10,141 research outputs found
Simulated CII observations for SPICA/SAFARI
We investigate the case of CII 158 micron observations for SPICA/SAFARI using
a three-dimensional magnetohydrodynamical (MHD) simulation of the diffuse
interstellar medium (ISM) and the Meudon PDR code. The MHD simulation consists
of two converging flows of warm gas (10,000 K) within a cubic box 50 pc in
length. The interplay of thermal instability, magnetic field and self-gravity
leads to the formation of cold, dense clumps within a warm, turbulent
interclump medium. We sample several clumps along a line of sight through the
simulated cube and use them as input density profiles in the Meudon PDR code.
This allows us to derive intensity predictions for the CII 158 micron line and
provide time estimates for the mapping of a given sky area.Comment: 4 pages, 5 figures, to appear in the proceedings of the workshop "The
Space Infrared Telescope for Cosmology & Astrophysics: Revealing the Origins
of Planets and Galaxies" (July 2009, Oxford, United Kingdom
SPIRE-FTS observations of RCW 120
The expansion of Galactic HII regions can trigger the formation of a new
generation of stars. However, little is know about the physical conditions that
prevail in these regions. We study the physical conditions that prevail in
specific zones towards expanding HII regions that trace representative media
such as the photodissociation region, the ionized region, and condensations
with and without ongoing star formation. We use the SPIRE Fourier Transform
Spectrometer (FTS) on board to observe the HII region RCW 120.
Continuum and lines are observed in the m range. Line intensities
and line ratios are obtained and used as physical diagnostics of the gas. We
used the Meudon PDR code and the RADEX code to derive the gas density and the
radiation field at nine distinct positions including the PDR surface and
regions with and without star-formation activity. For the different regions we
detect the atomic lines [NII] at m and [CI] at and m,
the ladder between the and levels and the
ladder between the and levels, as well as CH in absorption. We find gas temperatures in the range K for
densities of , and a high column density on the order
of that is in agreement with dust
analysis. The ubiquitousness of the atomic and CH emission suggests the
presence of a low-density PDR throughout RCW 120. High-excitation lines of CO
indicate the presence of irradiated dense structures or small dense clumps
containing young stellar objects, while we also find a less dense medium
() with high temperatures (K).Comment: 11 pages, 11 figures, accepted by A&
Discovery of new magnetic early-B stars within the MiMeS HARPSpol survey
To understand the origin of the magnetic fields in massive stars as well as
their impact on stellar internal structure, evolution, and circumstellar
environment, within the MiMeS project, we searched for magnetic objects among a
large sample of massive stars, and build a sub-sample for in-depth follow-up
studies required to test the models and theories of fossil field origins,
magnetic wind confinement and magnetospheric properties, and magnetic star
evolution.
We obtained high-resolution spectropolarimetric observations of a large
number of OB stars thanks to three large programs that have been allocated on
the high-resolution spectropolarimeters ESPaDOnS, Narval, and the polarimetric
module HARPSpol of the HARPS spectrograph. We report here on the methods and
first analysis of the HARPSpol magnetic detections. We identified the magnetic
stars using a multi-line analysis technique. Then, when possible, we monitored
the new discoveries to derive their rotation periods, which are critical for
follow-up and magnetic mapping studies. We also performed a first-look analysis
of their spectra and identified obvious spectral anomalies (e.g., abundance
peculiarities, Halpha emission), which are also of interest for future studies.
In this paper, we focus on eight of the 11 stars in which we discovered or
confirmed a magnetic field from the HARPSpol LP sample (the remaining three
were published in a previous paper). Seven of the stars were detected in
early-type Bp stars, while the last star was detected in the Ap companion of a
normal early B-type star. We report obvious spectral and multiplicity
properties, as well as our measurements of their longitudinal field strengths,
and their rotation periods when we are able to derive them. We also discuss the
presence or absence of Halpha emission with respect to the theory of
centrifugally-supported magnetospheres. (Abriged)Comment: 19 pages, 8 figures, accepted for publication in A&
The IRAM-30m line survey of the Horsehead PDR: IV. Comparative chemistry of H2CO and CH3OH
Aims. We investigate the dominant formation mechanism of H2CO and CH3OH in
the Horsehead PDR and its associated dense core. Methods. We performed deep
integrations of several H2CO and CH3OH lines at two positions in the Horsehead,
namely the PDR and dense core, with the IRAM-30m telescope. In addition, we
observed one H2CO higher frequency line with the CSO telescope at both
positions. We determine the H2CO and CH3OH column densities and abundances from
the single-dish observations complemented with IRAM-PdBI high-angular
resolution maps (6") of both species. We compare the observed abundances with
PDR models including either pure gas-phase chemistry or both gas-phase and
grain surface chemistry. Results. We derive CH3OH abundances relative to total
number of hydrogen atoms of ~1.2e-10 and ~2.3e-10 in the PDR and dense core
positions, respectively. These abundances are similar to the inferred H2CO
abundance in both positions (~2e-10). We find an abundance ratio H2CO/CH3OH of
~2 in the PDR and ~1 in the dense core. Pure gas-phase models cannot reproduce
the observed abundances of either H2CO or CH3OH at the PDR position. Both
species are therefore formed on the surface of dust grains and are subsequently
photodesorbed into the gas-phase at this position. At the dense core, on the
other hand, photodesorption of ices is needed to explain the observed abundance
of CH3OH, while a pure gas-phase model can reproduce the observed H2CO
abundance. The high-resolution observations show that CH3OH is depleted onto
grains at the dense core. CH3OH is thus present in an envelope around this
position, while H2CO is present in both the envelope and the dense core itself.
Conclusions. Photodesorption is an efficient mechanism to release complex
molecules in low FUV-illuminated PDRs, where thermal desorption of ice mantles
is ineffective.Comment: 12 pages, 5 tables, 7 figures; Accepted for publication in A&
Spectral dependence of purely-Kerr driven filamentation in air and argon
Based on numerical simulations, we show that higher-order nonlinear indices
(up to and , respectively) of air and argon have a dominant
contribution to both focusing and defocusing in the self-guiding of ultrashort
laser pulses over most of the spectrum. Plasma generation and filamentation are
therefore decoupled. As a consequence, ultraviolet wavelength may not be the
optimal wavelengths for applications requiring to maximize ionization.Comment: 14 pages, 4 figures (14 panels
Coupling and induced depinning of magnetic domain walls in adjacent spin valve nanotracks
The magnetostatic interaction between magnetic domain walls (DWs) in adjacent
nanotracks has been shown to produce strong inter-DW coupling and mutual
pinning. In this paper, we have used electrical measurements of adjacent
spin-valve nanotracks to follow the positions of interacting DWs. We show that
the magnetostatic interaction between DWs causes not only mutual pinning, as
observed till now, but that a travelling DW can also induce the depinning of
DWs in near-by tracks. These effects may have great implications for some
proposed high density magnetic devices (e.g. racetrack memory, DW logic
circuits, or DW-based MRAM).Comment: The following article has been accepted by the Journal of Applied
Physic
Near-field interaction between domain walls in adjacent Permalloy nanowires
The magnetostatic interaction between two oppositely charged transverse
domain walls (DWs)in adjacent Permalloy nanowires is experimentally
demonstrated. The dependence of the pinning strength on wire separation is
investigated for distances between 13 and 125 nm, and depinning fields up to 93
Oe are measured. The results can be described fully by considering the
interaction between the full complex distribution of magnetic charge within
rigid, isolated DWs. This suggests the DW internal structure is not appreciably
disturbed by the pinning potential, and that they remain rigid although the
pinning strength is significant. This work demonstrates the possibility of
non-contact DW trapping without DW perturbation and full continuous flexibility
of the pinning potential type and strength. The consequence of the interaction
on DW based data storage schemes is evaluated.Comment: 4 pages, 4 figures, 1 page supplimentary material (supporting.ps
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