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Mask bits for an SDSS spectrum

Each of these bits is set for each fiber and each pixel. Bits 0-15 indicate something about the spectrum as a whole, or at least about its red or blue half (corresponding to the two spectrographs). Within a spectrum, if these bits are set they will be set for all the bits in one or both of the halves. Bits 16-31 indicate something about each particular pixel.

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.

Bit name Binary digit Description
NOPLUG 0 Fiber not listed in plugmap file
BADTRACE 1 Bad trace from routine TRACE320CRUDE
BADFLAT 2 Low counts in fiberflat
BADARC 3 Bad arc solution
MANYBADCOLUMNS 4 More than 10% of pixels are bad columns
MANYREJECTED 5 More than 10% of pixels are rejected in extraction
LARGESHIFT 6 Large spatial shift between flat and object position
BADSKYFIBER 7 Sky fiber shows extreme residuals
NEARWHOPPER 8 DEPRECATED, no longer set as of BOSS DR9. Prior to DR9 meant within 2 fibers of a whopping fiber (exclusive)
WHOPPER 9 Whopping fiber, with a very bright source.
SMEARIMAGE 10 DEPRECATED. Prior to DR9 meant smear available for red and blue cameras
SMEARHIGHSN 11 DEPRECATED. Prior to DR9 meant S/N sufficient for full smear fit
SMEARMEDSN 12 DEPRECATED. Prior to DR9 meant S/N only sufficient for scaled median fit
NEARBADPIXEL 16 Bad pixel within 3 pixels of trace.
LOWFLAT 17 Flat field less than 0.5
FULLREJECT 18 Pixel fully rejected in extraction (INVVAR=0)
PARTIALREJECT 19 Some pixels rejected in extraction
SCATTEREDLIGHT 20 Scattered light significant
CROSSTALK 21 Cross-talk significant
NOSKY 22 Sky level unknown at this wavelength (INVVAR=0)
BRIGHTSKY 23 Sky level > flux + 10*(flux_err) AND sky > 1.25 * median(sky,99 pixels)
NODATA 24 DEPRECATED, should be ignored in favor of flagging on INVVAR=0. Prior to DR9 meant no data available in combine B-spline (INVVAR=0)
COMBINEREJ 25 Rejected in combine B-spline
BADFLUXFACTOR 26 Low flux-calibration or flux-correction factor
BADSKYCHI 27 Relative χ2 > 3 in sky residuals at this wavelength
REDMONSTER 28 Contiguous region of bad χ2 in sky residuals (with threshold of relative χ2 > 3).