A unicorn in monoceros: the 3 M⊙ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate
Monthly Notices of the Royal Astronomical Society(2021)
摘要
We report the discovery of the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby (
$d\sim 460\, \rm pc$
), bright (V ≃ 8.3 mag), evolved (T
eff, giant
≃ 4440 K, and L
giant
≃ 173 L
⊙
) red giant in a high mass function, f(M) = 1.72 ± 0.01 M
⊙
, nearly circular binary (P = 59.9 d, e ≃ 0). V723 Mon is a known variable star, previously classified as an eclipsing binary, but its All-Sky Automated Survey, Kilodegree Extremely Little Telescope, and Transiting Exoplanet Survey Satellite 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
$87.0^{\circ ^{+1.7^\circ }}_{-1.4^\circ }$
, a mass ratio of q ≃ 0.33 ± 0.02, a companion mass of M
comp
= 3.04 ± 0.06 M
⊙
, a stellar radius of R
giant
= 24.9 ± 0.7 R
⊙
, and a giant mass of M
giant
= 1.00 ± 0.07 M
⊙
. We identify a likely non-stellar, diffuse veiling component with contributions in the B and V band of
${\sim }63{{\ \rm per\ cent}}$
and
${\sim }24{{\ \rm per\ cent}}$
, 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 discs. The X-ray luminosity of the system is
$L_{\rm X}\simeq 7.6\times 10^{29}~\rm ergs~s^{-1}$
, corresponding to L/L
edd
∼ 10
−9
. The simplest explanation for the massive companion is a single compact object, most likely a black hole in the ‘mass gap’.
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关键词
binaries: spectroscopic,stars: black holes,stars: individual: V723 Mon
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