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The "Giraffe": Discovery of a 2−3 M_⊙ dark companion to a stripped red giant

Jayasinghe, T. and Thompson, Todd A. and Kochanek, C. S. and Stanek, K. Z. and Rowan, D. M. and Martin, D. V. and Vallely, P. J. and Hinkle, J. T. and Huber, D. and Isaacson, H. and Tayar, J. and Auchettl, K. and Ilyin, I. and Howard, A. W. and Badenes, C. (2022) The "Giraffe": Discovery of a 2−3 M_⊙ dark companion to a stripped red giant. . (Unpublished)

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We report the discovery of a massive ∼2−3 M⊙ object as a binary companion to 2M04123153+6738486 (2M0412). 2M0412 is an evolved (T_(eff,giant) ≃ 4200 K), luminous (L_(giant) ≃ 230 L_⊙) red giant in a circular P = 81.2 d binary. 2M0412 is a known variable star previously classified as a semi-regular variable. The ASAS-SN, ATLAS, TESS and ZTF light curves show that the giant is a nearly Roche lobe filling ellipsoidal variable with an inclination of 41.9∘ ± 0.1∘, a mass ratio of q ≃ 0.20 ± 0.01, a companion mass of M_(comp) = 2.97 ± 0.02 M_⊙, and a giant mass of M_(giant) = 0.60 ± 0.01 M_⊙ for a distance of ≃4 kpc. The mass of the giant indicates that its envelope is stripped. The cross-correlation functions of the Keck/HIRES and LBT/PEPSI spectra show a second RV signal implying a consistent mass ratio of q ≃ 0.20 ± 0.01. We also identify an orbital phase dependent, broad Hα emission line. The simplest explanation for the massive companion is a single mass-gap black hole or a high mass neutron star. A sufficiently faint stellar companion can only be made feasible by significantly reducing the distance to ≃3.5 kpc while simultaneously increasing the mass ratio to q ≃ 0.3, despite the multiple lines of evidence for q ≃ 0.2.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Jayasinghe, T.0000-0002-6244-477X
Thompson, Todd A.0000-0003-2377-9574
Kochanek, C. S.0000-0001-6017-2961
Rowan, D. M.0000-0003-2431-981X
Martin, D. V.0000-0002-7595-6360
Vallely, P. J.0000-0001-5661-7155
Hinkle, J. T.0000-0001-9668-2920
Huber, D.0000-0001-8832-4488
Isaacson, H.0000-0002-0531-1073
Tayar, J.0000-0002-4818-7885
Auchettl, K.0000-0002-4449-9152
Ilyin, I.0000-0002-0551-046X
Howard, A. W.0000-0001-8638-0320
Badenes, C.0000-0003-3494-343X
Alternate Title:The "Giraffe": Discovery of a 2−3 M⊙ dark companion to a stripped red giant
Additional Information:We thank Dr. J. Strader for a careful reading of this manuscript. We thank Dr. J. J. Eldridge for useful discussions on the BPASS models. We thank Dr. Marc Pinsonneault and Lyra Cao for useful discussions. We thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grants GBMF5490 and GBMF10501 to the Ohio State University, and also funded in part by the Alfred P. Sloan Foundation grant G-2021-14192. TJ, KZS and CSK are supported by NSF grants AST-1814440 and AST-1908570. TJ acknowledges support from the Ohio State Presidential Fellowship. TAT is supported in part by NASA grant 80NSSC20K0531. TAT acknowledges previous support from Scialog Scholar grant 24216 from the Research Corporation, from which this effort germinated. J.T.H. is supported by NASA award 80NSSC21K0136. D.H. acknowledges support from the Alfred P. Sloan Foundation, the National Aeronautics and Space Administration (80NSSC18K1585, 80NSSC19K0379), and the National Science Foundation (AST-1717000). CB acknowledges support from the National Science Foundation grant AST-1909022. Parts of this research were supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013 and the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav), through project number CE170100004. Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU) / University of Tokyo, the Korean Participation Group, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatories of China, New Mexico State University, New York University, University of Notre Dame, Observatário Nacional / MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autónoma de México, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium. This publication makes use of data products from the Two Micron All Sky Survey, as well as data products from the Wide-field Infrared Survey Explorer. This research was also made possible through the use of the AAVSO Photometric All-Sky Survey (APASS), funded by the Robert Martin Ayers Sciences Fund. The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona Board of Regents; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, The Leibniz Institute for Astrophysics Potsdam, and Heidelberg University; The Ohio State University, representing OSU, University of Notre Dame, University of Minnesota and University of Virginia. PEPSI was made possible by funding through the State of Brandenburg (MWFK) and the German Federal Ministry of Education and Research (BMBF) through their Verbundforschung grants 05AL2BA1/3 and 05A08BAC. This research is based on observations made with the Neil Gehrels Swift Observatory, obtained from the MAST data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This paper includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. We thank the ZTF and ATLAS projects for making their light curve data publicly available. This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France. This research also made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013, 2018). DATA AVAILABILITY. The photometric data are all publicly available. The spectra will be shared on reasonable request to the corresponding author.
Group:Astronomy Department, Zwicky Transient Facility
Funding AgencyGrant Number
Gordon and Betty Moore FoundationGBMF5490
Gordon and Betty Moore FoundationGBMF10501
Alfred P. Sloan FoundationG-2021-14192
Ohio State UniversityUNSPECIFIED
Scialog Fellow of Research Corporation24216
Australian Research CouncilCE170100013
Australian Research CouncilCE170100004
Department of Energy (DOE)UNSPECIFIED
Participating InstitutionsUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Robert Martin Ayers Sciences FundUNSPECIFIED
LBT Corporation PartnersUNSPECIFIED
Brandenburg Ministerium für Wissenschaft, Forschung und KulturUNSPECIFIED
Bundesministerium für Bildung und Forschung (BMBF)05AL2BA1/3
Bundesministerium für Bildung und Forschung (BMBF)05A08BAC
NASANAS 5-26555
W. M. Keck FoundationUNSPECIFIED
ZTF partner institutionsUNSPECIFIED
Subject Keywords:stars: black holes – (stars:) binaries: spectroscopic – stars: individual: 2MASS J04123153+6738486
Record Number:CaltechAUTHORS:20220228-183214006
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113634
Deposited By: George Porter
Deposited On:02 Mar 2022 00:05
Last Modified:02 Mar 2022 00:05

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