Quest for the upcoming periastron passage of an episodic dust maker and particle accelerating colliding wind binary: WR 125

Abstract

We have carried out a long term infrared and X-ray investigation of the colliding wind binary WR 125 (WC7 + O9III). The source was monitored using AstroSat−Soft X-ray Telescope and TIRCAM2 mounted at the back of 3.6 m Devasthal Optical Telescope. WR 125 appeared brighter in near infra-red K-band during the years 2017-2021 which is attributed to another episode of dust formation similar to the one reported during the likely periastron passage at the beginning of the 1990s. This is further supported by enhanced emission observed in W1 and W2 bands of WISE from 2018-19. By combining archival X-ray data sets with our new measurements, long-term variations have been noticed. The source reaches a lower emission state in June 2020 (close to the recent infrared maximum) which could be due to enhanced absorption of X-rays produced in the colliding wind region by the WC stellar wind close to the periastron in an eccentric orbit. The time interval between the previous and latest X-ray low states may indicate an orbital period of 28-29 years, in fair agreement with the recurrence time of episodic dust production. We also discuss published radio measurements in the context of a common picture based on a long period binary scenario. These results allow us to draw relevant guidelines for future multi-wavelength observations of WR 125.

TIFR Treasures for Astronomy from Ground to Space

“…It was made available to the Indian and Belgian astronomical community for scientific observations since May 2017. A number of important observations were carried out successfully since then (see, e.g., Anand et al 2020;Sharma et al 2020;Richichi et al 2020;Arora et al 2021). However, due to the availability of larger instruments, for instance, TANSPEC, ARIES-Devasthal Faint Object Spectrograph & Camera, and CCD imager, which can only be mounted on the axial port of DOT, it was decided to try out the TIRCAM2 camera at one of the side ports of DOT.…”