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Post Info TOPIC: BD +44 493
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RE: BD +44 493
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Title: Hubble Space Telescope Near-Ultraviolet Spectroscopy of the Bright CEMP-no Star BD+44 493
Author: Vinicius Placco, Timothy Beers, Ian Roederer, John Cowan, Anna Frebel, Dan Filler, Inese I. Ivans, James E. Lawler, Hendrik Schatz, Christopher Sneden, Jennifer Sobeck, Wako Aoki, Verne Smith

We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the extremely metal-poor star BD+44 493, a 9th magnitude sub-giant with [Fe/H] = -3.8 and enhanced carbon, based on data acquired with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. This star is the brightest example of a class of objects that, unlike the great majority of carbon-enhanced metal-poor (CEMP) stars, does not exhibit over-abundances of heavy neutron-capture elements (CEMP-no). In this paper, we validate the abundance determinations for a number of species that were previously studied in the optical region, and obtain strong upper limits for beryllium and boron, as well as for neutron-capture elements from zirconium to platinum, many of which are not accessible from ground-based spectra. The boron upper limit we obtain for BD+44 493, logeps(B) < -0.70, the first such measurement for a CEMP star, is the lowest yet found for very and extremely metal-poor stars. In addition, we obtain even lower upper limits on the abundances of beryllium, logeps(Be) < -2.3, and lead, logeps(Pb) < -0.23 ([Pb/Fe] < +1.90), than those reported by previous analyses in the optical range. Taken together with the previously measured low abundance of lithium, the very low upper limits on Be and B suggest that BD+44 493 was formed at a very early time, and that it could well be a bona-fide second-generation star. Finally, the Pb upper limit strengthens the argument for non-s-process production of the heavy-element abundance patterns in CEMP-no stars.

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Title: Chemical Analysis of the Ninth Magnitude Carbon-Enhanced Metal-Poor Star BD+44 493
Authors: H. Ito, W. Aoki, T.C. Beers, N. Tominaga, S. Honda

We present detailed chemical abundances for the bright carbon-enhanced metal-poor (CEMP) star BD+44 493, previously reported on by Ito et al. Our measurements confirm that BD+44 493 is an extremely metal-poor ([Fe/H]=-3.8) subgiant star with excesses of carbon and oxygen. No significant excesses are found for nitrogen and neutron-capture elements (the latter of which place it in the CEMP-no class of stars). Other elements that we measure exhibit abundance patterns that are typical for non-CEMP extremely metal-poor stars. No evidence for variations of radial velocity have been found for this star. These results strongly suggest that the carbon enhancement in BD+44 493 is unlikely to have been produced by a companion asymptotic giant-branch star and transferred to the presently observed star, nor by pollution of its natal molecular cloud by rapidly-rotating, massive, mega metal-poor ([Fe/H] < -6.0) stars. A more likely possibility is that this star formed from gas polluted by the elements produced in a "faint" supernova, which underwent mixing and fallback, and only ejected small amounts of elements of metals beyond the lighter elements. The Li abundance of BD+44 493 (A(Li)=log(Li/H)+12=1.0) is lower than the Spite plateau value, as found in other metal-poor subgiants. The upper limit on Be abundance (A(Be)=log(Be/H)+12<-1.8) is as low as those found for stars with similarly extremely-low metallicity, indicating that the progenitors of carbon- (and oxygen-) enhanced stars are not significant sources of Be, or that Be is depleted in metal-poor subgiants with effective temperatures of ~5400K.

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HIP 11396
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A Ninth-Magnitude Messenger from the Early Universe
Old stars are keys to understanding the nature of the first stars and the earliest stages of the formation of the universe. Observations with the Subaru Telescope, fitted with its High Dispersion Spectrograph (HDS), have yielded data about the chemical composition of an old, bright star - BD+44 493 - that shed light on how the early stars may have developed during the infancy of the universe.

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Position(2000): RA 02 26 49.7395, Dec +44 57 46.506

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BD +44 493
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Title: BD +44 493: A Ninth Magnitude Messenger from the Early Universe; Carbon Enhanced and Beryllium Poor
Authors: Hiroko Ito, Wako Aoki, Satoshi Honda, Timothy C. Beers

We present a 1D LTE chemical abundance analysis of the very bright (V=9.1) Carbon-Enhanced Metal-Poor (CEMP) star BD +44 493, based on high-resolution, high signal-to-noise spectra obtained with Subaru/HDS. The star is shown to be a subgiant with an extremely low iron abundance ([Fe/H]=-3.7), while it is rich in C ([C/Fe]=+1.3) and O ([O/Fe]=+1.6). Although astronomers have been searching for extremely metal-poor stars for decades, this is the first star found with [Fe/H]<-3.5 and an apparent magnitude V<12. Based on its low abundances of neutron-capture elements (e.g., [Ba/Fe]=-0.59), BD +44 493 is classified as a "CEMP-no" star. Its abundance pattern implies that a first-generation faint supernova is the most likely origin of its carbon excess, while scenarios related to mass loss from rapidly-rotating massive stars or mass transfer from an AGB companion star are not favoured. From a high-quality spectrum in the near-UV region, we set an very low upper limit on this star's beryllium abundance (A(Be)=log(Be/H)+12<-2.0), which indicates that the decreasing trend of Be abundances with lower [Fe/H] still holds at [Fe/H]<-3.5. This is the first attempt to measure a Be abundance for a CEMP star, and demonstrates that high C and O abundances do not necessarily imply high Be abundances.

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