60 research outputs found
Late Superhumps in WZ Sge-Type Dwarf Novae
We report on the detection of very stable modulations with periods
unexpectedly (~0.5%) longer than superhump periods during the slowly fading
stage of WZ Sge-type superoutbursts in three systems, GW Lib, V455 And and WZ
Sge. These periods are naturally explained by assuming that these modulations
are superhumps arising from matter near the tidal truncation radius. This
finding provides an additional support to the hypothetical idea of expansion of
the accretion disk well beyond the 3:1 orbital resonance in some low mass-ratio
systems. Combined with the effect of 2:1 resonance, we present an explanation
of the origin of positive period derivatives in certain short-period SU
UMa-type dwarf novae.Comment: Accepted by PASJ (Letters), 4 pages, 3 figure
Variability of the symbiotic X-ray binary GX 1+4: Enhanced activity near periastron passage
Context. GX 1+4 belongs to a rare class of X-ray binaries with red giant
donors, symbiotic X-ray binaries. The system has a history of complicated
variability on multiple timescales in the optical light and X-rays. The nature
of this variability remains poorly understood. Aims. We study variability of GX
1+4 on long time-scale in X-ray and optical bands. Methods. The presented X-ray
observations are from INTEGRAL Soft Gamma-Ray Imager and RXTE All Sky Monitor.
The optical observations are from INTEGRAL Optical Monitoring Camera. Results.
The variability of GX 1+4 both in optical light and hard X-ray emission (>17
keV) is dominated by ~50-70d quasi-periodic changes. The amplitude of this
variability is highest during the periastron passage, while during the
potential neutron star eclipse the system is always at minimum, which confirms
the 1161d orbital period that has had been proposed for the system based on
radial velocity curve. Neither the quasi-periodic variability or the orbital
period are detected in soft X-ray emission (1.3-12.2 keV), where the binary
shows no apparent periodicity.Comment: 8 pages, 7 figures, accepted for publication in A&
Discovery of a Promissing Candidate of WZ Sge-Type Dwarf Novae, ASAS 160048-4846.2: Evidence for Double-Peaked Humps
We report on time-resolved CCD photometry during the 2005 June outburst of a
dwarf nova, ASAS160048-4846.2. The observed light curves unambiguously showed
embryonic humps with a period of 0.063381(41) days, after which genuine
superhumps emerged with a period of 0.064927(3) days. Based on evidence for
double-peaked humps in the earlier stage of the outburst, this object might be
qualified as the seventh member of WZ Sge-type dwarf novae after Var Her 04. If
the former period is the same as, or very close to the orbital period of the
system, as in other WZ Sge systems, the fractional superhump excess is about
2.4{%}. This value is unexpectedly larger than that of other WZ Sge-type
dwarf novae. The early phase of our observing run provided evidence for the
transition from chaotic humps to genuine superhumps, together with increasing
the amplitude.Comment: 4 pages, 6 figures, submitted to PAS
Photometric Studies of a WZ Sge-Type Dwarf Nova Candidate, ASAS160048-4846.2
We report on our time-resolved CCD photometry during the 2005 June
superoutburst of a WZ Sge-type dwarf nova candidate, ASAS 160048-4846.2. The
ordinary superhumps underwent a complex evolution during the superoutburst. The
superhump amplitude experienced a regrowth, and had two peaks. The superhump
period decreased when the superhump amplitude reached to the first maximum,
successively gradually increased until the second maximum of the amplitude, and
finally decreased again. Investigating other SU UMa-type dwarf novae which show
an increase of the superhump period, we found the same trend of the superhump
evolution in superoutbursts of them. We speculate that the superhump regrowth
in the amplitude has a close relation to the increase of the superhump period,
and all of SU UMa-type dwarf novae with a superhump regrowth follow the same
evolution of the ordinary superhumps as that of ASAS 160048-4846.2.Comment: 7 pages, 4 figure
On the rotation periods of the components of the triple system TYC9300-0891-1AB/TYC9300-0529-1 in the Octans Association
Stellar rotation depends on different parameters. The range of values of
these parameters causes the dispersion in the rotation period distributions
observed in young stellar clusters/associations. We focus our investigation on
the effects of different circumstellar environments on stellar rotation. More
specifically, we are searching in stellar Associations for visual triple
systems where all stellar parameters are similar, with the only exceptions of
the unknown initial rotation period, and of the circum-stellar environment, in
the sense that one of the two about equal-mass components has a close-by third
'perturber' component. In the present study we analyse the 35-Myr old visual
triple system TYC 9300-0891-1AB + TYC 9300-0529-1 in the young Octans stellar
association consisting of three equal-mass K0V components. We collected from
the literature all information that allowed us to infer that the three
components are actually physically bound forming a triple system and are
members of the Octans Association. We collected broad-band photometric
timeseries in two observation seasons. We discovered that all the components
are variable, magnetically active, and from periodogram analysis we found the
unresolved components TYC 9300-0891-1AB to have a rotation period P = 1.383d
and TYC 9300-0529-1 a rotation period P = 1.634d. TYC 9300-0891-1A, TYC
9300-0891-1B, and TYC 9300-0529-1 have same masses, ages, and initial chemical
compositions. The relatively small 16% rotation period difference measured by
us indicates that all components had similar initial rotation periods and disc
lifetimes, and the separation of 157AU between the component A and the
'perturber' component B (or vice-versa) has been sufficiently large to prevent
any significant perturbation/shortening of the accretion-disc lifetime.Comment: Accepted by New Astronomy 201
Orbital Period Increase in ES Ceti
We report a long-term study of the eclipse times in the 10-minute helium
binary ES Ceti. The binary period increases rapidly, with P/P-dot = 6.2x10^6
yr. This is consistent with the assumption that gravitational radiation (GR)
drives the mass transfer, and appears to be the first dynamical evidence that
GR is indeed the driver of evolution in this class of very old cataclysmic
variables -- the AM Canum Venaticorum stars.Comment: PDF, 9 pages, 1 table, 1 figure; accepted, in press, ApJ; more info
at http://cbastro.org
LMC S154: the first Magellanic symbiotic recurrent nova
Classical nova outburst has been suggested for a number of extragalactic
symbiotic stars, but in none of the systems has it been proven. In this work we
study the nature of one of these systems, LMC S154. We gathered archival
photometric observations in order to determine the timescales and nature of
variability in this system. Additionally we carried out photometric and
spectroscopic monitoring of the system and fitted synthetic spectra to the
observations. Carbon abundance in the photosphere of the red giant is
significantly higher than that derived for the nebula, which confirms pollution
of the circumbinary material by the ejecta from nova outburst. The photometric
and spectroscopic data show that the system reached quiescence in 2009, which
means that for the first time all of the phases of a nova outburst were
observed in an extragalactic symbiotic star. The data indicate that most
probably there were three outbursts observed in LMC S154, which would make this
system a member of a rare class of symbiotic recurrent novae. The recurrent
nature of the system is supported by the discovery of coronal lines in the
spectra, which are observed only in symbiotic stars with massive white dwarfs
and with short-recurrence-time outbursts. Gathered evidence is sufficient to
classify LMC S154 as the first bona fide extragalactic symbiotic nova, which is
likely a recurrent nova. It is also the first nova with a carbon-rich donor.Comment: 16 pages, 7 figures, accepted for publication in A&
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