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ABSTRACT: This study of SDSS0804 is primarily concerned with the double-hump shape in
the light curve and its connection with the accretion disk in this bounce-back
system. Time-resolved photometric and spectroscopic observations were obtained
to analyze the behavior of the system between superoutbursts. A geometric model
of a binary system containing a disk with two outer annuli spiral density waves
was applied to explain the light curve and the Doppler tomography. Observations
were carried out during 2008-2009, after the object's magnitude decreased to
V~17.7(0.1) from the March 2006 eruption. The light curve clearly shows a
sinusoid-like variability with a 0.07 mag amplitude and a 42.48 min
periodicity, which is half of the orbital period of the system. In Sept. 2010,
the system underwent yet another superoutburst and returned to its quiescent
level by the beginning of 2012. This light curve once again showed a
double-humps, but with a significantly smaller ~0.01mag amplitude. Other types
of variability like a "mini-outburst" or SDSS1238-like features were not
detected. Doppler tomograms, obtained from spectroscopic data during the same
period of time, show a large accretion disk with uneven brightness, implying
the presence of spiral waves. We constructed a geometric model of a bounce-back
system containing two spiral density waves in the outer annuli of the disk to
reproduce the observed light curves. The Doppler tomograms and the
double-hump-shape light curves in quiescence can be explained by a model system
containing a massive >0.7Msun white dwarf with a surface temperature of
~12000K, a late-type brown dwarf, and an accretion disk with two outer annuli
spirals. According to this model, the accretion disk should be large, extending
to the 2:1 resonance radius, and cool (~2500K). The inner parts of the disk
should be optically thin in the continuum or totally void.
11/2012;
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ABSTRACT: We present preliminary results of long-term monitoring of the peculiar
cataclysmic variable FS Aurigae conducted during the 2010-2011 observational
season. The multicolor observations revealed, for the first time in photometric
data, the precession period of the white dwarf, previously seen only
spectroscopically. This is best seen in the (B-I) color index and reflects the
spectral energy distribution variability. Analysis of X-ray observations made
with Chandra and Swift, also revealed the existence of both the orbital and
precession periods in the light curve. We also show that the long-term
variability of FS Aur and the character of its outburst activity may be caused
by variations in the mass transfer rate from the secondary star as the result
of eccentricity modulation of a close binary orbit induced by the presence of a
third body on a circumbinary orbit.
11/2011;
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[hide abstract]
ABSTRACT: Precession is observed routinely in solid bodies of Solar system and it has
been invoked to explain number of phenomena observed in pulsars (i.e. Link
2003, Breton et al. 2008). White dwarfs also have been considered as possible
candidates of precessing stellar objects. In slowly rotating compact stars, the
precession period is extremely long and the amplitude of precession is small.
However, in rapid rotating neutron stars and white dwarfs, the precession
period is still within reasonable observational limits and can explain observed
periodicities exceeding spin periods by several times.
11/2011;
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E. Pavlenko,
V. Malanushenko, G. Tovmassian,
S. Zharikov,
T Kato,
N. Katysheva,
M. Andreev,
A. Baklanov,
K. Antonyuk,
N. Pit,
A. Sosnovskij,
S. Shugarov
[show abstract]
[hide abstract]
ABSTRACT: SDSS J080434.20+510349.2 is the 13th dwarf nova containing a pulsating white
dwarf. Among the accreting pulsators that have experienced a dwarf novae
outburst, SDSS J0804 has the most dramatic history of events within a short
time scale: the 2006 outburst with 11 rebrightenings, series of December 2006 -
January 2007 mini-outbursts, the 2010 outburst with 6 rebrightenings. Over
2006-2011, SDSS J080434.20+510349.2 in addition to positive 0.060^d superhumps
during the outburst and 1-month post-outburst stage, 0.059005^d orbital humps
in quiescence, displayed a significant short-term variations with periods P1 =
12.6 min, P2 = 21.7 min, P3 = 14.1 min and P4 = 4.28 min. The 12.6-min
periodicity first appeared 7 months after the 2006 outburst and was the most
prominent one during the following \sim 900 days. It was identified as
non-radial pulsations of the white dwarf. The period of this pulsations varied
within a range of 36 s, and amplitude changed from 0.013m to 0.03m.
Simultaneously one could observe the 21.7-min and 14.3-min periodicities with a
much lower significance level. During the minioutbursts the 21.7-min
periodicity became the most powerful, the 12.6-min periodicity was less
powerful, and the 12.6-min periodicity had the lowest significance. After the
2011 outburst the most prominent short-term periodicity appeared \sim 7 months
after the outburst, but at 4.28 min. We identified that variability with
periods P2, P3 and P4 could be additional pulsation modes, however the relation
of P4 to white dwarf pulsation also can't be excluded.
11/2011;
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[hide abstract]
ABSTRACT: We present here results of numerical calculations demonstrating that the very long periodic variability detected in the Cataclysmic Variable FS Aur can be the result of eccentricity modulation of a close binary (CB) orbit induced by the presence of a third body on a circumbinary orbit. A third component with a substellar mass on a circular, relatively close orbit, modulates the mass transfer rate of the binary on much longer time scales than periods within the triple system. We also report here preliminary results of X-ray observations of FS Aur, providing further evidence that it contains magnetic and freely precessing white dwarf. These two findings allow us to incorporate the new and previously stressed hypothesis on the nature of FS Aur into one consistent model. Comment: 6 pages, 7 figures, presented at the "Physics of Accreting Compact Binaries" Conference held in Kyoto, Japan on July 26 - 30, 2010
09/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We present here results of an optical spectroscopic study of a new Cataclysmic Variable SDSS J001856.93+345444.3. We demonstrate that the most probable value of the orbital period of the system is Porb = 0.6051 \pm 0.022 days (=14.5226 hours), based on the measurements of radial velocity of a complex of absorption features emanating from the K2-K4V type secondary component. However, the radial velocity measurements from the emission lines are best folded with the period Pem = 0.5743day (=13.78 hours). The gamma-velocity of the emission lines varies significantly from epoch to epoch. There is an underlying broader and weaker component to the emission lines, which we could not resolve. Based on the appearance of the emission lines, the presence of very strong He II lines and the moderate polarization detected by Dillon et al. (2008), we conclude that SDSS J0018+3454 is an asynchronous magnetic CV (Polar). Comment: 4 pages, 4 figure, posters presentation at "Physics of Accreting Compact Binaries" held in Kyoto Japan, 26-30 July, 2010
09/2010;
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Anjum S. Mukadam,
D. M. Townsley,
B. T. Gänsicke,
P. Szkody,
T. R. Marsh,
E. L. Robinson,
L. Bildsten,
A. Aungwerojwit,
M. R. Schreiber,
J. Southworth, [......],
S. V. Zharikov,
M. G. Hidas,
N. Baliber,
T. Brown,
P. A. Woudt,
B. Warner,
D. O'Donoghue,
D. A. H. Buckley,
R. Sefako,
and E. M. Sion
[show abstract]
[hide abstract]
ABSTRACT: Non-radial pulsations in the primary white dwarfs of cataclysmic variables can now potentially allow us to explore the stellar interior of these accretors using stellar seismology. In this context, we conducted a multi-site campaign on the accreting pulsator SDSS J161033.64–010223.3 (V386 Ser) using seven observatories located around the world in 2007 May over a duration of 11 days. We report the best-fit periodicities here, which were also previously observed in 2004, suggesting their underlying stability. Although we did not uncover a sufficient number of independent pulsation modes for a unique seismological fit, our campaign revealed that the dominant pulsation mode at 609 s is an evenly spaced triplet. The even nature of the triplet is suggestive of rotational splitting, implying an enigmatic rotation period of about 4.8 days. There are two viable alternatives assuming the triplet is real: either the period of 4.8 days is representative of the rotation period of the entire star with implications for the angular momentum evolution of these systems, or it is perhaps an indication of differential rotation with a fast rotating exterior and slow rotation deeper in the star. Investigating the possibility that a changing period could mimic a triplet suggests that this scenario is improbable, but not impossible. Using time-series spectra acquired in 2009 May, we determine the orbital period of SDSS J161033.64–010223.3 to be 83.8 ± 2.9 minutes. Three of the observed photometric frequencies from our 2007 May campaign appear to be linear combinations of the 609 s pulsation mode with the first harmonic of the orbital period at 41.5 minutes. This is the first discovery of a linear combination between non-radial pulsation and orbital motion for a variable white dwarf.
The Astrophysical Journal 04/2010; 714(2):1702. · 6.02 Impact Factor
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A. Aviles,
S. Zharikov, G. Tovmassian,
R. Michel,
M. Tapia,
M. Roth,
V. Neustroev,
C. Zurita,
M. Andreev,
A. Sergeev,
E. Pavlenko,
V. Tsymbal,
G. C. Anupama,
U. S. Kamath,
and D. K. Sahu
[show abstract]
[hide abstract]
ABSTRACT: We present infrared JHK photometry of the cataclysmic variable (CV) SDSS J123813.73 – 033933.0 and analyze it along with optical spectroscopy, demonstrating that the binary system is most probably comprised of a massive white dwarf with T eff = 12000 ± 1000 K and a brown dwarf of spectral type L4. The inferred system parameters suggest that this system may have evolved beyond the orbital period minimum and is a bounce-back system. SDSS J123813.73 – 033933.0 stands out among CVs by exhibiting the cyclical variability that Zharikov et al. called brightenings. These are not related to specific orbital phases of the binary system and are fainter than dwarf novae outbursts that usually occur on longer timescales. This phenomenon has not been observed extensively and, thus, is poorly understood. The new time-resolved, multi-longitude photometric observations of SDSS J123813.73 – 033933.0 allowed us to observe two consecutive brightenings and to determine their recurrence time. The period analysis of all observed brightenings during 2007 suggests a typical timescale that is close to a period of ~9.3 hr. However, the brightenings modulation is not strictly periodic, possibly maintaining coherence only on timescales of several weeks. The characteristic variability with double orbital frequency that clearly shows up during brightenings is also analyzed. The Doppler mapping of the system shows the permanent presence of a spiral arm pattern in the accretion disk. A simple model is presented to demonstrate that spiral arms in the velocity map appear at the location and phase corresponding to the 2:1 resonance radius and constitute themselves as double-humped light curves. The long-term and short-term variability of this CV is discussed together with the spiral arm structure of an accretion disk in the context of observational effects taking place in bounce-back systems.
The Astrophysical Journal 02/2010; 711(1):389. · 6.02 Impact Factor
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A. Aviles,
S. Zharikov, G. Tovmassian,
R. Michel,
M. Tapia,
M Roth,
V. Neustroev,
C. Zurita,
M. Andreev,
A. Sergeev,
E. Pavlenko,
V. Tsymbal,
G. C. Anupama,
U. S. Kamath,
D. K. Sahu
[show abstract]
[hide abstract]
ABSTRACT: We present infrared JHK photometry of the cataclysmic variable SDSS J123813.73-033933.0 (SDSS1238)and analyze it along with optical spectroscopy, demonstrating that the binary system is most probably comprised of a massive white dwarf with Teff=12000+/-1000 K and a brown dwarf of spectral type L4. The inferred system parameters suggest that this system may have evolved beyond the orbital period minimum and is a bounce-back system. SDSS1238 stands out among CVs by exhibiting the cyclical variability (brightenings). These are not related to specific orbital phases of the binary system and are fainter than dwarf novae outbursts, that usually occur on longer timescales. This phenomenon has not been observed extensively and, thus, is poor understood. The new time-resolved, multi-longitude photometric observations of SDSS1238 allowed us to observe two consecutive brightenings and to determine their recurrence time. The period analysis of all observed brightenings during 2007 suggests a typical timescale that is close to a period of ~9.3 hours. However, the brightenings modulation is not strictly periodic, possibly maintaining coherence only on timescales of several weeks. The characteristic variability with double orbital frequency that clearly shows up during brightenings is also analyzed. The Doppler mapping of the system shows the permanent presence of a spiral arm pattern in the accretion disk. A simple model is presented to demonstrate that spiral arms in the velocity map appear at the location and phase corresponding to the 2:1 resonance radius and constitute themselves as a double-humped light curves. The long-term and short-term variability of this CV is discussed together with the spiral arm structure of an accretion disk in the context of observational effects taking place in bounce-back systems. Comment: 24 pages, 9 figures, Accepted for publications in The Astrophysical Journal, typos added
01/2010;
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G. Stasinska,
C. Morisset, G. Tovmassian,
T. Rauch,
M. G. Richer,
M. Pena,
R. Szczerba,
T. Decressin,
C. Charbonnel,
L. Yungelson,
R. Napiwotzki,
S. Simon-Diaz,
L. Jamet
[show abstract]
[hide abstract]
ABSTRACT: The planetary nebula TS 01 (also called PN G 135.9+55.9 or SBS 1150+599A), with its record-holding low oxygen abundance and its double degenerate close binary core (period 3.9 h), is an exceptional object located in the Galactic halo. We have secured observational data in a complete wavelength range in order to pin down the abundances of half a dozen elements in the nebula. The abundances are obtained via detailed photoionization modelling taking into account all the observational constraints (including geometry and aperture effects) using the pseudo-3D photoionization code Cloudy_3D. The spectral energy distribution of the ionizing radiation is taken from appropriate model atmospheres. Both stellar components contribute to the ionization: the ``cool'' one provides the bulk of hydrogen ionization, and the ``hot'' one is responsible for the presence of the most highly charged ions, which explains why previous attempts to model the nebula experienced difficulties. The nebular abundances of C, N, O, and Ne are found to be respectively, 1/3.5, 1/4.2, 1/70, and 1/11 of the Solar value, with uncertainties of a factor 2. Thus the extreme O deficiency of this object is confirmed. The abundances of S and Ar are less than 1/30 of Solar. Standard models of stellar evolution and nucleosynthesis cannot explain the abundance pattern observed in the nebula. To obtain an extreme oxygen deficiency in a star whose progenitor has an initial mass of about 1 msun requires an additional mixing process, which can be induced by stellar rotation and/or by the presence of the close companion. We have computed a stellar model with initial mass of 1 msun, appropriate metallicity, and initial rotation of 100 kms, and find that rotation greatly improves the agreement between the predicted and observed abundances. Comment: to appear in Astronomy and Astrophysics
11/2009;
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V. A. R. M. Ribeiro,
M. F. Bode,
M. J. Darnley,
D. J. Harman,
A. M. Newsam,
T. J. O'Brien,
J. Bohigas,
J. M. Echevarría,
H. E. Bond,
V. H. Chavushyan,
R. Costero,
R. Coziol,
A. Evans,
S. P. S. Eyres,
J. León-Tavares,
M. G. Richer, G. Tovmassian,
S. Starrfield,
and S. V. Zharikov
[show abstract]
[hide abstract]
ABSTRACT: We report Hubble Space Telescope (HST) imaging, obtained 155 and 449 days after the 2006 outburst of the recurrent nova RS Ophiuchi, together with ground-based spectroscopic observations, obtained from the Observatorio Astronómico Nacional en San Pedro Mártir, Baja California, México and at the Observatorio Astrofísico Guillermo Haro, at Cananea, Sonora, México. The observations at the first epoch were used as inputs to model the geometry and kinematic structure of the evolving RS Oph nebular remnant. We find that the modeled remnant comprises two distinct co-aligned bipolar components; a low-velocity, high-density innermost (hour glass) region and a more extended, high-velocity (dumbbell) structure. This overall structure is in agreement with that deduced from radio observations and optical interferometry at earlier epochs. We find that the asymmetry observed in the west lobe is an instrumental effect caused by the profile of the HST filter and hence demonstrate that this lobe is approaching the observer. We then conclude that the system has an inclination to the line of sight of 39+1°–10. This is in agreement with the inclination of the binary orbit and lends support to the proposal that this morphology is due to the interaction of the outburst ejecta with either an accretion disk around the central white dwarf and/or a pre-existing red giant wind that is significantly denser in the equatorial regions of the binary than at the poles. The second epoch HST observation was also modeled. However, as no spectra were taken at this epoch, it is more difficult to constrain any model. Nevertheless, we demonstrate that between the two HST epochs the outer dumbbell structure seems to have expanded linearly. For the central (hour glass) region, there may be evidence of deceleration, but it is harder to draw firm conclusions in this case.
The Astrophysical Journal 09/2009; 703(2):1955. · 6.02 Impact Factor
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ABSTRACT: We present X-ray observations of the close binary nucleus of the planetary nebula PN G135.9+55.9 obtained with the XMM satellite. The nebula is the most oxygen-poor PN known to date and is located in the Galactic halo. It is known to harbor a close binary nucleus of which only one component can be observed in optical-UV range. New X-ray observations show that the invisible component is a very hot compact star. This finding allows us to reconstruct the immediate past of the object and predict its future. The parameters of the binary components we determine strongly suggest that the precursor was a symbiotic supersoft X-ray source that finished its life by Roche lobe overflow. PN G135.9+55.9 is an excelent candidate for a future type Ia supernova.
10/2007;
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ABSTRACT: Cataclysmic Variables (CV) are close binary systems, in which the primary, the more massive star, is a white dwarf. CVs usually exhibit a number of periodicities, most of which are now understood. However, recently, a new phenomenon was discovered that does not fit the standard picture. Two objects have been discovered to show periods that are much longer than orbital, and have no relation to it, either in light curves or in radial velocity (RV) variations measured from spectroscopy. Here, we show that the precession of the fast rotating magnetically accreting white dwarf can successfully explain these phenomena. The theory of compact objects predicts certain relations between the spin and precession periods, and our finding provides a good test for the theory and establishes a qualitative model to be explored both theoretically and observationally. Detection of precession can become a powerful tool in searching for the internal properties of compact stars, which would be otherwise inaccessible for us.
10/2006;
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[show abstract]
[hide abstract]
ABSTRACT: PN G135.9+55.9 is the most metal-poor PN known in our Galaxy. The central star resides in a short-period binary system with a compact component, probably a white dwarf. We describe new observations, which allowed us to determine the orbital period. The lower limit for the combined mass of both stars is close to the Chandrasekhar limit for white dwarfs, making this binary a possible progenitor of a supernova type Ia. The binary system must have recently emerged from a common envelope phase. Comment: Proceedings of the conference "Planetary Nebulae as Astronomical Tools", Gdansk, June/July 2005. To appear in AIP conference series
09/2005;
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[show abstract]
[hide abstract]
ABSTRACT: Informamos sobre los resultados de observaciones espectroscópicas Echelle y B&C del objeto con líneas de emisión FBS 0022 - 21 obtenidas en el Observatorio de San Pedro Mártir, México. Analizamos los espectros de las líneas de emisión junto con datos del óptico e IR disponibles. El espectro rico en FeII del objeto se asemeja fuertemente al del sistema binario peculiar Car. Se discuten las condiciones físicas que dan lugar a tal espectro y la naturaleza de este peculiar objeto.
Revista Mexicana de Astronomía y Astrofísica. 01/2004;
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J. Greiner,
S. Klose,
K. Reinsch,
H. M. Schmid,
R. Sari,
D. H. Hartmann,
C. Kouveliotou,
A. Rau,
E. Palazzi,
C. Straubmeier, [......],
A. Henden,
A. A. Kaas,
T. Grav,
J. Hjorth,
H. Pedersen,
R. A. M. J. Wijers,
A. Kaufer,
H S Park,
G Williams,
O. Reimer
[show abstract]
[hide abstract]
ABSTRACT: We report 31 polarimetric observations of the afterglow of GRB 030329 with high signal-to-noise and high sampling frequency. We establish the polarization light curve, detect sustained polarization at the percent level, and find significant variability of polarization degree and angle. The data imply that the afterglow magnetic field has small coherence length and is mostly random, probably generated by turbulence.
12/2003;
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J. Greiner,
S. Klose,
K. Reinsch,
H. M. Schmid,
R. Sari,
D. H. Hartmann,
C. Kouveliotou,
A. Rau,
E. Palazzi,
C. Straubmeier, [......],
A. Henden,
A. A. Kaas,
T. Grav,
J. Hjorth,
H. Pedersen,
R. A. M. J. Wijers,
A. Kaufer,
H S Park,
G Williams,
O. Reimer
[show abstract]
[hide abstract]
ABSTRACT: We report 31 polarimetric observations of the afterglow of GRB 030329 with high signal-to-noise and high sampling frequency. The data imply that the afterglow magnetic field has small coherence length and is mostly random, probably generated by turbulence. Comment: 2003 GRB Conference, Santa Fe, Oct. 2003, 1 ps-figure
12/2003;
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[show abstract]
[hide abstract]
ABSTRACT: PN G135.9+55.9 is a compact, high excitation nebula that has been identified recently as the most oxygen-poor halo planetary nebula. Given its very peculiar characteristics and potential implications in the realms of stellar and Galactic evolution, additional data are needed to firmly establish its true nature and evolutionary history. Here we present the first long-slit, high spectral resolution observations of this object in the lines of H$\alpha$ and He II 4686. The position-velocity data are shown to be compatible with the interpretation of PN G135.9+55.9 being a halo planetary nebula. In both emission lines, we find the same two velocity components that characterize the kinematics as that of an expanding elliptical envelope. The kinematics is consistent with a prolate ellipsoidal model with axis ratio about 2:1, a radially decreasing emissivity distribution, a velocity distribution that is radial, and an expansion velocity of 30 km/s for the bulk of the material. To fit the observed line profiles, this model requires an asymmetric matter distribution, with the blue-shifted emission considerably stronger than the red-shifted emission. We find that the widths of the two velocity components are substantially wider than those expected due to thermal motions, but kinematic structure in the projected area covered by the slit appears to be sufficient to explain the line widths. The present data also rule out the possible presence of an accretion disk in the system that could have been responsible for a fraction of the H$\alpha$ flux, further supporting the planetary nebula nature of PN G135.9+55.9. Comment: accepted by Astronomy & Astrophysics
08/2003;
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[show abstract]
[hide abstract]
ABSTRACT: We have observed several magnetic cataclysmic variables located in the range between 2 and 3 hours, known as the period gap. This work was prompted by the recent discovery of RX J1554.2+2721. It has 2.54 hours orbital period and shows almost pure cyclotron continuum in a low luminosity state, similar to HS1023+3900, HS0922+1333 and RBS206. These are low accretion rate polars (LARPs) known to have mass transfer rates of order of a few 10^-13Msun/year. The aim of the study was to find out, if magnetic systems filling the period gap are in any way different from their counterparts outside that range of periods. The only significant difference we encounter, is much higher number of asynchronous magnetic systems to-wards longer periods than below the gap.
03/2003;
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[show abstract]
[hide abstract]
ABSTRACT: FS Aur is a known dwarf nova with an orbital period of about 85.7 minutes. It has been assumed to be a member of the SU UMa subclass of cataclysmic variables (CVs), but previous searches for superhumps and superoutburst have been unsuccessful. We conducted a series of photometric and spectroscopic observations of FS Aur during quiescence. We confirmed its short orbital period from radial velocity measurements. However, the long-term photometry revealed an unexpected result: the system also shows a distinct 0.24 mag modulation in the BVR photometric bands with a period of 205.5 min, which is 2.4 times longer than the orbital period. We discuss various possible causes for such a peculiar behavior. Comment: 12 pages, 1 table, 12 figures, accepted for publication in PASP
02/2003;
