7 research outputs found
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
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae
We systematically surveyed period variations of superhumps in SU UMa-type
dwarf novae based on newly obtained data and past publications. In many
systems, the evolution of superhump period are found to be composed of three
distinct stages: early evolutionary stage with a longer superhump period,
middle stage with systematically varying periods, final stage with a shorter,
stable superhump period. During the middle stage, many systems with superhump
periods less than 0.08 d show positive period derivatives. Contrary to the
earlier claim, we found no clear evidence for variation of period derivatives
between superoutburst of the same object. We present an interpretation that the
lengthening of the superhump period is a result of outward propagation of the
eccentricity wave and is limited by the radius near the tidal truncation. We
interpret that late stage superhumps are rejuvenized excitation of 3:1
resonance when the superhumps in the outer disk is effectively quenched. Many
of WZ Sge-type dwarf novae showed long-enduring superhumps during the
post-superoutburst stage having periods longer than those during the main
superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to
be strongly correlated with the fractional superhump excess, or consequently,
mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with
multiple rebrightenings tend to have smaller period derivatives and are
excellent candidate for the systems around or after the period minimum of
evolution of cataclysmic variables (abridged).Comment: 239 pages, 225 figures, PASJ accepte
The 2001 Superoutburst of WZ Sagittae
We report the results of a worldwide campaign to observe WZ Sagittae during
its 2001 superoutburst. After a 23-year slumber at V=15.5, the star rose within
2 days to a peak brightness of 8.2, and showed a main eruption lasting 25 days.
The return to quiescence was punctuated by 12 small eruptions, of ~1 mag
amplitude and 2 day recurrence time; these "echo outbursts" are of uncertain
origin, but somewhat resemble the normal outbursts of dwarf novae. After 52
days, the star began a slow decline to quiescence.
Periodic waves in the light curve closely followed the pattern seen in the
1978 superoutburst: a strong orbital signal dominated the first 12 days,
followed by a powerful /common superhump/ at 0.05721(5) d, 0.92(8)% longer than
P_orb. The latter endured for at least 90 days, although probably mutating into
a "late" superhump with a slightly longer mean period [0.05736(5) d]. The
superhump appeared to follow familiar rules for such phenomena in dwarf novae,
with components given by linear combinations of two basic frequencies: the
orbital frequency omega_o and an unseen low frequency Omega, believed to
represent the accretion disk's apsidal precession. Long time series reveal an
intricate fine structure, with ~20 incommensurate frequencies. Essentially all
components occurred at a frequency n(omega_o)-m(Omega), with m=1, ..., n. But
during its first week, the common superhump showed primary components at n
(omega_o)-Omega, for n=1, 2, 3, 4, 5, 6, 7, 8, 9 (i.e., m=1 consistently); a
month later, the dominant power shifted to components with m=n-1. This may
arise from a shift in the disk's spiral-arm pattern, likely to be the
underlying cause of superhumps.
The great majority of frequency components ... . (etc., abstract continues)Comment: PDF, 54 pages, 4 tables, 21 figures, 1 appendix; accepted, in press,
to appear July 2002, PASP; more info at http://cba.phys.columbia.edu
Conditioned suppression or facilitation as a function of the behavioral baseline
Rats were exposed to a multiple schedule of reinforcement. During one component, a bar-press was followed by reinforcement only if it occurred between 15 and 20 sec after the previous response. This differential-reinforcement-of-low-rate (DRL) schedule produced a typical slow rate of responding. During the other component, reinforcement followed the first response to be emitted during limited periods of time which occurred at fixed intervals. These fixed-interval schedules with a limited hold produced higher response rates, described as `interval' or `ratio-like' behavior. Responding during the DRL component increased in frequency during a tone which ended with an unavoidable shock of low intensity, but decreased during the tone when the shock intensity was raised. The `interval' and `ratio-like' responding decreased in frequency during the tone at all shock intensities. Initial acceleration of the DRL responding appeared to be due to adventitious punishment of collateral behavior which was observed between the bar-presses. The more severe conditioned suppression during the fixed-interval components might be the result of the lower probability of reinforcement after any single response