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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 and 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–. 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 , 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. [ABSTRACT FROM AUTHOR]

The nearby star Procyon is a visual binary containing the F5 IV-V subgiant Procyon A, orbited in a 40.84-year period by the faint DQZ white dwarf (WD) Procyon B. Using images obtained over two decades with the Hubble Space Telescope, and historical measurements back to the 19th century, we have determined precise orbital elements. Combined with measurements of the parallax and the motion of the A component, these elements yield dynamical masses of 1.478 ± 0.012 M⊙ and 0.592 ± 0.006 M⊙ for A and B, respectively. The mass of Procyon A agrees well with theoretical predictions based on asteroseismology and its temperature and luminosity. Use of a standard core-overshoot model agrees best for a surprisingly high amount of core overshoot. Under these modeling assumptions, Procyon A’s age is ∼2.7 Gyr. Procyon B’s location in the H-R diagram is in excellent agreement with theoretical cooling tracks for WDs of its dynamical mass. Its position in the mass–radius plane is also consistent with theory, assuming a carbon–oxygen core and a helium-dominated atmosphere. Its progenitor’s mass was 1.9–2.2 M⊙, depending on its amount of core overshoot. Several astrophysical puzzles remain. In the progenitor system, the stars at periastron were separated by only ∼5 AU, which might have led to tidal interactions and even mass transfer; yet there is no direct evidence that these have occurred. Moreover the orbital eccentricity has remained high (∼0.40). The mass of Procyon B is somewhat lower than anticipated from the initial-to-final-mass relation seen in open clusters. The presence of heavy elements in its atmosphere requires ongoing accretion, but the place of origin is uncertain. [ABSTRACT FROM AUTHOR]