Calibration of the Distance Scale from Cepheids

Fouqué, P.; Storm, J.; Gieren, W.

doi:10.1007/978-3-540-39882-0_2

Cited by 55 publications

(73 citation statements)

References 31 publications

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“…The conversion from magnitude to flux takes into account the photometric system and the filter bandpass. During the fitting procedure, all flux densities <3 µm were corrected for interstellar extinction A λ = R λ E(B − V) using the total-to-selective absorption ratios R λ from Fouqué et al (2003) and Hindsley & Bell (1989). The mid-IR data were not corrected for the interstellar extinction, which we assumed to be negligible.…”

Section: Single Dust Shell Modelmentioning

confidence: 99%

Extended envelopes around Galactic Cepheids

Gallenne

Mérand

Kervella

et al. 2013

A&A

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Aims. We study the close environment of nearby Cepheids using high spatial resolution observations in the mid-infrared with the VLTI/MIDI instrument, a two-beam interferometric recombiner. Methods. We obtained spectra and visibilities for the classical Cepheids X Sgr and T Mon. We fitted the MIDI measurements, supplemented by B, V, J, H, K literature photometry, with the numerical transfer code DUSTY to determine the dust shell parameters. We used a typical dust composition for circumstellar environments. Results. We detect an extended dusty environment in the spectra and visibilities for both stars, although T Mon might suffer from thermal background contamination. We attribute this to the presence of a circumstellar envelope (CSE) surrounding the Cepheids. This is optically thin for X Sgr (τ 0.55 µm = 0.008), while it appears to be thicker for T Mon (τ 0.55 µm = 0.15). They are located at about 15−20 stellar radii. Following our previous work, we derived a likely period-excess relation in the VISIR PAH1 filter, f 8.6 µm [%]= 0.81(±0.04)P[day]. We argue that the impact of CSEs on the mid-IR period-luminosity (P−L) relation cannot be negligible because they can bias the Cepheid brightness by up to about 30%. For the K-band P−L relation, the CSE contribution seems to be lower (<5%), but the sample needs to be enlarged to firmly conclude that the impact of the CSEs is negligible in this band.

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Section: Single Dust Shell Modelmentioning

confidence: 99%

Extended envelopes around Galactic Cepheids

Gallenne

Mérand

Kervella

et al. 2013

A&A

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“…All flux densities <3 μm are corrected for interstellar extinction A λ = R λ E(B − V) using both the total-to-selective absorption ratios R λ from Fouqué et al (2003) and Hindsley & Bell (1989), and the color excess E(B − V) from Fouqué et al (2007).…”

Section: Spectral Energy Distribution Of Classical Cepheidsmentioning

confidence: 99%

Thermal infrared properties of classical and type II Cepheids

Gallenne

Kervella

Mérand

2012

A&A

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We present new thermal infrared (IR) photometry and spectral energy distributions (SEDs) of eight classical Cepheids (type I) and three type II Cepheids, using VISIR thermal IR photometric measurements, supplemented with literature data. We used the BURST mode of the instrument to get diffraction-limited images at 8.59, 11.25, and 11.85 μm. The SEDs show a IR excess at wavelengths longer than 10 μm in ten of the eleven stars. We tentatively attribute these excesses to circumstellar emission created by mass loss from the Cepheids. On the basis of some hypotheses for the dust composition, we estimate a total mass of the envelope ranging from 10 −10 to 10 −8 M . We also detect a spatially extended emission around AX Cir, X Sgr, W Sgr, Y Oph, and U Car, while we do not resolve the circumstellar envelope (CSE) of the other stars. The averaged circumstellar envelope brightnesses relative to the stellar photosphere are α(AX Cir) = 13.8 ± 2.5%, α(X Sgr) = 7.9 ± 1.4%, α(W Sgr) = 3.8 ± 0.6%, α(Y Oph) = 15.1 ± 1.4%, and α(U Car) = 16.3 ± 1.4% at 8.59 μm. With this study, we extend the number of classical Cepheids with detected CSEs from 9 to 14, confirming that at least a large fraction of all Cepheids are experiencing significant mass loss. The presence of these CSEs may also impact the future use of Cepheids as standard candles at near and thermal infrared wavelengths.

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“…For fitting the radial velocity data, Mérand et al (2005) applied a four-knot periodic cubic spline interpolation, in contrast to S11 and this work, where a Fourier expansion was used to fit the radial velocity data 5 . Finally, Mérand et al (2005) used all data points during the fitting procedure, while S11 excluded data points with φ > 0.8 due to the deviation of angular diameters at these phases during the fitting (probably caused by shock waves at minimum radius, see also Fouqué et al 2003;Kervella et al 2004). In Table 2, we also include the fitted p-factors if data points for φ > 0.8 are excluded, as in S11.…”

Section: Data Source For θmentioning

confidence: 99%

Calibrating the projection factor for Galactic Cepheids

Ngeow

Neilson

Nardetto

et al. 2012

A&A

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Context. The projection factor (p), which converts the radial velocity to pulsational velocity, is an important parameter in the Baade-Wesselink (BW) type analysis and distance scale work. The p-factor is either adopted as a constant or linearly depending on the logarithmic of pulsating periods. Aims. The aim of this work is to calibrate the p-factor if a Cepheid has both the BW distance and an independent distance measurement, and examine the p-factor for δ Cephei -the prototype of classical Cepheids. Methods. We calibrated the p-factor for several Galactic Cepheids that have both the latest BW distances and independent distances either from Hipparcos parallaxes or main-sequence fitting distances to Cepheid-hosted stellar clusters. Results. Based on 25 Cepheids, the calibrated p-factor relation is consistent with latest p-factor relation in literature. The calibrated p-factor relation also indicates that this relation may not be linear and may exhibit an intrinsic scatter. We also examined the discrepancy of empirical p-factors for δ Cephei, and found that the reasons for this discrepancy include the disagreement of angular diameters, the treatment of radial velocity data, and the phase interval adopted during the fitting procedure. Finally, we investigated the impact of the input p-factor in two BW methodologies for δ Cephei, and found that different p-factors can be adopted in these BW methodologies and yet result in the same angular diameters.

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Calibration of the Distance Scale from Cepheids

Cited by 55 publications

References 31 publications

Extended envelopes around Galactic Cepheids

Extended envelopes around Galactic Cepheids

Thermal infrared properties of classical and type II Cepheids

Calibrating the projection factor for Galactic Cepheids

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