On the periodicities present in the optical light curves of SMC Be/X-ray binaries

We present a comprehensive study of the periodic variations observed in OGLE I-band light curves of SMC Be/X-ray binaries, discovering new optical periodicities in 9 systems. We find that these periodicities derive from a number of mechanisms, notably disturbance of the decretion disk on the orbital period of the system, and aliased non-radial pulsations. We develop metrics that allow these mechanisms to be distinguished on the basis of the shape of the folded optical light curve, and use these metrics to categorise the periodicities present in \sim 50 SMC binary systems. We conclude that extreme care must be taken in the interpretation of the OGLE light curves since only around 30% of the periodicities present can be unambiguously attributed to orbital periods.Comment: 16 pages, 17 figures, accepted for publication in MNRA

Life History and Management Methods for Blueline Tilefish (Caulolatilus microps) from the United States Mid-Atlantic Region

Blueline tilefish (Caulolatilus microps) have recently undergone an increase in landings from waters off the US Mid-Atlantic region (Virginia-Massachusetts). Currently, life history characteristics of blueline tilefish in this area are undescribed. Additionally, appropriate indices of population abundance are not available for this region, necessitating the use of data-limited management methods to set restrictions for harvest of blueline tilefish in this area. This dissertation describes growth and reproductive characteristics of blueline tilefish caught off the coast of Virginia and explores improvements of data-limited management methods that have been applied to blueline tilefish in the US Mid-Atlantic. Blueline tilefish from the US Mid-Atlantic show a similar growth pattern to fish caught off North and South Carolina prior to the rise of commercial fishing for blueline tilefish in this area. This growth pattern is dissimilar from that observed more recently for fish from the US South Atlantic (east coast of Florida-North Carolina), with fish in the US Mid-Atlantic growing more slowly to larger maximum lengths. Blueline tilefish from the US Mid-Atlantic are gonochoristic multiple batch spawners that spawn, on average, every 1.44 days from May-November, with annual fecundities up to 50,000,000 oocytes for the largest individuals. Batch fecundity is correlated with total length in a similar fashion as seen previously in the US South Atlantic. These studies are the first to characterize growth and reproduction of blueline tilefish from the US Mid-Atlantic. Sensitivities of modal estimates and variabilities of total allowable catch (TAC), from data-limited management procedures (MP) applicable to blueline tilefish, to input values were analyzed to determine which inputs most impacted TAC. Natural mortality and mean maximum length from the von Bertalanffy growth equation had the greatest impacts. A composite MP was developed to incorporate distributions of TAC estimates from multiple MPs into a single, combined distribution that could be used to estimate a composite TAC. These analyses provide information that may enhance decision-making for management of data-limited fish stocks, such as blueline tilefish

X-ray Pulsations in the Supersoft X-ray Binary CAL 83

X-ray data reveal that the supersoft X-ray binary CAL 83 exhibits 38.4 minute pulsations at some epochs. These X-ray variations are similar to those found in some novae and are likely to be caused by nonradial pulsations the white dwarf. This is the first detection of pulsations in a classical supersoft X-ray binary.Comment: revised text; 11 pages and 3 figures; accepted for publication in the Astronomical Journa

A major outburst from the X-ray binary RX J0520.5-6932

We report on the analysis of 8 years of MAssive Compact Halo Objects (MACHO) data for the source RX J0520.5-6932. A regular period of 24.4 days has been confirmed, however this is manifest almost entirely in the red part of the spectrum. A major outburst, lasting approximately 200 days, was observed which increased the apparent brightness of the object by approximately 0.15 magnitudes without significantly altering its V-R colour index. This outburst was also seen in X-ray data. The evidence from this analysis points to the identification of this object as a Be/X-ray binary with a periodically variable circumstellar disk and a very early optical counterpart.Comment: Paper has been accepted by MNRA