53 research outputs found
Verifying timestamps of occultation observation systems
We describe an image timestamp verification system to determine the exposure
timing characteristics and continuity of images made by an imaging camera and
recorder, with reference to Coordinated Universal Time (UTC). The original use
was to verify the timestamps of stellar occultation recording systems, but the
system is applicable to lunar flashes, planetary transits, sprite recording, or
any area where reliable timestamps are required. The system offers good
temporal resolution (down to 2 msec, referred to UTC) and provides exposure
duration and interframe dead time information. The system uses inexpensive,
off-the- shelf components, requires minimal assembly and requires no
high-voltage components or connections. We also describe an application to load
FITS (and other format) image files, which can decode the verification image
timestamp. Source code, wiring diagrams and built applications are provided to
aid the construction and use of the device.Comment: 10 pages, 7 figures, accepted to Publications of the Astronomical
Society of Australia (PASA
Superhumps in Cataclysmic Binaries. XXIII. V442 Ophiuchi and RX J1643.7+3402
We report the results of long observing campaigns on two novalike variables:
V442 Ophiuchi and RX J1643.7+3402. These stars have high-excitation spectra,
complex line profiles signifying mass loss at particular orbital phases, and
similar orbital periods (respectively 0.12433 and 0.12056 d). They are
well-credentialed members of the SW Sex class of cataclysmic variables. Their
light curves are also quite complex. V442 Oph shows periodic signals with
periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar
signals at 0.11696(8) d and 4.05(12) d. We interpret these short and long
periods respectively as a "negative superhump" and the wobble period of the
accretion disk. The superhump could then possibly arise from the heating of the
secondary (and structures fixed in the orbital frame) by inner-disk radiation,
which reaches the secondary relatively unimpeded since the disk is not
coplanar.
At higher frequencies, both stars show another type of variability:
quasi-periodic oscillations (QPOs) with a period near 1000 seconds. Underlying
these strong signals of low stability may be weak signals of higher stability.
Similar QPOs, and negative superhumps, are quite common features in SW Sex
stars. Both can in principle be explained by ascribing strong magnetism to the
white dwarf member of the binary; and we suggest that SW Sex stars are
borderline AM Herculis binaries, usually drowned by a high accretion rate. This
would provide an ancestor channel for AM Hers, whose origin is still
mysterious.Comment: PDF, 41 pages, 4 tables, 16 figures; accepted, in press, to appear
December 2002, PASP; more info at http://cba.phys.columbia.edu
Superhumps in Cataclysmic Binaries. XXV. q_crit, epsilon(q), and Mass-Radius
We report on successes and failures in searching for positive superhumps in
cataclysmic variables, and show the superhumping fraction as a function of
orbital period. Basically, all short-period systems do, all long-period systems
don't, and a 50% success rate is found at P_orb=3.1+-0.2 hr. We can use this to
measure the critical mass ratio for the creation of superhumps. With a
mass-radius relation appropriate for cataclysmic variables, and an assumed mean
white-dwarf mass of 0.75 M_sol, we find a mass ratio q_crit=0.35+-0.02.
We also report superhump studies of several stars of independently known mass
ratio: OU Virginis, XZ Eridani, UU Aquarii, and KV UMa (= XTE J1118+480). The
latter two are of special interest, because they represent the most extreme
mass ratios for which accurate superhump measurements have been made. We use
these to improve the epsilon(q) calibration, by which we can infer the elusive
q from the easy-to-measure epsilon (the fractional period excess of P_superhump
over P_orb). This relation allows mass and radius estimates for the secondary
star in any CV showing superhumps. The consequent mass-radius law shows an
apparent discontinuity in radius near 0.2 M_sol, as predicted by the disrupted
magnetic braking model for the 2.1-2.7 hour period gap. This is effectively the
"empirical main sequence" for CV secondaries.Comment: PDF, 45 pages, 9 tables, 12 figures; accepted, in press, to appear
November 2005, PASP; more info at http://cba.phys.columbia.edu
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. II: The Second Year (2009-2010)
As an extension of the project in Kato et al. (2009, arXiv:0905.1757), we
collected times of superhump maxima for 61 SU UMa-type dwarf novae mainly
observed during the 2009-2010 season. The newly obtained data confirmed the
basic findings reported in Kato et al. (2009): the presence of stages A-C, as
well as the predominance of positive period derivatives during stage B in
systems with superhump periods shorter than 0.07 d. There was a systematic
difference in period derivatives for systems with superhump periods longer than
0.075 d between this study and Kato et al. (2009). We suggest that this
difference is possibly caused by the relative lack of frequently outbursting SU
UMa-type dwarf novae in this period regime in the present study. We recorded a
strong beat phenomenon during the 2009 superoutburst of IY UMa. The close
correlation between the beat period and superhump period suggests that the
changing angular velocity of the apsidal motion of the elliptical disk is
responsible for the variation of superhump periods. We also described three new
WZ Sge-type objects with established early superhumps and one with likely early
superhumps. We also suggest that two systems, VX For and EL UMa, are WZ
Sge-type dwarf novae with multiple rebrightenings. The O-C variation in OT
J213806.6+261957 suggests that the frequent absence of rebrightenings in very
short-Porb objects can be a result of sustained superoutburst plateau at the
epoch when usual SU UMa-type dwarf novae return to quiescence preceding a
rebrightening. We also present a formulation for a variety of Bayesian
extension to traditional period analyses.Comment: 63 pages, 77 figures, 1 appendix, Accepted for publication in PASJ,
data correctio
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. VIII: The Eighth Year (2015-2016)
Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we
collected times of superhump maxima for 128 SU UMa-type dwarf novae observed
mainly during the 2015-2016 season and characterized these objects. The data
have improved the distribution of orbital periods, the relation between the
orbital period and the variation of superhumps, the relation between period
variations and the rebrightening type in WZ Sge-type objects. Coupled with new
measurements of mass ratios using growing stages of superhumps, we now have a
clearer and statistically greatly improved evolutionary path near the terminal
stage of evolution of cataclysmic variables. Three objects (V452 Cas, KK Tel,
ASASSN-15cl) appear to have slowly growing superhumps, which is proposed to
reflect the slow growth of the 3:1 resonance near the stability border.
ASASSN-15sl, ASASSN-15ux, SDSS J074859.55+312512.6 and CRTS J200331.3-284941
are newly identified eclipsing SU UMa-type (or WZ Sge-type) dwarf novae.
ASASSN-15cy has a short (~0.050 d) superhump period and appears to belong to EI
Psc-type objects with compact secondaries having an evolved core. ASASSN-15gn,
ASASSN-15hn, ASASSN-15kh and ASASSN-16bu are candidate period bouncers with
superhump periods longer than 0.06 d. We have newly obtained superhump periods
for 79 objects and 13 orbital periods, including periods from early superhumps.
In order that the future observations will be more astrophysically beneficial
and rewarding to observers, we propose guidelines how to organize observations
of various superoutbursts.Comment: 123 pages, 162 figures, 119 tables, accepted for publication in PASJ
(including supplementary information
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