EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 385/ 1 Article

Free access article

Issue A&A
Volume 385, Number 1, April I 2002
Page(s) 111 - 130
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20020118



A&A 385, 111-130 (2002)
DOI: 10.1051/0004-6361:20020118

The presence of Nd and Pr in HgMn stars

L. Dolk1, G. M. Wahlgren1, H. Lundberg2, Z. S. Li2, U. Litzén1, S. Ivarsson1, I. Ilyin3 and S. Hubrig4

1  Atomic Astrophysics, Department of Astronomy, Lund University, Box 43, 22100 Lund, Sweden
2  Department of Physics, Lund Institute of Technology, Box 118, 22100 Lund, Sweden
3  Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
4  European Southern Observatory, Casilla 19001, Santiago 19, Chile

(Received 11 July 2001 / Accepted 7 January 2002 )

Abstract
Optical region spectra for a number of upper main sequence chemically peculiar (CP) stars have been observed to study singly and doubly ionized praseodymium and neodymium lines. In order to improve existing atomic data of these elements, laboratory measurements have been carried out with the Lund VUV Fourier Transform Spectrometer (FTS). From these measurements wavelengths and hyperfine structure (hfs) have been studied for selected $\ion{Pr}{ii}$, $\ion{Pr}{iii}$ and $\ion{Nd}{iii}$ lines of astrophysical interest. Radiative life times for some excited states of $\ion{Pr}{ii}$ have been determined with the aid of laser spectroscopy at the Lund Laser Center (LLC) and have been combined with branching fractions measured in the laboratory to calculate gf values for some of the stronger optical lines of $\ion{Pr}{ii}$. With the aid of the derived gf values and laboratory measurements of the hfs, a praseodymium abundance was derived from selected $\ion{Pr}{ii}$ lines in the spectrum of the Am star 32 Aqr. This abundance was used to derive astrophysical gf values for selected $\ion{Pr}{iii}$ lines in 32 Aqr, and these gf values were used to get a praseodymium abundance for the HgMn star HR 7775. The praseodymium abundance in HR 7775 was then utilized to derive astrophysical gf values for all observable $\ion{Pr}{iii}$ lines in this star. The neodymium abundance, derived from unblended lines of $\ion{Nd}{ii}$ in HR 7775, has been utilized to establish astrophysical gf values for observed $\ion{Nd}{iii}$ lines in the optical region of this star. Selected $\ion{Pr}{iii}$ and $\ion{Nd}{iii}$ lines have been identified and studied in a number of HgMn stars and three hot Am stars. The praseodymium and neodymium abundance change rapidly from an approximate 1-1.2 dex enhancement for the hot Am stars to 1.5-3 dex enhancement for the cool HgMn stars, indicating a well-defined boundary between the hot Am and HgMn stars in the vicinity of 10 500 K. The enhancement of praseodymium and neodymium in Am and HgMn stars may be explained by diffusive processes active in the stellar atmosphere, while the observed discontinuity might be explained by a thin hydrogen convection zone thought to be present for the Am stars, but absent in the HgMn stars. The absence of a convection zone would cause the diffused elements to gather higher in the atmosphere of HgMn stars compared to Am stars, and explain the observed increase in abundance.


Key words: atomic data -- stars: abundances -- stars: chemically peculiar

Offprint request: L. Dolk, linus.dolk@fysik.lu.se

SIMBAD Objects



© ESO 2002

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.