Kavli Affiliate: Avi Shporer
| First 5 Authors: Nicholas Scarsdale, Joseph M. Akana Murphy, Natalie M. Batalha, Ian J. M. Crossfield, Courtney D. Dressing
| Summary:
We present the discovery of two nearly identically-sized sub-Neptune
transiting planets orbiting HD 63935, a bright ($V=8.6$ mag), sun-like
($T_{eff}=5560K$) star at 49 pc. TESS identified the first planet, HD 63935 b
(TOI-509.01), in Sectors 7 and 34. We identified the second signal (HD 63935 c)
in Keck HIRES and Lick APF radial velocity data as part of our followup
campaign. It was subsequently confirmed with TESS photometry in Sector 34 as
TOI-509.02. Our analysis of the photometric and radial velocity data yields a
robust detection of both planets with periods of $9.0600 pm 0.007$ and $21.40
pm 0.0019$ days, radii of $2.99 pm 0.14$ and $2.90 pm 0.13$ $R_oplus$, and
masses of $10.8 pm 1.8$ and $11.1 pm 2.4$ $M_oplus$. We calculate densities
for planets b and c consistent with a few percent of the planet mass in
hydrogen/helium envelopes. We also describe our survey’s efforts to choose the
best targets for JWST atmospheric followup. These efforts suggest that HD 63935
b will have the most clearly visible atmosphere of its class. It is the best
target for transmission spectroscopy (ranked by Transmission Spectroscopy
Metric, a proxy for atmospheric observability) in the so-far uncharacterized
parameter space comprising sub-Neptune-sized (2.6 $R_oplus$ $<$ $R_p$ $<$ 4
$R_oplus$), moderately-irradiated (100 $F_oplus$ $<$ $F_p$ $<$ 1000
$F_oplus$) planets around G-stars. Planet c is also a viable target for
transmission spectroscopy, and given the indistinguishable masses and radii of
the two planets, the system serves as a natural laboratory for examining the
processes that shape the evolution of sub-Neptune planets.
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