Chemistry in protoplanetary disks

Coordinator: M. Hogerheijde, C. Brinch, E. van Dishoeck


Program is available and data products can be downloaded

Scientific justification:

Disks play a central role in the formation of stars and planetary systems. Since they are small, typically few hundred AU (few ''), they have traditionally been studied with millimeter interferometers. However, for isolated objects away from cloud material, high-frequency single dish data can also provide information on the gaseous content of protoplanetary disks, especially its chemistry (e.g., Dutrey et al. 1997, A&A 317, L55; Kastner et al. 1997, Science 277, 67; Thi et al. 2004, A&A 425, 955). High-frequency observations are particularly suitable for such studies, since the gas in disks in dense and relatively warm (e.g., van Zadelhoff et al. 2001, A&A 377, 566). The lines should reveal a characteristic double-peak profile due to rotation.
To demonstrate the feasibility of line observations of disks with APEX to the community, we propose observations of a few key molecules, CO, 13CO, CN and HCN, at 345 GHz using the APEX-2a receiver for one object. One of the best candidates is HD 100546, a nearby (d~100 pc) southern Herbig Ae star famous for its rich content of crystalline silicates (Malfait et al. 1998, A&A 332, L25), but other targets are possible as well. The molecules are chosen to be diagnostic of various chemical processes, e.g. the CN/HCN ratio is sensitive to the UV radiation field (van Zadelhoff et al. 2003, A&A 397, 789). Expected line intensities are 0.5 K for 12CO 3-2, 0.2 K for 13CO 3-2, 0.05-0.1 K for CN 3-2 and HCN 4-3.

Observational details
Source: HD 100546: RA= 11 33 25, DEC= -70 11 41 (J2000) V_LSR=0 km/s (unknown, but should be close to 0)
Receivers: Apex-2a
Backend: 128 MHz bandwidth
Central frequencies:

12CO 3-2 345.795
13CO 3-2 330.587
CN 3-2 340.248
HCN 4-3 354.506

Observing mode: Beam switching by 120-180" Required rms: 50 mK (T_A*) in 0.5 km/s bin 12CO
30 mK (T_A*) in 0.5 km/s bin 13CO
15 mK (T_A*) in 0.5 km/s bin CN, HCN
Note: CN and HCN should only be attempted if 12CO and 13CO detected
Required integration time:
15 min 12CO (high S/N to get line profile)
20 min 13CO
80 min CN
80 min HCN
(assuming T_sys=400 K)
Total: 3.2 hrs excluding overheads