Light curves of young stars from K2 (K2YSO)
Primary Investigator: Ann Marie Cody
HLSP Authors: Ann Marie Cody, Laura Venuti, Apoorva Thanvantri
Citations: See ADS Metrics
Over its mission lifetime, K2 observed hundreds of young stellar objects ("YSOs") at ages of less than 10 million years (Myr). The team has created and analyzed custom light curves for K2 long cadence (roughly 30-minute sampling rate) targets in four different young regions: Upper Scorpius, the rho Ophiuchus cluster, Taurus, and NGC 6530, the Lagoon Nebula Cluster. The photometric pipeline consists of a mixture of circular aperture photometry, psf photometry, and custom pixel masks for saturated stars. After removal of systematic trends related to pointing jitter, the best light curve was chosen for each target, maximizing photometric precision while avoiding blends with stellar neighbors. Outliers based on flux and image centroid position were flagged, with care to retain stellar flares and eclipses.
The resulting light curves are provided here as a function of cluster membership as well as circumstellar disk status, as determined in the listed reference papers. While alternate light curve versions exist for some of the targets, the reduction procedures for these products have been tuned to preserve all sources of astrophysical variability. Additionally, light curves for stars in the Lagoon superstamp region have never been released to the public previously. The full set of time series will facilitate further high-precision studies of YSO photometric variability, as well as searches for substellar companions.
- the region consists of "taurus" (Taurus association; K2 campaigns 4 and 13), "sco" (Upper Scorpius association; K2 campaign 2), "oph" (rho Ophiuchus cluster; K2 campaign 2), and "lagoon" (NGC 6530, the Lagoon Nebula Cluster; K2 Campaign 9)
- diskstatus is listed as "disks" (the star has a circumstellar disk), "maybedisks" (the star may have a circumstellar disk but the data are not conclusive), "nodisks" (the star has no disk detected), and in the case of the Lagoon, "unknowndisks" (no data available to assess disk status).
- starname is the object's EPIC id, if available. In the case of the Lagoon region, not all stars appear in the EPIC catalog, so an alternate name is used, as provided in Table 1 of Venuti et al. (2023, in prep).
- c<##> is the K2 campaign during which the time series was acquired.
Within each fits file, a data table contains five columns:
|TIME||Time observations in BKJD, or Barycentric Julian Date minus the Kepler mission start time offset of 2454833 days.|
|CADENCENO||Sequential cadence number since the start of the Kepler mission. In cases where a cadence is skipped, there was no usable data at that point.|
|FLUX||Measured brightness of the object in the chosen aperture, in units of electrons per second.|
|FLUX_ERR||Estimated uncertainty on the measured flux. This includes both the source photon counts as well as subtracted background. These uncertainties can be significantly overestimated, particularly in nebulous regions such as the Lagoon Nebula. If photometric uncertainty is important, the user is encouraged to make their own estimates based on the intrinsic scatter in the light curve after astrophysical variability trends are removed.|
The quality flag is set to either 0 ("good") or 1 ("bad") as an indication of whether the photometric pipeline detected the given point as either being an outlier (in flux and/or measured image centroid position) or having potentially corrupted flux data, as indicated by the original SAP_QUALITY flags in K2 mission image data. The K2YSO flags have been manually reviewed such that the user may reliably select only flag=0 points for ensuing analysis
A series of header keywords encapsulate key features of the target object and its photometry. The selected best photometric method ("APERTURE") is chosen from among circular apertures of 1, 2, 3, or 4-pixel radii, point-spread function fitting (PSF), or a custom pixel mask for the brightest objects. The star's sky position is stored in the pair of keywords RA_TARG and DEC_TARG. The total duration of observation (i.e., all time series points in the relevant K2 campaign) is listed under XPOSURE. The beginning and ending points of the time series are listed in both BKJD units (TSTART, TSTOP), as well as Modified Julian Date (MJD-BEG, MJD-END). The Kepler telescope acquired and stacked many images to create each image at roughly 30-minute cadence; FRAMETIM indicates the total of integration and readtime per exposure, while NUM_FRM shows how many exposures were stacked per point in the time series.
K2YSO light curves are available through the following bulk download files, separated by region of the sky:
K2YSO light curves are also available in the MAST Portal (web-based, cross-mission search interface) and Astroquery (Python package to search for and download files from Python scripts you write), and via the direct download table below. Set the Provenance Name filter to K2YSO in the Portal Advanced Search to find all or individual light curves.
from astroquery.mast import Observations all_obs = Observations.query_criteria(provenance_name="k2yso") data_products = Observations.get_product_list(all_obs) Observations.download_products(data_products)
A web-based interface for cross-mission searches of data at MAST or the Virtual Observatory
Search for and retrieve K2YSO data products programmatically.