A Generalization of the Cors Method to Determine Cepheid Radii: Theory and Application

Caccin, B.; Buonaura, B.; Onnembo, A.; Russo, G.; Sambuco, A. M.; Sollazzo, C.

doi:10.1017/s0252921100109030

Cited by 14 publications

(26 citation statements)

References 3 publications

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“…The original CORS method (Caccin et al 1981) is a variant of the classical Baade–Wesselink technique (Wesselink 1946) and was developed to derive the radii of pulsating stars. It relies on the surface brightness function: where m V is the apparent visual magnitude and α is the angular diameter of the star.…”

Section: The Cors Methodsmentioning

confidence: 99%

“…The methods currently used to derive Cepheid radii from photometric and spectroscopic data (radial velocity) are based on the classical Baade–Wesselink technique (Wesselink 1946). Among them, the surface brightness technique (Barnes & Evans 1976) and the CORS method (Caccin et al 1981) rely on solid physical bases. The reader interested in a detailed discussion concerning the different Baade–Wesselink methods is referred to Gautschy (1987).…”

Section: Introductionmentioning

confidence: 99%

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CORS Baade-Wesselink method in the Walraven photometric system: the period-radius and the period-luminosity relation of classical Cepheids

Molinaro¹,

Ripepi²,

Marconi³

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We present a new derivation of the CORS Baade–Wesselink method in the Walraven photometric system. We solved the complete Baade–Wesselink equation by calibrating the surface brightness function with a recent grid of atmosphere models. The new approach was adopted to estimate the mean radii of a sample of Galactic Cepheids for which are available precise light curves in the Walraven bands. Current radii agree, within the errors, quite well with Cepheid radii based on recent optical and near‐infrared interferometric measurements. We also tested the impact of the projection factor on the period–radius relation using two different values (p= 1.36, 1.27) that bracket the estimates available in the literature. We found that the agreement of our period–radius relation with similar empirical and theoretical period–radius relations in the recent literature improves by changing the projection factor from p= 1.36 to 1.27. Our period–radius relation is log R= (0.75 ± 0.03)log P+ (1.10 ± 0.03), with an rms = 0.03 dex. Thanks to accurate estimates of the effective temperature of the selected Cepheids, we also derived the period–luminosity relation in the V band and we found MV= (−2.78 ± 0.11)log P+ (−1.42 ± 0.11) with rms = 0.13 mag, for p= 1.27. It agrees quite well with recent results in the literature, while the relation for p= 1.36 deviates by more than 2σ. We conclude that, even taking into account the intrinsic dispersion of the obtained period–luminosity relations that is roughly of the same order of magnitude as the effect of the projection factor, the results of this paper seem to favour the value p= 1.27.

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Section: The Cors Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

CORS Baade-Wesselink method in the Walraven photometric system: the period-radius and the period-luminosity relation of classical Cepheids

Molinaro¹,

Ripepi²,

Marconi³

et al. 2011

Monthly Notices of the Royal Astronomical Society

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“…The main characteristic in Equation (3) is the estimate of the ΔB term as it contains the surface brightness function. Typically, the ΔB term has a small value (10 −3 to 10 −4 ; Onnembo et al 1985) and in the original Baade-Wesselink method it is neglected (see Caccin et al 1981). However, the Cepheid radii estimated by including the ΔB term (complete CORS method) in Equation (3) …”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…In the present work, we face the problem of the LMC distance by means of the CORS version of the Baade-Wesselink surface brightness technique (Caccin et al 1981;Ripepi et al 1997Ripepi et al , 2000Ruoppo et al 2004;Molinaro et al 2011), using recent photometric and spectroscopic data of a sample of Cepheids observed in the populous cluster NGC 1866. This object is one of the few young (∼10 8 yr; Brocato et al 1989) LMC clusters that are close enough to allow for detailed observation of individual stars (see, e.g., Mucciarelli et al 2011;Brocato et al 2003, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Cors Baade–wesselink Distance to the LMC NGC 1866 Blue Populous Cluster

Molinaro¹,

Ripepi²,

Marconi³

et al. 2012

ApJ

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We used optical, near-infrared photometry, and radial velocity data for a sample of 11 Cepheids belonging to the young LMC blue populous cluster NGC 1866 to estimate their radii and distances on the basis of the CORS Baade-Wesselink method. This technique, based on an accurate calibration of surface brightness as a function of (U − B), (V − K) colors, allows us to estimate, simultaneously, the linear radius and the angular diameter of Cepheid variables, and consequently to derive their distance. A rigorous error estimate on radii and distances was derived by using Monte Carlo simulations. Our analysis gives a distance modulus for NGC 1866 of 18.51 ± 0.03 mag, which is in agreement with several independent results.

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“…Several methods exist to measure distances to individual Galactic Cepheids. These include (a) direct parallax measurements (for example, based on Hipparcos, the Hubble Space Telescope (HST), and Gaia in the future), (b) Baade-Wesselink (BW)-type techniques (which come in several variants, including infrared surface-brightness methods, interferometric measurements of angular diameters, the CORS method of Caccin et al [1981], and others), (c) main-sequence (MS) fitting to open clusters or associations that host Cepheids, and (d) the light-echo technique (RS Pup is currently the only Cepheid with a distance measured using this technique). These methods have only been applied to fewer than ∼ 200 Cepheids, and in some cases more than one method may be applicable to a given Cepheid.…”

Section: Introductionmentioning

confidence: 99%

Wesenheit function for Galactic Cepheids: Application to the projection factors

Ngeow¹,

Neilson²,

Nardetto³

et al. 2012

Proc. IAU

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Abstract. Galactic Cepheids are necessary tools for calibrating the period-luminosity relation, but distances to individual Galactic Cepheids are difficult to measure precisely and their application is limited to a small number of techniques, such as direct parallax measurements, main-sequence fitting to open clusters that host Cepheids, and Baade-Wesselink (BW)-type methods. Here, we re-examine the application of Wesenheit functions in determining distances to more than 300 Galactic Cepheids by taking advantage of the fact that the Wesenheit function is extinction-free by definition. Wesenheit distances are used to calibrate the projection (p) factor for Galactic Cepheids that also have BW distances. Based on ∼70 Cepheids, we find that the period-p-factor relation may exhibit a nonlinear trend with a considerable scatter. We found discrepant p factors for δ Cephei in the literature. This may be due to inconsistent measurements of its angular diameter using different empirical techniques. We discuss the reason for the inconsistency in angular-diameter measurements and offer a possible remedy.

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A Generalization of the Cors Method to Determine Cepheid Radii: Theory and Application

Cited by 14 publications

References 3 publications

CORS Baade-Wesselink method in the Walraven photometric system: the period-radius and the period-luminosity relation of classical Cepheids

CORS Baade-Wesselink method in the Walraven photometric system: the period-radius and the period-luminosity relation of classical Cepheids

Cors Baade–wesselink Distance to the LMC NGC 1866 Blue Populous Cluster

Wesenheit function for Galactic Cepheids: Application to the projection factors

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