Baade-Wesselink Analysis Research Articles

The effect of metallicity on Cepheid period-luminosity relations from a Baade-Wesselink analysis of Cepheids in the Milky Way and Magellanic Clouds

Context. The extragalactic distance scale builds on the Cepheid period-luminosity (PL) relation. Decades of work have not yet convincingly established the sensitivity of the PL relation to metallicity. This currently prevents a determination of the Hubble constant accurate to 1% from the classical Cepheid-SN Ia method. Aims. In this paper we carry out a strictly differential comparison of the absolute PL relations obeyed by classical Cepheids in the Milky Way (MW), LMC, and SMC galaxies. Taking advantage of the substantial metallicity difference among the Cepheid populations in these three galaxies, we want to establish a possible systematic trend of the PL relation absolute zero point as a function of metallicity, and to determine the size of such an effect in the optical and near-infrared photometric bands. Methods. We used a IRSB Baade-Wesselink-type method to determine individual distances to the Cepheids in our samples in the MW, LMC, and SMC. For our analysis, we used a greatly enhanced sample of Cepheids in the SMC (31 stars) compared to the small sample (5 stars) available in our previous work. We used the distances to determine absolute Cepheid PL relations in the optical and near-infrared bands in each of the three galaxies. Results. Our distance analysis of 31 SMC Cepheids with periods of 4–69 days yields tight PL relations in all studied bands, with slopes consistent with the corresponding LMC and MW relations. Adopting the very accurately determined LMC slopes for the optical and near-infrared bands, we determine the zero point offsets between the corresponding absolute PL relations in the three galaxies. Conclusions. We find that in all bands the metal-poor SMC Cepheids are intrinsically fainter than their more metal-rich counterparts in the LMC and MW. In the K band the metallicity effect is −0.23 ± 0.06 mag dex−1, while in the V, (V − I) Wesenheit index it is slightly stronger, −0.34 ± 0.06 mag dex−1. We find suggestive evidence that the metallicity sensitivity of the PL relation might be nonlinear, being small in the range between solar and LMC Cepheid metallicity, and becoming steeper towards the lower-metallicity regime.

Blazhko modulation in the infrared

We present first direct evidence of modulation in the $K$-band of Blazhko-type RR Lyrae stars that are identified by their secular modulations in the I-band data of OGLE-IV. A method has been developed to decompose the $K$-band light variation into two parts originating from the temperature and the radius changes using synthetic data of atmosphere-model grids. The amplitudes of the temperature and the radius variations derived from the method for non-Blazhko RRab stars are in very good agreement with the results of the Baade-Wesselink analysis of RRab stars in the M3 globular cluster confirming the applicability and correctness of the method. It has been found that the Blazhko modulation is primarily driven by the change in the temperature variation. The radius variation plays a marginal part, moreover it has an opposite sign as if the Blazhko effect was caused by the radii variations. This result reinforces the previous finding based on the Baade-Wesselink analysis of M3 (NGC 5272) RR Lyrae, that significant modulation of the radius variations can only be detected in radial-velocity measurements, which relies on spectral lines that form in the uppermost atmospheric layers. Our result gives the first insight into the energetics and dynamics of the Blazhko phenomenon, hence it puts strong constraints on its possible physical explanations.

ξ1CMa: An Extremely Slowly Rotating Magnetic B0.7 IV Star

AbstractWe present our analysis of 6 years of ESPaDOnS spectropolarimetry of the magnetic β Cep star ξ1CMa (B1 III). This high-precision magnetometry is consistent with a rotational periodProt> 40 yr. Absorption line profiles can be reproduced with a non-rotating model. We constrainR⋆,L⋆, and the stellar age via a Baade-Wesselink analysis. Spindown due to angular momentum loss via the magnetosphere predicts an extremely long rotational period if the magnetic dipoleBd> 6 kG, a strength also inferred by the best-fit sinusoids to the longitudinal magnetic field measurementsBZwhen phased with a 60-yearProt.

Baade-Wesselink distances and the effect of metallicity in classical cepheids

The aim of this paper is to investigate the metallicity dependence of the $PL$-relation in $V$ and $K$ based on a sample of 68 Galactic Cepheids with individual Baade-Wesselink distances (some of the stars also have an HST-based parallax) and individually determined metallicities from high-resolution spectroscopy. Literature values of the $V$-band, $K$-band and radial velocity data have been collected for a sample of 68 classical cepheids that have their metallicity determined in the literature from high-resolution spectroscopy. Based on a $(V-K)$ surface-brightness relation and a projection factor derived in a previous paper, distances have been derived from a Baade-Wesselink analysis. $PL$- and $PLZ$-relations in $V$ and $K$ are derived. The effect of the adopted dependence of the projection factor on period is investigated. The change from a constant $p$-factor to one recently suggested in the literature with a mild dependence on $\log P$ results in a less steep slope by 0.1 unit, which is about the 1-sigma error bar in the slope itself. The observed slope in the $PL$-relation in $V$ in the LMC agrees with both hypotheses. In $K$ the difference between the Galactic and LMC slope is larger and would favour a mild period dependence of the $p$-factor. The dependence on metallicity in $V$ and $K$ is found to be marginal, and independent of the choice of $p$-factor on period. This result is severely limited by the small range in metallicity covered by the Galactic Cepheids.

The effect of metallicity on the Cepheid Period-Luminosity relation from a Baade-Wesselink analysis of Cepheids in the Galaxy and in the Small Magellanic Cloud

(ABRIDGED) We have applied the near-IR Barnes-Evans realization of the Baade-Wesselink method as calibrated by Fouque & Gieren (1997) to five metal-poor Cepheids with periods between 13 and 17 days in the Small Magellanic Cloud as well as to a sample of 34 Galactic Cepheids to determine the effect of metallicity on the period-luminosity (P-L) relation. For ten of the Galactic Cepheids we present new accurate and well sampled radial-velocity curves. The Baade-Wesselink analysis provides accurate individual distances and luminosities to the Cepheids in the two samples, allowing us to constrain directly, in a purely differential way, the metallicity effect on the Cepheid P-L relation. For the Galactic Cepheids we provide a new set of P-L relations which have zero-points in excellent agreement with astrometric and interferometric determinations. These relations can be used directly for the determination of distances to solar-metallicity samples of Cepheids in distant galaxies, circumventing any corrections for metallicity effects on the zero-point and slope of the P-L relation. We find evidence for both such metallicity effects in our data. Comparing our two samples of Cepheids at a mean period of about 15 days, we find a weak effect of metallicity on the luminosity similar to that adopted by the HST Key Project on the Extragalactic Distance Scale.

BVRIJKlight curves and radial velocity curves for selected Magellanic Cloud Cepheids $\!^{,}\!$

We present high-precision and well sampled BVRIJK light curves and radial velocity curves for a sample of five Cepheids in the SMC. In addition we present radial velocity curves for three Cepheids in the LMC. The low-metallicity ([Fe/H] ~ -0.7) SMC stars have been selected for use in a Baade-Wesselink type analysis to constrain the metallicity effect on the Cepheid Period-Luminosity relation. The stars have periods of around 15 days so they are similar to the Cepheids observed by the Extragalactic Distance Scale Key Project on the Hubble Space Telescope. We show that the stars are representative of the SMC Cepheid population at that period and thus will provide a good sample for the proposed analysis. The actual Baade-Wesselink analysis is presented in a companion paper. Based on data acquired at the Las Campanas Observatory, Chile, the Cerro Tololo Inter American Observatory, Chile, and the European Southern Observatory, Chile. Tables 10-27 are only available in electronic form 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/415/521

The MACHO Project Large Magellanic Cloud Variable-Star Inventory. XIII. Fourier Parameters for the First-Overtone RR Lyrae Variables and the LMC Distance

Shapes of RR Lyrae light curves can be described in terms of Fourier coefficients that past research has linked with physical characteristics such as luminosity, mass, and temperature. Fourier coefficients have been derived for the V and R light curves of 785 overtone RR Lyrae variables in 16 MACHO fields near the bar of the LMC. In general, the Fourier phase differences 21, 31, and 41 increase and the amplitude ratio R21 decreases with increasing period. The coefficients for both the V and R magnitudes follow these patterns, but the phase differences for the R curves are on average slightly greater, and their amplitudes are about 20% smaller, than the ones for the V curves. The 31 and R21 coefficients have been compared with those of the first-overtone RR Lyrae variables in the Galactic globular clusters NGC 6441, M107, M5, M3, M2, ω Centauri, and M68. The results indicate that many of the LMC variables have properties similar to the ones in M2, M3, M5, and the Oosterhoff type I variables in ω Cen, but they are different from the Oosterhoff type II variables in ω Cen. Equations derived from hydrodynamic pulsation models have been used to calculate the luminosity and temperature for the 330 bona fide first-overtone variables. The results indicate that they have log L in the range 1.6–1.8 L⊙ and log Teff between 3.85 and 3.87. Based on these temperatures, a mean color excess E(V-R) = 0.08 mag, equivalent to E(B-V) = 0.14 mag, has been estimated for these 330 stars. The 80 M5-like variables (selected according to their location in the 31–log P plot) are used to determine an LMC distance. After correcting for the effects of extinction and crowding, a mean apparent magnitude V0 = 18.99 ± 0.02 (statistical) ±0.16 (systematic) has been estimated for these 80 stars. Combining this with a mean absolute magnitude MV = 0.56 ± 0.06 for M5-like stars derived from Baade-Wesselink analyses, main-sequence fitting, Fourier parameters, and the trigonometric parallax of RR Lyrae, we derive an LMC distance modulus μ = 18.43 ± 0.06 (statistical) ±0.16 (systematic) mag. The large systematic error arises from the difficulties of correcting for interstellar extinction and for crowding.

Consistent distances from Baade-Wesselink analyses of Cepheids and RR Lyraes

By using the same algorithm in the Baade-Wesselink analyses of Galactic RR Lyrae and Cepheid variables, it is shown that, within 0.03 mag (1 sigma) statistical error, they yield the same distance modulus for the Large Magellanic Cloud. By fixing the zero point of the color-temperature calibration to those of the current infrared flux methods and using updated period-luminosity-color relations, we get an average value of 18.55 for the true distance modulus of the LMC.

The distance to Galactic globular clusters through RR Lyrae pulsational properties

By adopting the same approach outlined in De Santis & Cassisi (1999), we evaluate the absolute bolometric magnitude of the Zero Age Horizontal Branch (ZAHB) at the level of the RR Lyrae variable instability strip in selected galactic globular clusters. This allows us to estimate the ZAHB absolute visual magnitude for these clusters and to investigate its dependence on the cluster metallicity. The derived $M_V(ZAHB) - [Fe/H]$ relation, corrected in order to account for the luminosity difference between the ZAHB and the mean RR Lyrae magnitude, has been compared with some of the most recent empirical determinations in this field, as the one provided by Baade-Wesselink analyses, RR Lyrae periods, Hipparcos data for field variables and Main Sequence fitting based on Hipparcos parallaxes for field subdwarfs. As a result, our relation provides a clear support to the long distance scale. We discuss also another method for measuring the distance to galactic globular clusters. This method is quite similar to the one adopted for estimating the absolute bolometric magnitude of the ZAHB but it relies only on the pulsational properties of the Lyrae variables in each cluster. The reliability and accuracy of this method has been tested by applying it to a sample of globulars for which, due to the morphology of their horizontal branch (HB), the use of the commonly adopted ZAHB fitting is a risky procedure.

A photometric and spectroscopic study of the brightest northern Cepheids -- III. A high-resolution view of Cepheid atmospheres

We present new high-resolution (R=40000) spectroscopic observations of 18 bright northern Cepheids carried out at David Dunlap Observatory, in 1997. The measurements mainly extend those of presented in Paper I adding three more stars (AW Per, SV Vul, T Mon). The spectra were obtained in the interval of 5900 A and 6660 A. New radial velocities determined with the cross-correlation technique and the bisector technique are presented. We found systematic differences between the spectroscopic and CORAVEL-type measurements as large as 1-3 km/s in certain phases. We performed Baade-Wesselink analysis for CK Cam discovered by the Hipparcos satellite. The resulting radius is 31+/-1 Ro, which is in very good agreement with recent period-radius relation by Gieren et al. (1999). Observational pieces of evidence of possible velocity gradient affecting the individual line profiles are studied. The FWHM of the metallic lines, similarly to the velocity differences, shows a very characteristic phase dependence, illustrating the effect of global compression in the atmosphere. The smallest line widths always occur around the maximal radius, while the largest FWHM is associated with the velocity reversal before the minimal radius. Three first overtone pulsators do not follow the general trend: the largest FWHM in SU Cas and SZ Tau occurs after the smallest radius, during the expansion, while in V1334 Cyg there are only barely visible FWHM-variations. The possibility of a bright yellow companion of V1334 Cyg is briefly discussed. The observed line profile asymmetries can be partly associated with the velocity gradient, which is also supported by the differences between individual line velocities of different excitation potentials.

Analyses of the Short-Period Cepheid SU Cassiopeiae

Baade-Wesselink analyses of this important Galactic classical Cepheid provide new values for the radius, luminosity, distance, and mass and show SU Cas likely to be pulsating in the first overtone. Application of a modified Baade-Wesselink technique and the maximum likelihood method, which we have previously applied to δ Scuti–type variables, yield values of = 33.0 ± 1.1 R⊙, L = 1536 ± 291 L⊙, = -3.28, r = 486 ± 52 pc, mass (from the Baade-Wesselink radius), M = 6.5 ± 0.6 M⊙ (assuming first-overtone pulsation), and evolutionary mass, Mev = 5.5 ± 0.3 M⊙. The results are consistent with the Hipparcos satellite parallax, 2.31 ± 0.58 mas (433 pc), providing further support for overtone pulsation of SU Cas. In the course of the analyses, a modification to the maximum likelihood method, devised by one of us (W. J. F. W.), is presented as an alternative to the modifications of Laney & Stobie and Coulson, Caldwell, & Gieren.

The Red Horizontal-Branch Star HD 17072

We summarize the results of a spectroscopic analysis of HD 17072, finding it to be a metal-poor ([Fe/H] = -1.17) red horizontal-branch star with Teff = 5375 K and log g = 2.4. We also derive a radial velocity of 62.8 km s-1. It has the best determined Hipparcos trigonometric parallax among the metal-poor field horizontal-branch stars and supports the fainter luminosities for such stars found from statistical parallax and Baade-Wesselink analyses, in contradiction to the results of main-sequence fitting of metal-poor field dwarfs to globular cluster main sequences.

Ages of Globular Clusters fromHIPPARCOSParallaxes of Local Subdwarfs

We report here initial but strongly conclusive results for absolute ages of Galactic globular clusters (GGCs). This study is based on high-precision trigonometric parallaxes from the HIPPARCOS satellite coupled with accurate metal abundances ([Fe/H], [O/Fe], and [α/Fe]) from high-resolution spectroscopy for a sample of about thirty subdwarfs. Systematic effects due to star selection (Lutz-Kelker corrections to parallaxes) and the possible presence of undetected binaries in the sample of bona fide single stars are examined, and appropriate corrections are estimated. They are found to be small for our sample. The new data allow us to reliably define the absolute location of the main sequence (MS) as a function of metallicity. These results are then used to derive distances and ages for a carefully selected sample of nine globular clusters having metallicities determined from high-dispersion spectra of individual giants according to a procedure totally consistent with that used for the field subdwarfs. Very precise and homogeneous reddening values have also been independently determined for these clusters. Random errors for our distance moduli are ±0.08 mag, and systematic errors are likely of the same order of magnitude. These very accurate distances allow us to derive ages with internal errors of ~12% (±1.5 Gyr). The main results are: 1. HIPPARCOS parallaxes are smaller than corresponding ground-based measurements, leading, in turn, to longer distance moduli (~0.2 mag) and younger ages (~2.8 Gyr). 2. The distance to NGC 6752 derived from our MS fitting is consistent with that determined using the white dwarf cooling sequence. 3. The relation between the zero-age HB (ZAHB) absolute magnitude and metallicity for the nine program clusters is This relation is fairly consistent with some of the most recent theoretical models. Within quoted errors, the slope is in agreement with that given by the Baade-Wesselink (BW) analysis of RR Lyrae stars by Fernley and Clementini et al., while it is somewhat shallower than the relation given by Sandage. The zero-point is 0.2 to 0.3 mag brighter than that obtained with BW, while it agrees fairly well with that given by Sandage. A comparison with alternative relationships is briefly discussed. 4. The corresponding LMC distance modulus is (m - M)0 = 18.60 ± 0.07, in good agreement with the recent values of 18.70 ± 0.10 and 18.54 ± 0.2 derived by Feast & Catchpole and van Leeuwen et al., respectively, from HIPPARCOS parallaxes of Galactic Cepheid and Mira variables. 5. The age of the bona fide old globular clusters (Oosterhoff II and BHB), based on the absolute magnitude of the turnoff (a theoretically robust indicator) is where the error bar is the 95% confidence range. The rms scatter of individual ages around the mean value is ~10%, in agreement with expectations from observational errors alone (that is, we do not find it necessary to introduce a real age scatter among these clusters). A reliable study of the relative ages requires the use of age indicators better suited to this purpose and data for a larger sample of GGCs. 6. Allowing for a minimum delay of 0.5 Gyr from the birth of the universe until the formation of globular clusters, our age estimate is compatible with an Einstein-de Sitter model if H0 ≤ 64 km s-1 Mpc-1, or H0 ≤ 83 km s-1 Mpc-1 in a flat universe with Ωm = 0.2. Since these upper limits are well within the confidence range of most determinations of H0, we conclude that the present age of globular clusters does not conflict with standard inflationary models of the universe.

Baade-Wesselink Analysis of a Sample of Equal Period SMC Cepheids A progress report

AbstractWe present a progress report on a project to investigate the differences in absolute physical parameters for a sample of five equal period SMC Cepheids from a Baade-Wesselink analysis of the stars.

A pulsational approach to the luminosity of RR Lyrae variables

view Abstract Citations (13) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Pulsational Approach to the Luminosity of RR Lyrae Variables Castellani, V. ; de Santis, R. Abstract We show that the temperature scale of Butler, Dickens, & Epps (1978) for RR Lyrae pulsators appears tightly correlated with the two pulsational parameters, amplitude and period of the pulsation. Application of these 'pulsational' temperatures to the well-studied Galactic globular clusters M3 and M15 gives for these clusters a reddening E(B - V) = 0.01 and 0.08, respectively. Moreover, we show that pulsational parameters should give rather severe constraints on the visual magnitude of the pulsators. Calibration of a similar relation to pulsator magnitudes as given by Baade-Wesselink (BW) analyses supports this suggestion, though producing Mnu values in systematic disagreement with current evolutionary computations. We discuss the problem, showing that BW results can be reconciled with the current evolutionary scenario only assuming a value of the original He as low as Y = 0.19 plus a systematic error in the temperature scale. Conversely, one may save the evolutionary scenario with Y = 0.23 by assuming a systematic error in BW magnitudes. Publication: The Astrophysical Journal Pub Date: August 1994 DOI: 10.1086/174436 Bibcode: 1994ApJ...430..624C Keywords: Abundance; Galactic Clusters; Stellar Evolution; Stellar Luminosity; Stellar Temperature; Variable Stars; Astronomical Models; Cosmology; Stellar Oscillations; Astrophysics full text sources ADS | data products SIMBAD (6)

STUDIES OF LARGE-AMPLITUDE DELTA SCUTI VARIABLES. I. A CASE STUDY OF EH LIBRAE: ERRATUM

This is the first of a short series of papers on large-amplitude delta Scuti variables. The determination of Baade-Wesselink radii and luminosities for pulsating stars is a long-standing and highly desired goal since such quantiites provide necessary ingredients to produce standard candles. In a modest contribution towards attaining this continuing goal, we are determining the radii and luminosities of a selection of the large-amplitude delta Scuti stars. Optical and infrared photometry and cross-correlated radial velocity data have been obtained for the large-amplitude delta Scuti stars DY Herculis, EH Librae, and DY Pegasi. Fourier representations for B, V, I and J light curves and for the radial velocity curves were used in Baade-Wesselink analysis to derive minimum radii over the pulsation cycles. The resulting radii and their errors, mean bolometric luminosity and mean absolute bolomentric magnitudes will be discussed here and in the papers to follow. The Baade-Wesselink analysis yielded Rmin = 2.54 Rsun ± 0.35 Rsun, for EH Librae with a radius excursion of 0.098 Rsun. When combined with Joner's (1986) effective temperature, we found a mean bolometric luminosity of 22.2 Lsun and a mean absolute bolometric magnitude of 1.38.

STUDIES OF LARGE AMPLITUDE DELTA SCUTI VARIABLES: I. A CASE STUDY OF EH LIBRAE

ABSTRACT This is the first of a short series of papers on large-amplitude delta Scuti variables. The determination of Baade-Wesselink radii and luminosities for pulsating stars is a long-standing and highly desired goal since such quantiites provide necessary ingredients to produce standard candles. In a modest contribution towards attaining this continuing goal, we are determining the radii and luminosities of a selection of the large-amplitude delta Scuti stars. Optical and infrared photometry and cross-correlated radial velocity data have been obtained for the large-amplitude delta Scuti stars DY Herculis, EH Librae, and DY Pegasi. Fourier representations for B, V, I and J light curves and for the radial velocity curves were used in Baade-Wesselink analysis to derive minimum radii over the pulsation cycles. The resulting radii and their errors, mean bolometric luminosity and mean absolute bolomentric magnitudes will be discussed here and in the papers to follow. The Baade-Wesselink analysis yielded Rmin = 2.54 Rsun ± 0.35 Rsun, for EH Librae with a radius excursion of 0.098 Rsun. When combined with Joner's (1986) effective temperature, we found a mean bolometric luminosity of 22.2 Lsun and a mean absolute bolometric magnitude of 1.38.

BV PHOTOMETRY OF V9, THE ONLY RR LYRAE VARIABLE IN THE GLOBULAR CLUSTER 47 TUCANAE

ABSTRACT BV CCD photometry for the RR Lyrae variable V9 (Hv 810) in the globular cluster 47 Tuc is presented. Radial-velocity measurements indicate V9 is acluster member while two other candidates, V12 (HV 814) UX Tuc (HV 809) are not. A color-magnitude diagram is constructed from a subset of the 300 short-exposure CCD frames, showing V9 is unusually bright and hot relative to the red horizontal branch, and has an abonormally long pulsation period for its amplitude, both of which indicate it is highly evolved. There is also a suggestion of a "spike" in the light curve near phi~0.08, which could be caused by the emergence of the echo of the prior minimum-radius pressure wave bouncing off the helium core. The photometry will be utilized in a subsequent Baade-Wesselink analysis.

Studies of Large-Amplitude δ Scuti Variables

The determination of Baade-Wesselink radii and luminosities for pulsating stars are long-standing and highly desired goals since they provide the promise of being standard candles. In a modest contribution towards these goals, we have undertaken a programme to determine the radii and luminosities of the large-amplitude δ Scuti stars DY Herculis, EH Librae and DY Pegasi from optical and infrared photometry and cross-correlated radial velocity data. We use Fourier representations for V, I and J light curves and for the radial velocity curves in Baade-Wesselink analyses to derive minimum radii over the pulsation cycles. These radii and their errors and the mean bolometric luminosities and absolute magnitudes will be discussed here and in papers to follow. As a check, we also apply our method to the data and results of other groups.

The Infrared Period - 2.2/µm Magnitude Relation for RR Lyrae Stars

AbstractThe observational and theoretical basis for the log P vs. K-mag relation is reviewed. The observed gradient in all well observed globular clusters agrees well with the theoretical prediction. An indistinguishable result is found for field RR Lyrae stars whose absolute magnitudes have been determined from infrared Baade-Wesselink analyses. A full reference list is given for the source of these magnitudes. Application of the results to find the distance to globular clusters and the Galactic Centre is discussed.