6 research outputs found
X-ray Chemistry in the Envelopes around Young Stellar Objects
We have studied the influence of X-rays from a massive young stellar object
(YSO) on the chemistry of its own envelope by extending the models of Doty et
al. (2002) and Staeuber et al. (2004). The models are applied to the massive
star-forming region AFGL 2591 for different X-ray luminosities and plasma
temperatures. Enhanced column densities for several species are predicted. In
addition we present first detections of CO+ and SO+ toward AFGL 2591. These
molecular ions are believed to be high-energy tracers. Herschel-HIFI will be
able to observe other tracers like CH and CH+ whereas ALMA is well suited to
measure the size and geometry of the emitting region.Comment: To appear in "The Dusty and Molecular Universe: A Prelude to Herschel
and ALMA", Eds.: A. Wilson. To be published in ESA Conference Serie
Hydrides in Young Stellar Objects: Radiation tracers in a protostar-disk-outflow system
Context: Hydrides of the most abundant heavier elements are fundamental
molecules in cosmic chemistry. Some of them trace gas irradiated by UV or
X-rays. Aims: We explore the abundances of major hydrides in W3 IRS5, a
prototypical region of high-mass star formation. Methods: W3 IRS5 was observed
by HIFI on the Herschel Space Observatory with deep integration (about 2500 s)
in 8 spectral regions. Results: The target lines including CH, NH, H3O+, and
the new molecules SH+, H2O+, and OH+ are detected. The H2O+ and OH+ J=1-0 lines
are found mostly in absorption, but also appear to exhibit weak emission
(P-Cyg-like). Emission requires high density, thus originates most likely near
the protostar. This is corroborated by the absence of line shifts relative to
the young stellar object (YSO). In addition, H2O+ and OH+ also contain strong
absorption components at a velocity shifted relative to W3 IRS5, which are
attributed to foreground clouds. Conclusions: The molecular column densities
derived from observations correlate well with the predictions of a model that
assumes the main emission region is in outflow walls, heated and irradiated by
protostellar UV radiation.Comment: Astronomy and Astrophysics Letters, in pres
Water in Star-Forming Regions with the Herschel Space Observatory (WISH): Overview of key program and first results
`Water In Star-forming regions with Herschel' (WISH) is a key program on the
Herschel Space Observatory designed to probe the physical and chemical
structure of young stellar objects using water and related molecules and to
follow the water abundance from collapsing clouds to planet-forming disks.
About 80 sources are targeted covering a wide range of luminosities and
evolutionary stages, from cold pre-stellar cores to warm protostellar envelopes
and outflows to disks around young stars. Both the HIFI and PACS instruments
are used to observe a variety of lines of H2O, H218O and chemically related
species. An overview of the scientific motivation and observational strategy of
the program is given together with the modeling approach and analysis tools
that have been developed. Initial science results are presented. These include
a lack of water in cold gas at abundances that are lower than most predictions,
strong water emission from shocks in protostellar environments, the importance
of UV radiation in heating the gas along outflow walls across the full range of
luminosities, and surprisingly widespread detection of the chemically related
hydrides OH+ and H2O+ in outflows and foreground gas. Quantitative estimates of
the energy budget indicate that H2O is generally not the dominant coolant in
the warm dense gas associated with protostars. Very deep limits on the cold
gaseous water reservoir in the outer regions of protoplanetary disks are
obtained which have profound implications for our understanding of grain growth
and mixing in disks.Comment: 71 pages, 10 figures, PASP, in pres
Über die Aktivität von Reagenzien zur Thromboplastinzeit-Bestimmung (Quick-Wert) verschiedener Hersteller bei Konzentrationsveränderungen einzelner Gerinnungsfaktoren
Water in star-forming regions with the Herschel Space Observatory (WISH). I. Overview of key program and first results
Water In Star-forming regions with Herschel (WISH) is a key program on the Herschel Space Observatory designed to probe the physical and chemical structures of young stellar objects using water and related molecules and to follow the water abundance from collapsing clouds to planet-forming disks. About 80 sources are targeted, covering a wide range of luminosities—from low (105 L⊙)—and a wide range of evolutionary stages—from cold prestellar cores to warm protostellar envelopes and outflows to disks around young stars. Both the HIFI and PACS instruments are used to observe a variety of lines of H2O, H218O and chemically related species at the source position and in small maps around the protostars and selected outflow positions. In addition, high-frequency lines of CO, 13CO, and C18O are obtained with Herschel and are complemented by ground-based observations of dust continuum, HDO, CO and its isotopologs, and other molecules to ensure a self-consistent data set for analysis. An overview of the scientific motivation and observational strategy of the program is given, together with the modeling approach and analysis tools that have been developed. Initial science results are presented. These include a lack of water in cold gas at abundances that are lower than most predictions, strong water emission from shocks in protostellar environments, the importance of UV radiation in heating the gas along outflow walls across the full range of luminosities, and surprisingly widespread detection of the chemically related hydrides OH+ and H2O+ in outflows and foreground gas. Quantitative estimates of the energy budget indicate that H2O is generally not the dominant coolant in the warm dense gas associated with protostars. Very deep limits on the cold gaseous water reservoir in the outer regions of protoplanetary disks are obtained that have profound implications for our understanding of grain growth and mixing in disks