3,701 research outputs found
The Distribution of Ortho-H_2D+(1_1,0 - 1_1,1) in L1544: Tracing the Deuteration Factory in Prestellar Cores
Prestellar cores are unique laboratories for studies of the chemical and
physical conditions preceding star formation. We observed the prestellar core
L1544 in the fundamental transition of ortho-H2D+ (1_1,0-1_1,1) at different
positions over 100", and found a strong correlation between its abundance and
the CO depletion factor. We also present a tentative detection of the
fundamental transition of para-D2H+ (1_1,0-1_0,1) at the dust emission peak.
Maps in N2H+, N2D+, HCO+ and DCO+ are used, and interpreted with the aid of a
spherically symmetric chemical model that predicts the column densities and
abundances of these species as a function of radius. The correlation between
the observed deuterium fractionation of H3+, N2H+ and HCO+ and the observed
integrated CO depletion factor across the core can be reproduced by this
chemical model. In addition a simpler model is used to study the H2D+
ortho-to-para ratio. We conclude that, in order to reproduce the observed
ortho-H2D+ observations, the grain radius should be larger than 0.3 microns.Comment: 24 pages, 9 figures, accepted in ApJ (to be published in July 2006
Interferometric Observations of the Nuclear Region of Arp220 at Submillimeter Wavelengths
We report the first submillimeter interferometric observations of an
ultraluminous infrared galaxy. We observed Arp220 in the CO J=3-2 line and
342GHz continuum with the single baseline CSO-JCMT interferometer consisting of
the Caltech Submillimeter Observatory (CSO) and the James Clerk Maxwell
Telescope (JCMT). Models were fit to the measured visibilities to constrain the
structure of the source. The morphologies of the CO J=3-2 line and 342GHz
continuum emission are similar to those seen in published maps at 230 and
110GHz. We clearly detect a binary source separated by about 1 arcsec in the
east-west direction in the 342GHz continuum. The CO J=3-2 visibility
amplitudes, however, indicate a more complicated structure, with evidence for a
compact binary at some velocities and rather more extended structure at others.
Less than 30% of the total CO J=3-2 emission is detected by the interferometer,
which implies the presence of significant quantities of extended gas. We also
obtained single-dish CO J=2-1, CO J=3-2 and HCN J=4-3 spectra. The HCN J=4-3
spectrum, unlike the CO spectra, is dominated by a single redshifted peak. The
HCN J=4-3/CO J=3-2, HCN J=4-3/HCN J=1-0 and CO J=3-2/2-1 line ratios are larger
in the redshifted (eastern) source, which suggests that the two sources may
have different physical conditions. This result might be explained by the
presence of an intense starburst that has begun to deplete or disperse the
densest gas in the western source, while the eastern source harbors undispersed
high density gas.Comment: 17 pages, 9 figures, 4 Tables. accepted by Ap
Terahertz hot electron bolometer waveguide mixers for GREAT
Supplementing the publications based on the first-light observations with the
German Receiver for Astronomy at Terahertz frequencies (GREAT) on SOFIA, we
present background information on the underlying heterodyne detector
technology. We describe the superconducting hot electron bolometer (HEB)
detectors that are used as frequency mixers in the L1 (1400 GHz), L2 (1900
GHz), and M (2500 GHz) channels of GREAT. Measured performance of the detectors
is presented and background information on their operation in GREAT is given.
Our mixer units are waveguide-based and couple to free-space radiation via a
feedhorn antenna. The HEB mixers are designed, fabricated, characterized, and
flight-qualified in-house. We are able to use the full intermediate frequency
bandwidth of the mixers using silicon-germanium multi-octave cryogenic
low-noise amplifiers with very low input return loss. Superconducting HEB
mixers have proven to be practical and sensitive detectors for high-resolution
THz frequency spectroscopy on SOFIA. We show that our niobium-titanium-nitride
(NbTiN) material HEBs on silicon nitride (SiN) membrane substrates have an
intermediate frequency (IF) noise roll-off frequency above 2.8 GHz, which does
not limit the current receiver IF bandwidth. Our mixer technology development
efforts culminate in the first successful operation of a waveguide-based HEB
mixer at 2.5 THz and deployment for radioastronomy. A significant contribution
to the success of GREAT is made by technological development, thorough
characterization and performance optimization of the mixer and its IF interface
for receiver operation on SOFIA. In particular, the development of an optimized
mixer IF interface contributes to the low passband ripple and excellent
stability, which GREAT demonstrated during its initial successful astronomical
observation runs.Comment: Accepted for publication in A&A (SOFIA/GREAT special issue
The MuPix Telescope: A Thin, high Rate Tracking Telescope
The MuPix Telescope is a particle tracking telescope, optimized for tracking
low momentum particles and high rates. It is based on the novel High-Voltage
Monolithic Active Pixel Sensors (HV-MAPS), designed for the Mu3e tracking
detector. The telescope represents a first application of the HV-MAPS
technology and also serves as test bed of the Mu3e readout chain. The telescope
consists of up to eight layers of the newest prototypes, the MuPix7 sensors,
which send data self-triggered via fast serial links to FPGAs, where the data
is time-ordered and sent to the PC. A particle hit rate of 1 MHz per layer
could be processed. Online tracking is performed with a subset of the incoming
data. The general concept of the telescope, chip architecture, readout concept
and online reconstruction are described. The performance of the sensor and of
the telescope during test beam measurements are presented.Comment: Proceedings TWEPP 2016, 8 pages, 7 figure
Research Proposal for an Experiment to Search for the Decay {\mu} -> eee
We propose an experiment (Mu3e) to search for the lepton flavour violating
decay mu+ -> e+e-e+. We aim for an ultimate sensitivity of one in 10^16
mu-decays, four orders of magnitude better than previous searches. This
sensitivity is made possible by exploiting modern silicon pixel detectors
providing high spatial resolution and hodoscopes using scintillating fibres and
tiles providing precise timing information at high particle rates.Comment: Research proposal submitted to the Paul Scherrer Institute Research
Committee for Particle Physics at the Ring Cyclotron, 104 page
Glueballs, closed fluxtubes and eta(1440)
The component of the pseudoscalar has strong
affinity for glue. But its mass is incompatible with lattice simulations that
predict a much higher value for the glueball. As a consequence it has
been suggested that could signal physics beyond the Standard
Model. Here we argue that if glueballs are closed gluonic fluxtubes then
is a prime candidate for the glueball. Furthermore, in
the absence of parity violating terms its mass should be degenerate with that
of the glueball. We also suggest that the decay properties of such
glueballs could be employed as probes for extra dimensions.Comment: 11 page
Cool gas and dust in M33: Results from the Herschel M33 extended survey (HERM33ES)
We present an analysis of the first space-based far-IR-submm observations of
M 33, which measure the emission from the cool dust and resolve the giant
molecular cloud complexes. With roughly half-solar abundances, M33 is a first
step towards young low-metallicity galaxies where the submm may be able to
provide an alternative to CO mapping to measure their H content. In this
Letter, we measure the dust emission cross-section using SPIRE and
recent CO and \HI\ observations; a variation in is present from a
near-solar neighborhood cross-section to about half-solar with the maximum
being south of the nucleus. Calculating the total H column density from the
measured dust temperature and cross-section, and then subtracting the \HI\
column, yields a morphology similar to that observed in CO. The H/\HI\ mass
ratio decreases from about unity to well below 10% and is about 15% averaged
over the optical disk. The single most important observation to reduce the
potentially large systematic errors is to complete the CO mapping of M 33.Comment: 5 pages, 5 figures Accepted for publication in Astronomy and
Astrophysic
The Herschel Comprehensive (U)LIRG Emission Survey (HerCULES): CO Ladders, fine structure lines, and neutral gas cooling
(Ultra) Luminous Infrared Galaxies ((U)LIRGs) are objects characterized by
their extreme infrared (8-1000 m) luminosities (L and L). The Herschel Comprehensive ULIRG
Emission Survey (HerCULES; PI van der Werf) presents a representative
flux-limited sample of 29 (U)LIRGs that spans the full luminosity range of
these objects (10). With the \emph{Herschel
Space Observatory}, we observe [CII] 157 m, [OI] 63 m, and [OI] 145
m line emission with PACS, CO J=4-3 through J=13-12, [CI] 370 m, and
[CI] 609 m with SPIRE, and low-J CO transitions with ground-based
telescopes. The CO ladders of the sample are separated into three classes based
on their excitation level. In 13 of the galaxies, the [OI] 63 m emission
line is self absorbed. Comparing the CO excitation to the IRAS 60/100 m
ratio and to far infrared luminosity, we find that the CO excitation is more
correlated to the far infrared colors. We present cooling budgets for the
galaxies and find fine-structure line flux deficits in the [CII], [SiII], [OI],
and [CI] lines in the objects with the highest far IR fluxes, but do not
observe this for CO . In order to study the heating of the
molecular gas, we present a combination of three diagnostic quantities to help
determine the dominant heating source. Using the CO excitation, the CO J=1-0
linewidth, and the AGN contribution, we conclude that galaxies with large CO
linewidths always have high-excitation CO ladders, and often low AGN
contributions, suggesting that mechanical heating is important
Recommended from our members
GPs are from Mars, Administrators are from Venus: The Role of Misaligned Occupational Dispositions in Inhibiting Mandated Role Change
Research on mandated occupational role change focuses on jurisdictional conflict to explain change failure. Our study of the English National Health Service highlights the role of occupational dispositions in shaping how mandated role change is implemented by members of multiple occupational groups. We find that tension stemming from misaligned dispositions may emerge as members of different occupations interact during their role change implementation efforts. Depending on dispositional responses to tension, change may fail as members of the different occupations avoid interactions. This suggests that effective role change can be elusive even in the initial absence of conflicting occupational interests
- …