Stellar brightness vs. time measurements (light curves) for "A Search for Variable Stars in the Globular Cluster M4 with K2" by Joshua Wallace, Joel Hartman, Gaspar Bakos, and Waqas Bhatti These data are associated with the publication with the same title and authors as indicated above. Please cite that publication if you use these data. At time of submission of these light curves to the data archive, the paper was not published yet, and the archive rules prevent me from coming back later to edit these files and include the full publication information, so search for that publication if you can. Once it is published, the metadata field for this data submission should be edited to contain the Digital Object Identifier of the publication, so you may start your search there. These data are also associated with the PhD dissertation of Joshua Wallace, graduated from Princeton University in 2019. The data are light curves derived from images taken of the globular cluster M4 by the Kepler space telescope during the K2 portion of its mission, specifically during Campaign 2 of that mission, which occurred in 2014. A total of 3856 images were taken over approximately three months at a cadence of approximately half an hour. The purpose of these observations was to find stars and other objects that vary in brightness over time --- variable stars. -------------------------- License These data are copyright 2019 by Joshua Wallace, Joel Hartman, and Gaspar Bakos. These data are licensed under a Creative Commons Attribution 4.0 International License. You should have received a copy of the license along with these data. If not, see . -------------------------- General notes The files are in a compressed tarball, wallace_data.tgz, for convenience of download and storage. The tarball also contains a copy of this README. The table found in object_information.txt is included both in the tarball and as a separate file, the former because it is information that belongs with the light curves and the latter because it is a stand-alone table for Joshua Wallace's dissertation. This data set contains light curves for 4554 objects, stored in the comma-separated values (CSV) format. In this format, rows are separated in the file by new line characters and columns are separated by commas. There can be missing data. The light curves files are those files with names of format "*_lc.csv", with the * being a wildcard. All the light curve files start with either a "V", "S", or "W". The first row of each file is a header with labels for each column, and the rest of the each file contains data and just data. This data set also contains an additional table (object_information.txt) that records some additional information on each object and its associated light curve, including right ascension, declination, and magnitude (in Gaia G) of each object. This table is published as part of Joshua Wallace's dissertation. It is a plain text table, with a large and descriptive header marked by lines beginning with "#" characters and columns separated by arbitrary numbers of spaces. It is also planned that a machine-readable version of the table will be published with the publication indicated at the beginning of this document. -------------------------- File descriptions As mentioned, object_information.txt has its own descriptive header, which should be referenced for any questions on the formatting of that file. For the light curve files (those files ending in "_lc.csv"), included are data describing the time of observation and the observed brightnesses (in magnitudes) over seven different photometric apertures and as calculated at three different stages of our photometric processing. The portion of the file name preceding "_lc.csv" is the identifier we gave the object for our work and corresponds to an equivalent identifier listed in the "ID" column of the table in object_information.txt. The first line of each file is a header labeling each column. The first five columns are described below: - KBJD: This is Kepler Barycentric Julian Date, with conversion between KBJD and Barycentric Julian Date (BJD) being KBJD = BJD - 2454833.0 - raw_ap_chosen: this is the "raw" photometry directly as output by our photometric calculation before any post-processing clean up occurred. The "ap_chosen" portion of the name means that these are the results from the photometric aperture chosen as the aperture of choice for this object for our subsequent analysis. - post_decorr_ap_chosen: this is the photometry after applying a decorrelation against the roll to clean up much of the systematic effects present in the data from the K2 mission. This is again for the chosen aperture. - final_ap_chosen: this is the photometry after both applying the roll decorrelation and subsequently using the Trend Filtering Algorithm to further clean up the data. The designation of "final" means that these were the data used in our analysis; its processing was complete. This is again for the chosen aperture. - err_ap_chosen: this is the photometric error, in magnitudes, as determined by our photometric calculation. Errors were not additionally calculated for the subsequent processing steps and so the error values are applied to all three of raw_ap_chosen, post_decorr_ap_chosen, and final_ap_chosen. We found that the errors determined by our calculation were almost certainly underestimated relative to the final scatter of the light curves, likely due to still-uncorrected systematics in the data. The subsequent columns are all repeats of the latter four of the five columns described above for the seven different apertures. Those column headers ending in "0" corresponded to the smallest aperture, those ending in "1" corresponded to the second-smallest aperture, and so on up to "6". The aperture sizes used for our calculations were: 1.5, 1.75, 2.0, 2.25, 2.5, 2.75, and 3.0 pixels in radius. Note that the set of "*_ap_chosen" columns are a repeat of a set of one of the other columns with a specified aperture number. We included the "*_ap_chosen" columns as a convenience for those interested in working with the same versions of the light curves that we did without needing to determine, object-by-object, which columns should be referenced. Note also that for all objects and apertures, there are no data for any of the "post_decorr_ap_*" or "final_ap_*" columns for the first 49 rows. This is an intentional omission as the data did not allow for our roll decorrelation procedure to work for these 49 observations.