Publikace ÚTF

MOA-2011-BLG-262Lb: A SUB-EARTH-MASS MOON ORBITING A GAS GIANT PRIMARY OR A HIGH VELOCITY PLANETARY SYSTEM IN THE GALACTIC BULGE

Group of people, Heyrovský D.

We present the first microlensing candidate for a free-floating exoplanet–exomoon system, MOA-2011-BLG-262,
with a primary lens mass ofMhost ∼ 4 Jupitermasses hosting a sub-Earthmassmoon. The argument for an exomoon
hinges on the system being relatively close to the Sun. The data constrain the product MLπrel where ML is the
lens system mass and πrel is the lens–source relative parallax. If the lens system is nearby (large πrel), then ML is
small (a few Jupiter masses) and the companion is a sub-Earth-mass exomoon. The best-fit solution has a large
lens–source relative proper motion, μrel = 19.6 ± 1.6 mas yr−1, which would rule out a distant lens system unless
the source star has an unusually high proper motion. However, data from the OGLE collaboration nearly rule out
a high source proper motion, so the exoplanet+exomoon model is the favored interpretation for the best fit model.
However, there is an alternate solution that has a lower proper motion and fits the data almost as well. This solution is
compatible with a distant (so stellar) host.ABayesian analysis does not favor the exoplanet+exomoon interpretation,
so Occam’s razor favors a lens system in the bulge with host and companion masses of Mhost = 0.12+0.19
−0.06M and
mcomp = 18+28
−10M⊕, at a projected separation of a⊥ = 0.84+0.25
−0.14 AU. The existence of this degeneracy is an unlucky
accident, so current microlensing experiments are in principle sensitive to exomoons. In some circumstances, it will
be possible to definitively establish the mass of such lens systems through the microlensing parallax effect. Future
experiments will be sensitive to less extreme exomoons.
typ:article
journal:The Astrophysical Journal
volume:785:155
pages:13pp
year:2014

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