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We present a total of 12,436 photometric measures of 371 Ðeld stars of 26 quasars in the visible (UBV RI) and 22,276 photometric measures of 122 Ðeld stars of 13 quasars in the near-infrared (JHK), giving a total of 34,712 measures. Of these, 115 stars in 12 Ðelds are calibrated in both ranges. One further Ðeld, Mrk 421, was calibrated, but on close examination all sources were found to be probably nonstellar ; thus these results are not included here. The stars observed cover the range from V \ 11 to V \ 20 and from K \ 9 to K \ 17 and are well distributed around the sky north of declination [30¡. This represents the initial sample of an extensive catalog of calibrated Ðelds that will cover the northern sky down to declination [30¡ and that will cover a wide range of Galactic latitudes. These Ðelds will be useful both for photometry of AGNs in the range from B to K and also as faint calibration standards for large telescopes. The median absolute total error on the photometry, including all known error sources, ranges from 0.008 mag in J to 0.034 mag in B. These errors will be greatly reduced with the addition of further data in the future, although the Ðnal precision is fundamentally limited by the photometric errors in the existing lists of calibration stars used to calibrate these data.

TIGRE is a new robotic spectroscopy telescope located in central Mexico at the La Luz Observatory of the University of Guanajuato. The 1.2 m telescope is fiber-coupled to anéchelle spectrograph with a spectral resolving power exceeding 20 000 over most of the covered spectral range between 3800Å and 8800Å, with a small gap of 130Å around 5800 A. TIGRE operates robotically, i.e. it (normally) carries out all observations without any human intervention, including, in particular, the target selection in any given observing night. In this paper we describe the properties of the TIGRE instrumentation and its technical realization, as well as our first operational experience with the performance and efficiency of the overall system. Finally, we present some examples of recent TIGRE observations.

Context. Probing the structures of stellar winds is of prime importance for the understanding of massive stars. Based on their optical spectral morphology and variability, it has been suggested that the stars in the Oef class feature large-scale structures in their wind. Aims. High-resolution X-ray spectroscopy and time-series of X-ray observations of presumably single O-type stars can help us understand the physics of their stellar winds. Methods. We have collected XMM-Newton observations and coordinated optical spectroscopy of the O6 Ief star λ Cep to study its X-ray and optical variability and to analyse its high-resolution X-ray spectrum. We investigate the line profile variability of the He ii λ 4686 and Hα emission lines in our time series of optical spectra, including a search for periodicities. We further discuss the variability of the broadband X-ray flux and analyse the high-resolution spectrum of λ Cep using line-by-line fits as well as a code designed to fit the full high-resolution X-ray spectrum consistently.Results. During our observing campaign, the He ii λ 4686 line varies on a timescale of ∼18 h. On the contrary, the Hα line profile displays a modulation on a timescale of 4.1 days which is likely the rotation period of the star. The X-ray flux varies on timescales of days and could in fact be modulated by the same 4.1-day period as Hα, although both variations are shifted in phase. The highresolution X-ray spectrum reveals broad and skewed emission lines as expected for the X-ray emission from a distribution of windembedded shocks. Most of the X-ray emission arises within less than 2 R * above the photosphere. Conclusions. The properties of the X-ray emission of λ Cep generally agree with the expectations of the wind-embedded shock model. There is mounting evidence for the existence of large-scale structures that modulate the Hα line and about 10% of the X-ray emission of λ Cep.

Abstract. 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 ± 0.01, and R = 13.79 ± 0.01). A peculiar tendency to redden with increased brightness was detected throughout our observations. Moreover, in one season a good correlation between flux level and spectral slope is shown. This anomalous behaviour cannot be described by common flare models of blazars. The flux vs. spectral slope correlation observed in this and other blazars is worth further study.