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J/A+A/598/A54            Line list                               (Hansen+, 2017)

Something borrowed, something blue: The nature of blue metal-poor stars inferred from their colours and chemical abundances. Hansen C.J., Jofre P., Koch A., McWilliam A., Sneden C.S. <Astron. Astrophys. 598, A54 (2017)> =2017A&A...598A..54H (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics Keywords: stars: abundances - stars: blue stragglers - binaries: general - stars: fundamental parameters - stars: Population II - galaxies: halos Abstract: Blue metal-poor stars (BMPs) are main sequence stars that appear bluer and more luminous than normal turnoff stars. They were originally singled out by using B-V and U-B colour cuts. Early studies found that a larger fraction of field BMPs stars were binaries compared to normal halo stars. Thus, BMP stars are ideal field blue straggler candidates for investigating internal stellar evolution processes and binary interaction. In particular, the presence or depletion in lithium in their spectra is a powerful indicator of their origin. They are either old, halo blue stragglers experiencing internal mixing processes or mass transfer (Li-depletion), or intermediate-age, single stars of possibly extragalactic origin (2.2dex halo plateau Li). However, we note that internal mixing processes can lead to an increased level of Li. Hence, this study combines photometry and spectroscopy to unveil the origin of various BMP stars. We first show how to separate binaries from young blue stars using photometry, metallicity and lithium. Using a sample of 80 BMP stars (T>6300K), we find that 97% of the BMP binaries have (V-Ks)0<1.08±0.03, while BMP stars that are not binaries lie above this cut in two thirds of the cases. This cut can help classify stars that lack radial velocities from follow-up observations. We then trace the origin of two BMP stars from the photometric sample by conducting a full chemical analysis using new high-resolution and high signal-to-noise spectra. Based on their radial velocities, Li, α and s- and r-process abundances we show that BPS CS22874-042 is a single star (A(Li)=2.38±0.10dex) while with A(Li)=2.23±0.07dex CD-48 2445 is a binary, contrary to earlier findings. Our analysis emphasises that field blue stragglers can be segregated from single metal-poor stars, using (V-Ks) colours with a fraction of single stars polluting the binary sample, but not vice versa. These two groups can only be properly separated by using information from stellar spectra, illustrating the need for accurate and precise stellar parameters and high-resolution, high-S/N spectra in order to fully understand and classify this intriguing class of stars. Our high-resolution spectrum analysis confirms the findings from the colour cuts and shows that CS 22874-042 is single, while CD -48 2445 is most likely a binary. Moreover, the stellar abundances show that both stars formed in situ; CS 22874-042 carry traces of massive star enrichment and CD -48 2445 shows indications of AGB mass transfer mixed with gases ejected possibly from neutron star mergers. Description: Line list used in our analysis. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table4.dat 34 466 Line list
See also: J/ApJ/667/1267 : CrI transition probabilities (Sobeck+, 2007) J/ApJS/214/26 : Line lists for CN isotopes transitions (Sneden+, 2014) Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 8 F8.3 0.1nm lambda Wavelength 11- 14 F4.1 --- Species Atomic number (element.ionisation state) 17- 22 F6.3 [-] loggf Oscillator strength 25- 29 F5.3 eV Ex Excitation potential 32- 34 A3 --- Ref Reference (1)
Note (1): References as follows: WIE = Wiese et al. (1996, Atomic transition probabilities of carbon, nitrogen, and oxygen : a critical data compilation) SNE = Sneden et al. (2014, Cat. J/ApJS/214/26) LAW = Lawler et al. (2001ApJ...556..452L, 2001ApJ...563.1075L) SOB = Sobeck et al. (2007, Cat. J/ApJ/667/1267) YAN = Yan et al. (1998, Phys. Rev. A, 57, 1652) GAL = Gallagher et al. (2012A&A...538A.118G) BER = Bergemann et al. (2012MNRAS.427...27B)
Acknowledgements: Camilla Juul Hansen, camillajuul(at)
(End) Patricia Vannier [CDS] 30-Jan-2017
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