DR1 Caveats

There are several small caveats to watch out for in LAMOST DR1 data. Some affect only a few spectra, while some have wider impacts. This page contains a list of known caveats in LAMOST DR1 spectroscopic data. ALL OF THESES CAVEATS HAVE BEEN SOLVED IN LAMOST DR2.

1. Radial velocity error

DR1 pipeline adopted local Beijing Time rather than UTC during the correction from geocentric coordinates to heliocentric coordinates. Thus an error in radical velocity is introduced, with mean value of 0.36 km/s. This link list the related information, which includes the observed date, planid, spid, and the modifications to radial velocity.

Additionally, there are part of A–type stars whose RV error reaches 80km/s due to the wrong use of air wavelength rather than vacuum wavelength. They are listed on this page, which include obsid, observed date, planid, spid, and fiberid.

2. Spectral lines error coming from sub–exposure combination

The LAMOST spectra released in DR1 are combined from several sub–exposure. If one of the three sub–exposures is problematic, spectral lines may be erroneously scaled (clipped) during the B-spline fitting by using the wrong data points. There are 66838 spectra affected in DR1, which are listed here.

3. Offset of very bright targets

The position (α and δ) are artificially offset for the very bright stars to avoid exposure saturation. In DR1 catalogue, α and δ are not consistent with those in input catalogue. We list these stars and give the original position information (obsid, observed date, planid, spid, fiberid, distance, tra, and tdec) in this page.

4. Wrong fiber IDs

There are 9 fibers numbered with wrong IDs, which relate to 4396 spectra list in this file, and you can download these spectra here.

The updated DR1 catalog appears on CDS/VizieR, you may find it at this link. It is slightly different from the old version on DR1 homepage, due to 1) wrong fiber IDs correction, and 2) a few adds/removes for the ‘bad-fiber’ flags.