Saint Petersburg University of Aerospace Instrumentation
We fit various colour-magnitude diagrams (CMDs) of the high-latitude Galactic globular clusters NGC\,5024 (M53), NGC\,5053, NGC\,5272 (M3), NGC\,5466, and NGC\,7099 (M30) by isochrones from the Dartmouth Stellar Evolution Database and Bag of Stellar Tracks and Isochrones for α\alpha-enrichment [α\alpha/Fe]=+0.4=+0.4. For the CMDs, we use data sets from {\it Hubble Space Telescope}, {\it Gaia}, and other sources utilizing, at least, 25 photometric filters for each cluster. We obtain the following characteristics with their statistic uncertainties for NGC\,5024, NGC\,5053, NGC\,5272, NGC\,5466, and NGC\,7099, respectively: metallicities [Fe/H]=1.93±0.02=-1.93\pm0.02, 2.08±0.03-2.08\pm0.03, 1.60±0.02-1.60\pm0.02, 1.95±0.02-1.95\pm0.02, and 2.07±0.04-2.07\pm0.04 dex with their systematic uncertainty 0.1 dex; ages 13.00±0.1113.00\pm0.11, 12.70±0.1112.70\pm0.11, 11.63±0.0711.63\pm0.07, 12.15±0.1112.15\pm0.11, and 12.80±0.1712.80\pm0.17 Gyr with their systematic uncertainty 0.8 Gyr; distances (systematic uncertainty added) 18.22±0.06±0.6018.22\pm0.06\pm0.60, 16.99±0.06±0.5616.99\pm0.06\pm0.56, 10.08±0.04±0.3310.08\pm0.04\pm0.33, 15.59±0.03±0.5115.59\pm0.03\pm0.51, and 8.29±0.03±0.278.29\pm0.03\pm0.27 kpc; reddenings E(BV)=0.023±0.004E(B-V)=0.023\pm0.004, 0.017±0.0040.017\pm0.004, 0.023±0.0040.023\pm0.004, 0.023±0.0030.023\pm0.003, and 0.045±0.0020.045\pm0.002 mag with their systematic uncertainty 0.01 mag; extinctions AV=0.08±0.01A_\mathrm{V}=0.08\pm0.01, 0.06±0.010.06\pm0.01, 0.08±0.010.08\pm0.01, 0.08±0.010.08\pm0.01, and 0.16±0.010.16\pm0.01 mag with their systematic uncertainty 0.03 mag, which suggest the total Galactic extinction AV=0.08A_\mathrm{V}=0.08 across the whole Galactic dust to extragalactic objects at the North Galactic pole. The horizontal branch morphology difference of these clusters is explained by their different metallicity, age, mass-loss efficiency, and loss of low-mass members in the evolution of the core-collapse cluster NGC\,7099 and loose clusters NGC\,5053 and NGC\,5466.
We present new isochrone fits to the colour-magnitude diagrams of the Galactic globular clusters NGC\,6362 and NGC\,6723. We utilize 22 and 26 photometric filters for NGC\,6362 and NGC\,6723, respectively, from the ultraviolet to mid-infrared using data sets from {\it HST}, {\it Gaia}, unWISE, and other photometric sources. We use models and isochrones from the Dartmouth Stellar Evolution Database (DSED) and Bag of Stellar Tracks and Isochrones (BaSTI) for α\alpha-enhanced [α\alpha/Fe]=+0.4=+0.4 and different helium abundances. The metallicities [Fe/H]=1.04±0.07=-1.04\pm0.07 and 1.09±0.06-1.09\pm0.06 are derived from the red giant branch slopes in our fitting for NGC\,6362 and NGC\,6723, respectively. They agree with spectroscopic estimates from the literature. We find a differential reddening up to ΔE(BV)=0.13\Delta E(B-V)=0.13 mag in the NGC\,6723 field due to the adjacent Corona Australis cloud complex. We derive the following for NGC\,6362 and NGC\,6723, respectively: distances 7.75±0.03±0.157.75\pm0.03\pm0.15 (statistic and systematic error) and 8.15±0.04±0.158.15\pm0.04\pm0.15 kpc; ages 12.0±0.1±0.812.0\pm0.1\pm0.8 and 12.4±0.1±0.812.4\pm0.1\pm0.8 Gyr; extinctions AV=0.19±0.04±0.06A_\mathrm{V}=0.19\pm0.04\pm0.06 and 0.24±0.03±0.060.24\pm0.03\pm0.06 mag; reddenings E(BV)=0.056±0.01±0.02E(B-V)=0.056\pm0.01\pm0.02 and 0.068±0.01±0.020.068\pm0.01\pm0.02 mag. DSED provides systematically lower [Fe/H] and higher reddenings than BaSTI. However, the models agree in their relative estimates: NGC\,6723 is 0.44±0.040.44\pm0.04 kpc further, 0.5±0.10.5\pm0.1 Gyr older, ΔE(BV)=0.007±0.002\Delta E(B-V)=0.007\pm0.002 more reddened, and with 0.05±0.010.05\pm0.01 dex lower [Fe/H] than NGC\,6362. The lower metallicity and greater age of NGC\,6723 with respect to NGC\,6362 explain their horizontal branch morphology difference. This confirms age as the second parameter for these clusters. We provide lists of the cluster members from the {\it Gaia} Data Release 3.
We fit various colour-magnitude diagrams (CMDs) of the Galactic globular clusters NGC\,6397 and NGC\,6809 (M55) by isochrones from the Dartmouth Stellar Evolution Database (DSED) and Bag of Stellar Tracks and Isochrones (BaSTI) for α\alpha-enhanced [α\alpha/Fe]=+0.4=+0.4. For the CMDs, we use data sets from {\it HST}, {\it Gaia}, VISTA, and other sources utilizing 32 and 23 photometric filters for NGC\,6397 and NGC\,6809, respectively, from the ultraviolet to mid-infrared. We obtain the following characteristics for NGC\,6397 and NGC\,6809, respectively: metallicities [Fe/H]=1.84±0.02±0.1=-1.84\pm0.02\pm0.1 and 1.78±0.02±0.1-1.78\pm0.02\pm0.1 (statistic and systematic uncertainties); distances 2.45±0.02±0.062.45\pm0.02\pm0.06 and 5.24±0.02±0.185.24\pm0.02\pm0.18 kpc; ages 12.9±0.1±0.812.9\pm0.1\pm0.8 and 13.0±0.1±0.813.0\pm0.1\pm0.8 Gyr; reddenings E(BV)=0.178±0.006±0.01E(B-V)=0.178\pm0.006\pm0.01 and 0.118±0.004±0.010.118\pm0.004\pm0.01 mag; extinctions AV=0.59±0.01±0.02A_\mathrm{V}=0.59\pm0.01\pm0.02 and 0.37±0.01±0.040.37\pm0.01\pm0.04 mag; extinction-to-reddening ratio RV=3.320.28+0.32R_\mathrm{V}=3.32^{+0.32}_{-0.28} and 3.160.56+0.663.16^{+0.66}_{-0.56}. Our estimates agree with most estimates from the literature. BaSTI gives systematically higher [Fe/H] and lower reddenings than DSED. Despite nearly the same metallicity, age, and helium enrichment, these clusters show a considerable horizontal branch (HB) morphology difference, which must therefore be described by another parameter. This parameter must predominantly explain why the least massive HB stars (0.58-0.63 solar masses) are only found within NGC 6809. Probably they have been lost by the core-collapse cluster NGC\,6397 during its dynamical evolution and mass segregation. In contrast, NGC\,6809 has a very low central concentration and, hence, did not undergo this process.
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