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We have analysed a sample of 23 hot DAs to better understand the source of the circumstellar features reported in previous work. Unambiguous detections of circumstellar material are again made at eight stars. The velocities of the circumstellar material at three of the white dwarfs are coincident with the radial velocities of interstellar medium (ISM) along the sightline to the stars, suggesting that the objects may be ionizing the ISM in their locality. In three further cases, the circumstellar velocities are close to the ISM velocities, indicating that these objects are ionizing either the ISM or evaporated planetesimals/material in a circumstellar disc. The circumstellar velocity at WD 1614−084 lies far from the ISM velocities, indicating the ionization of either an undetected ISM component or circumstellar material. The material seen at WD 0232+035 can be attributed to the photoionization of material lost from its M dwarf companion. The measured column densities of the circumstellar material lie within the

We present new high-speed, multi-observatory, multi-instrument photometry of the eclipsing polar UZ For in order to measure precise mid-eclipse times with the aim of detecting any orbital period variations. When combined with published eclipse times and archival data spanning ~27 years, we detect departures from a linear and quadratic trend of ~60 s. The departures are strongly suggestive of two cyclic variations of 16(3) and 5.25(25) years. The two favoured mechanisms to drive the periodicities are either two giant extrasolar planets as companions to the binary (with minimum masses of 6.3(1.5)M(Jupiter) and 7.7(1.2)M(Jupiter)) or a magnetic cycle mechanism (e.g. Applegate's mechanism) of the secondary star. Applegate's mechanism would require the entire radiant energy output of the secondary and would therefore seem to be the least likely of the two, barring any further refinements in the effect of magnetic fieilds (e.g. those of Lanza et al.). The two planet model can provide realistic solutions but it does not quite capture all of the eclipse times measurements. A highly eccentric orbit for the outer planet would fit the data nicely, but we find that such a solution would be unstable. It is also possible that the periodicities are driven by some combination of both mechanisms. Further observations of this system are encouraged.

We measure the UV-optical color dependence of galaxy clustering in the local universe. Using the clean separation of the red and blue sequences made possible by the NUV - r color-magnitude diagram, we segregate the galaxies into red, blue and intermediate "green" classes. We explore the clustering as a function of this segregation by removing the dependence on luminosity and by excluding edge-on galaxies as a means of a non-model dependent veto of highly extincted galaxies. We find that \xi (r_p, \pi) for both red and green galaxies shows strong redshift space distortion on small scales -- the "finger-of-God" effect, with green galaxies having a lower amplitude than is seen for the red sequence, and the blue sequence showing almost no distortion. On large scales, \xi (r_p, \pi) for all three samples show the effect of large-scale streaming from coherent infall. On scales 1 Mpc/h < r_p < 10 Mpc/h, the projected auto-correlation function w_p(r_p) for red and green galaxies fits a power-law with slope \gamma ~ 1.93 and amplitude r_0 ~ 7.5 and 5.3, compared with \gamma ~ 1.75 and r_0 ~ 3.9 Mpc/h for blue sequence galaxies. Compared to the clustering of a fiducial L* galaxy, the red, green, and blue have a relative bias of 1.5, 1.1, and 0.9 respectively. The w_p(r_p) for blue galaxies display an increase in convexity at ~ 1 Mpc/h, with an excess of large scale clustering. Our results suggest that the majority of blue galaxies are likely central galaxies in less massive halos, while red and green galaxies have larger satellite fractions, and preferentially reside in virialized structures. If blue sequence galaxies migrate to the red sequence via processes like mergers or quenching that take them through the green valley, such a transformation may be accompanied by a change in environment in addition to any change in luminosity and color.

ABSTRA C T We present ultra-high-resolution (0.35 km s π1 FWHM) observations of the interstellar Ca K line towards seven nearby stars. The spectral resolution was sufficient to resolve the line profiles fully, thereby enabling us to detect hitherto unresolved velocity components, and to obtain accurate measurements of the velocity dispersions (b values). Absorption components with velocities similar to those expected for the Local Interstellar Cloud (LIC) and the closely associated ‘G cloud’ were identified towards six of the seven stars. However, in most cases the b values deduced for these components were significantly larger than the b < 2: 2k m s π 1 (i.e. Tk < 7000 K, vt < 1k m s π 1 ) expected for the LIC, and it is argued that this results from the presence of additional, spectrally unresolved, components having similar velocities and physical conditions. For two stars (d Vel and a Pav) we detect interstellar components with much smaller b values (1:1 6 0:3 and 0:8 6 0: 1k m s π 1 , respectively) than are expected for low-density clouds within the Local Bubble. In the case of the narrow a Pav component, we also find an anomalously large Na i/Ca ii column density ratio, which is indicative of a relatively high density. Thus it is possible that, in addition to LIC-type clouds, the local interstellar medium contains a population of previously undetected cooler and denser interstellar clouds.

L'etoile HD 168183 qui fait partie du complexe region H II geante-nuage moleculaire de M16 (NGC 6611) a ete observee par satellite avec une haute resolution. On a detecte des composantes d'absorption interstellaire aux vitesses −83, −38 et +40 kms −1 ; on suppose qu'un front de choc porte par vent stellaire, en interaction avec le gaz interstellaire neutre ambiant, est responsable d'une telle structure complexe des vitesses. On a egalement detecte une forte absorption de 5 des raies moleculaires 12 C 16 O UV et les donnees des raies d'absorption UV actuelles sont compatibles avec les observations radio de M16