The 1996-1997 Fading of V651 Monocerotis, the Binary Central Star of the Planetary Nebula NGC 2346
V651 Mon is the binary central star of the bipolar planetary nebula NGC 2346. The star showed the second-ever deep fading in 1996–1997, which was presumably caused by obscuration by a dust cloud in the planetary nebula, as was proposed to explain the 1981–1985 event. The entire duration of the 1996–1997 event was ∼400d, remarkably shorter than the 1981–1985 event, suggesting that the obscuring body was smaller or had a larger tangential velocity. The most remarkable feature in this event was the presence of a sharply defined transient clearing (brightening). From the time-scale of the variation, we propose an upper limit of the projected scale of several times ∼ 10 11 cm of the structure responsible for the brightening. This observation provides the first evidence for a sharply defined,
Photometric observations of the central star of the planetary nebula NGC 2346 in 1991/1992
Photoelectric UBV observations of the central star of the planetary nebula NGC 2346 obtained during 60 nights between October 1991 and February 1992 are presented (Tables 1 and 2). Four minima have been stated and can be interpreted in terms of occulting dust clouds, probably representing dense condensations of the planetary nebula. We derived R = AV/EB—V = 4.0. 
 
 
 
Photoelektrische UBV—Beobachtungen des Zentralsterns des Planetarischen Nebels NGC 2346, gemessen in 60 Nachten zwischen Oktober 1991 und Februar 1992, werden prasentiert (Tabellen 1 und 2). Es wurden in diesem Zeitraum vier Minima nachgewiesen, als deren Ursache Bedeckungen des Sternes durch Staubwolken angenommen werden konnen. Diese Wolken stellen moglicherweise dichte Kondensationen des Planetarischen Nebels dar. Es ergibt sich R = AV/EB—V = 4.0.
Mass Loss History of Evolved Stars
We provide high-resolution maps of the circumstellar dust shells of several dozen Asymptotic Giant Branch (AGB) stars using data from the Spitzer space telescope Multiband Imaging Photometer (MIPS) imaged at 70μm. AGB stars are the major contributors of chemical elements such as carbon, oxygen and silicon, which are essential to the existence of life in the universe, through mass loss processes that take place at the surface of the star. We probe the spatial distribution of cold (∼40 K) dust grains in order to trace the history of mass loss from the observed radial density variation in these shells. Our images illustrate that different morphologies may evolve because AGB stars can already interact with the interstellar medium (ISM) that surrounds them even at these early stages of the AGB mass loss history. Relative motion of the star as well as the ISM with respect to the local environment may be of particular importance for shell structure evolution.