On the Papaloizou-Pringle instability in tidal disruption events

We demonstrate that the compact, thick disc formed in a tidal disruption event may be unstable to non-axisymmetric perturbations in the form of the Papaloizou-Pringle instability. We show this can lead to rapid redistribution of angular momentum that can be parameterised in terms of an effective Shakura-Sunyaev $\alpha$ parameter. For remnants that have initially weak magnetic fields, this may be responsible for driving mass accretion prior to the onset of the magneto-rotational instability. For tidal disruptions around a $10^6$ M$_{\odot}$ black hole, the measured accretion rate is super-Eddington but is not sustainable over many orbits. We thus identify a method by which the torus formed in tidal disruption event may be significantly accreted before the magneto-rotational instability is established.Comment: 9 pages, 10 figures, accepted for publication in MNRAS. Movies of simulations available at https://youtu.be/kBLAjY8n9vI and https://youtu.be/F8F0tmLbX3

Long term time-lapse microgravity and geotechnical monitoring of relict salt-mines, Marston, Cheshire, UK.

The area around the town of Northwich in Cheshire, U. K., has a long history of catastrophic ground subsidence caused by a combination of natural dissolution and collapsing abandoned mine workings within the underlying Triassic halite bedrock geology. In the village of Marston, the Trent and Mersey Canal crosses several abandoned salt mine workings and previously subsiding areas, the canal being breached by a catastrophic subsidence event in 1953. This canal section is the focus of a long-term monitoring study by conventional geotechnical topographic and microgravity surveys. Results of 20 years of topographic time-lapse surveys indicate specific areas of local subsidence that could not be predicted by available site and mine abandonment plan and shaft data. Subsidence has subsequently necessitated four phases of temporary canal bank remediation. Ten years of microgravity time-lapse data have recorded major deepening negative anomalies in specific sections that correlate with topographic data. Gravity 2D modeling using available site data found upwardly propagating voids, and associated collapse material produced a good match with observed microgravity data. Intrusive investigations have confirmed a void at the major anomaly. The advantages of undertaking such long-term studies for near-surface geophysicists, geotechnical engineers, and researchers working in other application areas are discussed

Hubble Space Telescope WFPC2 Imaging of SN 1979C and Its Environment

The locations of supernovae in the local stellar and gaseous environment in galaxies contain important clues to their progenitor stars. As part of a program to study the environments of supernovae using Hubble Space Telescope (HST) imaging data, we have examined the environment of the Type II-L SN 1979C in NGC 4321 (M100). We place more rigorous constraints on the mass of the SN progenitor, which may have had a mass M \approx 17--18 M_sun. Moreover, we have recovered and measured the brightness of SN 1979C, m=23.37 in F439W (~B; m_B(max) = 11.6), 17 years after explosion. .Comment: 18 pages, 8 figures, submitted to PAS

Preliminary soilwater conductivity analysis to date clandestine burials of homicide victims

This study reports on a new geoscientific method to estimate the post-burial interval (PBI) and potential post-mortem interval (PMI) date of homicide victims in clandestine graves by measuring decomposition fluid conductivities. Establishing PBI/PMI dates may be critical for forensic investigators to establish time-lines to link or indeed rule out suspects to a crime. Regular in situ soilwater analysis from a simulated clandestine grave (which contained a domestic buried pig carcass) in a semi-rural environment had significantly elevated conductivity measurements when compared to background values. A temporal rapid increase of the conductivity of burial fluids was observed until one-year post-burial, after this values slowly increased until two years (end of the current study period). Conversion of x-axis from post-burial days to 'accumulated degree days' (ADDs) corrected for both local temperature variations and associated depth of burial and resulted in an improved fit for multiple linear regression analyses. ADD correction also allowed comparison with a previous conductivity grave study on a different site with a different soil type and environment; this showed comparable results with a similar trend observed. A separate simulated discovered burial had a conductivity estimated PBI date that showed 12% error from its actual burial date. Research is also applicable in examining illegal animal burials; time of burial and waste deposition. Further research is required to extend the monitoring period, to use human cadavers and to repeat this with other soil types and depositional environments

Warped accretion discs and the long periods in X-ray binaries

Precessing accretion discs have long been suggested as explanations for the long periods observed in a variety of X-ray binaries, most notably Her X-1/HZ Her. We show that an instability of the disc's response to the radiation reaction force from the illumination by the central source can cause the disc to tilt out of the orbital plane and precess in something like the required manner. The rate of precession and disc tilt obtained for realistic values of system parameters compare favourably with the known body of data on X-ray binaries with long periods. We explore other possible types of behaviour than steadily precessing discs that might be observable in systems with somewhat different parameters. At high luminosities, the inner disc tilts through more than 90 degrees, i.e. it rotates counter to the usual direction, which may explain the torque reversals in systems such as 4U 1626-67.Comment: submitted to MNRAS, 17-Dec-97, revised submit 2-Nov-98. 15 pages LaTeX, 11 postscript figures in-tex

In vivo length oscillations of indirect flight muscles in the fruit fly Drosophila virilis

We have used high-speed video microscopy to measure in vivo length oscillations of the indirect flight muscles of the fruit fly Drosophila virilis during tethered flight. The changes in muscle strain were measured by tracking the deformation of the thoracic exoskeleton at the origin and insertion of both the dorsal longitudinal (DLM) and the dorsal ventral (DVM) muscles. The mean peak-to-peak strain amplitudes were found to be 3.5% for the DLMs and 3.3% for the DVMs, although the strain amplitude within individual cycles ranged from 2 to 5%. These values are consistent with the small number of previous measurements of indirect flight muscle strain in other insects, but almost an order of magnitude greater than the strain amplitudes used in most biophysical studies of skinned Drosophila fibers. The results suggest that serial compliance within this sarcomere would need to relieve approximately 70% of the total strain in order for individual crossbridges to remain attached throughout a complete contraction-extension cycle

EM Cygni: a study of its eclipse timings

EM Cygni is a Z Cam-subtype eclipsing dwarf nova. Its orbital period variations were reported in the past but the results were in conflict to each other while other studies allowed the possibility of no period variation. In this study we report accurate new times of minima of this eclipsing binary and update its O-C diagram. We also estimate the mass transfer rate in EM Cygni system and conclude that the mass transfer is far from the critical value. The mass transfer rate determined from the eclipse timings is in agreement with the spectroscopically determined value.Comment: 5 pages, 4 figures, accepted for publication in Astronomische Nahrichte

Superhumps in Low-Mass X-Ray Binaries

We propose a mechanism for the superhump modulations observed in optical photometry of at least two black hole X-ray transients (SXTs). As in extreme mass-ratio cataclysmic variables (CVs), superhumps are assumed to result from the presence of the 3:1 orbital resonance in the accretion disc. This causes the disc to become non-axisymmetric and precess. However the mechanism for superhump luminosity variations in low mass X-ray binaries (LMXBs) must differ from that in CVs, where it is attributed to a tidally-driven modulation of the disc's viscous dissipation, varying on the beat between the orbital and disc precession period. By contrast in LMXBs, tidal dissipation in the outer accretion disc is negligible: the optical emission is overwhelming dominated by reprocessing of intercepted central X-rays. Thus a different origin for the superhump modulation is required. Recent observations and numerical simulations indicate that in an extreme mass-ratio system the disc area changes on the superhump period. We deduce that the superhumps observed in SXTs arise from a modulation of the reprocessed flux by the changing area. Therefore, unlike the situation in CVs, where the superhump amplitude is inclination-independent, superhumps should be best seen in low-inclination LMXBs, whereas an orbital modulation from the heated face of the secondary star should be more prominent at high inclinations. Modulation at the disc precession period (10s of days) may indicate disc asymmetries such as warping. We comment on the orbital period determinations of LMXBs, and the possibility and significance of possible permanent superhump LMXBs.Comment: 6 pages, 1 encapsulated figure. MNRAS in press; replaced to correct typographical error