Long-term monitoring of theta1 OriC: the spectroscopic orbit and an improved rotational period

TL;DR

This study presents long-term spectroscopic monitoring of theta1 OriC, refining its rotational period and detecting secular radial velocity changes, contributing to understanding its magnetic and rotational properties.

Contribution

The paper combines extensive data to improve the rotational period estimate and analyze long-term radial velocity trends of theta1 OriC.

Findings

Evidence for secular radial velocity change consistent with the interferometric orbit

Refined the stellar rotational period of theta1 OriC

Detected potential period changes in the near future

Abstract

The young O-type star theta1 OriC, the brightest star of the Trapezium cluster in Orion, is one of only two known magnetic rotators among the O stars. However, not all spectroscopic variations of this star can be explained by the magnetic rotator model. We present results from a long-term monitoring to study these unexplained variations and to improve the stellar rotational period. We want to study long-term trends of the radial velocity of theta1 OriC, to search for unusual changes, to improve the established rotational period and to check for possible period changes. We combine a large set of published spectroscopic data with new observations and analyze the spectra in a homogeneous way. We study the radial velocity from selected photo-spheric lines and determine the equivalent width of the Halpha and HeII4686 lines. We find evidence for a secular change of the radial velocity of theta1 OriC that is consistent with the published interferometric orbit. We refine the rotational period of theta1 OriC and discuss the possibility of detecting period changes in the near future.