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.
WISH: WATER IN STAR-FORMING REGIONS WITH HERSCHEL
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.
HS3F: HERSCHEL SPECTRAL SURVEYS OF STAR FORMATION REGIONS
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
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.