Herschel Guaranteed-Time Key Projects
at Arcetri

Arcetri scientists participate in two Herschel guaranteed-time (GT) Key Projects, in collaboration with the instrument consortia. Both regard spectroscopic observations of different classes of star-forming regions in the Galaxy.
    PI: Ewine van Dishoeck (Leiden University, The Netherlands)
    (OAA CoI's: Claudio Codella)

    Water is one of the most abundant and important molecules in star-forming regions, It becames the third most abundant species in the warm regions created by the presence of newly-formed stars: the inner protostellar envelopes where the dust is warmer than the ice evaporation temperature, and the regions where the collapsing matter interacts with the powerful jets from the protostar causing violent shocks. This enormous variation in abundance makes water a unique probe of the physical structure of the region, and of the fundamental chemical processes within the gas and between the gas and the grains. Water also plays an active role in the energy balance of the envelope. In all of these physical and chemical aspects, water provides highly complementary information to that derived from the commonly studied CO molecule.

    In this Herschel HIFI-led Key Program, we propose a comprehensive set of water observations towards a large sample of 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, H2 18O and the chemically related species O, OH, OH+ and H3 O+ will be observed. In addition, selected high-frequency lines of CO and 13 CO as well as dust continuum maps will be obtained with Herschel, and will be complemented by ground-based HDO, CO and continuum maps to ensure a self-consistent data set for analysis. The HIFI instrument will be used for the bulk of the time, but PACS spectroscopy will be added as well.

    (See WISH Homepage ).

    PI: C. Ceccarelli (Laboratoire d'astrophysique de Grenoble, France)
    (OAA CoI's: Claudio Codella, Andrea Lorenzani)

    The study of the molecular content of dense regions of the interstellar medium (ISM) has evolved enormously during the last few decades. It started with the detection of simple diatomic molecules, grew up with pioneer searches of polyatomic molecules, and today it has become a fully recognized discipline called Astrochemistry. The goals and the motivations matured and deepened: nowadays, one major goal of Astrochemistry is to obtain the most accurate census possible of the molecular content and complexity in some of the chemically richest regions of our Universe: the Star Forming Regions.

    The chemical composition of the matter and how it evolves with time have a strong influence on the evolution of the forming star. Indeed, the dynamics of the collapse is regulated by the mass of the collapsing matter, but also by its thermal status and the interaction of the matter with the magnetic field, both counteracting the gravitational force. Since gas cools mostly by line emission, knowing what molecules are formed and which lines are emitted in the different regions at different times is mandatory to understand the gas thermal balance.

    When observed at high resolution, lines are the only means to study the complex kinematic structure of Star Forming Regions, where infall and outflow motions are simultaneously present. Specific lines from specific species can probe different regions and, therefore, allow to reconstruct not only the physical structure but also the dynamical structure of the region.

    In the era of the molecular content census, unbiased surveys with high spectral resolution (~ 105 or more) in the radio to infrared spectral range, of Star Forming Regions are fundamental and essential tools. The frequency range covered by HSO-HIFI, 500-2000 GHz, is of particular relevance. In fact, given the temperatures involved, many molecular species abundant or particularly important in Star Forming Regions have transitions in the 500-2000 GHz range. Notably, light molecules like hydrides (a notable example is H2O), have ground transitions in this spectral range, while heavier molecules (notably CO) have high lying transitions. Hence, lines from the former can probe cold and warm gas, whereas lines from the latter probe the warm gas. Ideally, one would like to have the line spectrum in the 500-2000 GHz range in a large sample of objects, probing a large parameter space in the evolutionary state and mass. Comparison of the different spectra would very likely answer most of the questions still open about star formation. In practice, however, one can aim to obtain spectra in a relatively small, but well--selected sample of sources, representing the most important classes of star forming objects. These template spectra will guide follow-up studies in a large sample, constituting, therefore, a dataset of high archival value.

    (See HS3F Homepage ).


INAF - Osservatorio Astrofisico di Arcetri

Largo E. Fermi, 5 - 50125 Firenze
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