tokens: Double Star Catalog (WDS; Mason et al. 2001 ), a compilation of all published astrometric measurements of visual binaries. In response, the USNO group assembled all of the data on 40 Eri BC contained in the WDS. We also provided them with a precise measurement based on archival Hubble Space Telescope ( HST ) images obtained in 2006. Moreover, and crucially, in early 2017 they obtained two new high-precision observations with the speckle camera on the 26 inch telescope at the USNO in Washington, D.C. From these sources, there are 22 new measurements since the last one listed by H74 , covering 1974.8 to 2017.2—as well as 158 earlier observations between 1851.1 and 1973.8. Using these data, Mason et al. ( 2017 , hereafter MHM17 ) have computed updated elements for the 40 Eri BC orbit, leading to a significant revision of the dynamical masses. Although the semimajor axis is nearly unchanged from H74 , the new elements lead to a reduction in the orbital period to P = 230.29 ± 0.68 year—a 20% increase in P −2 , and thus in the masses, compared to H74 . The new dynamical mass for 40 Eri B based on the MHM17 analysis and the 2007 Hipparcos parallax is 0.573 ± 0.018 M . In the remainder of this paper, we will also re-evaluate other parameters of the WD, and then discuss the astrophysical implications of these new results. 4. Astrophysical Parameters of 40 Eri B The most precise method to determine the atmospheric parameters ( T eff and log g ) of DA WDs is the spectroscopic technique (Bergeron et al. 1992 ; hereafter BSL92 ; Liebert et al. 2005 ; hereafter LBH05 ; GBR11 ), wherein the observed Balmer line profiles are compared with predictions of modern model atmospheres using χ 2 minimization. The model atmospheres and synthetic spectra we use are similar to the pure-hydrogen LTE models described in Tremblay Bergeron ( 2009 , and references therein). In the case of 40 Eri B, the atmosphere is purely radiative, and thus the solution does not depend on uncertainties in the treatment of convective energy transport. As described in Section 2 (and in BSL92 , their Section 6.4 ), 40 Eri B, with a directly measured dynamical mass, is a key object to test the validity of the spectroscopic technique. We have available nine high signal-to-noise, medium-resolution (∼6 Å FWHM) spectra of 40 Eri B obtained over the past 25 years, mostly with the Steward Observatory 2.3 m telescope at Kitt Peak; details of these spectra are given by GBR11 . The individual spectroscopic determinations of T eff and log g from these spectra are plotted in Figure 1 . The standard deviations (combined in quadrature with the formal internal errors of the fits) are σ ( T eff ) = 220 K and σ (log g ) = 0.036, which are represented by the 1 σ and 2 σ ellipses in Figure 1 . These dispersions are similar to the typical external errors of 1.4% in T eff and 0.042 dex in log g found by LBH05 in fitting DA spectra (values corrected by Bédard et al. 2017 for a minor error in LBH05 ). By
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