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

Multiwavelength Studies of Hercules X-1 during Short High and Anomalous Low States: On-again, Off-again

We present results from multiwavelength observations of the Hercules X-1 system during a short high state (SHS) and during an anomalous low state (ALS). The magnitude of deviation from spin-up appears to be positively correlated with duration of the ALS. Such a correlation is consistent with an interpretation of the ALS in terms of a change in mass accretion rate that causes the disk to tilt and twist beyond the normal deviations that cause the 35 day cycle. A larger deviation from the average Ṁ results in a stronger disruption of the disk and causes the disk to take longer to settle back to its "normal" 35 day behavior. Our model - which includes X-ray heating of the disk and companion star, shadowing of the X-ray flux by the disk, and a contribution to the continuum emission from the accretion stream or hot spot - can consistently explain the observed changes in X-ray, ultraviolet (UV), and optical continuum light curves for both the SHS and ALS. The Bubble Space Telescope (HST) and Space Telescope Imaging Spectrograph (STIS) observations presented here are the first UV observations of sufficient spectral and temporal resolution to construct Doppler tomograms of the line emission. Doppler tomograms of the UV emission lines during SHS and ALS show the majority of the emission coming from the surface of the companion star rather than from the accretion disk. Tomograms made after separating the N v emission lines into broad and narrow components suggests that while the narrow component is associated with emission from the companion star, the broad component may be associated with emission from a distorted disk. The Doppler maps also show that heating over the inner face of HZ Her is not uniform and imply partial eclipse of the UV line emission by an accretion stream and/or hot spot

Keck II spectroscopy of mHz quasi-periodic oscillations in Hercules X-1

We present Keck II spectroscopy of an optical mHz quasi-periodic oscillations (QPOs) in the lightcurve of the X-ray pulsar binary Her X-1. In the power spectrum it appears as `peaked noise', with a coherency $\sim$2, a central frequency of 35 mHz and a peak-to-peak amplitude of 5%. However, the dynamic power spectrum shows it to be an intermittent QPO, with a lifetime of $\sim$hundred seconds, as expected if the lifetime of the orbiting material is equal to the thermal timescale of the inner disk. We have decomposed the spectral time series into constant and variable components and used blackbody fits to the resulting spectra to characterise the spectrum of the QPO variability and constrain possible production sites. We find that the spectrum of the QPO is best-fit by a small hot region, possibly the inner regions of the accretion disk, where the ballistic accretion stream impacts onto the disk. The lack of any excess power around the QPO frequency in the X-ray power spectrum, created using simultaneous lightcurves from XTE, implies that the QPO is not simply reprocessed X-ray variability.Comment: 10 pages, including 6 figures, accepted for publication by MNRA