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تسجيل مستخدم جديدA near-infrared and optical photometric study of the Sculptor dwarf spheroidal galaxy: implications for the metallicity spread
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We present here a detailed study of the Sculptor dSph galaxy red giant branch (RGB) and horizontal branch (HB) morphology, combining new near-infrared photometry from CIRSI, with optical data from the ESO WFI. For a Sculptor-like old and generally metal-poor system, the position of RGB stars on the colour-magnitude diagram is mainly metallicity dependent. The advantage of using optical-NIR colours is that the position of the RGB locus is much more sensitive to metallicity than with optical colours alone. In contrast the horizontal branch (HB) morphology is strongly dependent on both metallicity and age. Therefore a detailed study of both the RGB in optical-NIR colours and the HB can help break the age-metallicity degeneracy. Our measured photometric width of the Sculptor giant branch corresponds to a range in metallicity of 0.75 dex. We detect the RGB and AGB bumps in both the NIR and optical luminosity functions, and derive from them a mean metallicity of [M/H] = -1.3 +/- 0.1. From isochrone fitting we derive a mean metallicity of [Fe/H] = -1.42 with a dispersion of 0.2 dex. These photometric estimators are for the first time consistent with individual metallicity measurements derived from spectroscopic observations. No spatial gradient is detected in the RGB morphology within a radius of 13 arcmin, twice the core radius. On the other hand, a significant gradient is observed in the HB morphology index, confirming the `second parameter problem present in this galaxy. These observations are consistent with an early extended period of star formation continuing in time for a few Gyr. (Abridged)
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We present abundances for seven stars in the (extremely) low-metallicity tail of the Sculptor dwarf spheroidal galaxy, from spectra taken with X-shooter on the ESO VLT. Targets were selected from the Ca II triplet (CaT) survey of the Dwarf Abundances
and Radial Velocities Team (DART) using the latest calibration. Of the seven extremely metal-poor candidates, five stars are confirmed to be extremely metal-poor (i.e., [Fe/H]<-3 dex), with [Fe/H]=-3.47 +/- 0.07 for our most metal-poor star. All are around or below [Fe/H]=-2.5 dex from the measurement of individual Fe lines. These values are in agreement with the CaT predictions to within error bars. None of the seven stars is found to be carbon-rich. We estimate a 2-13% possibility of this being a pure chance effect, which could indicate a lower fraction of carbon-rich extremely metal-poor stars in Sculptor compared to the Milky Way halo. The [alpha/Fe] ratios show a range from +0.5 to -0.5, a larger variation than seen in Galactic samples although typically consistent within 1-2sigma. One star seems mildly iron-enhanced. Our program stars show no deviations from the Galactic abundance trends in chromium and the heavy elements barium and strontium. Sodium abundances are, however, below the Galactic values for several stars. Overall, we conclude that the CaT lines are a successful metallicity indicator down to the extremely metal-poor regime and that the extremely metal-poor stars in the Sculptor dwarf galaxy are chemically more similar to their Milky Way halo equivalents than the more metal-rich population of stars.
We present the high resolution spectroscopic study of five -3.9<=[Fe/H]<=-2.5 stars in the Local Group dwarf spheroidal, Sculptor, thereby doubling the number of stars with comparable observations in this metallicity range. We carry out a detailed an
alysis of the chemical abundances of alpha, iron peak, light and heavy elements, and draw comparisons with the Milky Way halo and the ultra faint dwarf stellar populations. We show that the bulk of the Sculptor metal-poor stars follows the same trends in abundance ratios versus metallicity as the Milky Way stars. This suggests similar early conditions of star formation and a high degree of homogeneity of the interstellar medium. We find an outlier to this main regime, which seems to miss the products of the most massive of the TypeII supernovae. In addition to its value to help refining galaxy formation models, this star provides clues to the production of cobalt and zinc. Two of our sample stars have low odd-to-even barium isotope abundance ratios, suggestive of a fair proportion of s-process; we discuss the implication for the nucleosynthetic origin of the neutron capture elements.
Based on a carefully constructed sample of dwarf stars, a new optical-near infrared photometric calibration to estimate the metallicity of late-type K and early-to-mid-type M dwarfs is presented. The calibration sample has two parts; the first part i
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We present a new distance estimation for the Milky Way dwarf spheroidal satellite Sculptor obtained from multi-epoch mid-infrared observations of RR Lyrae stars. The 3.6 {mu}m observations have been acquired with the Infrared Array Camera on board th
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