The binary star θ1 Ori C: orbital elements, evolutionary parameters and chemical composition

Abstract

About 200 eshelle spectra obtained with high spectral resolution and S/N ratio at 1-m and 6-m SAO RAS telescopes were used to investigate the radial velocity variability with time in both components of the θ1 Ori C binary system during its periastron passage. The quality of our spectra allowed us to find a methodical approach for the spectroscopic study of orbital motions of both components and to select lines suitable for this goal. The analysis has shown that the He II λ 4541, 5411 lines are suitable in case of the primary component and the Si III λ 4552 line — the secondary component. Radial velocities thus measured for both components from the spectra obtained over 20 years, along with the interferometric observations of relative positions of the components were used for construction of a combined 3D orbit of the system to derive its reliable orbital parameters. Orbital elements were determined with a good accuracy. For the dynamical distance we have found a value of about d = 415 ± 6 pc, and for the system mass – Msys = 44.8 ± 4.5 M⊙. A special method calculating the synthetic spectra in binaries taking into account the contribution of both components in their radiation is applied for the theoretical analysis of θ1 Ori C observable spectra. Atmospheric parameters are refined for the primary and are for the first time determined for the secondary component. The chemical composition of θ1 Ori C is determined, which coincides with the chemical composition of its surrounding Nebula.

Chemistry in Externally FUV-irradiated Disks in the Outskirts of the Orion Nebula Cluster

“…We have targeted two protoplanetary disk systems located in the ONC at a distance of 414 pc (e.g., Rzaev et al 2021). The two systems, 216-0939 and 253-1536A/B, are located in the outskirts of the ONC (projected distance of >0.9 pc from θ 1 Ori C), where the radiation field is estimated to be <10 3 G 0 (Mookerjea et al 2003), where G 0 is the average strength of the integrated ISRF; G 0 ≈ 1.6 × 10 −3 erg cm −2 s −1 (Draine 1978).…”

“…In this work, we present observations of two protoplanetary disks around pre-main sequence stars located in the outskirts of the Orion Nebula Cluster (ONC), which is the closest (∼414 pc) massive star-forming region (Menten et al 2007;Rzaev et al 2021). Our aim is to investigate the possible differences between the chemistry of isolated disks and of externally irradiated disks.…”

“…The ONC is an excellent laboratory to study these kinds of sources. This rich cluster has thousands of stars, but the radiation field is dominated by a single star: θ 1 Ori C (O'dell & Wen 1994;Smith et al 2005;Ricci et al 2008), a young (∼1 Myr; Hillenbrand 1997), massive (45 M e ; Kraus et al 2009;Rzaev et al 2021), O6-type star (O'Dell et al 2017. Hubble Space Telescope (HST) observations revealed hundreds of disks in Orion that are externally irradiated, some of them surrounded by a cometary ionization front-the so-called proplyds (O'dell et al 1993;O'dell & Wen 1994;Ricci et al 2008;Eisner et al 2018).…”