The "hidden" companion in LB-1 unveiled by spectral disentangling
TL;DR: In this article, the authors performed an orbital analysis and spectral disentangling of LS V +22 25 (LB-1) to elucidate the nature of the system, which revealed that LB-1 contains two components of comparable brightness in the optical.
Abstract: The intriguing binary LS V +22 25 (LB-1) has drawn much attention following claims of it being a single-lined spectroscopic binary with a 79-day orbit comprising a B-type star and a ~70 Msun black hole. Recent analyses have implied that the visible primary star is a stripped He-rich star. However, the nature of the secondary, which was proposed to be a black hole, a neutron star, or a main sequence star, remains unknown. Based on 26 newly acquired spectroscopic observations, we perform an orbital analysis and spectral disentangling of LB-1 to elucidate the nature of the system. Our analysis reveals that LB-1 contains two components of comparable brightness in the optical. The narrow-lined primary, which we estimate to contribute ~55% in the optical, has spectral properties that suggest that it is a stripped star: it has a small spectroscopic mass (~1 Msun) for a B-type star and it is He- and N-rich. The "hidden" secondary, which contributes about 45% of the optical flux, is a rapidly rotating (vsini ~ 300 km/s) B3 V star with a decretion disk -- a Be star. Hence, LB-1 does not contain a compact object. Instead, it is a rare Be binary system consisting of a stripped star (the former mass donor) and a Be star rotating at near its critical velocity (the former mass accretor). This system is a clear example that binary interactions play a decisive role in the production of rapid stellar rotators and Be stars.
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James Miller-Jones1, Arash Bahramian1, Jerome A. Orosz2, Ilya Mandel3, Ilya Mandel4, Ilya Mandel5, Lijun Gou6, Thomas J. Maccarone7, Coenraad J. Neijssel3, Coenraad J. Neijssel4, Coenraad J. Neijssel5, X. H. Zhao6, Janusz Ziółkowski, Mark J. Reid8, Phil Uttley9, Xueying Zheng6, Do-Young Byun10, Do-Young Byun11, Richard Dodson12, Victoria Grinberg13, Taehyun Jung11, Taehyun Jung10, Jeong-Sook Kim10, Benito Marcote14, Sera Markoff9, Maria Rioja12, Maria Rioja15, Maria Rioja16, A. Rushton17, A. Rushton18, David M. Russell19, Gregory R. Sivakoff20, Alexandra J. Tetarenko, Valeriu Tudose, Joern Wilms21 •
Curtin University1, San Diego State University2, Australian Research Council3, University of Birmingham4, Monash University, Clayton campus5, Chinese Academy of Sciences6, Texas Tech University7, Smithsonian Institution8, University of Amsterdam9, Korea Astronomy and Space Science Institute10, Korea University of Science and Technology11, University of Western Australia12, University of Tübingen13, Joint Institute for Nuclear Research14, Instituto Geográfico Nacional15, Commonwealth Scientific and Industrial Research Organisation16, University of Oxford17, University of Southampton18, New York University Abu Dhabi19, University of Alberta20, University of Erlangen-Nuremberg21
TL;DR: In this paper, the authors used radio astrometry to refine the distance to the black hole X-ray binary Cygnus X-1, which was found to be 2.22 − 0.17 + 0.18 kiloparsecs.
Abstract: The evolution of massive stars is influenced by the mass lost to stellar winds over their lifetimes. These winds limit the masses of the stellar remnants (such as black holes) that the stars ultimately produce. We use radio astrometry to refine the distance to the black hole X-ray binary Cygnus X-1, which we find to be 2.22 − 0.17 + 0.18 kiloparsecs. When combined with archival optical data, this implies a black hole mass of 21.2 ± 2.2 solar masses, higher than previous measurements. The formation of such a high-mass black hole in a high-metallicity system (within the Milky Way) constrains wind mass loss from massive stars.
106 citations
Tharindu Jayasinghe1, K. Z. Stanek1, Todd A. Thompson1, Christopher S. Kochanek1, D. M. Rowan1, Patrick J. Vallely1, Klaus G. Strassmeier2, Michael Weber2, Jason T. Hinkle, Franz-Josef Hambsch3, David V. Martin1, J. L. Prieto4, J. L. Prieto5, Thallis L. Pessi4, Daniel Huber, Katie Auchettl6, Katie Auchettl7, Laura A. Lopez1, Ilya Ilyin2, Carles Badenes8, Andrew W. Howard9, Howard Isaacson10, Howard Isaacson11, Simon J. Murphy12, Simon J. Murphy13 •
Ohio State University1, Leibniz Institute for Astrophysics Potsdam2, American Association of Variable Star Observers3, Diego Portales University4, Millennium Institute5, University of Melbourne6, University of California, Santa Cruz7, University of Pittsburgh8, California Institute of Technology9, University of California, Berkeley10, University of Southern Queensland11, Aarhus University12, University of Sydney13
TL;DR: The closest known black hole candidate as a binary companion to V723 Mon was discovered in this paper, where the authors used the SED and the absence of continuum eclipses to identify a likely non-stellar, diffuse veiling component with contributions in the $B$ and $V$-band.
Abstract: We report the discovery of the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby ($d\sim460\,\rm pc$), bright ($V\simeq8.3$~mag), evolved ($T_{\rm eff, giant}\simeq4440$ K, $L_{\rm giant}\simeq173~L_\odot$ and $R_{\rm giant}\simeq22 ~R_\odot$) red giant in a high mass function, $f(M)=1.72\pm 0.01~M_\odot$, nearly circular binary ($P=59.9$ d, $e\simeq 0$). V723 Mon is a known variable star, previously classified as an eclipsing binary, but its ASAS, KELT, and TESS light curves are those of a nearly edge-on ellipsoidal variable. Detailed models of the light curves constrained by the period, radial velocities and stellar temperature give an inclination of $i=87.0^\circ \pm 1.0^\circ$, a mass ratio of $q\simeq0.30\pm0.02$, a companion mass of $M_{\rm comp}=2.91\pm0.08~M_\odot$, a stellar radius of $R_{\rm giant}=23.6\pm1.0~R_\odot$, and a giant mass of $M_{\rm giant}=0.87\pm0.08~ M_\odot$. We identify a likely non-stellar, diffuse veiling component with contributions in the $B$ and $V$-band of ${\sim}64\%$ and ${\sim}23\%$, respectively. The SED and the absence of continuum eclipses imply that the companion mass must be dominated by a compact object. We do observe eclipses of the Balmer lines when the dark companion passes behind the giant, but their velocity spreads are low compared to observed accretion disks. The X-ray luminosity of the system is $L_{\rm X}\simeq1.0\times10^{30}~\rm ergs~s^{-1}$, corresponding to $L/L_{\rm edd}{\sim}10^{-9}$.The simplest explanation for the massive companion is a single compact object, most likely a black hole in the "mass gap", although a double neutron star binary is possible.
67 citations
TL;DR: In this paper, the authors argue that future observations of the black hole population will allow one to test this prediction, and use it to put constraints on new particles, such as axions, that would cause an additional instability.
Abstract: In the Standard Model, the so-called pair instability from creation of electron-positron pairs reduces the mass of low-metallicity population-III stars as they collapse, unless they are heavy enough to make the process inefficient, leading to an expected mass gap in the black hole spectrum. In this work, the authors argue that future observations of the black hole population will allow one to test this prediction, and use it to put constraints on new particles, such as axions, that would cause an additional instability.
47 citations
TL;DR: In this paper, the authors disentangle the observed composite spectra into two components: a rapidly rotating Be star and a slowly rotating B star with low surface gravity, and show that the system is a binary and does not contain a detached black hole.
Abstract: HR 6819 is a bright ($V=536$), blue star recently proposed to be a triple containing a detached black hole (BH) We show that the system is a binary and does not contain a BH Using spectral decomposition, we disentangle the observed composite spectra into two components: a rapidly rotating Be star and a slowly rotating B star with low surface gravity $(\log g \approx 275)$ Both stars show periodic radial velocity (RV) variability, but the RV semi-amplitude of the B star's orbit is $K_{\rm B}= (627 \pm 1)\,\rm km\,s^{-1}$, while that of the Be star is only $K_{\rm Be} = (45\pm 2)\,\rm km\,s^{-1}$ This implies that the B star is less massive by at least a factor of 10 The surface abundances of the B star bear imprints of CNO burning We argue that the B star is a bloated, recently stripped helium star with mass $\approx 05\,M_{\odot}$ that is currently contracting to become a hot subdwarf The orbital motion of the Be star obviates the need for a BH to explain the B star's motion A stripped-star model reproduces the observed luminosity of the system, while a normal star with the B star's temperature and gravity would be more than 10 times too luminous HR 6819 and the binary LB-1 probably formed through similar channels We use MESA models to investigate their evolutionary history, finding that they likely formed from intermediate-mass ($3-7\,M_{\odot}$) primaries stripped by slightly lower-mass secondaries and are progenitors to Be + sdOB binaries such as $\phi$ Persei The lifetime of their current evolutionary phase is on average $2\times 10^5$ years, of order half a percent of the total lifetime of the Be phase This implies that many Be stars have hot subdwarf and white dwarf companions, and that a substantial fraction ($20-100\%$) of field Be stars form through accretion of material from a binary companion
45 citations
Serena Vinciguerra1, Serena Vinciguerra2, Serena Vinciguerra3, Coenraad J. Neijssel1, Coenraad J. Neijssel3, Coenraad J. Neijssel4, Alejandro Vigna-Gómez, Ilya Mandel4, Ilya Mandel3, Ilya Mandel1, Philipp Podsiadlowski5, Thomas J. Maccarone6, Matt Nicholl7, Matt Nicholl4, Samuel Kingdon4, Alice Perry4, Francesco Salemi2 •
TL;DR: In this article, the authors compare the observed population of BeXRBs in the Small Magellanic Cloud with simulated populations of beXRB-like systems produced with the COMPAS population synthesis code, and find that at least 30% of the mass donated by the progenitor of the neutron star is typically accreted by the B-star companion.
Abstract: Be X-ray binaries (BeXRBs) consist of rapidly rotating Be stars with neutron star companions accreting from the circumstellar emission disk. We compare the observed population of BeXRBs in the Small Magellanic Cloud with simulated populations of BeXRB-like systems produced with the COMPAS population synthesis code. We focus on the apparently higher minimal mass of Be stars in BeXRBs than in the Be population at large. Assuming that BeXRBs experienced only dynamically stable mass transfer, their mass distribution suggests that at least 30% of the mass donated by the progenitor of the neutron star is typically accreted by the B-star companion. We expect these results to affect predictions for the population of double compact object mergers. A convolution of the simulated BeXRB population with the star formation history of the Small Magellanic Cloud shows that the excess of BeXRBs is most likely explained by this galaxy's burst of star formation around 20--40 Myr ago.
41 citations
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TL;DR: In this article, a weak distance prior is used to estimate the distances to all 1.33 billion stars with parallaxes published in the second Gaia data release, and the uncertainty in the distance estimate is characterized by the lower and upper bounds of an asymmetric confidence interval.
Abstract: For the vast majority of stars in the second Gaia data release, reliable distances cannot be obtained by inverting the parallax. A correct inference procedure must instead be used to account for the nonlinearity of the transformation and the asymmetry of the resulting probability distribution. Here, we infer distances to essentially all 1.33 billion stars with parallaxes published in the second Gaia data release. This is done using a weak distance prior that varies smoothly as a function of Galactic longitude and latitude according to a Galaxy model. The irreducible uncertainty in the distance estimate is characterized by the lower and upper bounds of an asymmetric confidence interval. Although more precise distances can be estimated for a subset of the stars using additional data (such as photometry), our goal is to provide purely geometric distance estimates, independent of assumptions about the physical properties of, or interstellar extinction toward, individual stars. We analyze the characteristics of the catalog and validate it using clusters. The catalog can be queried using ADQL at http://gaia.ari.uni-heidelberg.de/tap.html (which also hosts the Gaia catalog) and downloaded from http://www.mpia.de/~calj/gdr2_distances.html.
1,943 citations
TL;DR: In this paper, the authors used a weak distance prior that varies smoothly as a function of Galactic longitude and latitude according to a Galaxy model to infer distances to essentially all 1.33 billion stars with parallaxes published in the second Gaia data release.
Abstract: For the vast majority of stars in the second Gaia data release, reliable distances cannot be obtained by inverting the parallax. A correct inference procedure must instead be used to account for the nonlinearity of the transformation and the asymmetry of the resulting probability distribution. Here we infer distances to essentially all 1.33 billion stars with parallaxes published in the second \gaia\ data release. This is done using a weak distance prior that varies smoothly as a function of Galactic longitude and latitude according to a Galaxy model. The irreducible uncertainty in the distance estimate is characterized by the lower and upper bounds of an asymmetric confidence interval. Although more precise distances can be estimated for a subset of the stars using additional data (such as photometry), our goal is to provide purely geometric distance estimates, independent of assumptions about the physical properties of, or interstellar extinction towards, individual stars. We analyse the characteristics of the catalogue and validate it using clusters. The catalogue can be queried on the Gaia archive using ADQL at this http URL and downloaded from this http URL .
1,715 citations
490 citations
Gert Raskin1, H. Van Winckel1, Herman Hensberge2, Alain Jorissen3, Holger Lehmann, C. Waelkens1, G. Avila4, J. P. de Cuyper2, Pieter Degroote1, Rene Dubosson, L. Dumortier2, Y. Frémat2, Uwe Laux, Bernard Michaud, Johan Morren1, J. Perez Padilla1, Wim Pessemier1, S. Prins1, K. Smolders1, S. Van Eck3, J. Winkler •
TL;DR: The HERMES high-resolution spectrograph project as discussed by the authors is based on the white-pupil beam folding for high resolution spectroscopy with a spectral resolution of 85'000 (63'000) for the low-resolution fiber.
Abstract: The HERMES high-resolution spectrograph project aims at exploiting the specific potential of small but flexible telescopes in observational astrophysics. The optimised optical design of the spectrograph is based on the well-proven concept of white-pupil beam folding for high-resolution spectroscopy. In this contribution we present the complete project, including the spectrograph design and procurement details, the telescope adaptor and calibration unit, the detector system, as well as the optimised data-reduction pipeline. We present a detailed performance analysis to show that the spectrograph performs as specified both in optical quality and in total efficiency. With a spectral resolution of 85 000 (63 000 for the low-resolution fibre), a spectral coverage from 377 to 900 nm in a single exposure and a peak efficiency of 28%, HERMES proves to be an ideal instrument for building up time series of high-quality data of variable (stellar) phenomena.
480 citations
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