A SPECTROSCOPIC EXAMINATION OF ACCRETION DIAGNOSTICS FOR NEAR SOLAR MASS STARS IN IC 348
- Department of Astronomy, California Institute of Technology, MS 105-24, Pasadena, CA 91125 (United States)
High-resolution optical and moderate-resolution near-infrared spectra were obtained for 40 near solar mass ({approx}2.0-0.5 M{sub sun}) members of the 2-3 Myr old cluster IC 348 in order to examine established accretion diagnostics and the coupling between inner disk gas and hot, micron-sized dust grains inferred from thermal and mid-infrared excesses. The stellar sample was drawn from the cluster census of Luhman in 2003 with membership being confirmed by radial velocity analysis and the presence of strong Li I {lambda}6708 absorption. Of the stars included in this survey, 12 were classified by Lada in 2006 as hosting primordial, optically thick circumstellar disks, 5 as weak or transition disk systems, and 23 as non-excess stars using the measured slope of the stellar spectral energy distribution (SED) through the four Infrared Array Camera channels (3.6-8.0 {mu}m) of Spitzer Space Telescope. Using the velocity width of H{alpha} as an accretion indicator, we find that 11 primordial disk candidates are suspected accretors, suggesting a strong correlation between gaseous inner disks and optically thick dust emission. Of the five weak or transition disk systems observed, two (L21 and L67) exhibit spectroscopic features indicative of accretion. The presence of gas within the inner disk of these systems, which are free of infrared excess emission shortward of {approx}4.5 {mu}m, may place constraints upon the physical mechanism responsible for inner disk clearing. Mass accretion rates ( M-dot ) were determined for all suspected accretors using continuum excess measurements near {lambda}6500 and established relationships between He I {lambda}5876, H{alpha}, Ca II {lambda}8542, Pa{beta}, and Br{gamma} line fluxes and accretion luminosity. M-dot values were found to range from log M-dot = -8.7 to -7.2 M{sub sun} yr{sup -1}, with a median value of -8.1 M{sub sun} yr{sup -1}. Magnetospheric accretion models of H{alpha}, Pa{beta}, and Br{gamma} emission by Muzerolle et al. and Kurosawa et al. are found to be in relative agreement with observed fluxes and derived M-dot estimates. He I {lambda}10830 with its metastable lower level is confirmed to be a critical indicator of magnetospheric accretion, although deep subcontinuum absorption profiles often associated with its emission are not fully understood. No statistically significant correlation is found between M-dot and the slope of the SED from 3.6 to 8.0 {mu}m or from 8.0 to 24.0 {mu}m; however, the small number of suspected accretors examined does not allow broader conclusions to be drawn.
- OSTI ID:
- 21583040
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 136, Issue 2; Other Information: DOI: 10.1088/0004-6256/136/2/521; ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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