Observational evidence for dissociative shocks in the inner 100 AU of low-mass protostars using Herschel-HIFI

被引：35

作者：

Kristensen, L. E. ^{[1
,2
]}

van Dishoeck, E. F. ^{[1
,3
]}

Benz, A. O. ^{[4
]}

Bruderer, S. ^{[3
]}

Visser, R. ^{[5
]}

Wampfler, S. F. ^{[6
,7
]}

机构：

[1] Leiden Univ, Leiden Observ, NL-2300 RA Leiden, Netherlands

[2] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA

[3] Max Planck Inst Extraterr Phys, D-85748 Garching, Germany

[4] ETH, Inst Astron, CH-8093 Zurich, Switzerland

[5] Univ Michigan, Dept Astron, Ann Arbor, MI 48109 USA

[6] Univ Copenhagen, Nat Hist Museum Denmark, Ctr Star & Planet Format, DK-1350 Copenhagen K, Denmark

[7] Univ Copenhagen, Niels Bohr Inst, DK-2100 Copenhagen O, Denmark

来源：

ASTRONOMY & ASTROPHYSICS | 2013年 / 557卷

关键词：

astrochemistry; stars: formation; ISM: molecules; ISM: jets and outflows; YOUNG STELLAR OBJECTS; STAR-FORMING REGIONS; J CO OBSERVATIONS; NGC; 1333; SUBMILLIMETER ARRAY; EMBEDDED PROTOSTARS; PACS SPECTROSCOPY; LINE SPECTRA; KEY PROGRAM; HH; 46;

D O I：

10.1051/0004-6361/201321619

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

Aims. Herschel-HIFI spectra of H2O towards low-mass protostars show a distinct velocity component not seen in observations from the ground of CO or other species. The aim is to characterise this component in terms of excitation conditions and physical origin. Methods. A velocity component with an offset of similar to 10 km s(-1) detected in spectra of the H2O 1(10)-1(01) 557 GHz transition towards six low-mass protostars in the "Water in star-forming regions with Herschel" (WISH) programme is also seen in higher-excited H2O lines. The emission from this component is quantified and local excitation conditions are inferred using 1D slab models. Data are compared to observations of hydrides (high-J CO, OH+, CH+, C+, OH) where the same component is uniquely detected. Results. The velocity component is detected in all six targeted H2O transitions (E-up similar to 50-250 K), as well as in CO 16-15 towards one source, Ser SMM1. Inferred excitation conditions imply that the emission arises in dense (n similar to 5 x 10(6)-10(8) cm(-3)) and hot (T similar to 750 K) gas. The H2O and CO column densities are greater than or similar to 10(16) and 10(18) cm(-2), respectively, implying a low H2O abundance of similar to 10(-2) with respect to CO. The high column densities of ions such as OH+ and CH+ (both greater than or similar to 10(13) cm(-2)) indicate an origin close to the protostar where the UV field is strong enough that these species are abundant. The estimated radius of the emitting region is 100 AU. This component likely arises in dissociative shocks close to the protostar, an interpretation corroborated by a comparison with models of such shocks. Furthermore, one of the sources, IRAS 4A, shows temporal variability in the offset component over a period of two years which is expected from shocks in dense media. High-J CO gas detected with Herschel-PACS with T-rot similar to 700 K is identified as arising in the same component and traces the part of the shock where H-2 reforms. Thus, H2O reveals new dynamical components, even on small spatial scales in low-mass protostars.

引用

页数：13

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