Water is a key molecule for determining the physical and chemical structure of star-forming regions because of its large abundance variations --both in the gas and in the ice-- between warm and cold regions. In this HIFI-led Key Program, we propose a comprehensive set of water observations toward a large sample of well-characterized protostars, covering a wide range of masses and luminosities -- from the lowest to the highest mass protostars -- and a large range of evolutionary stages -- from the first stages represented by the pre-stellar cores to the last stages represented by the pre-main sequence stars surrounded only by their protostellar disks. Lines of H2O, H218O, H217O and chemically related hydrides will be observed. In addition, selected high-frequency lines of CO isotopes, [O I] as well as dust continuum maps will be obtained with HIFI and PACS, and will be complemented by ground-based HDO, CO and continuum maps to ensure a self-consistent data set for analysis. Limited mapping information on arcmin scale provides information on local variations due to outflows and clustered star formation. Together, the data will elucidate the physical processes responsible for the warm gas, probe dynamical processes associated with forming stars and planets, reveal the chemical evolution of water and the oxygen-reservoir, and test basic gas-grain chemical interactions. They will form an unique legacy for the community as a complement to future ground-based programs and for planning future space missions.
Publication
Water in star-forming regions with Herschel (WISH). III. Far-infrared cooling lines in low-mass young stellar objects . Karska A. et al. . Astronomy & Astrophysics, Volume 552, id.A141, 48 . 552 . 10.1051/0004-6361/201220028 . 2013A&A...552A.141K , OH far-infrared emission from low- and intermediate-mass protostars surveyed with Herschel-PACS . Wampfler S. F. et al. . Astronomy & Astrophysics, Volume 552, id.A56, 45 pp. . 552 . 10.1051/0004-6361/201219929 . 2013A&A...552A..56W , Origin of the hot gas in low-mass protostars. Herschel-PACS spectroscopy of HH 46 . van Kempen T. A. et al. . Astronomy and Astrophysics, Volume 518, id.L121, 6 pp. . 518 . 10.1051/0004-6361/201014615 . 2010A&A...518L.121V , Herschel observations of the hydroxyl radical (OH) in young stellar objects . Wampfler S. F. et al. . Astronomy and Astrophysics, Volume 521, id.L36, 6 pp. . 521 . 10.1051/0004-6361/201015112 . 2010A&A...521L..36W , The Herschel-PACS Legacy of Low-mass Protostars: The Properties of Warm and Hot Gas Components and Their Origin in Far-UV Illuminated Shocks . Karska Agata et al. . The Astrophysical Journal Supplement Series, Volume 235, Issue 2, article id. 30, 45 pp. (2018). . 235 . 10.3847/1538-4365/aaaec5 . 2018ApJS..235...30K , Modelling Herschel observations of hot molecular gas emission from embedded low-mass protostars . Visser R. et al. . Astronomy & Astrophysics, Volume 537, id.A55, 19 pp. . 537 . 10.1051/0004-6361/201117109 . 2012A&A...537A..55V , The Warm CO Gas along ...the UV-heated Outflow Cavity Walls: A Possible Interpretation for the Herschel-PACS CO Spectra of Embedded YSOs . Lee Seokho et al. . The Astrophysical Journal Supplement Series, Volume 217, Issue 2, article id. 30, 16 pp. (2015). . 217 . 10.1088/0067-0049/217/2/30 . 2015ApJS..217...30L , Water in star-forming regions: physics and chemistry from clouds to disks as probed by Herschel spectroscopy . van Dishoeck E. F. et al. . Astronomy and Astrophysics . null . null . 2021A&A...648A..24V , A Photon-dominated Region Model for the FIR Mid-J CO Ladder with Universal Rotational Temperature in Star Forming Regions . Lee Seokho et al. . The Astrophysical Journal Supplement, Volume 213, Issue 2, article id. 33, 23 pp. (2014). . 213 . 10.1088/0067-0049/213/2/33 . 2014ApJS..213...33L , Water in Star-forming Regions with the Herschel Space Observatory (WISH). I. Overview of Key Program and First Results . van Dishoeck E. F. et al. . Publications of the Astronomical Society of the Pacific, Volume 123, Issue 900, pp. 138 (2011). . 123 . 10.1086/658676 . 2011PASP..123..138V ,
Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
