TY - JOUR
T1 - Periodic optical variability and debris accretion in white dwarfs
T2 - A Test for a causal connection*
AU - Hallakoun, Na'ama
AU - Maoz, Dan
AU - Agol, Eric
AU - Brown, Warren R.
AU - Dufour, Patrick
AU - Farihi, Jay
AU - Gänsicke, Boris T.
AU - Kilic, Mukremin
AU - Kosakowski, Alekzander
AU - Loeb, Abraham
AU - Mazeh, Tsevi
AU - Mullally, Fergal
N1 - Publisher Copyright: © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2018/5/1
Y1 - 2018/5/1
N2 - Recent Kepler photometry has revealed that about half of white dwarfs (WDs) have periodic, low-level (~10-4 - 10-3), optical variations. Hubble Space Telescope (HST) ultraviolet spectroscopy has shown that up to about one half ofWDs are actively accreting rocky planetary debris, as evidenced by the presence of photospheric metal absorption lines. We have obtained HST ultraviolet spectra of sevenWDs that have been monitored for periodic variations, to test the hypothesis that these two phenomena are causally connected, i.e. that the optical periodic modulation is caused by WD rotation coupled with an inhomogeneous surface distribution of accreted metals. We detect photospheric metals in four out of the seven WDs. However, we find no significant correspondence between the existence of optical periodic variability and the detection of photospheric ultraviolet absorption lines. Thus, the null hypothesis stands, that the two phenomena are not directly related. Some other source of WD surface inhomogeneity, perhaps related to magnetic field strength, combined with the WD rotation, or alternatively effects due to close binary companions, may be behind the observed optical modulation. We report the marginal detection of molecular hydrogen in WDJ1949+4734, only the fourth known WD with detected H2 lines. We also re-classify J1926+4219 as a carbon-rich He-sdO subdwarf.
AB - Recent Kepler photometry has revealed that about half of white dwarfs (WDs) have periodic, low-level (~10-4 - 10-3), optical variations. Hubble Space Telescope (HST) ultraviolet spectroscopy has shown that up to about one half ofWDs are actively accreting rocky planetary debris, as evidenced by the presence of photospheric metal absorption lines. We have obtained HST ultraviolet spectra of sevenWDs that have been monitored for periodic variations, to test the hypothesis that these two phenomena are causally connected, i.e. that the optical periodic modulation is caused by WD rotation coupled with an inhomogeneous surface distribution of accreted metals. We detect photospheric metals in four out of the seven WDs. However, we find no significant correspondence between the existence of optical periodic variability and the detection of photospheric ultraviolet absorption lines. Thus, the null hypothesis stands, that the two phenomena are not directly related. Some other source of WD surface inhomogeneity, perhaps related to magnetic field strength, combined with the WD rotation, or alternatively effects due to close binary companions, may be behind the observed optical modulation. We report the marginal detection of molecular hydrogen in WDJ1949+4734, only the fourth known WD with detected H2 lines. We also re-classify J1926+4219 as a carbon-rich He-sdO subdwarf.
KW - Accretion, accretion discs
KW - Stars: Atmospheres
KW - Stars: Variables: General
KW - Techniques: Spectroscopic
KW - Ultraviolet: Planetary systems
KW - White dwarfs
UR - http://www.scopus.com/inward/record.url?scp=85043538446&partnerID=8YFLogxK
U2 - https://doi.org/10.1093/mnras/sty257
DO - https://doi.org/10.1093/mnras/sty257
M3 - مقالة
SN - 0035-8711
VL - 476
SP - 933
EP - 942
JO - MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
JF - MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
IS - 1
ER -