Long‐Baseline Interferometric Observations of Cepheids

Lane, Benjamin F.; Creech‐Eakman, M. J.; Nordgren, Tyler E.

doi:10.1086/340558

Cited by 60 publications

(88 citation statements)

References 37 publications

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“…By rescaling their relation with ours, we found a better agreement. The MW data used by Breitfelder et al (2016) include interferometric angular diameters (Lane et al 2002;Kervella et al 2004b;Gallenne et al 2012;Davis et al 2009) in addition to radial velocities, photometry, and trigonometric parallaxes measured with the Hubble Space Telescope (HST) Fine Guidance Sensor (Benedict et al 2007), and therefore lead to more robust and consistent estimates of the linear radii.…”

Section: Period-radius Relationmentioning

confidence: 99%

Observational calibration of the projection factor of Cepheids

Gallenne

Kervella

Mérand

et al. 2017

A&A

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Context. The Baade-Wesselink (BW) method, which combines linear and angular diameter variations, is the most common method to determine the distances to pulsating stars. However, the projection factor, p-factor, used to convert radial velocities into pulsation velocities, is still poorly calibrated. This parameter is critical on the use of this technique, and often leads to 5-10 % uncertainties on the derived distances. Aims. We focus on empirically measuring the p-factor of a homogeneous sample of 29 LMC and 10 SMC Cepheids for which an accurate average distances were estimated from eclipsing binary systems. Methods. We used the SPIPS algorithm, which is an implementation of the BW technique. Unlike other conventional methods, SPIPS combines all observables, i.e. radial velocities, multi-band photometry and interferometry into a consistent physical modelling to estimate the parameters of the stars. The large number and their redundancy insure its robustness and improves the statistical precision. Results. We successfully estimated the p-factor of several Magellanic Cloud Cepheids. Combined with our previous Galactic results, we find the following P − p relation: −0.08 ±0.04 (log P − 1.18) + 1.24 ±0.02 . We find no evidence of a metallicity dependent p-factor. We also derive a new calibration of the period-radius relation, log R = 0.684 ±0.007 (log P − 0.517) + 1.489 ±0.002 , with an intrinsic dispersion of 0.020. We detect an infrared excess for all stars at 3.6µm and 4.5µm, which might be the signature of circumstellar dust. We measure a mean offset of ∆m 3.6 = 0.057 ± 0.006 mag and ∆m 4.5 = 0.065 ± 0.008 mag. Conclusions. We provide a new P − p relation based on a multi-wavelength fit that can be used for the distance scale calibration from the BW method. The dispersion is due to the LMC and SMC width we took into account because individual Cepheids distances are unknown. The new P − R relation has a small intrinsic dispersion: 4.5 % in radius. This precision will allow us to accurately apply the BW method to nearby galaxies. Finally, the infrared excesses we detect again raise the issue of using mid-IR wavelengths to derive period-luminosity relation and to calibrate the Hubble constant. These IR excesses might be the signature of circumstellar dust, and are never taken into account when applying the BW method at those wavelengths. Our measured offsets may give an average bias of ∼ 2.8 % on the distances derived through mid-IR P − L relations.

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Section: Period-radius Relationmentioning

confidence: 99%

Observational calibration of the projection factor of Cepheids

Gallenne

Kervella

Mérand

et al. 2017

A&A

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“…Storm et al (2011) determined a distance of 255 ± 5 pc using IRSB method, for p = 1.39 (d/p = 183 ± 4 pc). Using a subset of data we used, Lane et al (2002) obtained d = 320 ± 32 pc with p = 1.43 (d/p = 223 ± 22 pc). Our method gives a distance of 296 ± 5 pc (d/p = 228 ± 4 pc), which is not consistent with Storm et al (2011).…”

Section: H_ctio -K_ctiomentioning

confidence: 99%

Cepheid distances from the SpectroPhoto-Interferometry of Pulsating Stars (SPIPS)

Mérand

Kervella

Breitfelder

et al. 2015

A&A

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Context. The parallax of pulsation, and its implementations such as the Baade-Wesselink method and the infrared surface brightness technique, is an elegant method to determine distances of pulsating stars in a quasi-geometrical way. However, these classical implementations in general only use a subset of the available observational data. Aims. Freedman & Madore (2010, ApJ, 719, 335) suggested a more physical approach in the implementation of the parallax of pulsation in order to treat all available data. We present a global and model-based parallax-of-pulsation method that enables including any type of observational data in a consistent model fit, the SpectroPhoto-Interferometric modeling of Pulsating Stars (SPIPS). Methods. We implemented a simple model consisting of a pulsating sphere with a varying effective temperature and a combination of atmospheric model grids to globally fit radial velocities, spectroscopic data, and interferometric angular diameters. We also parametrized (and adjusted) the reddening and the contribution of the circumstellar envelopes in the near-infrared photometric and interferometric measurements. Results. We show the successful application of the method to two stars: δ Cep and η Aql. The agreement of all data fitted by a single model confirms the validity of the method. Derived parameters are compatible with publish values, but with a higher level of confidence. Conclusions. The SPIPS algorithm combines all the available observables (radial velocimetry, interferometry, and photometry) to estimate the physical parameters of the star (ratio distance/p-factor, T eff , presence of infrared excess, color excess, etc). The statistical precision is improved (compared to other methods) thanks to the large number of data taken into account, the accuracy is improved by using consistent physical modeling and the reliability of the derived parameters is strengthened thanks to the redundancy in the data.

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“…Empirical Cepheid radii are generally derived either by means of the Baade Wesselink (BW) method (Moffet & Barnes 1987;Ripepi et al 1997;Gieren et al 1998, just to list a few examples) both in the classical form and in subsequent modified versions, or with interferometric coupled with trigonometric parallaxes techniques (Nordgren et al 2000;Lane et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Improvement of the CORS method for Cepheids radii determination based on Strömgren photometry

Ruoppo

Ripepi

Marconi

et al. 2004

A&A

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Abstract. In this paper we present a modified version of the CORS method based on a new calibration of the Surface Brightness function in the Strömgren photometric system. The method has been tested by means of synthetic light and radial velocity curves derived from nonlinear pulsation models. Detailed simulations have been performed to take into account the quality of real observed curves as well as possible shifts between photometric and radial velocity data. The method has been then applied to a sample of Galactic Cepheids with Strömgren photometry and radial velocity data to derive the radii and a new PR relation. As a result we find log R = (1.19 ± 0.09) + (0.74 ± 0.11) log P (rms = 0.07). The comparison between our result and previous estimates in the literature is satisfactory. Better results are expected from the adoption of improved model atmosphere grids.

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Long‐Baseline Interferometric Observations of Cepheids

Cited by 60 publications

References 37 publications

Observational calibration of the projection factor of Cepheids

Observational calibration of the projection factor of Cepheids

Cepheid distances from the SpectroPhoto-Interferometry of Pulsating Stars (SPIPS)

Improvement of the CORS method for Cepheids radii determination based on Strömgren photometry

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