In order to maximize the science return while minimizing running cost, the operational and maintenance requirements are being considered during the design of the GTC. Following this adopted integrated logistic support approach; GTC has produced the baselines of the GTC Operation and Maintenance Plans. These plans describe the science operation

We present Keck HIRES spectra of six late-M dwarfs and 11 L dwarfs. Our goal is to assign effective temperatures to the objects using detailed atmospheric models and fine analysis of the alkali resonance absorption lines of Cs I and Rb I. These yield mutually consistent results (+/-50 K) when we use ``cleared-dust'' models, which account for the

Recent observations and theoretical considerations have linked gamma-ray bursts with ultra-bright type Ibc supernovae (`hypernovae'). We here work out a specific scenario for this connection. Based on earlier work, we argue that especially the longest bursts must be powered by the Blandford-Znajek mechanism of electromagnetic extraction of spin

During the 1996/1997 outburst of the X-ray transient GRO J1655-40 the Wide Field Cameras onboard BeppoSAX observed the system with nearly continuous coverage during some stages of this outburst. On two occasions we find clear evidence for frequent dipping behaviour, characterized by several absorption dips occurring within one binary orbit. However

Recent observations show the existence of an increasing number of collimated outflows ejected by young, low-mass stars which are embedded in Hii regions. At distances of a few tens of au from the star, at least one lobe of these outflows will be shielded from the ambient ionizing radiation by the compact, high-extinction circumstellar disc. Within

Time series CCD photometry of the inner coma of active comets has been used over the last twenty years to determine the rotation period of their nucleus. Usually, the photometry is performed by using very small apertures with the aim of isolating as much as possible the brightness contribution of the nucleus with respect to the brightness of the