Detectability of deuterium in spectra of early-type stars

Context . Deuterium is easily destroyed in stellar interiors through nuclear fusion. It is therefore usually not expected to be present in stellar photospheres. Early-type stars, with radiative envelopes that mix slowly, may provide a favourable environment for the survival of recently accreted deuterium. Aims . In this study, we explore the detectability of deuterium in B-, A-, and F-type stars, which possess radiative envelopes that can delay the mixing and destruction of recently accreted material. Methods . We used synthetic spectra to generate model observations including deuterium, focusing on Balmer line regions, for stars with effective temperatures between 7500 K and 12 500 K and a surface gravity of log g = 4.0. To assess the detectability of deuterium, we employed a Markov chain Monte Carlo framework over a range of signal-to-noise ratios between 100 and 1000. We then applied this method to observed spectra of the A9 star HD 32115 and the B9.5 star 21 Peg. Results . We show how detection limits of deuterium abundance depend on signal-to-noise ratio, effective temperature, and projected rotational velocity. For example, for a 10000 K star, the detection limit decreases from D/H = −4.6 dex to −5.5 dex, as the signal-to-noise ratio increases from 100 to 1000. For HD 32115, we find an upper limit of D/H < −5.5 dex, and for 21 Peg < −4.9 dex. We conclude that the detection of deuterium on early-type stars may be possible in some heavily accretion-contaminated cases, providing a new diagnostic tool for the study of proto- or exo-planetary material.