Volume 527, March 2011
|Number of page(s)||9|
|Published online||24 January 2011|
Spatially extended emission around the Cepheid RS Puppis in near-infrared hydrogen lines
Adaptive optics imaging with VLT/NACO⋆
European Southern Observatory,
Alonso de Córdova 3107, Casilla
2 LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
Accepted: 21 December 2010
Context. It has been recently discovered that Cepheids harbor circumstellar envelopes (CSEs). RS Pup is the Cepheid that presents the most prominent circumstellar envelope known, the origin of which is not yet understood.
Aims. Our purpose is to estimate the flux contribution of the CSE around RS Pup at the one arcsecond scale (~2000 AU) and to investigate its geometry, especially regarding asymmetries, to constrain its physical properties.
Methods. We obtained near-infrared images in two narrow band filters centered on λ = 1.644 and 2.180 μm (NB_1.64 and IB_2.18, respectively) that comprise two recombination lines of hydrogen: the 12–4 and 7–4 (Brackett γ) transitions, respectively. We used NACO’s cube mode observations in order to improve the angular resolution with the shift-and-add technique, and to qualitatively study the symmetry of the spatially extended emission from the CSE with a statistical study of the speckle noise.
Results. We probably detect at a 2σ level an extended emission with a relative flux (compared with the star in the same filter) of 38 ± 17% in the NB_1.64 filter and 24 ± 11% in the IB_2.18 filter. This emission is centered on RS Pup and does not present any detectable asymmetry. We attribute the detected emission to the likely presence of an hydrogen envelope surrounding the star.
Key words: stars: variables: Cepheids / circumstellar matter / instrumentation: adaptive optics / atmospheric effects
© ESO, 2011
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