scholarly journals NGC 3105: a young open cluster with low metallicity

2018 ◽  
Vol 616 ◽  
pp. A124 ◽  
Author(s):  
J. Alonso-Santiago ◽  
A. Marco ◽  
I. Negueruela ◽  
H. M. Tabernero ◽  
N. Castro ◽  
...  
Keyword(s):  
Open Cluster ◽  
High Mass ◽  
Complete Analysis ◽  
Evolutionary Models ◽  
Chemical Abundances ◽  
Evolved Stars ◽  
Young Open Cluster ◽  
Red Supergiants ◽  
Low Metallicity ◽  
First Time

Context. NGC 3105 is a young open cluster hosting blue, yellow, and red supergiants. This rare combination makes it an excellent laboratory for constraining evolutionary models of high-mass stars. It has been poorly studied, and the fundamental parameters such as its age or distance are not well defined. Aims. We intend to characterise in an accurate way the cluster and its evolved stars, for which we derive for the first time atmospheric parameters and chemical abundances. Methods. We performed a complete analysis combining UBVR photometry with spectroscopy. We obtained spectra with classification purposes for 14 blue stars and high-resolution spectroscopy for an in-depth analysis of the six other evolved stars. Results. We identify 126 B-type likely members within a radius of 2.7 ± 0.6 arcmin, which implies an initial mass, Mcl ≈ 4100 M⊙. We find a distance of 7.2 ± 0.7 kpc for NGC 3105, placing it at RGC = 10.0 ± 1.2 kpc. Isochrone fitting supports an age of 28 ± 6 Ma, implying masses around 9.5 M⊙ for the supergiants. A high fraction of Be stars (≈25%) is found at the top of the main sequence down to spectral type b3. From the spectral analysis we estimate for the cluster an average νrad = +46.9 ± 0.9 km s−1 and a low metallicity, [Fe/H] = −0.29 ± 0.22. We also have determined, for the first time, chemical abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved stars. The chemical composition of the cluster is consistent with that of the Galactic thin disc. An overabundance of Ba is found, supporting the enhanced s-process. Conclusions. NGC 3105 has a low metallicity for its Galactocentric distance, comparable to typical LMC stars. It is a valuable spiral tracer in a very distant region of the Carina–Sagittarius spiral arm, a poorly known part of the Galaxy. As one of the few Galactic clusters containing blue, yellow, and red supergiants, it is massive enough to serve as a test bed for theoretical evolutionary models close to the boundary between intermediate- and high-mass stars.

scholarly journals A comprehensive study of NGC 2345, a young open cluster with a low metallicity

2019 ◽  
Vol 631 ◽  
pp. A124 ◽  
Author(s):  
J. Alonso-Santiago ◽  
I. Negueruela ◽  
A. Marco ◽  
H. M. Tabernero ◽  
C. González-Fernández ◽  
...  
Keyword(s):  
Open Cluster ◽  
Complete Analysis ◽  
Be Stars ◽  
Test Bed ◽  
Chemical Abundances ◽  
Evolved Stars ◽  
Depth Analysis ◽  
Young Open Cluster ◽  
High Fraction ◽  
Low Metallicity

Context. NGC 2345 is a young open cluster that hosts seven blue and red supergiants, low metallicity, and a high fraction of Be stars, which makes it a privileged laboratory to study stellar evolution. Aims. We aim to improve the determination of the cluster parameters and study the Be phenomenon. Our objective is also to characterise the seven evolved stars found in NGC 2345 by deriving their atmospheric parameters and chemical abundances. Methods. We performed a complete analysis combining for the first time ubvy photometry with spectroscopy as well as the Gaia Data Release 2. We obtained spectra with classification purposes for 76 stars and high-resolution spectroscopy for an in-depth analysis of the blue and red evolved stars. Results. We identify a new red supergiant and 145 B-type likely members within a radius of 18.7 ± 1.2 arcmin, which implies an initial mass, Mcl ≈ 5200 M⊙. We find a distance of 2.5 ± 0.2 kpc for NGC 2345, placing it at RGC = 10.2 ± 0.2 kpc. Isochrone fitting supports an age of 56 ± 13 Ma, implying masses around 6.5 M⊙ for the supergiants. A high fraction of Be stars (≈10%) is found. From the spectral analysis we estimate an average vrad = +58.6 ± 0.5 km s−1 and a low metallicity, [Fe/H] = −0.28 ± 0.07, for the cluster. We also determine chemical abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved stars. The chemical composition of the cluster is consistent with that of the Galactic thin disc. One of the K supergiants, S50, is a Li-rich star, presenting an A(Li) ≈ 2.1. An overabundance of Ba is found, supporting the enhanced s-process. Conclusions. NGC 2345 has a low metallicity for its Galactocentric distance, which is comparable to typical Large Magellanic Cloud stars. It is massive enough to serve as a test bed for theoretical evolutionary models for massive intermediate-mass stars.

scholarly journals Testing Evolutionary Models of Dwarf Irregular Galaxies through Gas and Stellar Metallicity Determinations in HII Galaxies

2012 ◽  
Vol 8 (S292) ◽  
pp. 254-254
Author(s):  
Pieter Westera ◽  
François Cuisinier ◽  
Didier Curty ◽  
Roland Buser
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Line Strength ◽  
Star Formation History ◽  
High Mass ◽  
Evolutionary Models ◽  
Homogeneous Sample ◽  
Irregular Galaxies ◽  
Low Metallicity ◽  
Dwarf Irregular Galaxies

AbstractDwarf irregular galaxies are usually low-metallicity objects, and show ongoing or very recent star formation, giving rise to their irregular appearance. Especially HII galaxies, a sub-category of dwarf irregulars showing unusually high star formation activity, are believed to be among the least evolved galaxies in existence today. Therefore, they are very interesting objects for studies of early galaxy evolution and of metallicity enrichment mechanisms.Several groups have developed theoretical evolutionary models of galaxies of this type, describing different possible formation and evolutionary scenarii, and varying factors such as gas infall and outflow, as well as the star formation history, and making predictions about their chemical evolution. One way to evaluate these models is by determining the metallicities of the different components of these galaxies, their gas and stars.We examine a sample of HII galaxies from the Sloan Digital Sky Survey, which possibly contains the largest homogeneous sample of HII galaxy spectra to date. Using very restrictive selection criteria, which guarantee a sample of high quality spectra and avoid “contamination” by spectra of objects of other nature, we defined a sample of ∼ 700 HII galaxies spectra.Through emission line strength calibrations and a detailed stellar population synthesis, we determined the metallicities of both the gas and the stellar content of these galaxies.For HII galaxies up to stellar masses of 5 × 109M⊙, we find enrichment mechanisms not to vary with galactic mass, being the same for low- and high-mass galaxies on average. They do seem to present a greater variety at the high-mass end, though, indicating a more complex assembly history. Our results favour galaxy evolutionary models featuring constantly infalling low-metallicity clouds that retain part of the galactic winds. Above 5 × 109M⊙ stellar mass, the retention of high metallicity gas by the galaxies' gravitational potential dominates.I would like to thank the Fundação de Amparo à Pesquisa do Estado do São Paulo (FAPESP) for financial support.

scholarly journals NGC 3293 revisited by the Gaia-ESO Survey

2014 ◽  
Vol 9 (S307) ◽  
pp. 140-141
Author(s):  
Thierry Semaan ◽  
Thierry Morel ◽  
Eric Gosset ◽  
Juan Zorec ◽  
Yves Frémat ◽  
...  
Keyword(s):  
Massive Stars ◽  
Open Cluster ◽  
Second Step ◽  
Chemical Abundances ◽  
Hot Stars ◽  
Fundamental Parameters ◽  
Medium Resolution ◽  
Young Open Cluster ◽  
Extended View

AbstractIn the framework of the Gaia-ESO survey we have determined the fundamental parameters of a large number of B-type stars in the Galactic, young open cluster NGC 3293. The determination of the stellar parameters is based on medium-resolution spectra obtained with FLAMES/GIRAFFE at ESO-VLT. As a second step, we adopted the accurate parameters to determine the chemical abundances of these hot stars. We present a comparison of our results with those obtained by the 'VLT-FLAMES survey of massive stars' (Evans et al. 2005). Our study increases the number of objects analysed and provides an extended view of this cluster.

scholarly journals Long-term spectral variability of the O4If+ star HD 15570 in the open cluster IC 1805

2003 ◽  
Vol 212 ◽  
pp. 224-225
Author(s):  
V. Francesco Polcaro ◽  
Roberto F. Viotti ◽  
Laura Norci ◽  
Corinne Rossi ◽  
Philippe R.J. Eenens ◽  
...  
Keyword(s):  
High Resolution ◽  
Open Cluster ◽  
High Mass ◽  
Evolutionary Stage ◽  
Deep Blue ◽  
San Pedro ◽  
Young Open Cluster ◽  
Random Variability ◽  
Model C

We present preliminary results concerning the O4If+ star HD 15570. Of-type supergiants are believed to represent an evolved evolutionary stage of very high mass stars (Minit > 40 M⊙). Their low numbers and extreme peculiarity make each of these objects worth of continuous monitoring. HD 15570 dominates the very young open cluster IC 1805 and is thought to have had an initial mass ≥ 100 M⊙. Low-, intermediate- and high-resolution spectra were collected at the Loiano and San Pedro Mártir telescopes since 1992. The comparison of our high- and low-resolution spectra shows clear variability of a number of spectral features. It is worth noticing, that the variation of Hα seems to follow a repeated secular trend, increasing its equivalent width from ~ 3Å to more than 8 Å in a few years. At the same time, its profile is varying, from a shape quite similar to the theoretical one corresponding to the Klein & Castor (1978) model C, to a much more developed P-Cygni profile, with a deep blue absorption wing. The possibility of instrumental effects is ruled out by the remarkable constancy of the nearby diffuse interstellar band at 6613 Å and of the He ii 6683 Å absorption. The Hβ profile variability is evident from the comparison of the 1996 and 1998 high-resolution spectra. The emission component, which is clearly visible at all epochs, is absent in the 1996 spectrum when the line appears in pure absorption. No relevant line-profile variation seems to be present in the He ii and N iii lines contributing to the ‘feature f’, that looks remarkably constant, as well as Hγ, while their equivalent widths seem to show a modest amount of random variability.

scholarly journals Chemical abundances of fast-rotating OB stars

2014 ◽  
Vol 9 (S307) ◽  
pp. 94-95
Author(s):  
Constantin Cazorla ◽  
Thierry Morel ◽  
Yaël Nazé ◽  
Gregor Rauw
Keyword(s):  
Massive Stars ◽  
Evolutionary Models ◽  
Rotating Stars ◽  
Chemical Abundances ◽  
Single Star ◽  
Ob Stars ◽  
Detailed Surface ◽  
Normal Nitrogen ◽  
First Time ◽  
Fast Rotating

AbstractFast rotation in massive stars is predicted to induce mixing in their interior, but a population of fast-rotating stars with normal nitrogen abundances at their surface has recently been revealed (Hunter et al.2009; Brott et al.2011, but see Maeder et al.2014). However, as the binary fraction of these stars is unknown, no definitive statements about the ability of single-star evolutionary models including rotation to reproduce these observations can be made. Our work combines for the first time a detailed surface abundance analysis with a radial-velocity monitoring for a sample of bright, fast-rotating Galactic OB stars to put strong constraints on stellar evolutionary and interior models.

Chemical abundances of four red supergiants star clusters (RSGCs) in Scutum-Crux arm

2019 ◽  
Vol 14 (S351) ◽  
pp. 189-191
Author(s):  
Sang-Hyun Chun
Keyword(s):  
High Resolution ◽  
Spectral Properties ◽  
Near Infrared ◽  
Milky Way ◽  
Star Clusters ◽  
Chemical Abundances ◽  
Red Supergiants ◽  
Low Metallicity ◽  
Effective Temperatures

AbstractWe investigate the spectral properties of red supergiant stars in the four RSGCs (RSGC2, RSGC3, RSGC4, RSGC5, and Alicante 10) in the Scutum-Crux arm of the Milky Way. The high-resolution (R: 45,000) near-infrared (H and K bands) spectra for 41 red supergiants were obtained using IGRINS at Gemini South telescope. The calibration of effective temperatures and gravities are derived based on the EWTi and EWCO using supergiants in IGIRNS library. The resulted temperatures and gravities are consistent with previous results. Model spectra were synthesized using derived stellar parameters from which we estimate metallicities and chemical abundances like α-elements. In our preliminary result, we find that overall four RSGCs indeed have sub-solar metallicities as already known in previous studies. The metallicity properties of RSGCs are far off the nominal metallicity trend in this region, and this suggests recent low-metallicity gas fueling into the inner disk and bulge.

scholarly journals Detection of rotational CO emission from the red-supergiants in the Large Magellanic Cloud

2015 ◽  
Vol 11 (A29B) ◽  
pp. 459-459
Author(s):  
Mikako Matsuura ◽  
B. Sargent ◽  
Bruce Swinyard ◽  
J.A. Yates ◽  
P. Royer ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Evolved Stars ◽  
Solar Metallicity ◽  
Red Supergiants ◽  
Low Metallicity ◽  
Co Emission ◽  
Loss Rates

AbstractIt is yet well understood how mass-loss rates from evolved stars depend on metallicities. With a half of the solar metallicity and the distance of only 50 kpc, the evolved stars of the Large Magellanic Cloud (LMC) are an ideal target for studying mass loss at low metallicity. We have obtained spectra of red-supergiants in the LMC, using the Hershel Space Observatory, detecting CO thermal lines fro J=6–5 up to 15–14 lines. Modelling CO lines with non-LTE Radiative transfer code suggests that CO lines intensities can be well explained with high gas-to-dust ratio, with no obvious reduction in mass-loss rate at the LMC. We conclude that the luminosities of the stars are primary factors on mass-loss rates, rather than the metallicity.

Trumpler 27 - A heavily reddened young open cluster with blue and red supergiants

1977 ◽  
Vol 215 ◽  
pp. 106 ◽  
Author(s):  
A. F. J. Moffat ◽  
M. P. Fitzgerald ◽  
P. D. Jackson
Keyword(s):  
Open Cluster ◽  
Young Open Cluster ◽  
Red Supergiants

scholarly journals Gemini-GRACES high-quality spectra of Kepler evolved stars with transiting planets

2020 ◽  
Vol 634 ◽  
pp. A29
Author(s):  
E. Jofré ◽  
J. M. Almenara ◽  
R. Petrucci ◽  
R. F. Díaz ◽  
Y. Gómez Maqueo Chew ◽  
...  
Keyword(s):  
Gravitational Interaction ◽  
Chemical Abundances ◽  
High Quality ◽  
Transiting Planets ◽  
Evolved Stars ◽  
Carbon Isotopic ◽  
Transit Times ◽  
Short Period ◽  
Red Giant ◽  
First Time

Aims. Kepler-278 and Kepler-391 are two of the three evolved stars known to date on the red giant branch (RGB) to host multiple short-period transiting planets. Moreover, the planets orbiting Kepler-278 and Kepler-391 are among the smallest discovered around RGB stars. Here we present a detailed stellar and planetary characterization of these remarkable systems. Methods. Based on high-quality spectra from Gemini-GRACES for Kepler-278 and Kepler-391, we obtained refined stellar parameters and precise chemical abundances for 25 elements. Nine of these elements and the carbon isotopic ratios, 12C∕13C, had not previously been measured. Also, combining our new stellar parameters with a photodynamical analysis of the Kepler light curves, we determined accurate planetary properties of both systems. Results. Our revised stellar parameters agree reasonably well with most of the previous results, although we find that Kepler-278 is ~15% less massive than previously reported. The abundances of C, N, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, and Ce, in both stars, are consistent with those of nearby evolved thin disk stars. Kepler-391 presents a relatively high abundance of lithium (A(Li)NLTE = 1.29 ± 0.09 dex), which is likely a remnant from the main-sequence phase. The precise spectroscopic parameters of Kepler-278 and Kepler-391, along with their high 12C∕13C ratios, show that both stars are just starting their ascent on the RGB. The planets Kepler-278b, Kepler-278c, and Kepler-391c are warm sub-Neptunes, whilst Kepler-391b is a hot sub-Neptune that falls in the hot super-Earth desert and, therefore, it might be undergoing photoevaporation of its outer envelope. The high-precision obtained in the transit times allowed us not only to confirm Kepler-278c’s TTV signal, but also to find evidence of a previously undetected TTV signal for the inner planet Kepler-278b. From the presence of gravitational interaction between these bodies we constrain, for the first time, the mass of Kepler-278b (Mp = 56 −13+37 M⊕) and Kepler-278c (Mp = 35 −21+9.9 M⊕). The mass limits, coupled with our precise determinations of the planetary radii, suggest that their bulk compositions are consistent with a significant amount of water content and the presence of H2 gaseous envelopes. Finally, our photodynamical analysis also shows that the orbits of both planets around Kepler-278 are highly eccentric (e ~ 0.7) and, surprisingly, coplanar. Further observations (e.g., precise radial velocities) of this system are needed to confirm the eccentricity values presented here.

scholarly journals Crystalline silicates in AGB and post-AGB stars

1999 ◽  
Vol 191 ◽  
pp. 208-220 ◽  
Author(s):  
L.B.F.M. Waters ◽  
F.J. Molster
Keyword(s):  
Asymptotic Giant Branch ◽  
High Mass ◽  
Agb Stars ◽  
Origin And Evolution ◽  
Evolved Stars ◽  
Quantitative Mineralogy ◽  
High Mass Loss ◽  
Dust Component ◽  
First Time ◽  
Central Stars

We discuss ISO spectroscopy of oxygen-rich dust shells surrounding evolved stars. The dust that condenses in the outflows of stars on the Asymptotic Giant Branch consists mainly of amorphous silicates and simple oxides. For high mass loss rates, crystalline silicates begin to appear at modest abundance. These crystalline silicates are cold and Fe-poor. ISO spectroscopy for the first time allows quantitative mineralogy of oxygen-rich circumstellar dust. Crystalline silicates are found at high abundance in sources with peculiar (disk) geometry, such as long-lived circum-binary disks. Some C-rich post-AGB stars, notably the Red Rectangle and several nebulae surrounding [WC] central stars of Planetary Nebulae, also show crystalline silicates. We speculate on the origin and evolution of the crystalline dust component in evolved stars.

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