Abstract. In this paper we present observations of η Carinae in the 1.3 mm and 7 mm radio continuum, during the 2003.5 low excitation phase. The expected minimum in the light curves was confirmed at both wavelengths and was probably due to a decrease in the number of UV photons available to ionize the gas surrounding the binary system. At 7 mm a very well defined peak was superimposed on the declining flux density. It presented maximum amplitude in 29 June 2003 and lasted for about 10 days. We show that its origin can be free-free emission from the gas at the shock formed by wind-wind collision, which is also responsible for the observed X-ray emission. Even though the shock strength is strongly enhanced as the two stars in the binary system approach each other, during periastron passage the X-ray emission is strongly absorbed and the 7 mm observations represent the only direct evidence of this event.

Abstract. A first CCD 512 × 512 camera working in scan mode (declination field 14 ) was mounted in 1994 on the Bordeaux CCD meridian circle. After a testing period, this camera was installed on the Valinhos CCD meridian circle (near São Paulo, Brazil), as part of a collaboration between Bordeaux Observatory and the Instituto Astronomico e Geofisico of São Paulo. A second improved CCD 1024 × 1024 camera, with a declination field of 28 , was installed on the Bordeaux instrument in June 1996. The mean internal precision of a single observation is about 0.04 in both coordinates for 9 ≤ V ≤ 14. In the same magnitude range, magnitudes can also be obtained with an internal precision of about 0.05 mag. Both instruments can participate efficiently in extending the HipparcosTycho frame, during the next decade. Among other duties, the Bordeaux CCD meridian circle is being used since January 1997 for completing the Méridien 2000 project. The characteristics of both instruments and some results obtained with them are presented in this paper.

Abstract. We present results of a microvariability polarization study in the violently variable quasar 3C279. We have resolved the polarization curves in the V band for this object down to timescales of minutes. We found two main components in the evolution of the degree of linear polarization, one consisting of a flicker with timescales of several tens of minutes and other component with far more significant variations on timescales of a few days. The linear polarization descended from ∼17% down to ∼8% in three nights. The polarization angle underwent a sudden change of more that 10 degrees in a few hours, perhaps indicating the injection of a new shock in the jet. The amplitude of the intranight flickering in the degree of polarization is at the level of ∼1%. These are probably the best sampled polarization data ever obtained for this object. We also performed IR observations and we provide a follow-up of the evolution of this source at such energies after the main polarization outburst.

Aims. In this work, we analyse the multiwavelength brightness variations and flaring activity of FSRQ PKS1510-089, aiming to constrain the position of the emission sources. Methods. We report 7 mm (43 GHz) radio and R-band polarimetric observations of PKS1510-089. The radio observations were performed at the Itapetinga Radio Observatory, while the polarimetric data were obtained at the Pico dos Dias Observatory. The 7 mm observations cover the period between 2011 and 2013, while the optical polarimetric observations were made between 2009 and 2012.Results. At 7 mm, we detected a correlation between four radio and γ-ray flares with a delay of about 54 days between them; the higher frequency counterpart occurred first. Using optical polarimetry, we detected a large variation in polarization angle (PA) within two days associated with the beginning of a γ-ray flare. Complementing our data with other data obtained in the literature, we show that PA presented rotations associated with the occurrence of flares. Conclusions. Our results can be explained by a shock-in-jet model, in which a new component is formed in the compact core producing an optical and/or γ-ray flare, propagates along the jet, and after some time becomes optically thin and is detected as a flare at radio frequencies. The variability in the polarimetric parameters can also be reproduced; we can explain large variation in both PA and polarization degree (PD), in only one of them, or in neither, depending on the differences in PA and PD between the jet and the new component.