We are delighted to present light curves of the very brightest stars observed by K2 - including the first magnitude stars Aldebaran and Spica, the Seven Sisters of the Pleiades, the Hyades giants and the blue supergiant ρ Leonis!

Kepler saturates around the eleventh magnitude, and looking at first magnitude stars ten thousand times brighter is therefore conventionally impossible. These light curves were obtained through a special 'halo photometry' method, which uses the unsaturated 'halo' around a saturated star and applies a Total Variation minimization (TV-min) algorithm to obtain nearly normal quality photometry. These are then additionally corrected with the k2sc Gaussian Process systematics-correction code to further correct pointing residuals.

We hope you are as excited as we are to look at the largest ever sample of the brightest ever stars to be observed with high-quality space photometry!

In this repository we include the entire set of scripts and metadata that went into producing the K2 Halo Campaign data release. We do so in order that this science is completely open and reproducible, so that the K2 Halo Campaign light curves can be kept up to date with new software or data releases, and to facilitate custom re-reductions of individual datasets. If you have any requests, notice any bugs, or have any suggestions, please do not hesitate to open an Issue on this GitHub page with your comments.

You will need to use git-lfs to download the .fits and .png data products. Remember to run git lfs pull to sync the files locally.

The final light curves will be made available as High Level Science Products on MAST. The reduction here should be considered pretty good but nevertheless preliminary and may be improved or extended by the time it goes live on MAST.

• In notebooks/ are the Jupyter notebooks used to generate all the scripts and explore the data.

• In data/ are the catalogues and scripts to download the TPFs.

• In reduced/ are the halophot reduction scripts, together with subdirectories for each campaign including the halo light curve fits files and diagnostic plots.

• In scripts/ are the k2sc call script and sbatch scripts to deploy this to the NYU HPC cluster.

• In release/ are the final k2sc light curves in MAST High Level Science Product format, together with k2sc + halophot diagnostic plots. Use these for your science!

  • There is no position information for C91, C92, C101, and there are no halo apertures for C112. As a result k2sc-corrected data are not available for these targets at the moment.

To perform a complete reduction, run the entire notebook download_stars.ipynb and execute the download commands in data/. Then on a slurm HPC platform use

sbatch reduced/sbatch_halo_all.sbatch
sbatch reduced/sbatch_halo_clip.sbatch
sbatch scripts/sbatch_k2sc_all.sbatch

There

The halo apertures were kindly provided by the K2 team as part of the Guest Observer programs GO6081-7081, GO8025, GO9923, GO10025, GO11047-13047, GO14003-16003, and GO17051-19051 (led by Daniel Huber), and as a DDT program in Campaign 4.

If you use these data pre-publication, please contact Pope, White, and Huber to include them and any relevant team members as co-authors.

A data release paper is in preparation (Pope et al., in prep).

Please also cite the original White et al. halo paper:

@ARTICLE{White2017,
   author = {{White}, T.~R. and {Pope}, B.~J.~S. and {Antoci}, V. and {P{\'a}pics}, P.~I. and
  {Aerts}, C. and {Gies}, D.~R. and {Gordon}, K. and {Huber}, D. and
  {Schaefer}, G.~H. and {Aigrain}, S. and {Albrecht}, S. and {Barclay}, T. and
  {Barentsen}, G. and {Beck}, P.~G. and {Bedding}, T.~R. and {Fredslund Andersen}, M. and
  {Grundahl}, F. and {Howell}, S.~B. and {Ireland}, M.~J. and
  {Murphy}, S.~J. and {Nielsen}, M.~B. and {Silva Aguirre}, V. and
  {Tuthill}, P.~G.},
    title = "{Beyond the Kepler/K2 bright limit: variability in the seven brightest members of the Pleiades}",
  journal = {\mnras},
archivePrefix = "arXiv",
   eprint = {1708.07462},
 primaryClass = "astro-ph.SR",
 keywords = {asteroseismology, techniques: photometric, stars: early type, stars: variables: general, open clusters and associations: individual: Pleiades},
     year = 2017,
    month = nov,
   volume = 471,
    pages = {2882-2901},
      doi = {10.1093/mnras/stx1050},
   adsurl = {http://adsabs.harvard.edu/abs/2017MNRAS.471.2882W},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}

Papers on Aldebaran, the Pleiades, ι Lib, ε Tauri, and ρ Leonis have already been published. Manuscripts are in preparation on the catalogue (Pope), Spica (Buzasi), variability in the main-sequence stars (Greklek-McKeon/Huber), chemically-peculiar stars (Luger/Pope), and Hyades giants (White). Please be kind!

The Kepler Smear Campaign includes 103 of the brightest stars observed in the nominal Kepler Mission, obtained via smear photometry. If you haven't had enough of high-quality light curves of very bright stars from the K2 Halo Campaign, this is where you need to go!

In addition to this, before the halo photometry GO proposals, the first few K2 campaigns more or less entirely missed observing very bright stars. Smear data are available for bright stars in these upon request.

The halo method has been extended to TESS as part of the TASOC pipeline - watch this space for exciting new results soon.