- ID:
- ivo://CDS.VizieR/J/A+A/626/A20
- Title:
- MONOS. I. Spectral classifications
- Short Name:
- J/A+A/626/A20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multiplicity in massive stars is a key element to understand the chemical and dynamical evolution of galaxies. Among massive stars, those of O type play a crucial role due to their high masses and short lifetimes. MONOS (Multiplicity Of Northern O-type Spectroscopic systems) is a project designed to collect information and study O-type spectroscopic binaries with {delta}>20{deg}. In this first paper we describe the sample and provide spectral classifications and additional information for objects with previous spectroscopic and/or eclipsing binary orbits. In future papers we will test the validity of previous solutions and calculate new spectroscopic orbits. The spectra in this paper have two sources: the Galactic O-Star Spectroscopic Survey (GOSSS), a project that is obtaining blue-violet R~2500 spectroscopy of thousands of massive stars, and LiLiMaRlin, a library of libraries of high-resolution spectroscopy of massive stars obtained from four different surveys (CAFE-BEANS, OWN, IACOB, and NoMaDS) and additional data from our own observing programs and public archives. We also use lucky images obtained with AstraLux. We present homogeneous spectral classifications for 92 O-type spectroscopic multiple systems and ten optical companions, many of them original.We discuss the visual multiplicity of each system with the support of AstraLux images and additional sources. For eleven O-type objects and for six B-type objects we present their first GOSSS spectral classifications. For two known eclipsing binaries we detect double absorption lines (SB2) or a single moving line (SB1) for the first time, to which we add a third system already reported by us recently. For two previous SB1 systems we detect their SB2 nature for the first time and give their first separate spectral classifications, something we also do for a third object just recently identified as a SB2. We also detect nine new astrometric companions and provide updated information on several others. We emphasize the results for two stars: for {sigma} Ori AaAbB we provide spectral classifications for the three components with a single observation for the first time thanks to a lucky spectroscopy observation obtained close to the Aa,Ab periastron and for {theta}^1^ Ori CaCb we add it to the class of Galactic Of?p stars, raising the number of its members to six. Our sample of O-type spectroscopic binaries contains more triple- or higher-order systems than double systems.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/710/L30
- Title:
- On the multiplicity of the O star Herschel 36
- Short Name:
- J/ApJ/710/L30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis of high-resolution optical spectroscopic observations of the zero-age main-sequence O star Herschel 36 spanning six years. This star is definitely a multiple system, with at least three components detected in its spectrum. Based on our radial-velocity (RV) study, we propose a picture of a close massive binary and a more distant companion, most probably in wide orbit about each other. The orbital solution for the binary, whose components we identify as O9V and B0.5V, is characterized by a period of 1.5415+/-0.0006 days. With a spectral type O7.5V, the third body is the most luminous component of the system and also presents RV variations with a period close to 498 days. Some possible hypotheses to explain the variability are briefly addressed and further observations are suggested.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/37
- Title:
- Optical interferometry of 6 O-type HD stars
- Short Name:
- J/ApJ/869/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present interferometric observations of six O-type stars that were made with the Precision Astronomical Visible Observations beam combiner at the Center for High Angular Resolution Astronomy (CHARA) Array. The observations include multiple brackets for three targets, {lambda} Ori A, {zeta} Oph, and 10 Lac, but there are only preliminary, single observations of the other three stars, {xi} Per, {alpha} Cam, and {zeta} Ori A. The stellar angular diameters range from 0.55mas for {zeta} Ori A down to 0.11mas for 10 Lac, the smallest star yet resolved with the CHARA Array. The rotational oblateness of the rapidly rotating star {zeta} Oph is directly measured for the first time. We assembled ultraviolet to infrared flux measurements for these stars, and then derived angular diameters and reddening estimates using model atmospheres and an effective temperature set by published results from analysis of the line spectrum. The model-based angular diameters are in good agreement with those observed. We also present estimates for the effective temperatures of these stars, derived by setting the interferometric angular size and fitting the spectrophotometry.
- ID:
- ivo://CDS.VizieR/J/A+A/560/A29
- Title:
- O-stars in VLT-FLAMES Tarantula Survey
- Short Name:
- J/A+A/560/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 30 Doradus (30 Dor) region of the Large Magellanic Cloud, also known as the Tarantula Nebula, is the nearest starburst region. It contains the richest population of massive stars in the Local Group and it is thus the best possible laboratory to investigate open questions in the formation and evolution of massive stars. Using ground based multi-object optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to establish the (projected) rotational velocity distribution for a sample of 216 presumably single O-type stars in 30 Dor. The size of the sample is large enough to obtain statistically significant information and to search for variations among sub-populations - in terms of spectral type, luminosity class, and spatial location - in the field of view. We measured projected rotational velocities, Vrot, by means of a Fourier transform method and a profile fitting method applied on a set of isolated spectral lines. We also used an iterative deconvolution procedure to infer the probability density, P(Veq), of the equatorial rotational velocity, Veq. The distribution of Vrot shows a two-component structure: a peak around 80km/s and a high-velocity tail extending up to ~600km/s. This structure is also present in the inferred distribution P(Veq) with around 80% of the sample having 0<Veq<=300km/s and the other 20% distributed in the high-velocity region. The presence of the low-velocity peak is consistent with that found in other studies for late O- and early B-type stars. Most of the stars in our sample rotate with a rate less than 20% of their break-up velocity. For the bulk of the sample, mass-loss in a stellar wind and/or envelope expansion is not efficient enough to significantly spin down these stars within the first few Myr of evolution. If massive-star formation results in stars rotating at birth with a large fraction of their break-up velocities, an alternative braking mechanism, possibly magnetic fields, is thus required to explain the present day rotational properties of the O-type stars in 30 Dor. The presence of a sizeable population of fast rotators is compatible with recent population synthesis computations that investigate the influence of binary evolution on the rotation rate of massive stars. Despite the fact that we have excluded stars that show significant radial velocity variations, our sample may have remained contaminated by post-interaction binary products. The fact that the high-velocity tail may be preferentially (and perhaps even exclusively), populated by post-binary interaction products, has important implications for the evolutionary origin of systems that produce gamma-ray bursts.
- ID:
- ivo://CDS.VizieR/J/ApJ/639/1069
- Title:
- Radial velocities in the Cas OB6 association
- Short Name:
- J/ApJ/639/1069
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of time-resolved spectroscopy of 13 O-type stars in the Cas OB6 stellar association. We conducted a survey for radial velocity variability in search of binary systems, which are expected to be plentiful in young OB associations.
- ID:
- ivo://CDS.VizieR/J/AJ/142/146
- Title:
- Radial Velocities of Galactic O-type stars I.
- Short Name:
- J/AJ/142/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial velocities for 18 Galactic O-type stars. These stars display small radial velocity scatter over timescales of one to two weeks. Some of them are long-period binaries while others are probably single stars. By fitting model spectra to our observed spectra we obtain estimates for effective temperature, log g, rotational velocity, and average radial velocity for each target.
- ID:
- ivo://CDS.VizieR/J/A+A/601/A34
- Title:
- Resolved astrometry of ten O-type binaries
- Short Name:
- J/A+A/601/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our long-term aim is to derive model-independent stellar masses and distances for long period massive binaries by combining apparent astrometric orbit with double-lined radial velocity amplitudes (SB2).We followed-up ten O+O binaries with AMBER, PIONIER and GRAVITY at the VLTI. Here, we report on 130 astrometric observations over the last seven years. We combined this dataset with distance estimates to compute the total mass of the systems. We also computed preliminary individual component masses for the five systems with available SB2 radial velocities. Nine of the ten binaries have their three-dimensional orbit well constrained. Four of them are known to be colliding wind, non-thermal radio emitters, and thus constitute valuable targets for future high angular resolution radio imaging. Two binaries break the correlation between period and eccentricity tentatively observed in previous studies. This suggests either that massive star formation produces a wide range of systems, or that several binary formation mechanisms are at play. Finally, we found that the use of existing SB2 radial velocity amplitudes can lead to unrealistic masses and distances.If not understood, the biases in radial velocity amplitudes will represent an intrinsic limitation for estimating dynamical masses from SB2+interferometry or SB2+Gaia. Nevertheless, our results can be combined with future Gaia astrometry to measure the dynamical masses and distances of the individual components with an accuracy of 5 to 15%, completely independently of the radial velocities.
- ID:
- ivo://CDS.VizieR/J/AJ/132/749
- Title:
- Rotational velocities of O stars in clusters
- Short Name:
- J/AJ/132/749
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study aimed at assessing whether low and high-mass stars form similarly. Our approach is (1) to examine the observed projected rotational velocities among a large sample of newly formed stars spanning a range in mass between 0.2 and 50M_{sun}_ and (2) to search for evidence of a discontinuity in rotational properties that might indicate a difference in the stellar formation process at some characteristic mass. Our database includes recently published values of vsini for young intermediate and low-mass stars in Orion, as well as new observations of O stars located in young clusters and OB associations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/416/817
- Title:
- RV catalog of O-type stars in IC 2944 and Cen OB2
- Short Name:
- J/MNRAS/416/817
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using an extended set of multi-epoch high resolution high signal-to-noise ratio optical spectra, we re-address the multiplicity properties of the O-type stars in IC 2944 and in the Cen OB2 association. We present new evidence of binarity for five objects and we confirm the multiple nature of another two. We derive the first orbital solutions for HD 100099, HD 101436 and HD 101190 and we provide additional support for HD 101205 being a quadruple system. The minimal spectroscopic binary fraction in our sample is f_min_=0.57. Using numerical simulations, we show that the detection rate of our observational campaign is close to 90%, leaving thus little room for undetected spectroscopic binary systems. The statistical properties of the O-star population in IC 2944 are similar, within the uncertainties, to the results obtained in the earlier papers in this series despite the fact that sample size effects limit the significance of the comparison. Using newly derived spectroscopic parallaxes, we reassess the distance to IC 2944 and obtained 2.3+/-0.3kpc, in agreement with previous studies. We also confirm that, as far as the O stars are concerned, the IC 2944 cluster is most likely a single entity.
- ID:
- ivo://CDS.VizieR/J/A+A/550/A107
- Title:
- RV catalogue of O stars in 30 Doradus
- Short Name:
- J/A+A/550/A107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Tarantula Nebula in the Large Magellanic Cloud is our closest view of a starburst region and is the ideal environment to investigate important questions regarding the formation, evolution and final fate of the most massive stars. We analyze the multiplicity properties of the massive O-type star population observed through multi-epoch spectroscopy in the framework of the VLT-FLAMES Tarantula Survey. With 360 O-type stars, this is the largest homogeneous sample of massive stars analyzed to date. We use multi-epoch spectroscopy and variability analysis to identify spectroscopic binaries. We also use a Monte-Carlo method to correct for observational biases. By modelling simultaneously the observed binary fraction, the distributions of the amplitudes of the radial velocity variations and the distribution of the time scales of these variations, we derive the intrinsic current binary fraction and period and mass-ratio distributions. We observe a spectroscopic binary fraction of 0.35+/-0.03, which corresponds to the fraction of objects displaying statistically significant radial velocity variations with an amplitude of at least 20km/s . We compute the intrinsic binary fraction to be 0.51+/-0.04. We adopt power-laws to describe the intrinsic period and mass-ratio distributions: f(log_10_P/d)~(log_10_ P/d)^pi^ (with log_10_P/d in the range 0.15-3.5) and f(q)~q^kappa^ with 0.1<q=M2/M1< 1.0. The power-law indexes that best reproduce the observed quantities are pi=-0.45+/-0.30 and kappa=-1.0+/-0.4. The period distribution that we obtain thus favours shorter period systems compared to an Opik law (pi=0). The mass ratio distribution is slightly skewed towards low mass ratio systems but remains incompatible with a random sampling of a classical mass function (kappa=-2.35). The binary fraction seems mostly uniform across the field of view and independent of the spectral types and luminosity classes. The binary fraction in the outer region of the field of view (r>7.8 , i.e. ~117pc) and among the O9.7 I/II objects are however significantly lower than expected from statistical fluctuations. The observed and intrinsic binary fractions are also lower for the faintest objects in our sample (Ks>15.5mag), which results from observational effects and the fact that our O star sample is not magnitude-limited but is defined by a spectral-type cutoff. We also conclude that magnitude-limited investigations are biased towards larger binary fractions. Using the multiplicity properties of the O stars in the Tarantula region and simple evolutionary considerations, we estimate that over 50% of the current O star population will exchange mass with its companion within a binary system. This shows that binary interaction is greatly affecting the evolution and fate of massive stars, and must be taken into account to correctly interpret unresolved populations of massive stars.
