For each mosaic that was successfully photometrically calibrated against one of the photometric reference catalogs, the resulting calibration metadata are archived in an ASDF-format file.

Obtaining the Files

If you are using daschlab, you can obtain one of these metadata files using the ExposureRow.photcal_asdf_url() method. This method returns a URL that you can fetch using a web browser or any standard HTTP client. The URL is a presigned AWS S3 link that is only valid for 15 minutes.

The underlying web API endpoint is GET /dasch/dr7/asset/photcal_asdf/{hexid}. You can use this endpoint to obtain the photometric calibration files outside of the daschlab framework.

Structure

ASDF files contain data organized into a hierarchical tree. The overall structure of the DASCH photometric calibration data tree is as follows, expressed in a JSON-like syntax:

{
  // The ID of the plate that this dataset applies to
  "plateid": <string>,

  // The name of the photometric reference catalog that this dataset applies to
  "refcat": <string>,

  // The hex ID of the astrometry “result” on which this calibration is based
  "astrom_id": <string>,

  // The plate series name associated with the input mosaic file
  "legacy_series": <string>,

  // The plate number associated with the input mosaic file
  "legacy_platenum": <integer>,

  // The serial number of the input mosaic file
  "legacy_mosnum": <integer>,

  // The DASCH rotation flag associated with the input mosaic file
  "legacy_rotation": <string>,

  "solutions": [
    // A list of solution records:
    {
      "defect_summary": {
        // The number of “fake” sources in the image
        "numfake": <integer>,

        // The number of “real” sources in the image
        "numreal": <integer>,

        // The fraction of “real” sources passing quality tests
        "ratio1": <float>,

        // The fraction of “fake” sources passing quality tests
        "ratio2": <float>,

        // The ratio of ”fake” to “real” sources
        "ratio3": <float>,
      },

      // The number of stars in the final calibrated output
      "n_calibrated_stars": <integer>,

      "defect_table": <table-of-defect-information>,
      "reference_stars": <table-of-reference-star-information>,

      // May be missing:
      "spatial_bin_curves": <spatial-bin-curve-collection>,

      "spatial_bin_metrics": <table-of-spatial-bin-metrics>,
      "local_bin_maps": <local-bin-map-collection>,

      // May be missing:
      "mag_dep_cal_cubes": <mag-dep-cal-cube-collection>
    }
  ],

  // The internal ID of the compute job that created this solution
  "job_id": <string>
}

Most of the action is in the solution records, each of which contains detailed information for the photometric calibration of a particular WCS solution. The zero'th item in the solutions list contains data for solnum = 0, the next one for solnum = 1, and so on.

Detailed Record Information (Alphabetical)

astrom_id

• Synopsis: The hex ID of the astrometry “result” on which this calibration is based
• Units/type: lower-case hexadecimal string

The input to the DASCH photometric pipeline is a mosaic with an astrometric calibration. This field identifies that input, in the form of a hexadecimal “result ID”.

job_id

• Synopsis: The internal ID of the compute job that created this solution
• Units/type: string

This field gives the identifier of the HPC job that created this calibration solution. If one has access to the Harvard HPC cluster, this could be used to look up the logfiles associated with the calibration job.

legacy_mosnum

• Synopsis: The serial number of the input mosaic file
• Units/type: small nonnegative integer

This is the mosnum field associated with the input FITS mosaic. It is described as “legacy” because it should only be needed to look up the mosaic file within the legacy DASCH data systems.

legacy_platenum

• Synopsis: The plate number associated with the input mosaic file
• Units/type: positive integer

This is the platenum field associated with the input FITS mosaic. It is described as “legacy” because it is only used to find the right input mosaic file. This field might differ from the actual plate number, if a plate was initially scanned and processed under the wrong number.

legacy_rotation

• Synopsis: The DASCH rotation flag associated with the input mosaic file
• Units/type: string; "", "r90", "r180", or "r270"

This rotation flag is yet another field needed to fully locate the input FITS mosaic file. It should not be relevant to scientific users.

legacy_series

• Synopsis: The plate series name associated with the input mosaic file
• Units/type: short string

This is the series field associated with the input FITS mosaic, identifying the associated plate series. It is described as “legacy” because it is only used to find the right input mosaic file. This field might differ from the actual plate series, if a plate was initially scanned and processed under the wrong identifier.

plateid

• Synopsis: The ID of the plate that this dataset applies to
• Units/type: short string

This is a standard Starglass/DASCH plate ID of the form <series><platenum>, where the plate number is padded out to five digits using leading zeros if needed.

This field gives the plate ID that was used at the time the photometric pipeline was run. If a plate was later discovered to have been processed under the wrong name, the value here might be incorrect. Likewise, the legacy_series and legacy_platenum fields might not agree with this field, if the plate was initially scanned and processed under the wrong identifier.

refcat

• Synopsis: The name of the photometric reference catalog that this dataset applies to
• Units/type: short string; either "apass" or "atlas"

There can be multiple photometric calibration files for each plate ID; one for each reference catalog.

solutions[solnum].defect_summary.numfake

• Synopsis: The number of “fake” sources in the image
• Units/type: nonnegative integer

This number counts sources that either have too much of a positional offset compared to the refcat (i.e., do not match anything in the refcat), or are blends. This will usually be much larger than numreal.

solutions[solnum].defect_summary.numreal

• Synopsis: The number of “real” sources in the image
• Units/type: nonnegative integer

This number counts sources that match an entry in the reference catalog and are not blends.

solutions[solnum].defect_summary.ratio1

• Synopsis: The fraction of “real” sources passing quality tests
• Units/type: float

The DASCH photometric pipeline includes a “defect” processing step that rejects SExtractor sources that are outliers in terms of local image metrics such as the source ellipticity and orientation. This number gives the fraction of “real” sources that pass five quality tests checking that the source is not an outlier in terms of: (1) FWHM, (2) ellipticity as a function of flux, (3) ellipticity over all sources, (4) flux as a function of SExtractor isophotal source size (ISO0), (5) SExtractor isophotal source size as a function of flux. Here, “real” sources are those that match to a catalog entry with small positional offset and do not appear to be blends, and that are not too close to the plate edge or too faint.

solutions[solnum].defect_summary.ratio2

• Synopsis: The fraction of “fake” sources passing quality tests
• Units/type: float

Similar to ratio1, except computed for the “fake” sources, which either have too much of a positional offset compared to the refcat or are blends.

solutions[solnum].defect_summary.ratio3

• Synopsis: The ratio of “fake” to “real” sources
• Units/type: float

This is equal to numfake divided by numreal.

solutions[solnum].defect_table["AFLAGS"]

• Synopsis: The updated AFLAGS after defect processing
• Units/type: bitfield

Updated AFLAGS values. Some of these will have had the DEFECT flag added (bit 25), if they did not pass the defect-detection tests.

solutions[solnum].defect_table["NUMBER"]

• Synopsis: The SExtractor NUMBER of a source in this image
• Units/type: nonnegative integer

This column identifies the source within the input image.

solutions[solnum].local_bin_maps.altitude

• Synopsis: The altitude of observation across the plate
• Units/type: degrees

DASCH plates can be sufficiently large on the sky that the altitude of the observation may vary nontrivially across the plate. This field is an estimate since it depends on the time at which the observation was made, and this is not always known precisely.

solutions[solnum].local_bin_maps.bright_magcor_error

• Synopsis: Estimated uncertainty in bright_magcor_local
• Units/type: magnitude

These are often NaN.

solutions[solnum].local_bin_maps.bright_magcor_local

• Synopsis: The local magnitude correction, as determined from bright stars only
• Units/type: magnitude

The “local calibration” stage of the DASCH photometry pipeline determines magnitude corrections in in a 50×50 grid of bins subdividing the mosaic image, to capture very localized phenomena such as clouds or plate damage. This field gives a set of such local corrections, as determined from the brightest stars in each bin. In particular, it is computed for all stars that are no more than two magnitudes fainter than the brightest star in the bin.

solutions[solnum].local_bin_maps.drad1_bin_count

• Synopsis: The number of stars used for the first-pass local-bin astrometry check
• Units/type: nonnegative integer

solutions[solnum].local_bin_maps.drad1_bin_size

• Synopsis: The number of bins combined during the first-pass local-bin astrometry check
• Units/type: nonnegative integer

The astrometry checks need a minimum number of stars in order to do their computations. If some local bin doesn’t contain enough stars, data from its neighbors are combined in order to build up the statistics. This field counts the number of bins that contributed to the calculations. The maximum value is 9, if all eight neighbors contributed to the computation. The minimum value is 0, for those cases where there are not enough stars to do the calculation even when data from neighbors are included.

solutions[solnum].local_bin_maps.drad1_ddec_median

• Synopsis: Median dec offset between the image and the catalog, from the first-pass local-bin astrometry check
• Units/type: arcsec

These values give the median declination offset between the DASCH’s star positions and the reference catalog within each local bin. This calculation will possibly include contributions from neighboring local bins as per drad1_bin_size.

solutions[solnum].local_bin_maps.drad1_ddec_rms

• Synopsis: RMS dec offset between the image and the catalog, from the first-pass local-bin astrometry check
• Units/type: arcsec

This field is calculated from the same data as drad1_ddec_median, but the RMS is taken rather than the median.

solutions[solnum].local_bin_maps.drad1_dra_median

• Synopsis: Median RA offset between the image and the catalog, from the first-pass local-bin astrometry check
• Units/type: arcsec

These values give the median RA offset between the DASCH’s star positions and the reference catalog within each local bin. This calculation will possibly include contributions from neighboring local bins as per drad1_bin_size.

solutions[solnum].local_bin_maps.drad1_dra_rms

• Synopsis: RMS RA offset between the image and the catalog, from the first-pass local-bin astrometry check
• Units/type: arcsec

This field is calculated from the same data as drad1_dra_median, but the RMS is taken rather than the median.

solutions[solnum].local_bin_maps.drad1_reject_count

• Synopsis: Number of stars rejected due to excessive RA/dec offsets, from the first-pass local-bin astrometry check
• Units/type: nonnegative integer

“Excessive” here is defined as a total offset greater than the limit after subtracting away the median offset in RA and dec. The limit is either three times the RMS offset within the bin, or three pixels on the image, whichever is smaller. Stars that are marked as blends, or having highly uncertain proper motions, do not contribute to this count.

solutions[solnum].local_bin_maps.drad2_bin_count

• Synopsis: The number of stars used for the second-pass local-bin astrometry check
• Units/type: nonnegative integer

Same as drad1_bin_count, but for the second-pass check. The second-pass check uses only stars that have passed the various filters applied during the photometric pipeline processing. These include defect and blend checks and cutoffs for overly faint sources.

solutions[solnum].local_bin_maps.drad2_bin_size

• Synopsis: The number of bins combined during the second-pass local-bin astrometry check
• Units/type: nonnegative integer

Same as drad1_bin_size, but for the second-pass check. The second-pass check uses only stars that have passed the various filters applied during the photometric pipeline processing. These include defect and blend checks and cutoffs for overly faint sources.

solutions[solnum].local_bin_maps.drad2_ddec_median

• Synopsis: Median dec offset between the image and the catalog, from the second-pass local-bin astrometry check
• Units/type: arcsec

Same as drad1_ddec_median, but for the second-pass check. The second-pass check uses only stars that have passed the various filters applied during the photometric pipeline processing. These include defect and blend checks and cutoffs for overly faint sources.

solutions[solnum].local_bin_maps.drad2_ddec_rms

• Synopsis: RMS dec offset between the image and the catalog, from the second-pass local-bin astrometry check
• Units/type: arcsec

Same as drad1_ddec_rms, but for the second-pass check. The second-pass check uses only stars that have passed the various filters applied during the photometric pipeline processing. These include defect and blend checks and cutoffs for overly faint sources.

solutions[solnum].local_bin_maps.drad2_dra_median

• Synopsis: Median RA offset between the image and the catalog, from the second-pass local-bin astrometry check
• Units/type: arcsec

Same as drad1_dra_median, but for the second-pass check. The second-pass check uses only stars that have passed the various filters applied during the photometric pipeline processing. These include defect and blend checks and cutoffs for overly faint sources.

solutions[solnum].local_bin_maps.drad2_dra_rms

• Synopsis: RMS RA offset between the image and the catalog, from the second-pass local-bin astrometry check
• Units/type: arcsec

Same as drad1_dra_rms, but for the second-pass check. The second-pass check uses only stars that have passed the various filters applied during the photometric pipeline processing. These include defect and blend checks and cutoffs for overly faint sources.

solutions[solnum].local_bin_maps.drad2_reject_count

• Synopsis: Number of stars rejected due to excessive RA/dec offsets, from the second-pass local-bin astrometry check
• Units/type: nonnegative integer

Same as drad1_reject_count, but for the second-pass check. The second-pass check uses only stars that have passed the various filters applied during the photometric pipeline processing. These include defect and blend checks and cutoffs for overly faint sources.

solutions[solnum].local_bin_maps.errout

• Synopsis: The estimated uncertainty in zout
• Units/type: magnitude

Many of these are NaN.

solutions[solnum].local_bin_maps.extinction

• Synopsis: The estimated atmospheric extinction across the plate
• Units/type: magnitude

This map gives the estimated atmospheric extinction across the plate, determined as a function of airmass and the plate’s bandpass response (i.e., red or blue). This field is an estimate since it depends on the time at which the observation was made, and this is not always known precisely.

solutions[solnum].local_bin_maps.npout

• Synopsis: The number of stars contributing to the zout calculation
• Units/type: nonnegative integer

solutions[solnum].local_bin_maps.reject_flag

• Synopsis: Error flags for local-bin calibrations
• Units/type: bitfield

This field records various flags that indicate that a local bin has poor-quality data. Bit 0, HIZOUT, is set if the absolute value of local-bin correction zout is larger than 0.5, or if errout is larger than 0.7. Bit 1, MEDIAN, is set if the median star brightness is within 0.5 mag of the limiting magnitude. Bit 2, DRAD, is set if the RMS astrometric error is above limit of 90 arcsec or 3 pixels, whichever is smaller.

solutions[solnum].local_bin_maps.zout

• Synopsis: The local-bin magnitude correction
• Units/type: magnitude

The magnitude correction for this local bin, determined as the median difference between the calibrated image magnitudes and the catalog values.

solutions[solnum].mag_dep_cal_cubes.bin_edge

• Synopsis: The faint edge of the bin along the magnitude axis
• Units/type: magnitude

This cube specifies the location of the faint edge of each magnitude bin, in the sense that a magnitude m is placed into bin i if bin_edge[i-1,*,*] <= m < bin_edge[i,*,*], using Python notation. The bins get fainter (bin_edge increases) as i increases. The nominal “bright” edge of the first bin is 0. The bins are uniform in X and Y: in other words, bin_edge[i,j,k] = bin_edge[i,q,r] for all values of j, k, q, and r.

solutions[solnum].mag_dep_cal_cubes.bin_median

• Synopsis: The median magnitude of the stars in each bin
• Units/type: magnitude

If the bin does not have enough data, the assigned value is the nominal bin center. For bin i, this is 0.5 * (bin_edge[i-1,*,*] + bin_edge[i,*,*]).

solutions[solnum].mag_dep_cal_cubes.bin_quality

• Synopsis: A per-bin solution quality metric
• Units/type: float

This is equal to magcor * sqrt(nstars) / magcal_rms. Some values may be NaN. The pipeline considers absolute values larger than unity to indicate acceptable solutions.

solutions[solnum].mag_dep_cal_cubes.bin_size

• Synopsis: The relative size of each bin
• Units/type: Positive integer

The magnitude-dependent calibration needs a minimum number of stars in order to do its computations. If some of the bins don’t contain enough stars, data from their neighbors in the x and y directions are combined in order to build up the statistics. This number is:

• 1 if no expansion was used
• 2 if the bin size was doubled on both image axes, touching all eight neighbors and quadrupling the bin area
• 4 if the bin size was quadrupled on both image axes, touching twenty-four neighbors and increasing the bin area by a factor of 16
• 6 if the bin size was sextupled, scaling as above
• 99 if it was not possible to get enough stars, and the bin contents are invalid.

solutions[solnum].mag_dep_cal_cubes.magcal_rms

• Synopsis: The RMS of the input calibration residuals within the bin
• Units/type: magnitude

Some bins may be NaNs.

solutions[solnum].mag_dep_cal_cubes.magcor

• Synopsis: The calibrated magnitude-dependent correction
• Units/type: magnitude

This is the per-bin magnitude correction offset determined by the calibration process. Some bins may be NaNs.

solutions[solnum].mag_dep_cal_cubes.nstars

• Synopsis: The number of stars contributing to the bin
• Units/type: Nonnegative integer

solutions[solnum].mag_dep_cal_cubes.xcoord

• Synopsis: The center of the bin along the x image axis
• Units/type: pixel

This cube specifies the position of the bin along the x image axis. The bins are uniform in magnitude and Y: in other words, xcoord[i,j,k] = xcoord[l,m,k] for all values of i, j, l, and m.

The bins on the image axes are increasing and nominally uniform, such there is one positive dx satisfying xcoord[*,*,k] + dx = xcoord[*,*,k+1] everywhere. The nominal domain of the k'th bin is [xcoord[*,*,k] - dx/2, xcoord[*,*,k] + dx/2], but see bin_size.

solutions[solnum].mag_dep_cal_cubes.ycoord

• Synopsis: The center of the bin along the y image axis
• Units/type: pixel

This cube specifies the position of the bin along the y image axis. The bins are uniform in magnitude and X: in other words, ycoord[i,j,k] = ycoord[l,j,m] for all values of i, j, l, and m.

The bins on the image axes are increasing and nominally uniform, such there is one positive dy satisfying ycoord[*,j,*] + dy = ycoord[*,j+1,*] everywhere. The nominal domain of the j'th bin is [ycoord[*,j,*] - dy/2, ycoord[*,j,*] + dy/2], but see bin_size.

solutions[solnum].n_calibrated_stars

• Synopsis: The number of magnitudes in the final calibrated output
• Units/type: nonnegative integer

This field gives the total number of stars in the output catalog that have valid calibrated magnitudes.

solutions[solnum].reference_stars["BFLAGS"]

• Synopsis: Photometric data processing flags for this reference star
• Units/type: bitfield

See BFLAGS in the lightcurve columns page.

solutions[solnum].reference_stars["cal_local"]

• Synopsis: Whether local calibration was applied to this reference star
• Units/type: integer, 0 or 1

If 1, this reference star had a “local calibration” magnitude correction applied.

solutions[solnum].reference_stars["color"]

• Synopsis: The star's color, according to the reference catalog
• Units/type: magnitude

See color in the catalog columns page.

solutions[solnum].reference_stars["dec"]

• Synopsis: The star's declination, according to the reference catalog
• Units/type: degrees

This value is the catalog declination, corrected for proper motion from the catalog epoch to the plate epoch.

solutions[solnum].reference_stars["dmag_iso"]

• Synopsis: Difference between rough-calibrated and reference magnitude
• Units/type: magnitude

This column is equal to [magcal_iso] - refmag. It gives the residual difference between the mostly-calibrated magnitudes and the catalog. If local calibration was successful in this star’s local bin, dmag_local gives an improved magnitude estimate.

solutions[solnum].reference_stars["dmag_local"]

• Synopsis: Difference between locally-calibrated and reference magnitude
• Units/type: magnitude

This column is equal to magcal_local - refmag. It gives the residual difference between the fully calibrated magnitudes and the catalog.

solutions[solnum].reference_stars["extinction"]

• Synopsis: The estimated atmospheric extinction at the star’s location
• Units/type: magnitude

This is derived from the star’s position on the plate and the extinction map. This value is an estimate because it depends on the star’s altitude, and hence the observing time, and this quantity is sometimes poorly known.

solutions[solnum].reference_stars["limiting_mag"]

• Synopsis: The estimated limiting magnitude at the star’s location
• Units/type: magnitude

This is the value found in [spatial_bin_metrics[].limiting_mag] for the [spatial_bin] index associated with this source.

[spatial_bin_metrics[].limiting_mag]: #solutions-solnum-spatial-bin-metrics-limiting-mag [spatial_bin]: #solutions-solnum-reference-stars-spatial-bin

solutions[solnum].reference_stars["local_bin"]

• Synopsis: The number of the local bin that this star belongs to
• Units/type: integer

This column specifies which one of the 2500 “local” (50×50 grid) bins this star was found in, in the plate image.

solutions[solnum].reference_stars["MAG_ISO"]

• Synopsis: The SExtractor isophotal magnitude of this star
• Units/type: instrumental magnitude

This is the uncalibrated (“instrumental”) magnitude provided by SExtractor based on its isophotal flux measurement. The DASCH photometric calibration pipeline uses the reference stars to establish calibration curves relating these to their reference magnitudes (the refmag column).

solutions[solnum].reference_stars["magcal_iso"]

• Synopsis: The rough-calibrated observed magnitude
• Units/type: magnitude

This is the observed source magnitude determined by the pipeline using only the calibration curves derived in annular (“spatial”) bins. If local calibration was successful, the magcal_local column gives an improved estimate.

solutions[solnum].reference_stars["magcal_iso_rms"]

• Synopsis: The estimated uncertainty of magcal_iso
• Units/type: magnitude

This uncertainty is estimated from the RMS residuals along the calibration curve associated with the star’s annular (“spatial”) bin. In particular, a smoothed curve of residual vs. reference magnitude is constructed, and the adopted uncertainty is derived from that curve.

solutions[solnum].reference_stars["magcal_local"]

• Synopsis: The locally-calibrated observed magnitude
• Units/type: magnitude

This is the observed source magnitude after the local magnitude correction has been applied, if possible.

solutions[solnum].reference_stars["magcal_local_error"]

• Synopsis: The estimated uncertainty in magcor_local
• Units/type: magnitude

This is the value found in local_bin_maps.errout for the local_bin index associated with this source.

solutions[solnum].reference_stars["magcor_local"]

• Synopsis: The applied local magnitude correction
• Units/type: magnitude

This is the value found in local_bin_maps.zout for the local_bin index associated with this source.

solutions[solnum].reference_stars["npoints_local"]

• Synopsis: The number of stars contributing to the magcor_local calculation
• Units/type: nonnegative integer

This is the value found in local_bin_maps.npout for the local_bin index associated with this source.

solutions[solnum].reference_stars["NUMBER"]

• Synopsis: The SExtractor NUMBER of this star
• Units/type: nonnegative integer

This column identifies the source within the input image.

solutions[solnum].reference_stars["ra"]

• Synopsis: The star's RA, according to the reference catalog
• Units/type: degree

This value is the catalog right ascension, corrected for proper motion from the catalog epoch to the plate epoch.

solutions[solnum].reference_stars["REF"]

• Synopsis: A unique textual name for this source
• Units/type: string

See ref_text in the catalog columns documentation.

solutions[solnum].reference_stars["refmag"]

• Synopsis: The star’s magnitude, according to the reference catalog
• Units/type: magnitude

See stdmag in the catalog columns documentation.

solutions[solnum].reference_stars["spatial_bin"]

• Synopsis: The number of the spatial bin that this star belongs to
• Units/type: integer, 1-9

This column specifies which one of the nine annular (“spatial”) bins this star was found in, in the plate image.

solutions[solnum].reference_stars["X_IMAGE"]

• Synopsis: The X image coordinate of this star
• Units/type: pixel

This is the X_IMAGE value determined by SExtractor.

solutions[solnum].reference_stars["Y_IMAGE"]

• Synopsis: The Y image coordinate of this star
• Units/type: pixel

This is the Y_IMAGE value determined by SExtractor.

solutions[solnum].spatial_bin_curves[spatial_bin]["flaggrid"]

• Synopsis: Calibration curve data-quality flags
• Units/type: small integer

Different values of this field indicate different characteristics of the individual samples of the calibration curve.

• 1: good quality point
• 0: this point is part of the bright-end extrapolation of the curve
• -1: this point is part of the faint-end extrapolation of the curve
• -2: this point is part of an interpolation in the middle of the curve, in a place where there were not enough measurements

solutions[solnum].spatial_bin_curves[spatial_bin]["griderr"]

• Synopsis: Curve output: estimated uncertainty in maggrid
• Units/type: magnitude

This column acts as an alternative y axis to the smoothed calibration curve. It gives the estimated incertainty in the calibrated output magnitudes maggrid, as a function of the input instrumental magnitudes given in the isogrid column. The uncertainty estimate is based on the RMS of the calibration residuals, smoothed as a function of the input magnitude.

solutions[solnum].spatial_bin_curves[spatial_bin]["isogrid"]

• Synopsis: Curve input: isophotal magnitude
• Units/type: instrumental magnitude

This column is essentially the x axis of the smoothed calibration curve. It samples input instrumental magnitudes (the SExtract MAG_ISO) values fairly uniformly across the range of observed values relevant to the input image. (Note, however, that under the hood the LOWESS smoothing process actually treats the calibrated magnitudes as the x axis, and the MAG_ISO values as the y axis.)

solutions[solnum].spatial_bin_curves[spatial_bin]["maggrid"]

• Synopsis: Curve output: calibrated magnitude
• Units/type: magnitude

This column is essentially the y axis of the smoothed calibration curve. It gives the calibrated output magnitudes that correspond to the input instrumental magnitudes given in the isogrid column.

solutions[solnum].spatial_bin_metrics["colorflag"]

• Synopsis: A quality flag for colorterm
• Units/type: small integer

This field assesses the quality of the colorterm computation:

• 2: good quality point
• 1: OK-quality point
• 3: reused colorterm from the previous (more inward) bin
• 0: unable to solve for colorterm

solutions[solnum].spatial_bin_metrics["colorterm"]

• Synopsis: The colorterm determined for this spatial bin
• Units/type: float

This number empirically characterizes the spectral response of the plate. See the colorterm reference documentation for more information.

solutions[solnum].spatial_bin_metrics["errorcolor"]

• Synopsis: The estimated uncertainty in colorterm
• Units/type: float

This uncertainty is determined from the least-squares residuals of the inputs used to solve for the colorterm.

solutions[solnum].spatial_bin_metrics["limiting_iso"]

• Synopsis: The estimated limiting instrumental magnitude in this spatial bin
• Units/type: instrumental magnitude

This is determined by applying the calibration curve to the value of limiting_mag.

solutions[solnum].spatial_bin_metrics["limiting_mag"]

• Synopsis: The estimated limiting magnitude in this spatial bin
• Units/type: magnitude

This is determined using various heuristics.

solutions[solnum].spatial_bin_metrics["max_bright_iso"]

• Synopsis: The estimated bright-limit instrumental magnitude in this spatial bin
• Units/type: instrumental magnitude

This is determined by applying the calibration curve to the value of max_bright_mag.

solutions[solnum].spatial_bin_metrics["max_bright_mag"]

• Synopsis: The estimated bright-limit magnitude in this spatial bin
• Units/type: magnitude

Sources brighter than this will be flagged as being beyond the reliability bounds of the calibration curve. The value is determined using various heuristics.

solutions[solnum].spatial_bin_metrics["n1"]

• Synopsis: The number of stars provided to the calibration curve computation
• Units/type: nonnegative integer

See also n2.

solutions[solnum].spatial_bin_metrics["n2"]

• Synopsis: The number of stars used in the calibration curve computation
• Units/type: nonnegative integer

This is the number of stars eventually used in the determination of the calibration curve, after filtering for outliers.

solutions[solnum].spatial_bin_metrics["rms"]

• Synopsis: RMS residual of the calibration curve computation
• Units/type: magnitude

This provides a scalar assessment of the tightness of the calibration curve fit, after rejecting various outliers and sigma-clipping. See also [spatial_bin_curves[].griderr] for a magnitude-dependent estimate of the uncertainty of the derived magnitudes.

[spatial_bin_curves[].griderr]: #solutions-solnum-spatial-bin-curves-spatial-bin-griderr

solutions[solnum].spatial_bin_metrics["spatial_bin"]

• Synopsis: The index number of the spatial bin in question
• Units/type: integer 1-9

Note that not all bins may have rows in the spatial_bin_metrics table, if they couldn't be solved.

solutions[solnum].spatial_bin_metrics["upper_limit"]

• Synopsis: A more conservative limiting magnitude
• Units/type: magnitude

This should really be called “lower limit”. It is defined as the magnitude m such that m + u = limiting_mag, where u is the estimated uncertainty in m as derived from the [spatial_bin_curves[].griderr] calibration curve. This means that this limit is somewhat brighter than limiting_mag.