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The gravitational redshift of Sirius B

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journal contribution
posted on 24.09.2019, 14:19 by SRG Joyce, MA Barstow, JB Holberg, HE Bond, SL Casewell, MR Burleigh
Einstein’s general theory of relativity predicts that the light from stars will be gravitationally shifted to longer wavelengths. We previously used this effect to measure the mass of the white dwarf Sirius B from the wavelength shift observed in its Hα line based on spectroscopic data from the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST), but found that the results did not agree with the dynamical mass determined from the visual-binary orbit. We have devised a new observing strategy using STIS, where the shift is measured relative to the Hα line of Sirius A rather than comparing it to a laboratory based rest wavelength. Sirius A was observed during the same orbit with HST. This strategy circumvents the systematic uncertainties which have affected previous attempts to measure Sirius B. We measure a gravitational redshift of 80.65 ± 0.77 km s−1. From the measured gravitational redshift and the known radius, we find a mass of 1.017 ± 0.025 M⊙ which is in agreement with the dynamical mass and the predictions of a C/O white dwarf mass–radius relation with a precision of 2.5 per cent.


Special thanks to Blair Porterfield, Joleen Carlberg and the team at STScI for all their help and advice during the phase 2 proposal. We thank the referee for helpful comments. SRGJ acknowledges support from the Science and Technology Facilities Council (STFC, UK). MAB acknowledges support from the Gaia post-launch support programme of the UK Space Agency and the Leicester Institute for Space and Earth Observation (LISEO). SLC acknowledges support from LISEO. J.B.H. and H.E.B. acknowledge support provided by the National Aeronautics and Space Administration (NASA) through grants from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.



Monthly Notices of the Royal Astronomical Society, 2018, 481 (2), pp. 2361-2370 (10)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society





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