58 research outputs found
The orbital and superhump periods of the dwarf nova SDSS J093249.57+472523.0
We report unfiltered CCD photometry of the eclipsing dwarf nova SDSS
J093249.57+472523.0 obtained during its first confirmed outburst in 2011 March.
The outburst amplitude was at least 3.0 magnitudes above mean quiescence and it
lasted at least 11 days, although we missed the beginning of the outburst.
Superhumps having peak-to-peak amplitude up to 0.3 magnitudes were present
during the outburst, thereby establishing it to be a member of the SU UMa
family. The mean superhump period was Psh = 0.06814(11) d. Analysis of our
measurements of eclipse times of minimum, supplemented with data from other
researchers, allowed us to measure the orbital period as Porb = 0.06630354(5)
d. The superhump period excess was epsilon = 0.028(1) which is consistent with
of SU UMa systems of similar Porb. The FWHM eclipse duration varied between 6
and 13 mins and the eclipse depth was up to 1.6 magnitudes.Comment: 15 pages, 4 figures. Accepted for publication in Journal of the
British Astronomical Associatio
BK Lyncis: The Oldest Old Nova?... And a Bellwether for Cataclysmic-Variable Evolution
We summarize the results of a 20-year campaign to study the light curves of
BK Lyncis, a nova-like star strangely located below the 2-3 hour orbital period
gap in the family of cataclysmic variables. Two apparent "superhumps" dominate
the nightly light curves - with periods 4.6% longer, and 3.0% shorter, than
P_orb. The first appears to be associated with the star's brighter states
(V~14), while the second appears to be present throughout and becomes very
dominant in the low state (V~15.7).
Starting in the year 2005, the star's light curve became indistinguishable
from that of a dwarf nova - in particular, that of the ER UMa subclass.
Reviewing all the star's oddities, we speculate: (a) BK Lyn is the remnant of
the probable nova on 30 December 101, and (b) it has been fading ever since,
but has taken ~2000 years for the accretion rate to drop sufficiently to permit
dwarf-nova eruptions. If such behavior is common, it can explain other puzzles
of CV evolution. One: why the ER UMa class even exists (because all members can
be remnants of recent novae). Two: why ER UMa stars and short-period novalikes
are rare (because their lifetimes, which are essentially cooling times, are
short). Three: why short-period novae all decline to luminosity states far
above their true quiescence (because they're just getting started in their
postnova cooling). Four: why the orbital periods, accretion rates, and
white-dwarf temperatures of short-period CVs are somewhat too large to arise
purely from the effects of gravitational radiation (because the unexpectedly
long interval of enhanced postnova brightness boosts the mean mass-transfer
rate). These are substantial rewards in return for one investment of
hypothesis: that the second parameter in CV evolution, besides P_orb, is time
since the last classical-nova eruption.Comment: PDF, 46 pages, 4 tables, 10 figures; in preparation; more info at
http://cbastro.org
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
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