38 K giants phosphorus abundance

We have observed full H- and K-band spectra at a spectral resolving power of R=45000 with IGRINS mounted on the Gemini South telescope, the Discovery Channel Telescope, and the Harlan J Smith Telescope at McDonald Observatory. Abundances were determined from spectral lines by modeling the synthetic spectrum that best matches the observed spectrum by chi-square minimization. For this task, we used the Spectroscopy Made Easy (SME) tool in combination with one-dimensional (1D) Model Atmospheres in a Radiative and Convective Scheme (MARCS) stellar atmosphere models.

The investigated sample of stars have reliable stellar parameters estimated using optical FIber-fed Echelle Spectrograph (FIES) spectra obtained in a previous study of a set of stars called GIants in the Local Disk (GILD). In order to determine the phosphorus abundances from the 16482.92 Angstrom phosphorus line, we needed to take special care blending the CO(7-4) line. With the stellar parameters known, we thus determined the C, N, and O abundances from atomic carbon and a range of nonblended molecular lines (CO, CN, and OH) which are plentiful in the H-band region of K giant stars, assuring an appropriate modeling of the blending CO(7-4) line.

We present the [P/Fe] versus [Fe/H] trend for K giant stars in the metallicity range of -1.2dex<[Fe/H]<0.4dex and enhanced phosphorus abundances for two metal-poor s-rich stars. We find that our trend matches well with the compiled literature sample of prominently dwarf stars and the limited number of giant stars. Our trend is found to be higher by 0.05-0.1dex compared to the theoretical chemical evolution trend resulting from the core collapse supernova (type II) of massive stars with the phosphorus yields arbitrarily increased by a factor of 2.75.

Thus the enhancement factor might need to be 0.05-0.1dex higher to match our trend. We also find an empirically determined primary behavior for phosphorus. Furthermore, the phosphorus abundance is found to be elevated by 0.6-0.9dex in the two s-enriched stars compared to the theoretical chemical evolution trend.