1,037 research outputs found
On Echo Outbursts and ER UMa Supercycles in SU UMa-type Cataclysmic Variables
I present a variation on Osaki's tidal-thermal-instability model for SU UMa
behavior. I suggest that in systems with the lowest mass ratios, the
angular-momentum dissipation in an eccentric disk is unable to sustain the disk
on the hot side of the thermal instability. This decoupling of the tidal and
thermal instabilities in systems with q < 0.07 allows a better explanation of
the `echo' outbursts of EG Cnc and the short supercycles of RZ LMi and DI UMa.
The idea might also apply to the soft X-ray transients.Comment: To appear in PASP, April 2001 (6 pages, 4 figs
Superhumps in a Peculiar SU UMa-Type Dwarf Nova ER Ursae Majoris
We report the photometry of a peculiar SU UMa-type dwarf nova - ER UMa for
ten nights during 1998 December and 1999 March covering a complete rise to the
supermaximum and a normal outburst cycle. Superhumps have been found during the
rise to the superoutburst. A negative superhump appeared in Dec.22 light curve,
while the superhump on the next night became positive and had large amplitude
and distinct waveform from that of the previous night. In the normal outburst
we captured, superhumps with larger or smaller amplitudes seem to always exist,
although it is not necessarily true for every normal outburst. These results
show great resemblance with V1159 Ori (Patterson et al. 1995). It is more
likely that superhumps occasionally exist at essentially all phases of the
eruption cycles of ER UMa stars, which should be considered in modeling.Comment: 4 pages, 5 figures, Accepted by ApJ Letter
Evolution of Giant Planets in Eccentric Disks
We investigate the interaction between a giant planet and a viscous
circumstellar disk by means of high-resolution, two-dimensional hydrodynamical
simulations. We consider planet masses that range from 1 to 3 Jupiter masses
(Mjup) and initial orbital eccentricities that range from 0 to 0.4. We find
that a planet can cause eccentricity growth in a disk region adjacent to the
planet's orbit, even if the planet's orbit is circular. Disk-planet
interactions lead to growth in a planet's orbital eccentricity. The orbital
eccentricities of a 2 Mjup and a 3 Mjup planet increase from 0 to 0.11 within
about 3000 orbits. Over a similar time period, the orbital eccentricity of a 1
Mjup planet grows from 0 to 0.02. For a case of a 1 Mjup planet with an initial
eccentricity of 0.01, the orbital eccentricity grows to 0.09 over 4000 orbits.
Radial migration is directed inwards, but slows considerably as a planet's
orbit becomes eccentric. If a planet's orbital eccentricity becomes
sufficiently large, e > ~0.2, migration can reverse and so be directed
outwards. The accretion rate towards a planet depends on both the disk and the
planet orbital eccentricity and is pulsed over the orbital period. Planet mass
growth rates increase with planet orbital eccentricity. For e~0.2 the mass
growth rate of a planet increases by approximately 30% above the value for e=0.
For e > ~0.1, most of the accretion within the planet's Roche lobe occurs when
the planet is near the apocenter. Similar accretion modulation occurs for flow
at the inner disk boundary which represents accretion toward the star.Comment: 20 pages 16 figures, 3 tables. To appear in The Astrophysical Journal
vol.652 (December 1, 2006 issue
Curious Variables Experiment (CURVE). CCD photometry of active dwarf nova DI UMa
We report an analysis of photometric behaviour of DI UMa, an extremely active
dwarf nova. The observational campaign (completed in 2007) covers five
superoutbursts and four normal outbursts. We examined principal parameters of
the system to understand peculiarities of DI UMa, and other active cataclysmic
variables. Based on precise photometric measurements, temporal light curve
behaviour, O-C analysis, and power spectrum analysis, we investigated physical
parameters of the system. We found that the period of the supercycle now equals
31.45 +/-0.3 days. Observations during superoutbursts infer that the period of
superhumps equals P_sh = 0.055318(11) days (79.66 +/- 0.02 min). During
quiescence, the light curve reveals a modulation of period P_orb = 0.054579(6)
days (78.59 +/- 0.01 min), which we interpret as the orbital period of the
binary system. The values obtained allowed us to determine a fractional period
excess of 1.35% +/- 0.02%, which is surprisingly small compared to the usual
value for dwarf novae (2%-5%). A detailed O-C analysis was performed for two
superoutbursts with the most comprehensive coverage. In both cases, we detected
an increase in the superhump period with a mean rate of dot_P/P_sh =
4.4(1.0)*10^{-5}. Based on these measurements, we confirm that DI UMa is
probably a period bouncer, an old system that reached its period minimum a long
time ago, has a secondary that became a degenerate brown dwarf, the entire
system evolving now toward longer periods. DI UMa is an extremely interesting
object because we know only one more active ER UMa star with similar
characteristics (IX Dra).Comment: Accepted for publication in Astronomy & Astrophysic
The statistical significance of the superhump signal in U Gem
Although its well determined mass ratio of q=\Msec/\Mwd=0.357\pm0.007
should avoid superoutbursts according to the thermal tidal instability model,
the prototypical dwarf nova U Gem experienced in 1985 an extraordinary long
outburst resembling very much superoutbursts observed in SU UMa systems.
Recently, the situation for the model became even worse as superhump detections
have been reported for the 1985 outburst of U Gem. The superhump signal is
noisy and the evidence provided by simple periodograms seems to be weak.
Therefore and because of the importance for our understanding of superoutbursts
and superhumps, we determine the statistical significance of the recently
published detection of superhumps in the AAVSO light curve of the famous long
1985 outburst of U Gem. Using Lomb-Scargle periodograms, analysis of variance
(AoV), and Monte-Carlo methods we analyse the 160 visual magnitudes obtained by
the AAVSO during the outburst and relate our analyse to previous superhump
detections. The 160 data points of the outburst alone do not contain a
statistically significant period. However, using additionally the
characteristics of superhumps detected previously in other SU UMa systems and
searching only for signals that are consistent with these, we derive a
significance for the superhump signal. The alleged appearance of an
additional superhump at the end of the outbursts appears to be statistically
insignificant. Although of weak statistical significance, the superhump signal
of the long 1985 outburst of U Gem can be interpreted as further indication for
the SU UMa nature of this outburst. This further contradicts the tidal
instability model as the explanation for the superhump phenomenon.Comment: 7 pages, 7 figures, accepted for publication in A&
In-the-Gap SU UMa-Type Dwarf Nova, Var73 Dra with a Supercycle of about 60 Days
An intensive photometric-observation campaign of the recently discovered SU
UMa-type dwarf nova, Var73 Dra was conducted from 2002 August to 2003 February.
We caught three superoutbursts in 2002 October, December and 2003 February. The
recurrence cycle of the superoutburst (supercycle) is indicated to be 60
d, the shortest among the values known so far in SU UMa stars and close to
those of ER UMa stars. The superhump periods measured during the first two
superoutbursts were 0.104885(93) d, and 0.10623(16) d, respectively. A
0.10424(3)-d periodicity was detected in quiescence. The change rate of the
superhump period during the second superoutburst was , which
is an order of magnitude larger than the largest value ever known. Outburst
activity has changed from a phase of frequent normal outbursts and infrequent
superoutbursts in 2001 to a phase of infrequent normal outbursts and frequent
superoutbursts in 2002. Our observations are negative to an idea that this star
is an related object to ER UMa stars in terms of the duty cycle of the
superoutburst and the recurrence cycle of the normal outburst. However, to
trace the superhump evolution throughout a superoutburst, and from quiescence
more effectively, may give a fruitful result on this matter.Comment: 9 pages, 8 figures, submitted to A&
Realization of a collective decoding of codeword states
This was also extended from the previous article quant-ph/9705043, especially
in a realization of the decoding process.Comment: 6 pages, RevTeX, 4 figures(EPS
Mass transfer in tidally unstable compact binaries
The 2001 outburst of WZ Sagittae has shown the most compelling evidence yet
for an enhancement of the mass transfer rate from the donor star during a dwarf
nova outburst in the form of hot-spot brightening. I show that even in this
extreme case, the brightening can be attributed to tidal heating near the
interaction point of an accretion stream with the expanding edge of an
eccentric accretion disc, with no need at all for an increase in the mass
transfer rate. Furthermore, I confirm previous suggestions that an increase in
mass transfer rate through the stream damps any eccentricity in an accretion
disc and suppresses the appearance of superhumps, in contradiction to
observations. Tidal heating is expected to be most significant in systems with
small mass ratios. It follows that systems like WZ Sagittae - which has a tiny
mass ratio - are those most likely to show a brightening in the hot-spot
region.Comment: 6 pages, 5 figures (eps/ps). Accepted for publication in MNRA
SDSS J210014.12+004446.0: A New Dwarf Nova with Quiescent Superhumps?
We report follow-up observations of the Sloan Digital Sky Survey Cataclysmic
Variable SDSS J210014.12+004446.0 (hereafter SDSS J2100). We obtained
photometry and spectroscopy in both outburst and quiescent states, providing
the first quiescent spectrum of this source. In both states, non-sinusoidal
photometric modulations are apparent, suggestive of superhumps, placing SDSS
J2100 in the SU UMa subclass of dwarf novae. However, the periods during
outburst and quiescence differ significantly, being 2.099 plus or minus 0.002
hr and 1.96 plus or minus 0.02 hr respectively. Our phase-resolved spectroscopy
during outburst yielded an estimate of about 2 hr for the orbital period,
consistent with the photometry. The presence of the shorter period modulation
at quiescence is unusual, but not unique. Another atypical feature is the
relative weakness of the Balmer emission lines in quiescence. Overall, we find
a close similarity between SDSS J2100 and the well-studied superhump
cataclysmic Variable V503 Cygni. By analogy, we suggest that the quiescent
modulation is due to a tilted accretion disk -- producing negative superhumps
-- and the modulation in outburst is due to positive superhumps from the
precession of an elliptical disk.Comment: 6 pages, 5 eps figures, accepted by PASP Dec. 16th, 200
Transport properties of the heavy fermion superconductor PrOsSb
We have measured the electrical resistivity, thermoelectric power, Hall
coefficient, and magnetoresistance (MR) on single crystals of
PrOsSb, LaOsSb and NdOsSb. All the
transport properties in PrOsSb are similar to those in
LaOsSb and NdOsSb at high temperatures, indicating
the localized character of 4-electrons. The transverse MR both in
LaOsSb and PrOsSb tends to saturate for wide field
directions, indicating these compounds to be uncompensated metals with no open
orbit. We have determined the phase diagram of the field induced ordered phase
by the MR measurement for all the principle field directions, which indicates
an unambiguous evidence for the singlet crystalline electric
field ground state.Comment: 7 pages, 10 figures, to appear in Physical Review
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