22 research outputs found
An artificial meteors database as a test for the presence of weak showers
We have constructed an artificial meteor database resembling in all details
the real sample collected by the observers of the Comets and Meteors Workshop
in the years 1996-1999. The artificial database includes the sporadic meteors
and also events from the following showers: Perseids, Aquarid complex, Alpha
Capricornids, July Pegasids and Sagittarids. This database was searched for the
presence of the radiants of two weak showers: Alpha Cygnids and Delphinids. The
lack of these radiants in the artificial database and their existence in the
real observations suggests that Alpha Cygnids and Delphinids are the real
showers and their radiants could not be formed as an effect of intersections of
back prolongated paths of meteors belonging to other showers.Comment: accepted for publication in A&A, 15 page
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