The "Giraffe": Discovery of a stripped red giant in an interacting binary with a ${\sim}2~M_\odot$ lower giant

T. Jayasinghe; Todd A. Thompson; C. S. Kochanek; K. Z. Stanek; D. M. Rowan; D. V. Martin; Kareem El-Badry; P. J. Vallely; J. T. Hinkle; D. Huber; H. Isaacson; J. Tayar; K. Auchettl; I. Ilyin; A. W. Howard; C. Badenes

doi:10.1093/mnras/stac2187

paper

The "Giraffe": Discovery of a stripped red giant in an interacting binary with a $\sim 2 M_{⊙}$ lower giant

arXiv:2201.11131 · doi:10.1093/mnras/stac2187

Abstract

We report the discovery of a stripped giant + lower giant binary, 2M04123153+6738486 (2M0412), identified during a search for non-interacting compact object-star binaries. 2M0412 is an evolved ( $T_{eff, giant} ≃ 4000$ K), luminous ( $L_{giant} ≃ 150 L_{⊙}$ ) red giant in a circular $P = 81.2$ day binary. 2M0412 is a known variable star previously classified as a semi-regular variable. The cross-correlation functions of follow-up Keck/HIRES and LBT/PEPSI spectra show an RV-variable second component with implied mass ratio $q = M_{giant} / M_{comp} ≃ 0.20 \pm 0.01$ . The ASAS-SN, ATLAS, TESS and ZTF light curves show that the giant is a Roche lobe filling ellipsoidal variable with an inclination of $49. 4^{\circ} \pm 0. 3^{\circ}$ , and a giant mass of $M_{giant} = 0.38 \pm 0.01 M_{⊙}$ for a distance of $≃ 3.7$ kpc. The mass of the giant indicates that its envelope has been stripped. The giant companion on the lower red giant branch has a mass of $M_{comp} = 1.91 \pm 0.03 M_{⊙}$ with $T_{eff, comp} ≃ 5000$ K, $L_{comp} ≃ 60 L_{⊙}$ and $R_{comp} ≃ 11 R_{⊙}$ . We also identify an orbital phase dependent, broad $H α$ emission line which could indicate ongoing accretion from the stripped red giant onto the companion.

arXiv commentRevised version of the paper following comments from the referee, submitted to MNRAS. arXiv admin note: text overlap with arXiv:2101.02212

The "Giraffe": Discovery of a stripped red giant in an interacting binary with a $\sim 2 M_{⊙}$ lower giant

Abstract

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The "Giraffe": Discovery of a stripped red giant in an interacting binary with a ∼2 M⊙​ lower giant

Abstract

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Cited by in corpus (11)

The "Giraffe": Discovery of a stripped red giant in an interacting binary with a $\sim 2 M_{⊙}$ lower giant