K2 Observations of
Open Clusters
Ann Marie Cody
NPP fellow at NASA Ames
November 2, 2015
Acknowledgm
ents
•Ames collaborators: Steve Howell, Tom Barclay,
Fergal Mullally, Susan Thompson, Geert
Barentsen, Jason Rowe, student interns: Bryan
Mann, Shishir Dholakia, Shashank Dholakia
•External collaborators: Lynne Hillenbrand, Trevor
David, John Stauffer, Luisa Rebull, Kevin Covey,
Adam Kraus, Michael Ireland, Stephanie Douglas,
Suzanne Aigrain
K2 is ideally suited to monitor star clusters
Large field of view
High precision
Long time baseline
Continuous time series
Bright, nearby targets – great
for follow-up
M35
Ground
vs.
K2
A. Vanderburg
Nardiello et al. (2015)
K2 is Contributing Enormously to Young Star
Science
Taurus!!
(300+ known
members)
K2 has a number of photometric pipelines
Official K2 pipeline: Light curves for
Campaigns 3, 4, 5 with PDC detrending
A. Vanderburg pipeline: Light curves for
Campaigns 0-4 with SFF detrending
 Other approaches- C. Huang et al. (2015);
Libralato et al. (2015); S. Aigrain in prep.
My pipeline: operates on both regular and
superstamp images
Superstamp Photometry: M35
Superstamp WCS solution 
•Track X,Y movement of individual sources
•Measure fluxes with range of moving circular
apertures
•Decorrelate flux vs. X,Y position
Decorrelate flux vs. X,Y position
Star clusters in the time domain: Science
Eclipsing binaries
Starspot properties and stellar rotation
Exploration of accretion and diskrelated variability
Search for young planets
~50 EBs in the M35 Superstamp
…but which are cluster members?
M35 Candidates
Field stars
Bouy et al. (2015)
Eclipsing Binaries are Yielding Clues to Early
Stellar Evolution
David
poster
David, Hillenbrand, Cody+ subm.
Star clusters in the time domain: Science
Eclipsing binaries
Starspot properties and stellar rotation
Exploration of accretion and diskrelated variability
Search for young planets
K2 reveals spot evolution and/or differential
rotation
M35
M35
USco
USco
Pleiades
Pleiades
Hyades
Hyades
K2 reveals spot evolution and differential rotation
 Can be difficult to differentiate the two phenomena (Aigrain
et al. 2015)
 ~20-30% of intermediate age stars show multiple light curve
frequencies
 Spot evolution appears on ~week timescales, if at all.
Currently comparing long-term spot behavior on the pre main
sequence vs. in older clusters. Mass dependence unclear.
Rebull
poster
The mass dependence of rotation at young ages
Covey
poster
Star clusters in the time domain: Science
Eclipsing binaries
Starspot properties and stellar rotation
Exploration of accretion and diskrelated variability
Search for young planets
Hartmann 1999
The space based photometry revolution on
young stars
CoRoT:
NGC 2264
MOST:
TaurusAuriga/
Lupus/
TW Hya
K2:
Sco-Cen/
ρ Oph/
Lagoon/
Taurus?
Sub-1% precision
• 20-80 days of continuous photometric monitoring
•
A Zoo of Young Star Light Curves
Flux Asymmetry
Light Curve Classification Scheme
Bursters
Purely
periodic
Eclipsing
binaries
Quasi-periodic
stars
Stochastic
stars
Stochasticity
Dippers
Cody+ 2014
Classes can now be selected statistically!
Cody et al. 2014
~20-30%: Quasi-periodic flux dips:
Circumstellar dust obscuration
New classes of young star behavior!
“Bursters”
[Embargoed slide.]
Bursters display a spatial spread on the sky
Star clusters in the time domain: Science
Eclipsing binaries
Starspot properties and stellar rotation
Exploration of accretion and diskrelated variability
Search for young planets
Many False Positives to Sort Through!
A candidate – but unclear whether it is a
cluster member
Found by high school
students Shashank &
Shishir Dholakia!
Summary
K2 is an excellent platform for photometric monitoring
of young to intermediate age star clusters.
The resulting time series are being used to contrain
stellar parameters, understand angular momentum
evolution, as well as magnetic spot properties.
More cluster data to come!
By the end of the mission, we may have a significant
enough sample to constraint planet occurrence rates
at young ages.