Close stellar binary systems by grazing envelope evolution

TL;DR

This paper proposes a grazing envelope evolution (GEE) process where a stellar companion grazes a giant star's envelope, accretes mass at high rates, launches jets to remove envelope material, and forms a close binary system, offering an alternative to traditional common envelope evolution.

Contribution

It introduces the GEE mechanism as a new pathway for close binary formation, involving high accretion rates and jet activity to prevent full envelope engulfment.

Findings

GEE can produce close binary systems without full envelope immersion.

High accretion rates and jet launching prevent common envelope formation.

GEE events may be observable as intermediate luminosity optical transients.

Abstract

I suggest a spiral-in process by which a stellar companion graze the envelope of a giant star while both the orbital separation and the giant radius shrink simultaneously, and a close binary system is formed. The binary system might be viewed as evolving in a constant state of `just entering a common envelope (CE) phase'. In cases where this process takes place it can be an alternative to the CE evolution where the secondary star is immerses in the giant's envelope. The grazing envelope evolution (GEE) is made possible only if the companion manages to accrete mass at a high rate and launch jets that remove the outskirts of the giant envelope, hence preventing the formation of a CE . The high accretion rate is made possible by the accretion disk that launches jets that efficiently carry the excess angular momentum and energy from the accreted mass. The orbital decay itself is caused by the gravitational interaction of the secondary star with the envelope inward to its orbit, i.e., dynamical friction (gravitational tide). Mass loss through the second Lagrangian point can carry additional angular momentum and envelope mass. The GEE lasts for tens to hundreds of years. The high accretion rate with peaks lasting months to years might lead to a bright object termed intermediate luminosity optical transient (ILOT; Red Novae; Red Transients). A bipolar nebula and/or equatorial ring are formed around the binary remnant