Chemical abundances in giants stars of the tidally disrupted globular cluster NGC 6712 from high-resolution infrared spectroscopy

摘要

We present abundances of C, N, O, F, Na, and Fe in six giant stars of thetidally disrupted globular cluster NGC 6712. The abundances were derived bycomparing synthetic spectra with high resolution infrared spectra obtained withthe Phoenix spectrograph on the Gemini South telescope. We find largestar-to-star abundance variations of the elements C, N, O, F, and Na. NGC 6712and M4 are the only globular clusters in which F has been measured in more thantwo stars, and both clusters reveal F abundance variations whose amplitude iscomparable to, or exceeds, that of O, a pattern which may be produced in M >5M_sun AGB stars. Within the limited samples, the F abundance in globularclusters is lower than in field and bulge stars at the same metallicity. NGC6712 and Pal 5 are tidally disrupted globular clusters whose red giant membersexhibit O and Na abundance variations not seen in comparable metallicity fieldstars. Therefore, globular clusters like NGC 6712 and Pal 5 cannot contributemany field stars and/or field stars do not form in environments with chemicalenrichment histories like that of NGC 6712 and Pal 5. Although our sample sizeis small, from the amplitude of the O and Na abundance variations, we infer alarge initial cluster mass and tentatively confirm that NGC 6712 was once oneof the most massive globular clusters in our Galaxy.