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A spectroscopic examination of accretion diagnostics for near solar mass stars in IC 348

Dahm, S. E. (2008) A spectroscopic examination of accretion diagnostics for near solar mass stars in IC 348. Astronomical Journal, 136 (2). pp. 521-547. ISSN 0004-6256.

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High-resolution optical and moderate-resolution near-infrared spectra were obtained for 40 near solar mass (~2.0-0.5 M⊙) 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 λ6708 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 μm) of Spitzer Space Telescope. Using the velocity width of Hα 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 ~4.5 μm, may place constraints upon the physical mechanism responsible for inner disk clearing. Mass accretion rates (M) were determined for all suspected accretors using continuum excess measurements near λ6500 and established relationships between He I λ5876, Hα, Ca II λ8542, Paβ, and Brγ line fluxes and accretion luminosity. M values were found to range from log M to –7.2 M⊙ yr^–1, with a median value of –8.1 M⊙ yr^–1. Magnetospheric accretion models of Hα, Paβ, and Brγ emission by Muzerolle et al. and Kurosawa et al. are found to be in relative agreement with observed fluxes and derived M estimates. He I λ10830 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 and the slope of the SED from 3.6 to 8.0 μm or from 8.0 to 24.0 μm; however, the small number of suspected accretors examined does not allow broader conclusions to be drawn.

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Dahm, S. E.0000-0002-2968-2418
Additional Information:© 2008 The American Astronomical Society. Received 2007 October 31; accepted 2008 April 18; published 2008 June 24. S.E.D. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-0502381. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We have made use of the SIMBAD database operated at CDS, Strasbourg, France, and the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center (IPAC)/California Institute of Technology, funded by NASA and the National Science Foundation. S.E.D. gratefully acknowledges Lynne Hillenbrand for support and helpful discussions as well as Suzan Edwards and Will Fischer for use of several HIRES observations of Taurus members that proved invaluable for this survey. S.E.D. also thanks an anonymous referee whose constructive comments significantly improved this paper. A special debt of gratitude goes out to Tom Barlow who wrote, and Patrick Shopbell who implemented minor patches to, the makee HIRES reduction software package allowing its use for the cross-disperser and echelle angles adopted for this survey.
Funding AgencyGrant Number
NSF Astronomy and Astrophysics Postdoctoral FellowshipAST-0502381
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:accretion, accretion disks; open clusters and associations: individual (IC348); stars: formation; stars: pre-main sequence
Issue or Number:2
Record Number:CaltechAUTHORS:DAHaj08a
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13844
Deposited By: Tony Diaz
Deposited On:06 Apr 2009 22:49
Last Modified:09 Mar 2020 13:18

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