305 research outputs found
Radial Velocity Variations in Pulsating Ap Stars III. The Discovery of 16.21 min Oscillations in Beta CrB
We present the analysis of 3 hrs of a rapid time series of precise stellar
radial velocity (RV) measurements (sigma = 4.5 m/s) of the cool Ap star Beta
CrB. The integrated RV measurements spanning the wavelength interval 5000-6000
Ang. show significant variations (false alarm probability = 10^-5) with a
period of 16.21 min (nu = 1028.17 micro Hz) and an amplitude of 3.54 +/- 0.56
m/s. The RV measured over a much narrower wavelength interval reveals one
spectral feature at 6272 Ang. pulsating with the same 16.21 min period and an
amplitude of 138 +/- 23 m/s. These observations establish Beta CrB to be a
low-amplitude rapidly oscillating Ap star.Comment: 5 Pages, 5 figure
Nonlinear Dynamics of a Bose-Einstein Condensate in a Magnetic Waveguide
We have studied the internal and external dynamics of a Bose-Einstein
condensate in an anharmonic magnetic waveguide. An oscillating condensate
experiences a strong coupling between the center of mass motion and the
internal collective modes. Due to the anharmonicity of the magnetic potential,
not only the center of mass motion shows harmonic frequency generation, but
also the internal dynamics exhibit nonlinear frequency mixing. We describe the
data with a theoretical model to high accuracy. For strong excitations we test
the experimental data for indications of a chaotic behavior.Comment: 4 pages, 4 figure
A Uniformly Derived Catalogue of Exoplanets from Radial Velocities
A new catalogue of extrasolar planets is presented by re-analysing a
selection of published radial velocity data sets using EXOFIT (Balan & Lahav
2009). All objects are treated on an equal footing within a Bayesian framework,
to give orbital parameters for 94 exoplanetary systems. Model selection
(between one- and two-planet solutions) is then performed, using both a visual
flagging method and a standard chi-square analysis, with agreement between the
two methods for 99% of the systems considered. The catalogue is to be made
available online, and this 'proof of concept' study may be maintained and
extended in the future to incorporate all systems with publicly available
radial velocity data, as well as transit and microlensing data.Comment: 16 pages, 6 figures, 6 table
The Photometric Period and Variability of the Cataclysmic Variable V849 Herculis (PG 1633+115)
We report time-resolved photometry of the cataclysmic variable V849 Her, and
measure a period of 0.1414 \pm 0.0030 days (3.394 \pm 0.072 hours). We also
present photometry taken over several weeks in 2010 and 2011, as well as light
curves from 1995 to 2011 by the American Association of Variable Star
Observers. The spectra, absolute magnitude derived from infrared magnitudes,
and variability all suggest that V849 Her is a nova-like variable. The shallow
(0.5-magnitude) low states we observe resemble the erratic low states of the VY
Sculptoris stars, although they may recur quasi-periodically over an average
cycle of 12.462 \pm 0.074 days.Comment: 18 pages, 9 figures, accepted for publication in New Astronom
Asteroseismology of the planet-hosting star mu Arae. II. Seismic analysis
As most exoplanets host stars, HD 160691 (alias mu Ara) presents a
metallicity excess in its spectrum compared to stars without detected planets.
This excess may be primordial, in which case the star would be completely
overmetallic, or it may be due to accretion in the early phases of planetary
formation, in which case it would be overmetallic only in its outer layers. As
discussed in a previous paper (Bazot and Vauclair 2004), seismology can help
choosing between the two scenarios. This star was observed during eight nights
with the spectrograph HARPS at La Silla Observatory. Forty three p-modes have
been identified (Bouchy et al. 2005). In the present paper, we discuss the
modelisation of this star. We computed stellar models iterated to present the
same observable parameters (luminosity, effective temperature, outer chemical
composition) while the internal structure was different according to the two
extreme assumptions : original overmetallicity or accretion. We show that in
any case the seismic constraints lead to models in complete agreement with the
external parameters deduced from spectroscopy and from the Hipparcos parallax
(L and Teff). We discuss the tests which may lead to a choice between the two
typical scenarios. We show that the ``small separation'' seem to give a better
fit for the accretion case than for the overmetallic case, but in spite of the
very good data the uncertainties are still too large to conclude. We discuss
the observations which would be needed to go further and solve this question.Comment: 16 pages, 8 figures, accepted in A&
XSS J00564+4548 and IGR J00234+6141 -- new cataclysmic variables from RXTE and INTEGRAL all sky surveys
We present the results of optical identification of two X-ray sources from
RXTE and INTEGRAL all sky surveys: XSS J00564+4548 and IGR J00234+6141. Using
the optical data from Russian-Turkish 1.5-m Telescope (RTT150) and SWIFT X-ray
observations, we show that these sources most probably are intermediate polars,
i.e. binary systems with accreting white dwarfs with not very strong magnetic
field (<~10 MG). Periodical oscillations of optical emission with periods 480 s
and 570 s were found. We argue that these periods most probably correspond to
the rotating periods of the white dwarfs in these systems. Further optical
observations scheduled at RTT150 will allow to study the parameters of these
systems in more detail.Comment: 5 pages, 8 figures, accepted for publication in Astronomy Letter
INTEGRAL and Swift/XRT observations on IGR J18179-1621
IGR J18179-1621 is a hard X-ray binary transient discovered recently by
INTEGRAL. Here we report on detailed timing and spectral analysis on IGR
J18179-1621 in X-rays based on available INTEGRAL and Swift data. From the
INTEGRAL analysis, IGR J18179-1621 is detected with a significance of 21.6
sigma in the 18-40 keV band by ISGRI and 15.3 sigma in the 3-25 keV band by
JEM-X, between 2012-02-29 and 2012-03-01. We analyze two quasisimultaneous
Swift ToO observations. A clear 11.82 seconds pulsation is detected above the
white noise at a confidence level larger than 99.99%. The pulse fraction is
estimated as 22+/-8% in 0.2-10 keV. No sign of pulsation is detected by
INTEGRAL/ISGRI in the 18-40 keV band. With Swift and INTEGRAL spectra combined
in soft and hard X-rays, IGR J18179-1621 could be fitted by an absorbed power
law with a high energy cutoff plus a Gaussian absorption line centered at 21.5
keV. An additional absorption intrinsic to the source is found, while the
absorption line is evidence for most probably originated from cyclotron
resonant scattering and suggests a magnetic field in the emitting region of
\sim 2.4 \times 10^12 Gauss.Comment: 5 pages, 3 figures, 1 table; accepted to MNRAS Letter
Cryptotomography: reconstructing 3D Fourier intensities from randomly oriented single-shot diffraction patterns
We reconstructed the 3D Fourier intensity distribution of mono-disperse
prolate nano-particles using single-shot 2D coherent diffraction patterns
collected at DESY's FLASH facility when a bright, coherent, ultrafast X-ray
pulse intercepted individual particles of random, unmeasured orientations. This
first experimental demonstration of cryptotomography extended the
Expansion-Maximization-Compression (EMC) framework to accommodate unmeasured
fluctuations in photon fluence and loss of data due to saturation or background
scatter. This work is an important step towards realizing single-shot
diffraction imaging of single biomolecules.Comment: 4 pages, 4 figure
1318 New Variable Stars in a 0.25 Square Degree Region of the Galactic Plane
We have conducted a deep photometric survey of a 0.5 deg x 0.5 deg area of
the Galactic Plane using the WFI instrument on the 2.2-m ESO telescope on La
Silla, Chile. The dataset comprises a total of 267 R-band images, 204 from a 16
day observation run in 2005, supplemented by 63 images from a six week period
in 2002. Our reduction employed the new numerical kernel difference image
analysis method as implemented in the PYSIS3 code and resulted in more than
500,000 lightcurves of stars down to a magnitude limit of R ~ 24.5. A search
for variable stars resulted in the detection of 1318 variables of different
types. 1011 of these are eclipsing or contact binary stars. A number of the
contact binaries have low mass-ratios and several of the detached binaries
appear to have low-mass components. Three candidate contact binaries have
periods at the known cut off including two with periods lower than any
previously published. Also identified are 3 possible pre-main sequence detached
eclipsing binaries.Comment: 54 pages, 17 figures, 11 tables, accepted by A&A. Photometry will be
available through CD
Long-term optical variability of PKS 2155-304
Aims: The optical variability of the blazar PKS 2155-304 is investigated to
characterise the red noise behaviour at largely different time scales from 20
days to O(>10 yrs). Methods: The long-term optical light curve of PKS 2155-304
is assembled from archival data as well as from so-far unpublished observations
mostly carried out with the ROTSE-III and the ASAS robotic telescopes. A
forward folding technique is used to determine the best-fit parameters for a
model of a power law with a break in the power spectral density function (PSD).
The best-fit parameters are estimated using a maximum-likelihood method with
simulated light curves in conjunction with the Lomb Scargle Periodogram (LSP)
and the first-order Structure Function (SF). In addition, a new approach based
upon the so-called Multiple Fragments Variance Function (MFVF) is introduced
and compared to the other methods. Simulated light curves have been used to
confirm the reliability of these methods as well as to estimate the
uncertainties of the best-fit parameters. Results: The light curve is
consistent with the assumed broken power-law PSD. All three methods agree
within the estimated uncertainties with the MFVF providing the most accurate
results. The red-noise behaviour of the PSD in frequency f follows a power law
with f^-{\beta}, {\beta}=1.8 +0.1/-0.2 and a break towards f^0 at frequencies
lower than f_min=(2.7 +2.2/-1.6 yrs)^-1.Comment: 10 pages, 8 figures, the ROTSE-light curve can be downloaded from
http://vizier.cfa.harvard.edu/viz-bin/VizieR?-source=J/A+A/531/A12
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