L71 The Astrophysical Journal, 521:L71–L74, 1999 August 10  1999. The American Astronomical Society. All rights reserved. Printed in U.S.A. DETECTION OF THE 62 MICRON CRYSTALLINE H 2 O ICE FEATURE IN EMISSION TOWARD HH 7 WITH THE INFRARED SPACE OBSERVATORY LONG-WAVELENGTH SPECTROMETER 1 Sergio Molinari, 2 Cecilia Ceccarelli, 3 Glenn J. White, 4 Paolo Saraceno, 5 Brunella Nisini, 6 Teresa Giannini, 6 and Emmanuel Caux 7 Received 1999 April 27; accepted 1999 June 9; published 1999 June 25 ABSTRACT We report the detection of the 62 mm feature of crystalline water ice in emission toward the bow-shaped Herbig-Haro object HH 7. Significant amounts of far-infrared continuum emission are also detected between 10 and 200 mm, so that Herbig-Haro objects cease to be pure emission-line objects at far-infrared wavelengths. The formation of crystalline water ice mantles requires grain temperatures K at the time of mantle formation, T  100 gr suggesting that we are seeing material processed by the HH 7 shock front. The deduced ice mass is ∼2 # M , , corresponding to a water column density N(H 2 O cm -2 ; an estimate of the [H 2 O]/[H] abundance -5 18 10 ) ∼ 10 yields values close to the interstellar gas-phase oxygen abundance. The relatively high dust temperature and the copious amounts of gas-phase water needed to produce the observed quantity of crystalline water ice suggest a scenario in which both dissociative and nondissociative shocks coexist. The timescale for ice mantle formation is of the order of ∼400 yr, so that the importance of gas-phase water cooling as a shock diagnostic may be greatly diminished. Subject headings: dust, extinction — infrared: ISM: continuum — infrared: ISM: lines and bands — ISM: Herbig-Haro objects — ISM: individual (HH 7) — ISM: lines and bands 1. INTRODUCTION Herbig-Haro (HH) objects (Haro 1950; Herbig 1951) are emission-line objects acting as signposts for the shock regions (Draine, Roberge, & Dalgarno 1983; Hollenbach & McKee 1989) originating at the interface between stellar winds accel- erated by young stellar objects and the circumstellar or cloud ambient material. The temperature of dust grains in these shock regions can rise to only a few hundred degrees at most in dissociative shocks (Hollenbach & McKee 1989), so that their thermal emission cannot be detected below 10 mm. The instruments on board the Infrared Space Observatory (ISO) satellite (Kessler et al. 1996) opened unprecedented pos- sibilities for far-infrared continuum studies of cold objects, in- cluding HH objects. In this Letter we present the data obtained with the Long- (LWS; Clegg et al. 1996) and Short-Wavelength Spectrometer (SWS; de Graauw et al. 1996) toward HH 7, the leading bow-shaped shock of the HH 7–11 chain emanating from the young stellar object SVS 13, in the star-forming region NGC 1333 in Perseus ( pc). Details about the obser- d = 350 vations and data reduction are given elsewhere (Molinari et al. 1999). In § 2 the additional data analysis procedures we adopted to derive a reliable continuum spectrum for HH 7 are discussed. Nomenclature for the 10 LWS detectors is described in the ISO 1 Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands, and the United Kingdom) with the participation of ISAS and NASA. 2 Infrared Processing and Analysis Center, California Institute of Technol- ogy, MS 100-22, Pasadena, CA 91125. 3 Laboratoire d’Astrophysique, Observatoire de Grenoble-BP 53, F-38041 Grenoble Cedex 09, France. 4 Department of Physics, Queen Mary and Westfield College, University of London, Mile End Road, London E1 4NS, UK; Stockholm Observatory, Salts- jo¨sbaden, Sweden. 5 CNR-Istituto di Fisica dello Spazio Interplanetario, Area di Ricerca Tor Vergata, via Fosso del Cavaliere I-00133 Roma, Italy. 6 Osservatorio Astronomico di Roma, via Frascati 33, I-00044 Monte Porzio, Italy. 7 CESR CNRS-UPS, BP 4346, F-31028 Toulouse Cedex 04, France. Data User Manual; 8 detectors SW1 to SW5 (43–90 mm) and LW1 to LW5 (80–197 mm) are sometimes referred to as “short” (SW) and “long” wavelength (LW) detectors, respectively. 2. RESULTS The LWS beam centered on HH 7 also includes object HH 8 somewhat 20 off-axis and HH 10 at the edge of the beam; these objects are, however, fainter than HH 7 at 2 mm (Molinari et al. 1999), and the beam profile suppresses their possible contribution even more. Apart from a contamination by the strong nearby source SVS 13, which will be discussed in detail in § 2.2, it is plausible to assume that HH 7 dominates the observed spectrum. 2.1. The 62 mm Feature In Figure 1 the complete spectra observed toward HH 7 and SVS 13 are shown. A broad feature extending from roughly 50 to 70 mm is clearly visible in the HH 7 spectrum. For clarity, the SW3 detector spectrum, with an offset applied to align it with the continuum of the adjacent detectors, is shown with plus signs. The primary concern was to make sure that the 50–70 mm feature was not a result of a residual instrumental effect and that it is intrinsic to HH 7. The passband calibration is known to be somewhat inaccurate for detector SW1 (it may be worse than 50% both in absolute and relative terms), which is the most sensitive to transients. Detectors SW2, SW3, and SW4, however, are stable in relative (passband) terms, and a conservative figure of 30% can be assumed for their absolute calibration accuracy. The possibility that the broad feature vis- ible on Figure 1 may be due to the near-IR leaks present in the LWS detectors filters 9 can also be excluded. Finally, this feature might result from contamination effects from the bright nearby source SVS 13, which is the candidate exciting source 8 Available at http://www.iso.vilspa.esa.es/manuals/lws_idum5. 9 Additional information is available at http://isowww.estec.esa.nl/notes/ lws_0197.html.