Oxygen and silicon abundances in Cygnus OB2

Context. Cygnus OB2 is a rich OB association in the Galaxy located at only ∼1.4 kpc from us which has experienced intense star formation in the last 20–25 Myr. Its stellar population shows a correlation between age and Galactic longitude. Exploring the chemical composition of its stellar content we will be able to check the degree of homogeneity of the natal molecular cloud and possible effects of self-enrichment processes. Aims. Our aim is to determine silicon and oxygen abundances for a sample of eight early-type slow rotators (with rotational velocities below 80 km s−1) in Cygnus OB2 in order to check possible inhomogeneities across the whole association and whether there exists a correlation of chemical composition with Galactic longitude. Methods. We have performed a spectroscopic analysis of a sample of late O and early B stars with low rotational velocity in Cygnus OB2, which have been chosen so as to cover the whole association area. We have carried out an analysis based on equivalent widths of metal lines, the wings of the H Balmer lines and FASTWIND stellar atmosphere models to determine their stellar fundamental parameters (effective temperature and surface gravity) as well as the silicon and oxygen surface abundances. Results. We derive a rather homogeneous distribution of silicon and oxygen abundances across the region, with average values of 12 + log(Si/H) = 7.53 ± 0.08 dex and 12 + log(O/H) = 8.65 ± 0.12 dex. Conclusions. We find a homogeneous chemical composition in Cygnus OB2 with no clear evidence for significant chemical self-enrichment, despite indications of strong stellar winds and possible supernovae during the history of the region. Comparison with different scenarios of chemical enrichment by stellar winds and supernovae point to star forming efficiencies not significantly above 10%. The degree of homogeneity that we find is consistent with the observed Milky Way oxygen gradient based on H II regions. We also find that the oxygen scatter within Cygnus OB2 is at least of the same order than among H II regions at similar Galactocentric distance.

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Evidence of vertical abundance stratification in the SB1 star HD 161660: a new HgMn

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3108 ◽

2020 ◽

Vol 499 (3) ◽

pp. 3720-3727

Author(s):

G Catanzaro ◽

M Giarrusso ◽

M Munari ◽

F Leone

Keyword(s):

Chemical Composition ◽

Rotational Velocity ◽

Homogeneous Distribution ◽

Atmospheric Parameters ◽

Isotopic Mixture ◽

Fundamental Parameters ◽

Solar Composition ◽

Chemical Pattern ◽

Balmer Lines ◽

Archive Data

ABSTRACT In this paper, we present a detailed spectroscopic study of the SB1 system HD 161660. New spectroscopic observations have been obtained by us with Catania Astrophysical Observatory Spectropolarimeter (CAOS@OAC). Combining these observations with archive data from [email protected], we derived atmospheric parameters as temperature and gravity (from the fit of Balmer lines), microturbulence and rotational velocity (from metal lines), and chemical composition. We found underabundances of helium, carbon, magnesium, sulphur and chromium, overabundances of neon, phosphorus, argon, manganese, xenon, and mercury. All other elements have solar composition. In particular, mercury abundance is derived taking into account an isotopic mixture different from the terrestrial one (essentially pure 202Hg). Considering this chemical pattern, we definitively confirm HD 161660 is an HgMn star. Further, variability of equivalent widths points out a non-homogeneous distribution of helium and magnesium over stellar surface. As to iron and phosphorus, we found a non-constant abundance with the optical depth, a result currently considered an evidence of vertical stratification. Finally, we improved the fundamental parameters characterizing the HD 161660 orbit.

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Conclusion

Highlights of Astronomy ◽

10.1017/s1539299600003312 ◽

1977 ◽

Vol 4 (2) ◽

pp. 217-218

Author(s):

R. Cayrel

Keyword(s):

Chemical Composition ◽

Basic Problem ◽

Stellar Atmosphere ◽

Stellar Atmospheres ◽

Classification Systems ◽

Spectral Classification ◽

Surface Layers ◽

Fundamental Parameters ◽

The Past ◽

Main Basis

This joint discussion has amply demonstrated that stellar atmospheres are not passive and dumb bodies just sitting there at the surface of a star.First of all the surface “feel” fundamental parameters of the star as a whole, specifically the ratio L/R2 and m/R2. As these fundamental parameters are affected by stellar evolution, the surface layers reflect to a large extent the degree of evolution of the star. This is the main basis for photometric and spectral classification systems. One could even claim that the observation of the stellar atmosphere would univocally determine the state of evolution of the star if i) it was always possible to determine the atmospheric abundances of the key elements to internal structure and ii) if the chemical composition of the atmosphere was always representative of the chemical composition of the whole star. Unfortunately a serious problem occurs for i) with the abundance of helium which element has no photospheric absorption line for all spectral types later than B and also with ii) in a more limited portion of the HR diagram, mainly in late B and A slow rotators. But whereas point i) is a mere problem of contingency, point ii) is a basic problem, greatly overlooked in the past, and to which one fourth of the joint discussion was devoted.

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The effects of surface fossil magnetic fields on massive star evolution: III. The case of τ Sco

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab893 ◽

2021 ◽

Author(s):

Z Keszthelyi ◽

G Meynet ◽

F Martins ◽

A de Koter ◽

A David-Uraz

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Massive Star ◽

Slow Rotation ◽

Single Star ◽

Surface Magnetic Field ◽

Fundamental Parameters ◽

Chemical Enrichment ◽

Star Models ◽

Nitrogen Excess

Abstract τ Sco, a well-studied magnetic B-type star in the Uτer Sco association, has a number of surprising characteristics. It rotates very slowly and shows nitrogen excess. Its surface magnetic field is much more complex than a purely dipolar configuration which is unusual for a magnetic massive star. We employ the cmfgen radiative transfer code to determine the fundamental parameters and surface CNO and helium abundances. Then, we employ mesa and genec stellar evolution models accounting for the effects of surface magnetic fields. To reconcile τ Sco’s properties with single-star models, an increase is necessary in the efficiency of rotational mixing by a factor of 3 to 10 and in the efficiency of magnetic braking by a factor of 10. The spin down could be explained by assuming a magnetic field decay scenario. However, the simultaneous chemical enrichment challenges the single-star scenario. Previous works indeed suggested a stellar merger origin for τ Sco. However, the merger scenario also faces similar challenges as our magnetic single-star models to explain τ Sco’s simultaneous slow rotation and nitrogen excess. In conclusion, the single-star channel seems less likely and versatile to explain these discrepancies, while the merger scenario and other potential binary-evolution channels still require further assessment as to whether they may self-consistently explain the observables of τ Sco.

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Influence of the precursor chemical composition on heavy metal adsorption properties of hemp (Cannabis Sativa) fibers based biocarbon

Journal of the Serbian Chemical Society ◽

10.2298/jsc170310080v ◽

2017 ◽

Vol 82 (12) ◽

pp. 1417-1431 ◽

Cited By ~ 2

Author(s):

Marija Vukcevic ◽

Biljana Pejic ◽

Ivana Pajic-Lijakovic ◽

Ana Kalijadis ◽

Mirjana Kostic ◽

...

Keyword(s):

Heavy Metal ◽

Chemical Composition ◽

Surface Area ◽

Active Sites ◽

Cannabis Sativa ◽

Lignin Content ◽

Area Measurement ◽

Bet Surface Area ◽

Homogeneous Distribution ◽

Hemp Fibers

Waste hemp (Cannabis sativa) fibers were used as sustainable and renewable raw materials for production of low-cost biocarbon sorbent for heavy metals removal. Carbon precursors of different chemical composition were obtained by oxidative and alkaline treatments of hemp fibers. Influence of lignocellulosic precursor chemical composition on hemp fibers-based biocarbon (HFB) characteristics was examined by BET surface area measurement, scanning electron microscopy and mass titration. It was found that lignin content and polymorphic transformation of cellulose increase the SBET of microporous HFBs, while hemicelluloses induce more homogeneous distribution of adsorption active sites. Heavy metal ions adsorption onto HFBs is primarily influenced by the amount of surface oxygen groups, while specific surface area plays a secondary role. Equilibrium data obtained for lead ions adsorption were analyzed by different nonlinear adsorption isotherms, and the best fitting model was chosen using standard deviation and Akaike information criterion (AICC). The maximum adsorption capacities of HFBs ranged from 103.1 to 116.3 mg Pb/g. Thermodynamic parameters showed that Pb2+ adsorption onto HFBs is a spontaneous and complex endothermic process, suggesting the coexistence of physisorption and chemisorption mechanisms.

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Tests of Evolution Models Using Eclipsing Binaries

Highlights of Astronomy ◽

10.1017/s1539299600011588 ◽

1995 ◽

Vol 10 ◽

pp. 419-422

Author(s):

J. Andersen

Keyword(s):

Chemical Composition ◽

Star Clusters ◽

Stellar Model ◽

Eclipsing Binaries ◽

Fundamental Parameter ◽

Fundamental Parameters ◽

Stellar Models ◽

Absolute Age ◽

Cluster Sequence ◽

Hr Diagram

Stellar models are the means by which we describe and understand the distribution of stars in the HR diagram. A stellar model is, in principle, completely specified by the three fundamental parameters mass, chemical composition, and age. Comparing the properties of models and real stars with the same parameters will tell us if our recipe for constructing stellar models is realistic. Unfortunately, the only star for which all three are known independently of stellar models is the Sun. For stars of other masses and ages we must devise observational tests in which at least one fundamental parameter is unknown. Two such popular test objects are double-lined eclipsing binaries and star clusters.In suitable eclipsing binaries we can determine both masses and chemical composition; the absolute age is unknown, but the same for both stars. Since evolution depends most sensitively on the mass, eclipsing binaries provide a very direct test of the models, but only for two points on a single isochrone. In star clusters, neither ages nor individual masses are known, but the detailed shape and population of a well-observed cluster sequence in the HR diagram provide a number of additional probes into the models.

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Optical and X-ray observations of stellar winds in Wolf-Rayet binaries

Symposium - International Astronomical Union ◽

10.1017/s007418090020212x ◽

1995 ◽

Vol 163 ◽

pp. 262-270

Author(s):

A. M. Cherepashchuk

Keyword(s):

Chemical Composition ◽

Core Temperature ◽

Stellar Winds ◽

Radial Expansion ◽

Core Radius ◽

X Ray ◽

The Core ◽

Basic Conclusion ◽

Helium Stars ◽

Colliding Winds

New spectrophotometric, photometric and polarimetric observations of V444 Cygni confirm the basic conclusion that the WN5 star has a small core radius (rc < 4 R⊙) and a high core temperature (Tc > 60 000 K), which are characteristic of massive helium stars. Values of rc < 3 — 6 R⊙ and Tc > 70 000 — 90 000 K for the core of the WN7 star in the Cygnus X-3 system agree well with this conclusion. A clumping structure of WR winds is suggested. X-ray observations of colliding winds in WR+O binaries suggest radial expansion and anomalous chemical composition of WR winds.

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Vertical structure and kinematics of the Galactic outer disk

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psz125 ◽

2019 ◽

Vol 72 (4) ◽

Author(s):

Nobuyuki Sakai ◽

Takumi Nagayama ◽

Hiroyuki Nakanishi ◽

Nagito Koide ◽

Tomoharu Kurayama ◽

...

Keyword(s):

Dwarf Galaxy ◽

Oscillatory Behavior ◽

Maximum Height ◽

Galactocentric Distance ◽

The North ◽

Vertical Density ◽

Galactic Longitude ◽

Maser Sources ◽

Galactic Warp ◽

North Galactic

Abstract We report on measurements of parallax and proper motion for four 22 GHz water maser sources as part of the VERA Outer Rotation Curve project. All the sources show Galactic latitudes of >2° and Galactocentric distances of >11 kpc at the Galactic longitude range of 95° < l < 126°. The sources trace the Galactic warp reaching to 200–400 pc, and also the signature of the warp to 600 pc toward the north Galactic pole. The new results, along with previous results in the literature, show that the maximum height of the Galactic warp increases with Galactocentric distance. Also, we examined velocities perpendicular to the disk for the sample, and found oscillatory behavior between the vertical velocities and Galactic heights. This behavior suggests the existence of bending (vertical density) waves, possibly induced by a perturbing satellite (e.g., the passage of the Sagittarius dwarf galaxy).

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Chemical evolution and stellar populations in the Sagittarius dwarf Spheroidal Galaxy

Proceedings of the International Astronomical Union ◽

10.1017/s1743921306010027 ◽

2006 ◽

Vol 2 (S235) ◽

pp. 330-330 ◽

Cited By ~ 1

Author(s):

L. Sbordone ◽

P. Bonifacio ◽

G. Giuffrida ◽

G. Marconi ◽

L. Monaco ◽

...

Keyword(s):

Chemical Composition ◽

Chemical Evolution ◽

Large Scale ◽

Automated Analysis ◽

Stellar Populations ◽

Dynamical Analysis ◽

Complex Object ◽

Main Body ◽

Stellar Content ◽

Chemical Anomalies

AbstractThe closest neighbour of the Milky Way (MW) the Sagittarius dwarf Spheroidal Galaxy (Sgr dSph) is being tidally destroyed by the interaction with our Galaxy, losing its stellar content along a huge stream clearly detectable within the Halo. This makes the Sgr dSph an ideal laboratory to study at the same time the chemical evolution of dwarf galaxies and their role in building bigger structures such as the MW. Since some years we are studying the stellar populations of the Sgr main body and stream, with particular attention to their detailed chemical composition. We collected detailed abundances (up to 22 elements, O to Eu) for 27 stars in the Sgr dSph main body, 5 in the associated globular cluster Terzan 7, and 12 more in the trailing Sgr tidal arm (UVES@VLT and SARG@TNG data). We are also conducting a large FLAMES@VLT chemical and dynamical analysis aimed at obtaining metallicities, alpha-elements content and radial velocities from automated analysis of the spectra. Finally, we just completed the first large scale photometric and spectroscopic survey of the stellar populations across all the dSph main body extension with VIMOS@VLT, aimed at exploring the variations in stellar populations and at deriving radial velocity memberships for future high resolution spectroscopic analysis. The picture emerging from all these studies portraits a large and extremely complex object, with signs of a long and still unclear evolution. Metallicity varies across three orders of magnitude ([Fe/H] from −3 to 0), CMDs change surprisingly from the core to the outskirts of the galaxy, and the chemical composition of the most metal rich objects show a very characteristic signature, with underabundant alpha elements, deficient Na, underabundant Fe-peak Mn, Co, Ni, Cu and Zn, and strongly enhanced n-capture elements La and Nd. This highly peculiar signature can also be effectively used to recognized stripped populations lost by Sgr in favour of the MW system, as clearly showed by the globular Palomar 12, which shows the same chemical anomalies detected in Sgr dSph.

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Searching for self-enrichment in Cygnus OB2

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317001880 ◽

2016 ◽

Vol 12 (S329) ◽

pp. 386-386

Author(s):

Sara R. Berlanas ◽

Artemio Herrero ◽

Fernando Comerón ◽

Anna Pasquali ◽

Sergio Simón-Díaz

Keyword(s):

Chemical Composition ◽

Interstellar Medium ◽

Massive Stars ◽

Composition Gradient ◽

Successive Generations ◽

Galactic Longitude

Cygnus OB2 is a rich and relatively close (d~1.4 kpc) OB association in our Galaxy. It represents an ideal testbed for our theories about self-enrichment processes produced by pollution of the interstellar medium by successive generations of massive stars. Comerón & Pasquali (2012, A&A, 543, A101) found a correlation between the age of young stellar groups in Cygnus OB2 and their Galactic longitude. If is associated with a chemical composition gradient, it could support these self-enrichment processes.

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Fundamental properties of Kepler and CoRoT targets – IV. Masses and radii from frequencies of minimum Δν and their implications

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2223 ◽

2019 ◽

Vol 489 (2) ◽

pp. 1753-1769 ◽

Cited By ~ 2

Author(s):

M Yıldız ◽

Z Çelik Orhan ◽

C Kayhan

Keyword(s):

Rotational Velocity ◽

Galactic Disc ◽

Ionization Zone ◽

Chemical Enrichment ◽

Fundamental Properties ◽

Diagnostic Potential ◽

The Difference ◽

The Masses ◽

Oscillation Frequencies

ABSTRACT Recently, by analysing the oscillation frequencies of 90 stars, Yıldız, Çelik Orhan & Kayhan have shown that the reference frequencies (νmin0, νmin1, and νmin2) derived from glitches due to He ii ionization zone have very strong diagnostic potential for the determination of their effective temperatures. In this study, we continue to analyse the same stars and compute their mass, radius, and age from different scaling relations including relations based on νmin0, νmin1, and νmin2. For most of the stars, the masses computed using νmin0 and νmin1 are very close to each other. For 38 stars, the difference between these masses is less than 0.024 M$\odot$. The radii of these stars from νmin0 and νmin1 are even closer, with differences of less than 0.007 R$\odot$. These stars may be the most well known solar-like oscillating stars and deserve to be studied in detail. The asteroseismic expressions we derive for mass and radius show slight dependence on metallicity. We therefore develop a new method for computing initial metallicity from this surface metallicity by taking into account the effect of microscopic diffusion. The time dependence of initial metallicity shows some very interesting features that may be important for our understanding of chemical enrichment of Galactic Disc. According to our findings, every epoch of the disc has its own lowest and highest values for metallicity. It seems that rotational velocity is inversely proportional to 1/2 power of age as given by the Skumanich relation.

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