Accretion in the high-field magnetic cataclysmic variable AR Ursae Majoris

Gary D. Schmidt, D. W. Hoard, Paula Szkody, Fulvio Melia, R. Kent Honeycutt, R. M. Wagner

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

AR UMa is the highest field example known of the magnetic cataclysmic variables, with a polar field Bp = 230 MG. We report here the results of a long program of photometry, spectroscopy, and spectropolarimetry of the object that was undertaken with the aim of gaining a better understanding of the role that the white dwarf field plays in shaping the properties of the magnetic systems. Only three accretion episodes, reaching mv ≤ 15 and covering a total of 9 months, were detected during the 4 yr of available photometry. Fortunately, the onset of one episode coincided with a week-long observing run, resulting in spectrophotometry and linear and circular spectropolarimetry that document the event. The long intervals of quiescence have enabled a determination of the orbital ephemeris that is now sufficiently precise to phase observations 20 yr old. The high-state observations lead to a number of conclusions regarding the system geometry. The white dwarf magnetic axis is inclined rather little to the spin axis, but the dipole is twisted in azimuth such that it lies nearly perpendicular to the stellar line of centers. Tomographic analysis of a wide variety of atomic species indicates that the white dwarf likely accretes in twin funnels that split off a ballistic gas stream reaching 30%-50% of the distance between the stars. A narrow high-velocity (KNHV ≈ 700 km s-1) emission-line component offset in phase from the main features suggests the existence of an additional gas stream, but the interpretation of this is not yet resolved. The system is viewed from a moderate inclination, which places the disfavored (retrograde) magnetic pole on the observed hemisphere at all times. We have investigated the possible effect that the white dwarf magnetosphere might have in restricting mass flow through L1, and therefore in giving rise to the unique, protracted low-accretion states of this object. However, the mechanisms considered are too weak and/or would give rise to consequences that are at odds with low-state observations. At the same time, the high magnetic field in AR UMa has yielded a new, powerful observational tool: phase-resolved Zeeman spectroscopy of the emission lines produced in the accretion stream(s). Future high-quality observations and sophisticated modeling of these features hold promise for three-dimensional reconstructions of the gas flow in high-field magnetic variables.

Original languageEnglish (US)
Pages (from-to)407-419
Number of pages13
JournalAstrophysical Journal
Volume525
Issue number1 PART 1
StatePublished - Nov 1 1999

Fingerprint

cataclysmic variables
accretion
magnetic field
gas streams
spectroscopy
magnetic fields
photometry
spectrophotometry
gas flow
gas
magnetic poles
azimuth
funnels
magnetosphere
mass flow
hemispheres
magnetospheres
ballistics
inclination
geometry

Keywords

  • Binaries: spectroscopic
  • Novae, cataclysmic variables
  • Stars: individual (AR Ursae Majoris)
  • Stars: magnetic fields

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Schmidt, G. D., Hoard, D. W., Szkody, P., Melia, F., Honeycutt, R. K., & Wagner, R. M. (1999). Accretion in the high-field magnetic cataclysmic variable AR Ursae Majoris. Astrophysical Journal, 525(1 PART 1), 407-419.

Accretion in the high-field magnetic cataclysmic variable AR Ursae Majoris. / Schmidt, Gary D.; Hoard, D. W.; Szkody, Paula; Melia, Fulvio; Honeycutt, R. Kent; Wagner, R. M.

In: Astrophysical Journal, Vol. 525, No. 1 PART 1, 01.11.1999, p. 407-419.

Research output: Contribution to journalArticle

Schmidt, GD, Hoard, DW, Szkody, P, Melia, F, Honeycutt, RK & Wagner, RM 1999, 'Accretion in the high-field magnetic cataclysmic variable AR Ursae Majoris', Astrophysical Journal, vol. 525, no. 1 PART 1, pp. 407-419.
Schmidt GD, Hoard DW, Szkody P, Melia F, Honeycutt RK, Wagner RM. Accretion in the high-field magnetic cataclysmic variable AR Ursae Majoris. Astrophysical Journal. 1999 Nov 1;525(1 PART 1):407-419.
Schmidt, Gary D. ; Hoard, D. W. ; Szkody, Paula ; Melia, Fulvio ; Honeycutt, R. Kent ; Wagner, R. M. / Accretion in the high-field magnetic cataclysmic variable AR Ursae Majoris. In: Astrophysical Journal. 1999 ; Vol. 525, No. 1 PART 1. pp. 407-419.
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