581 research outputs found
Photometric study of selected cataclysmic variables II. Time-series photometry of nine systems
We present time-series photometry of nine cataclysmic variables: EI UMa,
V844Her, V751 Cyg, V516 Cyg, GZ Cnc, TY Psc, V1315 Aql, ASAS J002511+1217.12,
V1315 Aql and LN UMa. The observations were conducted at various observatories,
covering 170 hours and comprising 7,850 data points in total.
For the majority of targets we confirm previously reported periodicities and
for some of them we give, for the first time, their spectroscopic orbital
periods. For those dwarf-nova systems which we observed during both quiescence
and outburst, the increase in brightness was followed by a decrease in the
amount of flickering. Quasi-periodic oscillations have either been discovered,
or were confirmed. For the eclipsing system V1315 Aql we have covered 9
eclipses, and obtained a refined orbital ephemeris. We find that, during its
long baseline of observations, no change in the orbital period of this system
has occurred. V1315 Aql also shows eclipses of variable depth.Comment: 30 pages, 16 figures, 4 tables. Submitted to JA
Investigations of the Non-Linear LMC Cepheid Period-Luminosity Relation with Testimator and Schwarz Information Criterion Methods
In this paper, we investigate the linearity versus non-linearity of the Large
Magellanic Cloud (LMC) Cepheid period-luminosity (P-L) relation using two
statistical approaches not previously applied to this problem: the testimator
method and the Schwarz Information Criterion (SIC). The testimator method is
extended to multiple stages for the first time, shown to be unbiased and the
variance of the estimated slope can be proved to be smaller than the standard
slope estimated from linear regression theory. The Schwarz Information
Criterion (also known as the Bayesian Information Criterion) is more
conservative than the Akaike Information Criterion and tends to choose lower
order models. By using simulated data sets, we verify that these statistical
techniques can be used to detect intrinsically linear and/or non-linear P-L
relations. These methods are then applied to independent LMC Cepheid data sets
from the OGLE project and the MACHO project, respectively. Our results imply
that there is a change of slope in longer period ranges for all of the data
sets. This strongly supports previous results, obtained from independent
statistical tests, that the observed LMC P-L relation is non-linear with a
break period at/around 10 days.Comment: 9 pages, 5 figures and 3 tables, PASP accepte
CCD time-series photometry of BQ Ind
We present CCD time-series photometry of BQ Ind, which is either a Population I
large-amplitude δ Scuti star or an SX Phoenicis star
First detection of phase-dependent colliding wind X-ray emission outside the Milky Way
After having reported the detection of X-rays emitted by the peculiar system
HD5980, we assess here the origin of this high-energy emission from additional
X-ray observations obtained with XMM-Newton. This research provides the first
detection of apparently periodic X-ray emission from hot gas produced by the
collision of winds in an evolved massive binary outside the Milky Way. It also
provides the first X-ray monitoring of a Luminous Blue Variable only years
after its eruption and shows that the dominant source of the X-rays is not
associated with the ejecta.Comment: 13 pages, 3 figures and 1 table, accepted for publication in ApJ
(letters
X-ray Light Curves and Accretion Disk Structure of EX Hydrae
We present X-ray light curves for the cataclysmic variable EX Hydrae obtained
with the Chandra High Energy Transmission Grating Spectrometer and the Extreme
Ultraviolet Explorer Deep Survey photometer. We confirm earlier results on the
shape and amplitude of the binary light curve and discuss a new feature: the
phase of the minimum in the binary light curve, associated with absorption by
the bulge on the accretion disk, increases with wavelength. We discuss several
scenarios that could account for this trend and conclude that, most likely, the
ionization state of the bulge gas is not constant, but rather decreases with
binary phase. We also conclude that photoionization of the bulge by radiation
originating from the white dwarf is not the main source of ionization, but that
it is heated by shocks originating from the interaction between the inflowing
material from the companion and the accretion disk. The findings in this paper
provide a strong test for accretion disk models in close binary systems.Comment: 19 pages, 4 figures, accepted for publication in the Ap
Long-term spectroscopic monitoring of the Luminous Blue Variable HD160529
We have spectroscopically monitored the galactic Luminous Blue Variable HD
160529 and obtained an extensive high-resolution data set that covers the years
1991 to 2002. During this period, the star evolved from an extended photometric
minimum phase towards a new visual maximum. In several observing seasons, we
covered up to four months with almost daily spectra. Our spectra typically
cover most of the visual spectral range with a high spectral resolution (about
20,000 or more). This allows us to investigate the variability in many lines
and on many time scales from days to years. We find a correlation between the
photospheric HeI lines and the brightness of the star, both on a time scale of
months and on a time scale of years. The short-term variations are smaller and
do not follow the long-term trend, strongly suggesting different physical
mechanisms. Metal lines also show both short-term and long-term variations in
strength and also a long-term trend in radial velocity. Most of the
line-profile variations can be attributed to changing strengths of lines.
Propagating features in the line profiles are rarely observed. We find that the
mass-loss rate of HD 160529 is almost independent of temperature, i.e. visual
brightness.Comment: 14 pages, 15 figures, accepted for publication in Astronomy &
Astrophysic
Long-Term Optical Monitoring of Eta Carinae. Multiband light curves for a complete orbital period
The periodicity of 5.5 years for some observational events occurring in Eta
Carinae manifests itself across a large wavelength range and has been
associated with its binary nature. These events are supposed to occur when the
binary components are close to periastron. To detect the previous periastron
passage of Eta Car in 2003, we started an intensive, ground-based, optical,
photometric observing campaign. We continued observing the object to monitor
its photometric behavior and variability across the entire orbital cycle. Our
observation program consisted of daily differential photometry from CCD images,
which were acquired using a 0.8 m telescope and a standard BVRI filter set at
La Plata Observatory. The photometry includes the central object and the
surrounding Homunculus nebula. We present up-to-date results of our observing
program, including homogeneous photometric data collected between 2003 and
2008. Our observations demonstrated that Eta Car has continued increasing in
brightness at a constant rate since 1998. In 2006, it reached its brightest
magnitude (V ~ 4.7) since about 1860s. The object then suddenly reverted its
brightening trend, fading to V = 5.0 at the beginning of 2007, and has
maintained a quite steady state since then. We continue the photometric
monitoring of Eta Car in anticipation of the next "periastron passage",
predicted to occur at the beginning of 2009.Comment: Accepted by A&A. The paper contains 3 figures and 2 table
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