11-12 Gyr old White Dwarfs 30 parsecs Away
  We present a detailed model atmosphere analysis of two of the oldest stars
known in the solar neighborhood, the high proper motion white dwarfs SDSS
J110217.48+411315.4 (hereafter J1102) and WD 0346+246 (hereafter WD0346). We
present trigonometric parallax observations of J1102, which places it at a
distance of only 33.7 +- 2.0 pc. Based on the state of the art model
atmospheres, optical, near-, mid-infrared photometry, and distances, we
constrain the temperatures, atmospheric compositions, masses, and ages for both
stars. J1102 is an 11 Gyr old (white dwarf plus main-sequence age), 0.62 Msol
white dwarf with a pure H atmosphere and Teff = 3830 K. WD0346 is an 11.5 Gyr
old, 0.77 Msol white dwarf with a mixed H/He atmosphere and Teff = 3650 K. Both
stars display halo kinematics and their ages agree remarkably well with the
ages of the nearest globular clusters, M4 and NGC 6397. J1102 and WD0346 are
the closest examples of the oldest halo stars that we know of.
