Phase‐resolved<i>Hubble Space Telescope</i>/STIS Spectroscopy of the Exposed White Dwarf in the High‐Field Polar AR Ursae Majoris

Gänsicke, B. T.; Schmidt, Gary D.; Jordan, S.; Szkody, Paula

doi:10.1086/321464

Cited by 33 publications

(47 citation statements)

References 22 publications

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“…In addition, they detected the 1s0-2s0 Ly component that violates the parity/magnetic moment rules. This '' forbidden '' line is enforced by the presence of a strong electric field in the atmosphere of the star: it has also been observed in the spectrum of the accreting magnetic white dwarf AR UMa (Gänsicke et al 2001).…”

Section: Introductionmentioning

confidence: 84%

A Multiwavelength Study of the High‐Field Magnetic White Dwarf EUVE J0317−85.5 (=RE J0317−853)

Vennes

Schmidt

Ferrario

et al. 2003

ApJ

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We present optical and ultraviolet photometry and spectroscopy and optical circular spectropolarimetry of the ultramassive, rapidly rotating, high-field magnetic white dwarf EUVE J0317À85.5. From the combined data sets, we establish an ephemeris for the photometric, spectroscopic, and polarimetric variations with a spin period of 725.7277 s, the fastest yet measured for an isolated white dwarf. We build a series of far-ultraviolet (FUV) and optical flux spectra as well as optical polarization spectra that describe the atmospheric properties as a function of rotation phase. Twelve components of the Lyman line series are identified in the FUV: seven of them are forbidden lines enforced by the electric field that permeates the strongly magnetized photosphere. Attempts at modeling the FUV and optical data with two classes of models indicate an unusual field structure on the star. Both offset-dipole and multipolar expansion models fail to adequately reproduce the spectroscopic and polarimetric properties simultaneously, and we postulate that the surface of EUVE J0317À85.5 may be punctuated by a high-field magnetic spot. Subject headings: stars: individual (EUVE J0317À85.5) -stars: magnetic fields -ultraviolet: starswhite dwarfs On-line material: color figure

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Section: Introductionmentioning

confidence: 84%

A Multiwavelength Study of the High‐Field Magnetic White Dwarf EUVE J0317−85.5 (=RE J0317−853)

Vennes

Schmidt

Ferrario

et al. 2003

ApJ

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“…Gänsicke et al (2002) also found that only two previously known short-period systems with HQS spectra failed to be identified as CVs; this "hit rate" of 90% underlines the extreme efficiency of the HQS of finding short period CVs. Five out of those 18 systems have measured white dwarf temperatures, all of them in the range 11 000-16 000 K (MR Ser, ST LMi, AR UMa, SW UMa, T Leo: Gänsicke et al 2001;Hamilton & Sion 2004;Araujo-Betancor et al 2005b;Gänsicke et al 2005). The remaining 13 systems all have spectra dominated by strong Balmer and He emission, suggesting accretion rates too high to detect the white dwarf.…”

Section: Post-bounce Cvs Expected In the Hqsmentioning

confidence: 99%

Dwarf novae in the Hamburg quasar survey: rarer than expected

Aungwerojwit¹,

Gänsicke²,

Rodríguez‐Gil

et al. 2006

A&A

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Aims. We report the discovery of five new dwarf novae that were spectroscopically identified in the Hamburg Quasar Survey (HQS), and discuss the properties of the sample of new dwarf novae from the HQS. Methods. Follow-up time-resolved spectroscopy and photometry have been obtained to characterise the new systems. Results. The orbital periods determined from analyses of the radial velocity variations and/or orbital photometric variability are P orb 105.1 min or P orb 109.9 min for HS 0417+7445, P orb = 114.3 ± 2.7 min for HS 1016+3412, P orb = 92.66 ± 0.17 min for HS 1340+1524, P orb = 272.317 ± 0.001 min for HS 1857+7127, and P orb = 258.02 ± 0.56 min for HS 2214+2845. HS 1857+7127 is found to be partially eclipsing. In HS 2214+2845 the secondary star of spectral type M3 ± 1 is clearly detected, and we estimate the distance to the system to be d = 390 ± 40 pc. We recorded one superoutburst of HS 0417+7445, identifying the system as a SU UMatype dwarf nova. HS 1016+3412 and HS 1340+1524 have rare outbursts, and their subtype is yet undetermined. HS 1857+7127 frequently varies in brightness and may be a Z Cam-type dwarf nova. HS 2214+2845 is a U Gem-type dwarf nova with a most likely cycle length of 71 d. Conclusions. To date, 14 new dwarf novae have been identified in the HQS. The ratio of short-period (<3 h) to long-period (>3 h) systems of this sample is 1.3, much smaller compared to the ratio of 2.7 found for all known dwarf novae. The HQS dwarf novae display typically infrequent or low-amplitude outburst activity, underlining the strength of spectroscopic selection in identifying new CVs independently of their variability. The spectroscopic properties of short-period CVs in the HQS, newly identified and previously known, suggest that most, or possibly all of them are still evolving towards the minimum period. Their total number agrees with the predictions of population models within an order of magnitude. However, the bulk of all CVs is predicted to have evolved past the minimum period, and those systems remain unidentified. This suggests that those post-bounce systems have markedly weaker Hβ emission lines compared to the average known short-period CVs, and undergo no or extremely rare outbursts.

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“…The polar AR Ursae Majoris (AR UMa) is inferred to contain a white dwarf (WD) that possesses a magnetic field of ∼240 MG-the strongest of the known polars (Schmidt et al 1996;Gänsicke et al 2001). Its optical observations show that it often changes between high and low brightness states, remaining in the low state for approximately 90% of the time.…”

Section: Introductionmentioning

confidence: 99%

“…However, if they are present, some might perhaps have been disguised by the emission lines from the MD (e.g., Mg I and Ca II). Here we re-examine the far-ultraviolet spectra in Gänsicke et al (2001), and fit the strongest metal absorption line of Si II with a Gaussian function plus a line. The result shows that the FWHM is 240±80 km s −1 , which is similar to that of the aluminum absorption doublet.…”

mentioning

confidence: 99%

Time-Variable Aluminum Absorption in the Polar Ar Ursae Majoris, and an Updated Estimate for the Mass of the White Dwarf

Justham

Liu

et al. 2016

ApJ

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We present spectra of the extreme polar AR Ursae Majoris (AR UMa), which display a clear Al I absorption doublet, alongside spectra taken less than a year earlier in which that feature is not present. Re-examination of earlier SDSS spectra indicates that the Al I absorption doublet was also present ≈8 years before our first nondetection. We conclude that this absorbing material is unlikely to be on the surface of either the white dwarf (WD) or the donor star. We suggest that this Al I absorption feature arises in circumstellar material, perhaps produced by the evaporation of asteroids as they approach the hot WD. The presence of any remaining reservoir of rocky material in AR UMa might help to constrain the prior evolution of this unusual binary system. We also apply spectral decomposition to find the stellar parameters of the M dwarf companion, and attempt to dynamically measure the mass of the WD in AR UMa by considering both the radial velocity curves of the H β emission line and the Na I absorption line. Thereby we infer a mass range for the WD in AR UMa of 0.91 M e <M WD <1.24 M e .

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Phase‐resolvedHubble Space Telescope/STIS Spectroscopy of the Exposed White Dwarf in the High‐Field Polar AR Ursae Majoris

Cited by 33 publications

References 22 publications

A Multiwavelength Study of the High‐Field Magnetic White Dwarf EUVE J0317−85.5 (=RE J0317−853)

A Multiwavelength Study of the High‐Field Magnetic White Dwarf EUVE J0317−85.5 (=RE J0317−853)

Dwarf novae in the Hamburg quasar survey: rarer than expected

Time-Variable Aluminum Absorption in the Polar Ar Ursae Majoris, and an Updated Estimate for the Mass of the White Dwarf

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