12,127 research outputs found
Optical Modulation in the X-Ray Binary 4U 1543-624 Revisited
The X-ray binary 4U 1543624 has been provisionally identified as an
ultracompact system with an orbital period of 18~min. We have carried
out time-resolved optical imaging of the binary to verify the ultra-short
orbital period. Using 140\,min of high-cadence -band photometry we recover
the previously-seen sinusoidal modulation and determine a period
\,min. In addition, we also see a 7.0\,mag\,min linear decay, likely related to variations in the
source's accretion activity. Assuming that the sinusoidal modulation arises
from X-ray heating of the inner face of the companion star, we estimate a
distance of 6.0--6.7\,kpc and an inclination angle of
34--61 (90\% confidence) for the binary. Given the
stability of the modulation we can confirm that the modulation is orbital in
origin and 4U 1543624 is an ultracompact X-ray binary.Comment: 6 pages, 3 figures, accepted for publication in Publications of the
Astronomical Society of Australia (PASA
Timing the Nearby Isolated Neutron Star RX J1856.5-3754
RX J1856.5-3754 is the X-ray brightest among the nearby isolated neutron
stars. Its X-ray spectrum is thermal, and is reproduced remarkably well by a
black-body, but its interpretation has remained puzzling. One reason is that
the source did not exhibit pulsations, and hence a magnetic field
strength--vital input to atmosphere models--could not be estimated. Recently,
however, very weak pulsations were discovered. Here, we analyze these in
detail, using all available data from the XMM-Newton and Chandra X-ray
observatories. From frequency measurements, we set a 2-sigma upper limit to the
frequency derivative of \dot\nu<1.3e-14 Hz/s. Trying possible phase-connected
timing solutions, we find that one solution is far more likely than the others,
and we infer a most probable value of \dot\nu=(-5.98+/-0.14)e-16 Hz/s. The
inferred magnetic field strength is 1.5e13 G, comparable to what was found for
similar neutron stars. From models, the field seems too strong to be consistent
with the absence of spectral features for non-condensed atmospheres. It is
sufficiently strong, however, that the surface could be condensed, but only if
it is consists of heavy elements like iron. Our measurements imply a
characteristic age of about 4 Myr. This is longer than the cooling and
kinematic ages, as was found for similar objects, but at almost a factor ten,
the discrepancy is more extreme. A puzzle raised by our measurement is that the
implied rotational energy loss rate of about 3e30 erg/s is orders of magnitude
smaller than what was inferred from the H-alpha nebula surrounding the source.Comment: 4 pages, 2 figures, 2 tables; accepted for publication in
Astrophysical Journal (Letters
Nearby, Thermally Emitting Neutron Stars
We describe a sample of thermally emitting neutron stars discovered in the
ROSAT All-Sky Survey. We discuss the basic observational properties of these
objects and conclude that they are nearby, middle-aged pulsars with moderate
magnetic fields that we see through their cooling radiation. While these
objects are potentially very useful as probes of matter at very high densities
and magnetic fields, our lack of understanding of their surface emission limits
their current utility. We discuss this and other outstanding problems: the
spectral evolution of one sources and the relation of this population to the
overall pulsar population.Comment: 9 pages, one table, 3 figures. To appear in the proceedings of "40
Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17,
2007, McGill University, Montreal, Canad
Thermal alteration of organic matter in recent marine sediments. 1: Pigments
Sediment from Tanner Basin, the outer continental shelf off Southern California, was analyzed for photosynthetic pigments and their derivatives, namely carotenes and chlorins. Samples of the sediment were also exposed to raised temperatures (65, 100, 150 C) for various periods of time (1 week, 1 month, 2 months). Analysis of the heat-treated sediment revealed the presence of alpha-ionene and 2,6-dimethylnapthalene, thermal degradation products of Betacarotente. Chlorins were converted to nickel porphyrins of both DPEP and etio series. Possible mechanisms of these transformations are presented
Effect of 22(S), 23(S)-Homobrassinolide on Adventitious Root Formation in Grape Rootstocks
In recent times, brassinosteroids have been identified as a group of hormones that regulate plant growthand development. They affect plant development from seed germination to senescence. The aim of thisresearch was to study the effects of brassinosteroids on the rooting of three American grapevine rootstocks(1103 Paulsen, 110 Richter and 99 Richter) used frequently to produce grafted grapevines. Rootstockcuttings were dipped for 10 minutes into five different concentrations of 22(S), 23(S)-homobrassinolide andplanted into a peat-perlite mixture. Data such as fresh and dry root weight, root number and developmentlevel were collected and assessed. Some shoot growth features were also determined. The results showedthat the grapevine rootstocks with the most significant response in improved root and shoot growth were1103 Paulsen, followed by 110 Richter. Root development level was influenced by both the rootstock andthe concentrations of the substance. The lowest concentration, 0.05 ppm, induced more root numbers in1103 Paulsen, while 0.15 ppm resulted in the highest number of roots in 99 Richter. A statistical analysis ofthe data revealed a significant difference between root development and shoot growth
A Search For Solar Hadronic Axions Using Kr-83
We introduce a new experimental method for solar hadronic axions search. It
is suggested that these axions are created in the Sun during M1 transition
between the first thermally excited level at 9.4 keV and the ground state in
. Our method is based on axion detection via resonant absorption
process by the same nucleus in the laboratory. We use proportional gas counter
filled with krypton to detect signals for axions. With this setup, target and
detector are the same which increases the efficiency of the experiment. At
present, an upper limit on hadronic axion mass of 5.5 keV at the 95% confidence
level is obtained.Comment: 3 pages, contribution to ISRP9 Conference in Cape Town 2003. Version
accepted by Radiat. Phys. Che
Modification of the Charge ordering in PrSrMnO Nanoparticles
Transport and magnetic properties have been studied in two sets of sol-gel
prepared PrSrMnO nanoparticles having average particle
size of 30 nm and 45 nm. Our measurements suggest that the formation of charge
ordered state is largely affected due to lowering of particle size, but the
ferromagnetic transition temperature () remains unaffected.Comment: Accepted in J. Appl. Phy
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