3,659 research outputs found
Thermal stability and nova cycles in permanent superhump systems
Archival data on permanent superhump systems are compiled to test the thermal
stability of their accretion discs. We find that their discs are almost
certainly thermally stable as expected. This result confirms Osaki's suggestion
(1996) that permanent superhump systems form a new subclass of cataclysmic
variables (CVs), with relatively short orbital periods and high mass transfer
rates. We note that if the high accretion rates estimated in permanent
superhump systems represent their mean secular values, then their mass transfer
rates cannot be explained by gravitational radiation, therefore, either
magnetic braking should be extrapolated to systems below the period gap or they
must have mass transfer cycles. Alternatively, a new mechanism that removes
angular momentum from CVs below the gap should be invoked.
We suggest applying the nova cycle scenarios offered for systems above the
period gap to the short orbital period CVs. Permanent superhumps have been
observed in the two non-magnetic ex-novae with binary periods below the gap.
Their post-nova magnitudes are brighter than their pre-outburst values. In one
case (V1974 Cyg) it has been demonstrated that the pre-nova should have been a
regular SU UMa system. Thus it is the first nova whose accretion disc was
observed to change its thermal stability. If the superhumps in this system
indicate persistent high mass transfer rates rather than a temporary change
induced by irradiation from the hot post-nova white dwarf, it is the first
direct evidence for mass transfer cycles in CVs. The proposed cycles are driven
by the nova eruption.Comment: 7 pages, 2 eps. figures, Latex, accepted for publication in MNRA
Does TV Col Have the longest Recorded Positive Superhumps?
Re-examination of extensive photometric data of TV Col reveals evidence for a
permanent positive superhump. Its period (6.4 h) is 16 percent longer than the
orbital period and obeys the well known relation between superhump period
excess and binary period. At 5.5-h, TV Col has an orbital period longer than
any known superhumping cataclysmic variable and, therefore, a mass ratio which
might be outside the range at which superhumps can occur according to the
current theory. We suggest several solutions for this problem.Comment: 5 pages, 2 eps. figures, Latex, proceedings of `Evolution of Binary
and Multiple Star Systems', a Meeting in Celebration of Peter Eggleton's 60th
Birthday, Bormio, Italy, ASP Conference Series, eds. Ph. Podsiadlowski et
al., ASP, San Francisc
A TiO study of the black-hole binary GRO J0422+32 in a very low state
We present 53 simultaneous photometric (I band) and spectroscopic (6900-9500
Angstroms) observations of J0422+32, taken during December 1997. From these we
determine that J0422+32 was in its lowest state yet observed, at
I=20.44+/-0.08. Using relative spectrophotometry, we show that it is possible
to correct very accurately for telluric absorption. Following this, we use the
TiO bands at 7055 Angstroms and 7589 Angstroms for a radial velocity study and
thereby obtain a semi-amplitude of 378+/-16kms-1, which yields
f(M)=1.191+/-0.021M_solar and q=9.0+2.2-2.7, consistent with previous
observations. We further demonstrate that this little explored method is very
powerful for such systems. We also determine a new orbital ephemeris of
HJD=2450274.4156+/-0.0009 + 0.2121600+/-0.0000002E.
We see some evidence for an ellipsoidal modulation, from which we determine
the orbital inclination of J0422+32 to be less than 45 degrees. We therefore
calculate a minimum mass for the primary of 2.22M_solar, consistent with a
black hole, but not necessarily the super-massive one proposed by Beekman et al
(1997). We obtain an M4-5 spectral type for the secondary star and determine
that the secondary contributes 38+/-2% of the flux that we observe from
J0422+32 over the range 6950-8400 Angstroms. From this we calculate the
distance to the system to be 1.39+/-0.15kpc.Comment: (1) Department of Physics, Keele University, Keele, Staffordshire,
ST5 5BG (2) Department of Astrophysics, Nuclear Physics Laboratory, Keble
Road, Oxfo rd, OX1 3RH Accepted, to appear in MNRAS 8 pages, 5 figure
Digital data averager improves conventional measurement system performance
Multipurpose digital averager provides measurement improvement in noisy signal environments. It provides increased measurement accuracy and resolution to basic instrumentation devices by an arithmetical process in real time. It is used with standard conventional measurement equipment and digital data printers
Black hole quasinormal modes using the asymptotic iteration method
In this article we show that the asymptotic iteration method (AIM) allows one
to numerically find the quasinormal modes of Schwarzschild and Schwarzschild de
Sitter (SdS) black holes. An added benefit of the method is that it can also be
used to calculate the Schwarzschild anti-de Sitter (SAdS) quasinormal modes for
the case of spin zero perturbations. We also discuss an improved version of the
AIM, more suitable for numerical implementation.Comment: 10 pages, LaTeX; references added; substantially expanded versio
Split fermion quasi-normal modes
In this paper we use the conformal properties of the spinor field to show how
we can obtain the fermion quasi-normal modes for a higher dimensional
Schwarzschild black hole. These modes are of interest in so called split
fermion models, where quarks and leptons are required to exist on different
branes in order to keep the proton stable. As has been previously shown, for
brane localized fields, the larger the number of dimensions the faster the
black hole damping rate. Moreover, we also present the analytic forms of the
quasi-normal frequencies in both the large angular momentum and the large mode
number limits.Comment: 11 pages, 7 figures, version 2 added reference
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