We present the oxygen abundance determination for 90 HII regions in the inner parts of the grand design galaxy M101. The abundances were derived employing the P method (Pilyugin, 2001A&A...369..594P). A comparison is made with previous determinations using another calibration and direct measurements of electron temperature to derive the oxygen

We present BVR photometric observations of the blazar PKS 0736+017. These observations were carried out with three telescopes in Mexico and two in Spain between December 1998 and April 2003. PKS 0736+017 shows remarkable variation at different timescales and amplitudes. Maximum brightness was detected on December 19, 2001 (B=14.90± 0.01, V=14.34±0

Optical spectra (range 600-690 nm; resolution 6000) were obtained during the current outburst of this black hole binary on July 4.65-4.75 UT with the Siding Spring 2.3-m telescope (+ DBS CCD spectrograph), right after the first visual reports appeared via vsnet-obs and vsnet-alert. The spectra were dominated by a very strong and broad H-alpha

We have analyzed low angular degree (low-l) solar p-mode frequency shifts extracted from two types of observations, both made by instruments on board the ESA/NASA Solar and Heliospheric Observatory satellite during a period that covers the rising phase of activity, cycle 23 (1995-2002). The first are full-disk (Sun-as-a-star) averages made in

We present estimates of CN and Mg overabundances with respect to Fe for early-type galaxies in eight clusters over a range of richness and morphology. Spectra were taken from the Sloan Digital Sky Survey Data Release 1 and from William Hershel Telescope and Centro Astronómico Hispano-Alemán observations. Abundances were derived from absorption

Presently seven superbursters have been identified representing 10% of the total Galactic X-ray burster population. Four superbursters were discovered with the Wide Field Cameras (WFCs) on BeppoSAX and three with the All-Sky Monitor and Proportional Counter Array on RXTE. We discuss the properties of superbursters as derived from WFC observations