A non-LTE abundance analysis of the post-AGB star ROA 5701

An analysis of high-resolution Anglo-Australian Telescope (AAT)/University College London Échelle Spectrograph (UCLÉS) optical spectra for the ultraviolet (UV)-bright star ROA 5701 in the globular cluster ω Cen (NGC 5139) is performed, using non-local thermodynamic equilibrium (non-LTE) model atmospheres to estimate stellar atmospheric parameters and chemical composition. Abundances are derived for C, N, O, Mg, Si and S, and compared with those found previously by Moehler et al. We find a general metal underabundance relative to young B-type stars, consistent with the average metallicity of the cluster. Our results indicate that ROA 5701 has not undergone a gas–dust separation scenario as previously suggested. However, its abundance pattern does imply that ROA 5701 has evolved off the asymptotic giant branch (AGB) prior to the onset of the third dredge-up.     

Evidence for an extreme climatic event on Achill Island,Co. Mayo,Ireland around 5200–5100 cal. yr BP

A range of detailed palaeoenvironmental analyses carried out on a series of three peat profiles from Achill Island, Co. Mayo, western Ireland, reveal evidence for an extreme climatic event, probably a storm or series of storms, around 5200–5100 cal. yr BP that caused the deposition of an extensive layer of silt across blanket peat. This event followed a period of relatively dry climate during which Neolithic communities expanded in the region. There was a subsequent period of continuing dry conditions allowing extensive colonisation of the peat by Pinus before a shift to wetter conditions characteristic of the later Holocene. The extreme climatic event is possibly linked to human abandonment of the area comparable to that observed from the work on the internationally significant Céide Fields in the same region. Copyright © 2005 John Wiley & Sons, Ltd.     

The deuterium abundance in the z= 0.7 absorber towards QSO PG1718+4807

We report on a further analysis of the ratio of deuterium to hydrogen (D/H) using Hubble Space Telescope ( HST ) spectra of the   z = 0.701  Lyman limit system towards the quasi-stellar object (QSO) PG1718+481. Initial analyses of this absorber found it gave a high D/H value, 1.8–  3.1 × 10⁻⁴  , inconsistent with several higher redshift measurements. It is thus important to critically examine this measurement. By analysing the velocity widths of the D  i , H  i and metal lines present in this system, Kirkman et al. report that the additional absorption in the blue wing of the Lyα line cannot be D  i , with a confidence level of 98 per cent. Here we present a more detailed analysis, taking into account possible wavelength shifts between the three sets of HST spectra used in the analysis. We find that the constraints on this system are not as strong as those claimed by Kirkman et al. The discrepancy between the parameters of the blue wing absorption and the parameters expected for D  i is marginally worse than 1σ.
Tytler et al. commented on the first analysis of Webb et al., reporting the presence of a contaminating lower redshift Lyman limit system, with  log[ N (H  i )] = 16.7  at   z = 0.602  , which biases the N (H  i ) estimate for the main system. Here we show that this absorber actually has  log[ N (H  i )] < 14.6  and does not impact on the estimate of N (H  i ) in the system of interest at   z = 0.701  .
The purpose of the present paper is to highlight important aspects of the analysis which were not explored in previous studies, and hence to help refine the methods used in future analyses of D/H in quasar spectra.     

Variable stars in the field of the old open cluster Melotte 66

We report the results of photometric monitoring of the Melotte 66 field in BVI filters. 10 variables were identified with nine being new discoveries. The sample includes eight eclipsing binaries of which four are W UMa type stars and one star is a candidate blue straggler. All four contact binaries are likely the members of the cluster based on their estimated distances. 10 blue stars with   U − B < −0.3  were detected inside a  14.8 × 22.8 arcmin²  field centred on the cluster. Time series photometry for seven of them showed no evidence for any variability. The brightest object in the sample of blue stars is a promising candidate for a hot subdwarf belonging to the cluster. We show that the anomalously wide main sequence of the cluster, reported in some earlier studies, results from a combination of two effects: variable reddening occurring across the cluster field and the presence of a rich population of binary stars in the cluster itself. The density profile of the cluster field is derived and the total number of the member stars with  16 < V < 21  or  2.8 < M _V < 7.8  is estimated conservatively at about 1100.