Ages and chemical compositions of massive clusters in NGC147 and M31

Abstract

We present estimates of ages, [Fe/H], helium content (Y) and abundances of C, N, Mg, Ca, and several other elements for the following globular clusters (GCs): GC7 in NGC147, and Mayall II, Mackey 1 and Mackey 6 in M31. Medium-resolution integrated-light spectra of the GCs were conducted with the 6m telescope. To derive the ages and abundances for the GCs we carried out their population synthesis using model stellar atmospheres, the Padova YZVAR isochrones and the Chabrier mass function. We compare the results with the corresponding data obtained using the same method for several massive Galactic GCs. We show that the differences in the light-element abundances between GCs with similar ages and metallicities may reach 0.5-0.6 dex. The corresponding differences for other elements are usually 2-3 times smaller. We suggest that at least partially the detected differences may be due to light-element abundance variations in the atmospheres of high-luminosity red giant branch stars as a consequence of the transportation of the produced elements to the surface layers.

Age and chemical composition of the globular cluster NGC 6652

“…The determined metallicity is 0.2 − 0.3 dex lower than the literature value (Zinn & West 1984). This systematic deviation is specific for our analysis (Sharina & Shimansky 2019). We argue that several hot HB stars contribute to the spectrum of NGC 6652 (Schiavon et al 2005).…”

“…In this section, we illustrate the comparison between synthetic spectra computed using our method (see Sharina & Shimansky 2019;Sharina et al 2018;Sharina et al 2017 and references therein), elemental abundances listed in Table 1, and different isochrones and the comparison between IL spectrum of NGC 6652 (Schiavon et al 2005), and the synthetic spectra computed applying different MFs: the Ch05 (equation 2 in that paper) and the Salpeter (1955) MFs. .2 shows a comparison between the observed continuum normalized spectrum of NGC 6652 and the synthetic IL spectra computed using the same isochrone and elemental abundances but different MFs.…”

“…We employ the IL spectrum of the Galactic GC NGC 6652 (Schiavon et al 2005) and our method (see e.g., Sharina & Shimansky 2019;Sharina et al 2018;Sharina et al 2017) to derive the age ∼ 13.6 ± 1 Gyr, Y = 0.26 ± 0.2, [Fe/H] = −1.2 ± 0.1 dex and abundances of chemical elements: C, N, O, Na, Mg, Ca, Ti, C and Mn. We conclude that the Ch05 MF and the isochrone Z = 0.002, Y = 0.26, log(age) = 10.15 (B08) allow us to reproduce well the shapes and intensities of the Balmer absorption lines in the observed spectrum.…”

“…In this work, we make use of the integrated spectrum of NGC 6652 from Schiavon et al (2005) and our population synthesis method (Sharina & Shimansky 2019;Sharina et al 2018;Sharina et al 2017 and references therein) to derive the helium mass fraction (Y), age and abundances of several chemical elements.…”