I datasuggest that the slope of the Galactic PL-relations may be shallowerthan that observed for LMC Cepheids, either for the whole period range,or that there is a break at short periods (near log P_0 ~ 0.7-0.8). Westress the importance of two systematic effects which influence thedistance to the LMC: the slopes of the Galactic PL-relations andmetallicity corrections. In order to assess the influence of thesevarious effects, we present 27 distance moduli (DM) to the LMC. Theseare based on three different colours (V,I,K), three different slopes(the slope observed for Cepheids in the LMC, a shallower slope predictedfrom one set of theoretical models, and a steeper slope as derived forGalactic Cepheids from the surface-brightness technique), and threedifferent metallicity corrections (no correction as predicted by one setof theoretical models, one implying larger DM as predicted by anotherset of theoretical models, and one implying shorter DM based onempirical evidence). We derive DM between 18.45 +/- 0.18 and 18.86 +/-0.12. The DM based on K are shorter than those based on V and I andrange from 18.45 +/- 0.18 to 18.62 +/- 0.19, but the DM in K could besystematically too low by about 0.1 magnitude because of a bias due tothe fact that NIR photometry is available only for a limited number ofstars. From the Wesenheit-index we derive a DM of 18.60 +/- 0.11,assuming the observed slope of LMC Cepheids and no metallicitycorrection, for want of more information. The DM to the LMC based on theparallax data can be summarised as follows. Based on the PL-relation inV and I, and the Wesenheit-index, the DM is 18.60 ± 0.11(± 0.08 slope)(^{+0.08}_{-0.15} ;metallicity), which is ourcurrent best estimate. Based on the PL-relation in K the DM is ;;;;18.52 +/- 0.18 (± 0.03 ;slope) (± 0.06 ;metallicity)(^{+0.10}_{-0} ;sampling ;bias). The random error is mostly due to thegiven accuracy of the hipparcos parallaxes and the number of Cepheids inthe respective samples. The terms between parentheses indicate thepossible systematic uncertainties due to the slope of the GalacticPL-relations, the metallicity corrections, and in the K-band, due to thelimited number of stars. Recent work by Sandage et al. (1999) indicatesthat the effect of metallicity towards shorter distances may be smallerin V and I than indicated here. From this, we point out the importanceof obtaining NIR photometry for more (closeby) Cepheids, as for themoment NIR photometry is only available for 27% of the total sample.This would eliminate the possible bias due to the limited number ofstars, and would reduce the random error estimate from 0.18 to about0.10 mag. Furthermore, the sensitivity of the DM to reddening,metallicity correction and slope are smallest in the K-band. Based ondata from the ESA HP astrometry satellite.
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Direct calibration of the Cepheid period-luminosity relation
After the first release of Hipparcos data, Feast & Catchpole gave anew value for the zero-point of the visual Cepheid period-luminosityrelation, based on trigonometric parallaxes. Because of the largeuncertainties on these parallaxes, the way in which individualmeasurements are weighted is of crucial importance. We thereforeconclude that the choice of the best weighting system can be aided by aMonte Carlo simulation. On the basis of such a simulation, it is shownthat (i) a cut-off in π or in σ_ππ introduces a strongbias; (ii) the zero-point is more stable when only the brightestCepheids are used; and (iii) the Feast & Catchpole weighting givesthe best zero-point and the lowest dispersion. After correction, theadopted visual period-luminosity relation is=-2.77logP-1.44+/-0.05. Moreover, we extend this study to thephotometric I band (Cousins) and obtain=-3.05logP-1.81+/-0.09.
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I- and JHK-band photometry of classical Cepheids in the HIPPARCOS catalog
By correlating the \cite[Fernie et al. (1995)]{F95} electronic databaseon Cepheids with the ``resolved variable catalog'' of the hipparcosmission and the simbad catalog one finds that there are 280 Cepheids inthe hipparcos catalog. By removing W Vir stars (Type ii Cepheids),double-mode Cepheids, Cepheids with an unreliable solution in thehipparcos catalog, and stars without photometry, it turns out that thereare 248 classical Cepheids left, of which 32 are classified asfirst-overtone pulsators. For these stars the literature was searchedfor I-band and near-infrared data. Intensity-mean I-band photometry onthe Cousins system is derived for 189 stars, and intensity-mean JHK dataon the Carter system is presented for 69 stars.
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A uvbyβ photometric calibration of iron abundances in supergiant stars.
A photometric reddening-free calibration for [Fe/H] valid for giant andsupergiant stars of intermediate temperature, has been obtained usingthe Stroemgren uvbyβ system. Galactic supergiants, supergiants inthe Magellanic Clouds and Galactic metal deficient red giants withspectroscopic determinations of [Fe/H] were used as calibrators. Thecalibration can be used to predict [Fe/H] with an accuracy of 0.33 dex,valid for stars with 0.14<[m_1_]<0.70 in the iron abundance range-2.5<[Fe/H]<+0.3. This shows the potential of supergiant stars astracers of iron abundances in other galaxies. Evidence that Galacticluminous F-G stars are intrinsically bluer than their counterparts inthe Magellanic Clouds is offered.
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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
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Calibrations of Mv, (Fe/H), and log G for yellow supergiant stars from O I 7774 and uvby-beta data
New calibrations of the absolute magnitude Mv from O I 7774data are derived from narrow-band photometry and low dispersionspectroscopy for AO-G2 low and high luminosity stars. The nonlineardependence of Mv from the equivalent width W(OI) and therelevance of the stellar temperature in the calibration are confirmed inagreement with previous calibrations obtained from high resolutionspectroscopy. Also functional formulas to estimate (Fe/H) and log g fromuvby-beta data for FO-G3 supergiants are offered. These calibrationspredict iron abundances and gravities for yellow supergiants withuncertainties not much higher than good spectroscopic determinations.
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The calibration of the Stromgren photometric system for A, F and early G supergiants. I - The observational data
An empirical calibration of the Stromgren uvby-beta photometric systemfor the A, F, and early G supergiants is being derived. This paperexplains the observational program and the photometric reductiontechniques used and presents a catalog of new Stromgren photometry forover 600 A, F, and G supergiants.
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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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Detection of Cepheid variables by the Infrared Astronomical Satellite
Using the IRAS Point-Source Catalog (PSC) as a data base, midand far-IRemission near Cepheids were searched for. Of the more than 700 Cepheidvariables listed in the General Catalogue of Variable Stars, sixty-eightconfirmed detections have been made in the PSC. The vast majority ofCepheids detected are bright, nearby classical Cepheids, whose IR fluxis simply that produced by the stellar photosphere. For those Cepheidsthat show IR excesses, it is speculated that the excesses are caused bythermal emission from dust formed by mass loss. The results arediscussed in the framework of simple mass-loss models for stars withmasses comparable to Cepheid variables.
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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.
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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.
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Cepheids and nonvariable supergiants
Photometric parameters for Cepheids in a previous paper are adapted foruse with nonvariable supergiants of similar temperature. The closecorrelation between the abundance and luminosity parameters forclassical, short-period Cepheids (SPC) confirms the nearlydispersionless luminosity temperature relation for these variables. Theassumptions that (1) the C-type variables are transiting the Cepheidtemperature for the first time, (2) the classical SPC are mostlytransiting for the second time, and (3) the long-period Cepheids (LPC)are a mixture of stars transiting for the first to third or fourth timesare found to be consistent with the various correlations of temperatureand luminosity parameters. The nonvariable supergiants with photometricparameters similar to those for the Cepheids are found to haveluminosities consistent with their spectroscopic luminosity class. Few,if any, nonvariable supergiants have temperatures and luminositiessimilar to the LPC.
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The Catalogue of Distances and Light Absorption for Cepheids
Not Available
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Five-channel photometry of cepheids and supergiants in the southern Milky Way.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976A&AS...24..413P&db_key=AST
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O stars and supergiants south of declination -53 0.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976AJ.....81..116H&db_key=AST
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Mitteilungen uber Veraenderliche der Bamberger Liste.
Not Available
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Discovery and study of bright variable stars.
Not Available
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Period-Control of the Cepheids V737 Cen and AX Cir
Not Available
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First Results from the Bamberg South-African Station
Not Available
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