Hot H2O Emission and Evidence for Turbulence in the Disk of a Young Star

Abstract : We report on the detection and analysis of hot rovibrational H2O emission from SVS 13, a young stellar object previously known to have strong CO overtone band head emission. Modeling of the high-resolution infrared spectrum shows that the H2O emission is characterized by temperatures of 1500 K, significantly lower than the temperatures that characterize the CO band head emission. The widths of the H2O lines are also found to be smaller than those of the CO lines. We construct a disk model of the emission that reproduces the CO and H2O spectrum. In this model, the H2O lines originate at somewhat larger disk radii ( 0.3 AU) than the CO overtone lines ( 0.1 AU). We find that the H2O abundance is about a factor of 10 lower than the calculated chemical equilibrium abundance. Large, approximately transonic, local line broadening is required to fit the profile of the CO band head. If this velocity dispersion is identified with turbulence, it is of significant interest regarding the transport of angular momentum in disks. Large local broadening is also required in modeling CO overtone emission from other young stellar objects, suggesting that large turbulent velocities may be characteristic of the upper atmospheres of the inner disks of young stars.

[1]  Peter H. Hauschildt,et al.  TiO and H2O Absorption Lines in Cool Stellar Atmospheres , 2000, astro-ph/0008465.

[2]  P. H. Hauschildt,et al.  Spectral Energy Distributions for Disk and Halo M Dwarfs , 2000, astro-ph/0001100.

[3]  Laurence S. Rothman,et al.  Reprint of: The HITRAN molecular spectroscopic database and HAWKS (HITRAN Atmospheric Workstation): 1996 edition , 1998 .

[4]  J. Igea,et al.  X-Ray Ionization of the Disks of Young Stellar Objects , 1999 .

[5]  J. Najita,et al.  Gas in the Terrestrial Planet Region of Disks: CO Fundamental Emission from T Tauri Stars , 2003 .

[6]  J. Carlstrom,et al.  Infrared CO Emission from Young Stars: Accretion Disks and Neutral Winds , 1995 .

[7]  M. Wolff,et al.  Erratum: "Astro-2 Observations of Interstellar Dust and Gas in the Large Magellanic Cloud" (ApJ, 460, 313 [1996]) , 1997 .

[8]  J. Tennyson,et al.  Spectral analysis of water vapour in cool stars , 2001, astro-ph/0110649.

[9]  C. Kulesa,et al.  CO Emission from Disks around AB Aurigae and HD 141569: Implications for Disk Structure and Planet Formation Timescales , 2003 .

[10]  S. E. Persson,et al.  Emission from CO Band Heads in Young Stellar Objects , 1987 .

[11]  B. Jones,et al.  Proper motions of Herbig-Haro objects. III - HH-7 through -11, HH-12, and HH-32 , 1983 .

[12]  David R. Alexander,et al.  THE LIMITING EFFECTS OF DUST IN BROWN DWARF MODEL ATMOSPHERES , 2001 .

[13]  P. Woodward,et al.  Synthesized spectra of turbulent clouds , 1994 .

[14]  Statistical Properties of Line Centroid Velocity Increments in the ρ Ophiuchi Cloud , 1998 .

[15]  L. Wallace,et al.  An atlas of a dark sunspot umbral spectrum from 1970 to 8640 cm(-1) (1.16 to 5.1 [microns]) , 1992 .

[16]  Donald N. B. Hall,et al.  Design for a 1--5-um cryogenic echelle spectrograph for the NASA IRTF , 1990, Astronomical Telescopes and Instrumentation.

[17]  Harry Partridge,et al.  The determination of an accurate isotope dependent potential energy surface for water from extensive ab initio calculations and experimental data , 1997 .

[18]  Turbulence in Accretion Disks: Vorticity Generation and Angular Momentum Transport via the Global Baroclinic Instability , 2002, astro-ph/0211629.

[19]  C. Aspin,et al.  Near-IR imaging photometry of NGC1333: a 3-Όm imaging survey , 1997 .

[20]  E. Falgarone,et al.  A signature of the intermittency of interstellar turbulence - The wings of molecular line profiles , 1990 .

[21]  H Germany,et al.  A Method of Correcting Near‐Infrared Spectra for Telluric Absorption , 2002, astro-ph/0211255.

[22]  E. Herbst,et al.  Two-dimensional distributions and column densities of gaseous molecules , 1999, astro-ph/0202062.

[23]  K. Horne,et al.  HST eclipse mapping of dwarf nova OY Carinae in quiescence: An 'Fe II curtain' with Mach approx. = 6 velocity dispersion veils the white dwarf , 1994 .

[24]  J. Pollack,et al.  Composition and radiative properties of grains in molecular clouds and accretion disks , 1994 .

[25]  A. Boss,et al.  Protostars and Planets VI , 2000 .

[26]  R. Thompson.  Infrared CO band emission in the Rho Ophiuchi source WL 16 , 1985 .

[27]  J. Carlstrom,et al.  Infrared CO emission from young stars : high-resolution spectroscopy , 1993 .

[28]  J. Hawley,et al.  A powerful local shear instability in weakly magnetized disks. I - Linear analysis. II - Nonlinear evolution , 1990 .

[29]  V. Dhillon,et al.  Supersonic line broadening in accretion discs , 1997 .

[30]  John T. Rayner,et al.  SpeX: A Medium‐Resolution 0.8–5.5 Micron Spectrograph and Imager for the NASA Infrared Telescope Facility , 2003 .

[31]  Joan Najita,et al.  Kinematic Diagnostics of Disks around Young Stars: CO Overtone Emission from WL 16 and 1548C27 , 1996 .

[32]  Alan T. Tokunaga,et al.  CSHELL: a high spectral resolution 1-5-μm cryogenic echelle spectrograph for the IRTF , 1993, Defense, Security, and Sensing.

[33]  P. H. Hauschildt,et al.  Infrared Spectra and Spectral Energy Distributions of Late M and L Dwarfs , 2000, astro-ph/0010174.

[34]  S. Ridgway,et al.  The circumstellar and nebular environment of the Becklin-Neugebauer object - 2-5 micron wavelength spectroscopy , 1983 .

[35]  Alan T. Tokunaga,et al.  Measurement of CO overtone line profiles in SVS 13 , 1992 .

[36]  J. Carr.  Near-infrared CO emission in young stellar objects , 1989 .

[37]  M. Miesch,et al.  Exponential Tails in the Centroid Velocity Distributions of Star-forming Regions , 1994, astro-ph/9412042.

[38]  B. Shustov.  Protostars and Planets II , 1987 .

[39]  J. Pety,et al.  Statistical Properties of Line Centroid Velocities and Centroid Velocity Increments in Compressible Turbulence , 1996 .

[40]  The Effects of UV Continuum and Lyα Radiation on the Chemical Equilibrium of T Tauri Disks , 2003, astro-ph/0305565.

[41]  Robert D. Mathieu,et al.  Evidence for Residual Material in Accretion Disk Gaps: CO Fundamental Emission from the T Tauri Spectroscopic Binary DQ Tauri , 2001 .

[42]  J. M. Stone,et al.  The Formation and Structure of a Strongly Magnetized Corona above a Weakly Magnetized Accretion Disk , 1999, astro-ph/9912135.

[43]  Alan T. Tokunaga,et al.  The Inner-Disk and Stellar Properties of the Young Stellar Object WL 16 , 1993 .

[44]  P. Bernath,et al.  Using Laboratory Spectroscopy to Identify Lines in the K- and L-Band Spectrum of Water in a Sunspot , 2000 .

[45]  U. Frisch.  Turbulence: The Legacy of A. N. Kolmogorov , 1996 .

[46]  B. Krauskopf,et al.  Proc of SPIE , 2003 .

[47]  Velocity field statistics in star-forming regions. I. Centroid velocity observations , 1998, astro-ph/9810427.

[48]  N. Calvet,et al.  Irradiation of Accretion Disks around Young Objects. I. Near-Infrared CO Bands , 1991 .