We report the discovery of a unique z= 6.027 galaxy, multiply imaged by the cluster Abell 383 and detected in new Hubble Space Telescope ACS and WFC3 imaging, as well as in Warm Spitzer observations. This galaxy was selected as a pair of i-dropouts; its suspected high redshift was confirmed by the measurement of a strong Lyman α line in both images using Keck/DEIMOS. Combining Hubble and Spitzer photometry after correcting for contamination by line emission (estimated to be a small effect), we identify a strong Balmer break of 1.5 mag. Taking into account the magnification factor of 11.4 ± 1.9 (2.65 ± 0.17 mag) for the brightest image, the unlensed AB magnitude for the source is 27.2 ± 0.05 in the H band, corresponding to a 0.4 L* galaxy, and 25.7 ± 0.08 at 3.6 μm. The UV slope is consistent with β˜ 2.0, and from the rest-frame UV continuum we measure a current star formation rate of 2.4 ± 1.1 M&sun; yr-1. The unlensed half-light radius is measured to be 300 pc, from which we deduce a star-forming surface density of ˜10 M&sun; yr-1 kpc-2. The Lyman α emission is found to be extended over ˜3 arcsec along the slit, corresponding to ˜5 kpc in the source plane. This can be explained by the presence of a much larger envelope of neutral hydrogen around the star-forming region. Finally, fitting the spectral energy distribution (SED) using seven photometric data points with simple SED models, we derive the following properties: very little reddening, an inferred stellar mass of M*= 6 × 109 M&sun;, and an inferred age of ˜800 Myr (corresponding to a redshift of formation of ˜18). The star formation rate of this object was likely much stronger in the past than at the time of observation, suggesting that we may be missing a fraction of galaxies at z˜ 6 which have already faded in rest-frame UV wavelengths

We present far-infrared (FIR) analysis of 68 brightest cluster galaxies (BCGs) at 0.08 < z < 1.0. Deriving total infrared luminosities directly from Spitzer and Herschel photometry spanning the peak of the dust component (24-500 μm), we calculate the obscured star formation rate (SFR). 22 +6.2 −5.3 % of the BCGs are detected in the farinfrared, with SFR = 1-150 M yr −1 . The infrared luminosity is highly correlated with cluster X-ray gas cooling times for cool-core clusters (gas cooling time <1 Gyr), strongly suggesting that the star formation in these BCGs is influenced by the cluster-scale cooling process. The occurrence of the molecular gas tracing Hα emission is also correlated with obscured star formation. For all but the most luminous BCGs (L TIR > 2 × 10 11 L ), only a small ( 0.4 mag) reddening correction is required for SFR(Hα) to agree with SFR FIR . The relatively low Hα extinction (dust obscuration), compared to values reported for the general star-forming population, lends further weight to an alternate (external) origin for the cold gas. Finally, we use a stacking analysis of non-cool-core clusters to show that the majority of the fuel for star formation in the FIR-bright BCGs is unlikely to originate from normal stellar mass loss.

Abstract. NN Ser is known to be a 17 mag pre-cataclysmic binary consisting of a hot white dwarf and a cool late type star orbiting each other with a period of 3 h 7 m . The system shows very deep eclipses and a pronounced reflection effect. Using the FORS instruments at the VLT the late type star could now be detected photometrically at 22.8 mag during eclipse and monitored spectroscopically. These data combined with earlier high speed photometric and phase-resolved spectroscopic observations form the basis for a determination of refined system parameters for NN Ser. The spectral type of the late type star is found to be M4.75. A model atmosphere analysis of the white dwarf yields a temperature of 57 000 ± 3000 K and log g = 7.6 ± 0.1. The presence of He in the atmosphere (N He = 2 ± 0.5 × 10 −4 by number) indicates that the white dwarf is a hydrogen-helium hybrid star of type DAO1. Since the derived radial velocity curves prevent an unambiguous determination of the mass ratio the white dwarf's mass of 0.54 ± 0.05 M is inferred using the results of the model atmosphere analysis and recent evolutionary models. The mass of the M star is determined via a well calibrated M-R relation to be 0.150 ± 0.008 M . The photometric measurements are analysed using a sophisticated light curve synthesis program and yield the following results: i = 84.6• ± 1.1• , R wd = 0.0189 ± 0.0010 R , and R Mstar (polar) = 0.174 ± 0.009 R . The shape of the cool star turns out to be slightly ellipsoidal. Its temperature at the un-heated hemisphere (backside) is 2 920 ± 70 K while the heated hemisphere (sub-stellar point) has a temperature of 7125 ± 200 K.

P/1996 N2 Elst-Pizarro was discovered with a tail of dust in July 1996 and was thus classified as periodic comet. From the orbit point of view it belongs to the outer asteroid belt and is very likely a member of the Themis family, a group of bodies originating from an asteroid collision. The absence of a coma and the presence of the needle-like anti-tail in August 1996 did not exclude the possibility of a sudden emission event which could have been caused by the impact of another minor body on the object. However, with the development of a normal tail between September and November 1996 it became obvious that the dust emission episode continued at least for 2 months after perihelion, a scenario that is typical for gas-driven cometary activity. However, it is still possible that a collision triggered the event. The paper summarizes the observational pro and cons for impact-induced activity in this object, possibly the first ever detected comet-asteroid of the solar system.

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