Spatially resolved near-infrared spectroscopy of the massive star-forming region IRAS 19410+2336

¹ Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Spain e-mail: leticia@iac.es
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁴ Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Serrano 121, 29006 Madrid, Spain
⁵ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁶ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile


Received: 6 June 2008
Accepted: 24 July 2008

Abstract

Aims. IRAS 19410+2336 is a young massive star forming region with an intense outflow activity. Outflows are frequently studied in the near-infrared (NIR) since the H₂ emission in this wavelength range often traces the shocked molecular gas. However, the mechanisms behind the H₂ emission detected in IRAS 19410+2336 have not been clarified yet. We present here spatially resolved NIR spectroscopy which allows us to verify whether the H₂ emission originates from thermal emission in shock fronts or from fluorescence excitation by non-ionizing UV photons. Moreover, NIR spectroscopy also offers the possibility of studying the characteristics of the putative driving source(s) of the H₂ emission by the detection of photospheric and circumstellar spectral features, and of the environmental conditions (e.g. extinction).

Methods. We obtained long-slit, intermediate-resolution, NIR spectra of IRAS 19410+2336 using LIRIS, the NIR imager/spectrographer mounted on the 4.2 m William Herschel Telescope. As a complement, we also obtained J, H and K_s images with the Las Campanas 2.5 m Du Pont Telescope, and archival mid-infrared (MIR) Spitzer images at 3.6, 4.5, 5.8 and 8.0 μm.

Results. We confirm the shocked nature of the H₂ emission, with an excitation temperature of about 2000 K, based on the analysis of relevant H₂ line ratios, ortho-to-para ratios and excitation diagrams. We have also identified objects with very different properties and evolutionary stages in IRAS 19410+2336. The most massive source at millimeter wavelengths, mm1, with a mass of a few tens of solar masses, has a bright NIR (and MIR) counterpart. This suggests that emission – probably coming through a cavity created by one of the outflows present in the region, or from the outflow cavity itself – is leaking at these wavelengths. The second most massive millimeter source, mm2, is only detected at 6 μm, suggesting that it could be a high-mass protostar still in its main accretion phase. The NIR spectra of some neighboring sources show CO first-overtone bandhead emission which is associated with neutral material located in the inner regions of the circumstellar environment of YSOs.