Astronomy & Astrophysics

Free access article

Issue		A&A Volume 429, Number 2, January II 2005
Page(s)		599 - 605
Section		Stellar structure and evolution
DOI		10.1051/0004-6361:20035751

A&A 429, 599-605 (2005)
DOI: 10.1051/0004-6361:20035751

Spectroscopic monitoring of the transition phase in nova V4745 Sgr

B. Csák¹, L. L. Kiss², A. Retter³, A. Jacob² and S. Kaspi⁴

¹ Department of Experimental Physics and Astronomical Observatory, University of Szeged, Dóm tér 9, 6720 Szeged, Hungary
e-mail: csakb@physx.u-szeged.hu
² School of Physics, University of Sydney 2006, Australia
³ Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802-6305, USA
⁴ School of Physics and Astronomy and the Wise Observatory, Tel Aviv University, Tel Aviv 69978, Israel

(Received 26 November 2003 / Accepted 6 August 2004)

Abstract
We present a spectroscopic monitoring of the transient nova V4745 Sagittarii ( Nova Sgr 2003 #1 ) covering ten months after its discovery. During this period the light curve showed a well expressed transient phase in the form of six rebrightenings, and the presented dataset is one of the best spectroscopic coverages of a classical nova during the transition phase. Low- and medium-resolution spectra revealed that the majority of spectral lines switched back to strong P-Cyg profiles during the mini-outbursts, similar to the spectra just after the major eruption. We interpret the observed phenomena as evidence for "echo-outbursts" resulting in episodes of secondary mass-ejections and propose that the transition phase in classical novae is driven by repetitive instabilities of the hydrogen shell burning on the surface of the white dwarf. From the available light curve data we estimate the absolute magnitude of the system of about $-8\fm3\pm0\fm5$ . All spectrophotometric evidence point toward a very low ( $E(B-V)<0\fm1$ ) interstellar reddening, leading to a rough distance estimate of V4745 Sgr ( $9~{\rm kpc}<d<19~{\rm kpc}$ ).

Key words: novae, cataclysmic variables -- stars: individual: V4745 Sgr

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