27 research outputs found
The first confirmed superoutburst of the SU UMa type dwarf nova SDSS J083931.35+282824.0
We report unfiltered CCD photometry of the first confirmed superoutburst of
the recently discovered dwarf nova, SDSS J083931.35+282824.0 in April 2010.
From a quiescence magnitude of ~19.8 it rose to 14.0, an outburst amplitude of
at least 5.8 magnitudes. Only the plateau phase of the outburst was observed
during which superhumps with peak-to-peak amplitude of up to 0.28 magnitudes
were present, confirming this to be an SU UMa type dwarf nova. The mean
superhump period was Psh = 0.07836(2) during the first 3 days and this
subsequently decreased to 0.07800(3) d. Analysis of the data revealed tentative
evidence for an orbital period Porb = 0.07531(25) d. The fractional superhump
period excess was epsilon = 0.039(6), which is consistent with other dwarf
novae of similar orbital period.Comment: 12 pages, 3 figures. Accepted for publication in the Journal of the
British Astronomical Associatio
Rapid Oscillations in Cataclysmic Variables. XVI. DW Cancri
We report photometry and spectroscopy of the novalike variable DW Cancri. The
spectra show the usual broad H and He emission lines, with an excitation and
continuum slope characteristic of a moderately high accretion rate. A
radial-velocity search yields strong detections at two periods, 86.1015(3) min
and 38.58377(6) min. We interpret these as respectively the orbital period
P_orb of the binary, and the spin period P_spin of a magnetic white dwarf. The
light curve also shows the spin period, plus an additional strong signal at
69.9133(10) min, which coincides with the difference frequency
1/P_spin-1/P_orb. These periods are stable over the 1 year baseline of
measurement.
This triply-periodic structure mimics the behavior of several
well-credentialed members of the "DQ Herculis" (intermediate polar) class of
cataclysmic variables. DQ Her membership is also suggested by the mysteriously
strong sideband signal (at nu_spin-nu_orb), attesting to a strong pulsed flux
at X-ray/EUV/UV wavelengths. DW Cnc is a new member of this class, and would be
an excellent target for extended observation at these wavelengths.Comment: PDF, 28 pages, 6 tables, 9 figures; accepted, in press, to appear
June 2004, PASP; more info at http://cba.phys.columbia.edu
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
IM Normae: The Death Spiral of a Cataclysmic Variable?
We present a study of the orbital light curves of the recurrent nova IM
Normae since its 2002 outburst. The broad "eclipses" recur with a 2.46 hour
period, which increases on a timescale of 1.28(16)x10^6 years. Under the
assumption of conservative mass-transfer, this suggests a rate near 10^-7
M_sol/year, and this agrees with the estimated /accretion/ rate of the
postnova, based on our estimate of luminosity. IM Nor appears to be a close
match to the famous recurrent nova T Pyxidis. Both stars appear to have very
high accretion rates, sufficient to drive the recurrent-nova events. Both have
quiescent light curves which suggest strong heating of the low-mass secondary,
and very wide orbital minima which suggest obscuration of a large "corona"
around the primary. And both have very rapid orbital period increases, as
expected from a short-period binary with high mass transfer from the low-mass
component. These two stars may represent a final stage of nova -- and
cataclysmic-variable -- evolution, in which irradiation-driven winds drive a
high rate of mass transfer, thereby evaporating the donor star in a paroxysm of
nova outbursts.Comment: PDF, 30 pages, 3 tables, 6 figures; accepted, in press, ApJ; more
info at http://cbastro.org