The Sirius System and Its Astrophysical Puzzles: Hubble Space Telescope and Ground-based Astrometry

Howard E. Bond, Gail H. Schaefer, Ronald L. Gilliland, Jay B. Holberg, Brian D. Mason, Irving W. Lindenblad, Miranda Seitz-Mcleese, W. David Arnett, Pierre Demarque, Federico Spada, Patrick A. Young, Martin A. Barstow, Matthew R. Burleigh, Donald Gudehus

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Sirius, the seventh-nearest stellar system, is a visual binary containing the metallic-line A1 V star Sirius A, the brightest star in the sky, orbited in a 50.13 year period by Sirius B, the brightest and nearest white dwarf (WD). Using images obtained over nearly two decades with the Hubble Space Telescope (HST), along with photographic observations covering almost 20 years and nearly 2300 historical measurements dating back to the 19th century, we determine precise orbital elements for the visual binary. Combined with the parallax and the motion of the A component, these elements yield dynamical masses of 2.063 ± 0.023 M and 1.018 ± 0.011 M for Sirius A and B, respectively. Our precise HST astrometry rules out third bodies orbiting either star in the system, down to masses of ∼15-25 MJup. The location of Sirius B in the Hertzsprung-Russell diagram is in excellent agreement with theoretical cooling tracks for WDs of its dynamical mass, and implies a cooling age of ∼126 Myr. The position of Sirius B on the mass-radius plane is also consistent with WD theory, assuming a carbon-oxygen core. Including the pre-WD evolutionary timescale of the assumed progenitor, the total age of Sirius B is about 228 ±10 Myr. We calculated evolutionary tracks for stars with the dynamical mass of Sirius A, using two independent codes. We find it necessary to assume a slightly subsolar metallicity, of about 0.85 Z, to fit its location on the luminosity-radius plane. The age of Sirius A based on these models is about 237-247 Myr, with uncertainties of ±15 Myr, consistent with that of the WD companion. We discuss astrophysical puzzles presented by the Sirius system, including the probability that the two stars must have interacted in the past, even though there is no direct evidence for this and the orbital eccentricity remains high.

Original languageEnglish (US)
Article number70
JournalAstrophysical Journal
Volume840
Issue number2
DOIs
StatePublished - May 10 2017

Fingerprint

astrometry
Hubble Space Telescope
astrophysics
stars
cooling
Hertzsprung-Russell diagram
stellar systems
radii
orbital elements
parallax
dating
eccentricity
metallicity
sky
coverings
diagram
luminosity
timescale
orbitals
oxygen

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Bond, H. E., Schaefer, G. H., Gilliland, R. L., Holberg, J. B., Mason, B. D., Lindenblad, I. W., ... Gudehus, D. (2017). The Sirius System and Its Astrophysical Puzzles: Hubble Space Telescope and Ground-based Astrometry. Astrophysical Journal, 840(2), [70]. https://doi.org/10.3847/1538-4357/aa6af8
Bond, Howard E. ; Schaefer, Gail H. ; Gilliland, Ronald L. ; Holberg, Jay B. ; Mason, Brian D. ; Lindenblad, Irving W. ; Seitz-Mcleese, Miranda ; Arnett, W. David ; Demarque, Pierre ; Spada, Federico ; Young, Patrick A. ; Barstow, Martin A. ; Burleigh, Matthew R. ; Gudehus, Donald. / The Sirius System and Its Astrophysical Puzzles : Hubble Space Telescope and Ground-based Astrometry. In: Astrophysical Journal. 2017 ; Vol. 840, No. 2.
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abstract = "Sirius, the seventh-nearest stellar system, is a visual binary containing the metallic-line A1 V star Sirius A, the brightest star in the sky, orbited in a 50.13 year period by Sirius B, the brightest and nearest white dwarf (WD). Using images obtained over nearly two decades with the Hubble Space Telescope (HST), along with photographic observations covering almost 20 years and nearly 2300 historical measurements dating back to the 19th century, we determine precise orbital elements for the visual binary. Combined with the parallax and the motion of the A component, these elements yield dynamical masses of 2.063 ± 0.023 M⊙ and 1.018 ± 0.011 M⊙ for Sirius A and B, respectively. Our precise HST astrometry rules out third bodies orbiting either star in the system, down to masses of ∼15-25 MJup. The location of Sirius B in the Hertzsprung-Russell diagram is in excellent agreement with theoretical cooling tracks for WDs of its dynamical mass, and implies a cooling age of ∼126 Myr. The position of Sirius B on the mass-radius plane is also consistent with WD theory, assuming a carbon-oxygen core. Including the pre-WD evolutionary timescale of the assumed progenitor, the total age of Sirius B is about 228 ±10 Myr. We calculated evolutionary tracks for stars with the dynamical mass of Sirius A, using two independent codes. We find it necessary to assume a slightly subsolar metallicity, of about 0.85 Z⊙, to fit its location on the luminosity-radius plane. The age of Sirius A based on these models is about 237-247 Myr, with uncertainties of ±15 Myr, consistent with that of the WD companion. We discuss astrophysical puzzles presented by the Sirius system, including the probability that the two stars must have interacted in the past, even though there is no direct evidence for this and the orbital eccentricity remains high.",
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Bond, HE, Schaefer, GH, Gilliland, RL, Holberg, JB, Mason, BD, Lindenblad, IW, Seitz-Mcleese, M, Arnett, WD, Demarque, P, Spada, F, Young, PA, Barstow, MA, Burleigh, MR & Gudehus, D 2017, 'The Sirius System and Its Astrophysical Puzzles: Hubble Space Telescope and Ground-based Astrometry', Astrophysical Journal, vol. 840, no. 2, 70. https://doi.org/10.3847/1538-4357/aa6af8

The Sirius System and Its Astrophysical Puzzles : Hubble Space Telescope and Ground-based Astrometry. / Bond, Howard E.; Schaefer, Gail H.; Gilliland, Ronald L.; Holberg, Jay B.; Mason, Brian D.; Lindenblad, Irving W.; Seitz-Mcleese, Miranda; Arnett, W. David; Demarque, Pierre; Spada, Federico; Young, Patrick A.; Barstow, Martin A.; Burleigh, Matthew R.; Gudehus, Donald.

In: Astrophysical Journal, Vol. 840, No. 2, 70, 10.05.2017.

Research output: Contribution to journalArticle

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T2 - Hubble Space Telescope and Ground-based Astrometry

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AU - Schaefer, Gail H.

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AU - Holberg, Jay B.

AU - Mason, Brian D.

AU - Lindenblad, Irving W.

AU - Seitz-Mcleese, Miranda

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AU - Demarque, Pierre

AU - Spada, Federico

AU - Young, Patrick A.

AU - Barstow, Martin A.

AU - Burleigh, Matthew R.

AU - Gudehus, Donald

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