Abstract Details

Name: Ambreesh Khurana
Affiliation: Tata Institute of Fundamental Research
Conference ID: ASI2021_425
Title : Solving the mystery of the production of wide extremely low-mass white dwarf binaries
Authors and Co-Authors : Ambreesh Khurana (Tata Institute of Fundamental Research), Chirag Chawla (Tata Institute of Fundamental Research), Sourav Chatterjee (Tata Institute of Fundamental Research)
Abstract Type : Poster
Abstract Category : Stars, ISM and Galaxy
Abstract : Extremely low-mass white dwarfs (ELM-WDs; M ≲ 0.3 M☉) cannot be produced via single stellar evolution within a Hubble time. These strange WDs are thought to be remnants of stars whose evolution got cut off when it was in the red giant branch (RGB) due to mass transfer (MT) to a close companion. Almost all observed ELM-WDs have companions in tight orbits with a median orbital period P ≈ 5.4 hr (Brown et al. 2016) giving credence to the above theoretical understanding of their formation. A recent detection of an ELM-WD in a wide orbit (P ≈ 450 day) with a 1.1 M☉ main-sequence star (Masuda et al. 2019) challenges this understanding. Its semi-major axis is at least an order of magnitude too large for it to have formed via MT during RGB. We propose that a typical ELM-WD binary formed inside a star cluster got dynamically modified and subsequently ejected from the cluster to create the observed wide ELM-WD--MS binary. Using millions of N-body simulations we show that strong non-resonant double exchange binary-binary encounters inside a star cluster can convert a typical tight-orbit ELM-WD binary into a wide ELM-WD binary similar to the one observed. We show that star clusters of mass ~ 10^4 M☉ are most efficient for our scenario. We further find that the production rate of wide ELM-WD binaries is 1.6 x 10^-6 Gyr^-1 per regular ELM-WD binary inside a cluster of mass 10^5 M☉. I will present our key results in my talk.