Infall, Outflow, Rotation and Deuteration in a Young Protostellar Candidate in Chamaeleon I
Coordinator: A. Belloche, B. Parise & P. Schilke
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Proposed observations for the APEX Science Verification
We propose to use the APEX-2A receiver to gain insight into the kinematics and chemical structureof the low-mass Class 0 protostellar candidate Cha-MMS1 in the Chamaeleon cloud I (150 pc, Knude& Høg 1998). We expect to 1) set new constraints on the outflow existing in the region and possiblyidentify Cha-MMS1 as its driving source, 2) discover infall and rotation motions in the envelope ofthis young protostar and 3) measure the degree of deuteration in the dense part of the envelope. Cha-MMS1, discovered at 1.3mm by Reipurth et al. (1996), is located in the active site of low-massstar formation Cederblad 110, where several Class I and Class III IRAS sources were identified (e.g.Prusti et al. 1991; Lehtinen et al. 2001). It is embedded in a C 18 O(1-0) clump (Haikala et al. 2005)and was observed at 2 and 3 mm in some molecular lines, e.g. N 2 H+ (1-0), by Kontinen et al. (2000).Using far infrared measurements, Lehtinen et al. (2001) showed that it is a cold (T bol = 20 K), faint(Lbol = 0.45 Lsun ), low-mass (M1.3mm = 0.45 Msun ) Class 0 protostar (Andre et al. 1993). In addition,
eReipurth et al. (1996) suggested that it could be the driving source of the Herbig-Haro objects andthe CO ouflow seen nearby, previously thought to be driven by one of the IRAS sources (Mattila et al.1989; Prusti et al. 1991). Cha-MMS1 is thus very similar to the young Class 0 protostar IRAM 04191located in Taurus (Belloche et al. 2002). However Lehtinen et al. (2003) failed to detect any cmemission toward Cha-MMS1, questioning its protostellar nature. They proposed that it could still bein the prestellar stage.
First, we propose to use APEX-2A to get a map in CO(3-2) to improve the constraints on theoutflow. Second, we want to map the dense core itself in N 2 H+ (4-3), which should help us to findrotation motions, and in HCO+ (4-3) to look for the classical signature of infall (e.g. Evans 1999).Finally, we want to integrate on the central position in H 13 CO+ (4-3), N2 D+ (4-3), and H2 D+ (110 -111 ).The former line should help us constraining the infall modeling. The second line will yield the degreeof deuteration via the N2 D+ /N2 H+ ratio. Furthermore, if the molecular depletion is still strong in theenvelope, we expect to detect the H2 D+ line (Stark et al. 1999; Caselli et al. 2003) and set constraintson the chemical models.
We assume a system temperature of 250 K for APEX-2A and a beam efficiency of 0.5. In positionswitching mode, we compute the sensitivities with the equation rms =2Tsys/sqrt(Bt_int) , with B the spectralresolution (100 kHz) and t_int the ON+OFF integration time. Taking as reference the observationsdone by Blake et al. (1995) and Stark et al. (1999, 2004) toward the Class 0 protostars NGC1333-IRAS 4A and IRAS 16293, and by Kontinen et al. (2000) toward Cha-MMS1, we expect peak antennatemperatures of 7 K for CO(3-2), 2 K for N 2 H+ (4-3), 2 K for HCO+ (4-3), 0.3 K for N2 D+ (4-3), 0.4K for H13 CO+ (4-3) and 0.3 K for H2 D+ (110 -111 ). We propose to get a 9 × 9 raster map in CO(3-2)with a step of 20" (2.7' × 2.7' in total) and a smaller 3 × 3 raster map with a step of 10". We willreach a rms of 0.35 K in 30 min in total. We also want to make a 5 × 5 raster map in N 2 H+ (4-3)and HCO+ (4-3) with a step of 20" and a smaller 3 × 3 raster map with a step of 10". We will reacha rms of 0.2 K in a total integration time of 34 min for each line. Then, deep integrations onthe central position in N2 D+ (4-3) and H13 CO+ (4-3) will reach a rms of 0.04 K in 26 minutes foreach line. Finally the deep integration on the central position in H 2 D+ (110 -111 ) will achieve a rms of0.03 K in 46 min (note that, since this line is very close to N 2 H+ (4-3), we might also detect it whilemapping in N2 H+ if it is stronger than expected). In total, we need an ON+OFF integration timeof 3h15. Assuming an observing efficiency of 33% including software/hardware efficiencies, tuning,pointing, focus and calibration, we ask for a total time of 10h. Cha-MMS1 ( 2000 = 11h 06m 31.s 7,2000 = -77 23 33 ) will transit around 11h LST in July (20:30 UT). Since the observations will bedone by night only, we ask for 2 slots of 5 hours between 13h and 18h LST.
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