The distribution of OB stars and dust in a Milky Way field at (l,b) = (335°, 0°)⋆

New photoelectric UBV photometry for 103 stars and MK spectroscopy for 110 stars are presented in a 21 deg² field at (l, b)=(335°, 0°); these are mostly OB stars and brighter than V = 14.4. Combined with other observations from the literature, these provide photoelectric UBV and slit or objective prism spectra for 111 of the 112 SLS stars in this region, and photoelectric measurements for a further 84 non-OB stars, some with spectra. Analysis of the data suggest the existence along the line-of-sight of three OB associations with the following properties: (a) (=Ara OB 1): $$\langle V_0-M_\upsilon\rangle=10.64$$s=0.08, 47 stars; $$\langle d\rangle=1.34$$ kpc; E(B−V)=0.82, s=0.02, s_E=0.20, 51 members; (b) $$\langle V_0-M_\upsilon\rangle=11.91$$, s=0.07, 25 stars; $$\langle d\rangle=2.41$$ kpc; E(B−V)=0.86, s=0.03, s_E=0.21, 25 members; (c) $$\langle V_0-M^{\text {mk}}_\upsilon\rangle=12.84,\enspace s_{\text{mk}}=0.13, 17\enspace\text{stars; }\langle d\rangle=3.69\text{ kpc};\enspace E^{ub\upsilon}(B-V)=0.92,\enspace s_{ub\upsilon}=0.05,\enspace s_E=0.26$, 19 members;$ and two dust associations with distances and colours excesses based on varying numbers of stars in their vicinity: (1) $$\langle V_0-M^{\text{mk}}_\upsilon\rangle=6.35,\enspace s_{\text{mk}}=0.29$$, 12 stars; ⟨d⟩=0.19 kpc; ⟨E^ubυL(B−V)⟩=0.21, s_ubυL=0.03, $$s^{ub\upsilon L=}_E0.00$$, 16 stars (2) $$\langle V_0-M^{\text{mk}}_\upsilon\rangle=9.19,\enspace s_{\text{mk}}=0.20$$, 14 stars; ⟨d⟩=0.69 kpc; ⟨E^ubυL(B−V)⟩=0.76, s_ubυL=0.01, $$s^{ub\upsilon L=}_E0.15$$, 12 stars Comparison with other spiral tracers places group A = Ara OB1 in the Sagittarius (–I) arm, group B on the bridge between arms – I and – II, and group C in the – II arm. Cloud 1 is associated with dust at the inner edge of the local arm, and cloud 2 with the interarm cloud G of FitzGerald.