DETECTION OF NEUTRAL PHOSPHORUS IN THE NEAR-ULTRAVIOLET SPECTRA OF LATE-TYPE STARS

Abstract

We report the detection of several absorption lines of neutral phosphorus (P, Z = 15) in archival near-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We derive phosphorus abundances or interesting upper limits in 14 late-type stars with metallicities spanning –3.8 < [Fe/H] <–0.1. Previously, phosphorus had only been studied in Galactic stars with –1.0 < [Fe/H] <+0.3. Iron lines reveal abundance offsets between the optical and ultraviolet regions, and we discuss and apply a correction factor to account for this offset. In stars with [Fe/H] >–1.0, the [P/Fe] ratio decreases toward the solar value with increasing metallicity, in agreement with previous observational studies. In stars with [Fe/H] <–1.0, <[P/Fe]> = +0.04 ± 0.10, which overlaps with the [P/Fe] ratios found in several high-redshift damped Lyman-α systems. This behavior hints at a primary origin in massive stars.