21 research outputs found
Superhumps in Cataclysmic Binaries. XXII. 1RXS J232953.9+062814
We report photometry of 1RXS J232953.9+062814, a recently discovered dwarf
nova with a remarkably short 64.2-minute orbital period. In quiescence, the
star's light curve is that of a double sinusoid, arising from the "ellipsoidal"
distortion of the Roche-lobe-filling secondary. During superoutburst, common
superhumps develop with a period 3-4% longer than P_orb. This indicates a mass
ratio M_2/M_1=0.19+-0.02, a surprisingly large value in so compact a binary.
This implies that the secondary star has a density 2-3 times higher than that
of other short-period dwarf novae, suggesting a secondary enriched by H-burning
prior to the common-envelope phase of evolution. We estimate i=50+-5 deg,
M_1=0.63 (+0.12, -0.09) M_sol, M_2=0.12 (+0.03, -0.02) M_sol, R_2=0.121
(+0.010, -0.007) R_sol, and a distance to the binary of 180+-40 pc.Comment: PDF, 17 pages, 3 tables, 5 figures; accepted, in press, to appear
June 2002, PASP; more info at http://cba.phys.columbia.edu
Superhump Evolution in the Ultrashort Period Dwarf Nova 1RXS J232953.9+062814
Abstract
We report on the evolution of superhumps and late superhumps in an ultrashort period dwarf nova, 1RXS J232953.9062814, during the superoutburst in 2001 November. Ordinary superhumps were observed throughout a plateau phase, a rapid fading phase, and a rebrightening phase. During the plateau phase, the superhump period increased with time at a large rate of . In conjunction with the rebrightening phenomenon, these characteristics indicate that an accretion disk expanded further outward from the resonance radius, which caused a large amount of left over matter at the outer disk, even after the superoutburst. In the post-outburst phase, we detected late superhumps superimposed on dominant double-peak modulations. Late superhumps were observed at least for 10 d without a significant period change. We detected the first normal outburst of this object on 2001 December 26. The interval between the superoutburst and this normal one is 53 d. This short recurrence time supports a high mass-transfer rate in this system. Concerning the evolutionary status of 1RXS J232953.9062814, we propose that it is a progenitor of AM CVn stars on the evolutionary course of the cataclysmic variable channel in which systems have a secondary star with a hydrogen-exhausted core
The Transit Ingress and the Tilted Orbit of the Extraordinarily Eccentric Exoplanet HD 80606b
We present the results of a transcontinental campaign to observe the 2009
June 5 transit of the exoplanet HD 80606b. We report the first detection of the
transit ingress, revealing the transit duration to be 11.64 +/- 0.25 hr and
allowing more robust determinations of the system parameters. Keck spectra
obtained at midtransit exhibit an anomalous blueshift, giving definitive
evidence that the stellar spin axis and planetary orbital axis are misaligned.
The Keck data show that the projected spin-orbit angle is between 32-87 deg
with 68.3% confidence and between 14-142 deg with 99.73% confidence. Thus the
orbit of this planet is not only highly eccentric (e=0.93), but is also tilted
away from the equatorial plane of its parent star. A large tilt had been
predicted, based on the idea that the planet's eccentric orbit was caused by
the Kozai mechanism. Independently of the theory, it is noteworthy that all 3
exoplanetary systems with known spin-orbit misalignments have massive planets
on eccentric orbits, suggesting that those systems migrate differently than
lower-mass planets on circular orbits.Comment: ApJ, in press [13 pg
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
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 First Post-Kepler Brightness Dips of KIC 8462852
We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <<1um, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term "secular" dimming, which may be caused by independent processes, or probe different regimes of a single process