Detections of Rovibrational H₂Emission from the Disks of T Tauri Stars

Abstract

We report the detection of quiescent H 2 emission in the v ¼ 1 ! 0 S(1) line at 2.12183 lm in the circumstellar environment of two classical T Tauri stars, GG Tau A and LkCa 15, in high-resolution (R ' 60; 000) spectra, bringing to four, including TW Hya and the weak-lined T Tauri star DoAr 21, the number of T Tauri stars showing such emission. The equivalent widths of the H 2 emission line lie in the range 0.02-0.10 Å , and in each case the central velocity of the emission line is centered at the star's systemic velocity. The line widths range from 9 to 14 km s À1 , in agreement with those expected from gas in Keplerian orbits in circumstellar disks surrounding K-type stars at distances !10 AU from the sources. UV fluorescence and X-ray heating are likely candidate mechanisms responsible for producing the observed emission. We present mass estimates from the measured line fluxes and show that the estimated masses are consistent with those expected from the possible mechanisms responsible for stimulating the observed emission. The high temperatures and low densities required for significant emission in the v ¼ 1 ! 0 S(1) line suggests that we have detected reservoirs of hot H 2 gas located in the low-density upper atmospheres of circumstellar disks of these stars.

A search for near-infrared molecular hydrogen emission in the CTTS LkH$\mathsf{\alpha}$ 264 and the debris disk 49 Ceti

“…The observed line is 10 km s −1 narrower and slightly fainter than the line observed by Itoh et al (2003a). The line flux observed is within the range of 1 to 7 × 10 −15 erg s −1 cm −2 line fluxes reported towards other classical T Tauri stars (Weintraub et al 2000;Bary et al 2003).…”

“…Since the detections are not very numerous, it would be useful to know if the T Tauri stars with detected H 2 near-infrared ro-vibrational emission are peculiar objects. In the case of H 2 emission detected in WTTS, DoAr 21 and V773 Tau are among the brightest X-ray WTTS (see Tables 1 and 4 of Bary et al 2003 and for V773 Tau the XEST data of Güdel et al 2007) 8 .…”

“…Bary et al (2003) suggest that a conversion factor of 10 7 −10 9 could be used for deducing the total mass of the gas from the masses obtained from the υ = 1−0 S(1) H 2 line. Applying such a conversion factor for LkHα 264 we obtain a total disk mass of 0.5 to 50 M and for 49 Cet a total disk mass of <0.04 to 0.4 M .…”

“…However, the detections of rovibrational H 2 emission from disks are relatively scarce compared to the large number of pre-main-sequence stars with gasrich disks that are known. So far the υ = 1−0 S(1) line has been detected in few classical T Tauri stars (CTTS): TW Hya, GG Tau A, LkCa 15 (Weintraub et al 2000;Bary et al 2002Bary et al , 2003, AA Tau, CW Tau, UY Aur, GM Tau (Shukla et al 2003), CS Cha (Weintraub et al 2005 (Weintraub et al 2005). Our CRIRES observations show, for the first time, the simultaneous detection of the υ = 1−0 S(1) and υ = 1−0 S(0) H 2 emission from a protoplanetary disk.…”

Origin of the wide-angle hot H2in DG Tauri

“…The associated magnetic fields would have A&A 564, A11 (2014) strong consequences for the formation and migration of planets (Fromang et al 2005;Bai & Stone 2013). The H 2 emission from warm (T = 1000-3000 K) gas was recently detected within 100 AU of more evolved T Tauri stars (TTSs) and Herbig Ae/Be stars, both in the near-infrared and far-ultraviolet (FUV) domains (e.g., Valenti et al 2000;Ardila et al 2002;Bary et al 2003;Carmona et al 2011). When studied at high spectral resolution, these lines split into two populations: most show narrow profiles centered on the stellar velocity, suggesting an origin in a warm disc atmosphere (quiescent H 2 ), but 30% of them display profiles blueshifted by 10-30 km s −1 , sometimes with blue wings extending up to -100 km s −1 , suggesting formation in an outflow (Takami et al 2004;Herczeg et al 2006;Greene et al 2010;Carmona et al 2011;France et al 2012).…”