Multicolour optical light curves of the companion star to the millisecond pulsar PSR J2051-0827
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Date
2022-08-25
Authors
Dhillon, V. S.
Kennedy, Mark R.
Breton, R. P.
Clark, C. J.
Mata Sánchez, D.
Voisin, G.
Breedt, E.
Brown, A. J.
Dyer, M. J.
Green, M. J.
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Publisher
Oxford University Press
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Abstract
We present simultaneous, multicolour optical light curves of the companion star to the black-widow pulsar PSR J2051−0827, obtained approximately 10 yr apart using ULTRACAM and HiPERCAM, respectively. The ULTRACAM light curves confirm the previously reported asymmetry in which the leading hemisphere of the companion star appears to be brighter than the trailing hemisphere. The HiPERCAM light curves, however, do not show this asymmetry, demonstrating that whatever mechanism is responsible for it varies on time-scales of a decade or less. We fit the symmetrical HiPERCAM light curves with a direct-heating model to derive the system parameters, finding an orbital inclination of 55.9+4.8−4.1 degrees, in good agreement with radio-eclipse constraints. We find that approximately half of the pulsar’s spin-down energy is converted to optical luminosity, resulting in temperatures ranging from approximately 5150+190−190 K on the day side to 2750+130−150 K on the night side of the companion star. The companion star is close to filling its Roche lobe (fRL=0.88+0.02−0.02) and has a mass of 0.039+0.010−0.011 M⊙, giving a mean density of 20.24+0.59−0.44 g cm−3 and an apsidal motion constant in the range 0.0036 < k2 < 0.0047. The companion mass and mean density values are consistent with those of brown dwarfs, but the apsidal motion constant implies a significantly more centrally condensed internal structure than is typical for such objects.
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Keywords
Stars: neutron , Pulsars: individual , PSR J2051−0827
Citation
Dhillon, V. S., Kennedy, M. R., Breton, R. P., Clark, C. J., Mata Sánchez, D., Voisin, G., Breedt, E., Brown, A. J., Dyer, M. J., Green, M. J. and Kerry, P. (2022) 'Multicolour optical light curves of the companion star to the millisecond pulsar PSR J2051−0827', Monthly Notices of the Royal Astronomical Society, 516(2), pp.2792-2800. doi: 10.1093/mnras/stac2357
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© 2022, the Authors. Published by Oxford University Press on behalf of Royal Astronomical Society. This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record [Dhillon, V. S., Kennedy, M. R., Breton, R. P., Clark, C. J., Mata Sánchez, D., Voisin, G., Breedt, E., Brown, A. J., Dyer, M. J., Green, M. J. and Kerry, P. (2022) 'Multicolour optical light curves of the companion star to the millisecond pulsar PSR J2051−0827', Monthly Notices of the Royal Astronomical Society, 516(2), pp.2792-2800. doi: 10.1093/mnras/stac2357] is available online at: https://doi.org/10.1093/mnras/stac2357