1,012 research outputs found
The high-field polar RX J1007.5-2017
We report optical and X-ray observations of the high-field polar
RXJ1007.5-2017 performed between 1990 and 2012. It has an orbital period of
208.60 min determined from the ellipsoidal modulation of the secondary star in
an extended low state. The spectral flux of the dM3- secondary star yields a
distance of 790+-105 pc. At low accretion levels, \RX{} exhibits pronounced
cyclotron emission lines. The second and third harmonic fall in the optical
regime and yield a field strength in the accretion spot of 94 MG. The source is
highly variable on a year-to-year basis and was encountered at visual
magnitudes between V \sim 20 and V \sim 16. In the intermediate state of 1992
and 2000, the soft X-ray luminosity exceeds the sum of the luminosities of the
cyclotron source, the hard X-ray source, and the accretion stream by an order
of magnitude. An X-ray high state, corresponding to the brightest optical
level, has apparently not been observed so far.Comment: To be published in A&
Neglected X-ray discovered polars: III. RX J0154.0-5947, RX J0600.5-2709, RX J0859.1+0537, RX J0953.1+1458, and RX J1002.2-1925
We report results on the ROSAT-discovered noneclipsing short-period polars RX
J0154.0-5947, RX J0600.5-2709, RX J0859.1+0537, RX J0953.1+1458, and RX
J1002.2-1925 collected over 30 years. We present accurate linear orbital
ephemerides that allow a correct phasing of data taken decades apart. Three of
the systems show cyclotron and Zeeman lines that yield magnetic field strengths
of 36 MG, 19 MG, and 33 MG for the last three targets, respectively. RX
J0154.0-5947, RX J0859.1+0537, and RX J1002.2-1925 show evidence for part-time
accretion at both magnetic poles, while RX J0953.1+1458 is a polar with a
stable one-pole geometry. RX J1002.2-1925 shows large variations in the shapes
of its light curves that we associate with an unstable accretion geometry.
Nevertheless, it appears to be synchronized. We determined the bolometric soft
and hard X-ray fluxes and the luminosities at the Gaia distances of the five
stars. Combined with estimates of the cyclotron luminosities, we derived
high-state accretion rates that range from
yr to yr for white
dwarf masses between 0.61 and 0.82 , in agreement with predictions
based on the observed effective temperatures of white dwarfs in polars and the
theory of compressional heating. Our analysis lends support to the hypothesis
that different mean accretion rates appply for the subgroups of short-period
polars and nonmagnetic cataclysmic variables.Comment: 24 pages, 11 figures, and 13 tables, accepted for publication in A&
Reliability Of A Novel Intracardiac Electrogram Method For AV And VV Delay Optimization And Comparability To Echocardiography Procedure For Determining Optimal Conduction Delays In CRT Patients
Background: Echocardiography is widely used to optimize CRT programming. A novel intracardiac electrogram method (IEGM) was recently developed as an automated programmer-based method, designed to calculate optimal atrioventricular (AV) and interventricular (VV) delays and provide optimized delay values as an alternative to standard echocardiographic assessment.Objective: This study was aimed at determining the reliability of this new method. Furthermore the comparability of IEGM to existing echocardiographic parameters for determining optimal conduction delays was verified.Methods: Eleven patients (age 62.9± 8.7; 81% male; 73% ischemic), previously implanted with a cardiac resynchronisation therapy defibrillator (CRT-D) underwent both echocardiographic and IEGM-based delay optimization.Results: Applying the IEGM method, concordance of three consecutively performed measurements was found in 3 (27%) patients for AV delay and in 5 (45%) patients for VV delay. Intra-individual variation between three measurements as assessed by the IEGM technique was up to 20 ms (AV: n=6; VV: n=4). E-wave, diastolic filling time and septal-to-lateral wall motion delay emerged as significantly different between the echo and IEGM optimization techniques (p < 0.05). The final AV delay setting was significantly different between both methods (echo: 126.4 ± 29.4 ms, IEGM: 183.6 ± 16.3 ms; p < 0.001; correlation: R = 0.573, p = 0.066). VV delay showed significant differences for optimized delays (echo: 46.4 ± 23.8 ms, IEGM: 10.9 ± 7.0 ms; p <0.01; correlation: R = -0.278, p = 0.407).Conclusion: The automated programmer-based IEGM-based method provides a simple and safe method to perform CRT optimization. However, the reliability of this method appears to be limited. Thus, it remains difficult for the examiner to determine the optimal hemodynamic settings. Additionally, as there was no correlation between the optimal AV- and VV-delays calculated by the IEGM method and the echo optimization, the use of the IEGM method and the comparability to the echo has not been definitely clarified
VLT observations of GRB 990510 and its environment
We present BVRI photometry and spectrophotometry of GRB990510 obtained with
the ESO VLT/Antu telescope during the late decline phase. Between days 8 and 29
after the burst, the afterglow faded from R=24.2 to ~26.4. The spectral flux
distribution and the light curve support the interpretation of the afterglow as
synchrotron emission from a jet. The light curve is consistent with the optical
transient alone but an underlying SN with maximum brightness R>27.4 or a galaxy
with R>27.6 (3-sigma upper limits) cannot be ruled out. To a 5-sigma detection
threshold of R=26.1, no galaxy is found within 6'' of the transient. A very
blue V~24.5 extended object which may qualify as a starburst galaxy is located
12'' SE, but at unknown redshift.Comment: 5 pages A&A Latex, accepted for publication in A&A Letter
Evolution of the polarization of the optical afterglow of the gamma-ray burst GRB 030329
We report 31 polarimetric observations of the afterglow of GRB 030329 with
high signal-to-noise and high sampling frequency. We establish the polarization
light curve, detect sustained polarization at the percent level, and find
significant variability of polarization degree and angle. The data imply that
the afterglow magnetic field has small coherence length and is mostly random,
probably generated by turbulence.Comment: Nature 426 (13. Nov. 2003), 2 figure
Testing Mode-Coupling Theory for a Supercooled Binary Lennard-Jones Mixture II: Intermediate Scattering Function and Dynamic Susceptibility
We have performed a molecular dynamics computer simulation of a supercooled
binary Lennard-Jones system in order to compare the dynamical behavior of this
system with the predictions of the idealized version of mode-coupling theory
(MCT). By scaling the time by the temperature dependent -relaxation
time , we find that in the -relaxation regime and
, the coherent and incoherent intermediate scattering functions, for
different temperatures each follows a -dependent master curve as a function
of scaled time. We show that during the early part of the -relaxation,
which is equivalent to the late part of the -relaxation, these master
curves are well approximated by the master curve predicted by MCT for the
-relaxation. This part is also fitted well by a power-law, the so-called
von Schweidler law. We show that the effective exponent of this power-law
depends on the wave vector if is varied over a large range. The early
part of the -relaxation regime does not show the critical decay
predicted by MCT. The -dependence of the nonergodicity parameter for
and are in qualitative agreement with MCT. On the time
scale of the late -relaxation the correlation functions show a
Kohlrausch-Williams-Watt behavior (KWW). The KWW exponent is
significantly different from the effective von Schweidler exponent . At low
temperatures the -relaxation time shows a power-law behavior
with a critical temperature that is the same as the one found previously for
the diffusion constant [Phys. Rev. Lett. {\bf 73}, 1376 (1994)]. The critical
exponent of this power-law and the von Schweidler exponent fulfill the
connection proposed by MCT between these two quantities. We also show that theComment: 28 Pages of REVTEX, Figures available from W. Ko
GeneLab: Scientific Partnerships and an Open-Access Database to Maximize Usage of Omics Data from Space Biology Experiments
NASA's mission includes expanding our understanding of biological systems to improve life on Earth and to enable long-duration human exploration of space. The GeneLab Data System (GLDS) is NASAs premier open-access omics data platform for biological experiments. GLDS houses standards-compliant, high-throughput sequencing and other omics data from spaceflight-relevant experiments. The GeneLab project at NASA-Ames Research Center is developing the database, and also partnering with spaceflight projects through sharing or augmentation of experiment samples to expand omics analyses on precious spaceflight samples. The partnerships ensure that the maximum amount of data is garnered from spaceflight experiments and made publically available as rapidly as possible via the GLDS. GLDS Version 1.0, went online in April 2015. Software updates and new data releases occur at least quarterly. As of October 2016, the GLDS contains 80 datasets and has search and download capabilities. Version 2.0 is slated for release in September of 2017 and will have expanded, integrated search capabilities leveraging other public omics databases (NCBI GEO, PRIDE, MG-RAST). Future versions in this multi-phase project will provide a collaborative platform for omics data analysis. Data from experiments that explore the biological effects of the spaceflight environment on a wide variety of model organisms are housed in the GLDS including data from rodents, invertebrates, plants and microbes. Human datasets are currently limited to those with anonymized data (e.g., from cultured cell lines). GeneLab ensures prompt release and open access to high-throughput genomics, transcriptomics, proteomics, and metabolomics data from spaceflight and ground-based simulations of microgravity, radiation or other space environment factors. The data are meticulously curated to assure that accurate experimental and sample processing metadata are included with each data set. GLDS download volumes indicate strong interest of the scientific community in these data. To date GeneLab has partnered with multiple experiments including two plant (Arabidopsis thaliana) experiments, two mice experiments, and several microbe experiments. GeneLab optimized protocols in the rodent partnerships for maximum yield of RNA, DNA and protein from tissues harvested and preserved during the SpaceX-4 mission, as well as from tissues from mice that were frozen intact during spaceflight and later dissected on the ground. Analysis of GeneLab data will contribute fundamental knowledge of how the space environment affects biological systems, and as well as yield terrestrial benefits resulting from mitigation strategies to prevent effects observed during exposure to space environments
Bipolar Jets and Orbital Dynamics of the Supersoft X-Ray Source RX J0019.8+2156
From 1994 to 1997 we monitored the optical spectrum of RXJ0019.8+2156. This
supersoft X-ray source is one of only two accreting white dwarfs in the Galaxy
thought to be burning hydrogen on their surface as a consequence of a high rate
of mass transfer from a binary companion. Accurate orbital ephemerides are
derived from radial velocity measure- ments of HeII emission lines, which
exhibit a stable velocity semi- amplitude of 71.2 +- 3.6 km/s. We report the
discovery of transient, low-velocity, bipolar jets. These jets are respresented
by redshifted and blueshifted pairs of emission lines with an outflow velocity
of v cos(i) = 815 km/s, where i is the binary inclination angle. When present,
the jet lines also exhibit an orbital modulation of 71 km/s, which indicates
that the jets are oriented nearly perpendicular to the orbital plane. On most
occasions, the Hline profiles are further altered by P Cygni absorption. We
show that the jets and the P Cygni features have very different temporal
characteristics and binary phase dependence. The jet material and the absorbing
wind must therefore occupy very different geometries. Finally, the measured
mass function is combined with binary evolution models to suggest a limit, i <
40 deg. A particular model invoked to explain a high rate of mass transfer
requires 16 < i < 25. However, at such small inclination it is difficult to
explain the large amplitude of the orbital light curve. By contrast, a simple
model fit to the jet outflow lines indicates an orbital inclination angle of 35
< i < 60.Comment: 49 pages, including 9 figs.; latex; aasms4.sty; revised manuscript
submitted to Astrophysical Journal, May 4, 199
A limit cycle model for long-term optical variations of V Sagittae: The second example of accretion wind evolution
V Sagittae shows quasi-periodic optical high (soft X-ray off) and low (soft
X-ray on) states with the total period of ~300 days. A binary model is
presented to explain orbital light curves both for the high and low states as
well as the transition mechanism between them. The binary model consists of a
white dwarf (WD), a disk around the WD, and a lobe-filling main-sequence (MS)
companion. In the optical high state, the mass transfer rate to the WD exceeds
the critical rate of ~1 x 10^{-6} Msun/yr, and the WD blows an optically thick,
massive wind. Surface layers of the disk are blown in the wind and the disk
surface extends to the companion or over. As a result, optical luminosity of
the disk increases by a magnitude because of its large irradiation effect. The
massive wind completely obscures soft X-rays. This corresponds to the optical
high/soft X-ray off state. The transition between optical high and low states
is driven by an attenuation of the mass transfer from the secondary. As the
mass supply stops, the WD wind weakens and eventually stops. The disk shrinks
to a Roche lobe size and the optical magnitude drops. This phase corresponds to
the optical low/soft X-ray on state. This cycle is repeated like a limit cycle.
The WD can grow in mass at the critical rate and eventually reach the
Chandrasekhar mass limit. This process is called ``accretion wind evolution,''
which is a key evolutionary process in a recently developed evolutionary
scenario of Type Ia supernovae. This evolutionary process was first confirmed
in the LMC supersoft X-ray source RX J0513.96951. Thus, V Sge is the second
example of accretion wind evolution.Comment: to appear in ApJ, 33 pages including figure
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