425 research outputs found
The X-ray transient XTE J1118+480: Multiwavelength observations of a low-state mini-outburst
We present multiwavelength observations of the newly discovered X-ray
transient XTE J1118+480 obtained in the rising phase of the 2000 April
outburst. This source is located at unusually high Galactic latitude and in a
very low absorption line of sight. This made the first EUVE spectroscopy of an
X-ray transient outburst possible. Together with our HST, RXTE, and UKIRT data
this gives unprecedented spectral coverage. We find the source in the low hard
state. The flat IR-UV spectrum appears to be a combination of optically thick
disk emission and flat spectrum emission, possibly synchrotron, while at higher
energies, including EUV, a typical low hard state power-law is seen. EUVE
observations reveal no periodic modulation, suggesting an inclination low
enough that no obscuration by the disk rim occurs. We discuss the nature of the
source and this outburst and conclude that it may be more akin to
mini-outbursts seen in GRO J0422+32 than to a normal X-ray transient outburst.Comment: 4 pages, 3 figures, replaced with accepted version. Uses
emulateapj5.st
Modeling the Low State Spectrum of the X-Ray Nova XTE J1118+480
Based on recent multiwavelength observations of the new X-ray nova XTE
J1118+480, we can place strong constraints on the geometry of the accretion
flow in which a low/hard state spectrum, characteristic of an accreting black
hole binary, is produced. We argue that the absence of any soft blackbody-like
component in the X-ray band implies the existence of an extended hot
optically-thin region, with the optically-thick cool disk truncated at some
radius R_{tr} > 55 R_{Schw}. We show that such a model can indeed reproduce the
main features of the observed spectrum: the relatively high optical to X-ray
ratio, the sharp downturn in the far UV band and the hard X-ray spectrum. The
absence of the disk blackbody component also underscores the requirement that
the seed photons for thermal Comptonization be produced locally in the hot
flow, e.g. via synchrotron radiation. We attribute the observed spectral break
at 2 keV to absorption in a warm, partially ionized gas.Comment: 6 pages, including 1 figure; LaTeX (emulateapj5.sty), to appear in
Ap
SuperWASP: Wide Angle Search for Planets
SuperWASP is a fully robotic, ultra-wide angle survey for planetary transits.
Currently under construction, it will consist of 5 cameras, each monitoring a
9.5 x 9.5 deg field of view. The Torus mount and enclosure will be fully
automated and linked to a built-in weather station. We aim to begin
observations at the beginning of 2003.Comment: 4 pages, 1 figure, to be published in proceedings of "Scientific
Frontiers in Research on Extrasolar Planets
Current Status of the SuperWASP Project
We present the current status of the SuperWASP project, a Wide Angle Search
for Planets. SuperWASP consists of up to 8 individual cameras using ultra-wide
field lenses backed by high-quality passively cooled CCDs. Each camera covers
7.8 x 7.8 sq degrees of sky, for nearly 500 sq degrees of sky coverage.
SuperWASP I, located in LaPalma, is currently operational with 5 cameras and is
conducting a photometric survey of a large numbers of stars in the magnitude
range ~7 to 15. The collaboration has developed a custom-built reduction
pipeline and aims to achieve better than 1 percent photometric precision. The
pipeline will also produce well sampled light curves for all the stars in each
field which will be used to detect: planetary transits, optical transients, and
track Near-Earth Objects. Status of current observations, and expected rates of
extrasolar planetary detections will be presented. The consortium members,
institutions, and further details can be found on the web site at:
http://www.superwasp.org.Comment: 3 pages, 2 figures, submitted to the Proceedings of the 13th Cool
Stars Workshop, Ed. F. Favata, ESA-S
Suppressed Far-UV stellar activity and low planetary mass-loss in the WASP-18 system
WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age (R′HK activity parameter lies slightly below the basal level; there is no significant time-variability in the log R′HK value; there is no detection of the star in the X-rays. We present results of far-UV observations of WASP-18 obtained with COS on board of HST aimed at explaining this anomaly. From the star’s spectral energy distribution, we infer the extinction (E(B − V) ≈ 0.01mag) and then the ISM column density for a number of ions, concluding that ISM absorption is not the origin of the anomaly. We measure the flux of the four stellar emission features detected in the COS spectrum (C II, C III, C IV, Si IV). Comparing the C II/C IV flux ratio measured for WASP-18 with that derived from spectra of nearby stars with known age, we see that the far-UV spectrum of WASP-18 resembles that of old (>5Gyr), inactive stars, in stark contrast with its young age. We conclude that WASP-18 has an intrinsically low activity level, possibly caused by star-planet tidal interaction, as suggested by previous studies. Re-scaling the solar irradiance reference spectrum to match the flux of the Si IV line, yields an XUV integrated flux at the planet orbit of 10.2 erg s−1 cm−2. We employ the rescaled XUV solar fluxes to model of the planetary upper atmosphere, deriving an extremely low thermal mass-loss rate of 10−20MJ Gyr−1. For such high-mass planets, thermal escape is not energy limited, but driven by Jeans escape
The first WASP public data release
The WASP (wide angle search for planets) project is an exoplanet transit survey that has been automatically taking wide field images since 2004. Two instruments, one in La Palma and the other in South Africa, continually monitor the night sky, building up light curves of millions of unique objects. These light curves are used to search for the characteristics of exoplanetary transits. This first public data release (DR1) of the WASP archive makes available all the light curve data and images from 2004 up to 2008 in both the Northern and Southern hemispheres. A web interface () to the data allows easy access over the Internet. The data set contains 3 631 972 raw images and 17 970 937 light curves. In total the light curves have 119 930 299 362 data points available between them
Fear, foraging and olfaction : how mesopredators avoid costly interactions with apex predators
Where direct killing is rare and niche overlap low, sympatric carnivores may appear to coexist without conflict. Interference
interactions, harassment and injury from larger carnivores may still pose a risk to smaller mesopredators. Foraging theory
suggests that animals should adjust their behaviour accordingly to optimise foraging efficiency and overall fitness, trading off
harvest rate with costs to fitness. The foraging behaviour of red foxes, Vulpes vulpes, was studied with automated cameras
and a repeated measures giving-up density (GUD) experiment where olfactory risk cues were manipulated. In Plitvice Lakes
National Park, Croatia, red foxes increased GUDs by 34% and quitting harvest rates by 29% in response to wolf urine. In
addition to leaving more food behind, foxes also responded to wolf urine by spending less time visiting food patches each
day and altering their behaviour in order to compensate for the increased risk when foraging from patches. Thus, red foxes
utilised olfaction to assess risk and experienced foraging costs due to the presence of a cue from gray wolves, Canis lupus.
This study identifies behavioural mechanisms which may enable competing predators to coexist, and highlights the potential
for additional ecosystem service pathways arising from the behaviour of large carnivores. Given the vulnerability of large
carnivores to anthropogenic disturbance, a growing human population and intensifying resource consumption, it becomes
increasingly important to understand ecological processes so that land can be managed appropriately.Table S1: Considerations proposed for the application of the giving-up density framework in field research and how the methodologies created in this paper accounted for these considerations.Table S2: Ethogram describing behaviours recorded (Bold font). Other behaviours that might accompany or be performed alongside those recorded are described in plain text.Bangor University, The UK Wolf Conservation Trust, The Coalbourn Charitable Trust, Ann Vernon Memorial Travel Fund and Sir Ian McKellen.http://link.springer.com/journal/442am2018Centre for Wildlife Managemen
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Photometric observations of the radio bright B[e]/X-ray binary CI Cam
We present multiwavelength (optical, IR, radio) observations of CI Cam, the optical counterpart to the transient X-ray source XTE J0421+560. Pre-outburst quiescent observations reveal the presence of a dusty envelope around the system. Pronounced short term variability is observed at all wavebands from U-K, but no indication of prior flaring of a similar magnitude to the 1998 April outburst is found in these data.
Data obtained during the 1998 April X-ray flare reveal pronounced optical-radio flaring. The optical flux was observed to quickly return to quiescent levels, while the radio flare was of much longer duration. The optical component is likely to result from a combination of free-free/free-bound emission, emission line and thermal dust emission, caused by re-radiation of the X-ray flux, while the behaviour of the multiwavelength radio data is consistent with emission from expanding ejecta emitting via the synchrotron mechanism.
Post-outburst (1998 August-1999 March) U-M broadband photometric observations reveal that while the optical (UBV) flux remains at pre-outburst quiescent levels, near IR (JHKLM) fluxes exceed the pre-outburst fluxes by ~0.5 magnitudes. Modelling the pre- and post-outburst spectral energy distribution of CI Cam reveals that the structure and/or composition of the dusty component of the circumstellar envelope appears to have changed. Due to a lack of information on the precise chemical composition of the dust within the system several explanations for this behaviour are possible, such as the production of new dust at the inner edge of the envelope, or modification of the composition of the dust due to X-ray irradiation
Multiwavelength observations revealing the outbursts of the two soft X-ray transients XTE J1859+226 and XTE J1118+480
We report here on multiwavelength observations of the two new soft X-ray
transients (SXTs) XTE J1859+226 and XTE J1118+480, which we observed with
HST/RXTE/UKIRT. For XTE J1118+480 we also used EUVE since it is located at a
very high galactic latitude and suffers from very low extinction. The two
sources exhibited very different behaviour. XTE J1859+226 seems quite normal
and therefore a good object for testing the accretion mechanisms in place
during the outbursts, XTE J1118+480 is much more unusual because it exhibits i)
a low X-ray to optical ratio and ii) a strong non-thermal contribution in the
radio to optical domain, which is likely to be due to synchrotron emission. We
concentrate here on the near-infrared (NIR) and optical observations of these
two systems.Comment: 4 pages, 6 figures, conference, Proceedings of the 4th INTEGRAL
Workshop (Alicante 2000), to be published in ESA-SP (2001
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