Volume 538, February 2012
|Number of page(s)||16|
|Section||Interstellar and circumstellar matter|
|Published online||27 January 2012|
Thermal infrared properties of classical and type II Cepheids
Diffraction limited 10 μm imaging with VLT/VISIR⋆,⋆⋆
LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris
5 place Jules Janssen,
2 European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Santiago 19, Chile
Received: 20 May 2011
Accepted: 24 November 2011
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.
Key words: circumstellar matter / stars: variables: Cepheids / stars: mass-loss / stars: imaging / infrared: stars
Based on observations made with ESO telescopes at Paranal observatory under program ID 081.D-0165(A).
Table 2 is only available in electronic form at http://www.aanda.org
© ESO, 2012
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