By two different methods , we show that LHS 4033 is an extremely massive white dwarf near its likely upper mass limit for destruction by unstable electron captures .
From the accurate trigonometric parallax reported herein , the effective temperature ( T _ { eff } = 10 , 900 K ) and the stellar radius ( R = 0.00368 R _ { \odot } ) are directly determined from the broad-band spectral energy distribution — the parallax method .
The effective temperature and surface gravity are also estimated independently from the simultaneous fitting of the observed Balmer line profiles with those predicted from pure-hydrogen model atmospheres — the spectroscopic method ( T _ { eff } = 10 , 760 K , \log g = 9.46 ) .
The mass of LHS 4033 is then inferred from theoretical mass-radius relations appropriate for white dwarfs .
The parallax method yields a mass estimate of 1.310–1.330 M _ { \odot } , for interior compositions ranging from pure magnesium to pure carbon , respectively , while the spectroscopic method yields an estimate of 1.318–1.335 M _ { \odot } for the same core compositions .
This star is the most massive white dwarf for which a robust comparison of the two techniques has been made .