EDP Sciences
Free access
Volume 399, Number 2, February IV 2003
Page(s) 681 - 686
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20021830

A&A 399, 681-686 (2003)
DOI: 10.1051/0004-6361:20021830

First far-UV observations of KQ Puppis with FUSE

R. González-Riestra1, C. Rossi2 and R. F. Viotti3

1  XMM Science Operations Centre, VILSPA, PO Box 50727, 28080 Madrid, Spain
2  Dipartimento di Fisica, Università La Sapienza, Piazzale Aldo Moro 3, 00185 Roma, Italy
3  Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Area di Ricerca Tor Vergata, Via del Fosso del Cavaliere 100, 00133 Roma, Italy

(Received 29 July 2002 / Accepted 20 November 2002 )

We report the first far-ultraviolet spectrum of the emission line spectroscopic binary KQ Pup (M2Iab+B0Ve), obtained with FUSE shortly after conjunction at orbital phase $\Phi =0.13$. The spectrum presents a sharp flux cutoff at 1040 Å; longwards, it is dominated by a large amount of resonant and low excitation transitions of neutral and singly ionized species, probably mostly of circumsystem origin, and by the Lyman absorption bands of H 2, whose strength corresponds to an interstellar H 2 column density of ~ $2\times 10^{20}$ cm -2, indicating a fraction of molecular hydrogen 2 N(H 2)/[ N(HI)+2 N(H 2)] of ~0.4. An N(HI)/ EB-V ratio of $4.3\times 10^{21}$ is derived from the IUE spectra. The long-term UV monitoring of KQ Pup with IUE, HST and FUSE reveals a large decrease of the far-UV flux since orbital phase 0.82 and occupying more than 0.3 of the orbital period. This "shell" episode is attributed to line absorption and to Ly $\alpha$ Rayleigh scattering due to an extended dense cool envelope in the line of sight of the B star.

Key words: stars: binaries: spectroscopic -- stars: individual: KQ Pup -- stars: mass-loss -- ultraviolet: stars

Offprint request: R. González-Riestra, rgonzale@xmm.vilspa.esa.es

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