Near infrared hydrogen lines as diagnostic of accretion and winds in T Tauri stars

Abstract

Abstract. From a sample of 50 T Tauri stars, mostly from the Taurus-Auriga complex, Paβ line profiles were obtained for 49 of the stars and Brγ profiles for 37 of the stars. Emission at Paβ was observed for 42 stars and emission at Brγ was found for 30 stars. The most conspicuous features in the line profiles is the almost complete absence of blueshifted absorption components and the relatively high frequency of inverse P Cygni profiles (IPC). At Paβ, 34% of the profiles are IPC while at Brγ 20% are IPC. The redshifted absorption features indicate infall at velocities of about 200 km s −1 , compatible with free fall from a few radii out. In general, line profiles are broad centrally peaked with slightly blueshifted line peaks. Existing wind and accretion models fail, in quantitative terms, to explain the shape of the observed profiles. Magnetospheric accretion models, being the currently preferred ones, produce lines too narrow (by ∼ 100 km s −1 FWHM), wings extending to velocities too low (by at least ∼ 100 km s −1 ) and with maximum normalized intensities too high by factors of a few. A qualitative agreement between some of the accretion model predicted profiles and some observations hint that emission in these lines might, at least partially, arise from infalling material. Definite claims regarding the origin of the emission in these lines cannot be made until models match observations much better than they currently do.

Spatially Resolved Spectroscopy of Sub-Au-Sized Regions of T Tauri and Herbig Ae/Be Disks

“…RY Tau, MWC 758, HD 142666, and AS 205 also have previously reported Brγ emission (Najita et al 1996b;Folha & Emerson 2001;Garcia Lopez et al 2006;Berthoud 2008). However, the equivalent widths of the Brγ emission are small relative to other sources (e.g., MWC 275 or DG Tau), and it is not surprising that we do not detect (or only marginally detect) Brγ emission from these objects here.…”

Direct evidence of a sub-stellar companion around CT Chamaeleontis

“…While this magnetospheric accretion model predicts a correlation between emission line strengths of hydrogen lines and accretion rate (Muzerolle et al 1998), as used to determine accretion rates from the H-α emission line, Folha & Emerson (2001) find no such agreement for the Pa-β emission line of approximately half of the 49 studied classical T-Tauri stars (see Whelan et al 2004, for a discussion). Interestingly, we did not find any emission in the Br-γ line around 2.166 Å.…”

Magnetically Channeled Accretion in T Tauri Stars

“…The relative success of MAMs in reproducing the shape and strength of optical and near IR emission line profiles of some CTTS provides additional support to the formation of at least part of the line emission in accretion columns (Hartmann et al 1994;Muzerolle et al 2001; for a more critical view see Ardila et al 2002b, Alencar & Basri 2000, Folha & Emerson 2001. Statistical correlations between line fluxes and mass accretion rates predicted by these models have been reported in samples of TTS for a variety of emission lines in the UV, optical, and near IR range (e.g.…”

“…Statistical correlations between line fluxes and mass accretion rates predicted by these models have been reported in samples of TTS for a variety of emission lines in the UV, optical, and near IR range (e.g. Beristain et al 2001, Johns-Krull et al 2000, Alencar & Basri 2000, Folha & Emerson 2001, Muzerolle et al 2001. Correlations have also been reported between mass loss rate and mass accretion rate (e.g., Ardila et al 2002) as expected from MAMs which predict that part of the accretion flow is diverted into the wind by the magnetic field (e.g.…”