323 research outputs found
A 6.4-hr positive superhump period in TV Col
Re-examination of photometric data of TV Col (Hellier, 1993) reveals positive
superhumps in addition to the negative superhumps previously known. The
superhump period is 0.265+/-0.005 day - about 16 percent longer than the
orbital period - which obeys the relation between superhump-period excess and
orbital period (Stolz and Schoembs 1984). As a confirmed permanent superhumper,
the accretion disc of TV Col is naturally thermally stable. Therefore, our
result supports the idea of Hellier and Buckley (1993) that the short-term
outbursts seen in its light curve are mass transfer events rather than thermal
instabilities in the disc. At 5.5-hr, TV Col has a longer orbital period than
any known superhumper, and thus a mass ratio which is probably outside the
range at which superhumps can occur according to current theory.Comment: 2 pages, Latex file, 2 .eps files. to appear in "Cataclysmic
Variables: a 60th Birthday Symposium in Honour of Brian Warner", held in
Oxforf, 12-16/4/99, eds. P. Charles, A. King, D. O'Donoghue, New Astronomy
Reviews. also available at:
ftp://ftp.astro.keele.ac.uk/pub/preprints/Oxford.htm
A study of discrete control signal fault conditions in the shuttle DPS
An analysis of the effects of discrete failures on the data processing subsystem is presented. A functional description of each discrete together with a list of software modules that use this discrete are included. A qualitative description of the consequences that may ensue due to discrete failures is given followed by a probabilistic reliability analysis of the data processing subsystem. Based on the investigation conducted, recommendations were made to improve the reliability of the subsystem
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
The Detection of a 3.5-h Period in the Classical Nova Velorum 1999 (V382 Vel) and the Long Term Behavior of the Nova Light Curve
We present CCD photometry, light curve and time series analysis of the
classical nova V382 Vel (N Vel 1999). The source was observed for 2 nights in
2000, 21 nights in 2001 and 7 nights in 2002 using clear filters. We report the
detection of a distinct period in the light curve of the nova P=0.146126(18) d
(3.5 h). The period is evident in all data sets, and we interpret it as the
binary period of the system. We also measured an increase in the amplitude
modulation of the optical light (in magnitude) by more than 55% from 2000 to
2001 and about 64% from 2001 to 2002. The pulse profiles in 2001 show
deviations from a pure sinusoidal shape which progressively become more
sinusoidal by 2002. The main cause of the variations in 2001 and 2002 can be
explained with the occultation of the accretion disk by the secondary star. We
interpret the observed deviations from a pure sinusoidal shape as additional
flux resulting from the aspect variations of the irradiated face of the
secondary star.Comment: 16 pages and 4 figures, accepted as it stands to be published in the
Astronomical Journal (AJ
A 6.3-h superhump in the cataclysmic variable TV Columbae: the longest yet seen
We present results from a two week multi-longitude photometric campaign on TV
Col held in 2001 January. The data confirm the presence of a permanent positive
superhump found in re-examination of extensive archive photometric data of TV
Col. The 6.3-h period is 15 per cent 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: 8 pages, 1 Latex file, 7 eps figures, MNRAS, accepte
Smoothed Particle Hydrodynamics Simulations of Apsidal and Nodal Superhumps
In recent years a handful of systems have been observed to show "negative"
(nodal) superhumps, with periods slightly shorter than the orbital period. It
has been suggested that these modes are a consequence of the slow retrograde
precession of the line of nodes in a disk tilted with respect to the orbital
plane. Our simulations confirm and refine this model: they suggest a roughly
axisymmetric, retrogradely-precessing, tilted disk that is driven at a period
slightly less than half the orbital period as the tidal field of the orbiting
secondary encounters in turn the two halves of the disk above and below the
midplane. Each of these passings leads to viscous dissipation on one face of an
optically-thick disk -- observers on opposite sides of the disk would each
observe one brightening per orbit, but 180 degrees out of phase with each
other.Comment: 11 pages. Accepted for publication in The ApJ Letter
SPH Simulations of Negative (Nodal) Superhumps: A Parametric Study
Negative superhumps in cataclysmic variable systems result when the accretion
disc is tilted with respect to the orbital plane. The line of nodes of the
tilted disc precesses slowly in the retrograde direction, resulting in a
photometric signal with a period slightly less than the orbital period. We use
the method of smoothed particle hydrodynamics to simulate a series of models of
differing mass ratio and effective viscosity to determine the retrograde
precession period and superhump period deficit as a function of
system mass ratio . We tabulate our results and present fits to both
and versus , as well as compare the
numerical results with those compiled from the literature of negative superhump
observations. One surprising is that while we find negative superhumps most
clearly in simulations with an accretion stream present, we also find evidence
for negative superhumps in simulations in which we shut off the mass transfer
stream completely, indicating that the origin of the photometric signal is more
complicated than previously believed.Comment: 14 pages, 15 figures. Accepted for publication in MNRA
Bose-Einstein Condensation on a Permanent-Magnet Atom Chip
We have produced a Bose-Einstein condensate on a permanent-magnet atom chip
based on periodically magnetized videotape. We observe the expansion and
dynamics of the condensate in one of the microscopic waveguides close to the
surface. The lifetime for atoms to remain trapped near this dielectric material
is significantly longer than above a metal surface of the same thickness. These
results illustrate the suitability of microscopic permanent-magnet structures
for quantum-coherent preparation and manipulation of cold atoms.Comment: 4 pages, 6 figures, Published in Phys. Rev. A, Rapid Com
A cyclical period variation detected in the updated orbital period analysis of TV Columbae
The two CCD photometries of the intermediate polar TV Columbae are made for
obtaining the two updated eclipse timings with high precision. There is an
interval time \sim 17yr since the last mid-eclipse time observed in 1991. Thus,
the new mid-eclipse times can offer an opportunity to check the previous
orbital ephemerides. A calculation indicates that the orbital ephemeris derived
by Augusteijn et al. (1994) should be corrected. Based on the proper linear
ephemeris (Hellier, 1993), the new orbital period analysis suggests a cyclical
period variation in the O-C diagram of TV Columbae. Using Applegate's mechanism
to explain the periodic oscillation in O-C diagram, the required energy is
larger than that a M0-type star can afford over a complete variation period
\sim 31.0(\pm 3.0)yr. Thus, the light travel-time effect indicates that the
tertiary component in TV Columbae may be a dwarf with a low mass, which is near
the mass lower limit \sim 0.08Msun as long as the inclination of the third body
high enough.Comment: 10 pages, 5 figure
Bose-Einstein Condensation on a Permanent-Magnet Atom Chip
We have produced a Bose-Einstein condensate on a permanent-magnet atom chip
based on periodically magnetized videotape. We observe the expansion and
dynamics of the condensate in one of the microscopic waveguides close to the
surface. The lifetime for atoms to remain trapped near this dielectric material
is significantly longer than above a metal surface of the same thickness. These
results illustrate the suitability of microscopic permanent-magnet structures
for quantum-coherent preparation and manipulation of cold atoms.Comment: 4 pages, 6 figures, Published in Phys. Rev. A, Rapid Com
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