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arXiv · 2511.02523

Dynamical Masses and Radiative Transfer Modeling of HD 698: a Be Binary in Evolutionary Transition

Ilfa A. Gabitova·Alex C. Carciofi·Tajan H. de Amorim·Mark Suffak·Anatoly S. Miroshnichenko·Sergey V. Zharikov·Amanda C. Rubio·Steve Danford·Alicia N. Aarnio·Peter Prendergast·Richard J. Rudy·Richard C. Puetter·R. Brad Perry·Aldiyar T. Agishev·Nadezhda L. Vaidman·Serik A. Khokhlov
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Abstract

We present a detailed analysis of the early post-mass-transfer binary HD 698 (V742 Cas) combining high-resolution optical spectroscopy, long-baseline interferometry, and radiative-transfer modeling. Counter-phased radial-velocity curves yield a circular orbit with P=55.927+/-0.001 d and component masses M_Be=7.48+/-0.07 M_sun and M_comp=1.23+/-0.02 M_sun. The Be primary is traced by broad H alpha wings, while narrow metallic absorption lines arise from a slowly rotating companion. The interferometric separation implies a dynamical distance of 888+/-5 pc. The spectral energy distribution is reproduced with E(B-V)=0.321+/-0.016 and a viscous decretion disk of base density rho_0~5x10^-12 g cm^-3 at r=R_eq, declining radially as rho(r)~r^-n with n=3.0. The companion is luminous and inflated, with T_eff=10.0(+0.2,-0.1) kK, R_comp=13.1+/-0.2 R_sun, and log(L/L_sun)=3.19, contributing significantly to the flux (L_comp/L_Be~0.3). Spectral line mismatches further suggest a hydrogen-poor, CNO-processed atmosphere, consistent with a stripped-envelope star. HD 698 thus adds to the emerging class of Be+bloated OB binaries, capturing a brief post-mass-transfer phase when the donor remains spectroscopically detectable prior to the subdwarf stage.

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Ilfa A. Gabitova, Alex C. Carciofi, Tajan H. de Amorim, Mark Suffak, Anatoly S. Miroshnichenko, Sergey V. Zharikov, Amanda C. Rubio, Steve Danford, Alicia N. Aarnio, Peter Prendergast, Richard J. Rudy, Richard C. Puetter, R. Brad Perry, Aldiyar T. Agishev, Nadezhda L. Vaidman, Serik A. Khokhlov. 2025-11-04. Dynamical Masses and Radiative Transfer Modeling of HD 698: a Be Binary in Evolutionary Transition. https://doi.org/10.3847/1538-4357/ae17bf

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