Lamost Spectrograph Response Curves: Stability and Application to Flux Calibration

Abstract

The task of flux calibration for LAMOST (Large sky Area Multi-Object Spectroscopic Telescope) spectra is difficult due to many factors. For example, the lack of standard stars, flat fielding for large field of view, and variation of reddening between different stars especially at low galactic latitudes etc. Poor selection, bad spectral quality, or extinction uncertainty of standared stars not only might induce errors to the calculated spectral response curve (SRC), but also might lead to failures in producing final 1D spectra. In this paper, we inspected spectra with Galactic latitude |b| ≥ 60• and reliable stellar parameters, determined through the LAMOST Stellar Parameter Pipeline (LASP), to study the stability of the spectrograph. To guarantee the selected stars had been observed by each fiber, we selected 37,931 high quality exposures of 29,000 stars from LAMOST DR2, and more than 7 exposures for each fiber. We calculated the SRCs for each fiber for each exposure, and calculated the statistics of SRCs for spectrographs with both the fiber variations and time variations. The result shows that the average response curve of each spectrograph (henceforth ASPSRC) is relatively stable with statistical errors ≤ 10%. From the comparison between each ASP-SRC and the SRCs for the same spectrograph obtained by 2D pipeline, we find that the ASPSRCs are good enough to use for the calibration. The ASPSRCs have been applied to spectra which were abandoned by LAMOST 2D pipeline due to the lack of standard stars, increasing the number of LAMOST spectra by 52,181 in DR2. Comparing those same targets with SDSS, the relative flux differences between SDSS spectra and that of LAMOST spectra with the ASPSRC method are less than 10%, which underlines that the ASPSRC method is feasible for LAMOST flux calibration.-3 -

Spectral classification and composites of galaxies in LAMOST DR4

“…The differences in both colors suggests that LAMOST spectra are bluer than SDSS photometry, and as the galactic latitude is lower, the difference is more and more greater. The most probable cause is that the uncertainty of reddening value of the standard stars contributes to some uncertainty in response curves (Du et al 2016). And the lower latitude the spectra lie in, the more uncertainty the response curves have.…”

Strong [OIII]λ5007 emission line compact galaxies in LAMOST DR9: Blueberries, Green Peas and Purple Grapes

“…The response curves of the 16 spectrographs have been removed from LAMOST spectra, but the spectra flux is not physically calibrated (Du et al 2016). We recalibrate the LAMOST spectra according to the SDSS gri photometry following Wang et al (2018) as described below: LAMOST spectra are convolved with the SDSS gri filters (Fukugita et al 1996) to obtain the synthetic magnitude for these three bands, then compared with the SDSS photometric magnitude.…”

The first photometric and spectroscopic analysis of the extremely low mass ratio contact binary NSVS 5029961

“…The spectroscopic observations of NSVS 5029961 were carried out by using LAMOST (The Large Sky Area Multi-Object Fiber Spectroscopic Telescope) from 2013 to 2017. LAM-OST, a special reflecting Schmidt telescope with resolution of around 1800 for low resolution mode, has a field of view of 5 • and covers the wavelength from 3700 Å to 9000 Å (Wang et al 1996;Cui et al 2012;Du et al 2016). 4000 optical fibers were installed on the focal surface, improving the rate of spectral acquisition (Cui et al 2012).…”