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IRS Scan-mapping of the Wasp-waist Nebula (IRAS 16253–2429). I. Derivation of Shock Conditions from H_2 Emission and Discovery of 11.3 μm PAH Absorption

Barsony, Mary and Wolf-Chase, Grace A. and Ciardi, David R. and O'Linger, JoAnn (2010) IRS Scan-mapping of the Wasp-waist Nebula (IRAS 16253–2429). I. Derivation of Shock Conditions from H_2 Emission and Discovery of 11.3 μm PAH Absorption. Astrophysical Journal, 720 (1). pp. 64-86. ISSN 0004-637X.

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The outflow driven by the Class 0 protostar, IRAS 16253–2429, is associated with bipolar cavities visible in scattered mid-infrared light, which we refer to as the Wasp-Waist Nebula. InfraRed Spectometer (IRS) scan mapping with the Spitzer Space Telescope of a ~1' × 2' area centered on the protostar was carried out. The outflow is imaged in six pure rotational (0-0 S(2) through 0-0 S(7)) H_2 lines, revealing a distinct, S-shaped morphology in all maps. A source map in the 11.3 μm polycyclic aromatic hydrocarbon (PAH) feature is presented in which the protostellar envelope appears in absorption. This is the first detection of absorption in the 11.3 μm PAH feature. Spatially resolved excitation analysis of positions in the blue- and redshifted outflow lobes, with extinction-corrections determined from archival Spitzer 8 μm imaging, shows remarkably constant temperatures of ~1000 K in the shocked gas. The radiated luminosity in the observed H_2 transitions is found to be 1.94 ± 0.05 × 10^(–5) L_⊙ in the redshifted lobe and 1.86 ± 0.04 × 10^(–5) L_⊙ in the blueshifted lobe. These values are comparable to the mechanical luminosity of the flow. By contrast, the mass of hot (T ~ 1000 K) H_2 gas is 7.95 ± 0.19 × 10^(–7) M_⊙ in the redshifted lobe and 5.78 ± 0.17 × 10^(–7) M_⊙ in the blueshifted lobe. This is just a tiny fraction, of order 10^(–3), of the gas in the cold (30 K), swept-up gas mass derived from millimeter CO observations. The H_2 ortho/para ratio of 3:1 found at all mapped points in this flow suggests previous passages of shocks through the gas. Comparison of the H_2 data with detailed shock models of Wilgenbus et al. shows the emitting gas is passing through Jump (J-type) shocks. Pre-shock densities of 10^4 cm^(–3)≤ n _H ≤ 10^5 cm^(–3) are inferred for the redshifted lobe and n _H ≤ 10^3 cm^(–3) for the blueshifted lobe. Shock velocities are 5 km s^(–1) ≤ v_s ≤ 10 km s^(–1) for the redshifted gas and v_s = 10 km s^(–1) for the blueshifted gas. Initial transverse (to the shock) magnetic field strengths for the redshifted lobe are in the range 10-32 μG, and just 3 μG for the blueshifted lobe. A cookbook for using the CUBISM contributed software for IRS spectral mapping data is presented in the Appendix.

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Ciardi, David R.0000-0002-5741-3047
Additional Information:© 2010 The American Astronomical Society. Received 2010 February 24; accepted 2010 June 30; published 2010 August 5. We are grateful to the scientific team that contributed to the successful Spitzer GO Cycle 3 proposal leading to the observations reported here, in alphabetical order: Hector Arce, David Cole, Angela Cotera, Adam Frank, Dirk Froebrich, Alyssa Goodman, Karl Haisch, Jr., Robert Hurt, Gerald Moriarty- Schieven, Randy Phelps, Mike Ressler, Raghvendra Sahai, Janet Simpson, M. D. Smith, and Jason Ybarra, and to Sean Carey who first suggested this project. We thank Tom Jarrett and Phil Appleton who advised us on data-taking strategy in order to avoid chip saturation through the peak-up arrays by the high zodiacal background toward our target. We also thank the Spitzer Science Center staff who took the data and developed the IRS data reduction pipeline. We especially thank the SSC teams that put on the Data Reduction Workshops and peopled the Help Desk. J. D. Smith and the team who provided the contributed CUBISM software are gratefully acknowledged. We are indebted to Patricia Monger and Robert Lupton, who have provided the SM plotting software and its documentation. This research has made use of SAOImage DS9, developed by Smithsonian Astrophysical Observatory; of NASA’s Astrophysics Data System (ADS) bibliographic services, and of the SIMBAD database, operated at CDS, Strasbourg, France. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. G.W.-C. and M.B. thank the Brinson Foundation for generous travel support necessary for the completion of this project and for providing funds to help cover publication costs. The anonymous referee whose suggestions improved the paper enormously is gratefully acknowledged.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:infrared: ISM; ISM: jets and outflows; ISM: magnetic fields; stars: formation; stars: individual (IRAS 16253–2429); stars: protostars
Issue or Number:1
Classification Code:PACS: 97.21.+a; 98.38.Bn; 95.85.Hp; 98.38.Dq; 98.38.Fs
Record Number:CaltechAUTHORS:20100928-112354106
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Official Citation:Mary Barsony et al 2010 ApJ 720 64 doi: 10.1088/0004-637X/720/1/64
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20194
Deposited By: Ruth Sustaita
Deposited On:29 Sep 2010 22:14
Last Modified:03 Oct 2019 02:06

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