LAMOST 2D Pipeline Jianjun Chen, Zhongrui Bai, Hanqin Qin Xulei Xue NAOC CAS, USTC , Beijing

2D file name and storage Example: rs-16b – fit Class+type-spID+color-planID-run-MJD  Data class: r(raw), p(product),t (temporary)  Data type: o(object), s(sky), f(flat), b(bias),a(arc), t(test)  spID: 1-16 for low-res spectrographs for mid-res spectrographs

2D file name and storage  Color: r(red), b(blue)  planID: plan ID from SSS  Run: the run number during each night  MJD: modified Julian Day, but here modified to in unit of minute  Data from each night stored in directory named by MJD or calendar date

2D pipeline  Scan files and pre-reduction  Tracing and extraction  Wavelength calibration  Flat correction  Sky subtraction  Flux calibration, combine 3 exposures and red & blue spectra

Scan files and pre-reduction  Subtract bias  Calculate inverse variance as noise  Scan files and read files to corresponding structures

Tracing and extraction  Find out the center positions of fiber profiles at ystart in a flat exposure  Along the dispersion direction, find the center and width for each fiber profile  Fit the fiber profiles along spatial direction to calculate the flux for each fiber rs-12r skyimage.fits ro-12r fit ro ps

Wavelength calibration  Iteratively calculate the correlation coefficient of one fiber arc lines with lines in table, to get the initial wavelength solution  Based on the line table, separate the arc spectrum next to the initial arc to sections, in each section only one strong line, and calculate the dispersion curve  Go to next arc spectrum, do it again 1D-rs-12r '.ps

Flat correction  Using B-spline to fit wave and flux in good fiber and to reconstruct the superflat  Divide the flat flux by superflat and get fiber efficiency curve fflat  Object flux divide fflat

sky subtraction  Locate sky emission lines, to correct the wavelength calibration  Calculate the emission line width  Using B-splines to reconstruct supersky  Subtract the supersky from object flux

Flux calibration (SDSS sky area)  Compare standard star flux (F-type sub dwarf) with flux of standard model, to derive spectrophotometric calibration  Combine 3 exposures  Combine red and blue

Some tests  sky_eff\FiberEff-12-r- flux.fit.ps sky_eff\FiberEff-12-r- flux.fit.ps  1D-ro-15r fit.ps 1D-ro-15r fit.ps  skysub-1D-ro-15r fit.ps skysub-1D-ro-15r fit.ps

Thanks!