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Hubble spectroscopy of LB-1: Comparison with B+black-hole and Be+stripped-star models

Context. LB-1 (alias ALS 8775) has been proposed as either an X-ray dim B-type star plus black hole (B+BH) binary or a Be star plus an inflated stripped star (Be+Bstr) binary. The latter hypothesis contingent upon the detection and characterization of the hidden broad-lined star in a composite optic...

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Published in:Astronomy and astrophysics (Berlin) 2021-05, Vol.649, p.A167
Main Authors: Lennon, D. J., Maíz Apellániz, J., Irrgang, A., Bohlin, R., Deustua, S., Dufton, P. L., Simón-Díaz, S., Herrero, A., Casares, J., Muñoz-Darias, T., Smartt, S. J., González Hernández, J. I., de Burgos, A.
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container_start_page A167
container_title Astronomy and astrophysics (Berlin)
container_volume 649
creator Lennon, D. J.
Maíz Apellániz, J.
Irrgang, A.
Bohlin, R.
Deustua, S.
Dufton, P. L.
Simón-Díaz, S.
Herrero, A.
Casares, J.
Muñoz-Darias, T.
Smartt, S. J.
González Hernández, J. I.
de Burgos, A.
description Context. LB-1 (alias ALS 8775) has been proposed as either an X-ray dim B-type star plus black hole (B+BH) binary or a Be star plus an inflated stripped star (Be+Bstr) binary. The latter hypothesis contingent upon the detection and characterization of the hidden broad-lined star in a composite optical spectrum. Aims. Our study is aimed at testing the published B+BH (single star) and Be+Bstr (binary star) models using a flux-calibrated UV-optical-IR spectrum. Methods. The Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST) was used to obtain a flux-calibrated spectrum with an accuracy of ∼1%. We compared these data with non-local thermal equilibrium (non-LTE) spectral energy distributions (SED) and line profiles for the proposed models. The Hubble data, together with the Gaia EDR3 parallax and a well-determined extinction, were used to provide tight constraints on the properties and stellar luminosities of the LB-1 system. In the case of the Be+Bstr model we adopted the published flux ratio for the Be and Bstr stars, re-determined the T eff of the Bstr using the silicon ionization balance, and inferred T eff for the Be star from the fit to the SED. Results. The UV data strongly constrain the microturbulence velocity to ≲2 km s −1 for the stellar components of both models. We also find stellar parameters consistent with previous results, but with greater precision enabled by the Hubble SED. For the B+BH single-star model, we find the parameters ( T eff , log( L / L ⊙ ), M spec / M ⊙ ) of the B-type star to be (15 300 ± 300 K, 3.23 −0.10 +0.09 , 5.2 −1.4 +1.8 ). For the Bstr star we obtain (12 500 ± 100 K, 2.70 −0.09 +0.09 , 0.8 −0.3 +0.5 ), and for the Be star (18 900 ± 200 K, 3.04 −0.09 +0.09 , 3.4 −1.8 +3.5 ). While the Be+Bstr model is a better fit to the He  I lines and cores of the Balmer lines in the optical, the B+BH model provides a better fit to the Si  IV resonance lines in the UV. The analysis also implies that the Bstr star has roughly twice the solar silicon abundance, which is difficult to reconcile with a stripped star origin. The Be star, on the other hand, has a rather low luminosity and a spectroscopic mass that is inconsistent with its possible dynamical mass. Conclusions. We provide tight constraints on the stellar luminosities of the Be+Bstr and B+BH models. For the former, the Bstr star appears to be silicon-rich, while the notional Be star appears to be sub-luminous for a classical Be star of its tempe
doi_str_mv 10.1051/0004-6361/202040253
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J. ; Maíz Apellániz, J. ; Irrgang, A. ; Bohlin, R. ; Deustua, S. ; Dufton, P. L. ; Simón-Díaz, S. ; Herrero, A. ; Casares, J. ; Muñoz-Darias, T. ; Smartt, S. J. ; González Hernández, J. I. ; de Burgos, A.</creator><creatorcontrib>Lennon, D. J. ; Maíz Apellániz, J. ; Irrgang, A. ; Bohlin, R. ; Deustua, S. ; Dufton, P. L. ; Simón-Díaz, S. ; Herrero, A. ; Casares, J. ; Muñoz-Darias, T. ; Smartt, S. J. ; González Hernández, J. I. ; de Burgos, A.</creatorcontrib><description>Context. LB-1 (alias ALS 8775) has been proposed as either an X-ray dim B-type star plus black hole (B+BH) binary or a Be star plus an inflated stripped star (Be+Bstr) binary. The latter hypothesis contingent upon the detection and characterization of the hidden broad-lined star in a composite optical spectrum. Aims. Our study is aimed at testing the published B+BH (single star) and Be+Bstr (binary star) models using a flux-calibrated UV-optical-IR spectrum. Methods. The Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST) was used to obtain a flux-calibrated spectrum with an accuracy of ∼1%. We compared these data with non-local thermal equilibrium (non-LTE) spectral energy distributions (SED) and line profiles for the proposed models. The Hubble data, together with the Gaia EDR3 parallax and a well-determined extinction, were used to provide tight constraints on the properties and stellar luminosities of the LB-1 system. In the case of the Be+Bstr model we adopted the published flux ratio for the Be and Bstr stars, re-determined the T eff of the Bstr using the silicon ionization balance, and inferred T eff for the Be star from the fit to the SED. Results. The UV data strongly constrain the microturbulence velocity to ≲2 km s −1 for the stellar components of both models. We also find stellar parameters consistent with previous results, but with greater precision enabled by the Hubble SED. For the B+BH single-star model, we find the parameters ( T eff , log( L / L ⊙ ), M spec / M ⊙ ) of the B-type star to be (15 300 ± 300 K, 3.23 −0.10 +0.09 , 5.2 −1.4 +1.8 ). For the Bstr star we obtain (12 500 ± 100 K, 2.70 −0.09 +0.09 , 0.8 −0.3 +0.5 ), and for the Be star (18 900 ± 200 K, 3.04 −0.09 +0.09 , 3.4 −1.8 +3.5 ). While the Be+Bstr model is a better fit to the He  I lines and cores of the Balmer lines in the optical, the B+BH model provides a better fit to the Si  IV resonance lines in the UV. The analysis also implies that the Bstr star has roughly twice the solar silicon abundance, which is difficult to reconcile with a stripped star origin. The Be star, on the other hand, has a rather low luminosity and a spectroscopic mass that is inconsistent with its possible dynamical mass. Conclusions. We provide tight constraints on the stellar luminosities of the Be+Bstr and B+BH models. For the former, the Bstr star appears to be silicon-rich, while the notional Be star appears to be sub-luminous for a classical Be star of its temperature and the predicted UV spectrum is inconsistent with the data. This latter issue can be significantly improved by reducing the T eff and radius of the Be star, at the cost, however, of a different mass ratio as a result. In the B+BH model, the single B-type spectrum is a good match to the UV spectrum. Adopting a mass ratio of 5.1 ± 0.1, from the literature, implies a BH mass of ∼21 −8 +9 M ⊙ .</description><identifier>ISSN: 0004-6361</identifier><identifier>EISSN: 1432-0746</identifier><identifier>DOI: 10.1051/0004-6361/202040253</identifier><language>eng</language><publisher>Heidelberg: EDP Sciences</publisher><subject>Astronomical models ; B stars ; Binary stars ; Black holes ; Flux ; Hubble Space Telescope ; Luminosity ; Parallax ; Parameters ; Resonance lines ; Silicon ; Space telescopes ; Spectrum analysis</subject><ispartof>Astronomy and astrophysics (Berlin), 2021-05, Vol.649, p.A167</ispartof><rights>Copyright EDP Sciences May 2021</rights><lds50>peer_reviewed</lds50><oa>free_for_read</oa><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-c2373-17d35d1785cf5df571a34579ddf4f14f6e195af862e448913baf7117afab496b3</citedby><cites>FETCH-LOGICAL-c2373-17d35d1785cf5df571a34579ddf4f14f6e195af862e448913baf7117afab496b3</cites><orcidid>0000-0003-3063-4867</orcidid></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><link.rule.ids>314,780,784,27924,27925</link.rule.ids></links><search><creatorcontrib>Lennon, D. J.</creatorcontrib><creatorcontrib>Maíz Apellániz, J.</creatorcontrib><creatorcontrib>Irrgang, A.</creatorcontrib><creatorcontrib>Bohlin, R.</creatorcontrib><creatorcontrib>Deustua, S.</creatorcontrib><creatorcontrib>Dufton, P. L.</creatorcontrib><creatorcontrib>Simón-Díaz, S.</creatorcontrib><creatorcontrib>Herrero, A.</creatorcontrib><creatorcontrib>Casares, J.</creatorcontrib><creatorcontrib>Muñoz-Darias, T.</creatorcontrib><creatorcontrib>Smartt, S. J.</creatorcontrib><creatorcontrib>González Hernández, J. I.</creatorcontrib><creatorcontrib>de Burgos, A.</creatorcontrib><title>Hubble spectroscopy of LB-1: Comparison with B+black-hole and Be+stripped-star models</title><title>Astronomy and astrophysics (Berlin)</title><description>Context. LB-1 (alias ALS 8775) has been proposed as either an X-ray dim B-type star plus black hole (B+BH) binary or a Be star plus an inflated stripped star (Be+Bstr) binary. The latter hypothesis contingent upon the detection and characterization of the hidden broad-lined star in a composite optical spectrum. Aims. Our study is aimed at testing the published B+BH (single star) and Be+Bstr (binary star) models using a flux-calibrated UV-optical-IR spectrum. Methods. The Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST) was used to obtain a flux-calibrated spectrum with an accuracy of ∼1%. We compared these data with non-local thermal equilibrium (non-LTE) spectral energy distributions (SED) and line profiles for the proposed models. The Hubble data, together with the Gaia EDR3 parallax and a well-determined extinction, were used to provide tight constraints on the properties and stellar luminosities of the LB-1 system. In the case of the Be+Bstr model we adopted the published flux ratio for the Be and Bstr stars, re-determined the T eff of the Bstr using the silicon ionization balance, and inferred T eff for the Be star from the fit to the SED. Results. The UV data strongly constrain the microturbulence velocity to ≲2 km s −1 for the stellar components of both models. We also find stellar parameters consistent with previous results, but with greater precision enabled by the Hubble SED. For the B+BH single-star model, we find the parameters ( T eff , log( L / L ⊙ ), M spec / M ⊙ ) of the B-type star to be (15 300 ± 300 K, 3.23 −0.10 +0.09 , 5.2 −1.4 +1.8 ). For the Bstr star we obtain (12 500 ± 100 K, 2.70 −0.09 +0.09 , 0.8 −0.3 +0.5 ), and for the Be star (18 900 ± 200 K, 3.04 −0.09 +0.09 , 3.4 −1.8 +3.5 ). While the Be+Bstr model is a better fit to the He  I lines and cores of the Balmer lines in the optical, the B+BH model provides a better fit to the Si  IV resonance lines in the UV. The analysis also implies that the Bstr star has roughly twice the solar silicon abundance, which is difficult to reconcile with a stripped star origin. The Be star, on the other hand, has a rather low luminosity and a spectroscopic mass that is inconsistent with its possible dynamical mass. Conclusions. We provide tight constraints on the stellar luminosities of the Be+Bstr and B+BH models. For the former, the Bstr star appears to be silicon-rich, while the notional Be star appears to be sub-luminous for a classical Be star of its temperature and the predicted UV spectrum is inconsistent with the data. This latter issue can be significantly improved by reducing the T eff and radius of the Be star, at the cost, however, of a different mass ratio as a result. In the B+BH model, the single B-type spectrum is a good match to the UV spectrum. Adopting a mass ratio of 5.1 ± 0.1, from the literature, implies a BH mass of ∼21 −8 +9 M ⊙ .</description><subject>Astronomical models</subject><subject>B stars</subject><subject>Binary stars</subject><subject>Black holes</subject><subject>Flux</subject><subject>Hubble Space Telescope</subject><subject>Luminosity</subject><subject>Parallax</subject><subject>Parameters</subject><subject>Resonance lines</subject><subject>Silicon</subject><subject>Space telescopes</subject><subject>Spectrum analysis</subject><issn>0004-6361</issn><issn>1432-0746</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2021</creationdate><recordtype>article</recordtype><recordid>eNo9kMtKAzEUhoMoWKtP4CbgssTm5DrjzpZqhYIbuw6ZSUKnTpsxmSJ9e6dUujr88F84H0KPQJ-BSphSSgVRXMGUUUYFZZJfoREIzgjVQl2j0cVxi-5y3g6SQcFHaL08VFXrce583aeY69gdcQx4NSPwgudx19nU5LjHv02_wbNJ1dr6m2ziELF7h2d-kvvUdJ13JPc24V10vs336CbYNvuH_ztG67fF13xJVp_vH_PXFakZ15yAdlw60IWsg3RBarBcSF06F0QAEZSHUtpQKOaFKErglQ0aQNtgK1Gqio_R07m3S_Hn4HNvtvGQ9sOkYVKoUhV6SI0RP7vq4cGcfDBdanY2HQ1Qc-JnTnTMiY658ON_39RhEA</recordid><startdate>202105</startdate><enddate>202105</enddate><creator>Lennon, D. 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L.</creatorcontrib><creatorcontrib>Simón-Díaz, S.</creatorcontrib><creatorcontrib>Herrero, A.</creatorcontrib><creatorcontrib>Casares, J.</creatorcontrib><creatorcontrib>Muñoz-Darias, T.</creatorcontrib><creatorcontrib>Smartt, S. J.</creatorcontrib><creatorcontrib>González Hernández, J. I.</creatorcontrib><creatorcontrib>de Burgos, A.</creatorcontrib><collection>CrossRef</collection><collection>Technology Research Database</collection><collection>Aerospace Database</collection><collection>Advanced Technologies Database with Aerospace</collection><jtitle>Astronomy and astrophysics (Berlin)</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Lennon, D. J.</au><au>Maíz Apellániz, J.</au><au>Irrgang, A.</au><au>Bohlin, R.</au><au>Deustua, S.</au><au>Dufton, P. L.</au><au>Simón-Díaz, S.</au><au>Herrero, A.</au><au>Casares, J.</au><au>Muñoz-Darias, T.</au><au>Smartt, S. J.</au><au>González Hernández, J. I.</au><au>de Burgos, A.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Hubble spectroscopy of LB-1: Comparison with B+black-hole and Be+stripped-star models</atitle><jtitle>Astronomy and astrophysics (Berlin)</jtitle><date>2021-05</date><risdate>2021</risdate><volume>649</volume><spage>A167</spage><pages>A167-</pages><issn>0004-6361</issn><eissn>1432-0746</eissn><abstract>Context. LB-1 (alias ALS 8775) has been proposed as either an X-ray dim B-type star plus black hole (B+BH) binary or a Be star plus an inflated stripped star (Be+Bstr) binary. The latter hypothesis contingent upon the detection and characterization of the hidden broad-lined star in a composite optical spectrum. Aims. Our study is aimed at testing the published B+BH (single star) and Be+Bstr (binary star) models using a flux-calibrated UV-optical-IR spectrum. Methods. The Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST) was used to obtain a flux-calibrated spectrum with an accuracy of ∼1%. We compared these data with non-local thermal equilibrium (non-LTE) spectral energy distributions (SED) and line profiles for the proposed models. The Hubble data, together with the Gaia EDR3 parallax and a well-determined extinction, were used to provide tight constraints on the properties and stellar luminosities of the LB-1 system. In the case of the Be+Bstr model we adopted the published flux ratio for the Be and Bstr stars, re-determined the T eff of the Bstr using the silicon ionization balance, and inferred T eff for the Be star from the fit to the SED. Results. The UV data strongly constrain the microturbulence velocity to ≲2 km s −1 for the stellar components of both models. We also find stellar parameters consistent with previous results, but with greater precision enabled by the Hubble SED. For the B+BH single-star model, we find the parameters ( T eff , log( L / L ⊙ ), M spec / M ⊙ ) of the B-type star to be (15 300 ± 300 K, 3.23 −0.10 +0.09 , 5.2 −1.4 +1.8 ). For the Bstr star we obtain (12 500 ± 100 K, 2.70 −0.09 +0.09 , 0.8 −0.3 +0.5 ), and for the Be star (18 900 ± 200 K, 3.04 −0.09 +0.09 , 3.4 −1.8 +3.5 ). While the Be+Bstr model is a better fit to the He  I lines and cores of the Balmer lines in the optical, the B+BH model provides a better fit to the Si  IV resonance lines in the UV. The analysis also implies that the Bstr star has roughly twice the solar silicon abundance, which is difficult to reconcile with a stripped star origin. The Be star, on the other hand, has a rather low luminosity and a spectroscopic mass that is inconsistent with its possible dynamical mass. Conclusions. We provide tight constraints on the stellar luminosities of the Be+Bstr and B+BH models. For the former, the Bstr star appears to be silicon-rich, while the notional Be star appears to be sub-luminous for a classical Be star of its temperature and the predicted UV spectrum is inconsistent with the data. This latter issue can be significantly improved by reducing the T eff and radius of the Be star, at the cost, however, of a different mass ratio as a result. In the B+BH model, the single B-type spectrum is a good match to the UV spectrum. Adopting a mass ratio of 5.1 ± 0.1, from the literature, implies a BH mass of ∼21 −8 +9 M ⊙ .</abstract><cop>Heidelberg</cop><pub>EDP Sciences</pub><doi>10.1051/0004-6361/202040253</doi><orcidid>https://orcid.org/0000-0003-3063-4867</orcidid><oa>free_for_read</oa></addata></record>
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subjects Astronomical models
B stars
Binary stars
Black holes
Flux
Hubble Space Telescope
Luminosity
Parallax
Parameters
Resonance lines
Silicon
Space telescopes
Spectrum analysis
title Hubble spectroscopy of LB-1: Comparison with B+black-hole and Be+stripped-star models
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