{
  "id": "1309.0854",
  "version": "v1",
  "published": "2013-09-03T22:29:07.000Z",
  "updated": "2013-09-03T22:29:07.000Z",
  "title": "Extended envelopes around Galactic Cepheids IV. T Monocerotis and X Sagittarii from mid-infrared interferometry with VLTI/MIDI",
  "authors": [
    "A. Gallenne",
    "A. Merand",
    "P. Kervella",
    "O. Chesneau",
    "J. Breitfelder",
    "W. Gieren"
  ],
  "comment": "Accepted for publication in Astronomy and Astrophysics",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "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 (tau(0.55microns) = 0.008), while it appears to be thicker for T Mon (tau(0.55micron) = 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(8.6micron)[%]= 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.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2013-09-03T22:29:07.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "galactic cepheids",
      "extended envelopes",
      "mid-infrared interferometry",
      "sagittarii",
      "high spatial resolution observations"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1051/0004-6361/201322257",
      "journal": "Astronomy and Astrophysics",
      "year": 2013,
      "month": "Oct",
      "volume": 558
    },
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1252660,
      "adsabs": "2013A&A...558A.140G"
    }
  }
}