Zobrazeno 1 - 10
of 380
pro vyhledávání: '"Cowan, John P."'
Autor:
Roederer, Ian U., Vassh, Nicole, Holmbeck, Erika M., Mumpower, Matthew R., Surman, Rebecca, Cowan, John J., Beers, Timothy C., Ezzeddine, Rana, Frebel, Anna, Hansen, Terese T., Placco, Vinicius M., Sakari, Charli M.
Publikováno v:
Science, 382, 1177-1180 (2023)
The heaviest chemical elements are naturally produced by the rapid neutron-capture process (r-process) during neutron star mergers or supernovae. The r-process production of elements heavier than uranium (transuranic nuclei) is poorly understood and
Externí odkaz:
http://arxiv.org/abs/2312.06844
Autor:
Sneden, Christopher, Boesgaard, Ann Merchant, Cowan, John J., Roederer, Ian U., Hartog, Elizabeth A. Den, Lawler, James E.
We have derived new detailed abundances of Mg, Ca, and the Fe-group elements Sc through Zn (Z = 21-30) for 37 main sequence turnoff very metal-poor stars ([Fe/H] <= -2.1). We analyzed Keck HIRES optical and near-UV high signal-to-noise spectra origin
Externí odkaz:
http://arxiv.org/abs/2304.06899
Autor:
Roederer, Ian U., Cowan, John J., Pignatari, Marco, Beers, Timothy C., Hartog, Elizabeth A. Den, Ezzeddine, Rana, Frebel, Anna, Hansen, Terese T., Holmbeck, Erika M., Mumpower, Matthew R., Placco, Vinicius M., Sakari, Charli M., Surman, Rebecca, Vassh, Nicole
Publikováno v:
Astrophysical Journal Vol. 936, p. 84 (2022)
We present new observational benchmarks of rapid neutron-capture process (r-process) nucleosynthesis for elements at and between the first (A ~ 80) and second (A ~ 130) peaks. Our analysis is based on archival ultraviolet and optical spectroscopy of
Externí odkaz:
http://arxiv.org/abs/2210.15105
Autor:
Ou, Xiaowei, Roederer, Ian U., Sneden, Christopher, Cowan, John J., Lawler, James E., Shectman, Stephen A., Thompson, Ian B.
We present vanadium (V) abundances for 255 metal-poor stars, derived from high-resolution optical spectra from the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coud\'{e} Spec
Externí odkaz:
http://arxiv.org/abs/2008.05500
Autor:
Cowan, John J., Sneden, Christopher, Roederer, Ian U., Lawler, James E., Hartog, Elizabeth A. Den, Sobeck, Jennifer S., Boesgaard, Ann Merchant
We have obtained new detailed abundances of the Fe-group elements Sc through Zn (Z=21-30) in three very metal-poor ([Fe/H] $\approx -3$) stars: BD 03 740, BD -13 3442 and CD -33 1173. High-resolution ultraviolet HST/STIS spectra in the wavelength ran
Externí odkaz:
http://arxiv.org/abs/2001.00541
Autor:
Sakari, Charli M., Roederer, Ian U., Placco, Vinicius M., Beers, Timothy C., Ezzeddine, Rana, Frebel, Anna, Hansen, Terese, Sneden, Christopher, Cowan, John J., Wallerstein, George, Farrell, Elizabeth M., Venn, Kim A., Matijevic, Gal, Wyse, Rosemary F. G., Bland-Hawthorn, Joss, Chiappini, Cristina, Freeman, Kenneth C., Gibson, Brad K., Grebel, Eva K., Helmi, Amina, Kordopatis, Georges, Kunder, Andrea, Navarro, Julio, Reid, Warren, Seabroke, George, Steinmetz, Matthias, Watson, Fred
A new moderately r-process-enhanced metal-poor star, RAVE J093730.5-062655, has been identified in the Milky Way halo as part of an ongoing survey by the R-Process Alliance. The temperature and surface gravity indicate that J0937-0626 is likely a hor
Externí odkaz:
http://arxiv.org/abs/1903.01480
Autor:
Cowan, John J., Sneden, Christopher, Lawler, James E., Aprahamian, Ani, Wiescher, Michael, Langanke, Karlheinz, Martínez-Pinedo, Gabriel, Thielemann, Friedrich-Karl
Publikováno v:
Rev. Mod. Phys. 93, 15002 (2021)
The production of about half of the heavy elements found in nature is assigned to a specific astrophysical nucleosynthesis process: the rapid neutron capture process (r-process). Although this idea has been postulated more than six decades ago, the f
Externí odkaz:
http://arxiv.org/abs/1901.01410
Autor:
Sakari, Charli M., Placco, Vinicius M., Farrell, Elizabeth M., Roederer, Ian U., Wallerstein, George, Beers, Timothy C., Ezzeddine, Rana, Frebel, Anna, Hansen, Terese, Holmbeck, Erika M., Sneden, Christopher, Cowan, John J., Venn, Kim A., Davis, Christopher Evan, Matijevic, Gal, Wyse, Rosemary F. G., Bland-Hawthorn, Joss, Chiappini, Cristina, Freeman, Kenneth C., Gibson, Brad K., Grebel, Eva K., Helmi, Amina, Kordopatis, Georges, Kunder, Andrea, Navarro, Julio, Reid, Warren, Seabroke, George, Steinmetz, Matthias, Watson, Fred
This paper presents the detailed abundances and r-process classifications of 126 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance. The stars were identified as metal-poor candidates from the RAdial Velocit
Externí odkaz:
http://arxiv.org/abs/1809.09156
Autor:
Holmbeck, Erika M., Beers, Timothy C., Roederer, Ian U., Placco, Vinicius M., Hansen, Terese T., Sakari, Charli M., Sneden, Christopher, Liu, Chao, Lee, Young Sun, Cowan, John J., Frebel, Anna
We report the discovery of a new actinide-boost star, 2MASS J09544277+5246414, originally identified as a very bright (V = 10.1), extremely metal-poor ([Fe/H] = -2.99) K giant in the LAMOST survey, and found to be highly r-process-enhanced (r-II; [Eu
Externí odkaz:
http://arxiv.org/abs/1805.11925
Autor:
Roederer, Ian U., Sneden, Christopher, Lawler, James E., Sobeck, Jennifer S., Cowan, John J., Boesgaard, Ann Merchant
Neutral Fe lines in metal-poor stars yield conflicting abundances depending on whether and how deviations from local thermodynamic equilibrium (LTE) are considered. We have collected new high resolution and high signal-to-noise ultraviolet (UV) spect
Externí odkaz:
http://arxiv.org/abs/1805.07390