M STARS IN THE TW HYA ASSOCIATION: STELLAR X-RAYS AND DISK DISSIPATION
- Chester F. Carlson Center for Imaging Science, School of Physics and Astronomy, and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester NY 14623 (United States)
- Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago 8320000 (Chile)
- INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134, Palermo (Italy)
- SETI Institute, 189 Bernardo Avenue, Mountain View, CA 94043, USA, NASA Ames Research Center, Moffett Field, CA 94035 (United States)
- Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States)
To investigate the potential connection between the intense X-ray emission from young low-mass stars and the lifetimes of their circumstellar planet-forming disks, we have compiled the X-ray luminosities (L {sub X}) of M stars in the ∼8 Myr old TW Hya Association (TWA) for which X-ray data are presently available. Our investigation includes analysis of archival Chandra data for the TWA binary systems TWA 8, 9, and 13. Although our study suffers from poor statistics for stars later than M3, we find a trend of decreasing L{sub X}/L{sub bol} with decreasing T {sub eff} for TWA M stars, wherein the earliest-type (M0–M2) stars cluster near log(L{sub X}/L{sub bol})≈−3.0 and then log(L{sub X}/L{sub bol}) decreases, and its distribution broadens, for types M4 and later. The fraction of TWA stars that display evidence for residual primordial disk material also sharply increases in this same (mid-M) spectral type regime. This apparent anticorrelation between the relative X-ray luminosities of low-mass TWA stars and the longevities of their circumstellar disks suggests that primordial disks orbiting early-type M stars in the TWA have dispersed rapidly as a consequence of their persistent large X-ray fluxes. Conversely, the disks orbiting the very lowest-mass pre-MS stars and pre-MS brown dwarfs in the Association may have survived because their X-ray luminosities and, hence, disk photoevaporation rates are very low to begin with, and then further decline relatively early in their pre-MS evolution.
- OSTI ID:
- 22862917
- Journal Information:
- The Astronomical Journal (Online), Vol. 152, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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