Near-infrared, IFU spectroscopy unravels the bow-shock HH99B ^*,**

¹ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy e-mail: [giannini;nisini;calzol]@oa-roma.inaf.it
² Università di Cagliari, via Università 40, 09124 Cagliari, Italy
³ Joint Astronomy Centre, 660 North A'ohk Place, University Park, Hilo, HI 96720, USA e-mail: c.davis@jach.hawaii.edu
⁴ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany e-mail: jochen@tls-tautenburg.de
⁵ Centre for Astrophysics & Planetary Science, School of Physical Sciences, The University of Kent, Canterbury CT2 7NR, UK e-mail: m.d.smith@kent.ac.uk

Received: 23 October 2007
Accepted: 21 December 2007

Abstract

Aims.We aim at characterising the morphology and the physical parameters governing the shock physics of the Herbig-Haro object HH99B. We obtained SINFONI-SPIFFI IFU spectroscopy (R ~ 2000-4000) between 1.10 and 2.45 μm detecting more than 170 emission lines, that, to a large extent, have never observed before in a Herbig-Haro object. Most of them come from ro-vibrational transitions of molecular hydrogen (v_up ≤ 7, E_up  38 000 K) and [] (E_up  30 000 K). In addition, we observed several hydrogen and helium recombination lines, along with fine-structure lines of ionic species. All the brightest lines appear resolved in velocity.

Methods.Intensity ratios of ionic lines were compared with predictions of NLTE models to derive bi-dimensional maps of extinction and electron density, along with estimates of temperature, fractional ionisation, and atomic hydrogen post-shock density. The H₂ line intensities were interpreted in the framework of Boltzmann diagrams, from which we have derived extinction and temperature maps of the molecular gas. From the intensity maps of bright lines (i.e. H₂ 2.122 μm and []1.644 μm), the kinematical properties of the shock(s) at work in the region were delineated. Finally, from selected [] lines, constraints on the spontaneous emission coefficients of the 1.257, 1.321, and 1.644 μm lines are provided.

Results.Visual extinction variations up to 4 mag emerge, showing that the usual assumption of constant extinction could be critical. The highest A_V is found at the bowhead (A_V ~ 4 mag) while diminishing along the flanks. The electron density increases from ~3  10³ cm^-3 in the receding parts of the shock to ~6  10³ cm^-3 in the apex, where we estimate a temperature of ~16 000 K from [] line ratios. Molecular gas temperature is lower in the bow flanks ( 3000 K), then progressively increases toward the head up to 6000 K. In the same zone, we are able to derive the iron gas-phase abundance (~60% of the solar value) from the []1.257/[]1.187 line ratio, along with the hydrogen fractional ionisation (up to 50% at the bowhead) and the atomic hydrogen post-shock gas density (~1  10⁴ cm^-3). The kinematical properties derived for the molecular gas substantially confirm earlier ones, while new information (e.g. v_shock ~ 115 km s^-1) is provided for the shock component responsible for the ionic emission. We also provide an indirect measure of the H₂ breakdown speed (between 70 and 90 km s^-1) and compute the inclination angle with respect to the line of sight. The map parameters, along with images of the observed line intensities, will be used to put stringent constraints on up-to-date shock models.