• DOI:10.1088/0004-637X/707/1/632
• Corpus ID: 28966631

The Pulsation of χ Cygni Imaged by Optical Interferometry: A Novel Technique to Derive Distance and Mass of Mira Stars

@article{Lacour2009ThePO,
  title={The Pulsation of $\chi$ Cygni Imaged by Optical Interferometry: A Novel Technique to Derive Distance and Mass of Mira Stars},
  author={Sylvestre Lacour and Eric Thi'ebaut and Guy Perrin and Serge Meimon and X. Haubois and Ettore Pedretti and Stephen T. Ridgway and John D. Monnier and J. P. Berger and Peter A. Schuller and H. Woodruff and A. Poncelet and Herv{\'e} Le Coroller and Rafael Millan-Gabet and Marc G. Lacasse and Wesley A. Traub},
  journal={The Astrophysical Journal},
  year={2009},
  volume={707},
  pages={632-643}
}

• S. Lacour, E. Thi'ebaut, +13 authors W. Traub
• Published 20 October 2009
• Physics
• The Astrophysical Journal

We present infrared interferometric imaging of the S-type Mira star χ Cygni. The object was observed at four different epochs in 2005-2006 with the Infrared-Optical Telescope Array optical interferometer (H band). Images show up to 40% variation in the stellar diameter, as well as significant changes in the limb darkening and stellar inhomogeneities. Model fitting gave precise time-dependent values of the stellar diameter, and reveals presence and displacement of a warm molecular layer. The star radius, corrected for limb darkening, has a mean value of 12.1 mas and shows a 5.1 mas amplitude pulsation. Minimum diameter was observed at phase 0.94 ± 0.01. Maximum temperature was observed several days later at phase 1.02 ± 0.02. We also show that combining the angular acceleration of the molecular layer with CO (Δ_v = 3) radial velocity measurements yields a 5.9 ± 1.5 mas parallax. The constant acceleration of the CO molecules—during 80% of the pulsation cycle—lead us to argument for a free-falling layer. The acceleration is compatible with a gravitational field produced by a 2.1^(+1.5)_(–0.7) solar mass star. This last value is in agreement with fundamental mode pulsator models. We foresee increased development of techniques consisting in combining radial velocity with interferometric angular measurements, ultimately allowing total mapping of the speed, density, and position of the diverse species in pulsation-driven atmospheres.