The K2 Galactic Caps Project -- Going Beyond the \textit{Kepler} Field and Ageing the Galactic Disc

Research output: Contribution to journalArticle

Authors

  • B. M. Rendle
  • C. Chiappini
  • M. Valentini
  • B. Mosser
  • R. A. García
  • S. Mathur
  • P. Jofré
  • C. C. Worley
  • L. Casagrande
  • L. Girardi
  • D. K. Feuillet
  • A. Gavel
  • L. Magrini
  • S. Khan
  • T. S. Rodrigues
  • J. A. Johnson
  • K. Cunha
  • R. L. Lane
  • C. Nitschelm

Colleges, School and Institutes

Abstract

Analyses of data from spectroscopic and astrometric surveys have led to conflicting results concerning the vertical characteristics of the Milky Way. Ages are often used to provide clarity, but typical uncertainties of $>$ 40\,\% restrict the validity of the inferences made. Using the \textit{Kepler} APOKASC sample for context, we explore the global population trends of two K2 campaign fields (3 and 6), which extend further vertically out of the Galactic plane than APOKASC. We analyse the properties of red giant stars utilising three asteroseismic data analysis methods to cross-check and validate detections. The Bayesian inference tool PARAM is used to determine the stellar masses, radii and ages. Evidence of a pronounced red giant branch bump and an [$\alpha$/Fe] dependence on the position of the red clump is observed from the radii distribution of the K2 fields. Two peaks in the age distribution centred at $\sim$5 and and $\sim$12 Gyr are found using a sample with $\sigma_{\rm{age}}$ $$ 0.1) [$\alpha$/Fe] stars. As a function of vertical distance from the Galactic mid-plane ($|Z|$), the age distribution shows a transition from a young to old stellar population with increasing $|Z|$ for the K2 fields. Further coverage of campaign targets with high resolution spectroscopy is required to increase the yield of precise ages achievable with asteroseismology.

Bibliographic note

17 pages, 16 figures. Accepted to MNRAS 01/08/2019. Updated manuscript

Details

Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Volume490
Issue number4
Publication statusPublished - 4 Nov 2019

Keywords

  • astro-ph.SR, astro-ph.GA