A detailed non-LTE analysis of LB-1: Revised parameters and surface abundances

S. Simón-Díaz; J. Maíz Apellániz; D. J. Lennon; J. I. González Hernández; C. Allende Prieto; N. Castro; A. De Burgos; P. L. Dufton; A. Herrero; B. Toledo-Padrón; S. J. Smartt

doi:10.1051/0004-6361/201937318

A detailed non-LTE analysis of LB-1: Revised parameters and surface abundances

S. Simón-Díaz^*, J. Maíz Apellániz, D. J. Lennon, J. I. González Hernández, C. Allende Prieto, N. Castro, A. De Burgos, P. L. Dufton, A. Herrero, B. Toledo-Padrón, S. J. Smartt

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

18 Citations (Scopus)

Abstract

Context. It has recently been proposed that LB-1 is a binary system at 4 kpc consisting of a B-type star of 8 M⊙ and a massive stellar black hole (BH) of 70 M⊙ . This finding challenges our current theories of massive star evolution and formation of BHs at solar metallicity. Aims. Our objective is to derive the effective temperature, surface gravity, and chemical composition of the B-type component in order to determine its nature and evolutionary status and, indirectly, to constrain the mass of the BH. Methods. We use the non-LTE stellar atmosphere code FASTWIND to analyze new and archival high-resolution data. Results. We determine (Teff, log g) values of (14 000 ± 500 K, 3.50 ± 0.15 dex) that, combined with the Gaia parallax, imply a spectroscopic mass, from log g, of 3.2+2.1-1.9 M⊙ and an evolutionary mass, assuming single star evolution, of 5.2+0.3-0.6 M⊙ . We determine an upper limit of 8 km s-1 for the projected rotational velocity and derive the surface abundances; we find the star to have a silicon abundance below solar, and to be significantly enhanced in nitrogen and iron and depleted in carbon and magnesium. Complementary evidence derived from a photometric extinction analysis and Gaia yields similar results for Teff and log g and a consistent distance around 2 kpc. Conclusions. We propose that the B-type star is a slightly evolved main sequence star of 3-5 M⊙ with surface abundances reminiscent of diffusion in late B/A chemically peculiar stars with low rotational velocities. There is also evidence for CN-processed material in its atmosphere. These conclusions rely critically on the distance inferred from the Gaia parallax. The goodness of fit of the Gaia astrometry also favors a high-inclination orbit. If the orbit is edge-on and the B-type star has a mass of 3-5 M⊙ , the mass of the dark companion would be 4-5 M⊙ , which would be easier to explain with our current stellar evolutionary models.

Original language	English
Article number	L7
Number of pages	8
Journal	Astronomy and Astrophysics
Volume	634
Early online date	31 Jan 2020
DOIs	https://doi.org/10.1051/0004-6361/201937318
Publication status	Published - 01 Feb 2020

Bibliographical note

Funding Information:
Acknowledgements. We thank R.-P. Kudritzki for his interesting suggestions for improvement of the first version of this Letter. We thank J. Hernández for his help with Gaia DR2 data. S-SD, DJL, AdB, AHD and JMA acknowledges support from the Spanish Government Ministerio de Ciencia, Innovación y Uni-versidades through grants PGC2018-095 049-B-C22 and PGC-2018-091 3741-B-C22. JIGH acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2013 Ramón y Cajal program RYC-2013-14875. JIGH and CAP acknowledge financial support from the Spanish Ministry project MICIU AYA2017-86389-P. SJS acknowledges funding from STFC Grant ST/P000312/1. Based on observations made with the Telescopio Nationale Galileo (TNG) and the Gran Telescopio Canarias (GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Insti-tuto de Astrofs´ica de Canarias, in the island of La Palma. This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under

Funding Information:
contract with the National Aeronautics and Space Administration. Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAMOST is operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences.

Publisher Copyright:
© ESO 2020.

Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.

Keywords

Binaries: spectroscopic
Stars: abundances
Stars: black holes
Stars: early-type
Stars: fundamental parameters
Techniques: spectroscopic

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

Access to Document

10.1051/0004-6361/201937318Licence: Unspecified

Cite this

@article{e581c624bafa48469d5a2767120ea527,

title = "A detailed non-LTE analysis of LB-1: Revised parameters and surface abundances",

abstract = "Context. It has recently been proposed that LB-1 is a binary system at 4 kpc consisting of a B-type star of 8 M⊙ and a massive stellar black hole (BH) of 70 M⊙ . This finding challenges our current theories of massive star evolution and formation of BHs at solar metallicity. Aims. Our objective is to derive the effective temperature, surface gravity, and chemical composition of the B-type component in order to determine its nature and evolutionary status and, indirectly, to constrain the mass of the BH. Methods. We use the non-LTE stellar atmosphere code FASTWIND to analyze new and archival high-resolution data. Results. We determine (Teff, log g) values of (14 000 ± 500 K, 3.50 ± 0.15 dex) that, combined with the Gaia parallax, imply a spectroscopic mass, from log g, of 3.2+2.1-1.9 M⊙ and an evolutionary mass, assuming single star evolution, of 5.2+0.3-0.6 M⊙ . We determine an upper limit of 8 km s-1 for the projected rotational velocity and derive the surface abundances; we find the star to have a silicon abundance below solar, and to be significantly enhanced in nitrogen and iron and depleted in carbon and magnesium. Complementary evidence derived from a photometric extinction analysis and Gaia yields similar results for Teff and log g and a consistent distance around 2 kpc. Conclusions. We propose that the B-type star is a slightly evolved main sequence star of 3-5 M⊙ with surface abundances reminiscent of diffusion in late B/A chemically peculiar stars with low rotational velocities. There is also evidence for CN-processed material in its atmosphere. These conclusions rely critically on the distance inferred from the Gaia parallax. The goodness of fit of the Gaia astrometry also favors a high-inclination orbit. If the orbit is edge-on and the B-type star has a mass of 3-5 M⊙ , the mass of the dark companion would be 4-5 M⊙ , which would be easier to explain with our current stellar evolutionary models.",

keywords = "Binaries: spectroscopic, Stars: abundances, Stars: black holes, Stars: early-type, Stars: fundamental parameters, Techniques: spectroscopic",

author = "S. Sim{\'o}n-D{\'i}az and {Ma{\'i}z Apell{\'a}niz}, J. and Lennon, {D. J.} and {Gonz{\'a}lez Hern{\'a}ndez}, {J. I.} and {Allende Prieto}, C. and N. Castro and {De Burgos}, A. and Dufton, {P. L.} and A. Herrero and B. Toledo-Padr{\'o}n and Smartt, {S. J.}",

note = "Funding Information: Acknowledgements. We thank R.-P. Kudritzki for his interesting suggestions for improvement of the first version of this Letter. We thank J. Hern{\'a}ndez for his help with Gaia DR2 data. S-SD, DJL, AdB, AHD and JMA acknowledges support from the Spanish Government Ministerio de Ciencia, Innovaci{\'o}n y Uni-versidades through grants PGC2018-095 049-B-C22 and PGC-2018-091 3741-B-C22. JIGH acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2013 Ram{\'o}n y Cajal program RYC-2013-14875. JIGH and CAP acknowledge financial support from the Spanish Ministry project MICIU AYA2017-86389-P. SJS acknowledges funding from STFC Grant ST/P000312/1. Based on observations made with the Telescopio Nationale Galileo (TNG) and the Gran Telescopio Canarias (GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Insti-tuto de Astrofs´ica de Canarias, in the island of La Palma. This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under Funding Information: contract with the National Aeronautics and Space Administration. Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAMOST is operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences. Publisher Copyright: {\textcopyright} ESO 2020. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.",

year = "2020",

month = feb,

day = "1",

doi = "10.1051/0004-6361/201937318",

language = "English",

volume = "634",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

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A detailed non-LTE analysis of LB-1: Revised parameters and surface abundances. / Simón-Díaz, S.; Maíz Apellániz, J.; Lennon, D. J.; González Hernández, J. I.; Allende Prieto, C.; Castro, N.; De Burgos, A.; Dufton, P. L.; Herrero, A.; Toledo-Padrón, B.; Smartt, S. J.

In: Astronomy and Astrophysics, Vol. 634, L7, 01.02.2020.

Research output: Contribution to journal › Article › peer-review

TY - JOUR

T1 - A detailed non-LTE analysis of LB-1: Revised parameters and surface abundances

AU - Simón-Díaz, S.

AU - Maíz Apellániz, J.

AU - Lennon, D. J.

AU - González Hernández, J. I.

AU - Allende Prieto, C.

AU - Castro, N.

AU - De Burgos, A.

AU - Dufton, P. L.

AU - Herrero, A.

AU - Toledo-Padrón, B.

AU - Smartt, S. J.

N1 - Funding Information: Acknowledgements. We thank R.-P. Kudritzki for his interesting suggestions for improvement of the first version of this Letter. We thank J. Hernández for his help with Gaia DR2 data. S-SD, DJL, AdB, AHD and JMA acknowledges support from the Spanish Government Ministerio de Ciencia, Innovación y Uni-versidades through grants PGC2018-095 049-B-C22 and PGC-2018-091 3741-B-C22. JIGH acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under the 2013 Ramón y Cajal program RYC-2013-14875. JIGH and CAP acknowledge financial support from the Spanish Ministry project MICIU AYA2017-86389-P. SJS acknowledges funding from STFC Grant ST/P000312/1. Based on observations made with the Telescopio Nationale Galileo (TNG) and the Gran Telescopio Canarias (GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Insti-tuto de Astrofs´ica de Canarias, in the island of La Palma. This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under Funding Information: contract with the National Aeronautics and Space Administration. Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAMOST is operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences. Publisher Copyright: © ESO 2020. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/2/1

Y1 - 2020/2/1

N2 - Context. It has recently been proposed that LB-1 is a binary system at 4 kpc consisting of a B-type star of 8 M⊙ and a massive stellar black hole (BH) of 70 M⊙ . This finding challenges our current theories of massive star evolution and formation of BHs at solar metallicity. Aims. Our objective is to derive the effective temperature, surface gravity, and chemical composition of the B-type component in order to determine its nature and evolutionary status and, indirectly, to constrain the mass of the BH. Methods. We use the non-LTE stellar atmosphere code FASTWIND to analyze new and archival high-resolution data. Results. We determine (Teff, log g) values of (14 000 ± 500 K, 3.50 ± 0.15 dex) that, combined with the Gaia parallax, imply a spectroscopic mass, from log g, of 3.2+2.1-1.9 M⊙ and an evolutionary mass, assuming single star evolution, of 5.2+0.3-0.6 M⊙ . We determine an upper limit of 8 km s-1 for the projected rotational velocity and derive the surface abundances; we find the star to have a silicon abundance below solar, and to be significantly enhanced in nitrogen and iron and depleted in carbon and magnesium. Complementary evidence derived from a photometric extinction analysis and Gaia yields similar results for Teff and log g and a consistent distance around 2 kpc. Conclusions. We propose that the B-type star is a slightly evolved main sequence star of 3-5 M⊙ with surface abundances reminiscent of diffusion in late B/A chemically peculiar stars with low rotational velocities. There is also evidence for CN-processed material in its atmosphere. These conclusions rely critically on the distance inferred from the Gaia parallax. The goodness of fit of the Gaia astrometry also favors a high-inclination orbit. If the orbit is edge-on and the B-type star has a mass of 3-5 M⊙ , the mass of the dark companion would be 4-5 M⊙ , which would be easier to explain with our current stellar evolutionary models.

AB - Context. It has recently been proposed that LB-1 is a binary system at 4 kpc consisting of a B-type star of 8 M⊙ and a massive stellar black hole (BH) of 70 M⊙ . This finding challenges our current theories of massive star evolution and formation of BHs at solar metallicity. Aims. Our objective is to derive the effective temperature, surface gravity, and chemical composition of the B-type component in order to determine its nature and evolutionary status and, indirectly, to constrain the mass of the BH. Methods. We use the non-LTE stellar atmosphere code FASTWIND to analyze new and archival high-resolution data. Results. We determine (Teff, log g) values of (14 000 ± 500 K, 3.50 ± 0.15 dex) that, combined with the Gaia parallax, imply a spectroscopic mass, from log g, of 3.2+2.1-1.9 M⊙ and an evolutionary mass, assuming single star evolution, of 5.2+0.3-0.6 M⊙ . We determine an upper limit of 8 km s-1 for the projected rotational velocity and derive the surface abundances; we find the star to have a silicon abundance below solar, and to be significantly enhanced in nitrogen and iron and depleted in carbon and magnesium. Complementary evidence derived from a photometric extinction analysis and Gaia yields similar results for Teff and log g and a consistent distance around 2 kpc. Conclusions. We propose that the B-type star is a slightly evolved main sequence star of 3-5 M⊙ with surface abundances reminiscent of diffusion in late B/A chemically peculiar stars with low rotational velocities. There is also evidence for CN-processed material in its atmosphere. These conclusions rely critically on the distance inferred from the Gaia parallax. The goodness of fit of the Gaia astrometry also favors a high-inclination orbit. If the orbit is edge-on and the B-type star has a mass of 3-5 M⊙ , the mass of the dark companion would be 4-5 M⊙ , which would be easier to explain with our current stellar evolutionary models.

KW - Binaries: spectroscopic

KW - Stars: abundances

KW - Stars: black holes

KW - Stars: early-type

KW - Stars: fundamental parameters

KW - Techniques: spectroscopic

U2 - 10.1051/0004-6361/201937318

DO - 10.1051/0004-6361/201937318

M3 - Article

AN - SCOPUS:85083974893

VL - 634

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 0004-6361

M1 - L7

ER -

A detailed non-LTE analysis of LB-1: Revised parameters and surface abundances

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

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