Glossary of Common Terms in the SDSS-III Data Model

Index

ANCILLARY_TARGET1, ANCILLARY_TARGET2

Ancillary targets are defined by the ancillary science teams. Depending on the tiling chunk, the appropriate description files referenced below can be found in $BOSSTILELIST_DIR/inputs/ancillary/bossN.

The flag definitions below are simply a copy from the sdssMaskbits.par file.

#------------ ancillary target selection flags
masktype ANCILLARY_TARGET1 64 "BOSS survey target flags for ancillary programs"
maskbits ANCILLARY_TARGET1  0 AMC        "defined in blake_boss_v2.descr"
maskbits ANCILLARY_TARGET1  1 FLARE1     "defined in blake_boss_v2.descr"
maskbits ANCILLARY_TARGET1  2 FLARE2     "defined in blake_boss_v2.descr"
maskbits ANCILLARY_TARGET1  3 HPM        "defined in blake_boss_v2.descr"
maskbits ANCILLARY_TARGET1  4 LOW_MET    "defined in blake_boss_v2.descr"
maskbits ANCILLARY_TARGET1  5 VARS       "defined in blake_boss_v2.descr"
maskbits ANCILLARY_TARGET1  6 BLAZGVAR   "defined in brandtxmm-andersonblazar-merged.descr "
maskbits ANCILLARY_TARGET1  7 BLAZR      "defined in brandtxmm-andersonblazar-merged.descr "
maskbits ANCILLARY_TARGET1  8 BLAZXR     "defined in brandtxmm-andersonblazar-merged.descr "
maskbits ANCILLARY_TARGET1  9 BLAZXRSAM  "defined in brandtxmm-andersonblazar-merged.descr "
maskbits ANCILLARY_TARGET1 10 BLAZXRVAR  "defined in brandtxmm-andersonblazar-merged.descr "
maskbits ANCILLARY_TARGET1 11 XMMBRIGHT  "defined in brandtxmm-andersonblazar-merged.descr "
maskbits ANCILLARY_TARGET1 12 XMMGRIZ  "defined in brandtxmm-andersonblazar-merged.descr "
maskbits ANCILLARY_TARGET1 13 XMMHR    "defined in brandtxmm-andersonblazar-merged.descr "
maskbits ANCILLARY_TARGET1 14 XMMRED   "defined in brandtxmm-andersonblazar-merged.descr "
maskbits ANCILLARY_TARGET1 15 FBQSBAL  "defined in master-BAL-targets.descr"
maskbits ANCILLARY_TARGET1 16 LBQSBAL  "defined in master-BAL-targets.descr"
maskbits ANCILLARY_TARGET1 17 ODDBAL   "defined in master-BAL-targets.descr"
maskbits ANCILLARY_TARGET1 18 OTBAL    "defined in master-BAL-targets.descr"
maskbits ANCILLARY_TARGET1 19 PREVBAL  "defined in master-BAL-targets.descr"
maskbits ANCILLARY_TARGET1 20 VARBAL   "defined in master-BAL-targets.descr"
maskbits ANCILLARY_TARGET1 21 BRIGHTGAL          "defined in bright_gal_v3.descr"
maskbits ANCILLARY_TARGET1 22 QSO_AAL         "defined in qsoals_v2.descr "
maskbits ANCILLARY_TARGET1 23 QSO_AALS        "defined in qsoals_v2.descr "
maskbits ANCILLARY_TARGET1 24 QSO_IAL         "defined in qsoals_v2.descr "
maskbits ANCILLARY_TARGET1 25 QSO_RADIO       "defined in qsoals_v2.descr "
maskbits ANCILLARY_TARGET1 26 QSO_RADIO_AAL   "defined in qsoals_v2.descr "
maskbits ANCILLARY_TARGET1 27 QSO_RADIO_IAL   "defined in qsoals_v2.descr "
maskbits ANCILLARY_TARGET1 28 QSO_NOAALS      "defined in qsoals_v2.descr "
maskbits ANCILLARY_TARGET1 29 QSO_GRI         "defined in sdss3_fan.descr "
maskbits ANCILLARY_TARGET1 30 QSO_HIZ         "defined in sdss3_fan.descr "
maskbits ANCILLARY_TARGET1 31 QSO_RIZ         "defined in sdss3_fan.descr "
maskbits ANCILLARY_TARGET1 32 RQSS_SF         "defined in rqss090630.descr"
maskbits ANCILLARY_TARGET1 33 RQSS_SFC        "defined in rqss090630.descr"
maskbits ANCILLARY_TARGET1 34 RQSS_STM        "defined in rqss090630.descr"
maskbits ANCILLARY_TARGET1 35 RQSS_STMC       "defined in rqss090630.descr"
maskbits ANCILLARY_TARGET1 36 SN_GAL1   "defined in ancillary_supernova_hosts_v5.descr"
maskbits ANCILLARY_TARGET1 37 SN_GAL2  "defined in ancillary_supernova_hosts_v5.descr"
maskbits ANCILLARY_TARGET1 38 SN_GAL3  "defined in ancillary_supernova_hosts_v5.descr"
maskbits ANCILLARY_TARGET1 39 SN_LOC   "defined in ancillary_supernova_hosts_v5.descr"
maskbits ANCILLARY_TARGET1 40 SPEC_SN    "defined in ancillary_supernova_hosts_v5.descr"
maskbits ANCILLARY_TARGET1 41 SPOKE      "defined in BOSS_slowpokes_v2.descr"
maskbits ANCILLARY_TARGET1 42 WHITEDWARF_NEW  "defined in WDv5_eisenste_fixed.descr"
maskbits ANCILLARY_TARGET1 43 WHITEDWARF_SDSS "defined in WDv5_eisenste_fixed.descr"
maskbits ANCILLARY_TARGET1 44 BRIGHTERL   "defined in sd3targets_final.descr"
maskbits ANCILLARY_TARGET1 45 BRIGHTERM   "defined in sd3targets_final.descr"
maskbits ANCILLARY_TARGET1 46 FAINTERL     "defined in sd3targets_final.descr"
maskbits ANCILLARY_TARGET1 47 FAINTERM   "defined in sd3targets_final.descr"
maskbits ANCILLARY_TARGET1 48 RED_KG        "defined in redkg.descr"
maskbits ANCILLARY_TARGET1 49 RVTEST        "defined in redkg.descr"
maskbits ANCILLARY_TARGET1 50 BLAZGRFLAT				"defined in		 anderson-blazar.par"
maskbits ANCILLARY_TARGET1 51 BLAZGRQSO				"defined in anderson-blazar.par	"
maskbits ANCILLARY_TARGET1 52 BLAZGX						"defined in anderson-blazar.par"
maskbits ANCILLARY_TARGET1 53 BLAZGXQSO				"defined in anderson-blazar.par"
maskbits ANCILLARY_TARGET1 54 BLAZGXR					"defined in anderson-blazar.par"
#maskbits ANCILLARY_TARGET1 55 BLAZXR						"defined in anderson-blazar.par"
maskbits ANCILLARY_TARGET1 56 BLUE_RADIO				"defined in tremonti-blue-radio.fits.gz"
maskbits ANCILLARY_TARGET1 57 CHANDRAV1				"defined in haggard-sf-accrete.fits"
maskbits ANCILLARY_TARGET1 58 CXOBRIGHT				"defined in brandt-xray.par"
maskbits ANCILLARY_TARGET1 59 CXOGRIZ					"defined in brandt-xray.par"
maskbits ANCILLARY_TARGET1 60 CXORED						"defined in brandt-xray.par"
maskbits ANCILLARY_TARGET1 61 ELG							"defined in kneib-cfht-elg.fits"
maskbits ANCILLARY_TARGET1 62 GAL_NEAR_QSO			"defined in weiner-qso-sightline.fits"
maskbits ANCILLARY_TARGET1 63 MTEMP						"defined in blake-transient-v3.fits"

masktype ANCILLARY_TARGET2 64 "additional BOSS survey target flags for ancillary programs"
maskbits ANCILLARY_TARGET2 0 HIZQSO82					"defined in mcgreer-hizqso.fits"
maskbits ANCILLARY_TARGET2 1 HIZQSOIR					"defined in mcgreer-hizqso.fits"
maskbits ANCILLARY_TARGET2 2 KQSO_BOSS				"defined in mcmahon-ukidss.fits"
maskbits ANCILLARY_TARGET2 3 QSO_VAR					"defined in butler-variable.fits.gz"
maskbits ANCILLARY_TARGET2 4 QSO_VAR_FPG			"defined in nathalie-ancillary3.par"
maskbits ANCILLARY_TARGET2 5 RADIO_2LOBE_QSO	"defined in kimball-radio-2lobe-qso.fits.gz"
maskbits ANCILLARY_TARGET2 6 STRIPE82BCG			"defined in alexie-bcgs.fits"
maskbits ANCILLARY_TARGET2 7 QSO_SUPPZ			"defined in qso_suppz.descr"
maskbits ANCILLARY_TARGET2 8 QSO_VAR_SDSS			"defined in VARQSO.descr"
maskbits ANCILLARY_TARGET2 9 QSO_WISE_SUPP			"defined in BOSS_QSO_targets_July_WISE.descr"

[Index]

APOGEE_TARGET1, APOGEE_TARGET2

No target flags defined yet.

[Index]

asinh magnitudes

Magnitudes within the SDSS are expressed as inverse hyperbolic sine (or "asinh") magnitudes, described in detail by Lupton, Gunn, & Szalay (1999). They are sometimes referred to informally as luptitudes.

The transformation from linear nanomaggie measurements to asinh magnitudes is designed to be virtually identical to the standard astronomical magnitude at high signal-to-noise ratio, but to behave reasonably at low signal-to-noise ratio and even at negative values of flux, where the logarithm in the Pogson magnitude fails.

The relation between detected flux f in maggies and asinh magnitude m is:

m = -(2.5/ln(10))*[asinh(f/2b)+ln(b)].

The parameter b is a softening parameter measured in maggies, and for the [u, g, r, i, z] bands has the values

[1.4, 0.9, 1.2, 1.8, 7.4] × 10-10

(Table 21 in Stoughton et al. 2002, the EDR paper). These choices reflect the typical 1-sigma noise of the sky in a point spread function sized aperture in 1 arcsec seeing.

Of some use may be the resulting asinh magnitudes of zero flux objects, which in each band are:

[24.6347, 25.1144, 24.8020, 24.3618, 22.8269]

and the asinh magnitude at which the difference between these magnitudes and Pogson magnitudes exceeds 1 percent:

[22.12, 22.60, 22.29, 21.85, 20.32]

For IDL users, the photoop product contains the routine "sdss_flux2lups", which converts fluxes in nanomaggies into asinh magnigtudes.

[Index]

BOSS_TARGET1, BOSS_TARGET2

Fiber assignment

For main survey quasars, fibers are assigned to objects with any of these BOSS_TARGET1 flags set:

  QSO_CORE_MAIN
  QSO_BONUS_MAIN
  QSO_KNOWN_MIDZ
  QSO_FIRST_BOSS

For main survey galaxies, fibers are assigned to objects with any of these BOSS_TARGET1 flags set:

  GAL_LOZ
  GAL_CMASS
  GAL_CMASS_SPARSE

Flag definitions

The flag definitions below are simply a copy from the sdssMaskbits.par file.

masktype BOSS_TARGET1 64 "BOSS survey primary target selection flags"
# galaxies
maskbits BOSS_TARGET1 0 GAL_LOZ             "low-z lrgs"
maskbits BOSS_TARGET1 1 GAL_CMASS           "dperp > 0.55, color-mag cut "
maskbits BOSS_TARGET1 2 GAL_CMASS_COMM      "dperp > 0.55, commissioning color-mag cut"
maskbits BOSS_TARGET1 3 GAL_CMASS_SPARSE    "GAL_CMASS_COMM & (!GAL_CMASS) & (i < 19.9) sparsely sampled"
maskbits BOSS_TARGET1 7 GAL_CMASS_ALL       "GAL_CMASS and the entire sparsely sampled region"
#maskbits BOSS_TARGET1 3 GAL_GRRED          "red in g-r"
#maskbits BOSS_TARGET1 4 GAL_TRIANGLE       "GAL_HIZ and !GAL_CMASS"
#maskbits BOSS_TARGET1 5 GAL_LODPERP        "Same as hiz but between dperp00 and dperp0"
maskbits BOSS_TARGET1 6 SDSS_KNOWN    "Matches a known SDSS spectra"

# qsos
maskbits BOSS_TARGET1 10 QSO_CORE           "restrictive qso selection: commissioning only"
maskbits BOSS_TARGET1 11 QSO_BONUS          "permissive qso selection:  commissioning only"
maskbits BOSS_TARGET1 12 QSO_KNOWN_MIDZ     "known qso between [2.2,9.99]"
maskbits BOSS_TARGET1 13 QSO_KNOWN_LOHIZ    "known qso outside of miz range. never target"
maskbits BOSS_TARGET1 14 QSO_NN             "Neural Net that match to sweeps/pass cuts"
maskbits BOSS_TARGET1 15 QSO_UKIDSS         "UKIDSS stars that match sweeps/pass flag cuts"
maskbits BOSS_TARGET1 16 QSO_KDE_COADD      "kde targets from the stripe82 coadd "
maskbits BOSS_TARGET1 17 QSO_LIKE           "likelihood method"
maskbits BOSS_TARGET1 18 QSO_FIRST_BOSS     "FIRST radio match"
maskbits BOSS_TARGET1 19 QSO_KDE            "selected by kde+chi2"
maskbits BOSS_TARGET1 40 QSO_CORE_MAIN      "Main survey core sample"
maskbits BOSS_TARGET1 41 QSO_BONUS_MAIN     "Main survey bonus sample"
maskbits BOSS_TARGET1 42 QSO_CORE_ED        "Extreme Deconvolution in Core"
maskbits BOSS_TARGET1 43 QSO_CORE_LIKE      "Likelihood that make it into core"

# standards
maskbits BOSS_TARGET1 20 STD_FSTAR          "standard f-stars"
maskbits BOSS_TARGET1 21 STD_WD             "white dwarfs"
maskbits BOSS_TARGET1 22 STD_QSO            "qso"

# template stars
maskbits BOSS_TARGET1 32 TEMPLATE_GAL_PHOTO     "galaxy templates "
maskbits BOSS_TARGET1 33 TEMPLATE_QSO_SDSS1     "QSO templates "
maskbits BOSS_TARGET1 34 TEMPLATE_STAR_PHOTO    "stellar templates "
maskbits BOSS_TARGET1 35 TEMPLATE_STAR_SPECTRO  "stellar templates (spectroscopically known)"

[Index]

BOSS_SPPLATE_MASKBITS

spPlate files combine multiple spectra for a single plate and have two masks, an "AND" mask and an "OR" mask. The spectra are constructed from 3 or more 15-minute observations, and the "AND" mask bits are set if that bit is set for each and every input observation. The "OR" mask bits are set if that bit is set for any of the observations. Usually, I only look at the "AND" mask.

The mask bits are set as follows: 

 0 NOPLUG          Fiber not listed in plugmap file
 1 BADTRACE        Bad trace from routine TRACE320CRUDE
 2 BADFLAT         Low counts in fiberflat
 3 BADARC          Bad arc solution
 4 MANYBADCOLUMNS  >10% pixels are bad columns
 5 MANYREJECTED    >10% pixels are rejected in extraction
 6 LARGESHIFT      Large spatial shift between flat and object pos'n
 7 BADSKYFIBER     Sky Fiber shows extreme residuals
 8 NEARWHOPPER     Within 2 fibers of a whopping fiber (inclusive)
10 SMEARIMAGE      Smear available for red and blue cameras (deprecated)
11 SMEARHIGHSN     S/N sufficient for full smear fit (deprecated)
12 SMEARMEDSN      S/N only sufficient for scaled median fit (deprecated)
16 NEARBADPIXEL    Bad pixel within 3 pixels of trace
17 LOWFLAT         Flat field less than 0.5
18 FULLREJECT      Pixel fully rejected in extraction (INVVAR=0)
19 PARTIALREJECT   Some pixels rejected in extraction
20 SCATTEREDLIGHT  Scattered light significant
21 CROSSTALK       Cross-talk significant
22 NOSKY           Sky level unknown at this wavelength (INVVAR=0)
23 BRIGHTSKY       Sky level > flux + 10*(flux error)
                   AND sky > 2.0 * median(sky,99 pixels)
24 NODATA          No data available in combine B-spline (INVVAR=0)
25 COMBINEREJ      Rejected in combine B-spline
26 BADFLUXFACTOR   Low flux-calibration or flux-correction factor
27 BADSKYCHI       Relative chi^2 > 3 in sky residuals at this wavelength
28 REDMONSTER      Contiguous region of bad chi^2 in sky residuals
                   (with threshhold of relative chi^2 > 3)

When low numbered bits (<16) are set, those will be set for half of the spectra — either the blue or red spectrograph. The higher-numbered bits (>=16) are set for individual pixels.

Which mask bits are important? The conditions that are considered very bad are already used to set the errors to infinity for the effected pixels (specifically, the inverse variance is set to zero). The most useful mask bit to look at is BRIGHTSKY, which indicates when the sky is so bright relative to the object that perhaps one shouldn't trust any of the object flux there. Our reported errors are meant to include sky-subtraction errors, but there are instances (particularly around 5577) where these errors may be untrustworthy.

[Index]

BOSSTILE_STATUS

BOSSTILE_STATUS is set for each target in the final-bossN.fits files by the bosstile product. It records the fate of each input target during the tiling process.

maskbits BOSSTILE_STATUS 0 TILED      # assigned a fiber
maskbits BOSSTILE_STATUS 1 NAKED      # not in area covered by tiles
maskbits BOSSTILE_STATUS 2 BOSSTARGET # in the high priority set of targets
maskbits BOSSTILE_STATUS 3 DECOLLIDED # in the decollided set of high priority
maskbits BOSSTILE_STATUS 4 ANCILLARY  # in the lower priority, ancillary set
maskbits BOSSTILE_STATUS 5 POSSIBLE_KNOCKOUT  # knocked out of at least one tile by BOSSTARGET
maskbits BOSSTILE_STATUS 6 IGNORE_PRIORITY # priority exceeds max (ANCILLARY only)
maskbits BOSSTILE_STATUS 7 TOOBRIGHT  # fibermag too bright
maskbits BOSSTILE_STATUS 9 CENTERPOST  # 92 arcsec collision with center post
maskbits BOSSTILE_STATUS 10 REPEAT  # included on more than one tile
maskbits BOSSTILE_STATUS 11 FILLER  # was a filler (not normal repeat)
maskbits BOSSTILE_STATUS 12 NOT_TILED_TARGET  # though in input file, not a tiled target
maskbits BOSSTILE_STATUS 13 OUT_OF_BOUNDS  # outside bounds for this sort of target (for restricted QSO geometry, e.g.)
maskbits BOSSTILE_STATUS 14 BAD_CALIB_STATUS  # bad CALIB_STATUS (CALIB_STATUS ne 0)
maskbits BOSSTILE_STATUS 15 PREVIOUS_CHUNK # included because not tiles in previous overlapping chunk
maskbits BOSSTILE_STATUS 16 KNOWN_OBJECT # galaxy has known redshift
maskbits BOSSTILE_STATUS 17 DUPLICATE # object was trimmed because it has an equal or higher priority duplicate in the input list
maskbits BOSSTILE_STATUS 18 DUPLICATE_PRIMARY # "primary" version of duplicate kept in the list for tiling
maskbits BOSSTILE_STATUS 19 DUPLICATE_TILED # object was trimmed as DUPLICATE, but primary for it was TILED

[Index]

CALIB_STATUS bitmask

The CALIB_STATUS bitmask describes the calibration status of a field and/or object.

[Index]

CLOUDCAM Status

The cloud camera status is built from an analysis of the 10 micron cloud cameras used at the APO site. The full history is stored in two files:

The software generating these files from the raw IRCAM data is in $PHOTOOP_DIR/pro/ircam.

In individual files in the reductions the CLOUDCAM flag gets set with the following possible values:

[Index]

Corrected survey coordinates

Corrected survey coordinates are usually referred to as "ceta" and "clambda". They are very similar to the regular SDSS survey coordinates (eta and lambda).

Corrected survey coordinates are an ordinary spherical coordinate system with ceta corresponding to a longitude (like phi) and clambda corresponding to a latitude (like 90-theta). ceta is usually taken to span the range [-180., 180.], and clambda to span the range [-90., 90]. (The only substantive difference from eta/lambda is in the choice of these ranges).

To fully specify the rotation of the coordinates use the rules: 

   (ceta,clambda)=(0,90.)   corresponds to (ra,dec)=(275.,0.)
   (ceta,clambda)=(57.5,0.) corresponds to (ra,dec)=(0.,90.)
   (ceta,clambda)=(0.,0.)   corresponds to (ra,dec)=(185.,32.5)

All values are in degrees, and here (ra,dec) is on the J2000 system.

Software to convert from ceta/clambda to ra/dec is provided in idlutils for IDL users (in the code "csurvey2eq" and "eq2csurvey"), as well as in the SDSSPix software package distributed by Ryan Scranton.

[Index]

fieldID parameter

The fieldID parameter is an integer uniquely identifying a detection in the photo catalog. It needs to be cast as unsigned 64-bit, though in many files we waste a few bytes and write it as an string to avoid FITS compliance issues.

The bits are assigned exactly as for objid, but setting the object id within the field to 0.

For IDL users, the function "sdss_fieldid()" in photoop will convert RUN, CAMCOL, FIELD, RERUN into a properly formatted fieldID.

[Index]

FRAMES_STATUS

The RESOLVE_STATUS flag describes what happened to this field during frames. In the fpFieldStat files it is returned as the "status" variable.

It is an integer, which can take the following values, with the associated meanings:

This information was inferred from $PHOTO_DIR/include/phFramestat.h.

[Index]

IMAGE_STATUS bitmask

The IMAGE_STATUS bitmask describes the quality of the observations of the field.

[Index]

IS_BEST flag

The IS_BEST flag is set for each observation (labeled by its MJD) of each plate. It is "1" if we consider that MJD to be the best observation of that plate, "0" otherwise.

[Index]

IS_PRIMARY flag

The IS_PRIMARY flag is set for each observation (labeled by its MJD) of each plate. It is "1" if we consider that MJD to be the best observation of that plate, and for it to be an acceptable observation from a science point of view (with PLATEQUALITY either 'marginal' or 'good'). It is "0" either if there is a better observation or if all observations are labeled 'bad'. A clean set of plates can be selected by demanding that IS_PRIMARY be equal to one. Note, however, that just because a plate is marked 'bad' does not always mean its spectra are useless.

[Index]

IS_TILE flag

The IS_TILE flag is set for each observation (labeled by its MJD) of each plate. It is "1" if we consider that PLATE-MJD to be the best instance of the TILE it is associated with in the SDSS Legacy survey. Tiles are unique RA/Dec centers. It is "0" otherwise, or if the plate is not associated with Legacy. To get well-defined targeting and window functions, one wants to use only plates that have IS_TILE of 1. A plate can be IS_TILE only if it is also IS_PRIMARY.

[Index]

MARVELS_TARGET1, MARVELS_TARGET2

No target flags defined yet.

[Index]

Nanomaggies

In SDSS-III, we express all fluxes in terms of nanomaggies, which are a convenient linear unit. They are 109 times the ratio of the source to the AB standard source in each band (3631 Jy).

To relate these quantities to standard magnitudes, an object with flux f in nMgy has magnitude:

m = [22.5 mag] − 2.5 log 10 f   .

[Index]

OBJC_TYPE

Gives the type of object assignment made by the photo pipeline, with possible values:

For IDL users, the function "sdss_objid()" in photoop will convert RUN, CAMCOL, FIELD, ID, RERUN into a properly formatted objID.

[Index]

objID parameter

The objID parameter is an integer uniquely identifying a detection in the photo catalog. It needs to be cast as unsigned 64-bit, though in many files we waste a few bytes and write it as an string to avoid FITS compliance issues.

The bits are assigned in objid as follows:

For IDL users, the function "sdss_objid()" in photoop will convert RUN, CAMCOL, FIELD, ID, RERUN into a properly formatted objID.

[Index]

PLATEQUALITY

The PLATEQUALITY string is set for each observation (labeled by its MJD) of each plate. For DR8 plates the definition varies depending on whether the plate is an SDSS plate (that is, has survey set to 'sdss'), a SEGUE-1 plate (that is, has survey set to 'segue1'), or a SEGUE-2 plate (that is, has survey set to 'segue2').

For SDSS plates, the conditions are based on the signal-to-noise and the fraction of bad pixels:

      PLATESN2>15 AND FBADPIX<0.05 -> 'good'
      PLATESN2>9 AND FBADPIX<0.13 -> 'marginal' (if not 'good')
      otherwise -> 'bad'

For SEGUE-1 plates, the conditions are based on the signal-to-noise of the main sequence turnoff at g=18, except for some special plates:

      for faint plates SN of turnoff @ g=18 > 16 for 'good'
      for bright plates SN of turnoff @ g=18 > 7.5 for 'good'
      for low-latitude or test plates, consult
         $SAS_DIR/data/segue1-hand.par

For SEGUE-2 plates, the conditions are also based on the signal-to-noise of the main sequence turnoff at g=18:

      median(SN for MS-turnoff @ g=18)>10 -> 'good'
      otherwise -> 'bad'

[Index]

RESOLVE_STATUS bitmask

The RESOLVE_STATUS bitmask describes the resolve status of a field and/or object: whether it is a primary survey object, a secondary observation, or the "best" observation but in an area not considered primary at all.

To get a unique set of objects across the whole survey, search for objects with SURVEY_PRIMARY set.

The following bits are exclusive, and exactly one of these bits will be set for each object: RUN_PRIMARY, RUN_RAMP, RUN_OVERLAPONLY, RUN_IGNORE, RUN_DUPLICATE. In addition, RUN_EDGE can be set for any object. If analyzing only a single run, one typically wants all unique objects within a run that are not at the edge of field. To select such objects, the RUN_PRIMARY bit should be set, and the RUN_EDGE bit should not be set.

Only objects that pass RUN_PRIMARY (or have RUN_RAMP set and are near the edge) are considered for SURVEY_PRIMARY. That trims out the "bright", "parent" and "sky" objects.

[Index]

Score

The "score" is a numerical rating for the quality of an SDSS imaging field. It ranges from 0 to 1. Within this range, values have the following meaning:

"Binned" data typically refers to "Apache Wheel" rapid scans performed for the purposes of ubercalibration.

The formula for this score is:

 sensitivity = (0.7 / (psf_fwhm[2] * sqrt(skyflux[2]))) < 0.4
 score = QEXIST * (0.1 + 0.5 * QPHOT + sensitivity) * (xbin GT 1 : 0.1:1)

where "psf_fwhm" is in arcsec and "skyflux" is in nanomaggies/arcsec2. The sensitivity is bounded between [0, 0.4] and is proportional to the theoretical point-source sensitivity in the r-band.

"QEXIST" is 1 if the field "exists", which is to say:

  PHOTO_STATUS = 0
  BAD_ROTATOR not set in any band
  BAD_ASTROM not set in any band
  BAD_FOCUS not set in any band
  SHUTTERS not set in any band

and 0 otherwise.

"QPHOT" is 1 if the field is photometric, which is to say: 

   Darker than 12 deg twi in r-band
   PSP_STATUS is <= 2 (in the lower 5 bits) in all bands
      (i.e. PSP_FIELD_NOPSF,PSP_FIELD_ABORTED,PSP_FIELD_MISSING,
            PSP_FIELD_OE_TRANSIENT are all not set)
   CLOUDY not set in any band
   UNKNOWN (possibly cloudy) not set in any band
   FF_PETALS not set in any band
   DEAD_CCD not set in any band
   NOISY_CCD not set in any band

For binned scans, however, there is no cut on PSP_STATUS.

[Index]

SDSS PSF models

There are several SDSS PSF models that are calculated.

PSF width

Double-gaussian PSF

Composite PSF

The composite PSF is estimated by the PSP pipeline and consists of

PSF = a1 exp(-r2/2s12) + a2 exp(-r2/2s22) + p (1+r2/sp2b)-b/2

K-L PSF

[Index]

SEGUE2_TARGET1, SEGUE2_TARGET2

Overview

segue2_target1 and segue2_target2 are 64-bit integers. They are bitmasks, and each bit describes the status of the object with respect to one of the target selection criteria. segue2_target1 is the science selection bitmask. segue2_target2 describes the standard, calibration and special target categories

SEGUE2_TARGET1

SEGUE2_TARGET2

More Information

For some examples of how to use these target selection bitmasks, see the SEGUE-2 wiki page attachment Segue2 Target Bits for the non-hexidecimally-minded.

For more details about the selection criteria, see the the SEGUE-2 wiki page attachment on target selection cuts.

[Index]

SEGUEB_TARGET1, SEGUEB_TARGET2

No target flags defined yet.

[Index]

specObjID parameter

The specObjID parameter is an integer uniquely identifying a spectrum in the spectroscopic catalog. It needs to be cast as unsigned 64-bit, though in many files we waste a few bytes and write it as an string to avoid FITS compliance issues.

The bits are assigned in specobjid as follows:

Note that this definition differs from that in DR7. For IDL users, the function "sdss_specobjid()" in sas will calculate this value. Note that implicitly MJD>=50000.

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TAI Time

TAI is the time given in units of seconds, and is determined at APO using GPS-based NTP servers.

To get the TAI time in Modifed Julian Date format, use MJD = TAI/(24*3600).

In practice at APO, there are several definition of MJD that can differ by of order seconds; when TAI is available it is the more reliable time source.

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ZWARNING Bitmask

The ZWARNING bitmask describes bad fits in the redshift-fitting code.

[Index]

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