Gas in the Terrestrial Planet Region of Disks: CO Fundamental Emission from T Tauri Stars

Abstract

We report the results of a high-resolution spectroscopic survey for CO fundamental emission from T Tauri stars. CO fundamental emission is frequently detected, with the likely origin of the emission in the circumstellar disk. An initial assessment of the line profiles indicates that the emission region includes the equivalent of the terrestrial planet region of our solar system, a result that suggests the utility of CO fundamental emission as a probe of disks at planet formation distances. Since fundamental emission is detected frequently from both close binary and apparently single stars, it appears that both low column density regions, such as disk gaps, and temperature inversion regions in disk atmospheres can produce significant emission. The estimated excitation temperature of the emitting gas is unexpectedly warm for the disk radii that they appear to probe. Thus, the surface gaseous component of inner disks may be significantly warmer than the surface dust component. We also detect CO emission from a transitional T Tauri star. Because fundamental emission from CO and its isotopes is sensitive to a wide range of gas masses, including masses5M È , CO fundamental emission may prove useful in measuring the residual gas content of dissipating disks. This may be an effective way to explore the gas dissipation timescale in inner disks and to thereby place constraints on the timescale for giant planet formation.

Radiative transfer in circumstellar disks

“…Considering the noise in the spectrum and the blending of 12 CO and 13 CO lines we therefore cannot find evidence for a different isotope ratio in our observations. The maximum temperature in the surface layers of the disk atmospheres is T = 950 K which is much smaller than the estimated excitation temperature of T ex = 1814 K found by Najita et al (2003) for DF Tau which has a similar spectrum but stronger v = 2−1 emission lines.…”

“…This line has been attributed to an absorption line in the telluric standard star used for the calibration of CTTS by Najita et al (2003). Since we used a telluric model to remove telluric absorption lines, we can relate the Pfβ feature unambiguously to an emission line intrinsic to GQ Lup.…”

“…NIRSPEC observations of protoplanetary disks have shown the capabilities of IR spectroscopy (Najita et al 2003). With the ESO IR spectrograph CRIRES (Kaeufl et al 2004) such observations have become available to a larger community of astronomers.…”

DIGIT survey of far-infrared lines from protoplanetary discs

“…The fundamental ro-vibrational CO band (∆v = 1) at 4.7 µm traces warm (T > 100 K) gas in the terrestrial planet-forming region (0.1-10 AU). This band is often observed in HAEBEs (e.g., Blake & Boogert 2004;Brittain et al 2007) and in TTS (e.g., Najita et al 2003;Salyk et al 2011). The bands are rotationally excited up to high J (>30), resulting in a T rot between 900 and 2500 K. The rotational temperature is much lower for 13 CO at ∼250 K .…”

TheHerschelview of GAS in Protoplanetary Systems (GASPS)

“…Dent et al 2005;Schaefer et al 2009), and near-IR lines which are only emitted from the hot inner parts of discs (e.g. Najita et al 2003;Brittain et al 2007). The high sensitivity of Herschel (Pilbratt et al 2010) opens an opportunity to systematically probe the gas phase of discs, in particular the warm atomic and molecular layer responsible for the bright gas emission lines in the far-IR.…”