A stripped helium star in the potential black hole binary LB-1

Abstract

The recently claimed discovery of a massive ($M_{\mathrm{BH}}=68_{-13}^{+11}{M}_{\odot }$) black hole in the Galactic solar neighborhood has led to controversial discussions because it severely challenges our current view of stellar evolution. A crucial aspect for the determination of the mass of the unseen black hole is the precise nature of its visible companion, the B-type star LS V+22 25. Because stars of different mass can exhibit B-type spectra during the course of their evolution, it is essential to obtain a comprehensive picture of the star to unravel its nature and, thus, its mass. To this end, we study the spectral energy distribution of LS V+22 25 and perform a quantitative spectroscopic analysis that includes the determination of chemical abundances for He, C, N, O, Ne, Mg, Al, Si, S, Ar, and Fe. Our analysis clearly shows that LS V+22 25 is not an ordinary main sequence B-type star. The derived abundance pattern exhibits heavy imprints of the CNO bi-cycle of hydrogen burning, that is, He and N are strongly enriched at the expense of C and O. Moreover, the elements Mg, Al, Si, S, Ar, and Fe are systematically underabundant when compared to normal main-sequence B-type stars. We suggest that LS V+22 25 is a stripped helium star and discuss two possible formation scenarios. Combining our photometric and spectroscopic results with the Gaia parallax, we infer a stellar mass of $1.1\pm 0.5M_{\odot }$. Based on the binary system's mass function, this yields a minimum mass of $2-3M_{\odot }$ for the compact companion, which implies that it may not necessarily be a black hole but a massive neutron- or main sequence star. The star LS V+22 25 has become famous for possibly having a very massive black hole companion. However, a closer look reveals that the star itself is a very intriguing object. Further investigations are necessary for complete characterization of this object.

Accepted for publication in A&A (Astronomy and Astrophysics)

References in corpus (41)

• The chemical composition of the Sun
• Gaia Data Release 2. Summary of the contents and survey properties
• Correcting for the Effects of Interstellar Extinction
• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• A 3D Dust Map Based on Gaia, Pan-STARRS 1 and 2MASS
• The Origin of Subdwarf B Star (I): the Formation Channels
• Gaia Data Release 2: Photometric content and validation
• The origin of sdB stars (II)
• Present-day cosmic abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models
• Spectroscopic Analysis of DA White Dwarfs: Stark Broadening of Hydrogen Lines Including Non-Ideal Effects
• The observed spiral structure of the Milky Way
• Discovery of a Candidate Black Hole - Giant Star Binary System in the Galactic Field
• New evolutionary sequences for extremely low mass white dwarfs: Homogeneous mass and age determinations, and asteroseismic prospects
• A detached stellar-mass black hole candidate in the globular cluster NGC 3201
• Spectrophotometric Libraries, Revised Photonic Passbands and Zero-points for UBVRI, Hipparcos and Tycho Photometry
• Milky Way Mass Models for Orbit Calculations
• A wide star-black-hole binary system from radial-velocity measurements
• Spectral models for binary products: Unifying Subdwarfs and Wolf-Rayet stars as a sequence of stripped-envelope stars
• A reanalysis of the Gaia Data Release 2 photometric sensitivity curves using HST/STIS spectrophotometry
• 3D kinematics of white dwarfs from the SPY project II
• Hot subdwarf binaries from the MUCHFUSS project - Analysis of 12 new systems and a study of the short-period binary population
• The ELM Survey. VII. Orbital Properties of Low Mass White Dwarf Binaries
• An ultra-massive fast-spinning white dwarf in a peculiar binary system
• The MUCHFUSS project - Searching for hot subdwarf binaries with massive unseen companions: Survey, target selection and atmospheric parameters
• Abundance studies of sdB stars using UV echelle HST/STIS spectroscopy
• The timescale of low-mass proto-helium white dwarf evolution
• A Metal-Rich Low-Gravity Companion to a Massive Millisecond Pulsar
• Hot subdwarf stars in close-up view I. Rotational properties of subdwarf B stars in close binary systems and nature of their unseen companions
• The orbits of subdwarf-B + main-sequence binaries. II. Three eccentric systems; BD+29 3070, BD +34 1543 and Feige 87
• Gaia Data Release 2 Catalogue of Extremely-low Mass White Dwarf Candidates
• The catalogue of radial velocity variable hot subluminous stars from the MUCHFUSS project
• Hot subdwarf stars in close-up view - III. Metal abundances of subdwarf B stars
• Hot subdwarf stars in close-up view - II. Rotational properties of single and wide binary subdwarf B stars
• A new method for an objective, ${\chi }^2$-based spectroscopic analysis of early-type stars
• The EREBOS project -- Investigating the effect of substellar and low-mass stellar companions on late stellar evolution
• A quantitative spectral analysis of 14 hypervelocity stars from the MMT survey
• Early type stars at high galactic latitudes II. Four evolved B-type stars of unusual chemical composition
• HD 49798: Its History of Binary Interaction and Future Evolution
• Quantitative spectral analysis of the sdB star HD 188112: a helium-core white dwarf progenitor
• Hot subdwarf wind models with accurate abundances I. Hydrogen dominated stars HD 49798 and BD+18${}^{\circ }$2647
• NLTE spectroscopic analysis of the ${}^3$He anomaly in subluminous B-type stars

Cited by in corpus (51)

• The 'hidden' companion in LB-1 unveiled by spectral disentangling
• A Unicorn in Monoceros: the $3M_{\odot }$ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate
• Properties of OB star-black hole systems derived from detailed binary evolution models
• Is HR 6819 a triple system containing a black hole? -- An alternative explanation
• Merger rate density of Population III binary black holes below, above, and in the pair-instability mass gap
• An X-ray quiet black hole born with a negligible kick in a massive binary within the Large Magellanic Cloud
• The Detection and Characterization of Be+sdO Binaries from HST/STIS FUV Spectroscopy
• A stripped-companion origin for Be stars: clues from the putative black holes HR 6819 and LB-1
• The Tarantula Massive Binary Monitoring VI: Characterisation of hidden companions in 51 single-lined O-type binaries, a flat mass-ratio distribution, and black-hole binary candidates
• Search for a Black Hole Binary in Gaia DR3 Astrometric Binary Stars with Spectroscopic Data
• Discovery of post-mass-transfer helium-burning red giants using asteroseismology
• Weighing in on black hole binaries with BPASS: LB-1 does not contain a 70M${}_{\odot }$ black hole
• Uncovering astrometric black hole binaries with massive main-sequence companions with Gaia
• Population Synthesis of Galactic Be-star Binaries with A Helium-star Companion
• Binarity at LOw Metallicity (BLOeM): a spectroscopic VLT monitoring survey of massive stars in the SMC
• Non-interacting black hole binaries with Gaia and LAMOST
• Search for Dormant Black Holes in Ellipsoidal Variables I. Revisiting the Expected Amplitudes of the Photometric Modulation
• Gaia Data Release 3: Ellipsoidal Variables with Possible Black-Hole or Neutron Star secondaries
• HR 6819 is a binary system with no black hole -- revisiting the source with infrared interferometry and optical integral field spectroscopy
• Stars stripped in binaries -- the living gravitational wave sources
• Astrometric excess noise in Gaia DR2 and the search for X-ray emitting binaries
• Astrometric excess noise in Gaia EDR3 and the search for X-ray binaries
• The X-ray emission of Be+stripped star binaries
• Data-driven spectroscopic estimates of absolute magnitude, distance and binarity -- method and catalog of 16,002 O- and B-type stars from LAMOST
• High Tide: A Systematic Search for Ellipsoidal Variables in ASAS-SN
• Gaia's Detectability of Black Hole-Main Sequence Star Binaries Formed in Open Clusters
• The B-type Binaries Characterisation Programme II. VFTS 291: A stripped star from a recent mass transfer phase
• Phase-dependent study of near-infrared disk emission lines in LB-1
• Birth of a Be star: an APOGEE search for Be stars forming through binary mass transfer
• Detectablity of Black Hole Binaries with Gaia: Dependence on Binary Evolution Models
• Probable Dormant Neutron Star in a Short-Period Binary System
• The "Giraffe": Discovery of a stripped red giant in an interacting binary with a $\sim 2M_{\odot }$ lower giant
• A search for compact object companions to high mass function single-lined spectroscopic binaries in Gaia DR3
• The spins of stripped B stars support magnetic internal angular momentum transport
• Hubble spectroscopy of LB-1: comparison with B+black-hole and Be+stripped-star models
• Search for Dormant Black Holes in Ellipsoidal Variables II. A Binary Modified Minimum Mass Ratio
• The mass distribution of stars stripped in binaries: The effect of metallicity
• To be or not to be a black hole: detailed binary population models as a sanity check
• The IACOB project XIII. Helium enrichment in O-type stars as a tracer of past binary interaction
• Newborn Be star systems observed shortly after mass transfer
• Galactic population of black holes in detached binaries with low-mass stripped helium stars: the case of LB-1 (LS~V+22~25)
• Detection of single-degenerate massive binaries with Gaia: The impact of blue supergiants, triples, mass precision, and high-precision parallax requirements
• Formation rate of LB-1-like systems through dynamical interactions
• Using radial velocities to reveal black holes in binaries: a test case
• HIP 15429: A newborn Be star on an eccentric binary orbit
• Everything that glitters is not gold: V1315 Cas is not a dormant black hole
• True Unicorns and False Positives: Simulated Probabilities of Dark Massive Companions to Bright Stars
• Two unseen massive white dwarf candidates in close binaries
• NGC 1850 BH1 is another stripped-star binary masquerading as a black hole
• The VLT-FLAMES survey of massive stars. NGC2004#115: A triple system hosting a possible short period B+BH binary
• EC 22536-5304: a lead-rich and metal-poor long-period binary