Abstract. We present the results of the dynamical analysis of the rich, hot, and X-ray very luminous galaxy cluster A2219, containing a powerful diffuse radio-halo. Our analysis is based on new redshift data for 27 galaxies in the cluster region, measured from spectra obtained at the TNG, with the addition of other 105 galaxies recovered from reduction of CFHT archive data in a cluster region of ∼5 radius (∼0.8 h −1 Mpc at the cluster distance) centered on the cD galaxy. The investigation of the dynamical status is also performed using X-ray data stored in the Chandra archive. Further, valuable information comes from other bands -optical photometric, infrared, and radio data -which are analyzed and/or discussed, too. We find that A2219 appears as a peak in the velocity space at z = 0.225, and select 113 cluster members. We compute a high value for the line-ofsight velocity dispersion, σ v = 1438 +109 −86 km s −1 , consistent with the high average X-ray temperature of 10.3 keV. If dynamical equilibrium is assumed, the virial theorem leads to M ∼ 2.8× 10 15 h −1 M for the global mass within the virial region. However, further investigation based on both optical and X-ray data shows significant signs of a young dynamical status. In fact, we find strong evidence for the elongation of the cluster in the SE-NW direction coupled with a significant velocity gradient, as well as for the presence of substructure both in optical data and X-ray data. Moreover, we point out the presence of several active galaxies. We discuss the results of our multi-wavelength investigation suggesting a complex merging scenario where the main, original structure is subject to an ongoing merger with a few clumps aligned in a filament in the foreground oriented in an oblique direction with respect to the line-of-sight. Our conclusion supports the view of the connection between extended radio emission and merging phenomena in galaxy clusters.

We studied the brightness and spectral evolution of the young eruptive star V1647 Ori during its recent outburst in the period 2004 FebruaryY2006 September. We performed a photometric follow-up in the bands V, R C , I C , J, H, and K s , as well as visible and near-IR spectroscopy. The main results derived from combining our data with those published by other authors are as follows: the brightness of V1647 Ori stayed more than 4 mag above the preoutburst level until 2005 October, when it started a rapid fading. In the high state we found a periodic component in the optical light curves with a period of 56 days. The delay between variations of the star and variations in the brightness of clumps of nearby nebulosity corresponds to an angle of 61 AE 14 between the axis of the nebula and the line of sight. The overall appearance of the infrared and optical spectra did not change in the period 2004 MarchY2005 March, although a steady decrease of H i emission-line fluxes could be observed. In 2006 May, in the quiescent phase, the He i 1.083 m line was observed in emission, contrary to its deep blueshifted absorption observed during the outburst. The J À H and H À K s color maps of the infrared nebula reveal an envelope around the star whose largest extension is about 18 00 (0.03 pc). The color distribution of the infrared nebula suggests reddening of the scattered light inside a thick circumstellar disk. Comparison of the K s and H images of McNeil's Nebula, the conical nebulosity illuminated by V1647 Ori, shows that HH 22A, the Spitzer infrared source, and the bright clump C of the nebula may be unrelated objects. We show that the observed properties of V1647 Ori could be interpreted in the framework of the thermal instability models of Bell and coworkers. V1647 Ori might belong to a new class of young eruptive stars, defined by relatively short timescales, recurrent outbursts, a modest increase in bolometric luminosity and accretion rate, and an evolutionary state earlier than that of typical EXors.

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