We present here the results of a search for new microquasars at low galactic latitudes, based on a cross-identification between the ROSAT all sky Bright Source Catalog (RBSC) and the NRAO VLA Sky Survey (NVSS) and follow-up observations. The results obtained up to now suggest that persistent/silent microquasars such as LS 5039 are rare objects in

The detection of optical counterparts of hot spots in radio galaxies has been a challenge in astrophysics since the 1960s. Being located at several 100 kpc away from the AGN, they represent the most striking sites of interaction between the AGN ejecta and the ambient inter-galactic medium. Particle acceleration is thought to drive their emission

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