Context. Massive stars play a dominant role in the process of clustered star formation, with their feedback into the molecular cloud through ionizing radiation, stellar winds, and outflows. The ...formation process of massive stars is poorly constrained because of their scarcity, the short formation timescale, and obscuration. By obtaining a census of the newly formed stellar population, the star formation history of the young cluster and the role of the massive stars within it can be unraveled. Aims. We aim to reconstruct the formation history of the young stellar population of the massive star-forming region RCW 36. We study several dozen individual objects, both photometrically and spectroscopically, looking for signs of multiple generations of young stars and investigating the role of the massive stars in this process. Methods. We obtain a census of the physical parameters and evolutionary status of the young stellar population. Using a combination of near-infrared photometry and spectroscopy we estimate the ages and masses of individual objects. We identify the population of embedded young stellar objects (YSOs) by their infrared colors and emission line spectra. Results. RCW 36 harbors a stellar population of massive and intermediate-mass stars located around the center of the cluster. Class 0/I and II sources are found throughout the cluster. The central population has a median age of 1.1 ± 0.6 Myr. Of the stars that could be classified, the most massive ones are situated in the center of the cluster. The central cluster is surrounded by filamentary cloud structures; within these, some embedded and accreting YSOs are found. Conclusions. Our age determination is consistent with the filamentary structures having been shaped by the ionizing radiation and stellar winds of the central massive stars. The formation of a new generation of stars is ongoing, as demonstrated by the presence of embedded protostellar clumps and two exposed protostellar jets.
ABSTRACT The contact phase expected to precede the coalescence of two massive stars is poorly characterized due to the paucity of observational constraints. Here we report on the discovery of VFTS ...352, an O-type binary in the 30 Doradus region, as the most massive and earliest spectral type overcontact system known to date. We derived the 3D geometry of the system, its orbital period day, components' effective temperatures-T1 = 42 540 280 K and T2 = 41 120 290 K-and dynamical masses- and Compared to single-star evolutionary models, the VFTS 352 components are too hot for their dynamical masses by about 2700 and 1100 K, respectively. These results can be explained naturally as a result of enhanced mixing, theoretically predicted to occur in very short-period tidally locked systems. The VFTS 352 components are two of the best candidates identified so far to undergo this so-called chemically homogeneous evolution. The future of VFTS 352 is uncertain. If the two stars merge, a very rapidly rotating star will be produced. Instead, if the stars continue to evolve homogeneously and keep shrinking within their Roche Lobes, coalescence can be avoided. In this case, tides may counteract the spin down by winds such that the VFTS 352 components may, at the end of their life, fulfill the requirements for long gamma-ray burst (GRB) progenitors in the collapsar scenario. Independently of whether the VFTS 352 components become GRB progenitors, this scenario makes VFTS 352 interesting as a progenitor of a black hole binary, hence as a potential gravitational wave source through black hole-black hole merger.
Aims. The formation of massive stars remains poorly understood and little is known about their birth multiplicity properties. Here, we aim to quantitatively investigate the strikingly low ...radial-velocity dispersion measured for a sample of 11 massive pre- and near-main-sequence stars (sigma sub(1D)= 5.6 + or - 0.2 kms super(-1)) in the very young massive star forming region M17, in order to obtain first constraints on the multiplicity properties of young massive stellar objects. Methods. We compute the radial-velocity dispersion of synthetic populations of massive stars for various multiplicity properties and we compare the obtained sigma sub(1D) distributions to the observed value. We specifically investigate two scenarios: a low binary fraction and a dearth of short-period binary systems. Results. Simulated populations with low binary fractions (f sub(bin)= 0.12 sub(-0.09) super(+0.16)) or with truncated period distributions (P sub(cutoff)> 9 months) are able to reproduce the low sigma sub(1D) observed within their 68%-confidence intervals. Furthermore, parent populations with f sub(bin)> 0.42 or P sub(cutoff)< 47 d can be rejected at the 5%-significance level. Both constraints are in stark contrast with the high binary fraction and plethora of short-period systems in few Myr-old, well characterized OB-type populations. To explain the difference in the context of the first scenario would require a variation of the outcome of the massive star formation process. In the context of the second scenario, compact binaries must form later on, and the cut-off period may be related to physical length-scales representative of the bloated pre-main-sequence stellar radii or of their accretion disks. Conclusions. If the obtained constraints for the M17's massive-star population are representative of the multiplicity properties of massive young stellar objects, our results may provide support to a massive star formation process in which binaries are initially formed at larger separations, then harden or migrate to produce the typical (untruncated) power-law period distribution observed in few Myr-old OB binaries.
The mass of the very massive binary WR21a Tramper, F; Sana, H; Fitzsimons, N. E ...
Monthly notices of the Royal Astronomical Society,
01/2016, Letnik:
455, Številka:
2
Journal Article, Web Resource
Recenzirano
Odprti dostop
We present multi-epoch spectroscopic observations of the massive binary system WR21a, which include the 2011 January periastron passage. Our spectra reveal multiple SB2 lines and facilitate an ...accurate determination of the orbit and the spectral types of the components. We obtain minimum masses of 64.4 ± 4.8 M⊙ and 36.3 ± 1.7 M⊙ for the two components of WR21a. Using disentangled spectra of the individual components, we derive spectral types of O3/WN5ha and O3Vz ((f*)) for the primary and secondary, respectively. Using the spectral type of the secondary as an indication for its mass, we estimate an orbital inclination of i = 58.8 ± 2
$_{.}^{\circ}$
5 and absolute masses of 103.6 ± 10.2 M⊙ and 58.3 ± 3.7 M⊙, in agreement with the luminosity of the system. The spectral types of the WR21a components indicate that the stars are very young (1–2 Myr), similar to the age of the nearby Westerlund 2 cluster. We use evolutionary tracks to determine the mass–luminosity relation for the total system mass. We find that for a distance of 8 kpc and an age of 1.5 Myr, the derived absolute masses are in good agreement with those from evolutionary predictions.
We present a spectroscopic analysis of Very Large Telescope/X-Shooter observations of six O-type stars in the low-metallicity (Z ~ 1/7 Z ) galaxies IC 1613, WLM, and NGC 3109. The stellar and wind ...parameters of these sources allow us, for the first time, to probe the mass loss versus metallicity dependence of stellar winds at metallicities below that of the Small Magellanic Cloud (at Z ~ 1/5 Z ) by means of a modified wind momentum versus luminosity diagram. The wind strengths that we obtain for the objects in WLM and NGC 3109 are unexpectedly high and do not agree with theoretical predictions. The objects in IC 1613 tend toward a higher than expected mass-loss rate, but remain consistent with predictions within their error bars. We discuss potential systematic uncertainties in the mass-loss determinations to explain our results. However, if further scrutinization of these findings point towards an intrinsic cause for this unexpected sub-SMC mass-loss behavior, implications would include a higher than anticipated number of Wolf-Rayet stars and Ib/Ic supernovae in low-metallicity environments, but a reduced number of long-duration gamma-ray bursts produced through a single-star evolutionary channel.
R144 is a WN6h star in the 30 Doradus region. It is suspected to be a binary because of its high luminosity and its strong X-ray flux, but no periodicity could be established so far. Here, we present ...new X-shooter multi-epoch spectroscopy of R144 obtained at the ESO Very Large Telescope. We detect variability in position and/or shape of all the spectral lines. We measure radial velocity variations with an amplitude larger than 250 km s−1 in N iv and N v lines. Furthermore, the N iii and N v line Doppler shifts are anticorrelated and the N iv lines show a double-peaked profile on six of our seven epochs. We thus conclude that R144 is a double-lined spectroscopic binary. Possible orbital periods range from two to six months, although a period up to one year is allowed if the orbit is highly eccentric. We estimate the spectral types of the components to be WN5-6h and WN6-7h, respectively. The high luminosity of the system (log L
bol/L 6.8) suggests a present-day total mass content in the range of about 200-300 M, depending on the evolutionary stage of the components. This makes R144 the most massive binary identified so far, with a total mass content at birth possibly as large as 400 M. We briefly discuss the presence of such a massive object, 60 pc away from the R136 cluster core in the context of star formation and stellar dynamics.
Aims. The formation of massive stars remains poorly understood and little is known about their birth multiplicity properties. Here, we aim to quantitatively investigate the strikingly low ...radial-velocity dispersion measured for a sample of 11 massive pre- and near-main-sequence stars (σ1D= 5.6 ± 0.2 km s-1) in the very young massive star forming region M 17, in order to obtain first constraints on the multiplicity properties of young massive stellar objects. Methods. We compute the radial-velocity dispersion of synthetic populations of massive stars for various multiplicity properties and we compare the obtained σ1D distributions to the observed value. We specifically investigate two scenarios: a low binary fraction and a dearth of short-period binary systems. Results. Simulated populations with low binary fractions (fbin = 0.12-0.09+0.16) or with truncated period distributions (Pcutoff > 9 months) are able to reproduce the low σ1D observed within their 68%-confidence intervals. Furthermore, parent populations with fbin > 0.42 or Pcutoff < 47 d can be rejected at the 5%-significance level. Both constraints are in stark contrast with the high binary fraction and plethora of short-period systems in few Myr-old, well characterized OB-type populations. To explain the difference in the context of the first scenario would require a variation of the outcome of the massive star formation process. In the context of the second scenario, compact binaries must form later on, and the cut-off period may be related to physical length-scales representative of the bloated pre-main-sequence stellar radii or of their accretion disks. Conclusions. If the obtained constraints for the M 17’s massive-star population are representative of the multiplicity properties of massive young stellar objects, our results may provide support to a massive star formation process in which binaries are initially formed at larger separations, then harden or migrate to produce the typical (untruncated) power-law period distribution observed in few Myr-old OB binaries.
Context.
Observations of massive stars in open clusters younger than ∼8 Myr have shown that a majority of them are in binary systems, most of which will interact during their life. While these can be ...used as a proxy of the initial multiplicity properties, studying populations of massive stars older than ∼20 Myr allows us to probe the outcome of these interactions after a significant number of systems have experienced mass and angular momentum transfer and may even have merged.
Aims.
Using multi-epoch integral-field spectroscopy, we aim to investigate the multiplicity properties of the massive-star population in the dense core of the ∼40 Myr old cluster NGC 330 in the Small Magellanic Cloud in order to search for possible imprints of stellar evolution on the multiplicity properties.
Methods.
We obtained six epochs of VLT/MUSE observations operated in wide-field mode with the extended wavelength setup and supported by adaptive optics. We extracted spectra and measured radial velocities for stars brighter than
m
F
814
W
= 19. We identified single-lined spectroscopic binaries through significant RV variability with a peak-to-peak amplitude larger than 20 km s
−1
. We also identified double-lined spectroscopic binaries, and quantified the observational biases for binary detection. In particular, we took into account that binary systems with similar line strengths are difficult to detect in our data set.
Results.
The observed spectroscopic binary fraction among stars brighter than
m
F
814
W
= 19 (approximately 5.5
M
⊙
on the main sequence) is
f
SB
obs
= 13.2 ± 2.0%. Considering period and mass ratio ranges from log(
P
) = 0.15−3.5 (about 1.4 to 3160 d),
q
= 0.1−1.0, and a representative set of orbital parameter distributions, we find a bias-corrected close binary fraction of
f
cl
= 34
−7
+8
%. This fraction seems to decline for the fainter stars, which indicates either that the close binary fraction drops in the B-type domain, or that the period distribution becomes more heavily weighted toward longer orbital periods. We further find that both fractions vary strongly in different regions of the color-magnitude diagram, which corresponds to different evolutionary stages. This probably reveals the imprint of the binary history of different groups of stars. In particular, we find that the observed spectroscopic binary fraction of Be stars (
f
SB
obs
= 2 ± 2%) is significantly lower than that of B-type stars (
f
SB
obs
= 9 ± 2%).
Conclusions.
We provide the first homogeneous radial velocity study of a large sample of B-type stars at a low metallicity (Fe/H ≲ −1.0). The overall bias-corrected close binary fraction (log(
P
) < 3.5 d) of the B-star population in NGC 330 is lower than the fraction reported for younger Galactic and Large Magellanic Cloud clusters in previous works. More data are needed, however, to establish whether the observed differences are caused by an age or a metallicity effect.
The Tarantula Massive Binary Monitoring Mahy, L.; Sana, H.; Abdul-Masih, M. ...
Astronomy and astrophysics (Berlin),
02/2020, Letnik:
634
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
Accurate stellar parameters of individual objects in binary systems are essential to constrain the effects of binarity on stellar evolution. These parameters serve as a prerequisite to ...probing existing and future theoretical evolutionary models.
Aims.
We aim to derive the atmospheric parameters of the 31 double-lined spectroscopic binaries in the Tarantula Massive Binary Monitoring sample. This sample, composed of detached, semi-detached and contact systems with at least one of the components classified as an O-type star, is an excellent test-bed to study how binarity can impact our knowledge of the evolution of massive stars.
Methods.
In the present paper, 32 epochs of FLAMES/GIRAFFE spectra are analysed by using spectral disentangling to construct the individual spectra of 62 components. We then apply the CMFGEN atmosphere code to determine their stellar parameters and their helium, carbon, and nitrogen surface abundances.
Results.
Among the 31 systems that we study in the present paper, we identify between 48 and 77% of them as detached, likely pre-interacting systems, 16% as semi-detached systems, and between 5 and 35% as systems in or close to contact phase. Based on the properties of their components, we show that the effects of tides on chemical mixing are limited. Components on longer-period orbits show higher nitrogen enrichment at their surface than those on shorter-period orbits, in contrast to expectations of rotational or tidal mixing, implying that other mechanisms play a role in this process. For semi-detached systems, components that fill their Roche lobe are mass donors. They exhibit higher nitrogen content at their surface and rotate more slowly than their companions. By accreting new material, their companions spin faster and are likely rejuvenated. Their locations in the
N
−
v
sin
i
diagram tend to show that binary products are good candidates to populate the two groups of stars (slowly rotating, nitrogen-enriched objects and rapidly rotating non-enriched objects) that cannot be reproduced through single-star population synthesis. Finally, we find no peculiar surface abundances for the components in (over-)contact systems, as has been suggested by evolutionary models for tidal mixing.
Conclusions.
This sample, consisting of 31 massive binary systems, is the largest sample of binaries composed of at least one O-type star to be studied in such a homogeneous way by applying spectral disentangling and atmosphere modelling. The study of these objects gives us strong observational constraints to test theoretical binary evolutionary tracks.
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