33 research outputs found
Photometric Study of Two Recently Discovered Variable Stars in the Field of BS Cas
Two recently discovered variable stars (CzeV134 = GSC 3682 0018 = USNO-A2.0
1425-1870026 and CzeV135 = GSC 3682 2051 = USNO-A2.0 1425-1825909 = V1094 Cas),
which have been identified in the field of the W UMa variable star BS Cas, are
studied in the present paper. The phase curves and finding charts for these
stars are presented. The ephemeris and other photometric parameters were
computed.
The phenomenological features indicate that the first star (CzeV134) is
probably a low-amplitude RRc Lyrae - type variable star with the period P =
0.419794\pm0.000029 d and the initial epoch T0 = HJD2453236.50412\pm0.00056.
The amplitude and the shape of the light curve are variable possibly indicating
the Blazhko phenomenon. The second star (CzeV135) was classified as an EW-type
binary system of subtype A. However, a {\beta} Lyrae type may not be excluded,
as various classification parameters lie in a range of overlapping values for
both classes. The period P=0.51429090\pm0.00000012 d and the initial epoch T0 =
HJD2454543.7920\pm0.0006. The O'Connell effect is clearly visible. There are
slight changes of this effect, noticeable while comparing different seasons of
observations. O-C diagrams for these stars were analyzed.Comment: 15 pages, 11 figures, 4 table
Precursor outbursts and superoutbursts in the SU UMa-type dwarf nova NN Camelopardalis
We report photometry of three outbursts of NN Cam in 2007, 2008 and 2009. The
2007 event started with a normal outburst, lasting about 4 days, which was a
precursor to a superoutburst lasting at least 13 days. Both the precursor and
the superoutburst had an amplitude of 4.9 mag above mean quiescence. Superhumps
with a maximum peak-to-peak amplitude of 0.22 mag were detected during the
superoutburst with a mean superhump period Psh = 0.07385(56) d. Psh decreased
continuously with dPsh /dt = -1.72(23) x 10-3. We used our measurement to
confirm that the shorter of two possible values of Porb reported by another
researcher is the correct one, Porb = 0.0717 d. The 2008 outburst was rather
poorly observed, although we present evidence that this too may have been a
superoutburst. The 2009 event was also a superoutburst, with Psh = 0.07414(44)
d, but we could find no evidence for a precursor. From the 2007 and 2009 data,
we report a superhump period excess of epsilon = 0.030(8) to 0.034(6), which is
typical for SU UMa dwarf novae of similar orbital period, and estimate the
binary mass ratio q = Mwd/Msec 0.11 to 0.17Comment: 20 pages, 10 figures, accepted for publication in the Journal of the
British Astronomical Associatio
The 2015 superoutburst of QZ Virginis: Detection of growing superhumps between the precursor and main superoutburst
We report on time-resolved photometry of the 2015 February-March
superoutburst of QZ Virginis. The superoutburst consisted of a separated
precursor, main superoutburst, and rebrightening. We detected superhumps with a
period of 0.061181(42) d between the precursor and main superoutburst. Based on
analyses of period changes and amplitudes of superhumps, the observed
superhumps were identified as growing superhumps (stage A superhumps). The
duration of stage A superhumps was about 5 d, unusually long for SU UMa-type
dwarf novae. Using the obtained stage A superhump period, we estimated the mass
ratio of QZ Vir to be 0.108(3). This value suggests that QZ Vir is an SU
UMa-type dwarf nova evolving toward the period minimum. Based on the present
and the previous observations regarding long-lasting stage A superhumps, a time
scale of stage A superhumps is likely to be determined by the mass ratio of the
system and the temperature of the accretion disk.Comment: 12 pages, 6 figures, published for PASJ, 69, 7
OT J075418.7+381225 and OT J230425.8+062546: Promising Candidates for the Period Bouncer
We report on photometric observations of two dwarf novae, OT J075418.7+381225
and OT J230425.8+062546, which underwent superoutburst in 2013 (OT J075418) and
in 2011 (OT J230425). Their mean period of the superhump was 0.0722403(26) d
(OT J074518) and 0.067317(35) d (OT J230425). These objects showed a very long
growing stage of the superhump (stage A) and a large period decrease in stage
A-B transition. The long stage A suggests slow evolution of the superhump due
to very small mass ratios of these objects. The decline rates during the
plateau phase in the superoutburst of these objects were lower than those of SU
UMa-type DNe with a similar superhump period. These properties were similar to
those of SSS J122221.7-311523, the best candidate for the period bouncer.
Therefore, these two DNe are regarded as good candidates for the period
bouncer. We estimated the number density of period bouncers roughly from our
observations in the recent five years. There is a possibility that these WZ
Sge-type dwarf novae with unusual outburst properties can account for the
missing population of the period bouncer expected from the evolutionary
scenario.Comment: 24 pages, 10 figures, accepted for publication in PAS
V1006 Cygni: Dwarf Nova Showing Three Types of Outbursts and Simulating Some Features of the WZ Sge-Type Behavior
We observed the 2015 July-August long outburst of V1006 Cyg and established
this object to be an SU UMa-type dwarf nova in the period gap. Our observations
have confirmed that V1006 Cyg is the second established object showing three
types of outbursts (normal, long normal and superoutbursts) after TU Men. We
have succeeded in recording the growing stage of superhumps (stage A
superhumps) and obtained a mass ratio of 0.26-0.33, which is close to the
stability limit of tidal instability. This identification of stage A superhumps
demonstrated that superhumps indeed slowly grow in systems near the stability
limit, the idea first introduced by Kato et al. 2014, arXiv:1406.6428). The
superoutburst showed a temporary dip followed by a rebrightening. The moment of
the dip coincided with the stage transition of superhumps, and we suggest that
stage C superhumps is related to the start of the cooling wave in the accretion
disk. We interpret that the tidal instability was not strong enough to maintain
the disk in the hot state when the cooling wave started. We propose that the
properties commonly seen in the extreme ends of mass ratios (WZ Sge-type
objects and long-period systems) can be understood as a result of weak tidal
effect.Comment: 8 pages, 2 figures (including the supporting information), accepted
for publication in PASJ (Letters
NY Serpentis: SU UMa-Type Nova in the Period Gap with Diversity of Normal Outbursts
We present photometric study of NY Ser, an in-the-gap SU UMa-type nova, in
2002 and 2013. We determined the duration of the superoutburst and the mean
superhump period to be 18 d and 0.10458 d, respectively. We detected in 2013
that NY Ser showed two distinct states separated by the superoutburst. A state
of rather infrequent normal outbursts lasted at least 44 d before the
superoutburst and a state of frequent outbursts started immediately after the
superoutburst and lasted at least for 34 d. Unlike a typical SU UMa star with
bimodal distribution of the outbursts duration, NY Ser displayed a diversity of
normal outbursts. In the state of infrequent outbursts, we detected a wide ~12
d outburst accompanied by 0.098 d orbital modulation but without superhumps
ever established in NY Ser. We classified this as the "wide normal outburst".
The orbital period dominated both in quiescence and during normal outbursts in
this state. In the state of the most frequent normal outbursts, the 0.10465 d
positive superhumps dominated and co-existed with the orbital modulation. In
2002 we detected the normal outburst of "intermediate" 5-6 d duration that was
also accompanied by orbital modulations.Comment: 26 pages, 16 figures, accepted in PAS
ASASSN-15jd: WZ Sge-type star with intermediate superoutburst between single and double ones
We present optical photometry of a WZ Sge-type dwarf nova (DN), ASASSN-15jd.
Its light curve showed a small dip in the middle of the superoutburst in 2015
for the first time among WZ Sge-type DNe. The unusual light curve implies a
delay in the growth of the 3:1 resonance tidal instability. Also, the light
curve is similar to those of other two WZ Sge-type stars, SSS
J122221.7311523 and OT J184228.1483742, which are believed to be the best
candidates for a period bouncer on the basis of their small values of the mass
ratio (). Additionally, the small mean superhump
amplitude ( 0.1 mag) and the long duration of no ordinary superhumps at the
early stage of the superoutburst are common to the best candidates for a period
bouncer. The average superhump period was = 0.0649810(78) d and no
early superhumps were detected. Although we could not estimate the mass ratio
of ASASSN-15jd with high accuracy, this object is expected to be a candidate
for a period bouncer, a binary accounting for the missing population of
post-period minimum cataclysmic variables, based on the above characteristics.Comment: 11 Pages, 10 Figures, 4 Tables, accepted for publication in PASJ
(includes supporting information
WZ Sge-type dwarf novae with multiple rebrightenings: MASTER OT J211258.65+242145.4 and MASTER OT J203749.39+552210.3
We report on photometric observations of WZ Sge-type dwarf novae, MASTER OT
J211258.65+242145.4 and MASTER OT J203749.39+552210.3 which underwent outbursts
in 2012. Early superhumps were recorded in both systems. During superoutburst
plateau, ordinary superhumps with a period of 0.060291(4) d (MASTER J211258)
and of 0.061307(9) d (MASTER J203749) in average were observed. MASTER J211258
and MASTER J203749 exhibited eight and more than four post-superoutburst
rebrightenings, respectively. In the final part of the superoutburst, an
increase in the superhump periods was seen in both systems. We have made a
survey of WZ Sge-type dwarf novae with multiple rebrightenings, and confirmed
that the superhump periods of WZ Sge-type dwarf novae with multiple
rebrightenings were longer than those of WZ Sge-type dwarf novae without a
rebrightening. Although WZ Sge-type dwarf novae with multiple rebrightenings
have been thought to be the good candidates for period bouncers based on their
low mass ratio (q) from inferred from the period of fully grown (stage B)
superhumps, our new method using the period of growing superhumps (stage A
superhumps), however, implies higher q than those expected from stage B
superhumps. These q values appear to be consistent with the duration of the
stage A superoutbursts, which likely reflects the growth time of the 3:1
resonance. We present a working hypothesis that the small fractional superhump
excesses for stage B superhumps in these systems may be explained as a result
that a higher gas pressure effect works in these systems than in ordinary SU
UMa-type dwarf novae. This result leads to a new picture that WZ Sge-type dwarf
novae with multiple rebrightenings and SU UMa-type dwarf novae without a
rebrightening (they are not period bouncers) are located in the same place on
the evolutionary track
Rapid Optical Variations Correlated with X-rays in the 2015 Second Outburst of V404 Cygni (GS 2023338)
We present optical multi-colour photometry of V404 Cyg during the outburst
from December, 2015 to January, 2016 together with the simultaneous X-ray data.
This outburst occurred less than 6 months after the previous outburst in
June-July, 2015. These two outbursts in 2015 were of a slow rise and rapid
decay-type and showed large-amplitude (2 mag) and short-term (10
min-3 hours) optical variations even at low luminosity (0.01-0.1).
We found correlated optical and X-ray variations in two 1 hour time
intervals and performed Bayesian time delay estimations between them. In the
previous version, the observation times of X-ray light curves were measured at
the satellite and their system of times was Terrestrial Time (TT), while those
of optical light curves were measured at the Earth and their system of times
was Coordinated Universal Time (UTC). In this version, we have corrected the
observation times and obtained a Bayesian estimate of an optical delay against
the X-ray emission, which is 30 s, during those two intervals. In
addition, the relationship between the optical and X-ray luminosity was at that time. These features can be
naturally explained by disc reprocessing.Comment: 14 pages, 8 figures, Accepted for publication in MNRAS (includes
supplementary information), plus an erratu
Is There a Third Component in the Intermediate Polar V405 Aur?
Variability of the spin period of the white dwarf in the V405 Aur (RX
J0558.0+5353) system using our observations and previously published maxima
timings is analyzed. As the phase light curve contains two nearly equal
photometric waves, one maximum was set as a "primary" one. The ephemeris for
the maxima of the "spin variability" (due to rotation of the magnetized white
dwarf) for recent seasons 2010-2012 is Tmax = HJD
2455882.470614(25)+0.00631314602(46)E. This corresponds to a significant
negative trend at the "O-C" diagram. Due to significant gaps in the
observational data and statistical error of timings, there may be some
suggestions on the spin period variability - a fast period "jump" in 2007y;
secular period variations; a cubic ephemeris (which may be interpreted by a
precession of the magnetic white dwarf at a time-scale of decades) or a
periodic change with a period of 6.2 years and semi-amplitude of 17.2\pm1.8
sec. For the present observations, more reliable are two latter models. To
distinguish between them, a continuation of monitoring is needed. The periodic
variations may be interpreted by a light time effect caused by a third body of
mass (M3 > 0.09M\odot), which corresponds to a low-mass star, but not to an
extra-solar planet. In this case, the system belongs to a rare class of
cataclysmic variables with a third body.Comment: 4 pages, 5 figures, to appear in the Conference Proceedings,
"Cz{,e}stochowski Ka{\l}endarz Astronomiczny 2014", ed. Bogdan Wszo{\l}ek
(2013). arXiv admin note: substantial text overlap with arXiv:1306.466