Phosphorus Abundances in the Hyades and Galactic Disk

Abstract

We have measured phosphorus abundances in nine disk stars between -1 < [Fe/H] < -0.5 and in 12 members of the Hyades open cluster using two P I lines at 1.06 µm. High resolution infrared spectra were obtained using Phoenix on Gemini South and abundances were determined by comparing synthetic spectra to the observations. The average abundance for the dwarf stars in our Hyades sample was < [P/Fe] > = -0.01 ± 0.06 and < [P/Fe] > = 0.03 ± 0.03 dex for the three giants. The consistency suggests abundances derived using the 1.06 µm P I lines are not subjected to temperature or luminosity dependent systematic effects at high metallicities. Our [P/Fe] ratios measured in disk stars are consistent with chemical evolution models with P yields increased by a factor of 2.75. We find [P/O], [P/Mg], [P/Si] and [P/Ti] ratios are consistent with the solar ratio over a range of -1.0 < [Fe/H] < 0.2 with the [P/Si] ratio increasing by ∼ 0.1 -0.2 dex at the lowest [Fe/H] ratios. Finally, the evolution of [P/Fe] with age is similar to other α elements, providing evidence that P is produced at the same sites.

Phosphorus-rich stars with unusual abundances are challenging theoretical predictions

“…Fig. 1) which lead to a value of [P/Fe]~+0.6 in agreement with literature studies 13 . We also must emphasize that the N abundances are measured via the CN molecular lines and thus are strongly dependent on the O and C abundances because of molecular equilibrium.…”

“…Phosphorus is extremely difficult to measure in stellar spectra because its lines are inherently weak and are only available in the near-IR or UV spectral ranges, which very few high-resolution spectrographs can actually cover. The astronomical restrictions are such that only few recent studies [1][2][3][4][5][6][7][8][9][10][11][12][13] have succeeded in measuring phosphorus in other stars than the Sun. Fortunately, the APOGEE spectrograph 14 (see Methods: Searching for P-rich stars) operates in the near-IR (Hband) and thus offers a unique opportunity to detect and measure phosphorus from stellar spectra.…”

New Fe i Level Energies and Line Identifications from Stellar Spectra. III. Initial Results from UV, Optical, and Infrared Spectra

“…These include heavier elements past the iron peak represented primarily by UV lines (e.g., Peterson 2011;Roederer et al 2016), and those whose IR lines are weak but detectable (e.g., Cunha et al 2017). Also included are lighter elements with sparse spectra such as fluorine (e.g., Jönsson et al 2014;Pilachowski & Pace 2015;Abia et al 2019) and phosphorus (e.g., Maas et al 2019). Heavy and light elements elucidate nucleosynthesis processes and environments at early epochs (Sneden et al 2008), and the delayed contribution of evolved asymptotic giant-branch stars (Pilachowski & Pace 2015).…”

The Influence of Stellar Phosphorus On Our Understanding of Exoplanets and Astrobiology

“…Infrared abundances, i.e., from the 1053.24 and 1058.44 nm lines, were determined by Caffau et al (2011Caffau et al ( , 2016Caffau et al ( , 2019, with 0.04 dex, 0.04 dex, and 0.12 dex average uncertainties, respectively. Similarly, although using the 1058.1 and 1059.6 nm lines, Maas et al (2017) measured phosphorus in 22 stars, with an average 0.07 dex uncertainty and Maas et al (2019a) had an average uncertainty of 0.08 dex in 21 stars from the disk and Hyades cluster. Masseron et al (2020) used the APOGEE survey DR14 to measure neutral P lines at 1571.15 and 1648.29 nm for 30 stars likely originating from the Galactic thick disk or halo, with an average uncertainty of 0.15 dex.…”