180 research outputs found
The changing UV and X-ray properties of the Of?p star CPD -28 2561
The Of?p star CPD -28 2561 was monitored at high energies with XMM-Newton and
HST. In X-rays, this magnetic oblique rotator displays bright and hard emission
that varies by ~55% with rotational phase. These changes occur in phase with
optical variations, as expected for magnetically confined winds; there are two
maxima and two minima in X-rays during the 73d rotational period of CPD -28
2561. However, contrary to previously studied cases, no significant hardness
variation is detected between minima and maxima, with the exception of the
second minimum which is slightly distinct from the first one. In the UV domain,
broad-band fluxes remain stable while line profiles display large variations.
Stronger absorptions at low velocities are observed when the magnetic equator
is seen edge-on, which can be reproduced by a detailed 3D model. However, a
difference in absorption at high velocities in the CIV and NV lines is also
detected for the two phases where the confined wind is seen nearly pole-on.
This suggests the presence of strong asymmetries about the magnetic equator,
mostly in the free-flowing wind (rather than in the confined dynamical
magnetosphere).Comment: 14 pages, 11 figures, accepted for publication by MNRA
X-ray emission from the double-binary OB-star system QZ Car (HD 93206)
X-ray observations of the double-binary OB-star system QZ Car (HD 93206)
obtained with the Chandra X-ray Observatory over a period of roughly 2 years
are presented. The orbit of systems A (O9.7 I+b2 v, PA = 21 d) and B (O8 III+o9
v, PB = 6 d) are reasonably well sampled by the observations, allowing the
origin of the X-ray emission to be examined in detail. The X-ray spectra can be
well fitted by an attenuated three temperature thermal plasma model,
characterised by cool, moderate, and hot plasma components at kT ~ 0.2, 0.7,
and 2 keV, respectively, and a circumstellar absorption of ~ 0.2 x 10^22 cm-2.
Although the hot plasma component could be indicating the presence of wind-wind
collision shocks in the system, the model fluxes calculated from spectral fits,
with an average value of ~ 7 x 10^-13 erg s-1 cm-2, do not show a clear
correlation with the orbits of the two constituent binaries. A semi-analytical
model of QZ Car reveals that a stable momentum balance may not be established
in either system A or B. Yet, despite this, system B is expected to produce an
observed X-ray flux well in excess of the observations. If one considers the
wind of the O8 III star to be disrupted by mass transfer the model and
observations are in far better agreement, which lends support to the previous
suggestion of mass-transfer in the O8 III + o9 v binary. We conclude that the
X-ray emission from QZ Car can be reasonably well accounted for by a
combination of contributions mainly from the single stars and the mutual
wind-wind collision between systems A and B.Comment: 11 pages, 7 figures. Accepted for the ApJS Special Issue on the
Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011.
All 16 CCCP Special Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
leas
On the multiplicity of the O-star Cyg OB2 #8A and its contribution to the gamma-ray source 3EG J2033+4118
We present the results of an intensive spectroscopic campaign in the optical
waveband revealing that Cyg OB2 #8A is an O6 + O5.5 binary system with a period
of about 21.9 d. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal
radio emitter. We discuss the binarity of this star in the framework of a
campaign devoted to the study of non-thermal emitters, from the radio waveband
to gamma-rays. In this context, we attribute the non-thermal radio emission
from this star to a population of relativistic electrons, accelerated by the
shock of the wind-wind collision. These relativistic electrons could also be
responsible for a putative gamma-ray emission through inverse Compton
scattering of photospheric UV photons, thus contributing to the yet
unidentified EGRET source 3EG J2033+4118.Comment: 8 pages, 4 figures, conference on "The Multiwavelength Approach to
Gamma-Ray Sources", to appear in Ap&S
A VLT/FLAMES survey for massive binaries in Westerlund 1: II. Dynamical constraints on magnetar progenitor masses from the eclipsing binary W13
Westerlund 1 is a young, massive Galactic starburst cluster that contains a
rich coeval population of Wolf-Rayet stars, hot- and cool-phase transitional
supergiants, and a magnetar. We use spectroscopic and photometric observations
of the eclipsing double-lined binary W13 to derive dynamical masses for the two
components, in order to determine limits for the progenitor masses of the
magnetar CXOU J164710.2-455216 and the population of evolved stars in Wd1. W13
has an orbital period of 9.2709+/-0.0015 days and near-contact configuration.
The shallow photometric eclipse rules out an inclination greater than 65
degrees, leading to lower limits for the masses of the emission-line optical
primary and supergiant optical secondary of 21.4+/-2.6Msun and 32.8+/-4.0Msun
respectively, rising to 23.2 +3.3/-3.0Msun and 35.4 +5.0/-4.6 Msun for our
best-fit inclination 62 +3/-4 degrees. Comparison with theoretical models of
Wolf-Rayet binary evolution suggest the emission-line object had an initial
mass in excess of 35Msun, with the most likely model featuring highly
non-conservative late-Case-A/Case-B mass transfer and an initial mass in excess
of 40Msun. This confirms the high magnetar progenitor mass inferred from its
membership in Wd1, and represents the first dynamical constraint on the
progenitor mass of any magnetar. The red supergiants in Wd1 must have similar
progenitor masses to W13 and are therefore amongst the most massive stars to
undergo a red supergiant phase, representing a challenge for population models
that suggest stars in this mass range end their redwards evolution as yellow
hypergiants. [ABRIDGED]Comment: Accepted for publication in A&A. 8 pages, 5 figures. See also
http://www.eso.org/public/news/eso1034/ from noon (CEST) Wed 18th Augus
X-ray emission from massive stars in Cyg OB2
We report on the analysis of the Chandra-ACIS data of O, B and WR stars in
the young association Cyg OB2. X-ray spectra of 49 O-stars, 54 B-stars and 3
WR-stars are analyzed and for the brighter sources, the epoch dependence of the
X-ray fluxes is investigated. The O-stars in Cyg\,OB2 follow a well-defined
scaling relation between their X-ray and bolometric luminosities: log(Lx/Lbol)
= -7.2 +/- 0.2. This relation is in excellent agreement with the one previously
derived for the Carina OB1 association. Except for the brightest O-star
binaries, there is no general X-ray overluminosity due to colliding winds in
O-star binaries. Roughly half of the known B-stars in the surveyed field are
detected, but they fail to display a clear relationship between Lx and Lbol.
Out of the three WR stars in Cyg OB2, probably only WR144 is itself responsible
for the observed level of X-ray emission, at a very low log(Lx/Lbol) = -8.8 +/-
0.2. The X-ray emission of the other two WR-stars (WR145 and 146) is most
probably due to their O-type companion along with a moderate contribution from
a wind-wind interaction zone.Comment: Accepted for an ApJS Special Issue devoted to the Chandra Cygnus OB2
Legacy Surve
INTEGRAL detection of hard X-rays from NGC 6334: Nonthermal emission from colliding winds or an AGN?
We report the detection of hard X-ray emission from the field of the
star-forming region NGC 6334 with the the International Gamma-Ray Astrophysics
Laboratory INTEGRAL. The JEM-X monitor and ISGRI imager aboard INTEGRAL and
Chandra ACIS imager were used to construct 3-80 keV images and spectra of NGC
6334. The 3-10 keV and 10-35 keV images made with JEM-X show a complex
structure of extended emission from NGC 6334. The ISGRI source detected in the
energy ranges 20-40 keV and 40-80 keV coincides with the NGC 6334 ridge. The
20-60 keV flux from the source is (1.8+-0.37)*10(-11) erg cm(-2) s(-1).
Spectral analysis of the source revealed a hard power-law component with a
photon index about 1. The observed X-ray fluxes are in agreement with
extrapolations of X-ray imaging observations of NGC 6334 by Chandra ACIS and
ASCA GIS. The X-ray data are consistent with two very different physical
models. A probable scenario is emission from a heavily absorbed, compact and
hard Chandra source that is associated with the AGN candidate radio source NGC
6334B. Another possible model is the extended Chandra source of nonthermal
emission from NGC 6334 that can also account for the hard X-ray emission
observed by INTEGRAL. The origin of the emission in this scenario is due to
electron acceleration in energetic outflows from massive early type stars. The
possibility of emission from a young supernova remnant, as suggested by earlier
infrared observations of NGC 6334, is constrained by the non-detection of 44Ti
lines.Comment: 8 pages, 8 figures, Astronomy and Astrophysics (in press
The filter wheel and filters development for the X-IFU instruments onboard Athena
Athena is the large mission selected by ESA in 2013 to investigate the science theme "Hot and Energetic Universe" and presently scheduled for launch in 2028. One of the two instruments located at the focus of the 12 m-long Athena telescope is the X-ray Integral Field Unit (X-IFU). This is an array of TES microcalorimeters that will be operated at temperatures of 50 mK in order to perform high resolution spectroscopy with an energy resolution down to 2.5 eV at energies < 7 keV. In order to cope with the large dynamical range of X-ray fluxes spanned by the celestial objects Athena will be observing, the X-IFU will be equipped with a filter wheel. This will allow the user to fine tune the instrument set-up based on the nature of the target, thus optimizing the scientific outcomes of the observation. A few positions of the filter wheel will also be used to host a calibration source and to allow the measurement of the instrument intrinsic background
Quasi-simultaneous XMM-Newton and VLA observation of the non-thermal radio emitter HD\168112 (O5.5III(f^+))
We report the results of a multiwavelength study of the non-thermal radio
emitter HD168112 (O5.5III(f^+)). The detailed analysis of two
quasi-simultaneous XMM-Newton and VLA observations reveals strong variability
of this star both in the X-ray and radio ranges. The X-ray observations
separated by five months reveal a decrease of the X-ray flux of ~30%. The radio
emission on the other hand increases by a factor 5-7 between the two
observations obtained roughly simultaneously with the XMM-Newton pointings. The
X-ray data reveal a hard emission that is most likely produced by a thermal
plasma at kT ~2-3 keV while the VLA data confirm the non-thermal status of this
star in the radio waveband. Comparison with archive X-ray and radio data
confirms the variability of this source in both wavelength ranges over a yet
ill defined time scale. The properties of HD168112 in the X-ray and radio
domain point towards a binary system with a significant eccentricity and an
orbital period of a few years. However, our optical spectra reveal no
significant changes of the star's radial velocity suggesting that if HD168112
is indeed a binary, it must be seen under a fairly low inclination.Comment: 17 pages, 11 figures (10 postscript + 1 gif
Impact of Mycoplasma hyopneumoniae and Lawsonia intracellularis on the performance of pigs divergently selected for feed efficiency
Feed efficiency (FE) is a valuable trait, yet how genetic selection for enhanced FE affects other processes such as response to disease is unknown. Disease from endemic respiratory and enteric pathogens such as Mycoplasma hyopneumoniae (Mh) and Lawsonia intracellularis (LI) are common in swine production. Therefore, the aim of this study was to examine if pigs selected for high versus low FE based on residual feed intake (RFI) respond differently to a dual respiratory and enteric challenge. Pigs selected for low RFI (LRFI, high feed efficiency) pigs are considered more FE compared to their high RFI (HRFI, low feed efficiency) selected counterparts. Using a 2 x 2 factorial design, 25 littermate pairs from the HRFI and 25 littermate pairs from the LRFI line (barrows, 50 ± 7 kg BW) were selected, with one pig from each pair assigned to individual pens in either the challenge or the non-challenge (control) rooms (n = 25 barrows per line/challenge). On days post inoculation (dpi) 0, the challenged pigs were inoculated with LI and Mh (MhLI). Feed intake, body weight, fecal swabs, and serum samples were collected and recorded weekly for 42 days. On dpi -2 and 47, 14 littermate pairs (n=7 barrows per line/challenge) were utilized for initial and final body composition scans using dual X-ray absorptiometry to calculate longitudinal whole body tissue accretion rates for lean, protein, fat, and bone mineral content. Serum antibody levels and fecal shedding of LI were used to confirm infection. Control pigs remained negative by all measures during the 6 week trial and MhLI inoculated pigs were confirmed positive via serological antibody responses by dpi 14 for LI and Mh. There were no interactions between RFI line and challenge status for any overall performance parameter (P \u3e 0.05). The six week MhLI challenge resulted in a 17% reduction in ADG, a 12% reduction in ADFI, and a 7% reduction in G:F versus controls (P \u3c 0.05). In addition, compared to the control pigs, MhLI challenge reduced lean, protein, and lipid accretion rates by 16% (P \u3c 0.05). Genetic selection for high FE resulted in decreased ADFI and increased G:F (P \u3c 0.01), but did not impact ADG or tissue accretion versus low FE pigs. Collectively, these results demonstrate that a dual enteric and respiratory pathogen challenge reduced ADG, ADFI, G:F and tissue accretion in growing pigs. Further, there was no evidence that selection for enhanced FE based on RFI index affects response to disease
Influence of a Liquid Nutritional Supplement on Water Intake in Experimental Beagle Dogs
Abstract The objectives were to evaluate the effects of a liquid nutritional supplement formulated for dogs on water intakes and urine output. A liquid nutritional supplement was tested by way of a crossover design in 8 experimental healthy Beagle dogs (4 males and 4 females, aged 9.3 years). The supplement (87 percent water, 2.7 percent protein, 2.6 percent fat, 0.4 percent crude fiber) was added to water and tested at 2 incorporation rates (50 or 70 ml/day/dog-D50 or D70) versus the control placebo (CO-water only). The dogs were kept in a controlled environment; water intakes and urine output were measured. Individual water intakes were characterised by large variations. Mean water intake increased significantly by 28 percent in dogs receiving the liquid nutritional supplement, in both genders, irrespectively of the dosage. Urine output was also increased, by 55 percent. Faeces scores remained unchanged. It was concluded that the liquid supplement increased water intake and urine output in a safe way, without increasing dramatically the daily dietary sodium chloride intake. The recommended dosage of the manufacturer-50 ml/day for dogs weighing 10 -20 kg BW is efficient. Increasing the dosage had no advantage, nor adverse effects. Increased water intake and urine output is of interest for dogs suffering from urolithiasis
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