The enigmatic multiple star VV Ori

Abstract

New photometry, including TESS data, have been combined with recent spectroscopic observations of the Orion Ib pulsating triple-star system VV Ori. This yields a revised set of absolute parameters with increased precision. Two different programs were utilized for the light curve analysis, with results in predictably close agreement. The agreement promotes confidence in the analysis procedures. The spectra were analysed using the {\sc FDBinary} program. The main parameters are as follows: $M_1 = 11.6 \pm 0.14$ and $M_2 = 4.8 \pm 0.06$ (M$_\odot$). We estimate an approximate mass of the wide companion as $M_3 = 2.0 \pm 0.3$ M$_\odot$. Similarly, $R_{1} = 5.11 \pm 0.03$, $R_2 = 2.51 \pm 0.02$, $R_3 = 1.8 \pm 0.1$ (R$_\odot$); $T_{\rm e 1} = 26600 \pm 300$, $T_{\rm e 2} = 16300 \pm 400$ and $T_{\rm e 3} = 10000 \pm 1000$ (K). The close binary's orbital separation is $a= 13.91$ (R$_\odot$); its age is $8 \pm 2$ (Myr) and its photometric distance is $396 \pm 7$ pc. The primary's $\beta$ Cep type oscillations support these properties and confirm our understanding of its evolutionary status. Examination of the well-defined $\lambda$6678 He I profiles reveals the primary to have a significantly low projected rotation: some 80\% of the synchronous value. This can be explained on the basis of the precession of an unaligned spin axis. This proposal can resolve also observed variations of the apparent inclination and address other longer-term irregularities of the system reported in the literature. This topic invites further observations and follow-up theoretical study of the dynamics of this intriguing young multiple star.Comment: 17 pages, 15 figures, 14 tables, accepted by MNRA