Context. The massive post-main sequence star W243 in the galactic starburst cluster Westerlund 1 has undergone a spectral transformation from a B2Ia supergiant devoid of emission features in 1981 to an A-type supergiant with a rich emission-line spectrum by 2002/03. Aims. We examine the continued evolution of W243 from 2002 to 2009 to understand its evolutionary state, current physical properti...

Phase-resolved spectroscopy of four AMCVn systems obtained with the William Herschel Telescope and the Gran Telescopio de Canarias (GTC) is presented. SDSS J120841.96+355025.2 was found to have an orbital period of 52.96±0.40min and shows the presence of a second bright spot in the accretion disc. The average spectrum contains strong Mg i and Si i/ii absorption lines most likely originating in ...

Context. The massive post-main sequence star W243 in the galactic starburst cluster Westerlund 1 has undergone a spectral transformation from a B2Ia supergiant devoid of emission features in 1981 to an A-type supergiant with a rich emission-line spectrum by 2002/03. Aims. We examine the continued evolution of W243 from 2002 to 2009 to understand its evolutionary state, current physical properti...

In this Paper we report on phase resolved I–band optical spectroscopic and photometric observations of Cir X–1 obtained with the Very Large Telescope. The spectra are dominated by Paschen absorption lines at nearly all orbital phases except near phase zero (coinciding with the X–ray dip) when the absorption lines are filled–in by broad Paschen emission lines. The radial velocity curve of the ab...

We report a serendipitous discovery of broad absorption lines that were newly formed in the spectrum of the high-redshift, luminous radio-loud quasar TEX 1726+344, in a time interval of only 12 years. This is the first quasar showing a transition from narrow absorption lines to broad absorption lines. It also becomes one of the few radio-loud broad absorption line quasars. The gas cloud respons...

For the first time we demonstrate a multiwavelength, ultrabroadband, continuous-wave, tunable, polycrystalline Cr2+:ZnSe spatially-dispersive laser, operating in the near IR spectral region. We show a dual-wavelength operation of the laser, tunable over a 600 nm spectral range (2200-2800 nm), an ultrabroadband operation of the laser, producing a continuous 135 nm wide spectrum centered at 2500 ...

We study theoretically the luminescence from quantum dots of a ring geometry. For high excitation intensities, photoexcited electrons and holes form Fermi seas. Close to the emission threshold, the single-particle spectral lines aquire weak many-body satellites. However, away from the threshold, the discrete luminescence spectrum is completely dominated by many-body transitions. We employ the L...

We present spectra of the optical transient of GRB 021004 obtained with the HobbyEberly Telescope starting 15.48, 20.31 hours, and 4.84 days after the γ-ray burst and a spectrum obtained with the H. J. Smith 2.7 m Telescope starting 14.31 hours after the γ-ray burst. GRB 021004 is the first burst afterglow for which the spectrum is dominated by absorption lines from high ionization species with...

We have observed sharp infrared spectral lines (Dn 60 MHz FWHM) in g-ray ionized para-H2 crystals. The lines are assigned to the Q1 0 transition of H2 near H3 and H, which becomes optically active and Stark shifted by the Coulomb fields of the ions. A simple model calculation gives a spectrum which agrees approximately with the observation. The spectrum stays the same over many days, demonstrat...

We calculate the quantum-limited shape of the comb lines from a mode-locked Ti:sapphire laser using experimentally-derived parameters for the linear response of the laser to perturbations. The free-running width of the comb lines is found across the laser spectrum. By modeling the effect of a simple feedback loop, we calculate the spectrum of the residual phase noise in terms of the quantum noi...