The sigma Orionis cluster is to date the star-forming region with the largest number of confirmed brown dwarfs and substellar objects below the deuterium burning mass limit. The most massive star, sigma Ori Aa, just in the cluster centre, is the sim2
0Msol-mass O9.5V star that illuminates the Horsehead Nebula, while the least massive object yet reported, S Ori 70, is only around 3 MJup. In the middle, there is a continuum of stars and substellar objects of all types (including magnetically active B2Vp stars, Herbig-Haro objects, FU Ori stars or T Tauri brown dwarfs) that makes the cluster a cornerstone in the study of the initial mass function, disc presence, X-ray emission or accretion at all mass domains. However, the derived masses strongly depend on the actual heliocentric distance to the cluster. Gaia will solve the dilemma.
This is the first of a series of works devoted to investigate cool dwarfs in wide multiple systems. Here, I present Koenigstuhl 4 A and B, two bright, intermediate M dwarfs with a common high proper-motion and separated by 299 arcsec. At the most pro
bable distance of the system, 19 pc, the projected physical separation is 5700 AU, which makes Koenigstuhl 4 AB to be one of the least bound binary systems with late-type components found to date. I also associate the primary with a ROSAT X-ray source for the first time.
Aims: I study new deep (DeltaV ~ 1.20-1.65 mag) occultation events of the delta Scuti, Herbig Ae/Be star V1247 Ori in the Ori OB1 b association. Methods: I use the V-band ASAS light curve of V1247 Ori, which covers the last nine years, together with
photometric data in the near-ultraviolet, visible, near-, and far-infrared taken from the literature. I carry out a periodogram analysis of the cleaned light curve and construct the spectral energy distribution of the star. Results: The star V1247 Ori is interesting for the study of the UX Orionis phenomenon, in which Herbig Ae/Be stars are occulted by their protoplanetary discs, for three reasons: brightness (V ~ 9.85 mag), large infrared excess at 20-100 mum (F_60 ~ 10 Jy), and photometric stability out of occultation (sigma(V) ~ 0.02 mag), which may help to determine the location and spatial structure of the occulting disc clumps.
