An optical spectrum of the afterglow of a gamma-ray burst at a redshift of z = 6.295.

The prompt gamma-ray emission from gamma-ray bursts (GRBs) should be detectable out to distances of z > 10 (ref. 1), and should therefore provide an excellent probe of the evolution of cosmic star formation, reionization of the intergalactic medium, and the metal enrichment history of the Universe. Hitherto, the highest measured redshift for a GRB has been z = 4.50 (ref. 5). Here we report the optical spectrum of the afterglow of GRB 050904 obtained 3.4 days after the burst; the spectrum shows a clear continuum at the long-wavelength end of the spectrum with a sharp cut-off at around 9,000 A due to Lyman alpha absorption at z approximately 6.3 (with a damping wing). A system of absorption lines of heavy elements at z = 6.295 +/- 0.002 was also detected, yielding the precise measurement of the redshift. The Si ii fine-structure lines suggest a dense, metal-enriched environment around the progenitor of the GRB.

Discovery of a Subsystem of Globular Clusters in M31: Possible Evidence for a Past Merging Event.

We found a subsystem of globular clusters in M31 that appears to have a formation history separate from the rest. The member clusters of this subsystem, identified from their distinct distribution in the metallicity-distance diagram, (1) have a common medium metallicity range of -0.9<&sqbl0;Fe&solm0;H&sqbr0;<-0.4, (2) have a line-of-sight velocity distribution with no significant projected rotational motion, and (3) are populated outside the inner subsystem of globular clusters of similar metallicity that shows a significant net rotational motion as a whole. We suggest that this subsystem of globular clusters was formed during a merging event of a dwarf galaxy that took place well after the initial collapse event when most of the globular clusters in M31 were formed.

Optically anisotropic crystalline grisms for astronomical spectrographs.

We show that a crystalline LiNbO(3) grism and a hybrid grism made of a LiNbO(3) transmission grating and a ZnS prism can be new and powerful dispersing elements with refractive indices high enough to realize high spectral resolution for visible to near-infrared astronomical spectrographs with transmission optics. We describe the basic principle and the limitation to minimizing the spectral separation that is due to the inherent birefringence of such an optically anisotropic crystal used for grisms.