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J/ApJ/658/1203      Nitrogen-enhanced metal-poor stars       (Johnson+, 2007)

A search for nitrogen-enhanced metal-poor stars. Johnson J.A., Herwig F., Beers T.C., Christlieb N. <Astrophys. J., 658, 1203-1216 (2007)> =2007ApJ...658.1203J
ADC_Keywords: Stars, carbon ; Abundances Keywords: nuclear reactions, nucleosynthesis, abundances - stars: abundances - stars: AGB and post-AGB - stars: carbon - stars: Population II Abstract: Theoretical models of very metal-poor intermediate-mass asymptotic giant branch (AGB) stars predict a large overabundance of primary nitrogen. The very metal-poor, carbon-enhanced, s-process-rich stars, which are thought to be the polluted companions of now extinct AGB stars, provide direct tests of the predictions of these models. Recent studies of the carbon and nitrogen abundances in metal-poor stars have focused on the most carbon-rich stars, leading to a potential selection bias against stars that have been polluted by AGB stars that produced large amounts of nitrogen and hence have small [C/N] ratios. We call these stars nitrogen-enhanced metal-poor (NEMP) stars and define them as having [N/Fe]>+0.5 and [C/N]←0.5. In this paper we report on the [C/N] abundances of a sample of 21 carbon-enhanced stars, all but three of which have [C/Fe]<+2.0. If NEMP stars were made as easily as carbon-enhanced metal-poor (CEMP) stars, then we expected to find between two and seven NEMP stars. Instead, we found no NEMP stars in our sample. Description: To observe the NH band, we require near-UV sensitivity; however, a resolution of 2-2.5Å is more than adequate. The Ritchey-Chretien (RC) spectrographs at Kitt Peak National Observatory (KPNO) and at Cerro Tololo Inter-American Observatory (CTIO) have these capabilities, allowing us to observe both northern and southern hemisphere targets. We observed eight stars at KPNO over three nights from 2003 August 30 to September 1. We also observed 20 stars over 6 nights at CTIO in two observing sessions: 2003 September 6-8 and 2004 November 26-28. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 61 29 Photometry data table10.dat 81 36 Additional literature values
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 12 A12 --- Name Star name 14- 19 F6.3 mag Vmag V magnitude 21- 25 F5.3 mag B-V ?=- B-V colour index 27- 32 F6.3 mag U-B ?=- U-B colour index 34- 38 F5.3 mag V-R ?=- V-R colour index 40- 44 F5.3 mag V-I ?=- V-I colour index 46- 50 F5.3 mag V-J ?=- V-J colour index 52- 56 F5.3 mag V-K ?=- V-K colour index 58- 61 F4.2 mag E(B-V) Galactic colour excess
Byte-by-byte Description of file: table10.dat
Bytes Format Units Label Explanations
1 A1 --- Sample [123] Sample (1) 3- 15 A13 --- Name Star name 17- 20 F4.2 [-] logeC C abundance (H=12) 22- 25 F4.2 [-] logeN N abundance (H=12) 27- 31 F5.2 [Sun] [Fe/H] Metallicity 33- 37 F5.2 [Sun] [C/N] Abundance, C/N 39- 77 A39 --- Ref Reference for abundances 79- 81 A3 --- s-el [Yes/No] s-process element rich star ?
Note (1): Flag as follows: 1 = Original Literature Sample 2 = New and Updated Literature Sample 3 = Nitrogen-rich Stars
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 23-Jan-2009
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