How much do underestimated field strengths from Zeeman-Doppler imaging affect spin-down torque estimates?. (arXiv:2002.11774v1 [astro-ph.SR])

How much do underestimated field strengths from Zeeman-Doppler imaging affect spin-down torque estimates?. (arXiv:2002.11774v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+See_V/0/1/0/all/0/1">Victor See</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lehmann_L/0/1/0/all/0/1">Lisa Lehmann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matt_S/0/1/0/all/0/1">Sean P. Matt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Finley_A/0/1/0/all/0/1">Adam J. Finley</a>

Numerous attempts to estimate the rate at which low-mass stars lose angular
momentum over their lifetimes exist in the literature. One approach is to use
magnetic maps derived from Zeeman-Doppler imaging (ZDI) in conjunction with
so-called “braking laws”. The use of ZDI maps has advantages over other methods
because it allows information about the magnetic field geometry to be
incorporated into the estimate. However, ZDI is known to underestimate
photospheric field strengths due to flux cancellation effects. Recently,
Lehmann et al. (2018) conducted synthetic ZDI reconstructions on a set of flux
transport simulations to help quantify the amount by which ZDI underestimates
the field strengths of relatively slowly rotating and weak activity solar-like
stars. In this paper, we evaluate how underestimated angular momentum-loss rate
estimates based on ZDI maps may be. We find that they are relatively accurate
for stars with strong magnetic fields but may be underestimated by a factor of
up to $sim$10 for stars with weak magnetic fields. Additionally, we
re-evaluate our previous work that used ZDI maps to study the relative
contributions of different magnetic field modes to angular momentum-loss. We
previously found that the dipole component dominates spin-down for most
low-mass stars. This conclusion still holds true even in light of the work of
Lehmann et al. (2018).

Numerous attempts to estimate the rate at which low-mass stars lose angular
momentum over their lifetimes exist in the literature. One approach is to use
magnetic maps derived from Zeeman-Doppler imaging (ZDI) in conjunction with
so-called “braking laws”. The use of ZDI maps has advantages over other methods
because it allows information about the magnetic field geometry to be
incorporated into the estimate. However, ZDI is known to underestimate
photospheric field strengths due to flux cancellation effects. Recently,
Lehmann et al. (2018) conducted synthetic ZDI reconstructions on a set of flux
transport simulations to help quantify the amount by which ZDI underestimates
the field strengths of relatively slowly rotating and weak activity solar-like
stars. In this paper, we evaluate how underestimated angular momentum-loss rate
estimates based on ZDI maps may be. We find that they are relatively accurate
for stars with strong magnetic fields but may be underestimated by a factor of
up to $sim$10 for stars with weak magnetic fields. Additionally, we
re-evaluate our previous work that used ZDI maps to study the relative
contributions of different magnetic field modes to angular momentum-loss. We
previously found that the dipole component dominates spin-down for most
low-mass stars. This conclusion still holds true even in light of the work of
Lehmann et al. (2018).

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