The IACOB spectroscopic database of Galactic OB stars

We present the IACOB spectroscopic database, the largest homogeneous database of high-resolution, high signal-to-noise ratio spectra of Northern Galactic OB-type stars compiled up to date. The spectra were obtained with the FIES spectrograph attached to the Nordic Optical Telescope. We briefly summarize the main characeristics and present status of the IACOB, first scientific results, and some future plans for its extension and scientific exploitation.Comment: 2 pages. Poster contribution to the proceedings of the IAU272 "Active OB stars: structure, evolution, mass loss and critical limits

Open cluster Dolidze 25: Stellar parameters and the metallicity in the Galactic Anticentre

The young open cluster Dolidze 25, in the direction of the Galactic Anticentre, has been attributed a very low metallicity, with typical abundances between $-0.5$ and $-0.7$ dex below solar. We intend to derive accurate cluster parameters and accurate stellar abundances for some of its members. We have obtained a large sample of intermediate- and high-resolution spectra for stars in and around Dolidze 25. We used the FASTWIND code to generate stellar atmosphere models to fit the observed spectra. We derive stellar parameters for a large number of OB stars in the area, and abundances of oxygen and silicon for a number of stars with spectral types around B0. We measure low abundances in stars of Dolidze 25. For the three stars with spectral types around B0, we find $0.3$ dex (Si) and $0.5$ dex (O) below the values typical in the solar neighbourhood. These values, even though not as low as those given previously, confirm Dolidze 25 and the surrounding H II region Sh2-284 as the most metal-poor star-forming environment known in the Milky Way. We derive a distance $4.5\pm0.3\:$kpc to the cluster ($r_{\textrm{G}}\approx12.3\:$kpc). The cluster cannot be older than $\sim3\:$Myr, and likely is not much younger. One star in its immediate vicinity, sharing the same distance, has Si and O abundances at most $0.15\:$dex below solar. The low abundances measured in Dolidze 25 are compatible with currently accepted values for the slope of the Galactic metallicity gradient, if we take into account that variations of at least $\pm0.15\:$dex are observed at a given radius. The area traditionally identified as Dolidze 25 is only a small part of a much larger star-forming region that comprises the whole dust shell associated with Sh2-284 and very likely several other smaller H II regions in its vicinity.Comment: Accepted for publication in Astronomy \& Astrophysics. 16 pages, 12 figure

Orbital and physical properties of the σ Ori Aa,Ab,B triple system

We provide a complete characterization of the astrophysical properties of the σ Ori Aa,Ab,B hierarchical triple system, and an improved set of orbital parameters for the highly eccentric σ Ori Aa,Ab spectroscopic binary. We compiled a spectroscopic dataset comprising 90 high-resolution spectra covering a total time span of 1963 days. We applied the Lehman-Filh ́es method for a detailed orbital analysis of the radial velocity curves and performed a combined quantitative spectroscopic analysis of the σ Ori Aa,Ab,B system by means of the stellar atmosphere code fastwind. We used our own plus other available information on photometry and distance to the system for measuring the radii, luminosities, and spectroscopic masses of the three components. We also inferred evolutionary masses and stellar ages using the Bayesian code bonnsai. The orbital analysis of the new radial velocity curves led to a very accurate orbital solution of the σ Ori Aa,Ab pair. We provided indirect arguments indicating that σ Ori B is a fast rotating early-B dwarf. The fastwind+bonnsai analysis showed that the Aa,Ab pair contains the hottest and most massive components of the triple system while σ Ori B is a bit cooler and less massive. The derived stellar ages of the inner pair are intriguingly younger than the one widely accepted for the σ Orionis cluster, at 3 ± 1 Ma. The outcome of this study will be of key importance for a precise determination of the distance to the σ Orionis cluster, the interpretation of the strong X-ray emission detected for σ Ori Aa,Ab,B, and the investigation of the formation and evolution of multiple massive stellar systems and substellar objects

Is macroturbulence in OB Sgs related to pulsations?

As part of a long term observational project, we are investigating the macroturbulent broadening in O and B supergiants (Sgs) and its possible connection with spectroscopic variability phenomena and stellar oscillations. We present the first results of our project, namely firm observational evidence for a strong correlation between the extra broadening and photospheric line-profile variations in a sample of 13 Sgs with spectral types ranging from O9.5 to B8.Comment: 2 pages, 1 figure. Poster contribution to the proceedings of the IAU272 "Active OB stars: structure, evolution, mass loss and critical limits

Sher 25: pulsating but apparently alone

The blue supergiant Sher25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula, which shows similarities to the triple-ring structure seen around SN1987A. From optical spectroscopy over six consecutive nights, we detect periodic radial velocity variations in the stellar spectrum of Sher25 with a peak-to-peak amplitude of ~12 km/s on a timescale of about 6 days, confirming the tentative detec-tion of similar variations by Hendry et al. From consideration of the amplitude and timescale of the signal, coupled with observed line profile variations, we propose that the physical origin of these variations is related to pulsations in the stellar atmosphere, rejecting the previous hypothesis of a massive, short-period binary companion. The radial velocities of two other blue supergiants with similar bipolar nebulae, SBW1 and HD 168625, were also monitored over the course of six nights, but these did not display any significant radial velocity variations.Comment: 9 pages, 7 figures. Accepted for publication in MNRA

MONOS: Multiplicity Of Northern O-type Spectroscopic systems - II. Orbit review and analysis for 35 single-lined spectroscopic binary systems and candidates

Context. Massive stars are a key element for understanding the chemical and dynamical evolution of galaxies. Stellar evolution is conditioned by many factors: Rotation, mass loss, and interaction with other objects are the most important ones for massive stars. During the first evolutionary stages of stars with initial masses (i.e., MZAMS) in the MZAMS ∼ 18–70  M⊙ range, they are of spectral type O. Given that stars in this mass range spend roughly 90% of their lifetime as O-type stars, establishing the multiplicity frequency and binary properties of O-type stars is crucial for many fields of modern astrophysics. Aims. The aim of the MONOS project is to collect information to study northern Galactic O-type spectroscopic binaries. In this second paper, we tackle the study of the 35 single-line spectroscopic binary (SB1) systems identified in the previous paper of the series, analyze our data, and review the literature on the orbits of the systems. Methods. We have measured ∼4500 radial velocities for a selection of diagnostic lines for the ∼700 spectra of the studied systems in our database, for which we have used two different methods: a Gaussian fit for several lines per object and cross-correlation with synthetic spectra computed with the FASTWIND stellar atmospheric code. We have also explored the photometric data delivered by the TESS mission to analyze the light curve (LC) of the systems, extracting 31 of them. We have explored the possible periods with the Lomb-Scargle method and, whenever possible, calculated the orbital solutions using the SBOP and GBART codes. For those systems in which an improved solution was possible, we merged our radial velocities with those in the literature and calculated a combined solution. Results. As a result of this work, of the 35 SB1 systems identified in our first paper we have confirmed 21 systems as SB1 with good orbits, discarded the binary nature of six stars (9 Sge, HD 192 281, HDE 229 232 AB, 68 Cyg, HD 108, and α Cam), and left six stars as inconclusive due to a lack of data. The remaining two stars are 15 Mon Aa, which has been classified as SB2, and Cyg OB2-22 C, for which we find evidence that it is most likely a triple system where the O star is orbiting an eclipsing SB1. We have also recalculated 20 new orbital solutions, including the first spectroscopic orbital solution for V747 Cep. For Cyg OB2-22 C, we have obtained new ephemerides but no new orbit.E.T.P., I.N.D. and S.S.D. acknowledge support from the Spanish Government Ministerio de Ciencia through grant AYA2015-68 012-C2-1/2-P. E.T.P. and J.M.A. acknowledge support from the Spanish Government Ministerio de Ciencia through grants AYA2016-75 931-C2-2-P and PGC2018-095 049-B-C22. R.H.B. acknowledges support from the ESAC Faculty Council Visitor Program and ANID FONDECYT Project 1211903. G.H. acknowledges support from the Spanish Government Ministerio de Ciencia through grant PGC2018-95049-B-CC22 and ESA Contract No. 4000-126507/19/ES/CM. This research has made use of the SIMBAD database, operated at CDS (Strasbourg, France), NASA’s Astrophysics Data System Bibliographic Services and the Python programming language (Python Software Foundation), Lightkurve, a Python package for Kepler and TESS data analysis (Lightkurve Collaboration 2018)

GU Monocerotis: A high-mass eclipsing overcontact binary in the young open cluster Dolidze 25

Context. The eclipsing binary GU Mon is located in the star-forming cluster Dolidze 25, which has the lowest metallicity measured in a Milky Way young cluster. Aims. GU Mon has been identified as a short-period eclipsing binary with two early B-type components. We set out to derive its orbital and stellar parameters. Methods. We present a comprehensive analysis, including B and V light curves and 11 high-resolution spectra, to verify the orbital period and determine parameters. We used the stellar atmosphere code FASTWIND to obtain stellar parameters and create templates for cross-correlation. We obtained a model to fit the light and radial-velocity curves using the Wilson-Devinney code iteratively and simultaneously. Results. The two components of GU Mon are identical stars of spectral type B1 V with the same mass and temperature. The light curves are typical of an EW-type binary. The spectroscopic and photometric analyses agree on a period of 0.896640 ± 0.000007 d. We determine a mass of 9.0 ± 0.6 M⊙ for each component and for temperatures of 28 000 ± 2000 K. Both values are consistent with the spectral type. The two stars are overfilling their respective Roche lobes, sharing a common envelope and, therefore the orbit is synchronised and circularised. Conclusions. The GU Mon system has a fill-out factor above 0.8, containing two dwarf B-type stars on the main sequence. The two stars are in a very advanced stage of interaction, with their extreme physical similarity likely due to the common envelope. The expected evolution of such a system very probably leads to a merger while still on the main sequence.This research is partially supported by the Spanish Ministerio de Economía y Competitividad under grants AYA2012-39364-C02-01/02 and AYA2015-68012-C2-1/2, and the European Union