Driving the beat: time-resolved spectra of the white dwarf pulsar AR Scorpii

dc.contributor.authorGarnavich, Peter M.
dc.contributor.authorLittelfield, Colin
dc.contributor.authorKafka, Stella
dc.contributor.authorKennedy, Mark R.
dc.contributor.authorCallanan, Paul J.
dc.contributor.authorBalsara, Dinshaw S.
dc.contributor.authorLyutikov, Maxim
dc.contributor.funderNational Science Foundationen
dc.contributor.funderUniversity of Notre Dameen
dc.contributor.funderRoyal Societyen
dc.date.accessioned2019-04-15T14:45:57Z
dc.date.available2019-04-15T14:45:57Z
dc.date.issued2019-02-11
dc.date.updated2019-04-15T14:25:20Z
dc.description.abstractWe obtained high temporal resolution spectroscopy of the unusual binary system AR Scorpii (AR Sco) covering nearly an orbit. The Hα emission shows a complex line structure similar to that seen in some polars during quiescence. Such emission is thought to be due to long-lived prominences originating on the red dwarf. A difference between AR Sco and these other systems is that the white dwarf (WD) in AR Sco is rapidly spinning relative to the orbital period. "Slingshot" prominences stable at 3 to 5 stellar radii require surface magnetic fields between 100 and 500 G. This is comparable to the estimated WD magnetic field strength near the surface of the secondary. Our time-resolved spectra also show emission fluxes, line equivalent widths, and continuum color varying over the orbit and the beat/spin periods of the system. During much of the orbit, the optical spectral variations are consistent with synchrotron emission with the highest energy electrons cooling between pulses. On the timescale of the beat/spin period we detect red- and blueshifted Hα emission flashes that reach velocities of 700 km s−1. Redshifted Balmer-emission flashes are correlated with the bright phases of the continuum beat pulses while blueshifted flashes appear to prefer the time of minimum in the beat light curve. We propose that much of the energy generated in AR Sco comes from fast magnetic reconnection events occurring near the inward face of the secondary and we show that the energy generated by magnetic reconnect ion can account for the observed excess luminosity from the system.en
dc.description.sponsorshipNational Science Foundation (NSF grants NSF-ACI-1533850, NSF-DMS-1622457, NSF-ACI-1713765, and NSF-DMS1821242); Notre Dame International (Notre Dame International); Royal Society (Newton International Fellowship)en
dc.description.statusPeer revieweden
dc.description.versionPublished Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.articleid67en
dc.identifier.citationGarnavich, P., Littlefield, C., Kafka, S., Kennedy, M., Callanan, P., Balsara, D. S. and Lyutikov, M. (2019) 'Driving the Beat: Time-resolved Spectra of the White Dwarf Pulsar AR Scorpii', The Astrophysical Journal, 872(1), 67 (11 pp). doi: 10.3847/1538-4357/aafb2cen
dc.identifier.doi10.3847/1538-4357/aafb2cen
dc.identifier.endpage1en
dc.identifier.issn1538-4357
dc.identifier.issued1en
dc.identifier.journaltitleThe Astrophysical Journalen
dc.identifier.startpage1en
dc.identifier.urihttps://hdl.handle.net/10468/7767
dc.identifier.volume872en
dc.language.isoenen
dc.publisherAmerican Astronomical Society; IOP Publishingen
dc.relation.urihttps://iopscience.iop.org/article/10.3847/1538-4357/aafb2c
dc.rights© 2019. The American Astronomical Society. All rights reserved.en
dc.subjectBinaries: closeen
dc.subjectStars: individual (AR Sco)en
dc.subjectNovae, cataclysmic variablesen
dc.subjectPulsars: generalen
dc.subjectStars: magnetic fielden
dc.subjectWhite dwarfsen
dc.titleDriving the beat: time-resolved spectra of the white dwarf pulsar AR Scorpiien
dc.typeArticle (peer-reviewed)en
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