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CMD of NGC 6316 obtained from the HST WFC3 data set used in this work, with the F814W and the F555W magnitudes plotted along the y-axis in the left and right panels, respectively.
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High-resolution Hubble Space Telescope optical observations have been used to analyze the stellar population and the structure of the poorly investigated bulge globular cluster NGC 6316. We constructed the first high-resolution reddening map in the cluster direction, which allowed us to correct the evolutionary sequences in the color–magnitude diag...
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Context 1
... used this calibrated star catalog to create the first deep CMD of the cluster (Figure 1). As mentioned in Section 1, NGC 6316 is located within the bulge causing its CMD to suffer from a considerable amount of contamination from field interlopers. ...
Context 2
... cluster's structural parameters have been derived by fitting the background-decontaminated profile with a singlemass King model (King 1966), assuming spherical symmetry and orbital isotropy. Following Raso et al. (2020), we performed the fit using an MCMC approach implemented by the emcee package (Foreman-Mackey et al. 2013, 2019). We Figure 7. Observed (empty circles) and background-subtracted (filled circles) density profile of NGC 6316. ...
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Most structural and evolutionary properties of galaxies strongly rely on the stellar initial mass function (IMF), namely the distribution of the stellar mass formed in each episode of star formation1–4. The IMF shapes the stellar population in all stellar systems, and so has become one of the most fundamental concepts of modern astronomy. Both cons...
Citations
... NGC6266 contains the second most BMPs among all GCs and its binary fraction in this work is f ≃3.5%. NGC6316 has similar color-magnitude diagram to 47 Tuc (Deras et al. 2023), which has the third most BMPs (f ≃0.7% in this work, 0.9% for WFC by M12), and its binary fraction is f ≃7.2%. The binary fractions of these BMP-related GCs contribute to understanding the formation of BMPs and their physical processes. ...
We need to resolve the individual stars for binary fraction determinations of stellar systems. Therefore, it is not possible to obtain the binary fractions for dense or distant stellar systems. % We proposed a method to determine the binary fraction of a dense or distant stellar system. The method is to first determine the binary fraction variation for any two adjacent regions and then add up those binary fraction variations along the radial direction to obtain the binary fraction for a stellar system. Binary fraction variation is derived by using ten binary fraction-sensitive spectral absorption feature indices (SAFIs) and the binary fraction variation calibrations in terms of these SAFIs. Using this method, we first presented the binary fraction variations for twenty-one Galactic globular clusters (GCs). By comparisons, we find that they agree well with the binary fractions based on the main-sequence fiducial line method by previous studies. This verifies that the above mentioned method is feasible. Next, we presented the binary fraction variations of thirteen Galactic GCs. We gave the relationships between binary fraction and various parameters, and found that binary fraction is negatively correlated with NHB and NRR, binary fraction of some studies is not strongly correlated with NBS, and the number of GCs with large binary fraction is greater at extreme blue horizontal branch population ratio. At last, if we want to obtain more accurate binary fraction, we suggest that the spectroscopic and photometric observations are conducted at an appropriate area interval for a stellar system.
... The field of view sampled by the adopted catalogs is affected by significant reddening variations, which can be easily appreciated as a spread of all the evolutionary sequence along the reddening vector (see decontaminated CMDs in the bottom middle panels of Figs. 1 and 2). This effect can heavily hamper a proper MP tagging and was thus corrected using a technique extensively used in the past by our group (e.g., Dalessandro et al. 2018c;Cadelano et al. 2020b;Deras et al. 2023). Briefly, we selected a sample of cluster stars in the I-band and F814W magnitude range from 11 to 18. ...
All multiple population (MP) formation models in globular clusters (GCs) predict that second population (SP) stars form more centrally concentrated than the first population (FP). As dynamical evolution proceeds, spatial differences are progressively erased and only dynamically young clusters are expected to retain a partial memory of the initial structural differences. In recent years, this picture has been supported by observations of the MP radial distributions of both Galactic and extragalactic GCs. However, more recent observations have suggested that in some systems, FPs might actually form more centrally segregated, with NGC 3201 being one significant example of such a possibility. Here, we present a detailed morphological and kinematic characterization of the MPs in NGC 3201, based on a combination of photometric and astrometric data. We show that the distribution of the SP is clearly bimodal. Specifically, the SP is significantly more centrally concentrated than the FP within $ cluster’s half-mass radius. Beyond this point, the SP fraction increases again, likely due to asymmetries in the spatial distributions of the two populations. The central concentration of the SP observed in the central regions implies that it formed more centrally concentrated than the FP, even more so than what is observed in the present-day. This interpretation is supported by the key information provided by the MP kinematic properties. Indeed, we find that the FP is isotropic across all the sampled cluster extension, while the velocity distribution of the SP becomes radially anisotropic in the cluster’s outer regions, as expected for the dynamical evolution of SP stars formed more centrally concentrated than the FP. The combination of spatial and kinematic observations provide key insights into the dynamical properties of this cluster and lend further support to scenarios in which the SP forms more centrally concentrated than the FP.
... In this context, we performed a detailed kinematic exploration using the ESO Multi-Instrument Kinematic Survey (MIKiS; Ferraro et al. 2018a;Lanzoni et al. 2018a,b;Leanza et al. 2022Leanza et al. , 2023Pallanca et al. 2023) and photometric investigation of GCs in different Galactic environments (e.g. Origlia et al. 2002Origlia et al. , 2003Valenti et al. 2010;Dalessandro et al. 2014;Pallanca et al. 2019Pallanca et al. , 2021aCadelano et al. 2020a;Raso et al. 2020;Deras et al. 2023) with the aim to perform a complete characterisation of these stellar systems in terms of structure, age, stellar content (see examples in Ferraro et al. 1997Ferraro et al. , 2009Lanzoni et al. 2010;Miocchi et al. 2013;Dalessandro et al. 2013;Pallanca et al. 2021b;Cadelano et al. 2022), and dynamical evolutionary stage (Ferraro et al. 2012Lanzoni et al. 2016). This approach led to the discovery of a few anomalous stel-Based on observations collected with the NASA/ESA HST (Prop. ...
... For every source in our catalogue, we then identified the n closest reference stars and computed the σ-clipped median of their geometric distances: the result is the ∆X value finally assigned to the source, which is transformed into the relative differential reddening δE(B − V) by using Eq. (1) in Deras et al. (2023). To increase the spatial resolution we iteratively performed this computation three times using the n = 100, 50, and 25 closest stars. ...
High-resolution Hubble Space Telescope (HST) optical observations have been used to perform the deepest photometric study of the poorly studied Galactic globular cluster NGC 6284. The deep colour-magnitude diagram (CMD) that we obtained reaches 6 mag below the main-sequence turnoff. We provide the first determination of the gravitational centre ( C grav ) and density profile of the system from resolved stars. We note that the gravitational centre is significantly offset (by 1.5 − 3″) from the values in the literature. The density profile shows the presence of a steep central cusp, unambiguously indicating that the cluster experienced the core-collapse phase. Updated values of the structural parameters and relaxation times of the system are provided. We also constructed the first high-resolution reddening map in the cluster direction, which allowed us to correct the evolutionary sequences in the CMD for the effects of differential reddening. Isochrone fitting to the corrected CMD provided us with new estimates of the cluster age, average colour excess, metallicity, and distance. We find an absolute age of 13.3 ± 0.4 Gyr, an average colour excess E ( B − V ) = 0.32 ± 0.01, a metallicity [Fe/H] = −1.36 ± 0.01, and a true distance modulus ( m − M ) 0 = 15.61 ± 0.04 that sets the cluster distance at 13.2 ± 0.2 kpc from the Sun. The superb quality of the CMD allowed a clear-cut identification of the red giant branch (RGB) bump, which is clearly distinguishable along the narrow RGB. The absolute magnitude of this feature turns out to be ∼0.2 mag fainter than the previous identification.
... (Stetson et al. 2019) by applying the method described inCadelano et al. (2020; see alsoDeras et al. 2023). ...
We used high-resolution spectra acquired with the Magellan Telescope to measure radial and rotational velocities of approximately 200 stars in the Galactic globular cluster NGC 3201. The surveyed sample includes blue straggler stars (BSSs) and reference stars in different evolutionary stages (main-sequence turnoff, subgiant, red giant, and asymptotic giant branches). The average radial velocity value (〈 V r 〉 = 494.5 ± 0.5 km s ⁻¹ ) confirms a large systemic velocity for this cluster and was used to distinguish 33 residual field interlopers. The final sample of member stars has 67 BSSs and 114 reference stars. Similarly to what is found in other clusters, the totality of the reference stars has negligible rotation (< 20 km s ⁻¹ ), while the BSS rotational velocity distribution shows a long tail extending up to ∼200 km s ⁻¹ , with 19 BSSs (out of 67) spinning faster than 40 km s ⁻¹ . This sets the percentage of fast-rotating BSSs to ∼28%. Such a percentage is roughly comparable to that measured in other loose systems ( ω Centauri, M4, and M55) and significantly larger than that measured in high-density clusters (as 47 Tucanae, NGC 6397, NGC 6752, and M30). This evidence supports a scenario where recent BSS formation (mainly from the evolution of binary systems) is occurring in low-density environments. We also find that the BSS rotational velocity tends to decrease for decreasing luminosity and surface temperature, similarly to what is observed in main-sequence stars. Hence, further investigations are needed to understand the impact of BSS internal structure on the observed rotational velocities.
... In the course of checking the outliers to explain their anomalous behaviour, it has been noticed that the photometric metallicity of two of the tree variables in NGC 6316 (V15, V18) underestimate the spectroscopic value significantly, while the Gaia proper-motion values of the third variable (V17) contradict its cluster membership status. Based on HST observations, Deras et al. ( 2023 ) have concluded in a recent paper that the cluster metallicity should be significantly lower than given in the Harris ( 2010 ) The goodness of the fits using more parameters and/or non-linear formulae are very similar. There is no formula which would yield a residual scatter better than 0.148 dex using the data set equation ( 2 ) has been defined on. ...
Photometric metallicity formulae of fundamental-mode RR Lyr (RRab) stars are presented using globular-cluster data exclusively. The aim is to check whether this selection may help increasing the overall accuracy of the fits and eliminating the systematic bias of the photometric results, namely that they tend to overestimate [Fe/H] of the most metal-poor variables. The G-band time-series data available in the Gaia DR3 archive and a new compilation of the published spectroscopic globular cluster [Fe/H] values on a uniform solar reference metallicity scale are utilized. We have derived a new [Fe/H]phot − P, ϕ31 formula, and have diagnosed that no significant increase in the accuracy of the fit can be achieved using non-linear or multi-parameter formulae. The best result is obtained when different formulae are applied for variables with Oosterhoff-type I and II properties. However, even this solution cannot eliminate the systematic bias of the results completely. This separation of the variables has also led to the conclusion that the photometric estimates of the [Fe/H] are less reliable for the Oo-type II variables than for the Oo-type I sample. Published [Fe/H]phot values and the results of the available photometric formulae in the Gaia G-band are compared with the present results. It is found that each of the solutions yields very similar results, with similar accuracy and systematic biases. Major differences are detected only in the zero-points of the [Fe/H] scales, and these offsets are larger than differences in the accepted solar reference values would explain.
... In the course of checking the outliers to explain their anomalous behaviour, it has been noticed that the photometric metallicity of two of the tree variables in NGC6316 (V15, V18) underestimate the spectroscopic value significantly, while the Gaia proper-motion values of the third variable (V17) contradict its cluster membership status. Based on HST observations, Deras et al. (2023) have concluded in a recent paper that the cluster metallicity should be significantly lower than given in the Harris (2010) V54/IC4499, V10/NGC5053, V202/NGC5272, V1/NGC6293, V8/NGC6453, V27/NGC6981, and V28/NGC7089. ...
Photometric metallicity formulae of fundamental-mode RR Lyr (RRab) stars are presented using globular-cluster data exclusively. The aim is to check whether this selection may help increasing the overall accuracy of the fits and eliminating the systematic bias of the photometric results, namely that they tend to overestimate [Fe/H] of the most metal-poor variables. The $G$-band time-series data available in the Gaia DR3 archive and a new compilation of the published spectroscopic globular cluster [Fe/H] values on a uniform solar reference metallicity scale are utilized. We have derived a new ${\mathrm{[Fe/H]}}_{\mathrm{phot}}- P,\varphi_{31}$ formula, and have diagnosed that no significant increase in the accuracy of the fit can be achieved using non-linear or multi-parameter formulae. The best result is obtained when different formulae are applied for variables with Oosterhoff-type I and II properties. However, even this solution cannot eliminate the systematic bias of the results completely. This separation of the variables has also led to the conclusion that the photometric estimates of the [Fe/H] are less reliable for the Oo-type II variables than for the Oo-type I sample. Published ${\mathrm{[Fe/H]}}_{\mathrm{phot}}$ values and the results of the available photometric formulae in the Gaia $G$-band are compared with the present results. It is found that each of the solutions yields very similar results, with similar accuracy and systematic biases. Major differences are detected only in the zero-points of the [Fe/H] scales, and these offsets are larger than differences in the accepted solar reference values would explain.
... Hence, to determine the structural parameters of KMK 88-10, we fitted the obtained profile with the family of spherical, isotropic, single-mass King models. The comparison was performed through a Monte Carlo Markov Chain fitting technique following the prescriptions by Raso et al. (2020), , and Deras et al. (2023). We assumed a χ 2 likelihood and flat priors for all fitting parameters. ...
In the context of a project aimed at characterizing the dynamical evolution of old globular clusters in the Large Magellanic Cloud, we have secured deep HST/WFC3 images of the massive cluster NGC 1835. In the field of view of the acquired images, at a projected angular separation of approximately 2′ from the cluster, we detected the small stellar system KMK 88-10. The observations provided the deepest color–magnitude diagram ever obtained for this cluster, revealing that it hosts a young stellar population with an age of 600–1000 Myr. The cluster surface brightness profile is nicely reproduced by a King model with a core radius r c = 4″ (0.97 pc), a half-mass radius r hm = 12″ (2.9 pc), and a concentration parameter c ∼ 1.3 corresponding to a truncation radius r t ∼ 81″ (19.5 pc). We also derived its integrated absolute magnitude ( M V = −0.71) and total mass ( M ∼ 80–160 M ⊙ ). The most intriguing feature emerging from this analysis is that KMK 88-10 presents a structure elongated in the direction of NGC 1835, with an intracluster overdensity that suggests the presence of a tidal bridge between the two systems. If confirmed, this would be the first evidence of a tidal capture of a small star cluster by a massive globular.
... Hence, to determine the structural parameters of KMK88-10, we fitted the obtained profile with the family of spherical, isotropic, single-mass King models. The comparison was performed through a Monte Carlo Markov Chain fitting technique following the prescriptions by Raso et al. (2020); Cadelano et al. (2022b); Deras et al. (2023). We assumed χ 2 likelihood and flat priors for all the fitting parameters. ...
In the context of a project aimed at characterizing the dynamical evolution of old globular clusters in the Large Magellanic Cloud, we have secured deep HST/WFC3 images of the massive cluster NGC 1835. In the field of view of the acquired images, at a projected angular separation of approximately 2 arcmin from the cluster, we detected the small stellar system KMK88-10. The observations provided the deepest color-magnitude diagram ever obtained for this cluster, revealing that it hosts a young stellar population with an age of 600-1000 Myr. The cluster surface brightness profile is nicely reproduced by a King model with a core radius rc = 4 arcsec (0.97 pc), an half-mass radius rhm = 12 arcsec (2.9 pc), and a concentration parameter c~1.3 corresponding to a truncation radius rt~81 arcsec (19.5 pc). We also derived its integrated absolute magnitude (MV=-0.71) and total mass (M~80-160 Msun). The most intriguing feature emerging from this analysis is that KMK88-10 presents a structure elongated in the direction of NGC 1835, with an intracluster over-density that suggests the presence of a tidal bridge between the two systems. If confirmed, this would be the first evidence of a tidal capture of a small star cluster by a massive globular.
... To characterize the BSS distribution in each of the investigated clusters, we took advantage of recent photometric studies performed by our group: Pallanca et al. (2019Pallanca et al. ( , 2021 for NGC 6440, Deras et al. (2023) for NGC 6316, Ferraro et al. (2018a) andB. Lanzoni et al. (2023, in preparation) for NGC 3201. ...
... 2. NGC 6316. Deep optical observations obtained with the HST WFC3 in the F555W and the F814W filters have recently been used to analyze the stellar population and the structure of this poorly investigated GC in the Galactic bulge (Deras et al. 2023). The data reduction procedure is very similar to that described above for NGC 6440, and all the details can be found in Deras et al. (2023). ...
... Deep optical observations obtained with the HST WFC3 in the F555W and the F814W filters have recently been used to analyze the stellar population and the structure of this poorly investigated GC in the Galactic bulge (Deras et al. 2023). The data reduction procedure is very similar to that described above for NGC 6440, and all the details can be found in Deras et al. (2023). Also in this case, a high-resolution extinction map in the direction of the system was determined and used to correct the CMD for the effects of differential reddening. ...
We have used the “dynamical clock” to measure the level of dynamical evolution reached by three Galactic globular clusters (namely, NGC 3201, NGC 6316, and NGC 6440). This is an empirical method that quantifies the level of central segregation of blue straggler stars (BSSs) within the cluster half-mass radius by means of the A rh + parameter, defined as the area enclosed between the cumulative radial distribution of BSSs and that of a lighter population. The total sample with homogeneous determinations of A rh + currently includes 59 clusters: 52 old GCs in the Milky Way (including the three investigated here), five old clusters in the Large Magellanic Cloud, and two young systems in the Small Magellanic Cloud. The three objects studied here nicely nest into the correlation between A rh + and the central relaxation time defined by the previous sample, thus proving and consolidating the use of the dynamical clock as an excellent tracer of the stage of dynamical evolution of a star cluster in different galactic environments. Finally, we discuss the advantages of using the dynamical clock as an indicator of the dynamical ages of star clusters, compared to the present-day central relaxation time.
... For this reason several years ago we initiated a systematic photometric and spectroscopic investigation of bulge GCs and their stellar populations (see Origlia et al. 1997Origlia et al. , 2001Origlia et al. , 2002Origlia & Rich 2004;Origlia et al. 2005;Valenti et al. 2005Valenti et al. , 2007Ferraro et al. 2009;Valenti et al. 2010Valenti et al. , 2011Ferraro et al. 2015;Saracino et al. 2015Saracino et al. , 2016Cadelano et al. 2017b;Pallanca et al. 2019;Saracino et al. 2019;Pallanca et al. 2021bPallanca et al. , 2021aCadelano et al. 2022;Leanza et al. 2022a;Deras et al. 2023). In this respect, the discovery that Terzan5 and Liller1 are not genuine GCs but host multi-iron and multiage stellar populations has opened a new line of investigation, providing the first detection of Bulge Fossil Fragments, the possible remnants of primordial giant clumps that contributed to the bulge formation, surviving the violent phase of its assembling (Ferraro et al. 2009;Lanzoni et al. 2010;Origlia et al. 2011Origlia et al. , 2013Massari et al. 2014;Ferraro et al. 2016;Origlia et al. 2019;Ferraro et al. 2021;Dalessandro et al. 2022). ...
In the context of a project aimed at characterizing the properties of star clusters in the Galactic bulge, here we present the determination of the internal kinematics and structure of the massive globular cluster NGC 6569. The kinematics has been studied by means of an unprecedented spectroscopic data set acquired in the context of the ESO-VLT Multi-Instrument Kinematic Survey of Galactic globular clusters, combining the observations from four different spectrographs. We measured the line-of-sight velocity of a sample of almost 1300 stars distributed between ∼0.″8 and 770″ from the cluster center. From a subsample of high-quality measures, we determined the velocity dispersion profile of the system over its entire radial extension (from ∼5″ to ∼200″ from the center), finding the characteristic behavior usually observed in globular clusters, with a constant inner plateau and a declining trend at larger radii. The projected density profile of the cluster has been obtained from resolved star counts, by combining high-resolution photometric data in the center, and the Gaia EDR3 catalog radially extended out to ∼ 20 ′ for a proper sampling of the Galactic field background. The two profiles are properly reproduced by the same King model, from which we estimated updated values of the central velocity dispersion, main structural parameters (such as the King concentration, the core, half mass, and tidal radii), total mass, and relaxation times. Our analysis also reveals a hint of ordered rotation in an intermediate region of the cluster (40″ < r < 90″, corresponding to 2 r c < r < 4.5 r c ), but additional data are required to properly assess this possibility.
