A Spectroscopic Survey of Field Red Horizontal-branch Stars

Abstract

A metallicity, chemical composition, and kinematic survey has been conducted for a sample of 340 candidate field red horizontal branch stars. High resolution, high signal-to-noise spectra were gathered with the McDonald Observatory 2.7m Tull and the Hobby-Eberly Telescope echelle spectrographs, and were used to determine effective temperatures, surface gravities, microturbulent velocities, [Fe/H] metallicities, and abundance ratios [X/Fe] for seven α and Fe-group species. The derived temperatures and gravities confirm that at least half of the candidates are true RHB stars, with (average) parameters T eff ∼ 5000 K, log g ∼ 2.5. From the α abundances alone the thin and thick Galactic populations are apparent in our sample. Space motions for 90% of the program stars were computed from Hipparcos and Gaia parallaxes and proper motions. Correlations between chemical compositions and Galactic kinematics clearly indicate the existence of both thin and thick disk RHB stars.

On the Use of Field RR Lyrae as Galactic Probes. III. The α-element Abundances*

“…Moreover, we selected several lines that could be measured over a significant fraction of the range in iron covered by the current RRL sample in order to verify that no systematic differences between different lines and chemical species influenced the trend in the [α/Fe] versus [Fe/H] plane. Finally, we also performed a comparison with spectroscopic standards (Arcturus) and with field metal-rich red HB stars (Afs , ar et al 2018). We found that our iron and α-element abun-dances are, within the errors, in remarkable agreement with similar estimates available in the literature.…”

The R-Process Alliance: A Comprehensive Abundance Analysis of HD 222925, a Metal-poor Star with an Extreme R-process Enhancement of [Eu/H] = −0.14*

“…We prioritize comparisons with analyses of large numbers of RHB stars in the field, which may help to minimize systematic uncertainties. Abundance ratios from the RHB star samples of Preston et al (2006), For & Sneden (2010), Roederer et al (2014a), and Afşar et al (2012Afşar et al ( , 2018 Battistini & Bensby (2015, and Hansen et al (2018) are shown by small gray dots in Figure 2. Figure 2 demonstrates that the abundances of elements with Z ≤ 30 in HD 222925 match those of other metal-poor field stars with −2 < [Fe/H] < −1.…”

“…Comparison of abundance ratios in HD 222925 (large black circle) with other field stars. The small gray crosses represent RHB stars from Preston et al (2006),For & Sneden (2010),Roederer et al (2014a), andAfşar et al (2012Afşar et al ( , 2018. The small gray dots represent dwarfs and giants fromBensby et al (2014),Roederer et al (2014a),Jacobson et al (2015),Battistini & Bensby (2015), and Hansen et al (2018.…”

Chemical Compositions of Red Giant Stars from Habitable Zone Planet Finder Spectroscopy

“…However, the RHB status of HIP 33578 is shared by many wkG stars. From its T eff = 5118 K and its photometry and parallax given in Afşar et al (2018a) we suggest that log(L/L 2.5, in the middle of the set of warmer wkG stars shown in the HR diagrams of Palacios et al (2016) (see their Figures 7 and 8). We tentatively assign HIP 33578 to the wkG subclass.…”

“…Girardi 2016). Afşar et al (2018a) (here after Afşar18a) have studied the detailed chemical compositions and kinematics of a sample of 340 candidate field RHB stars in the optical spectral region (3400−10900 Å). Their chemo-kinematical analysis of these candidates revealed the presence of more than 150 field RHB and RC stars, located both in the thin and thick disk of the Galaxy.…”