The Ever Changing Circumstellar Nebula Around UW Centauri

We present new images of the reflection nebula surrounding the R Coronae Borealis Star, UW Cen. This nebula, first detected in 1990, has changed its appearance significantly. At the estimated distance of UW Cen, this nebula is approximately 0.6 ly in radius so the nebula cannot have physically altered in only 8 years. Instead, the morphology of the nebula appears to change as different parts are illuminated by light from the central star modulated by shifting thick dust clouds near its surface. These dust clouds form and dissipate at irregular intervals causing the well-known declines in the R Coronae Borealis (RCB) stars. In this way, the central star acts like a lighthouse shining through holes in the dust clouds and lighting up different portions of the nebula. The existence of this nebula provides clues to the evolutionary history of RCB stars possibly linking them to the Planetary Nebulae and the final helium shell flash stars.Comment: To be published in ApJ Letters. 5 pages, 3 figures (2 in color

WR146 - observing the OB-type companion

We present new radio and optical observations of the colliding-wind system WR146 aimed at understanding the nature of the companion to the Wolf-Rayet star and the collision of their winds. The radio observations reveal emission from three components: the WR stellar wind, the non-thermal wind-wind interaction region and, for the first time, the stellar wind of the OB companion. This provides the unique possibility of determining the mass-loss rate and terminal wind velocity ratios of the two winds, independent of distance. Respectively, these ratios are determined to be 0.20+/-0.06 and 0.56+/-0.17 for the OB-companion star relative to the WR star. A new optical spectrum indicates that the system is more luminous than had been believed previously. We deduce that the ``companion'' cannot be a single, low luminosity O8 star as previously suggested, but is either a high luminosity O8 star, or possibly an O8+WC binary system.Comment: 9 pages, 5 figures, ftp://fto.drao.nrc.ca/pub/smd/wr146/accepted.ps.gz To be published in Monthly Notices of the Royal Astronomical Societ

A study of the kinematics and binary-induced shaping of the planetary nebula HaTr 4

We present the first detailed spatio-kinematical analysis and modelling of the planetary nebula HaTr 4, one of few known to contain a post-common-envelope central star system. Common envelope evolution is believed to play an important role in the shaping of planetary nebulae, but the exact nature of this role is yet to be understood. High spatial- and spectral- resolution spectroscopy of the [OIII]5007 nebular line obtained with VLT-UVES are presented alongside deep narrowband Ha+[NII]6584 imagery obtained using EMMI-NTT, and together the two are used to derive the three-dimensional morphology of HaTr 4. The nebula is found to display an extended ovoid morphology with an enhanced equatorial region consistent with a toroidal waist - a feature believed to be typical amongst planetary nebulae with post-common-envelope central stars. The nebular symmetry axis is found to lie perpendicular to the orbital plane of the central binary, concordant with the idea that the formation and evolution of HaTr 4 has been strongly influenced by its central binary.Comment: 9 pages, 5 figures, accepted for publication in MNRA

On the Abundance of Circumbinary Planets

We present here the first observationally based determination of the rate of occurrence of circumbinary planets. This is derived from the publicly available Kepler data, using an automated search algorithm and debiasing process to produce occurrence rates implied by the seven systems already known. These rates depend critically on the planetary inclination distribution: if circumbinary planets are preferentially coplanar with their host binaries, as has been suggested, then the rate of occurrence of planets with $R_p>6R_\oplus$ orbiting with $P_p<300$\ d is $10.0 ^{+18}_{-6.5}$\% (95\% confidence limits), higher than but consistent with single star rates. If on the other hand the underlying planetary inclination distribution is isotropic, then this occurrence rate rises dramatically, to give a lower limit of 47\%. This implies that formation and subsequent dynamical evolution in circumbinary disks must either lead to largely coplanar planets, or proceed with significantly greater ease than in circumstellar disks. As a result of this investigation we also show that giant planets (${>}10R_\oplus$) are significantly less common in circumbinary orbits than their smaller siblings, and confirm that the proposed shortfall of circumbinary planets orbiting the shorter period binaries in the Kepler sample is a real effect.Comment: Accepted for publication in MNRAS (1st August 2014). 12 pages. Update to match final version, including clarifications and new figures. Results are unchange

RISE: a fast-readout imager for exoplanet transit timing

By the precise timing of the low amplitude (0.005 - 0.02 magnitude) transits of exoplanets around their parent star it should be possible to infer the presence of other planetary bodies in the system down to Earth-like masses. We describe the design and construction of RISE, a fast-readout frame transfer camera for the Liverpool Telescope designed to carry out this experiment. The results of our commissioning tests are described as well as the data reduction procedure necessary. We present light curves of two objects, showing that the desired timing and photometric accuracy can be obtained providing that autoguiding is used to keep the target on the same detector pixel for the entire (typically 4 hour) observing run.Comment: Published in PROC SPIE, vol 7014, 70416

The evolutionary status of the hot R coronae borealis stars

The evolutionary status of the hot R CrB stars has long remained a matter of conjecture, primarily because of the relative dearth of relevant observational material. Previously the group had been thought to occupy a position intermediate in status between the EHe and R CrB classes as they have (at least at first glance) observational properties in common with both types of object. The photosphere of DY Cen has been quantitatively confirmed to be hydrogen-deficient and photometric variations suggest the star undergoes short period pulsations. Using a period-temperature relation applicable to hydrogen-deficient stars it would appear that this object has similar physical properties to both the EHe and R CrB stars. Narrow band imaging of V348 Sgr has shown that the associated nebula exhibits a bipolar structure and therefore must be closely related to planetary nebulae rather than H II regions. Spectroscopic observations have proved that the star in its present evolutionary state is incapable of ionising the nebula. Several scenarios for this behaviour are briefly discussed. The large helium enrichment found in the nebula indicates that processed material must have been ejected during the last major episode of mass loss. Evidence is presented that suggests a strong hydrogen abundance gradient exists within the nebula. A novel technique has been developed for determining reddening distances. Its main advantage over other similar methods is that both early and late-type stars may be used to establish the reddening-distance relationship. With more development this technique may prove to be an important tool in distance determinations for objects such as planetary nebulae etc. This technique was used to derive a distance of (4. 7±1.0) kpc for V348 Sgr. Using the core-mass relation for hydrogen-deficient stars implies that both V348 Sgr and MV Sgr are lower mass and luminosity objects than EHe and R CrB stars. The evidence presented in this thesis indicates that the hot R CrB group is not a homogeneous one. DY Cen is much more luminous and massive than the other members. The mass and luminosity of V348 Sgr and MV Sgr are consistent with the scenario that both have recently suffered a thermal pulse (causing re-ignition of a helium burning shell) and are currently looping back to the R CrB domain of the H R diagram

The effect of dust obscuration in RR Tel on optical and IR long-term photometry and Fe II emission lines

Infrared and optical photometric and spectroscopic observations of the symbiotic nova RR Tel are used to study the effects and properties of dust in symbiotic binaries containing a cool Mira component, as well as showing "obscuration events" of increased absorption, which are typical for such Miras. A set of photometric observations of the symbiotic nova RR Tel in different wavelength bands - visual from 1949 to 2002 and near-infrared (JHKL) from 1975 to 2002 - are presented. The variability due to the normal Mira pulsation was removed from the JHKL data, which were then compared with the AAVSO visual light curve. The changes of the Fe II emission line fluxes during the 1996-2000 obscuration episode were studied in the optical spectra taken with the Anglo-Australian telescope. We discuss the three periods during which the Mira component was heavily obscured by dust as observed in the different wavelength bands. A change in the correlations of J with other infrared magnitudes was observed with the colour becoming redder after JD2446000. Generally, J-K was comparable, while K-L was larger than typical values for single Miras. A distance estimate of 2.5 kpc, based on the IR data, is given. A larger flux decrease for the permitted than for the forbidden Fe II lines, during the obscuration episode studied, has been found. There is no evidence for other correlations with line properties, in particular with wavelength, which suggests obscuration due to separate optically thick clouds in the outer layers.Comment: 19 pages, 11 figures, 3 table

RR Lyrae Stars In The GCVS Observed By The Qatar Exoplanet Survey

We used the light curve archive of the Qatar Exoplanet Survey (QES) to investigate the RR Lyrae variable stars listed in the General Catalogue of Variable Stars (GCVS). Of 588 variables studied, we reclassify 14 as eclipsing binaries, one as an RS Canum Venaticorum-type variable, one as an irregular variable, four as classical Cepheids, and one as a type II Cepheid, while also improving their periods. We also report new RR Lyrae sub-type classifications for 65 variables and improve on the GCVS period estimates for 135 RR Lyrae variables. There are seven double-mode RR Lyrae stars in the sample for which we measured their fundamental and first overtone periods. Finally, we detect the Blazhko effect in 38 of the RR Lyrae stars for the first time and we successfully measured the Blazhko period for 26 of them.Comment: Accepted IBV