Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Limits on the Mass and Initial Entropy of 51 Eri b from Gaia EDR3
  Astrometry   51 Eri b is one of the only young planets consistent with a wide range of
possible initial entropy states, including the cold-start scenario associated
with some models of planet formation by core accretion. The most direct way to
constrain the initial entropy of a planet is by measuring its luminosity and
mass at a sufficiently young age that the initial conditions still matter. We
present the tightest upper limit on 51 Eri b's mass yet (M < 11 Mjup at
2$\sigma$) using a cross-calibration of Hipparcos and Gaia EDR3 astrometry and
the orbit-fitting code orvara. We also reassess its luminosity using a direct,
photometric approach, finding log(Lbol/Lsun) = -5.5$\pm$0.2 dex. Combining this
luminosity with the 24$\pm$3 Myr age of the $\beta$ Pic moving group, of which
51 Eri is a member, we derive mass distributions from a grid of evolutionary
models that spans a wide range of initial entropies. We find that 51 Eri b is
inconsistent with the coldest-start scenarios, requiring an initial entropy of
>8 $k_B$/baryon at 97% confidence. This result represents the first
observational constraint on the initial entropy of a potentially cold-start
planet, and it continues the trend of dynamical masses for directly imaged
planets pointing to warm- or hot-start formation scenarios.

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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: plasm-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-bio
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat
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The categories of this paper are: ao-sci
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The categories of this paper are: mtrl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-th
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The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: funct-an