Baptista, R., Morales-Rueda, L., Harlaftis, E. T., Marsh, T. R. and Steeghs, D. (2005) Tracing the spiral arms in IP Pegasi. Astronomy & Astrophysics, Vol.444 (No.1). pp. 201-211. doi:10.1051/0004-6361:20053399

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Abstract

We report the analysis of time-resolved spectroscopy of IP Pegasi in outburst with eclipse mapping techniques to investigate the location and geometry of the observed spiral structures. We were able to obtain an improved view of the spiral structures with the aid of light curves extracted in velocity bins matching the observed range of velocities of the spiral arms combined with a double default map tailored for reconstruction of asymmetric structures. Two-armed spiral structures are clearly seen in all eclipse maps. The arms are located at different distances from the disc centre. The “blue” arm is farther out in the disc (R = 0.55 ± 0.05 R L1 ) than the “red” arm (R = 0.30 ± 0.05 R L1 ). There is evidence that
the velocity of the emitting gas along the spiral pattern is lower than the Keplerian velocity for the same disc radius. The discrepancy is smaller in the outer arm (measured velocities 10–15 per cent lower than Keplerian) and is more significant in the inner arm (observed velocities up to 40 per cent lower than Keplerian). We measured the opening angle of the spirals from the azimuthal intensity distribution of the eclipse maps to
be φ = 25◦ ± 3◦ . A comparison with similar measurements on data at different outburst stages reveals that the opening angle of the spiral arms in IP Peg decreases while the outbursting accretion disc cools and shrinks, in agreement with the expected evolution of a tidally driven spiral
wave. The sub-Keplerian velocities along the spiral pattern and the clear correlation between the opening angle of the spirals and the outburst stage favors the interpretation of these asymmetric structures as tidally-induced spiral shocks.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Dwarf novae, Accretion (Astrophysics)
Journal or Publication Title:	Astronomy & Astrophysics
Publisher:	EDP Sciences
ISSN:	0004-6361
Official Date:	December 2005
Dates:	Date Event December 2005 Published
Volume:	Vol.444
Number:	No.1
Page Range:	pp. 201-211
DOI:	10.1051/0004-6361:20053399
Status:	Peer Reviewed
Access rights to Published version:	Open Access

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