The little-studied cluster Berkeley 90. II. The foreground ISM

Context: Nearly one century after their discovery, the carrier(s) of Diffuse Interstellar Bands is/are still unknown and there are few sightlines studied in detail for a large number of DIBs. Aims: We want to study the ISM sightlines towards LS III +46 11 and LS III +46 12, two early-O-type stellar systems, and LS III +46 11 B, a mid-B-type star. The three targets are located in the stellar cluster Berkeley 90 and have a high extinction. Methods: We use the multi-epoch high-S/N optical spectra presented in paper I (Ma\'iz Apell\'aniz et al. 2015), the extinction results derived there, and additional spectra. Results: We have measured equivalent widths, velocities, and FWHMs for a large number of absorption lines in the rich ISM spectrum in front of Berkeley 90. The absorbing ISM has at least two clouds at different velocities, one with a lower column density (thinner) in the K I lines located away from Berkeley 90 and another one with a higher column density (thicker) associated with the cluster. The first cloud has similar properties for both O-star sightlines but the second one is thicker for LS III +46 11. The comparison between species indicate that the cloud with a higher column density has a denser core, allowing us to classify the DIBs in a sigma-zeta scale, some of them for the first time. The LS III +46 12 sightline also has a high-velocity redshifted component.Comment: Accepted for publication in A&

VdBH 222: a starburst cluster in the inner Milky Way

Context. It has been suggested that the compact open cluster VdBH 222 is a young massive distant object.Aims. We set out to characterise VdBH 222 using a comprehensive set of multi-wavelength observations.Methods.We obtained multi-band optical (UBVR) and near-infrared (JHKS) photometry of the cluster field, as well as multi-object and long-slit optical spectroscopy for a large sample of stars in the field. We applied classical photometric analysis, as well as more sophisticated methods using the CHORIZOS code, to determine the reddening to the cluster. We then plotted dereddened HR diagrams and determined cluster parameters via isochrone fitting.Results. We have identified a large population of luminous supergiants confirmed as cluster members via radial velocity measurements. We find nine red supergiants (plus one other candidate) and two yellow supergiants. We also identify a large population of OB stars. Ten of them are bright enough to be blue supergiants. The cluster lies behind ≈7.5 mag of extinction for the preferred value of RV = 2.9. Isochrone fitting allows for a narrow range of ages between 12 and 16 Ma. The cluster radial velocity is compatible with distances of ~6 and ~10 kpc. The shorter distance is inconsistent with the age range and Galactic structure. The longer distance implies an age ≈ 12 Ma and a location not far from the position where some Galactic models place the far end of the Galactic bar.Conclusions. VdBH 222 is a young massive cluster with a likely mass >20 000 M⊙. Its population of massive evolved stars is comparable to that of large associations, such as Per OB1. Its location in the inner Galaxy, presumably close to the end of the Galactic bar, adds to the increasing evidence for vigorous star formation in the inner regions of the Milky Way

Direct Detection of the Tertiary Component in the Massive Multiple HD 150 136 with VLTI

Massive stars are of fundamental importance for almost all aspects of astrophysics, but there still exist large gaps in our understanding of their properties and formation because they are rare and therefore distant. It has been found that most O-stars are multiples. HD 150 136 is the nearest system to Earth with >100 M_sol, and provides a unique opportunity to study an extremely massive system. Recently, evidence for the existence of a third component in HD 150 136, in addition to the tight spectroscopic binary that forms the main component, was found in spectroscopic observations. Our aim was to image and obtain astrometric and photometric measurements of this component using long baseline optical interferometry to further constrain the nature of this component. We observed HD150136 with the near-infrared instrument AMBER attached to the ESO VLT Interferometer. The recovered closure phases are robust to systematic errors and provide unique information on the source asymmetry. Therefore, they are of crucial relevance for both image reconstruction and model fitting of the source structure. The third component in HD 150 136 is clearly detected in the high-quality data from AMBER. It is located at a projected angular distance of 7.3 mas, or about 13 AU at the line-of-sight distance of HD 150 136, at a position angle of 209 degrees East of North, and has a flux ratio of 0.25 with respect to the inner binary. We resolved the third component of HD 150 136 in J, H and K filters. The luminosity and color of the tertiary agrees with the predictions and shows that it is also an O main-sequence star. The small measured angular separation indicates that the tertiary may be approaching the periastron of its orbit. These results, only achievable with long baseline near infrared interferometry, constitute the first step towards the understanding of the massive star formation mechanisms

Lucky Spectroscopy, an equivalent technique to Lucky Imaging. Spatially resolved spectroscopy of massive close visual binaries using the William Herschel Telescope

CONTEXT: Many massive stars have nearby companions whose presence hamper their characterization through spectroscopy. AIMS: We want to obtain spatially resolved spectroscopy of close massive visual binaries to derive their spectral types. METHODS: We obtain a large number of short long-slit spectroscopic exposures of five close binaries under good seeing conditions, select those with the best characteristics, extract the spectra using multiple-profile fitting, and combine the results to derive spatially separated spectra. RESULTS: We demonstrate the usefulness of Lucky Spectroscopy by presenting the spatially resolved spectra of the components of each system, in two cases with separations of only ~0.3". Those are delta Ori Aa+Ab (resolved in the optical for the first time) and sigma Ori AaAb+B (first time ever resolved). We also spatially resolve 15 Mon AaAb+B, zeta Ori AaAb+B (both previously resolved with GOSSS, the Galactic O-Star Spectroscopic Survey), and eta Ori AaAb+B, a system with two spectroscopic B+B binaries and a fifth visual component. The systems have in common that they are composed of an inner pair of slow rotators orbited by one or more fast rotators, a characteristic that could have consequences for the theories of massive star formation.Comment: Accepted for publication in A&A, 7 page