Volume 558, October 2013
|Number of page(s)||9|
|Section||Interstellar and circumstellar matter|
|Published online||22 October 2013|
Extended envelopes around Galactic Cepheids
IV. T Monocerotis and X Sagittarii from mid-infrared interferometry with VLTI/MIDI⋆,⋆⋆
1 Universidad de Concepción, Departamento de Astronomía, 160 Casilla, Concepción, Chile
2 European Southern Observatory, Alonso de Córdova 3107, 19001 Casilla, Santiago 19, Chile
3 LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
4 Nice Sophia-Antipolis University, CNRS UMR 6525, Observatoire de la Côte d’Azur, BP 4229, 06304 Nice Cedex 4, France
Received: 10 July 2013
Accepted: 30 August 2013
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 (τ0.55 μm = 0.008), while it appears to be thicker for T Mon (τ0.55 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, f8.6 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.
Key words: techniques: high angular resolution / techniques: interferometric / circumstellar matter / stars: variables: Cepheids
Table 3 is only available in electronic form at http://www.aanda.org
© ESO, 2013
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.