Discovery of an M-type Companion to the Herbig Ae Star V1787 Ori

TL;DR

This paper reports the discovery of a low-mass M-type companion to the Herbig Ae star V1787 Ori, establishing it as a wide binary system with a rare low mass ratio, and discusses its formation mechanisms.

Contribution

The study identifies and characterizes a new M-type companion to V1787 Ori, revealing a rare low mass ratio in Herbig Ae/Be binaries and providing insights into wide binary formation.

Findings

V1787 Ori B is an M5 ± 2 star with a mass of ~0.39 M_sun.

V1787 Ori forms a wide binary with a separation of 2577 au.

The system has a low mass ratio of 0.23, uncommon in similar binaries.

Abstract

The intermediate mass Herbig Ae star V1787 Ori is a member of the L1641 star-forming region in the Orion A molecular cloud. We report the detection of an M-type companion to V1787 Ori at a projected separation of 6.66" (corresponding to 2577 au), from the analysis of VLT/NACO adaptive optics $K_s$-band image. Using astrometric data from Gaia DR2, we show that V1787 Ori A and B share similar distance ($d$ $\sim$ 387 pc) and proper motion, indicating that they are physically associated. We estimate the spectral type of V1787 Ori B to be M5 $\pm$ 2 from color--spectral type calibration tables and template matching using SpeX spectral library. By fitting PARSEC models in the Pan-STARRS color-magnitude diagram, we find that V1787 Ori B has an age of 8.1$^{+1.7}_{-1.5}$ Myr and a mass of 0.39$^{+0.02}_{-0.05}$ $M_\odot$. We show that V1787 Ori is a pre-main sequence wide binary system with a mass ratio of 0.23. Such a low mass ratio system is rarely identified in Herbig Ae/Be binary systems. We conclude this work with a discussion on possible mechanisms for the formation of V1787 Ori wide binary system.