Elemental abundance analyses with Coudé Echelle spectrograms from the TÜBİTAK National Observatory of Turkey: I. The HgMn stars 11 Per, HR 2801, and ν Cnc

The sn stars were first discoved by Abt & Levato when studying the spectral types in different open clusters. These stars present sharp Balmer lines, sharp metallic lines (C II, Si II, Ca II, Ti II, Fe II), and broad coreless He I lines. Some of the sn stars seem to be related to CP stars. Initially Abt & Levato proposed a shell-like nature to explain the sn stars, although this scenario was subsequently questioned. There is no general agreement about their origin. We aim to derive abundances for a sample of 9 stars, including sn and non-sn stars, to determine the possible relation between sn and CP stars and compare their chemical abundances. That most sn stars belong to open clusters allows us to search for a possible relation with fundamental parameters, including the age and rotation. We also study the possible contribution of different effects to the broad He I lines observed in these stars, such as Stark broadening and the possible He-stratification. Effective temperature and gravity were estimated by Strömgren photometry and then refined by requiring ionization and excitation equilibrium of Fe lines. We derived the abundances by fitting the observed spectra with synthetic spectra using an iterative procedure with the SYNTHE and ATLAS9 codes. We derived metallic abundances of 23 different chemical elements for 9 stars and obtained low projected rotational velocities for the sn stars in our sample (v sin i up to 69 km s −1 ). We also compared 5 stars that belong to the same cluster (NGC 6475) and show that the sn characteristics appear in the 3 stars with the lower rotational velocity. However, the apparent preference of sn stars for objects with the lower v sin i values should be taken with caution due to the small number of objects studied here. We analysed the photospheric chemical composition of sn stars and show that approximately ∼40% of them display chemical peculiarities (such as He-weak and HgMn stars) within a range of temperature of 10 300 K−14 500 K. However, there are also sn stars with solar or nearly-solar (i.e. non-CP) chemical composition. We have studied the possible contribution of different processes to the broad He I lines present in the sn stars. Although NLTE effects could not be completely ruled out, it seems that NLTE is not directly related to the broad He I profiles observed in the sn stars. The broad-line He I 4026 Å is the clearest example of the sn characteristics in our sample. We succesfully fit this line in 4 out of 7 sn stars by using the appropriate Stark broadening tables, while small differences appear in the other 3 stars. Studying the plots of abundance vs. depth for the He I lines resulted in some sn stars probably being stratified in He. However, a further study of variability in the He I lines would help for determining whether a possible non-uniform He superficial distribution could also play a role in these sn stars. We conclude that the broad He I lines that characterize the sn class could be modelled (at least in some of these stars) by the usual radiati...

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“…A similar strategy was applied in previous works (e.g. Adelman & Yuce 2010;Saffe et al 2011;Saffe 2011). Finally, the adopted values References.…”

Section: Atmospheric Parametersmentioning

confidence: 99%

On the nature of sn stars

Saffe

Levato

2014

A&A

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“…Its abundance pattern shows that it is the most rare earth rich Am star (Yüce et al 2011). c. Adelman & Yüce (2010)…”

Section: The Hr Diagram Searching On the Peculiaritymentioning

confidence: 99%

A More Powerful Approach For Studying the Abundances of Chemically Peculiar Stars

Yüce

2022

Turkish Journal of Astronomy and Astrophysics

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Üzerinde çalıştığımız kimyasal sıra dışı yıldızlarda, merkezden yüzeye ve atmosfere doğru, konveksiyon ve radyasyon mekanizmaları ile madde ve enerji taşınımı olmaktadır. Bu alanda yaptığımız geçmiş dönem yıldız analiz çalışmalarında, Dominion Astrofizik Gözlemevi’nden elde edilen (R=67000 ve Sinyal/Gürültü ~ 200) optik bölge spektrumlarının yüksek çözünürlüklü analizini içeren spektroskopik teknikler kullanmaktaydık. Bu yöntemle elde edilen verileri kullanarak, hem Güneş benzeri kimyasal bolluk gösteren normal yıldızların hem de B, A, ve erken-F tayf türü manyetik olmayan kimyasal sıra dışı yıldızların element bolluklarını araştırdık. Ayrıca, “Four College Automated Telescope” cihazından elde edilmiş fotometrik verileri kullanarak manyetik özellikli kimyasal sıra dışı yıldızların fotometrik verilerini de çalıştık ve yayınladık. Yeni dönem çalışmalarımızda ise Şili’deki “Cerro Tololo Interamerican Observatory” merkezinde bulunan, Chiron eşel spektrometresinden (R=80000 ve S/N > 500) elde edilen yüksek çözünürlüklü veriler kullanılarak yıldızların element bollukları hakkında, kesinliği daha yüksek analizler yer almaktadır. Bu çalışmalar sayesinde örneğin, yıldızlar arasındaki küçük bolluk farklarını ortaya koymak mümkün olabilmektedir. Kimyasal sıra dışı A yıldızları üzerine yaptığımız element bolluk analizlerinde, element bollukları ile bu yıldızların evrimleri arasında ilişki kurma imkanlarının doğabileceği düşünülmektedir. Bu yıldızlardaki element bolluklarının merkezden dışa doğru aynı mı yoksa farklı mı olduğunu bilmek önemli bir veridir, bu veri söz konusu yıldızların fotometrik ışık değişkenliklerini açıklamada kullanılabilir. Kısaca, kimyasal sıra dışı yıldızların element bolluk verileri daha geniş bir bağlamda analizlenerek bu yıldızların evrim durumları hakkında makul çıkarımlar yapılabileceği düşünülebilir.

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“…A similar strategy was applied in previous works (e.g. Adelman & Yuce 2010;Saffe et al 2011;Saffe 2011). Finally, the adopted values are shown in Table 2, together with the corresponding age of the cluster.…”

Section: Atmospheric Parametersmentioning

confidence: 99%

On the nature of sn stars. I. A detailed abundance study

Saffe,

Levato

2014

Preprint

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The sn stars were first discoved by Abt & Levato when studying the spectral types in different open clusters. These stars present sharp Balmer lines, sharp metallic lines (C II, Si II, Ca II, Ti II, Fe II), and broad coreless He I lines. Some of the sn stars seem to be related to CP stars. Initially Abt & Levato proposed a shell-like nature to explain the sn stars, although this scenario was subsequently questioned. There is no general agreement about their origin. We aim to derive abundances for a sample of 9 stars, including sn and non-sn stars, to determine the possible relation between sn and CP stars and compare their chemical abundances. That most sn stars belong to open clusters allows us to search for a possible relation with fundamental parameters, including the age and rotation. We also study the possible contribution of different effects to the broad He I lines observed in these stars, such as Stark broadening and the possible He-stratification. Effective temperature and gravity were estimated by Strömgren photometry and then refined by requiring ionization and excitation equilibrium of Fe lines. We derived the abundances by fitting the observed spectra with synthetic spectra using an iterative procedure with the SYNTHE and ATLAS9 codes. We derived metallic abundances of 23 different chemical elements for 9 stars and obtained low projected rotational velocities for the sn stars in our sample (vsini up to 69 km/s). We also compared 5 stars that belong to the same cluster (NGC 6475) and show that the sn characteristics appear in the 3 stars with the lower rotational velocity. However, the apparent preference of sn stars for objects with the lower vsini values should be taken with caution due to the small number of objects studied here. We analysed the photospheric chemical composition of sn stars and show that approximately ∼40% of them display chemical peculiarities (such as He-weak and HgMn stars) within a range of temperature of 10300 -14500 K. However, there are also sn stars with solar or nearly-solar (i.e., non-CP) chemical composition. We have studied the possible contribution of different processes to the broad He I lines present in the sn stars. Although NLTE effects could not be completely ruled out, it seems that NLTE is not directly related to the broad He I profiles observed in the sn stars. The broad-line He I 4026 Å is the clearest example of the sn characteristics in our sample. We succesfully fit this line in 4 out of 7 sn stars by using the appropriate Stark broadening tables, while small differences appear in the other 3 stars. Studying the plots of abundance vs depth for the He I lines resulted in some sn stars probably being stratified in He. However, a further study of variability in the He I lines would help for determining whether a possible non-uniform He superficial distribution could also play a role in these sn stars. We conclude that the broad He I lines that characterize the sn class could be modelled (at least in some of these stars) by the usual radiative transfer process ...

show abstract

Elemental abundance analyses with Coudé Echelle spectrograms from the TÜBİTAK National Observatory of Turkey: I. The HgMn stars 11 Per, HR 2801, and ν Cnc

Cited by 4 publications

References 57 publications

On the nature of sn stars

On the nature of sn stars

A More Powerful Approach For Studying the Abundances of Chemically Peculiar Stars

On the nature of sn stars. I. A detailed abundance study

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