Thermal infrared properties of classical and type II Cepheids

Gallenne, A.; Kervella, P.; Mérand, A.

doi:10.1051/0004-6361/201117307

Cited by 31 publications

(63 citation statements)

References 54 publications

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“…The discovery of the first CSE around the Cepheid Car made use of near-and mid-infrared interferometric observations . Similar detections were subsequently reported for other Cepheids (Mérand et al 2007Barmby et al 2011;Gallenne et al 2011), leading to the hypothesis that maybe all Cepheids are surrounded by a CSE.…”

Section: Introductionsupporting

confidence: 85%

“…It is worth mentioning that the excess is significantly higher for the longer-period Cepheid, T Mon, adding additional evidence about the correlation between the pulsation period and the CSE brightness suspected previously (Gallenne et al 2011;Mérand et al 2007). …”

Section: Visibility and Spectral Energy Distributionmentioning

confidence: 53%

“…5 we make a comparative study to remove the thermal sky background and qualitatively estimate the unbiased IR excess. Gallenne et al (2011) presented a probable correlation between the pulsation period and the CSE relative excess in the VISIR PAH1 filter. From our fitted DUSTY model, we estimated the CSE relative excess by integrating over the PAH1 filter profile.…”

Section: T Monmentioning

confidence: 85%

“…Secondly, their presence might induce a bias to distance determinations made with Baade-Wesselink methods and bias the calibration of the IR period-luminosity (P−L) relation. Our previous works (Gallenne et al 2011;Mérand et al 2007Mérand et al , 2006; Kervella et al 2006) showed that these CSEs have an angular size of a few stellar radii and a flux contribution to the photosphere ranging from a few percent to several tens of percent. While in the near-IR the CSE flux emission might be negligible compared with the Based on observations made with ESO telescopes at Paranal observatory under program ID 082.D-0066 Table 3 is only available in electronic form at http://www.aanda.org photospheric continuum, this is not the case in the mid-and far-IR, where the CSE emission dominates (Gallenne et al 2011;Kervella et al 2009).…”

Section: Introductionmentioning

confidence: 99%

“…Interestingly, a correlation starts to appear between the pulsation period and the CSE brightness in the near-and mid-IR bands: long-period Cepheids seem to show relatively brighter CSEs than short-period Cepheids, indicating that the mass-loss mechanism could be linked to stellar pulsation (Gallenne et al 2011;Mérand et al 2007). Cepheids with long periods have higher masses and larger radii, therefore if we assume that the CSE IR brightness is an indicator of the mass-loss rate, this would mean that heavier stars experience higher mass-loss rates.…”

Section: Introductionmentioning

confidence: 99%

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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: Introductionsupporting

confidence: 85%

Section: Visibility and Spectral Energy Distributionmentioning

confidence: 53%

Section: T Monmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Extended envelopes around Galactic Cepheids

Gallenne

Mérand

Kervella

et al. 2013

A&A

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Cepheid distances from the Baade–Wesselink method

Gieren¹,

Storm²,

Nardetto³

et al. 2012

Proc. IAU

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Recent progress on Baade-Wesselink (BW)-type techniques to determine the distances to classical Cepheids is reviewed. Particular emphasis is placed on the near-infrared surface-brightness (IRSB) version of the BW method. Its most recent calibration is described and shown to be capable of yielding individual Cepheid distances accurate to 6%, including systematic uncertainties. Cepheid distances from the IRSB method are compared to those determined from open cluster zero-age main-sequence fitting for Cepheids located in Galactic open clusters, yielding excellent agreement between the IRSB and cluster Cepheid distance scales. Results for the Cepheid period-luminosity (PL) relation in near-infrared and optical bands based on IRSB distances and the question of the universality of the Cepheid PL relation are discussed. Results from other implementations of the BW method are compared to the IRSB distance scale and possible reasons for discrepancies are identified.

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Circumstellar envelopes of Cepheids: a possible bias affecting the distance scale?

2012

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Circumstellar envelopes (CSEs) have been detected around many Cepheids, first based on long-baseline interferometry, and now also using other observing techniques. These envelopes are particularly interesting for two reasons: their presence could impact the Cepheid distance scale, and they may be valuable tracers of stellar mass loss. Here we focus on their potential impact on the calibration of the Cepheid distance scale. We consider the photometric contribution of the envelopes in the visible, near-, and thermal-infrared domains. We conclude that the impact of CSEs on the apparent luminosities of Cepheids is negligible at visible wavelengths and generally weak (<5%) in the near-infrared (λ ≈ 2 μm). In the thermal-infrared domain (λ ≈ 8 μm), the flux contribution of the CSEs differs depending on the pulsation period: it is relatively weak (<15%) for stars with periods shorter than P ≈ 10 days, but can reach ≈ 30% for long-period Cepheids. We specifically discuss the long-period Galactic Cepheid RS Puppis, which exhibits a very large circumstellar, dusty envelope, and we conclude that this is not a representative case. Overall, the contribution of CSEs to the usual period–luminosity relations (from the visible to the K band) is mostly negligible. They could affect calibrations at longer wavelengths, although the presence of envelopes may have been partially taken into account in the existing empirical calibrations.

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Thermal infrared properties of classical and type II Cepheids

Cited by 31 publications

References 54 publications

Extended envelopes around Galactic Cepheids

Extended envelopes around Galactic Cepheids

Cepheid distances from the Baade–Wesselink method

Circumstellar envelopes of Cepheids: a possible bias affecting the distance scale?

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