Browsing Research publications by Author "Ryan, Sean G."
Now showing items 41-60 of 65
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A low upper-limit on the lithium isotope ratio in HD140283
Aoki, W.; Inoue, S.; Kawanomoto, S.; Ryan, Sean G.; Smith, I.M.; Suzuki, T.K.; Takada-Hidai, M. (2004-12) -
Mg abundances in metal-poor halo stars as a tracer of early Galactic mixing
Arnone, E.; Ryan, Sean G.; Argast, D.; Norris, J.E.; Beers, T.C. (2005-02) -
The Most Metal-poor Stars. I : Discovery, Data and Atmospheric Parameters
Norris, John; Bessell, Michael; Yong, David; Christlieb, Norbert; Barklem, Paul; Asplund, Martin; Murphy, Michael; Beers, Timothy; Frebel, Anna; Ryan, Sean G. (2013-01)We report the discovery of 34 stars in the Hamburg/ESO Survey for metal-poor stars and the Sloan Digital Sky Survey that have [Fe/H] <~ -3.0. Their median and minimum abundances are [Fe/H] = -3.1 and -4.1, respectively, ... -
The Most Metal-poor Stars. II : Chemical Abundances of 190 Metal-poor Stars Including 10 New Stars with [Fe/H] <= -3.5
Yong, David; Norris, John; Bessell, Michael S.; Asplund, Martin; Beers, Timothy C.; Barklem, Paul S.; Frebel, Anna; Ryan, Sean G. (2013-01)We present a homogeneous chemical abundance analysis of 16 elements in 190 metal-poor Galactic halo stars (38 program and 152 literature objects). The sample includes 171 stars with [Fe/H] <= -2.5, of which 86 are extremely ... -
The Most Metal-poor Stars. III : The Metallicity Distribution Function and Carbon-enhanced Metal-poor Fraction
Yong, David; Norris, John; Bessell, Michael; Christlieb, Norbert; Asplund, Martin; Beers, Timothy; Barklem, Paul; Frebel, Anna; Ryan, Sean G. (2013)We examine the metallicity distribution function (MDF) and fraction of carbon-enhanced metal-poor (CEMP) stars in a sample that includes 86 stars with [Fe/H] <= -3.0, based on high-resolution, high signal-to-noise spectroscopy, ... -
The Most Metal-Poor Stars. IV : The Two Populations with [Fe/H] <~ -3.0
Norris, John; Yong, David; Bessell, Michael; Christlieb, Norbert; Asplund, Martin; Gilmore, G.F.; Wyse, Rosemary F. G.; Beers, Timothy; Barklem, Paul; Frebel, Anna; Ryan, Sean G. (2013-01-01)We discuss the carbon-normal and carbon-rich populations of Galactic halo stars having [Fe/H] lsim -3.0, utilizing chemical abundances from high-resolution, high signal-to-noise model-atmosphere analyses. The C-rich ... -
Neutron Capture Elements in s-Process-Rich, Very Metal-Poor Stars
Aoki, W.; Ryan, Sean G.; Norris, J.E.; Beers, T.C.; Ando, H.; Iwamoto, N.; Kajino, T.; Mathews, G.J.; Fujimoto, M.Y. (2001-11) -
The new record holder for the most iron-poor star: HE 1327−2326, a dwarf or subgiant with [Fe/H] = −5.4
Frebel, A.; Aoki, W.; Christlieb, N.; Ando, H.; Asplund, M.; Barklem, P.S.; Beers, T.C.; Eriksson, K.; Fechner, C.; Fujimoto, M.Y.; Honda, S.; Kajino, T.; Minezaki, T.; Nomoto, K.; Norris, J.E.; Ryan, Sean G.; Takada-Hidai, M.; Tsangarides, S.; Yoshii, Y. (2005)We describe the discovery of HE 1327−2326, a dwarf or subgiant with [Fe/H] = −5.4. The star was found in a sample of bright metal-poor stars selected from the Hamburg/ESO survey. Its abundance pattern is characterized by ... -
A new sample of extremely/ultra metal-poor stars
Perez, A. E. Garcia; Christlieb, N.; Ryan, Sean G.; Beers, T.C.; Aoki, W.; Asplund, M.; Barklem, P.S.; Bessell, M.S.; Eriksson, K.; Frebel, A.; Gustafsson, B.; Korn, A.J.; Nordstrom, B.; Norris, J.E. (2008-12)A sample of 30 very metal-poor stars from the Hamburg-European Southern Observatory (ESO) objective-prism survey have been observed at high spectral resolution at the Very Large Telescope (VLT) using the Ultraviolet and ... -
Nucleosynthesis and early chemical evolution in galaxies
Tsangarides, S.; Arnone, E.; Ryan, Sean G. (2003)Nucleosynthesis and galactic chemical evolution are inter-linked topics that merge various fields in astronomy and physics. Speakers at the RAS discussion meeting of January 2003 combined theory and observation in understanding ... -
Nucleosynthetic signatures of the first stars
Frebel, A.; Aoki, W.; Christlieb, N.; Ando, H.; Asplund, M.; Barklem, P.S.; Beers, T.C.; Eriksson, K.; Fechner, C.; Fujimoto, M.Y.; Honda, S.; Kajino, T.; Minezaki, T.; Nomoto, K.; Norris, J.E.; Ryan, Sean G.; Takada-Hidai, M.; Tsangarides, S.; Yoshii, Y. (2005-04) -
Observations of r- and s-process elements in population II stars
Ryan, Sean G. (2003) -
On the binarity of carbon-enhanced, metal-poor stars
Tsangarides, S.; Ryan, Sean G.; Beers, T.C. (2004) -
Oxygen Overabundance in the Extremely Iron-poor Star CS 29498-043
Aoki, W.; Norris, J.E.; Ryan, Sean G.; Beers, T.C.; Christlieb, N.; Tsangarides, S.; Ando, H. (2004-06) -
Primordial Lithium and Big Bang Nucleosynthesis
Ryan, Sean G.; Beers, T.C.; Olive, K.A.; Fields, B.D.; Norris, J.E. (2000)Recent determinations of the abundance of the light-element Li in very metal-poor stars show that its intrinsic dispersion is essentially zero and that the random error in the estimated mean Li abundance is negligible. ... -
Rapid Rotation of Ultra-Li-depleted Halo Stars and Their Association with Blue Stragglers
Ryan, Sean G.; Gregory, S.; Kolb, U.; Beers, T.C.; Kajino, T. (2002-05) -
s- and r-process elements in two very metal-poor stars
Ryan, Sean G.; Aoki, W.; Blake, L.A.J.; Norris, J.E.; Beers, T.C.; Gallino, R.; Busso, M.; Ando, H. (2001) -
The SALT HRS spectrograph : final design, instrument capabilities, and operational modes
Bramall, D.G.; Sharples, R.; Tyas, L.; Schmoll, J.; Clark, P.; Luke, P.; Looker, N.; Dipper, N.A.; Ryan, Sean G. (2010)The high-resolution chelle spectrograph, SALT HRS, is at an advanced stage of construction and will shortly become available to the user community of the Southern African Large Telescope (SALT). This paper presents a ... -
Spectral classification of photometrically selected AGB candidates in NGC 6822
Sibbons, L. F.; Ryan, Sean G.; Napiwotzki, Ralf; Thompson, G. P. (2015-02-02)Context. The ratio of C- and M-type asymptotic giant branch (AGB) stars is commonly used to estimate the metallicity of extragalactic populations. Sources in the AGB population must therefore be accurately classified as ... -
Spectroscopic Studies of Extremely Metal-Poor Stars with the Subaru High Dispersion Spectrograph. I. Observational Data
Honda, S.; Aoki, W.; Ando, H.; Izumiura, H.; Kajino, T.; Kambe, E.; Kawanomoto, S.; Noguchi, K.; Okita, K.; Sadakane, K.; Sato, B.; Takada-Hidai, M.; Takeda, Y.; Watanabe, E.; Beers, T.C.; Norris, J.E.; Ryan, Sean G. (2004-05)