28 research outputs found
The Central Star Candidate of the Planetary Nebula Sh2-71: Photometric and Spectroscopic Variability
We present the analysis of several newly obtained and archived photometric
and spectroscopic datasets of the intriguing and yet poorly understood 13.5-mag
central star candidate of the bipolar planetary nebula Sh2-71. Photometric
observations confirmed the previously determined quasi-sinusoidal lightcurve
with a period of 68 days and also indicated periodic sharp brightness dips,
possibly eclipses, with a period of 17.2 days. In addition, the comparison
between U and V lightcurves revealed that the 68-day brightness variations are
accompanied by a variable reddening effect of .
Spectroscopic datasets demonstrated pronounced variations in spectral profiles
of Balmer, helium and singly ionised metal lines and indicated that these
variations occur on a time-scale of a few days. The most accurate verification
to date revealed that spectral variability is not correlated with the 68-day
brightness variations. The mean radial velocity of the observed star was
measured to be 26 km/s with an amplitude of 40 km/s. The spectral
type was determined to be B8V through spectral comparison with synthetic and
standard spectra. The newly proposed model for the central star candidate is a
Be binary with a misaligned precessing disc.Comment: 9 pages, 6 figures (main article). 7 pages, 6 figures (appendix).
Accepted for publication in MNRA
The influence of binarity on the morpho-kinematics of planetary nebulae
The role of central star binarity in the shaping of planetary nebulae (PNe)
has been the subject of much debate, with single stars believed to be incapable
of producing the most highly collimated morphologies. However, observational
support for binary-induced shaping has been sadly lacking. Here, we highlight
the results of a continuing programme to spatio-kinematically model the
morphologies of all PNe known to contain a close binary central star.
Spatio-kinematical modelling is imperative for these objects, as it circumvents
the degeneracy between morphology and orientation which can adversely affect
determinations of morphology based on imaging alone. Furthermore,
spatio-kinematical modelling accurately determines the orientation of the
nebular shell, allowing the theoretically predicted perpendicular alignment,
between nebular symmetry axis and binary orbital plane, to be tested. To date,
every PN subjected to this investigation has displayed the predicted alignment,
indicating that binarity has played an important role in the formation and
evolution of these nebulae. The further results from this programme will be
key, not only in determining whether binary interaction is responsible for
shaping the studied PNe, but also in assessing the importance of binarity in
the formation and evolution of all PNe in general.Comment: 2 pages, 2 tables, proceedings of the IAU Symposium No. 283,
Planetary Nebulae: An Eye to the Futur
The influence of central star binarity on the morphologies of planetary nebulae
Central star binarity is often invoked as the main driver behind the shaping of aspherical planetary nebulae, however observational support for this hypothesis is lacking. This work presented in this thesis attempts to observationally test this theory by investigating the relationship between central star binarity and nebular morphology for several planetary nebulae. The discovery of six new binary central star systems is also reported. A detailed spatio-kinematical analysis of Abell 41 was performed, showing the nebula to have a bipolar morphology waisted by a toroidal structure, the symmetry axis of which is found to be perpendicular to the plane of the central binary. This alignment is exactly as predicted, indicating that the central binary, MT Ser, has played a significant role in shaping Abell 41. This is only the second planetary nebulae to have had this link, between binary and nebular inclination, explicitly shown. A spatio-kinematic model has been developed for ETHOS 1, indicating that its spectacular polar outflows are kinematically older than the central region of the nebula. This finding is discussed in the context of binary evolution, and it is concluded that the polar outflows in these nebulae are probably formed before their central binaries have entered the common-envelope phase. The central star of ETHOS 1 has yet to be the subject of detailed study, and as such, the orientation of the nebula could not be compared to that of its central binary. A spatio-kinematical analysis of SuWt 2 is presented, proving that the nebular ring is in fact at the waist of a much larger, extended bipolar structure. SuWt 2 is not known to contain a post-main sequence central star, required to eject and ionise the nebular shell, but rather a double A-type binary. The results of the analysis are discussed with relation to possible formation scenarios for SuWt 2. It is concluded that, while neither component of the double A-type binary could be the nebular progenitor, the presence of a third component to the system, which would have been the progenitor, cannot be ruled out. However, as there is no evidence that the central star of SuWt 2 is a binary alone, it is suggested that SuWt 2 should be removed from future lists of planetary nebulae known to host a binary central star. A sample of sixteen central stars of planetary nebulae, displaying morphological traits believed to be typical of central star binarity, were monitored for signs of periodic photometric variability associated with binarity. Six new photometrically variable close-binary stars were discovered, representing a ~15% increase on the previously known figure. The binary detection success rate from this investigation is compared to that of other surveys, and it is concluded that, while the results are promising, a more rigorous test is required to fully assess the extent to which specific morphological traits can be used as indicators of central star binarity.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Routine Antenatal Anti-D Prophylaxis in Women Who Are Rh(D) Negative: Meta-Analyses Adjusted for Differences in Study Design and Quality
Background: To estimate the effectiveness of routine antenatal anti-D prophylaxis for preventing sensitisation in pregnant Rhesus negative women, and to explore whether this depends on the treatment regimen adopted. Methods: Ten studies identified in a previous systematic literature search were included. Potential sources of bias were systematically identified using bias checklists, and their impact and uncertainty were quantified using expert opinion. Study results were adjusted for biases and combined, first in a random-effects meta-analysis and then in a random-effects metaregression analysis. Results: In a conventional meta-analysis, the pooled odds ratio for sensitisation was estimated as 0.25 (95 % CI 0.18, 0.36), comparing routine antenatal anti-D prophylaxis to control, with some heterogeneity (I 2 = 19%). However, this naïve analysis ignores substantial differences in study quality and design. After adjusting for these, the pooled odds ratio for sensitisation was estimated as 0.31 (95 % CI 0.17, 0.56), with no evidence of heterogeneity (I 2 = 0%). A meta-regression analysis wa
Practical considerations in case study research: the relationship between methodology and process
Older people count The Help the Aged income index for older people in England and Wales 2003
Includes one CD-ROMSIGLEAvailable from British Library Document Supply Centre- DSC:Vm03/50273 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Older people count The Help the Aged income index for older people in England and Wales 2003
Summary of 'Older people count'. Title from coverSIGLEAvailable from British Library Document Supply Centre- DSC:m03/25066 / BLDSC - British Library Document Supply CentreGBUnited Kingdo