High-resolution images of the L1551 bipolar outflow - Evidence for an expanding, accelerated shell

Moriarty‐Schieven, G. H.; Snell, R.; Strom, S. E.; Schloerb, F. P.; Strom, K. M.

doi:10.1086/165494

Cited by 40 publications

(21 citation statements)

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“…While the shell of relatively slow gas in the L1448 outflow is similar to what is seen in more evolved outflows like L1551 (e.g., Moriarty-Schieven et al 1987), and therefore likely composed of accelerated ambient gas, the nature of the EHV component is still mysterious. The symmetry, high speed, and fragmented appearance of the EHV gas initially suggested that it may consist of a collection of molecular "bullets" ejected by the central protostar and traveling along the outflow axis (Bachiller et al 1990).…”

Section: Introductionmentioning

confidence: 87%

A molecular survey of outflow gas: velocity-dependent shock chemistry and the peculiar composition of the EHV gas

Tafalla

Santiago-García

Hacar

et al. 2010

A&A

130

168

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Context. Bipolar outflows from Class 0 protostars often present two components in their CO spectra that have different kinematic behaviors: a smooth outflow wing and a discrete, extremely high-velocity (EHV) peak. Aims. To better understand the origin of these two outflow components, we have studied and compared their molecular composition. Methods. We carried out a molecular survey of the outflows powered by L1448-mm and IRAS 04166+2706, two sources with prominent wing and EHV components. For each source, we observed a number of molecular lines towards the brightest outflow position and used them to determine column densities for 12 different molecular species.Results. The molecular composition of the two outflows is very similar. It presents systematic changes with velocity that we analyze by dividing the outflow in three chemical regimes, two of them associated with the wing component and the other the EHV gas. The analysis of the two wing regimes shows that species like H 2 CO and CH 3 OH favor the low-velocity gas, while SiO and HCN are more abundant in the fastest gas. This fastest wing gas presents strong similarities with the composition of the "chemically active" L1157 outflow (whose abundances we re-evaluate in an appendix). We find that the EHV regime is relatively rich in O-bearing species compared to the wing regime. The EHV gas is not only detected in CO and SiO (already reported elsewhere), but also in SO, CH 3 OH, and H 2 CO (newly reported here), with a tentative detection in HCO + . At the same time, the EHV regime is relatively poor in C-bearing molecules like CS and HCN, for which we only obtain weak detections or upper limits despite deep integrations. We suggest that this difference in composition arises from a lower C/O ratio in the EHV gas. Conclusions. The different chemical compositions of the wing and EHV regimes suggest that these two outflow components have different physical origins. The wing component is better explained by shocked ambient gas, although none of the existing shock models explains all observed features. We hypothesize that the peculiar composition of the EHV gas reflects its origin as a dense wind from the protostar or its surrounding disk.

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Section: Introductionmentioning

confidence: 87%

A molecular survey of outflow gas: velocity-dependent shock chemistry and the peculiar composition of the EHV gas

Tafalla

Santiago-García

Hacar

et al. 2010

A&A

130

168

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“…The evolutionary algorithm, used here, is described in Promislov (1999). We estimated the effective HPBW of the reconstruction in a manner, similar to that used by Moriarty-Schieven et al (1987). For each point of a map we subtracted the contribution from the source leaving us with the noise fluctuations only.…”

Section: Observationsmentioning

confidence: 99%

Determination of molecular gas properties using methyl cyanide lines

et al. 2000

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A survey of 27 galactic star-forming regions in the 6 K −5 K , 5 K − 4 K , and 8 K − 7 K CH 3 CN lines at 110, 92, and 147 GHz, respectively, was made. Twenty-five sources were detected at 110 GHz, nineteen at 92 GHz, and three at 147 GHz. The strongest CH 3 CN emission arise in hot cores in the regions of massive star formation. CH 3 CN abundance in these objects is larger than 10 −9 due to grain mantle evaporation. Weaker CH 3 CN lines were found in a number of sources. They may arise either in warm (30-50 K) dense (10 5 -10 7 cm −3 ) clouds, or in hot regions accompanied by colder gas.

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“…Bachiller 1996). Part of this difficulty is due to the large variety of shapes and velocity patterns observed in the outflow-accelerated gas, which range from the almost parabolic shells of low velocity material detected in L1551 and Mon R2 (Moriarty-Schieven et al 1987;Meyers-Rice & Lada 1991) to the collimated jets of rapidly moving gas observed towards L1448-mm and HH211 (Bachiller et al 1990;Gueth & Guilloteau 1999). In addition to the molecular gas, optical observations of outflows often reveal an atomic component of higher excitation and collimation, probably due to recently shocked material either in the wind itself or at the interface between the wind and the cloud.…”

Section: Introductionmentioning

confidence: 99%

Shells, jets, and internal working surfaces in the molecular outflow from IRAS 04166+2706

Santiago-García¹,

Tafalla²,

Johnstone

et al. 2008

A&A

142

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Context. IRAS 04166+2706 in Taurus is one of the closest young stellar objects whose molecular outflow contains a highly collimated, rapidly moving component. Aims. The high symmetry and pristine appearance of this outflow suggests that its study could offer unique clues about the nature of its still mysterious underlying driving wind. Methods. We observed the IRAS 04166+2706 outflow with the IRAM Plateau de Bure interferometer in CO(J = 2-1) and SiO(J = 2-1), achieving angular resolutions of between 2 and 4 . To improve the quality of the CO(2-1) images, we added singledish data to the interferometer visibilities.Results. The outflow consists of two distinct components. At velocities of <10 km s −1 , the gas forms two opposed, approximately conical shells that have the YSO at their vertex. These shells coincide with the walls of evacuated cavities and appear to result from the acceleration of the ambient gas by a wide-angle wind. At velocities of >30 km s −1 , the gas forms two opposed jets that travel along the center of the cavities and whose emission is dominated by a symmetric collection of at least 7 pairs of peaks. The velocity field of this component presents a sawtooth pattern with the gas in the tail of each peak moving more rapidly than the gas at its head. This pattern and a systematic widening of the peaks with distance from the central source are consistent with the emission arising from internal working surfaces traveling along the jet due to variations in the velocity field of ejection. We interpret this component to be the true protostellar wind, and find its composition to be consistent with a chemical model of this wind. Conclusions. Our results favor outflow wind models that have simultaneously wide-angle and narrow components, and suggest that the EHV peaks observed in a number of outflows consist of internally-shocked wind material.

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High-resolution images of the L1551 bipolar outflow - Evidence for an expanding, accelerated shell

Cited by 40 publications

References 0 publications

A molecular survey of outflow gas: velocity-dependent shock chemistry and the peculiar composition of the EHV gas

A molecular survey of outflow gas: velocity-dependent shock chemistry and the peculiar composition of the EHV gas

Determination of molecular gas properties using methyl cyanide lines

Shells, jets, and internal working surfaces in the molecular outflow from IRAS 04166+2706

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