We present COSAS (CO Survey of late AGB Stars), a project to map and analyze the (CO)-C-12 J = 1-0 and J = 2-1 line emission in a representative sample of circumstellar envelopes around AGB and post-AGB stars. The survey was undertaken with the aim of investigating small-and large-scale morphological and kinematical properties of the molecular environment surrounding stars in the late AGB and early post-AGB phases. For this, COSAS combines the high sensitivity and spatial resolving power of the IRAM Plateau de Bure interferometer with the better capability of the IRAM 30 m telescope to map extended emission. The global sample encompasses 45 stars selected to span a range in chemical type, variability type, evolutionary state, and initial mass. COSAS provides means to quantify variations in the mass-loss rates, assess morphological and kinematical features, and to investigate the appearance of fast aspherical winds in the early post-AGB phase. This paper, which is the first of a series of COSAS papers, presents the results from the analyses of a first sample of 16 selected sources. The envelopes around late AGB stars are found to be mostly spherical, often mingled with features such as concentric arcs (RCas and TXCam), a broken spiral density pattern (TXCam), molecular patches testifying to aspherical mass-loss (WXPsc, IKTau, VCyg, and SCep), and also with well-defined axisymmetric morphologies and kinematical patterns (XHer and RXBoo). The sources span a wide range of angular sizes, from relatively compact (CRL 2362, OH 104.9+2.4 and CRL 2477) to very large (chi Cyg and TXCam) envelopes, sometimes partially obscured by self-absorption features, which particularly for IKTau and chi Cyg testifies to the emergence of aspherical winds in the innermost circumstellar regions. Strong axial structures with more or less complex morphologies are detected in four early post-AGB stars (IRAS 20028+3910, IRAS 23321+6545, IRAS 19475+3119 and IRAS 21282+5050) of the sub-sample.

Aims. The BL Lac object S5 0716+71 was observed in a global multi-frequency campaign to search for rapid and correlated flux density variability and signatures of an inverse-Compton (IC) catastrophe during the states of extreme apparent brightness temperatures.Methods. The observing campaign involved simultaneous ground-based monitoring at radio to IR/optical wavelengths and was centered around a 500-ks pointing with the INTEGRAL satellite (November 10-17, 2003). Here, we present the combined analysis and results of the radio observations, covering the cm- to sub-mm bands. This facilitates a detailed study of the variability characteristics of an inter- to intra-day variable IDV source from cm- to the short mm-bands. We further aim to constrain the variability brightness temperatures (T-B) and Doppler factors (delta) comparing the radio-bands with the hard X-ray emission, as seen by INTEGRAL at 3-200 keV.Results. 0716+714 was in an exceptionally high state and different (slower) phase of short-term variability, when compared to the past, most likely due to a pronounced outburst shortly before the campaign. The flux density variability in the cm- to mm-bands is dominated by a similar to 4 day time scale amplitude increase of up to similar to 35%, systematically more pronounced towards shorter wavelengths. The cross-correlation analysis reveals systematic time-lags with the higher frequencies varying earlier, similar to canonical variability on longer time-scales. The increase of the variability amplitudes with frequency contradicts expectations from standard interstellar scintillation (ISS) and suggests a source-intrinsic origin for the observed inter- day variability. We find an inverted synchrotron spectrum peaking near 90 GHz, with the peak flux increasing during the first 4 days. The lower limits to TB derived from the inter- day variations exceed the 1012 K IC-limit by up to 3-4 orders of magnitude. Assuming relativistic boosting, our different estimates of d yield robust and self-consistent lower limits of delta >= 5-33 - in good agreement with delta(VLBI) obtained from VLBI studies and the IC-Doppler factors delta(IC) > 14-16 obtained from the INTEGRAL data.Conclusions. The non-detection of S5 0716+714 with INTEGRAL in this campaign excludes an excessively high X-ray flux associated with a simultaneous IC catastrophe. Since a strong contribution from ISS can be excluded, we conclude that relativistic Doppler boosting naturally explains the apparent violation of the theoretical limits. All derived Doppler factors are internally consistent, agree with the results from different observations and can be explained within the framework of standard synchrotron-self-Compton (SSC) jet models of AGN.

The Global mm-VLBI Array is at present the most sensitive 3 mm-VLBI interferometer and provides images of up to 40 micro-arcsecond resolution. Using this array, we have monitored the rotation of the innermost jet in the quasar NRAO 150, which shows an angular speed of ~ 7 deg./yr. Future 3 mm arrays could include additional stations like ALMA, GBT, LMT, CARMA, SRT, Yebes, Nobeyama and Noto, which would allow to push VLBI at this wavelength to sensitivity and image quality levels comparable to those of present VLBI at centimeter wavelengths. This would improve our knowledge of the accretion systems and the magneto-hydrodynamics of the innermost jets in AGN and microquasars.

We present results from a large global VLBI survey of compact r dio sources at 86 GHz begun in October 2001. The main goal of the survey was to increase the t o al number of objects accessible for future 3-mm VLBI imaging by factors of 3∼ 5. The survey data attained the baseline sensitivity of 0.1 Jy, and image sensitivity of better than 10 mJy/ beam. To date, a total of 127 compact radio sources have been observed. The observations have yie ld d mages for 109 sources, and only 6 sources have not been detected †. Flux densities and sizes of core and jet components of all detected sources have been measured using Gaussian model fit ting. From these measurements, brightness temperatures have been estimated, taking into a ccount resolution limits of the data. Here, we compare the brightness temperatures of the cores an d econdary jet components with similar estimates obtained from surveys at longer waveleng ths (e.g. 15 GHz). This approach can be used to study the phenomena related to mechanisms of initi al jet acceleration (accelerating or decelerating sub-pc jets?) and jet composition (electronp sitron or electron-proton plasma?).

More than 40 years since the discovery of the AGNs, there are still fundamental questions related to the nature of these intriguing objects. In particular, the accretion processes onto their super-massive black holes and the mechanisms through which their relativistic jets are formed, accelerated and collimated are still not well understood. Great effort has been made during the last decade to push the mm-VLBI technique to progressively shorter wavelengths, offering the best tool to observe the innermost regions of the jets and study the physics involved in their behaviour.

A systematic study of circumstellar envelopes around evolved stars is currently being carried out with the IRAM Plateau de Bure interferometer and the Pico Veleta 30-m telescope. We are mapping the CSEs for a sample of 36 AGB and 9 early post-AGB stars, at angular scales down to 111, Using (CO)-C-12 J = 2-1 (230 GHz) and 1-0 (115 GHz) line emission. The sample stars have been selected to represent a large variety regarding their main stellar parameters such as variability, initial mass and photospheric chemistry. Our first results show an astoundingly large diversity of circumstellar characteristics. The (approximate) circular symmetry and smoothness observed in the brightness distribution of some CSEs (e.g. V Cyg) contrasts with the various axisymmetric distributions observed in other sources (e.g. RX Boo, IRAS 21282+5050, and V Hya) in their innermost CSE regions and/or in their overall envelopes. With the help of radiative transfer models we are determining the main properties of these CSEs: their mass-loss history, geometry, velocity field, degree of clumpiness, photodissociation radius, etc. We find that fluctuations in the AGB mass-loss process may regularly take place on time scales of similar to 10(2) yr.

We report on new developments in VLBI, with emphasis on experiments performed at the highest frequencies possible to date (so called mm-VLBI). We have observed the nucleus of M 87 (Virgo A) with global VLBI at 3 mm. We show a new image of the inner-most jet region with an angular resolution of approx. 300 x 60 micro-arcseconds. In terms of Schwarzschild radii, this leads to an upper limit of the jet base of approx. 100 x 20 Schwarzschild radii. We also report on two VLBI pilot-experiments, which demonstrate the technical feasibility of global VLBI at 150 and 230 GHz (2 mm and 1.3 mm). The experiments lead to upper limits to the size of the unresolved AGN-cores in the 25 - 30 micro-arcsecond range. The participation of new and near-future mm-telescopes (like APEX, CARMA, SMA, LMT, ALMA, etc.) in global mm-VLBI will provide the necessary sensitivity for the imaging of black holes and their immediate environment.

We present results from a large global VLBI(Very Long Baseline Interferometry) survey of compact radio sources at 86 GHz which started in October 2001. The main goal of the survey is to increase the total number of objects accessible for future 3mm-VLBI imaging by factors of 3-5. The survey data reach the baseline sensitivity of 0.1 Jy, and image sensitivity of better than 10 mJy/beam. To date, a total of 127 compact radio sources have been observed. The observations have yielded images for 109 sources, and only 6 sources have not been detected. Flux densities and sizes of core and jet components of all detected sources have been measured using Gaussian model fitting. From these measurements, brightness temperatures have been estimated, taking into account resolution limits of the data. Here, we compare the brightness temperatures of the cores and secondary jet components with similar estimates obtained from surveys at longer wavelengths (e.g. 15 GHz). This approach can be used to study questions related to mechanisms of initial jet acceleration (accelerating or decelerating sub-pc jets?) and jet composition (electron-positron or electron-proton plasma?).

The capabilities of the Global mm-VLBI Array are summarized and demonstrated through actual images from our monitoring of extragalactic radio jets. This sensitive 3mm-VLBI interferometer is able to provide images of up to 50 microarcseconds resolution. For the near future, ALMA, the GBT, the LMT, CARMA, SRT, Yebes, Nobeyama and Noto are some of the most sensitive stations suitable to participate in mm-VLBI. This future array, together with the present Global mm-VLBI Array, would achieve 10 times better sensitivities than nowadays. Image fidelity would also largely increased. T he addition of ALMA would improve the (u,v)-coverage for sources with low declination (<20 deg.) and facilitate the VLBI imaging of the Galactic Centre source SgrA*.

We summarize the present status of VLBI experiments at 3 mm (86 GHz), 2 mm (129-150 GHz) and 1.3 mm (215-230 GHz). We present and discuss a new 3 mm VLBI map of M87 (Virgo A), which has a spatial resolution of only approx. 20 Schwarzschild radii. We discuss recent VLBI results for SgrA* and argue in favor of new observations within an extended European mm-VLBI network, in order to search for variability. We discuss the possibilities to image the `event horizon' of a super-massive black hole at wavelengths < 2mm, and conclude that the addition of large and sensitive millimetre telescopes such as CARMA, the SMA, the LMT and ALMA will be crucial for this.

Global millimetre VLBI allows detailed studies of the most central jet regions of AGN with unprecedent spatial resolution of a few 100-1000 Schwartzschild radii to be made. Study of these regions will help to answer the question how the highly relativistic AGN jets are launched and collimated. Since the early 1990s, bright mm-sources have been observed with global 3 mm VLBI. Here we present new images from an ongoing systematic analysis of the available observations. In particular, we focus on the structure and structural evolution of the best observed AGN jets, taking 3C 454.3 as a characteristic example. This core-dominated and highly variable quasar shows a complex morphology with individual jet components accelerating superluminally towards the outer structure. We briefly discuss the X-ray properties of 3C 454.3 and present its radio- to X-ray large-scale brightness distribution.

Millimeter-VLBI images probe as deep as never before the nuclei of AGN. Global 3mm-VLBI where the VLBA is combined with sensitive European stations, gives CLEAN maps of a quality, which never before was so good. VLBI at 147 GHz yields transatlantic fringes for the first time. Now it will become possible to study the relation between jet kinematics and spectral activity with a few ten micro-arcsecond resolution at the shortest wavelengths.

In April 2002 an array of antennas operating at 129GHz successfully detected VLBI fringes on both continuum AGN and SiO maser sources. The 129GHz fringes on maser sources represent the highest frequency spectral line VLBI detections to date. The AGN 3C279 was detected on long baselines at both 129GHz (and at 147GHz, see Krichbaum et al in these proceedings) yielding fringe spacings of 50-56 micro arc seconds, an angular resolution record. The array consisted of the University of Arizona Kittpeak 12m antenna, the Heinrich Hertz 10m Telescope (HHT), and the IRAM 30m dish on Pico Veleta. At 129GHz, a number of evolved stars and several young stellar objects exhibit strong SiO maser emission in the v=1 J=3-2 transition. Preliminary cross power spectra of SiO masers around the red hypergiant VYCMa on the HHT-KittPeak baseline ~190km are consistent with multiple spatially separate maser spots associated with the star. Future observations will include continuum observations of the radio source at the Galactic Center, SgrA*, and higher frequency maser lines including HCN and methanol.

We show results from a 7 year VLBI monitoring programme of 3C273 at millimeter wavelengths. We find evidence for component acceleration, motion or rotation of fluid dynamical patterns in the VLBI jet, and evidence for an outburst-ejection relation between Gamma-ray flares and the appearance of new jet components.

We report a successful VLBI observation at 147 GHz (2.1 mm) on the 3 100 km long baseline between the telescopes at Metsahovi (Finland) and Pico Veleta (Spain). The sources 3C 273B and 3C 279 were detected with a SNR of similar to 10. For these sources we estimate that 25-30% of the total flux is detectable as correlated flux on the 3 100 km baseline, which gives at 147 GHz a lower limit of the brightness temperature of the inner VLBI jet region of similar to1 x 10(10) K.

At 147 GHz (2mm wavelength), we detected three prominent AGN (NRAO150, 3C279, 1633+382) with Very Long Baseline Interferometry (VLBI) with an angular resolution of only 18 micro-arcseconds on the baseline between two antennas in Arizona (10m HHT and 12m KittPeak) and the IRAM 30m antenna on Pico Veleta in Spain. This is a new world record in radio interferometry and astronomical imaging and opens fascinating future possibilities to directly image and study the innermost regions in Quasars and other Active Galactic Nuclei.