The Sirius System and Its Astrophysical Puzzles: Hubble Space Telescope and Ground-based Astrometry
- Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)
- The CHARA Array of Georgia State University, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Lunar and Planetary Laboratory, University of Arizona, 1541 E. University Boulevard, Tucson, AZ 85721 (United States)
- U.S. Naval Observatory, 3450 Massachusetts Avenue, Washington, DC 20392 (United States)
- Steward Observatory, 933 N. Cherry Ave., University of Arizona, Tucson, AZ 85721 (United States)
- Department of Astronomy, Yale University, Box 208101, New Haven, CT 06520 (United States)
- Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482, Potsdam (Germany)
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States)
- Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom)
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States)
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{sub ⊙} and 1.018±0.011 M{sub ⊙} 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 M{sub Jup}. 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{sub ⊙}, 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.
- OSTI ID:
- 22872736
- Journal Information:
- Astrophysical Journal, Vol. 840, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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