12 research outputs found
Gas and dust in the star-forming region rho Oph A: II. The gas in the PDR and in the dense cores
We investigate to what degree local physical and chemical conditions are
related to the evolutionary status of various objects in star-forming media.
rho Oph A displays the entire sequence of low-mass star formation in a small
volume of space. Using spectrophotometric line maps of H2, H2O, NH3, N2H+, O2,
OI, CO, and CS, we examine the distribution of the atomic and molecular gas in
this dense molecular core. The physical parameters of these species are
derived, as are their relative abundances in rho Oph A. Using radiative
transfer models, we examine the infall status of the cold dense cores from
their resolved line profiles of the ground state lines of H2O and NH3, where
for the latter no contamination from the VLA 1623 outflow is observed and line
overlap of the hyperfine components is explicitly taken into account. The
stratified structure of this photon dominated region (PDR), seen edge-on, is
clearly displayed. Polycyclic aromatic hydrocarbons (PAHs) and OI are seen
throughout the region around the exciting star S1. At the interface to the
molecular core 0.05 pc away, atomic hydrogen is rapidly converted into H2,
whereas OI protrudes further into the molecular core. This provides oxygen
atoms for the gas-phase formation of O2 in the core SM1, where X(O2)~ 5.e-8.
There, the ratio of the O2 to H2O abundance [X(H2O)~ 5.e-9] is significantly
higher than unity. Away from the core, O2 experiences a dramatic decrease due
to increasing H2O formation. Outside the molecular core, on the far side as
seen from S1, the intense radiation from the 0.5 pc distant early B-type star
HD147889 destroys the molecules. Towards the dark core SM1, the observed
abundance ratio X(O2)/X(H2O)>1, which suggests that this object is extremely
young, which would explain why O2 is such an elusive molecule outside the solar
system.Comment: accepted for publication in Astronomy & Astrophysics (25/08/2017) 20
pages, 17 figure
ALMA Resolves CI Emission from the beta Pictoris Debris Disk
The debris disk around ~Pictoris is known to contain gas. Previous
ALMA observations revealed a CO belt at 85 au with a distinct clump,
interpreted as a location of enhanced gas production. Photodissociation
converts CO into C and O within 50 years. We resolve CI emission at 492
GHz using ALMA and study its spatial distribution. CI shows the same clump as
seen for CO. This is surprising, as C is expected to quickly spread in azimuth.
We derive a low C mass (between and
M), indicating that gas production started only recently (within
5000 years). No evidence is seen for an atomic accretion disk inwards of
the CO belt, perhaps because the gas did not yet have time to spread radially.
The fact that C and CO share the same asymmetry argues against a previously
proposed scenario where the clump is due to an outward migrating planet
trapping planetesimals in an resonance; nor can the observations be explained
by an eccentric planetesimal belt secularly forced by a planet. Instead, we
suggest that the dust and gas disks should be eccentric. Such a configuration,
we further speculate, might be produced by a recent tidal disruption event.
Assuming that the disrupted body has had a CO mass fraction of 10%, its total
mass would be 3 .Comment: 30 pages, 15 figures, accepted by Ap
Darwin -— an experimental astronomy mission to search for extrasolar planets
As a response to ESA call for mission concepts for its Cosmic Vision 2015–2025 plan, we propose a mission called Darwin. Its primary goal is the study of terrestrial extrasolar planets and the search for life on them. In this paper, we describe different characteristics of the instrument
The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI): instrument and pre-launch testing
This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI), to be launched onboard of ESA's Herschel Space Observatory, by 2008. It includes the first results from the instrument level tests. The instrument is designed to be electronically tuneable over a wide and continuous frequency range in the Far Infrared, with velocity resolutions better than 0.1 km/s with a high sensitivity. This will enable detailed investigations of a wide variety of astronomical sources, ranging from solar system objects, star formation regions to nuclei of galaxies. The instrument comprises 5 frequency bands covering 480-1150 GHz with SIS mixers and a sixth dual frequency band, for the 1410-1910 GHz range, with Hot Electron Bolometer Mixers (HEB). The Local Oscillator (LO) subsystem consists of a dedicated Ka-band synthesizer followed by 7 times 2 chains of frequency multipliers, 2 chains for each frequency band. A pair of Auto-Correlators and a pair of Acousto-Optic spectrometers process the two IF signals from the dual-polarization front-ends to provide instantaneous frequency coverage of 4 GHz, with a set of resolutions (140 kHz to 1 MHz), better than < 0.1 km/s. After a successful qualification program, the flight instrument was delivered and entered the testing phase at satellite level. We will also report on the pre-flight test and calibration results together with the expected in-flight performance
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Infrared Space Observatory spectroscopy of HH 7–11 flow and its redshifted counterpart
We have used the two spectrometers on the Infrared Space Observatory to observe the HH 7-11 flow, its redshifted counterpart, and the candidate exciting source SVS 13 in the star formation region NGC 1333. We detect atomic ([O I] 63 μm, [O I] 145 μm, [Si II] 34.8 μm, [C II] 158 μm) and molecular (H2, CO, H2O) lines at various positions along the bipolar flow. Most of the observed lines can be explained in terms of shock-excited emission. In particular, our analysis shows that dissociative (J-type) and nondissociative (C-type) shocks are simultaneously present everywhere along both lobes of the flow. We confirm the low-excitation nature of the Herbig-Haro nebulosities, with shock velocities Vs [less than/similar to]40-50 km s-1. Toward both lobes of the outflow, we find preshock densities of n0 ~ 104 cm-3 for both the J and C components, implying B0 ~ 100 μG for B0αn00.5. In the central region of the flow, close to the exciting source, the preshock density deduced for the C-shock component is n0 ~ 105 cm-3, suggesting a magnetic field ~3 times stronger. We propose that the deficiency of gas-phase water in the post-C-shock regions is caused by freezing onto warm grains processed through the J-shock front and traveling along the magnetic field lines. The total observed cooling from the dissociative shock components is consistent with the power lost by a slow molecular outflow accelerated by a fast neutral HI wind. Finally, the skin of the cloud seen in projection toward the flow appears to be weakly photoionized by BD +30°549, the dominant illuminating source of the NGC 1333 reflection nebula