Search For Molecular Hydrogen Emission Research Articles

A search for near-infrared molecular hydrogen emission in the CTTS LkHα264 and the debris disk 49 Ceti

We report on the first results of a search for molecular hydrogen emission from protoplanetary disks using CRIRES, ESO’s new VLT Adaptive Optics high resolution near-infrared spectrograph. We observed the classical T Tauri star LkHα 264 and the debris disk 49 Cet, and searched for υ = 1− 0S (1) H 2 emission at 2.1218 µm, υ = 1− 0S (0) H 2 emission at 2.2233 µ ma ndυ = 2− 1S (1) H2 emission at 2.2477 µm. The H2 line at 2.1218 µm is detected in LkHα 264 confirming the previous observations by Itoh et al. (2003). In addition, our CRIRES spectra reveal the previously observed but not detected H2 line at 2.2233 µ mi n LkHα 264. An upper limit of 5.3 ×10 −16 erg s −1 cm −2 on the υ = 2− 1S (1) H 2 line flux in LkHα 264 is derived. The detected lines coincide with the rest velocity of LkHα 264. They have a FWHM of ∼20 km s −1 . This is strongly suggestive of a disk origin for the lines. These observations are the first simultaneous detection of υ = 1− 0S (1) andυ = 1− 0S (0) H 2 emission from a protoplanetary disk. 49 Cet does not exhibit H2 emission in any of the three observed lines. We derive the mass of optically thin H2 at T ∼ 1500 K in the inner disk of LkHα 264 and derive stringent limits in the case of 49 Cet at the same temperature. There are a few lunar masses of optically thin hot H2 in the inner disk (∼0.1 AU) of LkHα 264, and less than a tenth of a lunar mass of hot H2 in the inner disk of 49 Cet. The measured 1− 0S (0)/1− 0S (1) and 2− 1S (1)/1−0 S(1) line ratios in LkHα 264 indicate that the H2 emitting gas is at a temperature lower than 1500 K and that the H2 is most likely thermally excited by UV photons. The υ = 1− 0S (1) H 2 line in LkHα 264 is single peaked and spatially unresolved. Modeling of the shape of the line suggests that the disk should be seen close to face-on (i < 35 ◦ ) and that the line is emitted within a few AU of the LkHα 264 disk. A comparative analysis of the physical properties of classical T Tauri stars in which the H2 υ = 1−0 S(1) line has been detected and non-detected indicates that the presence of H2 emission is correlated with the magnitude of the UV excess and the strength of the Hα line. The lack of H2 emission in the NIR spectra of 49 Cet and the absence of Hα emission suggest that the gas in the inner disk of 49 Cet has dissipated. These results combined with previous detections of 12 CO emission at sub-mm wavelengths indicate that the disk surrounding 49 Cet should have an inner hole. We favor inner disk dissipation by inside-out photoevaporation, or the presence of an unseen low-mass companion as the most likely explanations for the lack of gas in the inner disk of 49 Cet.

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

We report on the first results of a search for molecular hydrogen emission from protoplanetary disks using CRIRES, ESO's new VLT Adaptive Optics high resolution near-infrared spectrograph. We observed the classical T Tauri star LkH α 264 and the debris disk 49 Cet, and searched for $\upsilon= 1{-}0$ S(1) H 2 emission at 2.1218 μ m, $\upsilon = 1{-}0$ S(0) H 2 emission at 2.2233 μ m and $\upsilon = 2{-}1$ S(1) H 2 emission at 2.2477 μ m. The H 2 line at 2.1218 μ m is detected in LkH α 264 confirming the previous observations by Itoh et al. (2003). In addition, our CRIRES spectra reveal the previously observed but not detected H 2 line at 2.2233 μ m in LkH α 264. An upper limit of 5.3 $\times 10^{-16}$ erg s -1 cm -2 on the $\upsilon = 2{-}1$ S(1) H 2 line flux in LkH α 264 is derived. The detected lines coincide with the rest velocity of LkH α 264. They have a FWHM of ~20 km s -1 . This is strongly suggestive of a disk origin for the lines. These observations are the first simultaneous detection of $\upsilon = 1{-}0$ S(1) and $\upsilon = 1{-}0$ S(0) H 2 emission from a protoplanetary disk. 49 Cet does not exhibit H 2 emission in any of the three observed lines. We derive the mass of optically thin H 2 at $T\sim1500$ K in the inner disk of LkH α 264 and derive stringent limits in the case of 49 Cet at the same temperature. There are a few lunar masses of optically thin hot H 2 in the inner disk (~0.1 AU) of LkH α 264, and less than a tenth of a lunar mass of hot H 2 in the inner disk of 49 Cet. The measured 1-0 S(0)/1-0 S(1) and 2-1 S(1)/1-0 S(1) line ratios in LkH α 264 indicate that the H 2 emitting gas is at a temperature lower than 1500 K and that the H 2 is most likely thermally excited by UV photons. The $\upsilon = 1{-}0$ S(1) H 2 line in LkH α 264 is single peaked and spatially unresolved. Modeling of the shape of the line suggests that the disk should be seen close to face-on ($i α 264 disk. A comparative analysis of the physical properties of classical T Tauri stars in which the H 2 $\upsilon = 1{-}0$ S(1) line has been detected and non-detected indicates that the presence of H 2 emission is correlated with the magnitude of the UV excess and the strength of the H α line. The lack of H 2 emission in the NIR spectra of 49 Cet and the absence of H α emission suggest that the gas in the inner disk of 49 Cet has dissipated. These results combined with previous detections of 12 CO emission at sub-mm wavelengths indicate that the disk surrounding 49 Cet should have an inner hole. We favor inner disk dissipation by inside-out photoevaporation, or the presence of an unseen low-mass companion as the most likely explanations for the lack of gas in the inner disk of 49 Cet.

An unbiased search for the signatures of protostars in the ρ Ophiuchi A molecular cloud

We present an unbiased search for molecular hydrogen emission in the L1688 cloud within the ρ Ophiuchi molecular cloud complex. Our near-infrared survey covers a connected region of extent 35´ $\times$ 35´. We detect several new H 2 flows but the total number of detected outflows is low and is consistent with the paucity of Class 0 and Class 1 sources in the molecular cloud. From the spatial distribution, their collimation and the individual shapes of the bow shocks, we suggest possible candidates for the outflow sources. Most of the candidate driving sources are deeply embedded in dense cores of the molecular cloud. A very young outflow arises from the newly discovered Class 0 source MMS 126. Two major outflows in the NE–SW direction arise from the YLW 15 and YLW 16 Class I sources. Three additional outflows, which both extend over several arcminutes, arise from the Class I sources YLW 31 and YLW 52. Flow directions are generally NE–SW, perpendicular to the elongation directions of the cloud filaments. The apparent extents of molecular flows are related to either the widths of cloud filaments or to the separation between filaments. The estimated jet power needed to continuously drive and excite the detected portions of the shocked H 2 outflows lies in the range 0.02-0.2 $L_\odot$. Given the critical dependence on the environment, however, the total sizes and powers of the outflows may be considerably larger.

Molecular hydrogen emission from T Tauri stars

Results are presented for a search for molecular hydrogen emission in the v = 1-0 S(1) line at 2.2 microns in five T Tauri stars, including T Tau itself, RY Tau, SU Aur, DK Tau, and HL Tau. Molecular hydrogen emission was detected only in T Tau; the results suggest that the emitting region is probably larger than 5 arcsec (2.5-sigma confidence level) and that the emission is probably centered on the star. Upper limits on the line strengths are given for the other four stars. Various excitation mechanisms for the H2 in T Tau are considered, and the mass-loss rate and neutral-particle density in the shocked region are estimated for the case of shock excitation.