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 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

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

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

Solar-like oscillations in the metal-poor subgiant nu Indi: II. Acoustic spectrum and mode lifetime

Convection in stars excites resonant acoustic waves which depend on the sound speed inside the star, which in turn depends on properties of the stellar interior. Therefore, asteroseismology is an unrivaled method to probe the internal structure of a star. We made a seismic study of the metal-poor subgiant star nu Indi with the goal of constraining its interior structure. Our study is based on a time series of 1201 radial velocity measurements spread over 14 nights obtained from two sites, Siding Spring Observatory in Australia and ESO La Silla Observatory in Chile. The power spectrum of the high precision velocity time series clearly presents several identifiable peaks between 200 and 500 uHz showing regularity with a large and small spacing of 25.14 +- 0.09 uHz and 2.96 +- 0.22 uHz at 330 uHz. Thirteen individual modes have been identified with amplitudes in the range 53 to 173 cm/s. The mode damping time is estimated to be about 16 days (1-sigma range between 9 and 50 days), substantially longer than in other stars like the Sun, the alpha Cen system or the giant xi Hya.Comment: 5 pages, 7 figures, A&A accepte

Outbursts on normal stars. FH Leo misclassified as a novalike variable

We present high resolution spectroscopy of the common proper motion system FH Leo (components HD 96273 and BD+07 2411B), which has been classified as a novalike variable due to an outburst observed by Hipparcos, and we present and review the available photometry. We show from our spectra that neither star can possibly be a cataclysmic variable, instead they are perfectly normal late-F and early-G stars. We measured their radial velocities and derived the atmospheric fundamental parameters, abundances of several elements including Fe, Ni, Cr, Co, V, Sc, Ti, Ca and Mg, and we derive the age of the system. From our analysis we conclude that the stars do indeed constitute a physical binary. However, the observed outburst cannot be readily explained. We examine several explanations, including pollution with scattered light from Jupiter, binarity, microlensing, background supernovae, interaction with unseen companions and planetary engulfment. While no explanation is fully satisfactory, the scattered light and star-planet interaction scenarios emerge as the least unlikely ones, and we give suggestions for further study.Comment: 8 pages, 7 figures. Accepted for publication in A&

Swift X-ray Observations of Classical Novae

The new gamma-ray burst mission Swift has obtained pointed observations of several classical novae in outburst. We analyzed all the observations of classical novae from the Swift archive up to 30 June, 2006. We analyzed usable observations of 12 classical novae and found 4 non-detections, 3 weak sources and 5 strong sources. This includes detections of 2 novae exhibiting spectra resembling those of Super Soft X-ray binary Source spectra (SSS) implying ongoing nuclear burning on the white dwarf surface. With these new Swift data, we add to the growing statistics of the X-ray duration and characteristics of classical novae.Comment: Accepted for ApJ; this version contains additional material: 18 pages, 16 figure

The Swift X-ray flaring afterglow of GRB 050607

The unique capability of the Swift satellite to perform a prompt and autonomous slew to a newly detected Gamma-Ray Burst (GRB) has yielded the discovery of interesting new properties of GRB X-ray afterglows, such as the steep early lightcurve decay and the frequent presence of flares detected up to a few hours after the GRB trigger. We present observations of GRB 050607, the fourth case of a GRB discovered by Swift with flares superimposed on the overall fading X-ray afterglow. The flares of GRB 050607 were not symmetric as in previously reported cases, showing a very steep rise and a shallower decay, similar to the Fast Rise, Exponential Decay that are frequently observed in the gamma-ray prompt emission. The brighter flare had a flux increase by a factor of approximately 25,peaking for 30 seconds at a count rate of approximately 30 counts s-1, and it presented hints of addition short time scale activity during the decay phase. There is evidence of spectral evolution during the flares. In particular, at the onset of the flares the observed emission was harder, with a gradual softening as each flare decayed. The very short time scale and the spectral variability during the flaring activity are indicators of possible extended periods of energy emission by the GRB central engine. The flares were followed by a phase of shallow decay, during which the forward shock was being refreshed by a long-lived central engine or by shells of lower Lorentz factors, and by a steepening after approximately 12 ks to a decay slope considered typical of X-ray afterglows.Comment: 23 pages, 5 figures, Accepted by the Astrophysical Journa

The early X-ray afterglows of optically bright and dark Gamma-Ray Bursts

A systematical study on the early X-ray afterglows of both optically bright and dark gamma-ray bursts (B-GRBs and D-GRBs) observed by Swift has been presented. Our sample includes 25 GRBs. Among them 13 are B-GRBs and 12 are D-GRBs. Our results show that the distributions of the X-ray afterglow fluxes ($F_{X}$), the gamma-ray fluxes ($S_{\gamma}$), and the ratio ($R_{\gamma, X}$) for both the D-GRBs and B-GRBs are similar. The differences of these distributions for the two kinds of GRBs should be statistical fluctuation. These results indicate that the progenitors of the two kinds of GRBs are the same population. Their total energy explosions are comparable. The suppression of the optical emissions from D-GRBs should results from circumburst but not their central engine.Comment: 10 pages, 3 figures, 1 table; accepted by ChJA