Prospects for detecting the astrometric signature of Barnard’s Star b. (arXiv:1811.05920v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Tal_Or_L/0/1/0/all/0/1">Lev Tal-Or</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zucker_S/0/1/0/all/0/1">Shay Zucker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ribas_I/0/1/0/all/0/1">Ignasi Ribas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Anglada_Escude_G/0/1/0/all/0/1">Guillem Anglada-Escud&#xe9;</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reiners_A/0/1/0/all/0/1">Ansgar Reiners</a>

A low-amplitude periodic signal in the radial-velocity (RV) time-series of
Barnard’s Star was recently attributed to a planetary companion with a minimum
mass of ${sim}3.2$ $M_oplus$ at an orbital period of ${sim}233$ days. The
proximity of Barnard’s Star to the Sun raises the question whether the true
mass of the planet can be constrained by accurate astrometric measurements. We
review the astrometric capabilities and limitations of current and upcoming
astrometric instruments. By combining the assumption of an isotropic
probability distribution of the orbital orientation with the RV analysis
results, we calculate the probability distribution function of the planet’s
astrometric signature. We conclude that there is a probability of only
${sim}1%$ that Gaia observations will detect it. Observations with the Hubble
Space Telescope (HST) may increase the detection probability to ${sim}10%$.
In case of no detection, the implied mass upper limit with HST observations
would be ${sim}8$ $M_oplus$, which will place the planet in the super-Earth
mass range. In the next decade, observations with the Wide-Field Infrared Space
Telescope (WFIRST) may increase the prospects of measuring the planet’s true
mass to ${sim}99%$.

A low-amplitude periodic signal in the radial-velocity (RV) time-series of
Barnard’s Star was recently attributed to a planetary companion with a minimum
mass of ${sim}3.2$ $M_oplus$ at an orbital period of ${sim}233$ days. The
proximity of Barnard’s Star to the Sun raises the question whether the true
mass of the planet can be constrained by accurate astrometric measurements. We
review the astrometric capabilities and limitations of current and upcoming
astrometric instruments. By combining the assumption of an isotropic
probability distribution of the orbital orientation with the RV analysis
results, we calculate the probability distribution function of the planet’s
astrometric signature. We conclude that there is a probability of only
${sim}1%$ that Gaia observations will detect it. Observations with the Hubble
Space Telescope (HST) may increase the detection probability to ${sim}10%$.
In case of no detection, the implied mass upper limit with HST observations
would be ${sim}8$ $M_oplus$, which will place the planet in the super-Earth
mass range. In the next decade, observations with the Wide-Field Infrared Space
Telescope (WFIRST) may increase the prospects of measuring the planet’s true
mass to ${sim}99%$.

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