spPlate

Summary:

Combined spectra for one plate. The spPlate files contain the combined spectra for all exposures of a given plate. There are typically four 900s exposures which may have been taken in a single night, or over multiple nights. This page is an updated summary of the SDSS2 spPlate data model .

Naming Convention:

spPlate-PLATE4-MJD5.fits, where PLATE4 is the zero-padded, four-digit plate number and MJD5 is the five-digit MJD.

Regex:

spPlate-[0-9]{4}-[0-9]{5}\.fits

Contents

Number	EXTNAME	Type	Contents
HDU0	FLUX	IMAGE	Flux in units of 10-17 erg/s/cm2/Å.
HDU1	IVAR	IMAGE	Inverse variance (\(1/\sigma^2\)) for HDU 0
HDU2	ANDMASK	IMAGE	AND mask
HDU3	ORMASK	IMAGE	OR mask
HDU4	WAVEDISP	IMAGE	Wavelength dispersion in pixels
HDU5	PLUGMAP	BINTABLE	Plug-map structure from plPlugMapM file
HDU6	SKY	IMAGE	Average sky flux in units of 10-17 erg/s/cm2/Å.

FITS Header Units

HDU0

EXTNAME = FLUX

Data: FITS image [float64]

HDU1

EXTNAME = IVAR

Data: FITS image [float64]

HDU2

EXTNAME = ANDMASK

Data: FITS image [int32]

HDU3

EXTNAME = ORMASK

Data: FITS image [int32]

HDU4

EXTNAME = WAVEDISP

Data: FITS image [float64]

HDU5

EXTNAME = PLUGMAP

Required Header Keywords

Header	Value	Type	Comment
XTENSION	BINTABLE	str	Binary table written by MWRFITS v1.8
BITPIX	8	int	Required value
NAXIS	2	int	Required value
NAXIS1	250	int	Number of bytes per row
NAXIS2	NFIBER	int	Number of rows
PCOUNT	0	int	Normally 0 (no varying arrays)
GCOUNT	1	int	Required value
TFIELDS	34	int	Number of columns in table

Required Data Table Columns

Column	Type	Comment
OBJID	int32[5]
HOLETYPE	char[6]
RA	double
DEC	double
MAG	float[5]
STARL	float
EXPL	float
DEVAUCL	float
OBJTYPE	char[16]
XFOCAL	double
YFOCAL	double
SPECTROGRAPHID	int32
FIBERID	int32
THROUGHPUT	int32
PRIMTARGET	int32
SECTARGET	int32
OFFSETID	int32
SCI_EXPTIME	float
SOURCETYPE	char[7]
LAMBDA_EFF	float
ZOFFSET	float
BLUEFIBER	int32
BOSS_TARGET1	int64
BOSS_TARGET2	int64
ANCILLARY_TARGET1	int64
ANCILLARY_TARGET2	int64
RUN	int32
RERUN	char[5]
CAMCOL	int32
FIELD	int32
ID	int32
CALIBFLUX	float[5]
CALIBFLUX_IVAR	float[5]
SFD_EBV	float

HDU6

EXTNAME = SKY

FITS Image: Average sky flux

Required Header Keywords

Header	Value	Type	Comment
XTENSION	IMAGE	str	Image Extension created by MWRFITS v1.4a
BITPIX	-32	int	Data is 32-bit float
NAXIS	2	int	Number of data axes
NAXIS1	NPIX	int	Width
NAXIS2	NFIBER	int	Height

Data: FITS image [float64]

Notes and Examples

Additional HDUs may be present for engineering purposes, but are not supported and are subject to change. Users should refrain from using HDUs not listed here.

There are 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, only “AND” mask is of interest.

The mask bits are set as follows. The authoritative definition of mask bits is in idlutils/data/sdss/sdssMaskbits.par, with an alternate parsing at the data release documentation. They are included here for convenience:

Bit	Name	Description
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 (deprecated)
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 (deprecated; 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.

Dispersion and sky: The dispersion per pixel and the sky flux are computed at each pixel by re-weighting the individual spectra at each pixel according to their formal errors. This re-weighting is only approximate.

Sky wavelengths: Note that the sky lines are slightly shifted in the reductions because we transform the velocities to the barycenter of the solar system. Each exposure that contributes to the co-added spectra will have slightly different barycenter correction, so the “average sky” contains a superposition of these slightly-offset sky lines. These shifts keep the object spectra as-measured at the barycenter, regardless of the time of year or the Earth’s rotation relative to the spectroscopic targets.

Doodles

See sdR

Superscript^superscript

Subscript_subscript

Generate html with:

rst2html.py -gdts datamodel_test.rst datamodel_test.html

With docutils installed by MacPorts, I have to do:

rst2html-2.7.py -gdts datamodel_test.rst datamodel_test.html