${}^{18}$O${/}^{17}$O abundance ratio toward a sample of massive star forming regions with parallax distances

Abstract

The ${}^{18}$O${/}^{17}$O abundance ratio is, in principle, a powerful tool to estimate the relative contributions of massive stars and low- to intermediate-mass stars to the chemical enrichment of galaxies. We present ${}^{18}$O${/}^{17}$O ratios derived from simultaneous observations of C${}^{18}$O and C${}^{17}$O 1-0 toward fifty-one massive star forming regions with the Institut de Radioastronomie Millimétrique (IRAM) 30 meter telescope. Simultaneous observations of HC${}^{18}$O${}^{+}$ 1-0 and HC${}^{17}$O${}^{+}$ 1-0 with the Yebes 40m telescope toward five sources from this sample were also done to test the consistency of ${}^{18}$O${/}^{17}$O ratios derived from different isotopic pairs. From our improved measurements, resulting in smaller errors than previous work in the literature, we obtain a clear trend of increasing ${}^{18}$O${/}^{17}$O ratio with increasing galactocentric distance (D${}_{GC}$), which provides a significant constraint on Galactic chemical evolution (GCE) models. Current GCE models have to be improved in order to explain the observed C${}^{18}$O/C${}^{17}$O 1-0 gradient.

15 pages, 5 figures, 1 table, Accepted for publication in MNRAS

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