Andry Rajoelimanana

Very Long-term Optical Variability of High Mass X-ray Binaries in the SMC

We have studied the very long-term temporal properties of the optical emission from Be X-ray binaries (BeX) in the Small Magellanic Cloud over a ~ 16 yr baseline, using light curves from the MACHO and OGLE databases. All the BeX in our sample display superorbital variations, many of them quasi-periodic on timescales of ~ 200-3000 d. These long-term variations are believed to be related to the formation and depletion of the circumstellar disc around the Be star and we compare and contrast their behaviour with that of the LMCs prototypical BeX, A0538-66. The great majority of sources show a correlation of outburst amplitude with brightness (the opposite to that seen in A0538-66) although the amplitudes are mostly small (< 0.1 mag). We suggest this is an orbital inclination effect. In addition, we have also detected many of their optical orbital periodicities, visible as a series of precisely regular outbursts. Furthermore, the amplitude of these periodic outbursts can vary through the long-term superorbital cycle, and we discuss mechanisms which can produce this effect, as well as examining an apparent correlation between these periodicities. As a by-product of this variation survey we have compiled a list of all the reported SMC BeX orbital and superorbital periodicities at optical and X-ray wavelengths.

Optical and X-ray properties of CAL 83 – I. Quasi-periodic optical and supersoft variability

We have studied the long-term (∼ years) temporal variability of the prototype supersoft X-ray source (SSS) CAL 83 in the LMC, using data from the MACHOand OGLE projects. The CAL 83 light curve exhibits dramatic brightness changes of ∼ 1 mag on timescales of ∼ 450 days, and spends typically ∼ 200 days in the optical low state. Combined with archival XMM-NewtonX-ray observations these represent the most extensive X-ra y/optical study to date of this system, and reveal in much greater detail that th e X-ray light curve is anticorrelated with the optical behaviour. This is remarkably s imilar to the behaviour of the “transient” SSS, RX J0513.9-6951, where the SSS outbursts recur on a timescale of ∼ 168 days, and also anti-correlate with the optical flux. We performed s imple blackbody fits to both high and low state X-ray spectra, and find that the blackbody tempe rature and luminosity decrease when the optical counterpart brightens. We interpret these long-term variations in terms of the limit-cycle model of Hachisu & Kato (2003a), which provides further support for these systems containing massive (∼ 1.3 M⊙) white dwarfs. In addition, we have refined their orbital periods in the MACHO and OGLE-III light curves to values of 1.047529(1) days and 0.762956(5) days for CAL 83 and RX J0513.9-6951, respectively.

On the impossible NGC 4372 V1 and V2: an extended AGB to the [Fe/H] = −2.2 cluster

The asymptotic giant branch (AGB) of the globular cluster NGC 4372 appears to extend to unexpectedly high luminosities. We show, on the basis of proper motions and spatial distribution, that the extended AGB is indeed a likely part of the cluster. We also present the first spectra of the very cool (2600 K), very luminous (8000 L⊙), very dusty, oxygen-rich, purported long-period variable stars V1 and V2 that define the AGB tip. In particular, on the basis of their radial velocities, we conclude that V1 and V2 are probably members. We find that V1 and V2 are likely undergoing the superwind phase that terminates their nuclear-burning evolution. We hypothesise that the mass-loss processes that terminate the AGB are inhibited in NGC 4372 due to a lack of atmospheric pulsation and the high gas-to-dust ratio in the ejecta, leading to a delay in the associated enhanced mass loss and dust production. Previously predicted, but never observed, this explains the high mass of the white dwarf in Pease 1 in M15 without the need to invoke a stellar merger. If commonplace, this phenomenon has implications for the mass return from stars, the production of carbon stars and supernovae through the Universe’s history, and the AGB contribution to light from unresolved metal-poor populations.

Very long-term optical variability of high-mass X-ray binaries in the Small Magellanic Cloud

We have studied the very long-term temporal properties of the optical emission from Be X-ray binaries (BeX) in the Small Magellanic Cloud over a ~ 16 yr baseline, using light curves from the MACHO and OGLE databases. All the BeX in our sample display superorbital variations, many of them quasi-periodic on timescales of ~ 200-3000 d. These long-term variations are believed to be related to the formation and depletion of the circumstellar disc around the Be star and we compare and contrast their behaviour with that of the LMCs prototypical BeX, A0538-66. The great majority of sources show a correlation of outburst amplitude with brightness (the opposite to that seen in A0538-66) although the amplitudes are mostly small (< 0.1 mag). We suggest this is an orbital inclination effect. In addition, we have also detected many of their optical orbital periodicities, visible as a series of precisely regular outbursts. Furthermore, the amplitude of these periodic outbursts can vary through the long-term superorbital cycle, and we discuss mechanisms which can produce this effect, as well as examining an apparent correlation between these periodicities. As a by-product of this variation survey we have compiled a list of all the reported SMC BeX orbital and superorbital periodicities at optical and X-ray wavelengths.

Transient emission of selected CRTS Cataclysmic Variables

We present optical photometric and spectroscopic observations of three SU UMa-type dwarf novae, i.e. AR Pic, QW Ser and V521 Peg, conducted in 2016 and 2017. These sources were selected from the Catalina Real-Time Transient Survey and observed during quiescence, outburst (AR Pic and QW Ser) and superoutburst (V521 Peg). For AR Pic, strong flickering in the light curves and an asymmetric double-peaked H

Diagnostic Studies for Excretion Be - Star Disc Evolution in Be/X-Ray Binary Systems Utilizing SALT Spectroscopy

\beta

Multi-Wavelength Properties of Be/XRay Binaries in the Magellanic Clouds

emission line in the spectra, confirmed the presence of a very active hot spot. During outburst, detected on 18 February 2017, it exhibited a

Observations of Flaring Fermi-LAT Blazars and Prospects in Spectro-Polarimetry with SALT-RSS

\sim 3.3

Very long-term optical variability of high-mass X-ray binaries in the Small Magellanic Cloud: Very long optical variability in BeX sources

magnitude brightening. The projected velocity of the inner edge of the accretion disc is

Long‐Term Optical/X‐ray Variability of CVs, LMXBs and BeX Sources

\sim 2000 \rm~km~s^{-1}