Astrophysical Implications of a New Dynamical Mass for the Nearby White Dwarf 40 Eridani B

Abstract

The bright, nearby DA-type white dwarf (WD) 40 Eridani B is orbited by the M dwarf 40 Eri C, allowing determination of the WD's mass. Until recently, however, the mass depended on orbital elements determined four decades ago, and that mass was so low that it created several astrophysical puzzles. Using new astrometric measurements, the binary-star group at the U.S. Naval Observatory has revised the dynamical mass upward, to 0.573 ± 0.018 M ⊙ . In this paper we use model-atmosphere analysis to update other parameters of the WD, including effective temperature, surface gravity, radius, and luminosity. We then compare these results with WD interior models. Within the observational uncertainties, theoretical cooling tracks for CO-core WDs of its measured mass are consistent with the position of 40 Eri B in the H-R diagram; equivalently, the theoretical mass-radius relation (MRR) is consistent with the star's location in the massradius plane. This consistency is, however, achieved only if we assume a "thin" outer hydrogen layer, with q H = M H /M WD ≃ 10 −10 . We discuss other evidence that a significant fraction of DA WDs have such thin H layers, in spite of expectation from canonical stellar-evolution theory of "thick" H layers with q H ≃ 10 −4 . The cooling age of 40 Eri B is ∼122 Myr, and its total age is ∼1.8 Gyr. We present the MRRs for 40 Eri B and three other nearby WDs in visual binaries with precise mass determinations, and show that the agreement of current theory with observation is excellent in all cases.

Effect of minimal length uncertainty on the mass–radius relation of white dwarfs

“…Since most white dwarfs occurring in Nature have their cores composed of these elements, they are expected to have masses much lower than 1.46 M ⊙ and radii much larger than 650 km. These conclusions are consistent with the observations of non-magnetic white dwarfs that are usually found to be in the mass range from 0.17 M ⊙ [21] to 1.33 M ⊙ [44,43,26,20] with radii ranging from 0.0153 R ⊙ (10644 km) to 0.0071 R ⊙ (4939 km) [40,41,42,7].…”

The McDonald Accelerating Stars Survey (MASS): White Dwarf Companions Accelerating the Sun-like Stars 12 Psc and HD 159062

“…These Sirius-like benchmark systems are valuable because they can be directly characterized with photometry and spectroscopy-yielding an effective temperature, bolometric luminosity, radius, and spectral classification -and the total system age and progenitor metallicity can be determined from the host star. These combined with a mass measurement provide fundamental tests of white dwarf massradius relations and cooling models (e.g., Bond et al 2017b;Bond et al 2017a;Serenelli et al 2020). Follow-up spectroscopy and multiwavelength photometry of 12 Psc B and HD 159062 B are needed to better characterize these companions and carry out robust tests of cooling models.…”

“…Dynamical masses represent anchor points of stellar astronomy. Direct mass measurements are important to calibrate models of stellar and substellar evolution, especially during phases in which physical properties change significantly with time-for example throughout the pre-main-sequence, along the evolved subgiant and giant branches, and as white dwarfs, brown dwarfs, and giant planets cool and fade over time (e.g., Hillenbrand & White 2004;Konopacky et al 2010;Bond et al 2017a;Dupuy & Liu 2017;Parsons et al 2017;Snellen & Brown 2018;Brandt et al 2019;Simon et al 2019). Masses are traditionally determined with absolute astrometry of visual binaries or radial-velocity (RV) monitoring of either eclipsing or visual binaries.…”

Weighing stars from birth to death: mass determination methods across the HRD

“…The mass-radius relation for white dwarfs is relatively well constrained from direct eclipsing binary measurements (Parsons et al 2017), which yield 2.4% median uncertainty for the masses, and from determinations of dynamical masses in the Sirius, Procyon, and 40 Eri systems (Bond et al 2015(Bond et al , 2017a. In the latter case, modelling the stellar flux is generally needed to constrain the white dwarf radius, although one exception is when a gravitational redshift is available (Joyce et al 2018;Pasquini et al 2019).…”