OB Stars

Targeting Overview

Picture of the distribution of OB stars in the X-Y plane of the Galaxy. Outlines of several spiral arms are visible.
Distribution of OB targets from Zari et al. 2021

MWM is targeting OB stars using their high luminosities and blue intrinsic colors. The main sample selection is done in the spirit of the SDSS-V requirement of a known and well-defined selection function, and is therefore based on Gaia DR2 photometry and astrometry combined with the 2MASS photometric information. First, all objects whose absolute magnitude in the K photometric band is smaller than -0.61 are selected, which roughly corresponds to a B3 main-sequence star. Ultimately, several color cuts are applied to clean the sample from intrinsically bright red giant- and asymptotic giant-branch stars, as well as from objects with unnaturally blue colors. The target selection and its rationale is described more fully in Zari et al. (2021). In addition, a few thousand Cepheids from the catalog of Inno et al. (2021).


OB Star Cartons in Targeting Generation v0.5.3

The OB cartons for target generation v0.5.3 use magnitudes from the 2MASS Point Source Catalog and Gaia DR2 and parallaxes (in mas) and rule from Gaia DR2.

  • mwm_ob_core
    • parallax < 10((10-K-0.61)/5)
    • G < 16
    • J-K-0.25(G-K) < 0.10
    • J-K-0.25(G-K)> -0.30
    • J-H<0.15(G-K)+0.05
    • J-H > 0.15(G-K)-0.15
    • J-K < 0.23(G-K)+0.03
    • G > 2(G-K)+3.0
    • Cross-match separation between Gaia DR2 and 2MASS < 1″
    • ruwe < 1.4
  • mwm_ob_cepheids


All OB star program cartons take the bright_3x1 cadence.

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