Spitzer transit follow-up of planet candidates from the K2 mission. (arXiv:1901.05855v1 [astro-ph.EP])

Spitzer transit follow-up of planet candidates from the K2 mission. (arXiv:1901.05855v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Livingston_J/0/1/0/all/0/1">John H. Livingston</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Crossfield_I/0/1/0/all/0/1">Ian J. M. Crossfield</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Werner_M/0/1/0/all/0/1">Michael W. Werner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gorjian_V/0/1/0/all/0/1">Varoujan Gorjian</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Petigura_E/0/1/0/all/0/1">Erik A. Petigura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ciardi_D/0/1/0/all/0/1">David R. Ciardi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dressing_C/0/1/0/all/0/1">Courtney D. Dressing</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fulton_B/0/1/0/all/0/1">Benjamin J. Fulton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hirano_T/0/1/0/all/0/1">Teruyuki Hirano</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schlieder_J/0/1/0/all/0/1">Joshua E. Schlieder</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sinukoff_E/0/1/0/all/0/1">Evan Sinukoff</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kosiarek_M/0/1/0/all/0/1">Molly Kosiarek</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Akeson_R/0/1/0/all/0/1">Rachel Akeson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Beichman_C/0/1/0/all/0/1">Charles A. Beichman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Benneke_B/0/1/0/all/0/1">Björn Benneke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Christiansen_J/0/1/0/all/0/1">Jessie L. Christiansen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hansen_B/0/1/0/all/0/1">Bradley M. S. Hansen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Howard_A/0/1/0/all/0/1">Andrew W. Howard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Isaacson_H/0/1/0/all/0/1">Howard Isaacson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Knutson_H/0/1/0/all/0/1">Heather A. Knutson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Krick_J/0/1/0/all/0/1">Jessica Krick</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Martinez_A/0/1/0/all/0/1">Arturo O. Martinez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sato_B/0/1/0/all/0/1">Bun'ei Sato</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tamura_M/0/1/0/all/0/1">Motohide Tamura</a>

We present precision 4.5 $mu$m Spitzer transit photometry of eight planet
candidates discovered by the K2 mission: K2-52 b, K2-53 b, EPIC 205084841.01,
K2-289 b, K2-174 b, K2-87 b, K2-90 b, and K2-124 b. The sample includes four
sub-Neptunes and two sub-Saturns, with radii between 2.6 and 18 $R_oplus$, and
equilibrium temperatures between 440 and 2000 K. In this paper we identify
several targets of potential interest for future characterization studies,
demonstrate the utility of transit follow-up observations for planet validation
and ephemeris refinement, and present new imaging and spectroscopy data. Our
simultaneous analysis of the K2 and Spitzer light curves yields improved
estimates of the planet radii, and multi-wavelength information which help
validate their planetary nature, including the previously un-validated
candidate EPIC 205686202.01 (K2-289 b). Our Spitzer observations yield an order
of magnitude increase in ephemeris precision, thus paving the way for efficient
future study of these interesting systems by reducing the typical transit
timing uncertainty in mid-2021 from several hours to a dozen or so minutes.
K2-53 b, K2-289 b, K2-174 b, K2-87 b, and K2-90 b are promising radial velocity
(RV) targets given the performance of spectrographs available today or in
development, and the M3V star K2-124 hosts a temperate sub-Neptune that is
potentially a good target for both RV and atmospheric characterization studies.

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