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 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 61 29 Photometry data
table10.dat 81 36 Additional literature values
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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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
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Byte-by-byte Description of file: table10.dat
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Bytes Format Units Label Explanations
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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 ?
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Note (1): Flag as follows:
1 = Original Literature Sample
2 = New and Updated Literature Sample
3 = Nitrogen-rich Stars
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 23-Jan-2009