Identifying Multiple Populations in M71 Using CN

Abstract

We have observed the CN features at ∼3800Å and 4120Å as well as the CH band at ∼4300Å for 145 evolved stars in the Galactic globular cluster M71 using the multi-object spectrograph, Hydra, on the WIYN-3.5m telescope. We use these measurements to create two δCN indices finding that both distributions are best fit by two populations, a CN-enhanced and CN-normal. We find that 42 ± 4% of the RGB stars in our sample are CN-enhanced. The percentage of CN-enhanced is 40 ± 13% for the AGB and 33 ± 9% for the HB stars, which suggests there are no missing second generation stars at these stages of stellar evolution. The two generations also separate in magnitude and color on the HB, which allows us to find the difference in He abundance between the two populations by fitting appropriate ZAHBs. The broad range of distances from the cluster's center covered by our sample allows us to study the dependence of the ratio of the number of first to second population stars on the distance from the cluster's center, and we find that this ratio does not vary radially and that the two populations are spatially mixed. Finally, we compare our identification of multiple populations with the classification based on the Na-O anti-correlation and the HST UV photometry, and we find good agreement with both methods.

The rotation of selected globular clusters and the differential rotation of M3 in multiple populations from the SDSS-IV APOGEE-2 survey

“…Observational evidence have showed differences in spatial distribution between FG and SG stars. For dynamically younger clusters, the SG is more concentrated than the FG (Sollima et al 2007;Bellini et al 2009;Lardo et al 2011;Cordero et al 2014;Boberg, Friel, & Vesperini 2016;Lee 2017;Gerber, Friel, & Vesperini 2020). On the other hand, the two generations are completely mixed in globular clusters with more advanced evolutionary stages (Dalessandro et al 2014;Nardiello et al 2015;Cordero et al 2015;Gerber, Friel, & Vesperini 2018.…”

Multiple populations in low mass globular clusters: Palomar 13

“…Since our estimation of CN and CH spectral indices partially depends on the spectral shape, we carefully calibrated the observed 1d spectra based on their stellar model spectra in the following steps. This calibration procedure was partially inspired by the work of Gerber et al (2020). In order to generate model spectra, stellar parameters are required.…”

Simulations of globular clusters within their parent galaxies: multiple stellar populations and internal kinematics

“…47 Tuc in Milone et al 2018 andNGC3201 in Carretta et al 2010a), equivalent concentrations of 1G and 2G stars (e.g. M71 in Gerber et al 2020) and on rarer occasions, a centrally concentrated 1G (i.e. M15 in Larsen et al 2015 or M80 in Dalessandro et al 2018).…”