Naked-Eye Stars in Kepler and K2

Benjamin Pope

NASA Sagan Fellow, NYU

Slides available at

K2 Photometry

credit: Geert Barentsen

To extract photometry, you can just sum the pixel values in a window containing the whole PSF...

but the pixels have different gains ("inter- and intra-pixel sensitivity variation")...

and the pixel window doesn't necessarily track the whole PSF perfectly ("aperture losses").

For sufficiently bright stars, though, light fills the CCD wells with electrons that spill up and down the column, ruining the photometry as they leave the aperture.
Kepler saturates on stars brighter than ~ 11th mag (log scale: 5 mag = factor of 100) - but we want to look at stars 10k times brighter.

CCD Smear

To calibrate this 'smear' the Kepler detectors have two smear registers not exposed to light


102 KIC targets with Kp < 9 were untargeted or significantly undertargeted during Kepler - mostly giants and hot stars.

Gaia-Kepler HR Diagram

The smear data give you a 1D projection of flux in the whole module - including untargeted bright stars

Smear Profile
We have used these smear data to construct light curves for all the missing stars down to Kp=9!

We find no transiting planets, but detect one new eclipsing binary

We detect solar-like oscillations in 34 red giants

We detect classical variability in 26 BAF stars...

including five 'hump and spike' Rossby mode detections

With TRES spectra from Latham and Bieryla & asteroseismic constraints we measure abundances for the giants


Using the asteroseismology and spectroscopy we measure the giants' masses


This new sample of asteroseismic + spectroscopic benchmark stars doubles those available from the Gaia-ESO survey

All Kepler Smear Campaign data are available online at

Halo Photometry

What if we just look at unsaturated pixels?

Thanks to DDT time and GO programs, we have apertures to cover the unsaturated 'halo'!

Flux \(f_i \) at cadence i is a sum over j pixels \(p_{ij}\) with weights \(w_j\):

\[ f_i \equiv \sum\limits_i w_j p_{ij} \]

To find the appropriate weights, we instead minimize the Total Variation \[\begin{align} TV \equiv \dfrac{\sum_i |f_i - f_{i-1}|} {\sum_i f_i } \end{align} \]

All K2 Halo data are available online at


Πλειάδες, the Seven Sisters

Alcyone, Atlas (dad), Electra, Maia, Merope, Taygeta, Pleione (mum)

Combined Figure

Atlas lightcurve: raw (top) and halo (bottom)

White, Pope et al., 2017

Combined FigureCombined Figure

Lightcurves of All Seven Bright Pleiades

White, Pope et al., 2017


α Tauri

الدبران ,the follower

... follows the Pleiades!

Hatzes & Cochran, 1993 claimed an early detection of a \(628.96 \pm 0.90\) d RV planet around Aldebaran - finally confirmed in Hatzes et al., 2015!

Detection of p-mode oscillations at 2.2 μHz

Aldebaran K2 Light Curve

Without this asteroseismology, we have

\[M = 1.27^{+0.24}_{-0.20} \, \mathrm{M_{\odot}}\] and age \(4.9^{+3.6}_{-2.0} \, \rm Gyr \)

With this new constraint, we have

\[M = 1.16^{+0.07}_{-0.07} \, \mathrm{M_{\odot}}\] and age \(6.4^{+1.4}_{-1.1} \, \rm Gyr \)

Using MESA models, we find that on the main sequence Aldebaran b had a semi-major axis of \(1.50 \pm 0.03 \) AU and Aldebaran had a luminosity \(2.0 \pm 0.7 \, L_\odot \)...

so Aldebaran b had an insolation comparable to Earth when its star was on the main sequence.

Data Releases

All Kepler Smear Campaign data are available online at

K2 Halo Campaign data are available online at

See Arentoft's paper on ε Tau, Buysschaert's on ι Lib, and Bowman's talk up next on ρ Leonis

Posters by Buzasi (Spica) and Greklek-McKeon (classifications)

More to come!

Halo generalizes well to TESS data. Watch for TASOC paper on β Hydri (White et al., in prep)