Extragalactic Astronomy with the VLTI: a new window on the Universe

Interferometry in the optical and near infrared has so far played a marginal role in Extragalactic Astronomy. Active Galactic Nuclei are the brightest and most compact extragalactic sources, nonetheless only a very limited number could be studied with speckle interferometry and none with long baseline interferometry. The VLTI will allow the study of moderately faint extragalactic objects with very high spatial resolution thus opening a new window on the universe. With this paper we focus on three scientific cases to show how AMBER and MIDI can be used to tackle open issues in extragalactic astronomy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnetic and velocity fields of active regions

We have observed about 15 active regions on the Sun, with the Advanced Stokes Polarimeter and Dick Dunn Telescope at NSO/SP to map the Stokes parameters in the photospheric Fe 6302.5 Å and chromospheric Mg I 5173 Å lines, during 1999‐2002. The observations are corrected for dark current, gain, instrumental polarization and cross‐talk using ASP pipeline. The wavelength calibration is carried out using the O₂ telluric line 6302 Å which is also present in the observations. The photospheric and chromospheric longitudinal magnetograms are made from the Stokes V profiles, which were intercalibrated with the Kitt Peak magnetograms. The plasma motions are inferred from the line bisector measurements at different positions of the spectral line. In this paper we present the height dependence of Doppler velocity scatter plots of a sunspot in the photospheric Fe I 6302 Å line.     

The radio structure of 45 quasars atz < 1.5

Radio maps at 5 GHz with an angular resolution of 1 to 2 arcsec and a dynamic range ≳ 200:1 are presented for a sample of 45 radio quasars at redshifts between 0.2 and 1.5. The sources were imaged from observations made with the Very Large Array with the aim of investigating the epoch dependence of misalignments and asymmetries in their extended radio structure. Maps of some of the larger radio sources are presented also at a frequency of 1.5 GHz with a typical angular resolution of ≈ 4 arcsec. The radio structure of most of the quasars reported here has been delineated in considerably greater detail than available in the literature.     

A complete infrared Einstein ring in the gravitational lens system B1938 + 666

We report the discovery, using NICMOS on the Hubble Space Telescope , of an arcsec-diameter Einstein ring in the gravitational lens system B1938+666. The lensing galaxy is also detected, and is most likely an early-type galaxy. Modelling of the ring is presented and compared with the radio structure from MERLIN maps. We show that the Einstein ring is consistent with the gravitational lensing of an extended infrared component, centred between the two radio components.     

Resonant tidal disruption in galactic nuclei

It has recently been shown by Rauch 38 Tremaine that the rate of angular momentum relaxation in nearly Keplerian star clusters is greatly increased by a process termed 'resonant relaxation'; it was also argued, via a series of scaling arguments, that tidal disruption of stars in galactic nuclei containing massive black holes could be noticeably enhanced by this process. We describe here the results of numerical simulations of resonant tidal disruption which quantitatively test the predictions made by Rauch 38 Tremaine. The simulation method is based on an N -body routine incorporating cloning of stars near the loss cone and a semirelativistic symplectic integration scheme. Normalized disruption rates for resonant and non-resonant nuclei are derived at orbital energies both above and below the critical energy, and the corresponding angular momentum distribution functions are found. The black hole mass above which resonant tidal disruption is quenched by relativistic precession is determined. We also briefly describe the discovery of chaos in the Wisdom–Holman symplectic integrator applied to highly eccentric orbits and propose a modified integration scheme that remains robust under these conditions. We find that resonant disruption rates exceed their non-resonant counterparts by an amount consistent with the predictions; in particular, we estimate the net tidal disruption rate for a fully resonant cluster to be about twice that of its non-resonant counterpart. No significant enhancement in rates is observed outside the critical radius. Relativistic quenching of the effect is found to occur for hole masses M  >  M _Q  = (8 ± 3) × 10⁷  M . The numerical results combined with the observed properties of galactic nuclei indicate that for most galaxies the resonant enhancement to tidal disruption rates will be very small.     

黑子活动区流场精细结构

本文通过太阳活动区光球和色球速度场和磁场观测资料,讨论了黑子活动区附近流场的精细结构,论述了太阳大气中物质的流动呈纤维结构,以及速度场纤维与磁场,色球纤维和网络结构之间的关系。     

Observations of the gamma-ray flux from the galaxy Mk 501

We present two-year-long observations of the flux of very-high-energy (～10¹² eV) gamma rays from the active galactic nucleus Mk 501 performed with a Cherenkov detector at the Crimean Astrophysical Observatory. A gamma-ray flux from the object was shown to exist at confidence levels of 11 and 7 standard deviations for 1997 and 1998, respectively. The flux varied over a wide range. The mean flux at energies >10¹² eV, as inferred from the 1997 and 1998 data, is (5.0±0.6)×10^?11 and (3.7±0.6)×10^?11 cm^?2 s^?1, respectively. The errors are the sum of statistical observational and modeling errors. The mean power released in the form of gamma rays is ～2×10⁴³ erg s^?1 sr^?1.     

一种新的10米光学/红外望远镜

结合中国的实际情况提出了一 新的中国２１世纪的１０米光学／红外望远镜的方案,它是属于一种非常规概念设计的望远镜。这种新的大望远镜方案吸收了或主要参考了Ａｒｅｃｉｂｏ射电望远镜、美国的ＨｏｂｂｙＥｂｅｒｌｙ９米望远镜和ＬＡＭＯＳＴ方案的前身一光谱巡天望远镜方案。它的主镜是六角形子镜拼成的球面,在观测过程中主镜不动,由焦面的改正镜做跟踪,造价约为同样口径的常规设计望远镜的五分之一,并能满足绝大部分天文