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sdss / lvmdrp

Local Volume Mapper (LVM) Data Reduction Pipeline
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Underestimation of fluxes in blue arm #130

Open nataschasattler opened 3 months ago

nataschasattler commented 3 months ago

In M20, we see an underestimation of the fluxes, especially in the blue arm (using DRP version 1.0.4.dev0 and the resulting SFrames). We compared the LVM fluxes with measured long-slit fluxes by Garcia-Rojas+2006 (GR, https://ui.adsabs.harvard.edu/abs/2006MNRAS.368..253G). Therefore we used the fluxes in the fiber that corresponds best to the region of the GR long-slit. In the attached plot we compare each flux normalized to Hb from LVM (y-axis) and the GR paper (x-axis). flux_comparison

We used for M20 the following early science frames: MJD 60214 (Frames 5584, 5585, 5588, 5589) MJD 60216 (Frames 5735, 5736) MJD 60217 (Frames 5833, 5834)

ajmejia commented 3 months ago

Hi @nataschasattler, I think we fixed this issue in the current version of the pipeline in master branch. Could you please reduce your exposures again with that version of the pipeline?

You may also need to pull from lvmcore repository to be able to run the latest version of the DRP.

nataschasattler commented 2 months ago

with the DRP version of 3rd of September, it seems to be a bit better I guess but the difference is not striking flux_comparison3

ndrory commented 2 months ago

I now think this is related to a problem with the GAIA XP spectra at < 4000 Angstrom. See, for example, https://arxiv.org/abs/2404.14626 Fig. 1