\'Echelle Spectroscopy of the Chemically Peculiar Star $\theta^1$ Ori F

TL;DR

This study presents the first detailed spectral analysis of the chemically peculiar star θ¹ Ori F, revealing its elemental overabundances, spectral type, and potential non-membership in the Orion Trapezium, offering insights into CP star evolution.

Contribution

It provides the first measurement of θ¹ Ori F's radial velocity and detailed spectral classification, challenging its assumed association with the Orion Trapezium cluster.

Findings

θ¹ Ori F is a chemically peculiar star with overabundant silicon and phosphorus.

Radial velocity is approximately 24 km/s, with possible marginal variability.

The star is likely not a member of the Orion Trapezium cluster.

Abstract

We analyse \'Echelle spectra of $\theta^1$ Ori F obtained by us on six nights unevenly distributed along six years; we identify several hundred spectral lines and measure, for the first time, the star's heliocentric radial velocity. We also collect and discuss previously published photometry of $\theta^1$ OriF . We find that $\theta^1$ Ori F is a Chemically Peculiar (CP) star with overabundant silicon and phosphorus, and possibly other elements as well. From the singly ionised Fe, Cr and Ti lines we estimate its spectral type to be between B7 and B8. The radial velocity of $\theta^1$ Ori F is possibly marginally variable, with an average of $24 \pm 4.2$ kms, (standard deviation), in good agreement with the mean radial velocity of the Orion Nebula Cluster members, and about 5 kms smaller than the average of the other Trapezium components. We cast doubt on the coeval nature of this star relative to the other Trapezium components, and present arguments that almost certainly exclude its membership to the Orion Trapezium. $\theta^1$ Ori F turns out to be enigmatic in several respects, and is probably an important link for understanding the evolutionary stage at which the CP phenomenon sets on.