Estimation of Stellar Metal Abundance. II : A Recalibration of the Ca II K Technique, and the Autocorrelation Function Method

Original article can be found at: http://www.iop.org/EJ/journal/aj Copyright American Astronomical Society DOI: 10.1086/300727 [Full text of this article is not available in the UHRA]We have recalibrated a method for the estimation of stellar metal abundance, parameterized as [Fe/H], based on medium-resolution (1–2 Å) optical spectra (the majority of which cover the wavelength range 3700–4500 Å). The equivalent width of the Ca II K line (3933 Å) as a function of [Fe/H] and broadband B-V color, as predicted from spectrum synthesis and model atmosphere calculations, is compared with observations of 551 stars with high-resolution abundances available from the literature (a sevenfold increase in the number of calibration stars that were previously available). A second method, based on the Fourier autocorrelation function technique first described by Ratnatunga & Freeman, is used to provide an independent estimate of [Fe/H], as calibrated by comparison with 405 standard-star abundances. Metallicities based on a combination of the two techniques for dwarfs and giants in the color range 0.30 ≤ (B-V)0 ≤ 1.2 exhibit an external 1 σ scatter of approximately 0.10–0.20 dex over the abundance range -4.0 ≤ [Fe/H] ≤ 0.5. Particular attention has been given to the determination of abundance estimates at the metal-rich end of the calibration, where our previous attempt suffered from a considerable zero-point offset. Radial velocities, accurate to approximately 10 km s-1, are reported for all 551 calibration stars.Peer reviewe

Baade’s window and APOGEE: Metallicities, ages, and chemical abundances

International audienceContext. Baade’s window (BW) is one of the most observed Galactic bulge fields in terms of chemical abundances. Owing to its low and homogeneous interstellar absorption it is considered the perfect calibration field for Galactic bulge studies.Aims. In the era of large spectroscopic surveys, calibration fields such as BW are necessary for cross calibrating the stellar parameters and individual abundances of the APOGEE survey.Methods. We use the APOGEE BW stars to derive the metallicity distribution function (MDF) and individual abundances for α- and iron-peak elements of the APOGEE ASPCAP pipeline (DR13), as well as the age distribution for stars in BW.Results. We determine the MDF of APOGEE stars in BW and find a remarkable agreement with that of the Gaia-ESO survey (GES). Both exhibit a clear bimodal distribution. We also find that the Mg-metallicity planes of the two surveys agree well, except for the metal-rich part ([Fe/H] > 0.1), where APOGEE finds systematically higher Mg abundances with respect to the GES. The ages based on the [C/N] ratio reveal a bimodal age distribution, with a major old population at ~ 10 Gyr, with a decreasing tail towards younger stars. A comparison of stellar parameters determined by APOGEE and those determined by other sources reveals detectable systematic offsets, in particular for spectroscopic surface gravity estimates. In general, we find a good agreement between individual abundances of O, Na, Mg, Al, Si, K, Ca, Cr, Mn, Co, and Ni from APOGEE with that of literature values.Conclusions. We have shown that in general APOGEE data show a good agreement in terms of MDF and individual chemical abundances with respect to literature works. Using the [C/N] ratio we found a significant fraction of young stars in BW

The Role of Culture and Gender in E-commerce Entrepreneurship: Three Jordanian Case Studies

The number of entrepreneurs using e-commerce to start their own online business up is continuously growing. In this chapter, the current literature on e-commerce entrepreneurship is reviewed and attention is paid to the situation in Jordan, a representative Middle East and Northern Africa (MENA) country. In particular, our focus is on the role of culture and gender on local potential, nascent and new e-entrepreneurs. Three Jordan case studies are presented (ZINC, Oasis500 and CashBasha), showing an increased attention and support for entrepreneurship in general, and e-entrepreneurship in particular, in Jordan. In addition, some special programs are aimed at promoting women e-entrepreneurship, since it is seen as a way to overcome some of the cultural barriers to female entrepreneurial activity