DASCH: Digital Access to a Sky Century @ Harvard
A New Look at the Temporal Universe

Database Variables

This page contains reference tables useful mostly to the DASCH pipeline developers and to researchers who have been provided with DASCH photometry results.

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We do not expect access to our scanning and lightcurve database until the campus reopens. Please monitor Plan for a Safe Campus Reopening for the latest information concerning the return of faculty, staff, and researchers to campus.

Table of Variables Used in the Photometry Database
A2FLAGSintAdditional photometry warning flags
AFLAGSintPhotometry warning flags
AFLAGSBitscharListing of bits set in the photometry warning flags
AFLAGS_1intPhotometry warning flags
AFLAGS_2intPhotometry warning flags
aveADUintctAverage ADU level for all of the tile
aveTileSaturationintctAverage number of saturated pixels per tile
B2FLAGSintAdditional photometry processing flags
BACKGROUNDdoublectBackground at centroid position
BFLAGSintPhotometry processing flags
BFLAGSBitscharListing of bits set in the photometry processing flags
BFLAGS_1intPhotometry processing flags
BFLAGS_2intPhotometry processing flags
binningintBinning (1x1 or 16x16) of the mosaic used for WCS fitting
BlendedmagdoublemagFor case B and BD objects, the effective magnitude of all of the GSC2.3.2 objects within the blend.
Blendedmag_1doublemagFor case B and BD objects, the effective magnitude of all of the GSC2.3.2 objects within the blend.
Blendedmag_2doublemagFor case B and BD objects, the effective magnitude of all of the GSC2.3.2 objects within the blend.
CAL_FLAGintDeprecated, now part of BFLAGS
cal_localintbitIf 1, local calibration was used; otherwise 0; becomes part of BFLAGS
catalogNumberintctCalibration Catalog 0 = gsc2.3.2, 1 = KIC, 2 = APASS, 3 = experimental
centerSourceenumSource of J2000 RA and DEC 'Catalog', 'Logbook','imWCS' or 'WCS'
classDescriptioncharDescription of plate class
datecharY-M-D,h:m:sGeocentric exposure date (See ExposureDate for Date)
Date_1doubleJDGeocentric Julian date of plate or Heliocentric Julian date of an image
Date_2doubleJDGeocentric Julian date of plate or Heliocentric Julian date of an image
decdoubledegDeclination in degrees
DecPMdoublemas/yrDeclination proper motion in mas/yr
dec_2doubledegCatalog star declination, precessed to current epoch
dmag_isodoublemagdifference between the lowess-fitted magnitude and catalog magnitude
dmag_localdoublemagdifference between locally corrected calibrated isophotal magnitude and the catalog magnitude
dradRMS2doublearcsecRMS positional error in arcsec per smoothing bin (final tnx adjustment in recover_points)
ELLIPTICITYdoubleSee sextractor manual. (1 - B_IMAGE/A_IMAGE)
errorcolordoubleyesRMS Error in the color correction term
errorTypesetLogbook error type
ExposureDatedoubleJDGeocentric Julian date of plate or Heliocentric Julian date of an image
exposureNumberintctThe zero-based exposure number listed in the logbooks, or -1 if WCS fitting finds more solutions than logbook entries.
exposureNumber_1intctThe zero-based exposure number listed in the logbooks, or -1 if WCS fitting finds more solutions than logbook entries.
exposureNumber_2intctThe zero-based exposure number listed in the logbooks, or -1 if WCS fitting finds more solutions than logbook entries.
extinctiondoublemagExtinction estimate for an image.
extinction_1doublemagExtinction estimate for an image.
extinction_2doublemagExtinction estimate for an image.
fatalErrorintterminating condition of the photometry pipeline for this plate.
fittedPlateScaledoublearcsec/m-3Average plate scale from available WCS fits in arc seconds per mm
FitWCSsetWCS fitting and pipeline status
flagdoublePlotting flag.
FLUX_ISOdoublectIsophotal flux. See sextractor manual.
FLUX_MAXdoublectPeak flux above background. See sextractor manual.
FWHM_IMAGEdoublepixFWHM assuming a gaussian core. See sextractor manual.
FWHM_WORLDdoubledegFWHM assuming a gaussian core. See sextractor manual.
galacticbinintctGalactic Bin Sequence for Scanning
GMAGFlagintGSC2.3.2 magnitude origin
gsc_bin_indexintA spatial index of approximately 1/4096 degree used to sort images in the input star catalog and the photometry database.
hJDdoubleJDHeliocentric Julian Day
hourAnglecharHH:MM:SSLogbook hour angle
ISO0intpix2Isophotal area at level 0. See sextractor manual.
ISO1intpix2Isophotal area at level 1. See sextractor manual.
ISO2intpix2Isophotal area at level 2. See sextractor manual.
ISO3intpix2Isophotal area at level 3. See sextractor manual.
ISO4intpix2Isophotal area at level 4. See sextractor manual.
ISO5intpix2Isophotal area at level 5. See sextractor manual.
ISO6intpix2Isophotal area at level 6. See sextractor manual.
ISO7intpix2Isophotal area at level 7. See sextractor manual.
ISOAREA_WORLDdoubledeg2Isophotal image area in square degrees. See sextractor manual.
jacketJPEGenumbitIf 'yes' a plate jacket JPEG image is available, otherwise 'no'
KMAGFlagintKepler magnitude origin
KRON_RADIUSdoubleKron apertures in units of A or B. See sextractor manual.
latitudedoubledegObservatory latitude in degrees
limiting_isodoublemagInstrumental isophotal magnitude which corresponds to the lowess limiting magnitude
limiting_magdoublemaglowess limiting magnitude
limiting_mag_localdoublemagLocally corrected limiting magnitude
local_bin_indexshortLocal calibration bin number (ix + (nx * iy))
logRemarkenumbitIf 'Y' a logbook remark is present, otherwise 'N'. Deprecated.
magcal_isodoublemagmagnitude estimate from lowess fitting
magcal_iso_rmsdoublemagerror in the lowess fitting algorithm
magcal_localdoublemaglocally corrected magnitude
magcal_local_errordoublemag(ERROUT in contour_plot_clip_smooth_correct2.f) rms of the needed median magnitude correction
magcal_local_rmsdoublemagError of the locally corrected magnitude.
magcal_local_rms_1doublemagError of the locally corrected magnitude.
magcal_local_rms_2doublemagError of the locally corrected magnitude.
magcal_magdepdoublemagmagnitude-dependent corrected magnitude
magcal_magdep_rmsdoublemagError of the magnitude-dependent correction
magcor_localdoublemag(ZOUT in contour_plot_clip_smooth_correct2.f) median magnitude correction needed in a given plate ragion
magdep_binintMagnitude-dependent calibration bin number (ixb + (kxb*iyb) * (kxb*kyb*imagb))
MAGFlagintGSC2.3.2 magnitude origin
MAGFlag_1intGSC2.3.2 magnitude origin
MAGFlag_2intGSC2.3.2 magnitude origin
MAG_APERdoublemagFixed aperture magnitude vector. See sextractor manual.
MAG_AUTOdoublemagKron-like elliptical aperture magnitude. See sextractor manual.
MAG_ISOdoublemagSee sextractor manual. isophotal magnitude
maskIndexintctIndex (one-based) of this mask
maxTileSaturationintctMaximum number of saturated pixels in any tile
max_bright_isodoublemagIsophotal magnitude corresponding to the brightest reliable magnitude in a spatial bin.
max_bright_magdoublemagBrightest reliable lowess magnitude in a spatial bin.
mosaicCommentcharMosaic comment
mosaicNumberintctMosaic number for this plate
n1intctTotal points read by annular9.m for a lowess fit attempt.
n2intctActual number of points used by annular9.m for a lowess fit attempt.
nearbyObjectscharNearby object of interest @ distance in arcsec
nearbyVSXcharNearby VSX object of interest @ distance in arcsec
nextseriescharNext logbook series in logbook linked list
notescharLogbook transcription comment
npoints_localintct(NPOUT in contour_plot_clip_smooth_correct2.f) number of stars used for the median magnitude correction
NUMBERintSextractor object number in an image. See sextractor manual.
orientationenumSeries plate orientation North Forward or Left, Mirrored (deprecated)
photFailFlagintctphotometry table insertion failed
PlatecharHCO plate designation (series and number within series)
plateClasscharPlate class
plateJPEGenumbitIf plate JPEG exists, 'yes'; otherwise 'no'
plateNumberintThe sequential number assigned to a plate in a given plate series from a single telescope or lens
plateVersionIdintVersion Id from the photplates table
plate_distdoubledegdistance in degrees from the plate center
prevseriescharPrevious series in the logbook linked list
qualityintPlate quality flags
qualitybitscharListing of bits set in plate quality flags
radoubledegRight Ascension in degrees
RaPMdoublemas/yrRight Ascension proper motion in mas/yr
ra_2doubledegCatalog star Right Ascension, precessed to plate epoch
REFcharThe catalog id
referenceintPage reference in History of the Plate Series by Martha Hazen
refmagdoublemagSynonym for the Stdmag, the GSC2.3.2 magnitude.
REFNumberlongStar reference designation expressed as an integer
rejectFlagintLocal calibration bin rejection reason.
reject_reasonintLightcurve rejection reason.
reject_reason1intUnmasked reject_reason for a lightcurve image
reject_reason2intMasked reject_reason for a lightcurve image
releaseFieldintctDASCH release field (1-12)
rmsdoublemagThe average locally corrected magnitude rms error for an entire spatial bin.
rotationintdegAngle in degrees between original mosaic and mosaic with North up.
scanCommentcharScan comment
scanDatecharY-M-D,h:m:sDate scanned
scanNumberintScan number for this plate
seriescharPlate series indicating the telescope or lens used to photograph the plate
seriesIdintIndex into the plate series table
solutionNumberintThe zero-based exposure number in the order found by astrometry.wcs in a multiple exposure image
solutionNumber_1intThe zero-based exposure number in the order found by astrometry.wcs in a multiple exposure image
solutionNumber_2intThe zero-based exposure number in the order found by astrometry.wcs in a multiple exposure image
spatial_binshortbyteannular ring on the plate where the star appears (1 = centermost, 9 = outermost)
startcharHH:MM:SSLogbook time of exposure start
stopcharHH:MM:SSLogbook time of exposure end
THETA_J2000doubledegImage angle in degrees East of North. See sextractor manual.
timeAccuracydoubledAccuracy of logbook time in days
timeSourceenumbitExposure time source, either 'Catalog' or 'Logbook'
upper_limitdoublemagupper limit: limiting_mag - 2*error, where the error is the overall RMS in the annular9.m photom fitting
verifiedenumbitObservatory location is approximate if 'no'; otherwise 'yes';
versionIdintIndex into the photometry version table for GSC2.3.2 stars
WCSSourceenumbitSource of the WCS fit, either 'Logbook' or 'imWCS'
wLongitudedoubledegWest Longitude of the observatory in degrees
X_IMAGEdoublepixMosaic x-axis pixel position of the image. See sextractor manual.
yeardoubleyrCalendar year of an image
Y_IMAGEdoublepixMosaix y-axis pixel position of the image. See sextractor manual.

Number of database variables: 150

Notes on Database Variables

Plate Selection

Plates are referenced by a plate series which usually identifies individual telescopes; and a plate number, which usually increases monotonically for every plate exposed at the telescope. Any disk files related to a plate have the extended designation:
rotationString is null for zero degrees and r{rotation} for other angles
solutionString is null for the first solution and _s{solutionNumber} for successive solutions of a multiple-exposure plate
qualifierString is null for the primary GSC2.3.2-calibrated database stream, _{qualifier} for alternate streams such as 'kepler' for photometry data calibrated with the Kepler Input Catalog and 'apass' for data calibrated with the APASS catalog)
fileSuffix defines the type of file.

Observatory Location

Telescopes did not necessary remain at one location but were moved between observatories worldwide

Plate Class

The plate class serves to identify the kind of exposure that was taken and is useful in filtering out plates that may require special techniques for analysis or for selecting plates taken with particular filters or gratings.

Plate Jacket Photographs

Prior to scanning, a photograph was taken of every plate jacket to capture standard plate information and additional notations that may have been made by observers or researchers

Plate Annotation Photographs

Many researchers made ink annotations on the rear of plates to identify objects. If such annotations were found prior to scanning, they were photographed and then the annotations were cleaned from the plate. The emulsion side of the plates was never cleaned.

Fitted Plate Scale

Average plate scale from available WCS fits in arc seconds per mm. This column can not be comprehensive because of the following anomalies:
  • The mc series notably has two separate scales because the telescope was refigured after plate 3499. Plates subsequent to 4171 were taken with a curved plate holder.
  • The mb series uses a different telescope between plates 2389 and 2721 inclusive.
These anomalies are currently hard-coded in the database access software.

Exposure Information

Many of the plates have multiple exposures to increase the dynamic range of the emulsion, include calibration fields, or look for short-period brightness changes. For each exposure, the Right Ascension and Declination are calculated for the center of the plate.

Geocentric and Heliocentric Dates

The time of the exposure is expressed as a geocentric date. The corresponding heliocentric date is calculated with reference to the right ascension and declination of the center of the plate. Since some plate series contain plates which cover wide areas of the sky, the heliocentric date may vary significantly from the value at the center of the plate.

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We do not expect access to our scanning and lightcurve database until the campus reopens. Please monitor Plan for a Safe Campus Reopening for the latest information concerning the return of faculty, staff, and researchers to campus.

For Starbase tables provided by the website, a lower case "date" column header represents a geocentric date and an upper case "Date" column header represents a heliocentric date.

For a discussion of the accuracy of the heliocentric dates in the DASCH lightcuves, see Time Accuracy

Plate Center Source and Date Source

The initial digitization effort involved typing in the card catalog for the stacks. Approximately 129,000 catalog entries were digitized prior to the availability of initial results from the plate scanner. At this point, the scanner results showed that the Julian Date information available in the card catalog was not of sufficient accuracy for the discovery of objects such as eclipsing binaries. The decision was then made to photograph and digitize the logbooks which were the source of the card catalog data. Information from the card catalog is still designated as Catalog and this information will be eventually replaced by information from the logbooks which are designated by Logbook. Because the logbook plate centers have a median error of about 0.5 degrees, these logbook plate centers will eventually be replaced with the results of wcs fitting to star catalogs which are designated by imWCS or WCS. For the source of the exposure time, only Catalog and Logbook apply.

Exposure Notes

The digitized card catalog information contains a remarks field which is preserved in the database.

Nearby Objects

This list consists of a series of nearby objects followed by their distance in arcseconds. The list is valid only to within 0.5 degrees of a given search center. The list consists of one of each of the following three object types:

Time Accuracy

There are a number of automated checks possible on the digitized logbook data. The results of these checks is a time accuracy estimate to give researchers an indication of the reliability of the quoted time. Time accuracy is not available for catalog entries. A default value of -1 is used for an unknown time accuracy.

For individual photometric observations, the website uses heliocentric dates calculated with Jessics Mink's WCSTools package. This package provides UT values where valid and extrapolations of UT for earlier dates. Because the package does not provide barycentric dates, the website accuracy can not be better than approximately 2.6 seconds.

For most DASCH plates the time accuracy of a photometric flare can not be better then the exposure time of the plate. A 90 minute patrol exposure has a timeAccuracy of +/- 45 minutes. The median exposure time for all of our logbook entries is 45 minutes. We have only ~180,000 logbook exposures with a timeAccuracy > 1 minute and an exposure time between 1 and 20 minutes.

A detailed description of time algorithms with references in Jessica Mink's WCSTools software. These references appear in the utdt (Compute difference between UT and dynamical time (ET-UT)) subroutine in the dateutil.c module.

The two lightcurves on the left show a test of the correctness of Jessica's algorithms over 100 years. These lightcurves are of the eclipsing variable DV Cet from the DASCH public website. This particular variable was selected from the AAVSO VSX catalog using the "E" eclipsing binary variable type from the GCVS Variability Types list. The lc_ATLAS2_986321200_DV_Cet.gif shows good coverage from 1900 to 1990 because this eclipsing binary is close to the North Galactic Pole where DASCH lightcurves have the largest plate counts. The lc_ATLAS2_986321200_DV_Cet_folded.gif is a folded lightcurve at this star's published period of 1.1619738 days. Here the 7 digit period accuracy means that this binary is accurate to 3 seconds over 90 years. The range of errors in the minimum time of the lightcurve is approximately 90 minutes.

Logbook Information

The database contains images of 663 bound logbook volumes and approximately 500 loose leaf logbooks. Some of the data has been digitized at Harvard and in India, but currently the data is being digitized by volunteers at the American Museum of Natural History in New York City. We appreciate the assistance of Dr Michael Shara, Curator, Dept. of Astrophysics, Holly Klug, Supervisor of Explainer Programs, Dept. of Volunteer Services and their team of volunteers.

Exposure Start and Stop Times

Exposure start and stop times were generally recorded in Local Sidereal Time, but in some cases Eastern Standard Time or Universal Time was used. The time type in use can usually be determined from the plate center right ascension and the hour angle. The final reported exposure time in the plate exposure information table is the average of the start and stop times. These times are given to a varying number of significant digits and are used to initialze the time accuracy entry.

Hour Angle

The hour angle was reported not only in the standard sense of increasing time West of the meridian, but sometimes the opposite. Occasionally errors in the sign of the angle can be detected from the context of the rest of the observation.

Logbook Remark

Because comments entered into the logbooks have no defined formats, the typists were instructed to enter either Y or N. Some transcriptions, however, do have transcriptions of the original logbook remark. If this field is blank, the logbook remark was not transcribed or may appear in the notes column.

Logbook Notes

Entries are usually entered at Harvard for certain targets of opportunity. These notes contain the reason for transcription.

Errors Detected by Automated Checks

A number of automatic checks of the logbook data is possible. If one of these checks fail, then the reported time accuracy is reduced accordingly or simply set to 1 day if the actual error magnitude is not obvious. The following definition list shows the error check flags that appear in the database should one of these tests fail. The versions referred to below are used to differentiate new logbook data being entered into the database from previously existing logbook data.

Error CodeDescription
Discrepancy Discrepancy between India and Cambridge transcriptions. (Deprecated because of exposure number uncertainty for multiple exposures)
E vs W Fixed E Hour angle mistaken for W or vice-versa. Automatically corrected
Bad Date Fixed Bad date fixed from nearby data (Not yet implemented)
Bad Date Bad date which has not been corrected
12H Fixed 12 Hour LST error Fixed
Exposure Times Disagree Exposure Times Disagree
Non-Numeric Exposure Non-numeric exposure time
Daylight Exposure Exposure while sun is up
Bad Volume Number Volume numbers disagree
HA not LST minus RA Error in Hour Angle
Field Length Exceeded Field Length Exceeded
Bad Remark Remark field not "Y" or "N", corrected to "N"
Bad Multiple (OLD) Multiple exposures on different pages - compared with old version
Bad Multiple (NEW) Multiple exposures on different pages - compared with current version
Decreasing plateNumber Plate number not monotonically increasing
Unknown Time Type Unable to determine if time is LST, UT, or EST because longitide is missing
Below Horizon The telescope is apparently pointing below the horizon
Bad Page Error decoding the logbook volume and page
Bad Time Type Best type type is not the expected time type
Unrecognized Time Type Can not decode the time type in the transcription
Unexpected Time Type Transcription time type disagrees with the ranges table
Bad RA Right Ascension less than 0 hours or greater than 24 hours. NOTE: In some cases, the Right Ascension was deliberately written greater than 24 hours. For these cases, 24 hours should be subtracted from the Right Ascension.
Bad Declination Declination less than -90 degrees or greater than +90 degrees. Note: In some cases, the Declination was deliberately written greater than 90 degrees or less than 90 degrees. For these cases, subtract positive declinations from 180 and negative declinations from -180 and add 12H to the hour angle.
Incomplete Julian Day Julian Day fractional part is missing
Julian Day Mismatch Transcribed Julian Day does not match calculated Julian Day
Time Decreasing Exposure time not monotonically increasing

Scan and Mosaic Information

Scan Number If a plate is scanned multiple times, the scan number keeps track of individual scans.

Mosaic Number

If a second mosaic must be created from a single scan using a new mosaic algorithm, the mosaic number identifies the algorithm. If available, a new mosaic number is assigned with the corresponding scan number. If not available, new mosaic numbers are assigned from unused scan and mosaic numbers. Afterwards, a new scan number will not be assigned an existing scan or mosaic number.

Scan Date

The scan date is important for identifying early scans which are likely to be of lower quality while the scanner was being tested. Because of the mutually exclusive means of assigning scan and mosaic numbers, the scan date is a better way to determine the order of scanning.

Average Tile ADU

Tiles are individual exposures of the scanner camera which are later combined into a mosaic. Since the scanner camera has a 12 bit CCD readout, the average tile ADU will range from the bias level of 50 ADU to the maximum level of 4095 ADU.

Average and Maximum Tile Saturation

In order to improve the dynamic range for dark plates, the scanner exposure time is automatically adjusted. However, pixels imaging film defects and other areas of missing emulsion will saturate. The saturation count is the number of pixels at 4095 ADU on a per tile basis. Since there are 16M pixels per exposure, this is the upper limit of saturation.

Scan Comment

If the average and maximum tile saturation levels reach preset amounts, the scanner software will automatically enter Saturation Error in this field. The scanner operator is free to add any additional comments describing the state of the plate or the reason for the scan.

Mosaic Comment

If a special issue arises with the creation of the mosaic, a comment will be entered here. Currently, the only comment for some mosaics is Linearity Bug which means that the mosaic should be rejected because of a bug in the early version of the mosaic algorithm.

Mosaic Binning

Normally, the mosaic algorithm generates two mosaics simultaneously. These are the full size mosaics with 1 in this field and a 16 x 16 binned mosaic with 16 in this field. Some other binning factors for early mosaics are also present, but the binning factor must be a power of two.

WCS Fit Solution

This entry indicates whether the stars on a mosaic have been fitted to a standard catalog so that an accurate plate center is known.

Mosaic Rotation

If a WCS fit solution is available, this entry indicates how much the original mosaic must be rotated in a clockwise direction so that North is up.

Photometry Pipeline Information

Plotting Symbols

The following plotting symbols are used. These symbols are defined for the WIP Plotting Software Package. The plotting codes appear in the flags database column listed above.

SymbolPlotting CodeDescription
Solid circle17for a good point
Small solid circle17.5for a good point at the edge of the plate
Open circle22for a large error point
Small open circle22.5for a large error point at the edge of the plate
Arrow pointing down31for not found at the indicated limiting magnitude
Small arrow pointing down31.5for not found at the edge of the plate
Asterisk 3 for a suspected plate defect
Triangle 7 for a high astrometric error object
Open square 6 for a Pickering Wedge object
Solid square 16 for an object with high or unknown extinction
Arrow pointing up 30 for an object too bright for the photometric algorithm
Diamond 11.5 for a blended object
Cusped square 10.5 for a high local correction object
Letter b 98.5 for an object considered blended by sextractor, but not by the pipeline because of the low threshold we used in running sextractor
Letter c 99.5 for a good object without color correction
Letter q 13.5 for a good object in a plate with: multiple exposures, gratings, red or yellow filters, Pickering Wedge, spectra, fails colorterm metropolis algorithm, or fails colorterm limits.


This field is a bitmap of photometry pipeline warnings which exclude a magnitude measurement from being included in the summary statistics for a star. Bits 16-18 come from the GSC2.3.2 class field, but only the code for a non-star is currently defined. Bits 20-23 are cases of blended stars. A case B blend is a single image that covers multiple GSC2.3.2 stars. A case C blend is a single GSC2.3.2 star that can be matched to multiple images. A case D blend is multiple GSC2.3.2 stars matching multiple images. Processing of this blend involves subdividing it into smaller groups of matches with the above blend designations: i.e. DA, DB, and DC. The showflags utility can decode the AFLAGS field into its constituent bits. Bits marked with an asterisk below are not used to filter measurements when computing overall lightcurve RMS values on the website home page.

Bit PositionDecimal ValueHexadecimal ValueDescription
6 64 40 *Object has a high background level
7 128 80 *Plate fails quality criterion
8 256 100 Unmatched object on a multiple-exposure plate
9 512 200 *Object has more than 1.1 hour time uncertainty preventing an accurate extinction calculation
10 1024 400 *Object is a multiple exposure blend
11 2048 800 Maximum isophotonic rms exceeded
12 4096 1000 Maximum locally smoothed rms exceeded
13 8192 2000 Star too close to the limiting magnitude
14 16384 4000 Star is in bin 9
15 32768 8000 Object rejected because bin has unknown drad.
16-18 65536 10000 Galaxy (not in GSC 2.3.2)
16-18 131072 20000 Blend (not in GSC 2.3.2)
16-18 196608 30000 Object is Non-star
16-18 262144 40000 Unclassified (not in GSC 2.3.2)
16-18 327680 50000 *Defect (not in GSC 2.3.2)
16-18 458752 70000 Duplicate Star (Added for DASCH project)
19 524288 80000 *Uncertain catalog magnitude (In the APASS catalog all Tycho2 and GSC2.3.2 objects are marked variable to remove them from the magnitude calculation algorithms.)
20 1048576 100000 *Case B - blended
21 2097152 200000 Case C - overlapping Sextractor hits for one GSC star
22 4194304 400000 Case D - mixture of cases B and C
23 8388608 800000 Object has a drad three times the bin drad or is in a bad spatial bin or local bin
24 16777216 1000000 *Object is a Pickering Wedge object
25 33554432 2000000 Object fails the defect filter
26 67108864 4000000 *Copy of the Sextractor blended flag
27 134217728 8000000 Rejected blended object - avoid plotting a limiting magnitude.
28 268435456 10000000 Rejected because of high smoothing correction
29 536870912 20000000 Object is too bright for accurate magnitudes
30 1073741824 40000000 *Object is within 23.5 degrees of horizon


This field is a bitmap of photometry pipeline conditions which provide additional information concerning how the image was processed. Bits 12-15 are GSC2.3.2 magnitude substitution flags which depend on the setting of bit 23. The showflags utility can decode the BFLAGS field into its constituent bits. Note that bits 12-15 now contain the definitions defined in MAGFlags below.

Bit PositionDecimal ValueHexadecimal ValueDescription
0 1 1 Object has neighbors
1 2 2 Object was blended with another
2 4 4 At least one pixel is saturated
3 8 8 Object is too close to the image boundary
4 16 10 Object aperture data incomplete or corrupted
5 32 20 Object isophotal data incomplete or corrupted
6 64 40 Memory overflow during deblending
7 128 80 Memory overflow during extraction
8 256 100 Magnitude adjusted for a blended star (currently unused)
9 512 200 Object has low drad but it is in a high drad bin (currently unused)
10 1024 400 Object PSF considered saturated (ISO5/ISO4 > 0.7) and ((BACKGROUND+FLUX_MAX) > 7500)
11 2048 800 Magnitude-dependent calibration has been applied.
12 4096 1000 JMag substituted for JpgMag (deprecated)
13 8192 2000 BMag substituted for JpgMag (deprecated)
14 16384 4000 RMag substituted for FpgMag (deprecated)
15 32768 8000 VMag substituted for FpgMag (deprecated)
16 65536 10000 Good star processed by the pipeline
17 131072 20000 Star has been calibrated with the lowess fit
18 262144 40000 Star has been locally calibrated
19 524288 80000 Magnitude has been corrected for extinction
20 1048576 100000 Magnitude calibration not possible because the star is too bright
21 2097152 200000 Bin has a valid color correction
22 4194304 400000 Color correction used the metropolis algorighm
23 8388608 800000 Interpret bits 12-15 as Kepler Input Catalog Source bits;
24 16777216 1000000 Match at end of pipeline.
25 33554432 2000000 High proper motion uncertainty
27 134217728 8000000 Spatial bin fails QUALITY_COLORTERM
28 268435456 10000000 Ra and dec have been adjusted by the bin medians
29 536870912 20000000 This plate has an uncertain Julian Date
30 1073741824 40000000 Catalog position corrected for proper motion


This field is a bitmap of status flags which summarize the state of pipeline processing for the mosaic.

NameDecimal ValueDescription
Selected 1 Selected for fitting
MikeShawFit 2 Previously fitted by Mike Shaw (deprecated)
Completed 4 Fitting process successful
Copied 8 Fit results copied to head cluster (deprecated)
MultFailedAstrometry 16 Fit results failed AstrometryWCS for next exposure
MultFailedSeparation 32 Fit results failed the separation criteria for the next exposure
MultSucceeded 64 Fit results succeeded for the next exposure
StaleSolution 128 Better astrometry invalidates this solution
StaleExposureNumber 256 The exposure number of this solution has been changed
Wedge 512 This is a Pickering Wedge plate
FilterBlendedTimeout 1024 The filterblended routine timed out
NoAllObjects 2048 The allobjects file for this solution is missing
DuplicateREFCount 4096 This solution shares the same stars with a previous solution
ColortermCrash 8192 The colorterm.m script has crashed and needs to be rerun
InaccuratePV 16384 The SCAMP polynomial fit has significant inaccuracy
NoneFile 32768 The {}_none.db file produced by filter_multiple is present. NOTE: this entry is an internal software flag that does not appear in database files.


This variable contains flags used in the processing of the GSC2.3.2 catalog. These flags are necessary because the GSC2.3.2 catalog contains magnitudes from multiple source catalogs which used different color filters. Furthermore, there are bugs in the GSC2.3.2 catalog which generate multiple entries for certain bright sources. The goal to put all of the GSC2.3.2 objects on a single color system became possible with the availability of the Kepler Input Catalog. Initially, bits 1-4 were used to identify simple substitutions of JMag or BMag for an unavailable JpgMAG; and RMag or VMag for an unavailable FpgMAG. These definitions are now deprecated. Bits 5-6 are used to eliminate duplicate references to a star and then cleared once this goal has been accomplished. When the Kepler Input Catalog became available, color transformations are now used to put all of the six different populations in the GSC2.3.2 catalog into the reference system of the Kepler Input Catalog and then into the JpgMAG/FpgMAG reference system of the majority of GSC2.3.2 stars. The labels beginning with COLOR identify these six populations. These labels were chosen so as not to create a conflict with the older definitions during pipeline processing. For the Kepler Input Catalog, definitions preceded by KEPLER_CQ designate the source of the Kepler catalog object. This variable is currently unused for the APASS catalog.

LabelBitDecimal ValueHexadecimal ValueDescription
COLOR_JPGMAG_FPGMAG x 0 0 No substitutions
COLOR_BMAG_FOR_JPGMAG x 3 3 BMag substituted for JpgMag
COLOR_VMAG_FOR_FPGMAG x 4 4 VMag substituted for FpgMag
COLOR_VMAG_BMAG_FOR_JPGMAG_FPGMAG x 5 5 BMag substituted for JpgMag and VMag substituted for FpgMag
COLOR_TYCHO x 6 6 This is a Tycho Source
COLOR_SKYMAP x 7 7 This is a Skymap Source
JMAG_FOR_JPGMAG 1 1 1 JMag substituted for JpgMag (deprecated)
BMAG_FOR_JPGMAG 2 2 2 BMag substituted for JpgMag (deprecated)
RMAG_FOR_FPGMAG 3 4 4 RMag substituted for FpgMag (deprecated)
VMAG_FOR_FPGMAG 4 8 8 VMag substituted for FpgMag (deprecated)
SAME_LOCATION 5 16 10 Rejected because location (RA and DEC) is identical (INTERNAL)
SAME_ENTRY 6 32 20 Rejected because all fields are identical. (INTERNAL)
DUPLICATE_PAIR 7 64 40 Part of a pair of location identical objects. Reject only objects with bit 6 set (INTERNAL)
TYCHO_SOURCE 8 128 80 This is a Tycho source (INTERNAL)
SKYMAP_SOURCE 9 256 100 This is a Skymap source (INTERNAL)
KEPLER_CQ_SCP 0 Kepler Catalog Source, valid when BFLAGS bit 23 is set
KEPLER_CQ_2MASS 1 Kepler Catalog Source, valid when BFLAGS bit 23 is set
KEPLER_CQ_PHOTO 2 Kepler Catalog Source, valid when BFLAGS bit 23 is set
KEPLER_CQ_TYBV 3 Kepler Catalog Source, valid when BFLAGS bit 23 is set
KEPLER_CQ_UNCAL 4 Kepler Catalog Source, valid when BFLAGS bit 23 is set
KEPLER_CQ_NOCAL 5 Kepler Catalog Source, valid when BFLAGS bit 23 is set


On December 11, 2009, Sumin Tang made the following request to eliminate common causes of outliers in her search for interesting variables: Only use the very good points AND(not blends, not defects, not high drad, not within 23.5 degrees of horizon, not in bin 9, not within 0.5 mag of the limiting magnitude, not high iso rms, not high local smoothing rms, not Pickering wedge object) in good blue plates AND(colorterm between -0.5 and 0.25 in the bin, colorflag==2, not dny plates, not dnr plates, not multiple exposures, not Pickering wedge plates) for the calculation of min_local, max_local, range_local, min_local2, max_local2, range_local2, median_local, rms_local, ngood, clip_median_local, clip_rms_local, clip_ngood, median_iso, range_iso in the ID table. For individual images, most of these conditions are handled by selecting only magntiudes with AFLAGS equal to zero. The remaining conditions are handled by this plate quality flag which marks plates that are second quality. Note that the colorterm flag does not appear in the database because this condition is dependent on the annular_bin that the image appears in. The colorterm limits were shifted to -0.067 to 0.283 when the recalibrated GSC2.3.2 catalog was introduced in January, 2010. These new colorterm limits represent the 5% and 95% tails of the new colorterm distribution for blue plates in the M44 region. Colorterm limits were revised again in November, 2012 after over 30,000 plates were scanned and additional calibration catalogs came into use. For the GSC2.3.2 catalog, the colorterm bit is set when the colorterm is outside the -0.097 to 0.410 range; for the Kepler Input Catalog, the range is -0.102 to 0.409; and the APASS calibration, the range is -0.146 to 0.195.

NOTE: in the following table, bits 10 and 11 are not in all data tables provided by the website. These bits appear only in some of the tables provided by the website lightcurve plotter and may appear only if specifically requested by the user.

NameBit PositionDecimal ValueDescription
multiple 0 1 Multiple exposure plate
grating 1 2 Grating plate
color 2 4 Color filter used for plate
colorterm 3 8 Image fails colorterm limits
wedge 4 16 Pickering Wedge plate
spectra 5 32 Spectra plate
saturated 6 64 Saturated Images (ISO5/ISO4 > 0.7) and ((BACKGROUND+FLUX_MAX) > 7500)
nomagdep 7 128 Image not Magnitude-dependent Corrected
patrol 8 256 Wide-Field Patrol Telescopes
nonpatrol 9 512 Narrow Field Telescopes
limiting 10 1024 Show Limiting Magnitudes
undetected11 2048 Plot plates where the object was not detected
trailed 12 4096 Image trailed (ELLIPTICITY exceeds 0.6)


Catalog reference number. For GSC2.3.2, these numbers begin with N or S, Kepler Input Catalog numbers are prepended with KIC. Tycho2 catalog numbers are prepended with T. APASS DR8 catalog objects are based on Right Ascension and declination: APASS_Jhhmmss.sSddmmss. The ATLAS REFCAT2 has objid values ranging from 1067906928546 to 215982419254548927 which currently can not fit into the REFNumber format described below. For this reason the website uses the record number in the ATLAS REFCAT2 database with the format ATLAS2_<record number> where the record number has a range from 1 to 992637834. However, the lightcurve query will recognize light queries in the format REFCAT2_<objid> and convert these references to sky positions. Finally, unmatched objects have the format DASCH_Jhhmmss.sSddmmss. Since the website dynamically creates positions for unmatched objects, these positions can change with each database update.


In order to reduce disk space, GSC2.3.2, Kepler, APASS, and DASCH designations were replaced with a sixty-four bit integer. To convert from the catalog reference (REF) to the integer (REFNumber), the following rules apply:

Unmatched objects Replace NONEwith 0
GSC2.3.2 Replace N with 11 and S with 12. Be sure to retain any leading zeroes in the numeric part of the GSC2.3.2 identification.
Kepler Input Catalog KIC catalog numbers are prepended with K. For REFNumber, replace K with 2
DASCH DASCH and APASS designations are similar to SDSS designations which are based on Right Ascension and declination. DASCH Jhhmmss.sSddmmss becomes 3hhmmsssSddmmss where S is 1 for positive declination and 2 for negative declination. For example, DASCH J083039.3+140709 becomes 308303931140709. The only difference with APASS designations is that a 4 prefix replaces the 3 prefix.
Tycho2 Catalog numbers are prepended with T. For REFNumber, replace T with 5
ATLAS refcat2 record numbers are prepended with ATLAS2_. For REFNumber, remove ATLAS2_ and replace it with 9.


These flags are set whenever the collection of images in the local bin do not meet overall quality requirements for the local bin. Such flagged images are not used in statistical analyses.

NameDecimal ValueDescription
DMAG_REJECT_HIZOUT 1 local correction bin rejected because the local correction is out of range
DMAG_REJECT_MEDIAN 2 local correction bin rejected because median brightness dimmer than the limiting magnitude
DMAG_REJECT_DRAD 4 local correction bin rejected because majority of stars have high drad


The lightcurve plotter compiles summaries of the reasons why individual magntiude measurements should be rejected from consideration. These flags are compiled mostly from AFLAGS with some additional error conditions.

Bit Name Bit PositionDecimal ValueHexadecimal ValueDescription
ERROR 0 1 1 Error processing this Plate
OFFPLATE 1 2 2 Object not on plate
BINFAILURE 2 4 4 No data for this spatial bin
UNDETECTED 3 8 8 Object undetected on this plate
WEDGE 4 16 10 Object is a Pickering wedge
DRAD 5 32 20 Object has high DRAD
DEFECT 6 64 40 Object failed the defect filter
HIZOUT 7 128 80 Object in bad spatial bin
BLEND_NOMATCH 8 256 100 Object in glare of brighter object
BLEND 9 512 200 Object is blended
BIN9 10 1024 400 Object is in bin 9
LOCAL_RMS 11 2048 800 Object has high locally calibrated RMS
LIMITING_MAG 12 4096 1000 Object within 0.75 mag of the limiting magnitude
TOO_BRIGHT 13 8192 2000 Object is too bright
LOW_ALTITUDE 14 16384 4000 Object is too close to the horizon
ISO_RMS 15 32768 8000 Object has high lowess RMS
DRADBIN 16 131072 20000 Object is in a bin with too high RMS drad
COMPLEX_BLEND 17 262144 40000 Object has a case c or d blend
MULTIPLE_BLEND 18 524288 80000 Object is a multiple blend
UNCERTAIN_DATE 19 1048576 100000 Object has an uncertain date for extinction calculation
MULTIPLE_NONE 20 2097152 200000 Unmatched object on a multiple exposure plate
QUALITY 21 4194304 400000 Plate fails quality criterion - see quality
SATURATED 22 8388608 800000 Object is saturated
NOMAGDEP 23 167772161000000 Object has no magnituded-dependent correction.
BACKGROUND 24 335544322000000 Object has a high background level.


These error codes are generated by the CheckProgress routine which is used to ensure completeness when the pipeline is rerun for all plates because of major revisions. Codes less than 100 indicate completed execution. Codes between 99 and 1000 indicate incomplete execution. Codes greater than or equal to 999 are software consistency checks.

NameDecimal ValueDescription
FATAL_NO_MATCHFILE 1 No match file found
FATAL_NO_ALLOBJECTS 2 recover_points failed
FATAL_ASTROMETRY 3 find_astrometry2 failed
FATAL_ASTROMETRY2 4 find_astrometry2 failed. None file does not exist
FATAL_MAX_SOLUTION 5 Too many solutions
FATAL_MULT_FAILED_SEPARATION 7 Second solution is too close to the first
FATAL_MISSING_ALLOBJECTS 8 Allobjects missing for higher order solution
FATAL_NO_FILTER_MULTIPLE 100 filter_multiple did not run
FATAL_NO_ASTROMETRY 200 find_astrometry2 did not run
FATAL_STALE_FILTER_MULTIPLE 300 Latest summary allobjects file not later than individual solution allobject file
FATAL_NO_SUMMARY_ALLOBJECTS 400 Summary allobjects file does not exist
FATAL_NO_WCSHISTORY 500 No AstrometryWCS history available
FATAL_STALE_ALLOBJECTS 600 Allobjects stale for higher order solution - run filter_multiple
FATAL_STALE_ALLOBJECTS2 700 Allobjects stale for higher order solution - run rest of pipeline
FATAL_MISSING_MATCHFILE 800 matchfile missing for higher order solution
FATAL_STALE_MATCHFILE 900 stale matchfile for higher order solution
FATAL_UNKNOWN_MOSAIC_STATE 20000 Unknown mosaic state
FATAL_NO_LAST_MOSAIC 30000 Could not get the last mosaic
FATAL_ORPHAN_NEXT_MOSAIC 40000 Have next mosaic but no astromfithistory
FATAL_ORPHAN_NEXT_MOSAIC2 50000 Have next mosaic but no find_astrometry
FATAL_ORPHAN_NEXT_MOSAIC3 60000 Have next mosaic but no none file
FATAL_ORPHAN_LAST_SUCCESS 70000 Have successful next mosaic but no astromfithistory
FATAL_ORPHAN_LAST_SUCCESS2 80000 Have successful next mosaic but no find_astrometry
FATAL_ORPHAN_LAST_SUCCESS3 90000 Have successful next mosaic but no none file
FATAL_ORPHAN_GOOD_ASTROMFITHISTORY 100000 Have good astromfithistory but no find_astrometry
FATAL_ORPHAN_GOOD_ASTROMFITHISTORY2 110000 Have good astromfithistory but no none file
FATAL_ORPHAN_SUCCESS_FILE 120000 Have an astrometry success file, but no none file


This is the estimated error of the locally corrected magnitude measurement. Since adding the spatial bin rms and local correction bin rms in quadrature produces errors which are higher than the rms of the final lightcurve for constant stars, the following procedure recalculates the error based on stars of similar magnitude in the spatial bin.

  1. For each spatial bin, take all of the images which have successfully completed local calibration and sort them by magcal_local, the locally corrected and magnitude-dependent corrected magnitude.
  2. After sorting, divide the images into magnitude bins with 20 stars per bin. Within each bin find the 3-sigma clipped rms of (magcal_local - Stdmag) where Stdmag is the catalog magnitude adjusted by extinction. Since the mean and median values of this rms are expected to be zero, the rms calculation is zero-based rather than based on the mean.
  3. For every image within the spatial bin and magnitude bin, use the rms calculated in step 2. Images dimmer the limiting magnitude will have the rms set to 99.0 and images brighter than the brightest magnitude will use the rms of the brightest magnitude bin.


Extinction estimate for an image. Because most observations used a single color filter, accurate extinction coefficients are not available. The DASCH project uses the following approximations documented in a private communication from Sumin Tang dated Thu 12/10/09 9:12 PM.

  • blue plates: extinction coefficient = 0.4 - 0.2*(elevation/2300m)
  • yellow plates: extinction coefficient = 0.25 - 0.11*(elevation/2300m)
  • red plates: extinction coefficient = 0.2 - 0.1*(elevation/2300m)
The extinction coefficient is multiplied by the airmass given in atmospheres to provide the extinction in magnitudes for every local bin on each plate. Calibration curves use catalog manitudes adjusted by this extinction value.

DS9 support

As of March 10, 2020 all versions of DS9 support images extracted from the full size DASCH mosaics.

Before this date, only DS9 versions from 7.0.0 through 7.4 correctly display sky coordinates. See DS9 version 7.4 for Fedora or Centos linux or DS9 for other operating systems.