521 research outputs found
The methanol lines and hot core of OMC2-FIR4, an intermediate-mass protostar, with Herschel/HIFI
In contrast with numerous studies on the physical and chemical structure of low- and high-mass protostars, much less is known about their intermediate-mass counterparts, a class of objects that could help to elucidate the mechanisms of star formation on both ends of the mass range. We present the first results from a rich HIFI spectral dataset on an intermediate-mass protostar, OMC2-FIR4, obtained in the CHESS (Chemical HErschel Survey of Star forming regions) key programme. The more than 100 methanol lines detected between 554 and 961 GHz cover a range in upper level energy of 40 to 540 K. Our physical interpretation focusses on the hot core, but likely the cold envelope and shocked regions also play a role in reality, because an analysis of the line profiles suggests the presence of multiple emission components. An upper limit of 10^(-6) is placed on the methanol abundance in the hot core, using a population diagram, large-scale source model and other considerations. This value is consistent with abundances previously seen in low-mass hot cores. Furthermore, the highest energy lines at the highest frequencies display asymmetric profiles, which may arise from infall around the hot core
The CHESS spectral survey of star forming regions: Peering into the protostellar shock L1157-B1 - II. Shock dynamics
Context. The outflow driven by the low-mass class 0 protostar L1157 is the prototype of the so-called chemically active outflows. The bright bowshock B1 in the southern outflow lobe is a privileged testbed of magneto-hydrodynamical (MHD) shock models, for which dynamical and chemical processes are strongly interdependent.
Aims. We present the first results of the unbiased spectral survey of the L1157-B1 bowshock, obtained in the framework of the key program “Chemical HErschel Surveys of star forming regions” (CHESS). The main aim is to trace the warm and chemically enriched gas and to infer the excitation conditions in the shock region.
Methods. The CO 5-4 and o-H2_O 1_(10)–1_(01) lines have been detected at high-spectral resolution in the unbiased spectral survey of the HIFI-band 1b spectral window (555–636 GHz), presented by Codella et al. in this volume. Complementary ground-based observations in the submm window help establish the origin of the emission detected in the main-beam of HIFI and the physical conditions in the shock.
Results. Both lines exhibit broad wings, which extend to velocities much higher than reported up to now. We find that the molecular emission arises from two regions with distinct physical conditions : an extended, warm (100 K), dense (3 × 10^5 cm^(-3)) component at low-velocity, which dominates the water line flux in Band 1; a secondary component in a small region of B1 (a few arcsec) associated with high-velocity, hot (>400 K) gas of moderate density ((1.0–3.0) × 10^4 cm^(-3)), which appears to dominate the flux of the water line at 179μm observed with PACS. The water abundance is enhanced by two orders of magnitude between the low- and the high-velocity component, from 8 × 10^(-7) up to 8 × 10^(-5). The properties of the high-velocity component agree well with the predictions of steady-state C-shock models
Principal Component Analysis of Cavity Beam Position Monitor Signals
Model-independent analysis (MIA) methods are generally useful for analysing
complex systems in which relationships between the observables are non-trivial
and noise is present. Principle Component Analysis (PCA) is one of MIA methods
allowing to isolate components in the input data graded to their contribution
to the variability of the data. In this publication we show how the PCA can be
applied to digitised signals obtained from a cavity beam position monitor
(CBPM) system on the example of a 3-cavity test system installed at the
Accelerator Test Facility 2 (ATF2) at KEK in Japan. We demonstrate that the PCA
based method can be used to extract beam position information, and matches
conventional techniques in terms of performance, while requiring considerably
less settings and data for calibration
Herschel/HIFI discovery of interstellar chloronium (H_2Cl^+)
We report the first detection of chloronium, H_2Cl^+, in the interstellar medium, using the HIFI instrument aboard the Herschel Space Observatory.
The 2_(12)−1_(01) lines of ortho-H^(35)_2 Cl^+ and ortho-H^(37)_2 Cl^+ are detected in absorption towards NGC 6334I, and the 1_(11)−0_(00) transition of para-H^(35)_2 Cl^+ is
detected in absorption towards NGC 6334I and Sgr B2(S). The H_2Cl^+ column densities are compared to those of the chemically-related species
HCl. The derived HCl/H_2Cl^+ column density ratios, ~1–10, are within the range predicted by models of diffuse and dense photon dominated
regions (PDRs). However, the observed H_2Cl^+ column densities, in excess of 10^(13) cm^(−2), are significantly higher than the model predictions. Our
observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints
for astrochemical models
Detection of interstellar oxidaniumyl: Abundant H_2O^+ towards the star-forming regions DR21, Sgr B2, and NGC6334
Aims. We identify a prominent absorption feature at 1115 GHz, detected in first HIFI spectra towards high-mass star-forming regions, and interpret its astrophysical origin.
Methods. The characteristic hyperfine pattern of the H_2O^+ ground-state rotational transition, and the lack of other known low-energy transitions in this frequency range, identifies the feature as H_2O^+ absorption against the dust continuum background and allows us to derive the velocity profile of the absorbing gas. By comparing this velocity profile with velocity profiles of other tracers in the DR21 star-forming region, we constrain the frequency of the transition and the conditions for its formation.
Results. In DR21, the velocity distribution of H_2O^+ matches that of the [C_(II)] line at 158 μm and of OH cm-wave absorption, both stemming from the hot and dense clump surfaces facing the H_(II)-region and dynamically affected by the blister outflow. Diffuse foreground gas dominates the absorption towards Sgr B2. The integrated intensity of the absorption line allows us to derive lower limits to the H_2O^+ column density of 7.2 × 10^(12) cm^(−2) in NGC 6334, 2.3 × 10^(13) cm^(−2) in DR21, and 1.1 × 10^(15) cm^(−2) in Sgr B2
Beam Profile Measurements and Simulations of the PETRA Laser-Wire
The Laser-wire will be an essential diagnostic tool at the International
Linear Collider. It uses a finely focussed laser beam to measure the transverse
profile of electron bunches by detecting the Compton-scattered photons (or
degraded electrons) downstream of where the laser beam intersects the electron
beam. Such a system has been installed at the PETRA storage ring at DESY, which
uses a piezo-driven mirror to scan the laser-light across the electron beam.
Lat- est results of experimental data taking are presented and compared to
detailed simulations using the Geant4 based program BDSIM.Comment: 3 pagesm 4 figures. Submitted as a conference paper for the Particle
Accelerator Conference 2005 (PAC05
Laserwire at the Accelerator Test Facility 2 with Sub-Micrometre Resolution
A laserwire transverse electron beam size measurement system has been
developed and operated at the Accelerator Test Facility 2 (ATF2) at KEK.
Special electron beam optics were developed to create an approximately 1 x 100
{\mu}m (vertical x horizontal) electron beam at the laserwire location, which
was profiled using a 150 mJ, 71 ps laser pulse with a wavelength of 532 nm. The
precise characterisation of the laser propagation allows the non-Gaussian
transverse profiles of the electron beam caused by the laser divergence to be
deconvolved. A minimum vertical electron beam size of 1.07 0.06 (stat.)
0.05 (sys.) {\mu}m was measured. A vertically focussing quadrupole just
before the laserwire was varied whilst making laserwire measurements and the
projected vertical emittance was measured to be 82.56 3.04 pm rad.Comment: 17 pages, 26 figures, submitted to Phys. Rev. ST Accel. Beam
Detection of OH+ and H_2O+ towards Orion KL
We report observations of the reactive molecular ions OH+, H_(2)O+, and H_(3)O+ towards Orion KL with Herschel/HIFI. All three N = 1-0 fine-structure transitions of OH+ at 909, 971, and 1033 GHz and both fine-structure components of the doublet ortho-H_(2)O+ 1_(11)–0_(00) transition at 1115 and 1139 GHz were detected; an upper limit was obtained for H_(3)O+. OH+ and H_(2)O+ are observed purely in absorption, showing a narrow component at the source velocity of 9 km s^(-1), and a broad blueshifted absorption similar to that reported recently for HF and para-H_(2)^(18)O, and attributed to the low velocity outflow of Orion KL. We estimate column densities of OH+ and H_(2)O+ for the 9 km s^(-1) component of 9 ± 3 × 10^(12) cm^(-2) and 7 ± 2 × 10^(12) cm^(-2), and those in the outflow of 1.9 ± 0.7 × 10^(13) cm^(-2) and 1.0 ± 0.3 × 10^(13) cm^(-2). Upper limits of 2.4 × 10^(12) cm^(-2) and 8.7 × 10^(12) cm^(-2) were derived for the column densities of ortho and para-H_(3)O+ from transitions near 985 and 1657 GHz. The column densities of the three ions are up to an order of magnitude lower than those obtained from recent observations of W31C and W49N. The comparatively low column densities may be explained by a higher gas density despite the assumption of a very high ionization rate
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