169 research outputs found
KUV 01584-0939: A Helium-transferring Cataclysmic Variable with an Orbital Period of 10 Minutes
High speed photometry of KUV 01584-0939 (alias Cet3) shows that is has a
period of 620.26 s. Combined with its hydrogen-deficient spectrum, this implies
that it is an AM CVn star. The optical modulation is probably a superhump, in
which case the orbital period will be slightly shorter than what we have
observed.Comment: Published by PASP. See also the latest Early-Release Research Paper
website of the PAS
Large-Scale Structures Behind the Milky Way from Near-IR Surveys
About 25% of the optical extragalactic sky is obscured by the dust and stars
of our Milky Way. Dynamically important structures might still lie hidden in
this zone. Various approaches are presently being employed to uncover the
galaxy distribution in the Zone of Avoidance (ZOA) but all suffer from
(different) limitations and selection effects.
We investigated the potential of using the DENIS NIR survey for studies of
galaxies behind the obscuration layer of our Milky Way and for mapping the
Galactic extinction. As a pilot study, we recovered DENIS I, J and K band
images of heavily obscured but optically still visible galaxies. We determined
the I, J and K band luminosity functions of galaxies on three DENIS strips that
cross the center of the nearby, low-latitude, rich cluster Abell 3627. The
extinction-corrected I-J and J-K colours of these cluster galaxies compare well
with that of an unobscured cluster. We searched for and identified galaxies at
latitudes where the Milky Way remains fully opaque (|b|
4-5mag) - in a systematic search as well as around positions of galaxies
detected with the blind HI survey of the ZOA currently conducted with the
Multibeam Receiver of the Parkes Radiotelescope.Comment: 12 pages, including 5 PS figures, LaTeX, uses crckapb.sty and
epsf.tex. Better resolved figures available upon request. To appear in
proceedings of the 3rd Euroconference (Meudon, France, June 1997) on ``The
Impact of Near IR Surveys'', Kluwer 199
A return to strong radio flaring by Circinus X-1 observed with the Karoo Array Telescope test array KAT-7
Circinus X-1 is a bright and highly variable X-ray binary which displays
strong and rapid evolution in all wavebands. Radio flaring, associated with the
production of a relativistic jet, occurs periodically on a ~17-day timescale. A
longer-term envelope modulates the peak radio fluxes in flares, ranging from
peaks in excess of a Jansky in the 1970s to an historic low of milliJanskys
during the years 1994 to 2007. Here we report first observations of this source
with the MeerKAT test array, KAT-7, part of the pathfinder development for the
African dish component of the Square Kilometre Array (SKA), demonstrating
successful scientific operation for variable and transient sources with the
test array. The KAT-7 observations at 1.9 GHz during the period 13 December
2011 to 16 January 2012 reveal in temporal detail the return to the
Jansky-level events observed in the 1970s. We compare these data to
contemporaneous single-dish measurements at 4.8 and 8.5 GHz with the HartRAO
26-m telescope and X-ray monitoring from MAXI. We discuss whether the overall
modulation and recent dramatic brightening is likely to be due to an increase
in the power of the jet due to changes in accretion rate or changing Doppler
boosting associated with a varying angle to the line of sight.Comment: 7 pages, 5 figures, accepted for publication in MNRAS 14 May 201
Dwarf Nova Oscillations and Quasi-Periodic Oscillations in Cataclysmic Variables - VIII. VW Hyi in outburst observed with the Southern African Large Telescope
We analyse four light curves obtained at high time resolution (~ 0.1 s) with
the 11-m Southern African Large Telescope, at the ends of two normal outbursts
and one superoutburst of the dwarf nova VW Hyi. All of these contain at least
some Dwarf Nova Oscillations (DNOs), which, when at their highest amplitudes,
are seen in unprecedented detail. In addition to the expected DNOs with periods
> 20 s we find a previously unknown modulation at 13.39 s, but none at shorter
periods. The various DNOs and their interaction with the longer period
Quasi-periodic Oscillations are interpreted in terms of the model of
magnetically controlled flow from an accretion disc proposed earlier in this
series of papers. Our observations include rare DNOs very late in outburst; we
find that the fundamental period does not increase beyond ~ 90 s, which is the
same value that the independent ``longer period DNOs'' converge on.Comment: Accepted for publication in MNRAS. 7 pages, 10 figures, 2 table
Filming the evolution of symbiotic novae with VLBI: The 2021 explosion of RS Oph
Fifteen years after its previous outburst, the symbiotic recurrent nova RS Oph exploded again on 2021 Aug 8th, its first outburst during the Fermi era. In symbiotic novae, the material ejected from the surface of the white dwarf (WD) after the thermonuclear runaway drives a strong shock through the dense circumstellar gas produced by the red giant (RG) wind. This nova is a perfect real-Time laboratory for studying physical processes as diverse as accretion, thermonuclear explosions, shock dynamics and particle acceleration; in many ways it is like a supernova remnant on fast forward. The experience of its previous outburst and that of 2010 for V407 (the symbiotic nova that has been extensively observed during the Fermi era), indicates that a large sensitivity and a broad range of baseline lengths are necessary to follow its evolution over a period of several weeks. This would provide unique constraints on major outstanding problems, including the emission mechanisms, the physical processes at work, the presence and location of shock acceleration, the geometry of the system, and the density of the RG wind. We present preliminary results from the EVN+e-MERLIN observations carried out on weeks/months time scales after the August explosion
The rapidly pulsating sdO star, SDSS J160043.6+074802.9
A spectroscopic analysis of SDSS J160043.6+074802.9, a binary system
containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields
Teff = 70 000 +/- 5000 K and log g = 5.25 +/- 0.30, together with a most likely
type of K3V for the secondary star. We compare our results with atmospheric
parameters derived by Fontaine et al. (2008) and in the context of existing
evolution models for sdO stars. New and more extensive photometry is also
presented which recovers most, but not all, frequencies found in an earlier
paper. It therefore seems probable that some pulsation modes have variable
amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO
models show those having log g > 5.3 to be more likely to be unstable and
capable of driving pulsation in the observed frequency range.Comment: 14 pages, 12 figures, accepted for publication in MNRAS, 2009
September
A spectroscopic analysis of the eclipsing nova-like EC 21178−5417 – discovery of spiral density structures
We present phase-resolved optical spectroscopy of the eclipsing nova-like cataclysmic variable EC 21178−5417 obtained between 2002 and 2013. The average spectrum of EC 21178−5417 shows broad double-peaked emission lines from He II 4686 Å (strongest feature) and the Balmer series. The high-excitation feature, C III/N III at 4640–4650 Å, is also present and appears broad in emission. A number of other lines, mostly He I, are clearly present in absorption and/or emission
SDSS J160043.6+074802.9: a very rapid sdO pulsator
We report the serendipitous discovery of the Sloan Digital Sky Survey star,
SDSS J160043.6+074802.9 to be a very rapid pulsator. The variation is dominated
by a frequency near 8380 microHz (period = 119.33 s) with a large amplitude
(0.04 mag) and its first harmonic at 16760 microHz (59.66 s; 0.005 mag). In
between these frequencies, we find at least another 8 variations with periods
between 62 and 118 seconds and amplitudes between about 0.007 and 0.003 mag;
weaker oscillations might also be present. Preliminary spectrograms from the
performance verification phase of the Southern African Large Telescope indicate
that SDSS J160043.6+074802.9 is a spectroscopic binary consisting of an sdO
star and a late-type main-sequence companion. This makes it the first
unambiguous detection of such an sdO star to pulsate, and certainly the first
found to exhibit multi-frequency variations.Comment: 7 pages, 6 figures (figure 4 at reduced resolution, original
available on request). Accepted for publication in MNRA
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