The K2 Galactic Archaeology Program Data Release. I. Asteroseismic Results from Campaign 1

Stello, Dennis; Zinn, Joel; Elsworth, Yvonne; Garcia, Rafael A.; Kallinger, Thomas; Mathur, Savita; Mosser, Benoit; Sharma, Sanjib; Chaplin, William J.; Davies, Guy; Huber, Daniel; Jones, Caitlin D.; Miglio, Andrea; Silva Aguirre, Victor

The K2 Galactic Archaeology Program Data Release. I. Asteroseismic Results from Campaign 1,
The Astrophysical Journal, Vol. 835, Issue 1

Abstract

NASA’s K2 mission is observing tens of thousands of stars along the ecliptic, providing data suitable for large-scale asteroseismic analyses to inform galactic archaeology studies. Its first campaign covered a field near the north Galactic cap, a region never covered before by large asteroseismic-ensemble investigations, and was therefore of particular interest for exploring this part of our Galaxy.

Here we report the asteroseismic analysis of all stars selected by the K2 Galactic Archaeology Program during the mission’s “north Galactic cap” campaign 1. Our consolidated analysis uses six independent methods to measure the global seismic properties, in particular the large frequency separation and the frequency of maximum power. From the full target sample of 8630 stars we find about 1200 oscillating red giants, a number comparable with estimates from galactic synthesis modeling. Thus, as a valuable by-product we find roughly 7500 stars to be dwarfs, which provide a sample well suited for galactic exoplanet occurrence studies because they originate from our simple and easily reproducible selection function.

In addition, to facilitate the full potential of the data set for galactic archaeology, we assess the detection completeness of our sample of oscillating red giants. We find that the sample is at least nearly complete for stars with 40 ≲ ν_max μHz ≲ 270 and ν_{max, detect}< 2.6×10⁶ ×2^-Kp μHz. There is a detection bias against helium core burning stars with ν_max ~30 μHz, affecting the number of measurements of Δν and possibly also ν_max . Although we can detect oscillations down to Kp = 15, our campaign 1 sample lacks enough faint giants to assess the detection completeness for stars fainter than Kp~14.5.