DRnext: Lightcurve Data Table Columns

This page documents the columns of the lightcurve data tables exposed by the daschlab analysis toolkit. Different data sources (e.g. the “Cannon” data access portal) may use different names or expose somewhat different sets of data.

The essential columns are:

time, the time associated with the lightcurve point (HJD midpoint)
magcal_magdep, the best calibrated magnitude (band depends on refcat choice)
magcal_local_rms, the best uncertainty estimate on magcal_magdep
limiting_mag_local, the limiting magnitude of the plate at the source position; for nondetections, this is the lower limit on the source magnitude. (You might colloquially call this an “upper limit”, but fainter magnitudes are larger numbers, after all.)

Columns by Category

Some columns are listed in multiple sub-sections here, if appropriate.

Identity

Name	Unit/Type	Description
`local_id`	nonnegative integer	A unique number identifying this lightcurve point
`sxt_number`	positive integer	The SExtractor source identifier (`NUMBER` column)

Astrometry

Name	Unit/Type	Description
`drad_rms2`	arcsec per bin	RMS positional error per smoothing bin
`pos`	Astropy SkyCoord	The fitted source position in this image

When a lightcurve is exported, the pos column may need to be broken into individual columns. In this case you will instead see:

Name	Unit/Type	Description
`ra_deg`	deg	The RA encoded in `pos`
`dec_deg`	deg	The declination encoded in `pos`

Data Quality

Name	Unit/Type	Description
`aflags`	bit flags	DASCH photometric data quality flags
`a2flags`	bit flags	“Additional AFLAGS”
`bflags`	bit flags	DASCH photometric data processing flags
`b2flags`	bit flags	“Additional BFLAGS”
`drad_rms2`	arcsec per bin	RMS positional error per smoothing bin
`local_bin_reject_flag`	bit flags	Data quality flags associated with the “local bin” calibration
`plate_quality_flag`	bit flags	Data quality flags associated with plate-level metrics
`reject`	bit flags	Flags that you set to mark points as rejected

Source Image

Name	Unit/Type	Description
`background`	counts	Background level at the source position (SExtractor `BACKGROUND` column)
`ellipticity`	real number	Ellipticity of source image (SExtractor `ELLIPTICITY` column)
`fwhm_image`	pixels	FWHM of source image assuming Gaussianity (SExtractor `FWHM_IMAGE` column)
`fwhm_world`	deg	FWHM of source image assuming Gaussianity (SExtractor `FWHM_WORLD` column)
`image_x`	pixels	X coordinate of the isophotal image centroid (SExtractor `X_IMAGE` column)
`image_y`	pixels	Y coordinate of the isophotal image centroid (SExtractor `Y_IMAGE` column)
`iso_area_world`	deg²	Area of the isophotal source image (SExtractor `ISOAREA_WORLD` column)
`kron_radius`	real number	Kron radius (SExtractor `KRON_RADIUS` column)
`plate_dist`	deg	Distance of the source from the plate center
`theta_j2000`	deg	Orientation of source image ellipse, East from North (SExtractor `THETA_J2000` column)
`sxt_iso0`	integer pixels²	Source image isophotal area at threshold level 0 (SExtractor `ISOAREA_IMAGE` columns?)
`sxt_iso1`	integer pixels²	Source image isophotal area at threshold level 1 (SExtractor `ISOAREA_IMAGE` columns?)
`sxt_iso2`	integer pixels²	Source image isophotal area at threshold level 2 (SExtractor `ISOAREA_IMAGE` columns?)
`sxt_iso3`	integer pixels²	Source image isophotal area at threshold level 3 (SExtractor `ISOAREA_IMAGE` columns?)
`sxt_iso4`	integer pixels²	Source image isophotal area at threshold level 4 (SExtractor `ISOAREA_IMAGE` columns?)
`sxt_iso5`	integer pixels²	Source image isophotal area at threshold level 5 (SExtractor `ISOAREA_IMAGE` columns?)
`sxt_iso6`	integer pixels²	Source image isophotal area at threshold level 6 (SExtractor `ISOAREA_IMAGE` columns?)
`sxt_iso7`	integer pixels²	Source image isophotal area at threshold level 7 (SExtractor `ISOAREA_IMAGE` columns?)

Photometry

Name	Unit/Type	Description
`magcal_magdep`	mag	Calibrated magnitude after LOWESS, local, and magnitude-dependent calibration. Use this value.
`magcal_local_rms`	mag	Uncertainty in `magcal_local`; preferred by legacy tools for `magcal_magdep` too — why??
`limiting_mag_local`	mag	Locally corrected limiting magnitude for source detection
`extinction`	mag	Local extinction estimate from the photometric calibration process
`flux_iso`	counts	Isophotal flux (SExtractor `FLUX_ISO` column)
`flux_max`	counts	Peak flux above the background (SExtractor `FLUX_MAX` column)
`mag_aper`	uncalibrated mag	Circular aperture magnitude (which one??) (SExtractor `MAG_APER(?)` columns)
`mag_auto`	uncalibrated mag	“Kron-like” aperture magnitude (SExtractor `MAG_AUTO` column)
`mag_iso`	uncalibrated mag	Isophotal magnitude (SExtractor `MAG_ISO` column)
`magcal_iso`	mag	Calibrated isophotal magnitude after LOWESS process
`magcal_iso_rms`	mag	Error in the LOWESS fit
`magcal_local`	mag	Calibrated magnitude after LOWESS and “local calibration”
`magcal_local_error`	mag	RMS of the needed median magnitude correction in the “local calibration” process
`magcor_local`	mag	Median magnitude correction needed in the “local calibration” region
`magcal_magdep_rms`	mag	Uncertainty in `magcal_magdep`; why do legacy tools not use this??

Timing

Name	Unit/Type	Description
`time`	Astropy Time	HJD midpoint of the exposure time.
`time_accuracy`	days	Estimated accuracy of `time`.

Catalog Match Information

Name	Unit/Type	Description
`blended_mag`	mag	Effective combined magnitude of refcat objects covered by this source
`catalog_dec`	deg	Catalog star declination, precessed to plate’s epoch
`catalog_ra`	deg	Catalog star right ascension, precessed to plate’s epoch
`gsc_bin_index`	nonnegative integer	Spatial index value based on GSC binning; needed by some low-level APIs
`pm_dec`	mas/yr	Cataloged source proper motion in declination
`pm_ra_cosdec`	mas/yr	Cataloged source proper motion in right ascension, including cos(δ) term

Plate / Exposure Identification

Name	Unit/Type	Description
`expnum`	nonnegative integer	The exposure number that this detection comes from
`mosnum`	nonnegative integer	The mosaic number of the FITS file used for analysis
`platenum`	nonnegative integer	The number of the plate
`plate_local_id`	nonnegative integer	The “local ID” of the matched plate in the daschlab plates table
`series`	short string	The lowercase series name of the plate
`series_id`	nonnegative integer	A small internal integer corresponding to `series`
`solnum`	nonnegative integer	The WCS solution number corresponding to `expnum`

Calibration Pipeline Information

See also “data quality” and “photometry”.

Name	Unit/Type	Description
`dasch_mask_index`	positive integer	Index of the mask file used for pipeline defect processing
`dasch_photdb_version_id`	positive integer	Internal version number of the binary photometry record
`dasch_plate_version_id`	positive integer	Internal version number of the plate photometry record
`local_bin_index`	nonnegative integer	Bin number used in the “local calibration”
`magdep_bin`	nonnegative integer	Bin number used in the magnitude-dependent calibration
`npoints_local`	nonnegative integer	Number of stars used for the median magnitude correction in “local calibration”
`spatial_bin`	integer between 1 and 9 (inclusive)	Annular ring number for the “spatial” calibration

Detailed Column Information (Alphabetical)

`aflags`

Synopsis: DASCH photometric data quality flags
Units/type: bit field
Available for nondetections: no

FIXME: not yet documented here; see associated remarks in the Legacy Data Guide. If you’re reading this, please email the scientific contact to request that the documentation of this item be improved!