The first results from the Herschel-HIFI mission

This paper contains a summary of the results from the first years of observations with the HIFI instrument onboard ESA's Herschel space observatory. The paper starts by outlining the goals and possibilities of far-infrared and submillimeter astronomy, the limitations of the Earth's atmosphere, and the scientific scope of the Herschel-HIFI mission. The presentation of science results from the mission follows the life cycle of gas in galaxies as grouped into five themes: Structure of the interstellar medium, First steps in interstellar chemistry, Formation of stars and planets, Solar system results and Evolved stellar envelopes. The HIFI observations paint a picture where the interstellar medium in galaxies has a mixed, rather than a layered structure; the same conclusion may hold for protoplanetary disks. In addition, the HIFI data show that exchange of matter between comets and asteroids with planets and moons plays a large role. The paper concludes with an outlook to future instrumentation in the far-infrared and submillimeter wavelength ranges.Comment: Invited review paper to appear in Advances of Space Research; 32 pages, 9 figures. See http://www.sron.rug.nl/~vdtak/adspres.pdf for a 14-page journal-style versio

Recent Astrochemical Results on Star-Forming Regions

This review discusses recent results on the astrochemistry of (mostly high-mass) star-forming regions. After an introduction on the use of chemistry in astrophysics and some basic concepts of astrochemistry, specific results are presented. Highlighted areas are the use of chemistry in the search for massive circumstellar disks, the interaction of molecular clouds with cosmic rays, and the feedback effects of protostellar irradiation on the parent molecular cloud. The review concludes with a discussion of future observational opportunities.Comment: Contribution to proceedings of conference "Massive Star Formation: Observations confront Theory" (Heidelberg 2007); 8 DIN A4 pages. Version 2: some references adde

Star & planet formation: Upcoming opportunities in the space-based infrared

While ALMA and JWST are revolutionizing our view of star and planet formation with their unprecedented sensitivity and resolution at submillimeter and near-IR wavelengths, many outstanding questions can only be answered with observations in the thermal (mid- and far-) infrared domain. Many of these questions require space-based observations, to achieve the necessary sensitivity and/or wavelength coverage. In particular, how do interstellar clouds develop filamentary structures and dense cores? What are the masses and luminosities of objects at the earliest stages of star formation? What are the gas masses of planet-forming disks, and how do these disks disperse during planet formation? How is refractory and volatile material distributed within the disks, and how does this evolve with time? This article reviews how upcoming and planned balloon-borne and space-based telescopes for the mid- and far-infrared will address these questions, and outlines which further missions will be needed beyond 2030, when the ELTs will be in full operation.Comment: Contribution to the proceedings of the 7th Chile-Cologne-Bonn symposium: Physics and Chemistry of Star Formation; 5 pages. Version 2 includes useful comments on the original version; version 3 includes further comment

Limits on the cosmic-ray ionization rate toward massive young stars

Recent models of the envelopes of seven massive protostars are used to analyze observations of H3+ infrared absorption and H13CO+ submillimeter emission lines toward these stars, and to constrain the cosmic-ray ionization rate zeta. The H13CO+ gives best-fit values of zeta=(2.6+/- 1.8) x 10^-17 s^-1, in good agreement with diffuse cloud models and with recent Voyager/Pioneer data but factors of up to 7 lower than found from the H3+ data. No relation of zeta with luminosity or total column density is found, so that local (X-ray) ionization and shielding against cosmic rays appear unimportant for these sources. The difference between the H3+ and H13CO+ results and the correlation of N(H3+) with heliocentric distance suggest that intervening clouds contribute significantly to the H3+ absorptions in the more distant regions. The most likely absorbers are low-density (<~10^4 cm^-3) clouds with most carbon in neutral form or in CO.Comment: To be published in A&A 358 (Letters); 4 pages including 3 figure

Observations and models of the embedded phase of high-mass star formation

This paper is a review and an update on recent work on the physical and chemical structure of the envelopes of newly born massive stars, at the stages preceding ultracompact H II regions. It discusses methods and results to determine total mass, temperature and density structure, ionization rate, and depth-dependent chemical composition.Comment: 8 pages incl 4 figures, to appear in "Hot Star Workshop III: The Earliest Phases of Massive Star Birth" (ed. P.A. Crowther) (ASP). Uses newpasp.sty (included

The chemistry of high-mass star formation

This paper reviews the chemistry of star-forming regions, with an emphasis on the formation of high-mass stars. We first outline the basic molecular processes in dense clouds, their implementation in chemical models, and techniques to measure molecular abundances. Then, recent observational, theoretical and laboratory developments are reviewed on the subjects of hot molecular cores, cosmic-ray ionization, depletion and deuteration, and oxygen chemistry. The paper concludes with a summary of outstanding problems and future opportunities.Comment: 10 A4 pages, 1 colour figure; invited review, to appear in "Massive Star Birth - A Crossroads of Astrophysics" (CUP), eds. R. Cesaroni, E. Churchwell, M. Felli, and C.M. Walmsle

The ionization rates of galactic nuclei and disks from Herschel/HIFI observations of water and its associated ions

(Abridged) We present Herschel/HIFI spectra of the H2O 1113 GHz and H2O+ 1115 GHz lines toward five nearby prototypical starburst/AGN systems, and OH+ 971 GHz spectra toward three of these. The beam size of 20" corresponds to resolutions between 0.35 and 7 kpc. The observed line profiles range from pure absorption (NGC 4945, M82) to P-Cygni indicating outflow (NGC 253, Arp 220) and inverse P-Cygni indicating infall (Cen A). The similarity of the H2O, OH+, and H2O+ profiles to each other and to HI indicates that diffuse and dense gas phases are well mixed. We estimate column densities assuming negligible excitation (for absorption features) and using a non-LTE model (for emission features), adopting calculated collision data for H2O and OH+, and rough estimates for H2O+. Column densities range from ~10^13 to ~10^15 cm^-2 for each species, and are similar between absorption and emission components, indicating that the nuclear region does not contribute much to the emission in these ground-state lines. The N(H2O)/N(H2O+) ratios of 1.4-5.6 indicate an origin of the lines in diffuse gas, and the N(OH+)/N(H2O+) ratios of 1.6-3.1 indicate a low H2 fraction (~11%) in the gas. Adopting recent Galactic values for the average gas density and the ionization efficiency, we find ionization rates for our sample galaxies of ~3x10^-16 s^-1 which are similar to the value for the Galactic disk, but ~10x below that of the Galactic Center and ~100x below estimates for AGN from excited-state H3O+ lines. We conclude that the ground-state lines of water and its associated ions probe primarily non-nuclear gas in the disks of these centrally active galaxies. Our data thus provide evidence for a decrease in ionization rate by a factor of ~10 from the nuclei to the disks of galaxies, as found before for the Milky Way.Comment: Accepted for publication in Astronomy & Astrophysics; 8 pages, 8 figure