April 4, 2012: Bram Ochsendorf (Leiden Observatory, Netherlands) has requested monitoring by AAVSO observers of the R CrB variable V854 Cen in support of observations to be made using the XSHOOTER instrument on the Very Large Telescope (VLT) of the European Southern Observatory's La Silla Paranal Observatory in Chile. Ochsendorf and colleagues have already observed V854 Cen at maximum and now need to observe it during a fading episode.
From now through August 2012, please keep a close eye on V854 Cen, which is visual magnitude ~7.2 at maximum, and report your observations to the AAVSO. Nightly observations (V band preferred, visual and other bands welcome) are requested, with more frequent coverage if the star begins to decline. If V854 Cen fades to or goes below visual magnitude 8.0, please report your observations immediately.
According to observations in the AAVSO International Database, V854 Cen is currently at visual magnitude 7.2.
Ochsendorf and Dr. A.G.G.M. Tielens write: "As part of our studies on the the role of molecules in space, we are studying the molecular inventory and the formation and evolution of these molecules in their birth sites, such as the R CrB stars...
"Over the last 20 years, we have learned that we live in a molecular Universe, a Universe where molecules are an important component of the interstellar medium and where molecular processes play an important role in shaping the Universe around us. The most complex molecules are formed in stellar ejecta by processes akin to those in terrestrial sooting environments. R Coronae Borealis stars are C-rich, late type giants which are losing mass by ejecting small, directional puffs of smoke and gas. When one of these puffs is directed along the sight-line, the star is occulted by the dust forming in the ejecta as the gas cools. As more and more dust is formed, the intense, direct light from the central star is blocked more effectively. Eventually, these cloudlets will disperse and mix into the expanding dust and gas shell. The stellar light curve is therefore characterized by deep declines towards minimum which occur irregularly whenever one of these smoke puffs happens to be in our sightline. The visual light curve shows drops by ~8 magnitudes and a typical timescale for a decline and a rise is about 4-6 months.
"The R CrB star V854 Cen is a prototypical example of this class of objects. Its ejecta are a rich source of interstellar molecules, and species such as the dicarbon radical (C2), the fullerene C60, and large Polycyclic Aromatic Hydrocarbon molecules have been observed in the spectra of this star. The smoke puffs along the line of sight act as occulting screens, blocking out the blinding starlight, and allowing us to probe in detail the molecules in the immediate surroundings of the star. Our goal is to probe the characteristics of these molecules in the cold molecular ejecta surrounding this object."
Coordinates: RA 14 34 49.41 Dec -39 33 19.2 (2000.0)
Finder charts may be plotted using the AAVSO International Variable Star Plotter (VSP) at http://www.aavso.org/vsp.
Please report observations to the AAVSO International Database as V854 CEN.
This AAVSO Special Notice was compiled by Elizabeth O. Waagen.
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