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Journal ArticleDOI

A naked-eye triple system with a nonaccreting black hole in the inner binary

TL;DR: In this article, it was shown that HR 6819 is a hierarchical triple, consisting of a B3 III star and an unseen companion in a circular orbit with a radial-velocity semi-amplitude of 61.3 km s−1 of the inner star and its minimum (probable) mass of 5.0 M ⊙ (6.3
Abstract: Several dozen optical echelle spectra demonstrate that HR 6819 is a hierarchical triple. A classical Be star is in a wide orbit with an unconstrained period around an inner 40 d binary consisting of a B3 III star and an unseen companion in a circular orbit. The radial-velocity semi-amplitude of 61.3 km s−1 of the inner star and its minimum (probable) mass of 5.0 M ⊙ (6.3 ± 0.7 M ⊙ ) imply a mass of the unseen object of ≥4.2 M ⊙ (≥5.0 ± 0.4 M ⊙ ), that is, a black hole (BH). The spectroscopic time series is stunningly similar to observations of LB-1. A similar triple-star architecture of LB-1 would reduce the mass of the BH in LB-1 from ∼70 M ⊙ to a level more typical of Galactic stellar remnant BHs. The BH in HR 6819 probably is the closest known BH to the Sun, and together with LB-1, suggests a population of quiet BHs. Its embedment in a hierarchical triple structure may be of interest for models of merging double BHs or BH + neutron star binaries. Other triple stars with an outer Be star but without BH are identified; through stripping, such systems may become a source of single Be stars.

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Citations
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Journal ArticleDOI
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.

76 citations

Journal ArticleDOI
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

Journal ArticleDOI
TL;DR: In this article, a gas accretion-driven mechanism that can build up black hole masses rapidly in dense, gas-rich nuclear star clusters (NSCs) is presented, which leads to extremely fast growth, scaling stellar mass remnant seed black holes up to intermediate mass black holes (IMBHs).
Abstract: While the formation of the first black holes at high redshift is reasonably well understood though debated, massive black hole formation at later cosmic epochs has not been adequately explored. We present a gas accretion driven mechanism that can build up black hole masses rapidly in dense, gas-rich nuclear star clusters (NSCs). Wind-fed supra-exponential accretion of an initially wandering black hole in NSCs can lead to extremely fast growth, scaling stellar mass remnant seed black holes up to intermediate mass black holes (IMBHs). Operating throughout cosmic time, growth via this new channel is modulated by the gas supply, and premature termination results in the formation of lower mass black holes with masses in the range of 50 - few 100 solar masses, filling in the so-called mass gap. However, in most gas-rich NSCs, growth is unimpeded, inevitably leading to the formation of IMBHs with masses ranging from 100 - 100,000 solar masses. A spate of new detection spanning the full range of the IMBH mass function - from the LIGO-VIRGO source GW190521 to the emerging population of 10^5 solar mass black holes harbored in low-mass dwarf galaxies - are revealing this elusive population. Naturally accounting for the detected presence of off-center IMBHs in low-mass dwarfs, this new pathway also predicts the existence of an extensive population of wandering non-central black holes in more massive galaxies would be detectable via tidal disruption events and as GW sources. Gas-rich NSCs serve as incubators for the continual formation of black holes over a wide range in mass throughout cosmic time.

52 citations

Journal ArticleDOI
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

Journal ArticleDOI
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.

39 citations

References
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Journal ArticleDOI
TL;DR: In this article, the average extinction law over the 3.5 micron to 0.125 wavelength range was derived for both diffuse and dense regions of the interstellar medium. And the validity of the law over a large wavelength interval suggests that the processes which modify the sizes and compositions of grains are stochastic in nature.
Abstract: The parameterized extinction data of Fitzpatrick and Massa (1986, 1988) for the ultraviolet and various sources for the optical and near-infrared are used to derive a meaningful average extinction law over the 3.5 micron to 0.125 wavelength range which is applicable to both diffuse and dense regions of the interstellar medium. The law depends on only one parameter R(V) = A(V)/E(B-V). An analytic formula is given for the mean extinction law which can be used to calculate color excesses or to deredden observations. The validity of the law over a large wavelength interval suggests that the processes which modify the sizes and compositions of grains are stochastic in nature and very efficient.

11,704 citations


"A naked-eye triple system with a no..." refers methods in this paper

  • ...For the dereddening of the measured fluxes, the reddening E(B−V) = 0.135 mag listed by Wegner (2002) for HR 6819 and the extinction parameterization by Cardelli et al. (1989) were applied together with the standard value of the Galactic totalto-selective extinction ratio, RV = 3.1....

    [...]

Journal ArticleDOI
TL;DR: In this article, a new reduction of the Hipparcos data was published, which claimed accuracies for nearly all stars brighter than magnitude Hp = 8 to be better, by up to a factor 4, than in the original catalog.
Abstract: Context. A new reduction of the astrometric data as produced by the Hipparcos mission has been published, claiming accuracies for nearly all stars brighter than magnitude Hp = 8 to be better, by up to a factor 4, than in the original catalog ue. Aims. The new Hipparcos astrometric catalogue is checked for the quality of the data and the consistency of the formal errors as well as the possible presence of error correlations. The differences with the earlier publication are explained. Methods. The internal errors are followed through the reduction proc ess, and the external errors are investigated on the basis of a comparison with radio observations of a small selection of stars, and the distribution of negative parallaxes. Error co rrelation levels are investigated and the reduction by more than a factor 10 as obtained in the new catalogue is explained. Results. The formal errors on the parallaxes for the new catalogue are confirmed. The presence of a small amount of additional noise , though unlikely, cannot be ruled out. Conclusions. The new reduction of the Hipparcos astrometric data provides an improvement by a factor 2.2 in the total weight compared to the catalogue published in 1997, and provides much improved data for a wide range of studies on stellar luminosities and local galactic kinematics.

4,203 citations


"A naked-eye triple system with a no..." refers background in this paper

  • ...Neither the Gaia (DR2 Gaia Collaboration 2018, π = 2.915 mas) nor the Hipparcos (van Leeuwen 2007, π = 4.29 mas) parallax solutions for HR 6819 consider binarity; they are therefore highly uncertain....

    [...]

Journal ArticleDOI
TL;DR: A new and complete catalog of the main properties of the 1509 pulsars for which published information currently exists, which includes all spin-powered pulsars, as well as anomalous X-ray pulsars and soft gamma-ray repeaters showing coherent pulsed emission.
Abstract: We have compiled a new and complete catalog of the main properties of the 1509 pulsars for which published information currently exists. The catalog includes all spin-powered pulsars, as well as anomalous X-ray pulsars and soft gamma-ray repeaters showing coherent pulsed emission, but excludes accretion-powered systems. References are given for all data listed. We have also developed a new World Wide Web interface for accessing and displaying either tabular or plotted data with the option of selecting pulsars to be displayed via logical conditions on parameter expressions. The Web interface has an expert mode giving access to a wider range of parameters and allowing the use of custom databases. For users with locally installed software and database on Unix or Linux systems, the catalog may be accessed from a command-line interface. C-language functions to access specified parameters are also available. The catalog is updated from time to time to include new information.

2,985 citations


"A naked-eye triple system with a no..." refers background in this paper

  • ...At the temperature and 2 The ATNF catalog (Manchester et al. 2005) is maintained at https: //www.atnf.csiro.au/research/pulsar/psrcat/ L3, page 3 of 11 luminosity of a B3 III star, radiative winds are intrinsically very weak (Krtička 2014) and are ineffective over a separation of >0.22 au (the…...

    [...]

Journal ArticleDOI
TL;DR: The Transiting Exoplanet Survey Satellite (TESS) as discussed by the authors will search for planets transiting bright and nearby stars using four wide-field optical charge-coupled device cameras to monitor at least 200,000 main-sequence dwarf stars.
Abstract: The Transiting Exoplanet Survey Satellite (TESS) will search for planets transiting bright and nearby stars. TESS has been selected by NASA for launch in 2017 as an Astrophysics Explorer mission. The spacecraft will be placed into a highly elliptical 13.7-day orbit around the Earth. During its 2-year mission, TESS will employ four wide-field optical charge-coupled device cameras to monitor at least 200,000 main-sequence dwarf stars with I C ≈4−13 for temporary drops in brightness caused by planetary transits. Each star will be observed for an interval ranging from 1 month to 1 year, depending mainly on the star’s ecliptic latitude. The longest observing intervals will be for stars near the ecliptic poles, which are the optimal locations for follow-up observations with the James Webb Space Telescope. Brightness measurements of preselected target stars will be recorded every 2 min, and full frame images will be recorded every 30 min. TESS stars will be 10 to 100 times brighter than those surveyed by the pioneering Kepler mission. This will make TESS planets easier to characterize with follow-up observations. TESS is expected to find more than a thousand planets smaller than Neptune, including dozens that are comparable in size to the Earth. Public data releases will occur every 4 months, inviting immediate community-wide efforts to study the new planets. The TESS legacy will be a catalog of the nearest and brightest stars hosting transiting planets, which will endure as highly favorable targets for detailed investigations.

2,604 citations

Journal ArticleDOI
TL;DR: In this paper, the authors search the literature to find papers announcing the discovery of pulsars or giving improved parameters for them, and then they enter these papers' data into a new pulsar catalogue that can be accessed via a web interface or from the command line (on Solaris or Linux machines).
Abstract: The number of known pulsars has significantly increased over the previous few years. We have searched the literature to find papers announcing the discovery of pulsars or giving improved parameters for them. Data from the papers have been entered into a new pulsar catalogue that can be accessed via a web interface or from the command line (on Solaris or Linux machines). The user may request over 120 different parameters, select pulsars of interest, generate custom variables and choose between different ways of displaying or tabulating the data. Full bibliographic references are available on all observed parameters.

2,541 citations

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