Metallicity and distance of NGC 6362 from its RR Lyrae and SX Phoenicis stars

Ferro, A. Arellano; Ahumada, J. A.; Fierro, I. H. Bustos; Calderón, J. H.; Morrell, N.

doi:10.1002/asna.201813465

Cited by 5 publications

(1 citation statement)

References 48 publications

(63 reference statements)

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“…Only one RRab is known and two double-mode or RRd stars are also present. The distribution of RRab-RRc stars shows a clear segregation around the first overtone red edge, represented as a vertical dashed line identified in several other clusters, which seems to be the rule among OoII clusters (Arellano Ferro et al 2018). A parameter that helps to describe the morphology of the HB is the Lee index (Lee 1990) defined as L = (B-R)/(B+V+R), where B and R are the number of stars to the blue or red sides of the instability strip respectively, and V is the number of variable stars within the instability strip.…”

Section: The Structure Of the Horizontal Branch Of M13mentioning

confidence: 73%

A new study of the variable star population in the Hercules globular cluster (M13; NGC 6205)★

Deras

Ferro

Lázaro

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present the results from V I CCD time-series photometry of the globular cluster M13 (NGC 6205). From the Fourier decomposition of the light curves of RRab and RRc stars we found an average metallicity of [Fe/H]zw = -1.58 ± 0.09. The distance to the cluster was estimated as 7.1 ± 0.1 kpc from independent methods related to the variable star families RR Lyrae, SX Phe and W Virginis, from the luminosity of the theoretical ZAHB and from the orbit solution of a newly discovered contact binary star. The RR Lyrae pulsation modes are segregated by the red edge of the first overtone instability strip in this OoII type cluster. A membership analysis of 52,800 stars in the field of the cluster is presented based on Gaia-DR2 proper motions which enabled the recognition of 23,070 likely cluster members, for 7,630 of which we possess V I photometry. The identification of member stars allowed the construction of a clean CMD and a proper ZAHB and isochrone fitting, consistent with a reddening, age and distance of 0.02 mag, 12.6 Gyrs and 7.1 kpc respectively. We report seven new variables; one RRc, two SX Phe stars, three SR and one contact binary. V31 presents double-mode nature and we confirm V36 as RRd. Fifteen variable star candidates are also reported. The analysis of eighteen stars in the field of the cluster, reported as RR Lyrae from the Gaia-DR2 data base reveals that at least seven are not variable. We noted the presence of a high velocity star in the field of the cluster.

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Section: The Structure Of the Horizontal Branch Of M13mentioning

confidence: 73%

A new study of the variable star population in the Hercules globular cluster (M13; NGC 6205)★

Deras

Ferro

Lázaro

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Isochrone fitting of Galactic globular clusters – IV. NGC 6362 and NGC 6723

Gontcharov

Khovritchev

Mosenkov

et al. 2022

Monthly Notices of the Royal Astronomical Society

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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 HST, 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–enhanced [α/Fe]=+0.4 and different helium abundances. The metallicities [Fe/H]=−1.04 ± 0.07 and −1.09 ± 0.06 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(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 ± 0.15 (statistic and systematic error) and 8.15 ± 0.04 ± 0.15 kpc; ages 12.0 ± 0.1 ± 0.8 and 12.4 ± 0.1 ± 0.8 Gyr; extinctions AV = 0.19 ± 0.04 ± 0.06 and 0.24 ± 0.03 ± 0.06 mag; reddenings E(B − V) = 0.056 ± 0.01 ± 0.02 and 0.068 ± 0.01 ± 0.02 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 ± 0.04 kpc further, 0.5 ± 0.1 Gyr older, ΔE(B − V) = 0.007 ± 0.002 more reddened, and with 0.05 ± 0.01 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 Gaia Data Release 3.

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Gaia parallax of Milky Way globular clusters – A solution of mixture model

Shao

2019

Monthly Notices of the Royal Astronomical Society

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We have established a mixture model approach to derive the parallax of the Milky Way globular clusters. It avoids the problem of cluster membership determination and provides a completely independent astrometrical solution by purely using the parallax data. This method is validated with simulated clusters of Pancino et al. (2017). We have resolved 120 real globular clusters by the mixture model using parallaxes of the second data release of Gaia . They construct the largest direct parallax sample up to now. In comparing with other direct parallax results based on cluster members, including 75 clusters of Gaia Collaboration et al. (2018), our method presents its accuracy, especially for some particular clusters. A systematic offset of −27.6 ± 1.7 µas, together with a scatter of 22.8 ± 1.3 µas is found in comparing with other indirect parallax measurements. They are consistent with the global value and the variation of the zero-point of current Gaia parallaxes. Distances of several specific nearby globular clusters are discussed while the closest ones can reach high precisions, even taking the systematic error into account.

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Metallicity and distance of NGC 6362 from its RR Lyrae and SX Phoenicis stars

Cited by 5 publications

References 48 publications

A new study of the variable star population in the Hercules globular cluster (M13; NGC 6205)★

A new study of the variable star population in the Hercules globular cluster (M13; NGC 6205)★

Isochrone fitting of Galactic globular clusters – IV. NGC 6362 and NGC 6723

Gaia parallax of Milky Way globular clusters – A solution of mixture model

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