Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra

Laura Ingleby, Nuria Calvet, Gregory Herczeg, Alex Blaty, Frederick Walter, David Ardila, Richard Alexander, Suzan Edwards, Catherine Espaillat, Scott G. Gregory, Lynne Hillenbrand, Alexander Brown

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Abstract

We analyze the accretion properties of 21 low-mass T Tauri stars using a data set of contemporaneous near-UV (NUV) through optical observations obtained with the Hubble Space Telescope Imaging Spectrograph and the ground-based Small and Medium Aperture Research Telescope System, a unique data set because of the nearly simultaneous broad wavelength coverage. Our data set includes accreting T Tauri stars in Taurus, Chamaeleon I, η Chamaeleon, and the TW Hydra Association. For each source we calculate the accretion rate (\dot{M}) by fitting the NUV and optical excesses above the photosphere, produced in the accretion shock, introducing multiple accretion components characterized by a range in energy flux (or density) for the first time. This treatment is motivated by models of the magnetospheric geometry and accretion footprints, which predict that high-density, low filling factor accretion spots coexist with low-density, high filling factor spots. By fitting the UV and optical spectra with multiple accretion components, we can explain excesses which have been observed in the near-IR. Comparing our estimates of \dot{M} to previous estimates, we find some discrepancies; however, they may be accounted for when considering assumptions for the amount of extinction and variability in optical spectra. Therefore, we confirm many previous estimates of the accretion rate. Finally, we measure emission line luminosities from the same spectra used for the \dot{M} estimates, to produce correlations between accretion indicators (Hβ, Ca II K, C II], and Mg II) and accretion properties obtained simultaneously.
Original languageEnglish
Article number112
Number of pages20
JournalAstrophysical Journal
Volume767
Issue number2
DOIs
Publication statusPublished - Apr 2013

Keywords

  • accretion
  • accretion disks – stars
  • chromospheres – stars
  • pre-main sequence – ultraviolet
  • stars

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    Ingleby, L., Calvet, N., Herczeg, G., Blaty, A., Walter, F., Ardila, D., Alexander, R., Edwards, S., Espaillat, C., Gregory, S. G., Hillenbrand, L., & Brown, A. (2013). Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra. Astrophysical Journal, 767(2), [112]. https://doi.org/10.1088/0004-637X/767/2/112