A sensitive survey for¹³CO, CN, H₂CO, and SO in the disks of T Tauri and Herbig Ae stars

Abstract

Aims. We investigate the suitability of several molecular tracers, in particular CN N = 2−1 line emission, as a confusion-free probe of the kinematics of circumstellar disks. Methods. We use the IRAM 30-m telescope to perform a sensitive search for CN N = 2−1 in 42 T Tauri or Herbig Ae systems located principally in the Taurus-Auriga region. 13 CO J = 2−1 is observed simultaneously to provide an indication of the level of confusion with the surrounding molecular cloud. The bandpass also contains two transitions of ortho-H 2 CO, one of SO and the C 17 O J = 2−1 line which provide complementary information on the nature of the emission. Results. While 13 CO is in general dominated by residual emission from the cloud, CN exhibits a high disk detection rate >50% in our sample. We even report CN detection in stars for which interferometric searches failed to detect 12 CO, presumably because of obscuration by a foreground, optically thick, cloud. Comparison between CN and o-H 2 CO or SO line profiles and intensities divide the sample in two main categories. Sources with SO emission are bright and have strong H 2 CO emission, leading in general to [H 2 CO/CN] > 0.5. Furthermore, their line profiles, combined with a priori information on the objects, suggest that the emission is coming from outflows or envelopes rather than from a circumstellar disk. On the other hand, most sources have [H 2 CO/CN] < 0.3, no SO emission, and some of them exhibit clear double-peaked profiles characteristics of rotating disks. In this second category, CN is likely tracing the proto-planetary disks. From the line flux and opacity derived from the hyperfine ratios, we constrain the outer radii of the disks, which range from 300 to 600 AU. The overall gas disk detection rate (including all molecular tracers) is ∼68%, and decreases for fainter continuum sources. Conclusions. The current study demonstrates that gas disks, like dust disks, are ubiquitous around young PMS stars in regions of isolated star formation, and that a large fraction of them have R out > ∼ 300 AU. It also shows the potential of the CN N = 2−1 transition to probe the kinematics of these disks, thereby measuring the stellar mass, using high resolution observations with ALMA.

Dynamical Masses of Low-mass Stars in the Taurus and Ophiuchus Star-forming Regions

“…Most disks in our sample were found to be smaller than those in the Guilloteau et al (2013) sample. However, this is probably a selection bias: the targets of our ALMA study have T eff s cooler than the stars in our pilot studies (Guilloteau et al 2013. Indeed, there is no difference in disk size in our new sample between the L1495 and L1688 regions.…”

“…To overcome this, we tested the detectability of the hyperfine-split CN 2-1 transition radiated by circumstellar disks. We found that the CN lines were good tracers of disk emission of targets in the Taurus SFR and were free of molecular absorption (Guilloteau et al 2013). We then used the Plateau de Bure interferometer to measure the masses of 11 stars in the Taurus SFR ).…”

The hybrid disks: a search and study to better understand evolution of disks

“…DL Tau A dust disk around DL Tau was first detected by Beckwith et al (1990), followed by the observation of CO gas (Koerner & Sargent 1995;Simon et al 2000), CN , and H 2 CO (Guilloteau et al 2013), despite strong confusion. While the CO and CN extends out to ∼460 au, the dust disk is smaller, with an outer radius of 150-180 au (Guilloteau et al 2011;Kwon et al 2015).…”

The jet and the disk of the HH 212 low-mass protostar imaged by ALMA: SO and SO2emission

“…On the other hand, sulfur bearing species have long been searched in protoplanetary disks associated with evolved young stellar objects (i.e. Class I-II) but only CS has been routinely observed while SO is hard to detect: Dutrey et al (2011) reported no detection of SO (and H 2 S) from three prototypical protoplanetary disks; Fuente et al (2010) reported a detection in the disk of the T Tauri star AB Aur; and Guilloteau et al (2013) showed that SO is exceptionally observed in disks with only one definite detection on a sample of 42 T Tauri and Herbig Ae stars towards 04302+2247. The statistics regarding disks around Class 0 protostars is even poorer.…”