H I OBSERVATIONS OF THE ASYMPTOTIC GIANT BRANCH STAR X HERCULIS: DISCOVERY OF AN EXTENDED CIRCUMSTELLAR WAKE SUPERPOSED ON A COMPACT HIGH-VELOCITY CLOUD
- MIT Haystack Observatory, Off Route 40, Westford, MA 01886 (United States)
- IRAM, 300 Rue de la Piscine, Domaine Universitaire, 38406 Saint Martin d'Heres (France)
- GEPI, UMR 8111, Observatoire de Paris, 5 Place J Janssen, F-92195 Meudon Cedex (France)
- LERMA, UMR 8112, Observatoire de Paris, 61 av. de l'Observatoire, F-75014 Paris (France)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-42, Cambridge, MA 02138 (United States)
We report H I 21 cm line observations of the asymptotic giant branch (AGB) star X Her obtained with the Robert C. Byrd Green Bank Telescope (GBT) and the Very Large Array. We have unambiguously detected H I emission associated with the circumstellar envelope of the star, with a mass totaling M{sub HI} {approx} 2.1 x 10{sup -3} M{sub sun}. The H I distribution exhibits a head-tail morphology, similar to those previously observed around the AGB stars Mira and RS Cnc. The tail is elongated along the direction of the star's space motion, with a total extent of {approx}> 6.'0 (0.24 pc) in the plane of the sky. We also detect a systematic radial velocity gradient of {approx}6.5 km s{sup -1} across the H I envelope. These results are consistent with the H I emission tracing a turbulent wake that arises from the motion of a mass-losing star through the interstellar medium (ISM). GBT mapping of a 2{sup 0} x 2{sup 0} region around X Her reveals that the star lies (in projection) near the periphery of a much larger H I cloud that also exhibits signatures of interaction with the ISM. The properties of the cloud are consistent with those of compact high-velocity clouds. Using {sup 12}CO J = 1-0 observations, we have placed an upper limit on its molecular gas content of N{sub H2} < 1.3 x 10{sup 20} cm{sup -2}. Although the distance to the cloud is poorly constrained, the probability of a chance coincidence in position, velocity, and apparent position angle of space motion between X Her and the cloud is extremely small, suggesting a possible physical association. However, the large H I mass of the cloud ({approx}>2.4 M{sub sun}) and the blueshift of its mean velocity relative to X Her are inconsistent with an origin tied directly to ejection from the star.
- OSTI ID:
- 21583242
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 141, Issue 2; Other Information: DOI: 10.1088/0004-6256/141/2/60; ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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