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We present ground-based and Hubble Space Telescope optical observations of the X-ray flash ( XRF) 020903, covering 300 days. The afterglow showed a very rapid rise in the first day, followed by a relatively slow decay in the next few days. There was a clear bump in the light curve after similar to 25 days, accompanied by a drastic change in the spectral energy distribution. The light curve and the spectral energy distribution are naturally interpreted as describing the emergence and subsequent decay of a supernova ( SN), similar to SN 1998bw. At peak luminosity, the SN is estimated to be 0.8 +/- 0.1 mag fainter than SN 1998bw. This argues in favor of the existence of a SN associated with this XRF. A spectrum obtained 35 days after the burst shows emission lines from the host galaxy. We use this spectrum to put an upper limit on the oxygen abundance of the host at [O/H] <= 0.6 dex. We also discuss a possible trend between the softness of several bursts and the early behavior of the optical afterglow, in the sense that XRFs and X-ray-rich gamma- ray bursts ( GRBs) seem to have a plateau phase or even a rising light curve. This can be naturally explained in models in which XRFs are similar to GRBs but are seen off the jet axis.
In the favoured core-accretion model of formation of planetary systems, solid planetesimals accumulate to build up planetary cores, which then accrete nebular gas if they are sufficiently massive. Around M-dwarf stars ( the most common stars in our Galaxy), this model favours the formation of Earth-mass (M+) to Neptune-mass planets with orbital radii of 1 to 10 astronomical units (AU), which is consistent with the small number of gas giant planets known to orbit M-dwarf host stars(1-4). More than 170 extrasolar planets have been discovered with a wide range of masses and orbital periods, but planets of Neptune's mass or less have not hitherto been detected at separations of more than 0.15 AU from normal stars. Here we report the discovery of a 5.5(-2.7)(+5.5)M(+) planetary companion at a separation of 2.6(- 0.6)(+1.5) AU from a 0.22(-0.11)(+0.21)M(.) M-dwarf star, where M-. refers to a solar mass. (We propose to name it OGLE- 2005-BLG-390Lb, indicating a planetary mass companion to the lens star of the microlensing event.) The mass is lower than that of GJ876d (ref. 5), although the error bars overlap. Our detection suggests that such cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory.
This paper presents four color intermediate-band photometry of the cluster A2218 carried out using the Wise Observatory 1 m telescope. A2218 is one of the richest clusters in the Abell catalogue, with richness class 4. We find that A2218 has an unusually low fraction of blue galaxies for its redshift (z=0.171), and is populated mainly by E/S0 galaxies, while starburst systems are very scarce. The few starbursting galaxies present populate the faint end of the cluster luminosity function, close to the limiting magnitude of our observations. The difference between A2218 and other clusters at similar redshifts is very remarkable, underlining the influence of cluster richness on the evolution of its member galaxies.
We analyze the photometric data obtained by PLANET and OGLE on the caustic-crossing binary-lens microlensing event OGLE-2002-BLG-069. Thanks to the excellent photometric and spectroscopic coverage of the event, we are able to constrain the lens model up to the known ambiguity between close and wide binary lenses. The detection of annual parallax in combination with measurements of extended-source effects allows us to determine the mass, distance and velocity of the lens components for the competing models. While the model involving a close binary lens leads to a Bulge- Disc lens scenario with a lens mass of M = (0.51 ± 0.15) M-&ODOT; and distance of D-L = (2.9 ± 0.4) kpc, the wide binary lens solution requires a rather implausible binary black-hole lens ( M &GSIM; 126 M-&ODOT;). Furthermore we compare current state-of-the-art numerical and empirical models for the surface brightness profile of the source, a G5III Bulge giant. We find that a linear limb-darkening model for the atmosphere of the source star is consistent with the data whereas a PHOENIX atmosphere model assuming LTE and with no free parameter does not match our observations
The eclipsing binary system V356 Sgr is of considerable interest, since it is probably at the very end of its mass transfer phase, i.e. between beta Lyrae and Algol. Hence, the binary provides an opportunity to directly examine the exposed core of a star for signatures of nuclear burning, and to test stellar evolution models. The system is composed of an early B star accreting matter from a Roche-lobe filling A2 II star. Recently, with progress in the UV spectral region, significant revision of previous values for absolute parameters has been made. Therefore, we find it justified and important to present a new photometric solution. Our model is compared to an early disk model, and is discussed in the framework of mass transfer processes in this binary system