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LAMOST 2D Pipeline

LAMOST 2D Pipeline. Jianjun Chen, Zhongrui Bai, Hanqin Qin Xulei Xue NAOC CAS, USTC 2008-12-3, Beijing. 2D file name and storage. Example: rs-16b-7654321-03 – 77174720.fit Class+type-spID+color-planID-run-MJD Data class: r(raw), p(product),t (temporary)

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LAMOST 2D Pipeline

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  1. LAMOST 2D Pipeline Jianjun Chen, Zhongrui Bai, Hanqin Qin Xulei Xue NAOC CAS, USTC 2008-12-3, Beijing

  2. 2D file name and storage Example: rs-16b-7654321-03 –77174720.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 17-32 for mid-res spectrographs

  3. 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

  4. 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

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

  6. 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-20081011-skyimage.fits ro-12r-20081012-47-78799941.fit ro-16-20081001-376-78784084.ps

  7. 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-20081011-15-78799307'.ps

  8. 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

  9. 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

  10. 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

  11. Some tests • 20081003sky_eff\FiberEff-12-r-flux.fit.ps • 1D-ro-15r-20081001-376-78784084.fit.ps • skysub-1D-ro-15r-20081001-376-78784084.fit.ps

  12. Thanks!

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