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Contains fulltext : 91723.pdf (Author’s version preprint ) (Open Access)

We report the first results of our programme to obtain multi-epoch radial velocity measurements of stars with a strong far-UV excess to identify post common-envelope binaries (PCEBs). The targets have been identified using optical photometry from SDSS DR4, ultraviolet photometry from GALEX GR2 and proper motion information from SDSS DR5. We have obtained spectra at two or more epochs for 36 targets. Three of our targets show large radial velocity shifts (>50km/s) on a timescale of hours or days and are almost certainly PCEBs. For one of these targets (SDSS J104234.77+644205.4) we have obtained further spectroscopy to confirm that this is a PCEB with an orbital period of 4.74h and semi-amplitude K =165 km/s. Two targets are rapidly rotating K-dwarfs which appear to show small radial velocity shifts and have strong Ca II H+K emission lines. These may be wind-induced rapidly rotating (WIRRing) stars. These results show that we can use GALEX and SDSS photometry to identify PCEBs that cannot be identified using SDSS photometry alone, and to identify new WIRRing stars. A more comprehensive survey of stars identified using the methods developed in this paper will lead to a much improved understanding of common envelope evolution., 11 pages, 7 figures, accepted for publication in MNRAS

Gamma-ray burst afterglow observations in the Swift era have a perceived lack of achromatic jet breaks compared with the BeppoSAX era. We present our multi-wavelength analysis of GRB060206 as an illustrative example of how inferences of jet breaks from optical and X-ray data might differ. The results of temporal and spectral analyses are compared, and attempts are made to fit the data within the context of the standard blast wave model. We find that while the break appears more pronounced in the optical and evidence for it from the X-ray alone is weak, the data are actually consistent with an achromatic break at about 16 h. This break and the light curves fit standard blast wave models, either as a jet break or as an injection break. As the pre-Swift sample of afterglows are dominated by optical observations, and in the Swift era most well-sampled light curves are in the X-ray, caution is needed when making a direct comparison between the two samples, and when making definite statements on the absence of achromatic breaks.

We have obtained low and medium resolution spectra of 9 brown dwarf candidate members of Coma Berenices and the Hyades using SpEX on the NASA InfaRed Telescope Facility and LIRIS on the William Herschel Telescope. We conclude that 7 of these objects are indeed late M or early L dwarfs, and that two are likely members of Coma Berenices, and four of the Hyades. Two objects, cbd40 and Hy3 are suggested to be a field L dwarfs, although there is also a possibility that Hy3 is an unresolved binary belonging to the cluster. These objects have masses between 71 and 53 M$_{\rm Jup}$, close to the hydrogen burning boundary for these clusters, however only an optical detection of Lithium can confirm if they are truly substellar., 7 pages, 4 figures, 6 tables. Accepted for publication in MNRAS

Contains fulltext : 34787.pdf (Publisher’s version ) (Closed access) We present the results of follow-up observations of white-dwarf + M-dwarf binaries identified using spectra obtained as part of the SPY survey. Spectra of the Halpha region were obtained with the SPIRAL spectrograph on the AAT telescope. Of the eleven stars observed, seven are binaries with periods in the range 2.8 hours to 7.7 days. We also show that one of our targets, WD 0137-349, has a brown dwarf companion. 15th European Workshop on White Dwarfs