The DR4 International is the same as the version of internal DR4 (dr4_v2) published to domestic users at the end of 2017 which is a subsample of internal DR5. Now we find a few problems about the data in internal DR4 that also exist in DR4 international version. For consistency with the internal DR4, no revision is made for the international version. We will solve these problems and update the data in the following DR5 International version.
In order to better utilize the data for LAMOST users, we list these problems in DR4 International and the detailed description can be found in the following link: http://dr4.lamost.org/doc/The-warning.
We compare the parameters of DR4 with those of DR3 and SDSS. The results are shown as follows.
(1). We select targets which have both dr4_v2 and DR3 parameters, and compare their atmospheric parameters (Teff, logg, [Fe/H]) and rv of the two versions in following figures. The average values and standard deviations of differences of the two versions are also shown in the figures.
(2). The histograms of the differences between dr4_v2 and DR3 for atmospherical parameters (Teff, logg, [Fe/H]) and rv are shown as follows. The differences of parameters are divided into four groups according to the snr, represented by different colors.
The difference of parameters between LAMOST dr4_v2 and SDSS (DR14 and APOGEE) are shown in this section.
(1). The following figures show the comparisons of atmospherical parameters (Teff, logg, [Fe/H]) as well as rv between LAMOST dr4_v2 and SDSS DR14. For the parameters of logg, a branch is seen in the bottom-right of the top-right panel. It could be explained by the inhomogeneous distribution of the atmospherical parameters for the ELODIE library. There are holes for giants in the ELODIE library, making the estimations of the initial guess for atmospherical parameters in the giant holes inaccurate.
(2). The histograms of the differences of atmospherical parameters (Teff, logg, [Fe/H]) as well as rv between LAMOST dr4_v2 and APOGEE are provided as follows. In comparison with APOGEE, the differences of parameters are divided into four groups according to snr. We also plot the mean values and the standard deviations corresponding to each snr bin in the figures.