A Study of the Elements Copper Through Uranium in Sirius A: Contributions From Stis and Ground-Based Spectra

Abstract

We determine abundances or upper limits for all of the 55 stable elements from copper to uranium for the A1 Vm star Sirius. The purpose of the study is to assemble the most complete picture of elemental abundances with the hope of revealing the chemical history of the brightest star in the sky, apart from the Sun. We also explore the relationship of this hot metallic-line (Am) star to its cooler congeners, as well as the hotter, weakly-or non-magnetic mercury-manganese (HgMn) stars. Our primary observational material consists of Hubble Space Telescope (HST ) spectra taken with the Space Telescope Imaging Spectrograph (STIS) in the ASTRAL project. We have also used archival material from the COP ERN ICU S satellite, and from the HST Goddard High-Resolution Spectrograph (GHRS), as well as ground-based spectra from Furenlid, Westin, Kurucz, Wahlgren, and their coworkers, ESO spectra from the UVESPOP project, and NARVAL spectra retrieved from PolarBase. Our analysis has been primarily by spectral synthesis, and in this work we have had the great advantage of extensive atomic data unavailable to earlier workers. We find most abundances as well as upper limits range from 10 to 100 times above solar values. We see no indication of the huge abundance excesses of 1000 or more that occur among many chemically peculiar (CP) stars of the upper main sequence. The picture of Sirius as a hot Am star is reinforced.

Detection of Pb II in the Ultraviolet Spectra of Three Metal-Poor Stars

“…These spectra show the Pb ii line at 2203.534 Å, which is the only Pb ii transition accessible in near-UV, optical, or near-infrared spectra of late-type stars. This line has been observed previously in the spectra of a few chemically-peculiar Atype stars (e.g., Faraggiana 1989;Cowley et al 2016). Previous attempts (Roederer et al 2014b) to detect the Pb ii line in STIS E230M spectra (R ≡ λ/∆λ = 30,000) of metal-poor stars have been unsuccessful.…”

The Sirius System and Its Astrophysical Puzzles: Hubble Space Telescope and Ground-based Astrometry∗

“…However, L11, and earlier Richer et al (2000), suggested that the abundance patterns, in particular deficiencies of C and O, and near-solar N, are at least qualitatively consistent with accretion of CNO-processed material having occurred at the time SiriusB was an AGB star. The enrichments of the heavy elements Sr, Y, Zr, and Ba found by L11 (3-30 times solar), and of Cu and heavier elements found by Cowley et al (2016; generally 10-100 times solar), may also be indicative of accretion of s-process elements. In addition, any mass accretion might have resulted in helium enrichment of the atmosphere, which would increase element abundance ratios relative to hydrogen.…”

“…It is a hot WD with a purehydrogen photosphere and a spectral type of DA2. The classical spectral type of Sirius A is A1 V (Morgan et al 1953), but high-resolution spectra reveal surface overabundances of heavy elements by factors of as much as ∼10 to 100 relative to solar (e.g., Cowley et al 2016 and references therein). Thus Sirius A is generally considered to be a hot metallic-line (Am) star.…”

The effect of hyperfine splitting on Stark broadening for three blue-green Cu i lines in laser-induced plasma

“…Since it is hardly possible to study all the necessary parameters within a single work, we focused on selected copper lines for the following reasons. Copper is present in stellar atmospheres in a considerable amount and is usually involved in studies of stellar metallicities (Mishenina et al 2011;Cowley et al 2016), classification of stars and evolution of the Galaxy (Yan et al 2015). The astrophysical site for the synthesis of copper is not yet well established (Shi et al 2014), and future research is required.…”