ACCRETION RATES FOR T TAURI STARS USING NEARLY SIMULTANEOUS ULTRAVIOLET AND OPTICAL SPECTRA

By L. Ingleby, N. Calvet, G. Herczeg, Alexander D Blaty, F. Walter, D. Ardila, Richard Alexander, S. Edwards, Catherine C. Espaillat, S. Gregory and 2 more. 2013

140 citations recorded by the source corpus.

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 () 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 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 estimates, to produce correlations between accretion indicators (Hβ, Ca ii K, C ii], and Mg ii) and accretion properties obtained simultaneously.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/fd6d476bbb9c1e004e8aedce376b1a520d546334

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In Astronomy and Astrophysics

1. S. Andrews
2. D. Wilner
3. G. Herczeg
4. L. Testi
5. A. Natta
6. N. Calvet
7. Jonathan P. Williams
8. L. Hartmann

In Instrumentation

1. S. Andrews
2. D. Wilner
3. A. Hughes
4. L. Testi
5. G. Herczeg
6. A. Natta
7. L. Hillenbrand
8. Jacob B. Simon

Citations in the corpus

• CHIRON—A Fiber Fed Spectrometer for Precise Radial Velocities (2013, background): “To date, four publications that have made use of CHIRON data have appeared in peer-reviewed journals (Tokovinin 2013; Shore et al. 2013; Ingleby et al. 2013; Ratajczak et al. 2013), with additional papers submitted and in preparation.”
• Turbulence in the TW Hya Disk (2018, result): “This accretion limit is also consistent with the measured accretion rate onto the star (2×10−9 M yr−1; Alencar & Batalha 2002; Herczeg et al. 2004; Ingleby et al. 2013).”
• X-Shooter study of accretion in Chamaeleon I (2015, methodology): “…spectrum is obtained only from space telescopes and is then used to derive Ṁacc for relatively small samples of YSOs (e.g., Gullbring et al. 2000; Ingleby et al. 2013), recent instruments mounted on very large telescopes give the community access to large quantity of spectra in the region of…”
• A spectroscopic survey of Herbig Ae/Be stars with X-shooter – I. Stellar parameters and accretion rates (2015, background): “This UV-excess has been measured in both brown dwarfs (Herczeg & Hillenbrand 2008; Herczeg, Cruz & Hillenbrand 2009; Rigliaco et al. 2012) and CTTs (Calvet et al. 2004; Gullbring et al. 2000; Calvet et al. 2004; Ingleby et al. 2013).”
• AN OPTICAL SPECTROSCOPIC STUDY OF T TAURI STARS. I. PHOTOSPHERIC PROPERTIES (2014, methodology): “Veiling Estimates at Ca I 4227 Veiling can be accurately measured from high resolution spectroscopy (e.g. Basri & Batalha 1990; Hartigan et al. 1991) or estimated from low resolution spectrophotometric fitting (e.g. Fischer et al. 2011; Ingleby et al. 2013).”
• Accretion onto Pre-Main-Sequence Stars (2016, methodology): “This difficulty is overcome by invoking the presence of multiple accretion flows with different densities, and therefore different values of the energy flux F (Ingleby et al. 2013), as expected from simulations based on actual magnetic field structures (Section 2.2).”