490 research outputs found
Is the slope of the intrinsic Baldwin effect constant?
We investigate the relationship between emission-line strength and continuum
luminosity in the best-studied nearby Seyfert 1 galaxy NGC5548. Our analysis of
13 years of ground-based optical monitoring data reveals significant
year-to-year variations in the observed H-beta emission-line response in this
source. More specifically, we confirm the result of Gilbert and Peterson (2003)
of a non-linear relationship between the continuum and H-beta emission-line
fluxes. Furthermore, we show that the slope of this relation is not constant,
but rather decreases as the continuum flux increases. Both effects are
consistent with photoionisation model predictions of a luminosity-dependent
response in this line.Comment: 9 pages, 6 figures, accepted for publication in MNRA
T Pyxidis: The First Cataclysmic Variable with a Collimated Jet
We present the first observational evidence for a collimated jet in a
cataclysmic variable system; the recurrent nova T Pyxidis. Optical spectra show
bipolar components of H with velocities , very similar
to those observed in the supersoft X-ray sources and in SS 433. We argue that a
key ingredient of the formation of jets in the supersoft X-ray sources and T
Pyx (in addition to an accretion disk threaded by a vertical magnetic field),
is the presence of nuclear burning on the surface of the white dwarf.Comment: 10 pages 2 figures to appear in ApJ Letter
A Far-Ultraviolet Survey of 47 Tucanae.II The Long-Period Cataclysmic Variable AKO 9
We present time-resolved, far-ultraviolet (FUV) spectroscopy and photometry
of the 1.1 day eclipsing binary system AKO 9 in the globular cluster 47
Tucanae. The FUV spectrum of AKO 9 is blue and exhibits prominent C IV and He
II emission lines. The spectrum broadly resembles that of long-period,
cataclysmic variables in the galactic field.
Combining our time-resolved FUV data with archival optical photometry of 47
Tuc, we refine the orbital period of AKO 9 and define an accurate ephemeris for
the system. We also place constraints on several other system parameters, using
a variety of observational constraints. We find that all of the empirical
evidence is consistent with AKO 9 being a long-period dwarf nova in which mass
transfer is driven by the nuclear expansion of a sub-giant donor star. We
therefore conclude that AKO 9 is the first spectroscopically confirmed
cataclysmic variable in 47 Tuc.
We also briefly consider AKO 9's likely formation and ultimate evolution.
Regarding the former, we find that the system was almost certainly formed
dynamically, either via tidal capture or in a 3-body encounter. Regarding the
latter, we show that AKO 9 will probably end its CV phase by becoming a
detached, double WD system or by exploding in a Type Ia supernova.Comment: 40 pages, 11 figures, to appear in the Dec 20 issue of ApJ; minor
changes to match final published versio
Cataclysmic variables are a key population of gravitational wave sources for LISA
The gravitational wave (GW) signals from the Galactic population of cataclysmic variables (CVs) have yet to be carefully assessed. Here, we estimate these signals and evaluate their significance for Laser Interferometer Space Antenna (LISA). First, we find that at least three known systems are expected to produce strong enough signals to be individually resolved within the first four years of LISAâs operation. Secondly, CVs will contribute significantly to the LISA Galactic binary background, limiting the missionâs sensitivity in the relevant frequency band. Third, we predict a spike in the unresolved GW background at a frequency corresponding to the CV minimum orbital period. This excess noise may impact the detection of other systems near this characteristic frequency. Fourth, we note that the excess noise spike amplitude and location associated with Pmin ⌠80âmin can be used to measure the CV space density and period bounce location with complementary and simple GW biases compared to the biases and selection effects plaguing samples selected from electromagnetic signals. Our results highlight the need to explicitly include the Galactic CV population in the LISA mission planning, both as individual GW sources and generators of background noise, as well as the exciting prospect of characterising the CV population through their GW emission
The Evolution of X-ray Bursts in the "Bursting Pulsar" GRO J1744-28
GRO J1744-28, commonly known as the `Bursting Pulsar', is a low mass X-ray
binary containing a neutron star and an evolved giant star. This system,
together with the Rapid Burster (MXB 1730-33), are the only two systems that
display the so-called Type II X-ray bursts. These type of bursts, which last
for 10s of seconds, are thought to be caused by viscous instabilities in the
disk; however the Type II bursts seen in GRO J1744-28 are qualitatively very
different from those seen in the archetypal Type II bursting source the Rapid
Burster. To understand these differences and to create a framework for future
study, we perform a study of all X-ray observations of all 3 known outbursts of
the Bursting Pulsar which contained Type II bursts, including a population
study of all Type II X-ray bursts seen by RXTE. We find that the bursts from
this source are best described in four distinct phenomena or `classes' and that
the characteristics of the bursts evolve in a predictable way. We compare our
results with what is known for the Rapid Burster and put out results in the
context of models that try to explain this phenomena.Comment: Accepted to MNRAS Aug 17 201
The serendipituous discovery of a short-period eclipsing polar in 2XMMp
We report the serendipituous discovery of the new eclipsing polar 2XMMp
J131223.4+173659. Its striking X-ray light curve attracted immediate interest
when we were visually inspecting the source products of the 2XMMp catalogue.
This light curve revealed its likely nature as a magnetic cataclysmic variable
of AM Herculis (or polar) type with an orbital period of ~92 min, which was
confirmed by follow-up optical spectroscopy and photometry. 2XMMp
J131223.4+173659 probably has a one-pole accretion geometry. It joins the group
of now nine objects that show no evidence of a soft component in their X-ray
spectra despite being in a high accretion state, thus escaping ROSAT/EUVE
detection. We discuss the likely accretion scenario, the system parameters, and
the spectral energy distribution.Comment: Accepted for publication in A&
Dynamics of Line-Driven Winds from Disks in Cataclysmic Variables. II. Mass Loss Rates and Velocity Laws
We analyze the dynamics of 2D stationary line-driven winds from accretion
disks in cataclysmic variables (CVs), by generalizing the Castor, Abbott and
Klein theory. In paper 1, we have solved the wind Euler equation, derived its
two eigenvalues, and addressed the solution topology and wind geometry. Here,
we focus on mass loss and velocity laws. We find that disk winds, even in
luminous novalike variables, have low optical depth, even in the strongest
driving lines. This suggests that thick-to-thin transitions in these lines
occur. For disks with a realistic radial temperature, the mass loss is
dominated by gas emanating from the inner decade in r. The total mass loss rate
associated with a luminosity 10 Lsun is 10^{-12} Msun/yr, or 10^{-4} of the
mass accretion rate. This is one order of magnitude below the lower limit
obtained from P Cygni lines, when the ionizing flux shortwards of the Lyman
edge is supressed. The difficulties with such small mass loss rates in CVs are
principal, and confirm our previous work. We conjecture that this issue may be
resolved by detailed nonLTE calculations of the line force within the context
of CV disk winds, and/or better accounting for the disk energy distribution and
wind ionization structure. We find that the wind velocity profile is well
approximated by the empirical law used in kinematical modeling. The
acceleration length scale is given by the footpoint radius of the wind
streamline in the disk. This suggests an upper limit of 10 Rwd to the
acceleration scale, which is smaller by factors of a few as compared to values
derived from line fitting.Comment: 14 pages, 3 Postscript figures, also from
http://www.pa.uky.edu/~shlosman/publ.html. Astrophysical Journal, submitte
Discovery of a bright eclipsing cataclysmic variable
We report on the discovery of J0644+3344, a bright deeply eclipsing
cataclysmic variable (CV) binary. Spectral signatures of both binary components
and an accretion disk can be seen at optical wavelengths. The optical spectrum
shows broad H I, He I, and He II accretion disk emission lines with deep narrow
absorption components from H I, He I, Mg II and Ca II. The absorption lines are
seen throughout the orbital period, disappearing only during primary eclipse.
These absorption lines are either the the result of an optically-thick inner
accretion disk or from the photosphere of the primary star. Radial velocity
measurements show that the H I, He I, and Mg II absorption lines phase with the
the primary star, while weak absorption features in the continuum phase with
the secondary star. Radial velocity solutions give a 150+/-4 km/s
semi-amplitude for the primary star and 192.8+/-5.6 km/s for the secondary. The
individual stellar masses are 0.63-0.69 Mdot for the primary and 0.49-0.54 Mdot
for the secondary. The bright eclipsing nature of this binary has helped
provide masses for both components with an accuracy rarely achieved for CVs.
This binary most closely resembles a nova-like UX UMa or SW Sex type of CV.
J0644+3344, however, has a longer orbital period than most UX UMa or SW Sex
stars. Assuming an evolution toward shorter orbital periods, J0644+3344 is
therefore likely to be a young interacting binary. The secondary star is
consistent with the size and spectral type of a K8 star, but has an M0 mass.Comment: 10 pages, 13 figure, accepted for publication in A&
- âŠ