Astronomy & Astrophysics

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Issue		A&A Volume 409, Number 3, October III 2003
Page(s)		1007 - 1015
Section		Stellar atmospheres
DOI		10.1051/0004-6361:20031160

A&A 409, 1007-1015 (2003)
DOI: 10.1051/0004-6361:20031160

The enigmatic outburst of V445 Puppis - A possible helium nova?

N. M. Ashok and D. P. K. Banerjee

Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India
e-mail: orion@prl.ernet.in
(Received 22 January 2003 / Accepted 16 July 2003)

Abstract
JHK spectroscopic and photometric observations are reported for the enigmatic, nova-like, variable V445 Puppis which erupted at the end of 2000. The near-IR spectra are hydrogen-deficient and unusually rich in CI lines. The important CI lines are found to be positioned at 1.133, 1.166, 1.175, 1.189, 1.26 and 1.689 $\mu$ m. Model calculations for the CI lines are done to make the identification of the lines secure. Photometric data, taken on January 2.90 UT, 2001 shortly after the outburst, show the formation of an optically thin dust shell around V445 Puppis. The temperature and upper limit for the mass of the dust shell are estimated to be 1800 K and $M{_{\rm dust}} \sim 10{^{\rm -9}}~M_\odot$ respectively. A subsequent episode of massive dust formation - indicated by the observed, deep visual dimming - is also seen in JHK images of early November 2001. V445 Puppis has shown two unusual properties for a nova: (i) the hydrogen-deficiency and He/C enrichment of the object as seen from optical and IR data and (ii) synchrotron radio emission which was detected nearly a year after its outburst by other workers. The strange nature of the object is discussed and it is shown that it is difficult to place it in the known categories of eruptive variables viz. novae (classical, recurrent or symbiotic); born-again AGB stars; the new class of eruptive variables like V838 Mon; and RCB/HdC stars. Tentative evidence for an accretion disk and binarity of the V445 Puppis system is presented. It is debated whether V445 Puppis is a rare helium nova or a unique object.

Key words: stars: individual: V445 Puppis -- infrared: stars -- stars: novae, cataclysmic variables -- techniques: spectroscopic

Offprint request: N. M. Ashok, ashok@prl.ernet.in

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