We use the reddening-free Q index Qₔ-₆, ₆-ₑ= (u-g) -2. 099 (g-r) to photometrically identify OB-stars in the SkyMapper catalog to retrieve 474 509 candidate OB stars spanning more than half of the Galactic equator strip (|b|<5^) with a gap in the longitude interval 50<l<200. A comparison with previously identified OB-associations suggests the presence of potential new, hitherto unknown star groups in the southern sky. An analysis of the dependence of the height z above the Galactic midplane on Q -index confirms that our candidate OB stars reside predominantly in the thin disk.
Golovatskaya et al. (Mon,) studied this question.