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Hot Gas Lines in T Tauri Stars Smith ScholarWorks Astronomy: Faculty Publications Astronomy 7-2013 Hot Gas Lines in T Tauri Stars David R. Ardila California Institute of Technology Gregory J. Herczeg Peking University Scott G. Gregory California Institute of Technology Laura Ingleby University of Michigan Kevin France University of Colorado, Boulder See next page for additional authors Follow this and additional works at: https://scholarworks.smith.edu/ast_facpubs Part of the Astrophysics and Astronomy Commons Recommended Citation Ardila, David R.; Herczeg, Gregory J.; Gregory, Scott G.; Ingleby, Laura; France, Kevin; Brown, Alexander; Edwards, Suzan; Johns-Krull, Christopher; Linsky, Jeffrey L.; Yang, Hao; Valenti, Jeff A.; Abgrall, Hervé; Alexander, Richard D.; Bergin, Edwin; Bethell, Thomas; Brown, Joanna M.; Calvet, Nuria; Espaillat, Catherine; Hillenbrand, Lynne A.; Hussain, Gaitee; Roueff, Evelyne; Schindhelm, Eric R.; and Walter, Frederick M., "Hot Gas Lines in T Tauri Stars" (2013). Astronomy: Faculty Publications, Smith College, Northampton, MA. https://scholarworks.smith.edu/ast_facpubs/23 This Article has been accepted for inclusion in Astronomy: Faculty Publications by an authorized administrator of Smith ScholarWorks. For more information, please contact [email protected] Authors David R. Ardila, Gregory J. Herczeg, Scott G. Gregory, Laura Ingleby, Kevin France, Alexander Brown, Suzan Edwards, Christopher Johns-Krull, Jeffrey L. Linsky, Hao Yang, Jeff A. Valenti, Hervé Abgrall, Richard D. Alexander, Edwin Bergin, Thomas Bethell, Joanna M. Brown, Nuria Calvet, Catherine Espaillat, Lynne A. Hillenbrand, Gaitee Hussain, Evelyne Roueff, Eric R. Schindhelm, and Frederick M. Walter This article is available at Smith ScholarWorks: https://scholarworks.smith.edu/ast_facpubs/23 The Astrophysical Journal Supplement Series, 207:1 (43pp), 2013 July doi:10.1088/0067-0049/207/1/1 C 2013. The American Astronomical Society. All rights reserved. Printed in the U.S.A. HOT GAS LINES IN T TAURI STARS David R. Ardila1, Gregory J. Herczeg2, Scott G. Gregory3,4, Laura Ingleby5, Kevin France6, Alexander Brown6, Suzan Edwards7, Christopher Johns-Krull8, Jeffrey L. Linsky9,HaoYang10, Jeff A. Valenti11, Herve´ Abgrall12, Richard D. Alexander13, Edwin Bergin5, Thomas Bethell5, Joanna M. Brown14, Nuria Calvet5, Catherine Espaillat14, Lynne A. Hillenbrand3, Gaitee Hussain15, Evelyne Roueff12, Eric R. Schindhelm16, and Frederick M. Walter17 1 NASA Herschel Science Center, California Institute of Technology, MC 100-22, Pasadena, CA 91125, USA; [email protected] 2 The Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China 3 Cahill Center for Astronomy and Astrophysics, California Institute of Technology, MC 249-17, Pasadena, CA 91125, USA 4 School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, UK 5 Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109, USA 6 Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389, USA 7 Department of Astronomy, Smith College, Northampton, MA 01063, USA 8 Department of Physics and Astronomy, Rice University, Houston, TX 77005, USA 9 JILA, University of Colorado and NIST, 440 UCB Boulder, CO 80309-0440, USA 10 Institute for Astrophysics, Central China Normal University, Wuhan 430079, China 11 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 12 LUTH and UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, Place J. Janssen, F-92195 Meudon, France 13 Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK 14 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 78, Cambridge, MA 02138, USA 15 ESO, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen,¨ Germany 16 Department of Space Studies, Southwest Research Institute, Boulder, CO 80303, USA 17 Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA Received 2012 August 26; accepted 2013 April 11; published 2013 June 10 ABSTRACT For Classical T Tauri Stars (CTTSs), the resonance doublets of N v,Siiv, and C iv,aswellastheHeii 1640 Å line, trace hot gas flows and act as diagnostics of the accretion process. In this paper we assemble a large high-resolution, high-sensitivity data set of these lines in CTTSs and Weak T Tauri Stars (WTTSs). The sample comprises 35 stars: 1 Herbig Ae star, 28 CTTSs, and 6 WTTSs. We find that the C iv,Siiv, and N v lines in CTTSs all have similar shapes. We decompose the C iv and He ii lines into broad and narrow Gaussian components (BC and NC). The most common (50%) C iv line morphology in CTTSs is that of a low-velocity NC together with a redshifted BC. For CTTSs, a strong BC is the result of the accretion process. The contribution fraction of the NC to the C iv line flux in CTTSs increases with accretion rate, from ∼20% to up to ∼80%. The velocity centroids of the BCs and NCs are such that VBC 4 VNC, consistent with the predictions of the accretion shock model, in at most 12 out of 22 CTTSs. We do not find evidence of the post-shock becoming buried in the stellar photosphere due to the pressure of the accretion flow. The He ii CTTSs lines are generally symmetric and narrow, with FWHM and redshifts comparable to those of WTTSs. They are less redshifted than the CTTSs C iv lines, by ∼10 km s−1. The amount of flux in the BC of the He ii line is small compared to that of the C iv line, and we show that this is consistent with models of the pre-shock column emission. Overall, the observations are consistent with the presence of multiple accretion columns with different densities or with accretion models that predict a slow-moving, low-density region in the periphery of the accretion column. For HN Tau A and RW Aur A, most of the C iv line is blueshifted suggesting that the C iv emission is produced by shocks within outflow jets. In our sample, the Herbig Ae star DX Cha is the only object for which we find a P-Cygni profile in the C iv line, which argues for the presence of a hot (105 K) wind. For the overall sample, the Si iv and N v line luminosities are correlated with the C iv line luminosities, although the relationship between Si iv and C iv shows large scatter about a linear relationship and suggests that TW Hya, V4046 Sgr, AA Tau, DF Tau, GM Aur, and V1190 Sco are silicon-poor, while CV Cha, DX Cha, RU Lup, and RW Aur may be silicon-rich. Key words: protoplanetary disks – stars: pre-main sequence – stars: variables: T Tauri, Herbig Ae/Be – surveys – ultraviolet: stars 1. INTRODUCTION The observed long rotational periods, the large widths of the Balmer lines, and the presence of optical and UV excesses of Classical T Tauri stars (CTTSs) are low-mass, young stellar CTTSs are naturally explained by the magnetospheric accretion objects surrounded by an accretion disk. They provide us with a paradigm (e.g., Uchida & Shibata 1984; Koenigl 1991; Shu et al. laboratory in which to study the interaction between stars, mag- 1994). According to this paradigm, the gas disk is truncated netic fields, and accretion disks. In addition to optical and longer some distance from the star (∼5 R∗; Meyer et al. 1997)by wavelength excesses, this interaction is responsible for a strong the pressure of the stellar magnetosphere. Gas from the disk ultraviolet (UV) excess, Lyα emission, and soft X-ray excesses, slides down the stellar gravitational potential along the magnetic all of which have a significant impact on the disk evolution, the field lines, reaching speeds comparable to the free-fall velocity − rate of planet formation, and the circumstellar environment. (∼300 km s 1). These velocities are much larger than the local 1 The Astrophysical Journal Supplement Series, 207:1 (43pp), 2013 July Ardila et al. ∼20 km s−1 sound speed (but less than the Alfven´ speed of of the accretion process. Our long-term goal is to clarify the ∼500 km s−1 implied by a 2 kG magnetic field; Johns-Krull UV evolution of young stars and its impact on the surrounding 2007). The density of the accretion stream depends on the accretion disk. accretion rate and the filling factor but it is typically of the We analyze the resonance doublets of N v (λλ1238.82, order of ∼1012 cm−3 (pre-shock; see Calvet & Gullbring 1998). 1242.80), Si iv (λλ1393.76, 1402.77), and C iv (λλ1548.19, The supersonic flow, confined by the magnetic field, produces 1550.77), as well as the He ii (λ1640.47) line. If they are pro- a strong shock upon reaching the star, which converts most of duced by collisional excitation in a low-density medium, their the kinetic energy of the gas into thermal energy (e.g., Lamzin presence suggests a high temperature (∼105 K, assuming col- 1995). lisional ionization equilibrium) or a photoionized environment. The gas reaches temperatures of the order of a million degrees In solar-type main sequence stars, these “hot” lines are formed at the shock surface and cools radiatively until it merges with in the transition region, the narrow region between the chromo- the stellar photosphere. Part of the cooling radiation will heat sphere and the corona, and they are sometimes called transition- the stellar surface, resulting in a hot spot, observed spectroscop- region lines. ically as an excess continuum (the “veiling”). Cooling radiation The C iv resonance doublet lines are among the strongest emitted away from the star will illuminate gas before the shock lines in the UV spectra of CTTSs (Ardila et al. 2002). Using surface, producing a radiative precursor of warm (T ∼ 104 K), International Ultraviolet Explorer (IUE) data, Johns-Krull et al. ionized gas (Calvet & Gullbring 1998).
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