Results 51 to 60 of about 210,874 (237)

Chemical abundances in Seyfert galaxies – IX. Helium abundance estimates

Monthly Notices of the Royal Astronomical Society, 2022
ABSTRACT For the first time, the helium abundance relative to hydrogen (He/H), which relied on direct measurements of the electron temperature, has been derived in the narrow line regions (NLRs) from a local sample of Seyfert 2 nuclei.
O L Dors, M Valerdi, P Freitas-Lemes, A C Krabbe, R A Riffel, E B Amôres, R Riffel, M Armah, A F Monteiro, C B Oliveira   +9 more
openaire   +2 more sources

Chemical abundances and metallicity of Planetary Nebulae [PDF]

Symposium - International Astronomical Union, 1997
Confrontations of the dredge-up theory with observed patterns of chemical abundances of planetary nebulae (PNs) have been carried out by many authors (see, e.g., Kaler & Jacoby 1990, 1991; Stasińska & Tylenda 1990). Although these studies suggest that the observational abundance ratios of PNs can qualitatively be explained by the current dredge-
C. Y. Zhang, Sun Kwok
openaire   +2 more sources

Optical Spectroscopy and Photoionization Model of Planetary Nebula NGC 6572

Journal of Mathematical and Fundamental Sciences
We investigated NGC 6572 through optical spectroscopy to determine its kinematical and chemical properties. Two intermediate dispersion spectra (R~5000) centered around Hα and Hβ were used to derive the nebular expansion velocity from emission lines ...
Muhammad Fajrin, Hakim Luthfi Malasan, Evan Irawan Akbar   +2 more
doaj   +1 more source

High-precision chemical abundances of Galactic building blocks

Astronomy & Astrophysics, 2022
Context. Sequoia is a retrograde kinematic substructure in the nearby Galactic halo, whose properties are a matter of debate. For example, previous studies do not necessarily agree on the chemical abundances of Sequoia stars, which are important for understanding its nature. Aims.
Matsuno, Tadafumi, Koppelman, Helmer H., Helmi, Amina, Aoki, Wako, Ishigaki, Miho N., Suda, Takuma, Yuan, Zhen, Hattori, Kohei   +7 more
openaire   +3 more sources

Chemical sensitivity to the ratio of the cosmic-ray ionization rates of He and H2 in dense clouds [PDF]

, 2006
Aim: To determine whether or not gas-phase chemical models with homogeneous and time-independent physical conditions explain the many observed molecular abundances in astrophysical sources, it is crucial to estimate the uncertainties in the calculated ...
Baldwin, Bergin, Boger, Charnley, Dalgarno, E. Herbst, F. Selsis, G. Massacrier, Glassgold, Graedel, Herbst, Le Bourlot, Le Bourlot, Le Teuff, Lee, Pagani, Pineau des Forets, Shalabiea, Smith, Snell, Terzieva, V. Wakelam, Wakelam, Wakelam, Wakelam   +24 more
core   +3 more sources

The Missing Link of Sulfur Chemistry in TMC-1: The Detection of c-C3H2S from the GOTHAM Survey

The Astrophysical Journal
We present the spectroscopic characterization of cyclopropenethione in the laboratory and detect it in space using the Green Bank Telescope Observations of TMC-1: Hunting Aromatic Molecules survey.
Anthony J. Remijan, P. Bryan Changala, Ci Xue, Elsa Q. H. Yuan, Miya Duffy, Haley N. Scolati, Christopher N. Shingledecker, Thomas H. Speak, Ilsa R. Cooke, Ryan Loomis, Andrew M. Burkhardt, Zachary T. P. Fried, Gabi Wenzel, Andrew Lipnicky, Michael C. McCarthy, Brett A. McGuire   +15 more
doaj   +1 more source

The ¹⁷O/¹⁸O Ratio of Post-AGB Sources: Canonical and Non-Canonical Populations

Galaxies
Stellar evolution models serve as tools to derive stellar parameters from elemental and isotopic abundance ratios. For low-to-intermediate mass evolved stars, C/O, 12C/13C, and 17O/18O ratios are proxies of the initial mass, a largely unknown parameter ...
Javier Alcolea, Elisa Masa, Theo Khouri, Miguel Santander-García, Iván Gallardo Cava, Hans Olofsson, Carmen Sánchez Contreras, Valentín Bujarrabal, Wouter H. T. Vlemmings, Daniel Tafoya   +9 more
doaj   +1 more source

Chemical Abundances in Galactic Bulge Pn [PDF]

Symposium - International Astronomical Union, 1993
We present abundance determinations, in particular of carbon, and C/O ratios, for 11 Galactic bulge planetary nebulae (PN) based on our low resolution UV data from IUE observations and optical spectrophotometry from the Anglo-Australian Telescope. We compare the observed abundances with those predicted by dredge-up theory for the high metallicity ...
R. E. S. Clegg, Nicholas A. Walton, M. J. Barlow   +2 more
openaire   +2 more sources

Stellar evolution with SMC chemical abundances [PDF]

International Astronomical Union Colloquium, 1981
Evolutionary computations are presented for massive stars between 20 Mo and 100 Mo with chemical abundances holding for the Small Magellanic Cloud, i.e. X = .76 and Z = .003. Mass loss by stellar wind is taken into account during core hydrogen burning.
D. Vanbeveren, P. Hellings
openaire   +2 more sources

Planetary nebulae in the inner Milky Way: new abundances [PDF]

, 2009
The study of planetary nebulae in the inner-disk and bulge gives important information on the chemical abundances of elements such as He, N, O, Ar, Ne, and on the evolution of these abundances, which is associated with the evolution of intermediate-mass ...
Cavichia, O., Costa, R. D. D., Maciel, W. J.   +2 more
core   +2 more sources