Extended envelopes around Galactic Cepheids

I. 𝓁 Carinae from near and mid-infrared interferometry with the VLTI

LESIA, UMR 8109, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France e-mail: Pierre.Kervella@obspm.fr

Received: 9 June 2005
Accepted: 25 October 2005

Abstract

We present the results of long-baseline interferometric observations of the bright southern Cepheid 𝓁 Carinae in the infrared N (m) and K (m) bands, using the MIDI and VINCI instruments of the VLT Interferometer. We resolve in the N band a large circumstellar envelope (CSE) that we model with a Gaussian of (≈ AU) half width at half maximum. The signature of this envelope is also detected in our K band data as a deviation from a single limb darkened disk visibility function. The superimposition of a Gaussian CSE on the limb darkened disk model of the Cepheid star results in a significantly better fit of our VINCI data. The extracted CSE parameters in the K band are a half width at half maximum of , comparable to the N band model, and a total brightness of 4% of the stellar photosphere. A possibility is that this CSE is linked to the relatively large mass loss rate of 𝓁 Car. Though its physical nature cannot be determined from our data, we discuss an analogy with the molecular envelopes of RV Tauri, red supergiants and Miras.