Search

Low mass ratio contact binary systems are more likely to have unstable orbits and potentially merge. In addition, such systems exhibit characteristics such as starspots and high energy emissions (UV) suggestive of chromospheric and magnetic activity. Light curve modelling of ten contact binary systems is reported. All were found to be of extreme low mass ratio ranging from 0.122 to 0.24 and three were found to be potentially unstable and possible merger candidates. Filling of the infrared Calcium absorption lines is a marker of increased chromospheric activity. We use the available LAMOST spectra along with matched standard spectra (broadened for rotation) to measure the excess filling of the central core depression flux of the two main infrared Calcium absorption lines at 8542 and 8662 angstroms. We find that all reported contact binaries have excess filling of the core flux in the infrared Calcium lines. Three of the systems reported were also observed by the GALEX mission and we find that all three have features of excess ultraviolet emissions further adding evidence for increased chromospheric activity in low mass ratio contact binaries. Analysis of both orbital stability and absorption line filling is dependent on the determination of geometric and absolute parameters from light curve modelling. Not an insignificant number of contact binary light curves exhibit the O'Connell effect, usually attributed to starspots. We discuss the inclusion of starspots in light curve solutions and how they influence the geometric and absolute parameters, Comment: 17 Pages 2 Figures 5 Tables Accepted - Research in Astronomy and Astrophysics (RAA)

The orbital stability of contact binary systems has been receiving considerable attention recently. Theoretical studies indicate that merger is likely to occur at very low mass ratios, but the actual mass ratio at which merger may take place is likely to be variable and dependent on the mass of the primary. We consider the effects of metal content on the orbital stability of contact binary systems by modelling the gyration radius of a rotating and tidally distorted primary component at various values of metallicity in the range -1.25 to +0.5. We determine the instability mass ratio range for contact binary systems with a low mass primary in the range 0.6M(sun) to 1.4M(sun) at various metallicity levels and show that systems with low metallicity have an instability mass ratio lower than those with higher metal content and therefore are likely to be more stable. We illustrate the effect through light curve analysis of two otherwise very similar contact binary systems, except for different metallicity. While both would be considered unstable if metallicity was not taken into consideration, only one remains in that category after appropriate adjustments based on metallicity have been made., Comment: 9 pages, 7 Figures and 5 Tables Accepted Monthly Notices of Royal Astronomical Society (MNRAS)

The study reports photometric and spectroscopic observations of two recently recognised contact binary systems. Both systems show total eclipses and analysis of the light curves indicate both have a very low mass ratios of less than 0.3. We derive absolute parameters from colour and distance based calibrations and show that although both have low mass ratios they are likely to be in a stable orbit and unlikely to merge. In other respects both systems have characteristics similar to other contact binaries with the secondary larger and brighter than main sequence counterparts and we also find that the secondary is considerably denser than the primary in both systems., Comment: 10 pages. 3 Figures. 1 Table Accepted - Research in Astronomy and Astrophysics (RAA)

Multi-band (B, V and R) photometric and spectroscopic observations of six poorly studied contact binaries carried out at the Western Sydney University and Las Cumbres Observatory were analysed using a recent version of the Wilson-Devenney code. All six were found to be of extreme low mass ratio ranging from 0.073 to 0.149. All are of F spectral class with the mass of the primary component ranging from 1.05Msun to 1.48Msun. None show light curve features of enhanced choromospheric activity (O'Connell Effect) however five of the six do have significant ultraviolet excess indicating presence of increased magnetic and chromospheric activity. Period analysis based on available survey data suggests two systems have a slowly increasing period suggesting mass transfer from the secondary to the primary, two have a slow declining period with likely mass transfer from primary to the secondary while one shows a steady period and one undergoing transition from a declining to increasing period suggesting possible mass transfer reversal. We also compare light curve solutions against theoretical markers of orbital stability and show that three of six systems have mass ratios within the theoretical instability limit and maybe regarded as potential merger candidates., Comment: 10 Pages. 5 Tables. 4 Figures. Accepted Publications of the Astronomical Society of the Pacific

Photometric observations and analysis of twelve previously poorly studied contact binary systems is presented. All show total eclipses and have extremely low mass ratios ranging from 0.072 to 0.15. Also, all show characteristics of orbital instability with mass ratios within the theoretical orbital instability range. Although none demonstrate a significant O'Connell effect at least nine of the systems have other indicators of increased chromospheric and magnetic activity., Comment: 11 Pages, 2 Figures Accepted Publications of the Astronomical Society of the Pacific (PASP)

The study presents a simplified method to identify potential bright red nova progenitors based on the amplitude of the light curve and infrared (J-H) colour of a contact binary system. We employ published criteria for contact binary orbital instability to show that the amplitude of the light curve for a given contact system with a low mass (< 1.4Msun) primary must be less than a specified value for it to be potentially unstable. Using this we search the photometric data of a large survey to identify about 50 potential bright red nova progenitors. We analyse the survey photometry of each to determine the mass ratio and from the estimated mass of the primary other physical parameters of the systems. We show that each system has physical characteristics indicating potential orbital instability. Using the absolute parameters from our sample we model the expected instability separation and period for low mass contact binary systems, Comment: Accepted - Journal of Astrophysics and Astronomy

The study presents photometric analysis of the completely eclipsing contact binary systems TYC 8351-1081-1 and ASAS J210406-0522.3. TYC 8351-1081-1 is an extremely low mass ratio (q=0.086) system with high degree of contact (f=0.66) while ASAS J210406-0522.3 is found to be in marginal contact (f=0.08) with a relatively low mass ratio of 0.272. There is good thermal contact in both systems with only a small difference in the temperature of the components. The systems have been observed by a number sky surveys over the past 20 years. We compare the light curve solutions from up to three of these surveys and find that survey photometric data manually analysed is robust and yields results comparable to dedicated ground based photometry. There is evidence of significant luminosity transfer from the primary to the secondary, on the order of 0.5LJ for TYC 8351-1081-1 and 0.06LJ for ASAS J210406-0522.3. There appears to be no change in period of either system over the past 20 years and theoretical angular momentum loss is below current measurement threshold in both cases. We also show that the mass ratio and separation are well above the theoretical values for orbital instability in both cases. As would be expected, the density of the secondary components is significantly higher relative to the primary., Comment: 9 Pages, 3 Tables and 4 Figures Accepted Journal of Astrophysics and Astronomy

We present 1 to 10GHz radio continuum flux density, spectral index, polarisation and Rotation Measure (RM) images of the youngest known Galactic Supernova Remnant (SNR) G1.9+0.3, using observations from the Australia Telescope Compact Array (ATCA). We have conducted an expansion study spanning 8 epochs between 1984 and 2017, yielding results consistent with previous expansion studies of G1.9+0.3. We find a mean radio continuum expansion rate of ($0.78 \pm 0.09$) per cent year$^{-1}$ (or $\sim8900$ km s$^{-1}$ at an assumed distance of 8.5 kpc), although the expansion rate varies across the SNR perimeter. In the case of the most recent epoch between 2016 and 2017, we observe faster-than-expected expansion of the northern region. We find a global spectral index for G1.9+0.3 of $-0.81\pm0.02$ (76 MHz$-$10 GHz). Towards the northern region, however, the radio spectrum is observed to steepen significantly ($\sim -$1). Towards the two so called (east & west) "ears" of G1.9+0.3, we find very different RM values of 400-600 rad m$^{2}$ and 100-200 rad m$^{2}$ respectively. The fractional polarisation of the radio continuum emission reaches (19 $\pm$ 2)~per~cent, consistent with other, slightly older, SNRs such as Cas~A., Comment: 17 Pages, 13 Figures