A Search for Nitrogen-Enhanced Metal-Poor Stars

Details A Search for Nitrogen-Enhanced Metal-Poor Stars A Search for Nitrogen-Enhanced Metal-Poor Stars

2006-08-30

arxiv.org/abs/astro-ph/0608666v1

Astronomy and Astrophysics

Astrophysics

14 pages, 7 figures, to be published in ApJ

Scientific paper

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. Therefore, this observational bias is not an important contributor to the apparent dearth of N-rich stars. Our [C/N] values are in the same range as values reported previously in the literature (-0.5 to +2.0), and all stars are in disagreement with the predicted [C/N] ratios for both low-mass and high-mass AGB stars. We suggest that the decrease in [C/N] from the low-mass AGB models is due to enhanced extra-mixing, while the lack of NEMP stars may be caused by unfavorable mass ratios in binaries or the difficulty of mass transfer in binary systems with large mass ratios.

Affiliated with

Also associated with

No associations

Rating

A Search for Nitrogen-Enhanced Metal-Poor Stars does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with A Search for Nitrogen-Enhanced Metal-Poor Stars, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A Search for Nitrogen-Enhanced Metal-Poor Stars will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-75306