10 research outputs found
Discovery of a Promissing Candidate of WZ Sge-Type Dwarf Novae, ASAS 160048-4846.2: Evidence for Double-Peaked Humps
We report on time-resolved CCD photometry during the 2005 June outburst of a
dwarf nova, ASAS160048-4846.2. The observed light curves unambiguously showed
embryonic humps with a period of 0.063381(41) days, after which genuine
superhumps emerged with a period of 0.064927(3) days. Based on evidence for
double-peaked humps in the earlier stage of the outburst, this object might be
qualified as the seventh member of WZ Sge-type dwarf novae after Var Her 04. If
the former period is the same as, or very close to the orbital period of the
system, as in other WZ Sge systems, the fractional superhump excess is about
2.4{%}. This value is unexpectedly larger than that of other WZ Sge-type
dwarf novae. The early phase of our observing run provided evidence for the
transition from chaotic humps to genuine superhumps, together with increasing
the amplitude.Comment: 4 pages, 6 figures, submitted to PAS
Photometric Studies of a WZ Sge-Type Dwarf Nova Candidate, ASAS160048-4846.2
We report on our time-resolved CCD photometry during the 2005 June
superoutburst of a WZ Sge-type dwarf nova candidate, ASAS 160048-4846.2. The
ordinary superhumps underwent a complex evolution during the superoutburst. The
superhump amplitude experienced a regrowth, and had two peaks. The superhump
period decreased when the superhump amplitude reached to the first maximum,
successively gradually increased until the second maximum of the amplitude, and
finally decreased again. Investigating other SU UMa-type dwarf novae which show
an increase of the superhump period, we found the same trend of the superhump
evolution in superoutbursts of them. We speculate that the superhump regrowth
in the amplitude has a close relation to the increase of the superhump period,
and all of SU UMa-type dwarf novae with a superhump regrowth follow the same
evolution of the ordinary superhumps as that of ASAS 160048-4846.2.Comment: 7 pages, 4 figure
Constraints on the Progenitor of SN 2016gkg From Its Shock-Cooling Light Curve
SN 2016gkg is a nearby Type IIb supernova discovered shortly after explosion.
Like several other Type IIb events with early-time data, SN 2016gkg displays a
double-peaked light curve, with the first peak associated with the cooling of a
low-mass extended progenitor envelope. We present unprecedented
intranight-cadence multi-band photometric coverage of the first light-curve
peak of SN 2016gkg obtained from the Las Cumbres Observatory Global Telescope
network, the Asteroid Terrestrial-impact Last Alert System, the Swift satellite
and various amateur-operated telescopes. Fitting these data to analytical
shock-cooling models gives a progenitor radius of ~25-140 solar radii with
~2-30 x 10^-2 solar masses of material in the extended envelope (depending on
the model and the assumed host-galaxy extinction). Our radius estimates are
broadly consistent with values derived independently (in other works) from HST
imaging of the progenitor star. However, the shock-cooling model radii are on
the lower end of the values indicated by pre-explosion imaging. Hydrodynamical
simulations could refine the progenitor parameters deduced from the
shock-cooling emission and test the analytical models.Comment: Accepted by ApJ
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