1,195 research outputs found
1RXSJ062518.2+733433: A bright, soft intermediate polar
We present the results of 50 hours time-resolved R-band photometry of the
ROSAT all-sky survey source 1RXSJ062518.2+733433. The source was identified by
Wei et al. (1999) as a cataclysmic variable. Our photometry, performed in 10
nights between February 11, 2003, and March 21, 2003, reveals two stable
periodicities at 19.7874 and 283.118 min, which are identified as probable spin
and orbital periods of the binary. We therefore classify 1RXSJ062518.2+733433
as an intermediate polar. Analysis of the RASS X-ray observations reveal a
variability of 100% in the X-ray flux and a likely soft X-ray excess. The new
IP thus joins the rare group of soft IPs with only four members so far.Comment: submitted to A&A, 5 pages, 6 figures of reduced qualit
V405 Peg (RBS 1955): A Nearby, Low-Luminosity Cataclysmic Binary
(Abridged). The cataclysmic binary V405 Peg, originally discovered as ROSAT
Bright Source (RBS) 1955 (= 1RXS J230949.6+213523), shows a strong contribution
from a late-type secondary star in its optical spectrum, which led Schwope et
al. to suggest it to be among the nearest cataclysmic binaries. We present
extensive optical observations of V405 Peg. Time-series spectroscopy shows the
orbital period, Porb, to be 0.1776469(7) d (= 4.2635 hr), or 5.629 cycle/d. We
classify the secondary as M3 - M4.5. Astrometry with the MDM 2.4m telescope
gives a parallax 7.2 +- 1.1 milli-arcsec, and a relative proper motion of 58
mas/yr. Our best estimate of the distance yields d = 149 (+26, -20) pc. The
secondary stars's radial velocity has K2 = 92 +- 3 km/s, indicating a fairly
low orbital inclination if the masses are typical. Extensive I-band time-series
observations in the show the system varying between a minimum brightness level
of I = 14.14 and states of enhanced activity about 0.2 mag brighter. While the
low-state shows an ellipsoidal modulation, an additional photometric modulation
appears in the high state, with 0.1 mag amplitude and period 220-280 min. The
frequency of this modulation appears to be stable for a month or so, but no
single period was consistently detected from one observing season to the next.
We estimate the system luminosity by combining optical measurements with the
archival X-ray spectrum. The implied mass accretion rate is orders of
magnitudes below the predictions for the standard angular momentum loss above
the period gap. The system may possibly belong to a largely undiscovered
population of hibernating CVs.Comment: 11 figures; 7 of these are .png or .jpg to save space. In press for
Publications of the Astronomical Society of the Pacifi
The changing accretion states of the intermediate polar MU Camelopardalis
We study the timing and spectral properties of the intermediate polar MU
Camelopardalis (1RXS J062518.2+733433) to determine the accretion modes and
the accretion geometry from multi-wavelength, multi-epoch observational data.
Light curves in different observed energy ranges (optical, UV, X-ray) are
extracted. The timescales of variability in these light curves are determined
using Analysis of Variance. Phase-resolved X-ray spectra are created with
respect to the most prominent detected periodicities and each fitted with an
identical model, to quantify the differences in the fitted components. The
published tentative value for the spin period is unambiguously identified with
the rotation period of the white dwarf. We detect a distinct soft X-ray
component that can be reproduced well by a black body. The analysis of data
obtained at different epochs demonstrates that the system is changing its
accretion geometry from disk-dominated to a combination of disk- plus
stream-dominated, accompanied with a significant change in brightness at
optical wavelengths.Comment: Accepted for publication in Astron. Astrophys., 13 pages, 10 figure
Performance of the ATLAS Precision Muon Chambers under LHC Operating Conditions
For the muon spectrometer of the ATLAS detector at the large hadron collider
(LHC), large drift chambers consisting of 6 to 8 layers of pressurized drift
tubes are used for precision tracking covering an active area of 5000 m2 in the
toroidal field of superconducting air core magnets. The chambers have to
provide a spatial resolution of 41 microns with Ar:CO2 (93:7) gas mixture at an
absolute pressure of 3 bar and gas gain of 2?104. The environment in which the
chambers will be operated is characterized by high neutron and background with
counting rates of up to 100 per square cm and second. The resolution and
efficiency of a chamber from the serial production for ATLAS has been
investigated in a 100 GeV muon beam at photon irradiation rates as expected
during LHC operation. A silicon strip detector telescope was used as external
reference in the beam. The spatial resolution of a chamber is degraded by 4 ?m
at the highest background rate. The detection efficiency of the drift tubes is
unchanged under irradiation. A tracking efficiency of 98% at the highest rates
has been demonstrated
Resolution and Efficiency of the ATLAS Muon Drift-Tube Chambers at High Background Rates
The resolution and efficiency of a precision drift-tube chamber for the ATLAS
muon spectrometer with final read-out electronics was tested at the Gamma
Irradiation Facility at CERN in a 100 GeV muon beam and at photon irradiation
rates of up to 990 Hz/square cm which corresponds to twice the highest
background rate expected in ATLAS. A silicon strip detector telescope was used
as external reference in the beam. The pulse-height measurement of the read-out
electronics was used to perform time-slewing corrections which lead to an
improvement of the average drift-tube resolution from 104 microns to 82 microns
without irradiation and from 128 microns to 108 microns at the maximum expected
rate. The measured drift-tube efficiency agrees with the expectation from the
dead time of the read-out electronics up to the maximum expected rate
Resonantly enhanced second-harmonic generation using III-V semiconductor all-dielectric metasurfaces
Nonlinear optical phenomena in nanostructured materials have been challenging
our perceptions of nonlinear optical processes that have been explored since
the invention of lasers. For example, the ability to control optical field
confinement, enhancement, and scattering almost independently, allows nonlinear
frequency conversion efficiencies to be enhanced by many orders of magnitude
compared to bulk materials. Also, the subwavelength length scale renders phase
matching issues irrelevant. Compared with plasmonic nanostructures, dielectric
resonator metamaterials show great promise for enhanced nonlinear optical
processes due to their larger mode volumes. Here, we present, for the first
time, resonantly enhanced second-harmonic generation (SHG) using Gallium
Arsenide (GaAs) based dielectric metasurfaces. Using arrays of cylindrical
resonators we observe SHG enhancement factors as large as 104 relative to
unpatterned GaAs. At the magnetic dipole resonance we measure an absolute
nonlinear conversion efficiency of ~2X10^(-5) with ~3.4 GW/cm2 pump intensity.
The polarization properties of the SHG reveal that both bulk and surface
nonlinearities play important roles in the observed nonlinear process
Construction and Test of MDT Chambers for the ATLAS Muon Spectrometer
The Monitored Drift Tube (MDT) chambers for the muon spectrometer of the AT-
LAS detector at the Large Hadron Collider (LHC) consist of 3-4 layers of
pressurized drift tubes on either side of a space frame carrying an optical
monitoring system to correct for deformations. The full-scale prototype of a
large MDT chamber has been constructed with methods suitable for large-scale
production. X-ray measurements at CERN showed a positioning accuracy of the
sense wires in the chamber of better than the required 20 ?microns (rms). The
performance of the chamber was studied in a muon beam at CERN. Chamber
production for ATLAS now has started
A Cosmic Ray Measurement Facility for ATLAS Muon Chambers
Monitored Drift Tube (MDT) chambers will constitute the large majority of
precision detectors in the Muon Spectrometer of the ATLAS experiment at the
Large Hadron Collider at CERN. For commissioning and calibration of MDT
chambers, a Cosmic Ray Measurement Facility is in operation at Munich
University. The objectives of this facility are to test the chambers and
on-chamber electronics, to map the positions of the anode wires within the
chambers with the precision needed for standalone muon momentum measurement in
ATLAS, and to gain experience in the operation of the chambers and on-line
calibration procedures.
Until the start of muon chamber installation in ATLAS, 88 chambers built at
the Max Planck Institute for Physics in Munich have to be commissioned and
calibrated. With a data taking period of one day individual wire positions can
be measured with an accuracy of 8.3 micrometers in the chamber plane and 27
micrometers in the direction perpendicular to that plane.Comment: 14+1 pages, 11 figures, contributed paper to the EPS2003 conference,
Aache
Calculation of Spectral Darkening and Visibility Functions for Solar Oscillations
Calculations of spectral darkening and visibility functions for the
brightness oscillations of the Sun resulting from global solar oscillations are
presented. This has been done for a broad range of the visible and infrared
continuum spectrum. The procedure for the calculations of these functions
includes the numerical computation of depth-dependent derivatives of the
opacity caused by p modes in the photosphere. A radiative-transport code was
used for this purpose to get the disturbances of the opacities from temperature
and density fluctuations. The visibility and darkening functions are obtained
for adiabatic oscillations under the assumption that the temperature
disturbances are proportional to the undisturbed temperature of the
photosphere. The latter assumption is the only way to explore any opacity
effects since the eigenfunctions of p-mode oscillations have not been obtained
so far. This investigation reveals that opacity effects have to be taken into
account because they dominate the violet and infrared part of the spectrum.
Because of this dominance, the visibility functions are negative for those
parts of the spectrum. Furthermore, the darkening functions show a
wavelength-dependent change of sign for some wavelengths owing to these opacity
effects. However, the visibility and darkening functions under the assumptions
used contradict the observations of global p-mode oscillations, but it is
beyond doubt that the opacity effects influence the brightness fluctuations of
the Sun resulting from global oscillations
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