Hostname: page-component-586b7cd67f-2plfb Total loading time: 0 Render date: 2024-11-30T12:49:40.791Z Has data issue: false hasContentIssue false

The Three-Dimensional Structure of EUV Accretion Regions of AM Her Stars: Analysis of EUVE Light Curves

Published online by Cambridge University Press:  12 April 2016

Martin M. Sirk
Affiliation:
Center for EUV Astrophysics, 2150 Kittredge St., University of California, Berkeley, CA 94720-5030, USA
Steve B. Howell
Affiliation:
Planetary Sciences Institute, Astrophysics Group, 620 North Sixth Ave., Tucson, AZ 85705, USA

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

We present EUV light curves for a number of AM Her systems observed either as guest observer targets or with the EUVE Right Angle Program. We have formed light curves for eight AM Her stars and show in our presentation the similarities and differences present. We draw some conclusions by grouping the systems by inclination, magnetic field strength, and accretion region geometry. In order to understand the physical structures responsible for the EUV emissions, we have developed a software model to generate synthetic light curves. We find that the EUV accretion regions in the systems UZ For, VV Pup, and AM Her cannot be fit with a flat spot confined to the white dwarf surface, regardless of its shape or brightness profile. Rather, a small, symmetric, raised spot is the only shape consistent with the data. The light curves for systems EF Eri, RE1149+28, AN UMa, and V834 Cen show evidence for additional structure that precedes the primary accretion region in phase. Our model indicates that a large portion of the light curve in each system is seen in absorption. Finally, in three systems, we detect a very gradual rise and fall in the EUV flux (<5% of the peak flux) at phases when the spot is completely obscured behind the white dwarf (WD) limb. We attribute this detection to emission from the accretion column that decreases exponentially with distance from the WD and detect emission at heights up to 15% of the WD radius.

Type
VI. Cataclysmic Variable Stars
Copyright
Copyright © Kluwer 1996

References

Bailey, J. & Cropper, M.S. 1991, MNRAS, 253, 27 Google Scholar
Bowyer, S. & Malina, R.F. 1991, in Extreme Ultraviolet Astronomy, ed. Malina, R.F. & Bowyer, S., New York: Pergamon Press, 397 Google Scholar
Cropper, M.S. 1990, Space Sci. Rev., 54, 195 CrossRefGoogle Scholar
Howell, S.B., Sir, M.M., Malina, R.F., Mittaz, J.P.D., & Mason, K.O. 1995, ApJ, 439, 991 Google Scholar
Liebert, J. & Stockman, H.S. 1985, in Cataclysmic Variables and Low-Mass X-ray Binaries, Ed. Lamb, D.Q. & Patterson, J., Dordrecht: Reidel, 151 Google Scholar
Malina, R.F., et al. 1994, AJ, 107, 751 Google Scholar
McDonald, K., et al. 1995, AJ, 108, 5 Google Scholar
Vennes, S., Szkody, P., Sion, E.M., & Long, K.S. 1995, ApJ, 445, 921 Google Scholar
Warren, J.K., Sirk, M.M., & Vallerga, J.V. 1995, ApJ, 445, 909 Google Scholar