Dust size and spatial distributions in debris discs: predictions for exozodiacal dust dragged in from an exo-Kuiper belt. (arXiv:2007.01313v1 [astro-ph.EP])

Dust size and spatial distributions in debris discs: predictions for exozodiacal dust dragged in from an exo-Kuiper belt. (arXiv:2007.01313v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Rigley_J/0/1/0/all/0/1">Jessica K. Rigley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wyatt_M/0/1/0/all/0/1">Mark C. Wyatt</a>

The SEDs of some nearby stars show mid-infrared excesses from warm habitable
zone dust, known as exozodiacal dust. This dust may originate in collisions in
a planetesimal belt before being dragged inwards. This paper presents an
analytical model for the size distribution of particles at different radial
locations in such a scenario, considering evolution due to destructive
collisions and Poynting-Robertson (P-R) drag. Results from more accurate but
computationally expensive numerical simulations of this process are used to
validate the model and fit its free parameters. The model predicts 11 $mu$m
excesses ($R_{11}$) for discs with a range of dust masses and planetesimal belt
radii using realistic grain properties. We show that P-R drag should produce
exozodiacal dust levels detectable with the Large Binocular Telescope
Interferometer (LBTI) ($R_{11} > 0.1%$) in systems with known outer belts;
non-detection may indicate dust depletion, e.g. by an intervening planet. We
also find that LBTI could detect exozodiacal dust dragged in from a belt too
faint to detect at far-infrared wavelengths, with fractional luminosity $fsim
10^{-7}$ and radius $sim 10-80$ au. Application to systems observed with LBTI
shows that P-R drag can likely explain most (5/9) of the exozodiacal dust
detections in systems with known outer belts; two systems ($beta$ Uma and
$eta$ Corvi) with bright exozodi may be due to exocomets. We suggest that the
three systems with exozodiacal dust detections but no known belt may have cold
planetesimal belts too faint to be detectable in the far-infrared. Even systems
without outer belt detections could have exozodiacal dust levels $R_{11} >
0.04%$ which are problematic for exo-Earth imaging.

The SEDs of some nearby stars show mid-infrared excesses from warm habitable
zone dust, known as exozodiacal dust. This dust may originate in collisions in
a planetesimal belt before being dragged inwards. This paper presents an
analytical model for the size distribution of particles at different radial
locations in such a scenario, considering evolution due to destructive
collisions and Poynting-Robertson (P-R) drag. Results from more accurate but
computationally expensive numerical simulations of this process are used to
validate the model and fit its free parameters. The model predicts 11 $mu$m
excesses ($R_{11}$) for discs with a range of dust masses and planetesimal belt
radii using realistic grain properties. We show that P-R drag should produce
exozodiacal dust levels detectable with the Large Binocular Telescope
Interferometer (LBTI) ($R_{11} > 0.1%$) in systems with known outer belts;
non-detection may indicate dust depletion, e.g. by an intervening planet. We
also find that LBTI could detect exozodiacal dust dragged in from a belt too
faint to detect at far-infrared wavelengths, with fractional luminosity $fsim
10^{-7}$ and radius $sim 10-80$ au. Application to systems observed with LBTI
shows that P-R drag can likely explain most (5/9) of the exozodiacal dust
detections in systems with known outer belts; two systems ($beta$ Uma and
$eta$ Corvi) with bright exozodi may be due to exocomets. We suggest that the
three systems with exozodiacal dust detections but no known belt may have cold
planetesimal belts too faint to be detectable in the far-infrared. Even systems
without outer belt detections could have exozodiacal dust levels $R_{11} >
0.04%$ which are problematic for exo-Earth imaging.

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