Pushing the Limits, Episode 2: K2 Observations of Extragalactic RR Lyrae Stars in the Dwarf Galaxy Leo IV

Molnár, L. and Pál, A. and Plachy, E. and Ripepi, V. and Moretti, M.I. and Szabó, R. and Kiss, L.L. (2015) Pushing the Limits, Episode 2: K2 Observations of Extragalactic RR Lyrae Stars in the Dwarf Galaxy Leo IV. The Astrophysical Journal, 812. p. 2. ISSN 2041-8205

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Abstract

We present the first observations of extragalactic pulsating stars in the K2 ecliptic survey of the Kepler space telescope. The variability of all three RR Lyrae stars in the dwarf spheroidal galaxy Leo IV was successfully detected, at a brightness of Kp ≈ 21.5 mag, from data collected during Campaign 1. We identified one modulated star and another likely Blazhko candidate with periods of 29.8 ± 0.9 days and more than 80 days, respectively. EPIC 210282473 represents the first star beyond the Magellanic Clouds for which the Blazhko period and cycle-to-cycle variations in the modulation were unambiguously measured. The photometric [Fe/H] indices of the stars agree with earlier results that Leo IV is a very metal-poor galaxy. Two out of the three stars blend with brighter background galaxies in the K2 frames. We demonstrate that image subtraction can be reliably used to extract photometry from faint confused sources, which will be crucial not only for the K2 mission but also for future space photometric missions.

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