The IACOB project Holgado, G.; Simón-Díaz, S.; Herrero, A. ...
Astronomy and astrophysics (Berlin),
09/2022, Letnik:
665
Journal Article
Recenzirano
Odprti dostop
Context.
Stellar rotation is of key importance in the formation process, the evolution, and the final fate of massive stars.
Aims.
We perform a reassessment of the empirical rotational properties of ...Galactic massive O-type stars using the results from a detailed analysis of ground-based multi-epoch optical spectra obtained in the framework of the IACOB & OWN surveys.
Methods.
Using high-quality optical spectroscopy, we established the velocity distribution for a sample of 285 apparently single and single-line spectroscopic binary (SB1) Galactic O-type stars. We also made use of the rest of the parameters from the quantitative spectroscopic analysis presented in prior IACOB papers (mainly
T
eff
, log
g
, and multiplicity) to study the
v
sin
i
behavior and evolution from the comparison of subsamples in different regions of the spectroscopic Hertzsprung–Rusell diagram (sHRD). Our results are compared to the main predictions – regarding current and initial rotational velocities – of two sets of well-established evolutionary models for single stars, as well as from population synthesis simulations of massive stars that include binary interaction.
Results.
We reassess the known bimodal nature of the
v
sin
i
distribution, and find a non-negligible difference between the
v
sin
i
distribution of single and SB1 stars. We provide empirical evidence supporting the proposed scenario that the tail of fast rotators is mainly produced by binary interactions. Stars with extreme rotation (>300 km s
−1
) appear as single stars that are located in the lower zone of the sHRD. We notice little rotational braking during the main sequence, a braking effect independent of mass (and wind strength). The rotation rates of the youngest observed stars lean to an empirical initial velocity distribution with ⪅20% of critical velocity. Lastly, a limit in
v
sin
i
detection below 40–50 km s
−1
seems to persist, especially in the upper part of the sHRD, possibly associated with the effect of microturbulence in the measurement methodology used.
Context.
The spectroscopic characterization of many O-type stars is hampered by a nearby companion.
Aims.
We want to obtain spatially resolved spectroscopy of close O-type visual binaries to derive ...their spectral types.
Methods.
We used the Space Telescope Imaging Spectrograph (STIS) of the
Hubble
Space Telescope (HST) to obtain long-slit blue-violet spectroscopy of eight Galactic O-type stars with nearby visual companions and used spatial-profile fitting to extract the separate spectra. We also used the ground-based Galactic O-Star Spectroscopic Survey to study more distant visual components.
Results.
We spatially resolve seven of the eight systems, present spectra for their components, and obtain their spectral types. Those seven multiple systems are
ι
Ori Aa,Ab,B; 15 Mon Aa,Ab,C;
τ
CMa Aa,Ab,B,C,D,E; HD 206 267 Aa,Ab,C,D; HD 193 443 A,B; HD 16 429 Aa,Ab; and IU Aur A,B. This is the first time that spatially resolved spectroscopy of the close visual binaries of those systems is obtained. We establish the applicability of the technique as a function of the separation and magnitude difference of the binary.
ABSTRACT
The evolution of massive stars is not completely understood. Several phenomena affect their birth, life, and death, multiplicity being one of them. In this context, the OWN and MONOS ...projects are systematically observing O- and WN-type stars whose multiplicity status is unknown. Their major goal considers the necessity of determining absolute parameters of massive stars. We have collected spectra of HD 93249 A and ALS 12502 A aiming at characterizing their binary nature. For both stars, we analysed high-resolution spectra and combined them with Transiting Exoplanet Survey Satellite (TESS) observations to be compared with binary models constructed by means of the phoebe code. We discovered that the radial velocity of HD 93249 A varies with a period of 2.97968 ± 0.00001 d and that the system presents ellipsoidal light variations. We disentangled the composite spectra and classified its components as O9 III and B1.5 III, respectively. Confirmed as a spectroscopic binary, HD 93249 A can no longer be used as spectral classification standard. ALS 12502 A turned out to be a detached eclipsing binary in the TESS and Gaia data. These results enable us to determine absolute parameters for each component in the system.
Context.
The spectral classifications of the Galactic O-Star Spectroscopic Survey (GOSSS) and the astrometric and photometric data from
Gaia
have significantly improved our ability to measure ...distances and determine memberships of stellar groups (clusters, associations, or parts thereof) with OB stars. In the near future, the situation will be further improved thanks to subsequent
Gaia
data releases and new photometric and spectroscopic surveys.
Aims.
We initiated a program to identify and determine the membership of Galactic stellar groups with OB stars and measure distances to them. Given the data currently available, we started with the identification and distance determinations of groups with O stars. In this paper, we concentrate on groups that contain stars with the earliest spectral subtypes.
Methods.
We used GOSSS to select Galactic stellar groups with O2–O3.5 stars and the method described in paper 0 of this series, which combines
Gaia
DR2
G
+
G
BP
+
G
RP
photometry, positions, proper motions, and parallaxes to assign robust memberships and measure distances. We also included Collinder 419 and NGC 2264, the clusters cited in that paper, to generate our first list of 16 O-type Galactic stellar groups.
Results.
We derived distances, determined the membership, and analyzed the structure of sixteen Galactic stellar groups with O stars, Villafranca O-001 to Villafranca O-016, including the fourteen groups with the earliest-O-type optically accessible stars known in the Milky Way. We compared our distance with previous results from the literature and establish that the best consistency is with (the small number of) VLBI parallaxes and the worst is with kinematic distances. Our results indicate that very massive stars can form in relatively low-mass clusters or even in near-isolation, as is the case for the Bajamar star in the North America nebula. This lends support to the hierarchical scenario of star formation, where some stars are born in well-defined bound clusters but others are born in associations that are unbound from the beginning: groups of newborn stars come in many shapes and sizes. We propose that HD 64 568 and HD 64 315 AB could have been ejected simultaneously from Haffner 18 (Villafranca O-012 S). Our results are consistent with a difference of ≈20
μ
as in the
Gaia
DR2 parallax zero point between bright and faint stars.
We present HK spectra of three sources located in the N 66 region of the Small Magellanic Cloud. The sources display prominent stellar Brγ and extended H2 emission, and exhibit infrared excesses at λ ...> 2 μm. Based on their spectral features, and photometric spectral energy distributions, we suggest that these sources are massive young stellar objects. The findings are interpreted as evidence of on-going high mass star formation in N 66.
ABSTRACT
We present a new spectroscopic orbit of the O-type binary system HD 152147. We identify absorption lines in both components and use their radial velocities to determine the orbit, which ...results in a period of P = 50.2199 ± 0.0007 d, an eccentricity e = 0.738 ± 0.007, and a mean separation between the components of asin i = 151 ± 1 R⊙. Considering that the distance to the system is 1600 pc, this implies an angular separation of ∼0.44 mas, making it suitable for modern interferometric observations. In addition, we determine the fundamental stellar parameters of each component by means of a quantitative spectral analysis. We obtain Ma = 31.9−34.6 M⊙ and Ra = 17−24 R⊙ for the primary, and Mb = 14−15 M⊙ and Rb = 5−10 R⊙ for the secondary. We apply models with rotation to try to characterize the evolutionary status of the HD 152147 system. We find that the two components are compatible with a common age of 4.5 Myr. We also detect variations in the profile of Hα that are not modulated by the orbital cycle. Moreover, TESS photometry also presents intrinsic variability and was analysed for periodicities. We find a most relevant frequency of 20 times the orbital one, in a TESS data set that includes the periastron passage, and we interpret it as a tidally induced pulsation that seems to dissipate on a time-scale shorter than the orbital cycle because it is not present in another TESS data set that nearly covers the apoastron.
ABSTRACT
The GALANTE optical photometric survey is observing the northern Galactic plane and some adjacent regions using seven narrow- and intermediate-filters, covering a total of 1618 deg2. The ...survey has been designed with multiple exposure times and at least two different air masses per field to maximize its photometric dynamic range, comparable to that of Gaia, and ensure the accuracy of its photometric calibration. The goal is to reach at least 1 per cent accuracy and precision in the seven bands for all stars brighter than AB magnitude 17 while detecting fainter stars with lower values of the signal-to-noise ratio. The main purposes of GALANTE are the identification and study of extinguished O+B+WR stars, the derivation of their extinction characteristics, and the cataloguing of F and G stars in the solar neighbourhood. Its data will be also used for a variety of other stellar studies and to generate a high-resolution continuum-free map of the Hα emission in the Galactic plane. We describe the techniques and the pipeline that are being used to process the data, including the basis of an innovative calibration system based on Gaia DR2 and 2MASS photometry.
A magnetic massive star has experienced a stellar merger Frost, A J; Sana, H; Mahy, L ...
Science (American Association for the Advancement of Science),
2024-Apr-12, 2024-04-12, 20240412, Letnik:
384, Številka:
6692
Journal Article
Recenzirano
Massive stars (those ≥8 solar masses at formation) have radiative envelopes that cannot sustain a dynamo, the mechanism that produces magnetic fields in lower-mass stars. Despite this, approximately ...7% of massive stars have observed magnetic fields, the origin of which is debated. We used multi-epoch interferometric and spectroscopic observations to characterize HD 148937, a binary system of two massive stars. We found that only one star is magnetic and that it appears younger than its companion. The system properties and a surrounding bipolar nebula can be reproduced with a model in which two stars merged (in a previous triple system) to produce the magnetic massive star. Our results provide observational evidence that magnetic fields form in at least some massive stars through stellar mergers.
ABSTRACT
We present the first spectroscopic orbit of the O-type double-lined star HD 168112 A,B. We analyse 101 high-resolution optical spectra identifying the absorption lines of both components. ...The orbital solution presents a relatively long period, P = 513.52 ± 0.01 d, and a high eccentricity, e = 0.743 ± 0.005. The binary system consists of two very similar stars of minimum masses of ∼25 M⊙, effective temperatures of ∼40 000 K, and surface gravities of ∼3.7 dex. The system has a minimum semimajor axis a sin i ∼ 1000 R⊙. We confirm that the A and B visual components identified via interferometry do correspond to the spectroscopic ones. We also analyse the underlying stellar groups using Gaia DR3 data and ground-based spectroscopy as part of the Villafranca project, determining that NGC 6604 is at a distance of $1942^{+38}_{-36}$ pc and giving spectral classifications for 23 massive stellar systems in Villafranca O-035 and the surrounding Ser OB2 association, for which we provide the most complete census of massive stars to date.
In this paper, we present high-resolution HST/COS observations of the extreme magnetic O star NGC 1624-2. These represent the first ultraviolet spectra of this archetypal object. We examine the ...variability of its wind-sensitive resonance lines, comparing it to that of other known magnetic O stars. In particular, the observed variations in the profiles of the Civ and Siiv doublets between low state and high state are the largest observed in any magnetic O-type star, consistent with the expected properties of NGC 1624-2's magnetosphere. We also observe a redshifted absorption component in the low state, a feature not seen in most stars. We present preliminary modelling efforts based on the Analytic Dynamical Magnetosphere (ADM) formalism, demonstrating the necessity of using non-spherically symmetric models to determine wind/magnetospheric properties of magnetic O stars.
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