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In the past years, we have undertaken an extensive investigation of LMC and SMC star clusters based on HST data. We present photometry and astrometry of stars in 101 fields observed with the WFC/ACS, UVIS/WFC3 and NIR/WFC3 cameras. These fields comprise 113 star clusters. We provide differential-reddening maps and illustrate various scientific outcomes that arise from the early inspection of the photometric catalogs. In particular, we provide new insights on the extended main-sequence turn-off (eMSTO) phenomenon: i) We detected eMSTOs in two clusters, KMHK361 and NGC265, which had no previous evidence of multiple populations. This finding corroborates the conclusion that the eMSTO is a widespread phenomenon among clusters younger than ~2 Gyr. ii) The homogeneous color-magnitude diagrams (CMDs) of 19 LMC clusters reveal that the distribution of stars along the eMSTO depends on cluster age. iii) We discovered a new feature along the eMSTO of NGC1783, which consists of a distinct group of stars going on the red side of the eMSTO in CMDs composed of ultraviolet filters. Furthermore, we derived the proper motions of stars in the fields of view of clusters with multi-epoch images. Proper motions allowed us to separate the bulk of bright field stars from cluster members and investigate the internal kinematics of stellar populations in various LMC and SMC fields. As an example, we analyze the field around NGC346 to disentangle the motions of its stellar populations, including NGC364 and BS90, young and pre-MS stars in the star-forming region associated with NGC346, and young and old field stellar populations of the SMC. Based on these results and the fields around five additional clusters, we find that young SMC stars exhibit elongated proper-motion distributions that point toward the LMC, thus bringing new evidence for a kinematic connection between the LMC and SMC., Comment: 37 pages, 27 figures, accepted for publication in Astronomy & Astrophysics

The Color Magnitude Diagram (CMD) morphology of the "extended" main sequence turnoff (eMSTO) and upper main sequence (MS) of the intermediate age ($\lesssim 2$ Gyr) Large Magellanic Cloud Cluster NGC 1783 shows the presence of a small group of UV-dim stars, that, in the ultraviolet Hubble Space Telescope filters, are located at colors on the red side of the typical "fan" shape displayed by the eMSTO. We model the UV-dim stars by assuming that some of the stars which would intrinsically be located on the left side of the eMSTO are obscured by a ring of dust due to grain condensation at the periphery of the excretion disc expelled when they spin at the high rotation rates typical of stars in the Be stage. A reasonably low optical depth at 10$\mu$ is necessary to model the UV-dim group. Introduction of dust in the interpretation of the eMSTO may require a substantial re-evaluation of previous conclusions concerning the role of age and/or rotation spreads in the MC clusters: the entire eMSTO can be populated by dusty stars, and the reddest UV-dim stars simply represents the tail of the distribution with both maximum obscuration and the dust ring seen along the line of sight. The model stars having higher rotational projected velocity ($v \sin$ i) are predicted to be preferentially redder than the slowly-rotating stars. The mass loss responsible for the dust may also cause the non-monotonic distribution of stars in the upper main sequence, with two peaks and gaps showing up in the UV CMD., Comment: 11 pages, 13 figures. This is a pre-copyedited, author-produced PDF of an article (stad851) accepted for publication in MNRAS following peer review

Several observational studies have shown that many Galactic globular clusters (GCs) are characterised by internal rotation. Theoretical studies of the dynamical evolution of rotating clusters have predicted that, during their long-term evolution, these stellar systems should develop a dependence of the rotational velocity around the cluster's centre on the mass of stars, with the internal rotation increasing for more massive stars. In this paper we present the first observational evidence of the predicted rotation-mass trend. In our investigation, we exploited the $\mathit{Gaia}$ Data Release 3 catalogue of three GCs: NGC 104 (47 Tuc), NGC 5139 ($\omega$ Cen) and NGC 5904 (M 5). We found clear evidence of a cluster rotation-mass relation in 47 Tuc and M 5, while in $\omega$ Cen, the dynamically youngest system among the three clusters studied here, no such trend was detected., Comment: 6 pages, 4 figures, 1 table. Accepted for publication in MNRAS Letters

We present our final study of the white dwarf cooling sequence (WD CS) in the globular cluster NGC 6752. The investigation is the main goal of a dedicated Hubble Space Telescope large Program, for which all the observations are now collected. The WD CS luminosity function (LF) is confirmed to peak at m_F606W = 29.3+/-0.1, consistent within uncertainties with what has been previously reported, and is now complete down to m_F606W~29.7. We have performed robust and conclusive comparisons with model predictions that show how the theoretical LF for hydrogen envelope WD models closely follow the shape of the empirical LF. The magnitude of the peak of the observed LF is matched with ages between 12.7 and 13.5 Gyr, consistent with the cluster age derived from the main sequence turn off and subgiant branch. We also find that the impact of multiple populations within the cluster on the WD LF for m_F606W below 27.3 is negligible, and that the presence of a small fraction of helium envelope objects is consistent with the data. Our analysis reveals a possible hint of an underestimate of the cooling timescales of models in the magnitude range 28.1 < m_F606W < 28.9. Finally, we find that hydrogen envelope models calculated with a new tabulation of electron conduction opacities in the transition between moderate and strong degeneracy provide WD ages that are too small in comparison to the Main Sequence turnoff age., 16 pages, 13 figures. Accepted for publication in MNRAS on 2022, November 4. Associated files soon at this https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/NGC6752_IV/

We present a numerical study, based on Monte Carlo simulations, aimed at defining new empirical parameters measurable from observations and able to trace the different phases of star cluster dynamical evolution. As expected, a central density cusp, deviating from the King model profile, develops during the core collapse (CC) event. Although the slope varies during the post-CC oscillations, the cusp remains a stable feature characterizing the central portion of the density profile in all post-CC stages. We then investigate the normalized cumulative radial distribution (nCRD) drawn by all the cluster stars included within one half the tridimensional half-mass radius (R, 18 pages, 11 figures, accepted for publication in ApJ

We introduce a new set of zoom-in cosmological simulations with sub-pc resolution, intended to model extremely faint, highly magnified star-forming stellar clumps, detected at z=6.14 thanks to gravitational lensing. The simulations include feedback from individual massive stars (in both the pre-supernova and supernova phases), generated via stochastic, direct sampling of the stellar initial mass function. We adopt a modified 'delayed cooling' feedback scheme, specifically created to prevent artificial radiative loss of the energy injected by individual stars in very dense gas (n~10^3-10^5 cm^{-3}). The sites where star formation ignites are characterised by maximum densities of the order of 10^5 cm^{-3} and gravitational pressures P/k>10^7 K/cm^3, corresponding to the values of the local, turbulent regions where the densest stellar aggregates form. The total stellar mass at z=6.14 is 3.4x10^7 M_sun, in satisfactory agreement with the observed stellar mass of the observed systems. The most massive clumps have masses of ~10^6 M_sun and half-mass sizes of ~100 pc. These sizes are larger than the observed ones, including also other samples of lensed high-redshift clumps, and imply an average density one order of magnitude lower than the observed one. In the size-mass plane, our clumps populate a sequence that is intermediate between the ones of observed high-redshift clumps and local dSph galaxies., MNRAS, accepted for publication. 24 pages, 17 figures

We introduce a new prescription for the evolution of globular clusters (GCs) during the initial embedded gas phase into a Monte Carlo method. With a simplified version of the Monte Carlo MOCCA code embedded in the AMUSE framework, we study the survival of GCs after the removal of primordial gas. We first test our code and show that our results for the evolution of mass and Lagrangian radii are in good agreement with those obtained with N-body simulations. The Monte Carlo code enables a more rapid exploration of the evolution of systems with a larger number of stars than N-body simulations. We have carried out a new survey of simulations to explore the evolution of globular clusters with up to $N = 500000$ stars for a range of different star formation efficiencies and half-mass radii. Our study shows the range of initial conditions leading to the clusters' dissolution and those for which the clusters can survive this early evolutionary phase., 13 pages, 6 figures

Disentangling distinct stellar populations along the red-giant branches (RGBs) of Globular Clusters (GCs) is possible by using the pseudo two-color diagram dubbed chromosome map (ChM). One of the most intriguing findings is that the so-called first-generation (1G) stars, characterized by the same chemical composition of their natal cloud, exhibit extended sequences in the ChM. Unresolved binaries and internal variations in helium or metallicity have been suggested to explain this phenomenon. Here, we derive high-precision Hubble Space Telescope photometry of the GCs NGC6362 and NGC6838 and build their ChMs. We find that both 1G RGB and main-sequence (MS) stars exhibit wider ChM sequences than those of second-generation (2G). The evidence of this feature even among unevolved 1G MS stars indicates that chemical inhomogeneities are imprinted in the original gas. We introduce a pseudo two-magnitude diagram to distinguish between helium and metallicity, and demonstrate that star-to-star metallicity variations are responsible for the extended 1G sequence. Conversely, binaries provide a minor contribution to the phenomenon. We estimate that the metallicity variations within 1G stars of 55 GCs range from less than [Fe/H]~0.05 to ~0.30 and mildly correlate with cluster mass. We exploit these findings to constrain the formation scenarios of multiple populations showing that they are qualitatively consistent with the occurrence of multiple generations. In contrast, the fact that 2G stars have more homogeneous iron content than the 1G challenges the scenarios based on accretion of material processed in massive 1G stars onto existing protostars., 18 pages, 13 figures, accepted for publication in MNRAS

Recent work has shown that NIR Hubble Space Telescope (HST) photometry allows us to disentangle multiple populations (MPs) among M dwarfs of globular clusters (GCs) and investigate this phenomenon in very low-mass (VLM) stars. Here, we present the color-magnitude diagrams (CMDs) of nine GCs and the open cluster NGC 6791 in the F110W and F160W bands of HST, showing that the main sequences (MSs) below the knee are either broadened or split thus providing evidence of MPs among VLM stars. In contrast, the MS of NGC 6791 is consistent with a single population. The color distribution of M-dwarfs dramatically changes between different GCs and the color width correlates with the cluster mass. We conclude that the MP ubiquity, variety, and dependence on GC mass are properties common to VLM and more-massive stars. We combined UV, optical, and NIR observations of NGC 2808 and NGC 6121 (M 4) to identify MPs along with a wide range of stellar masses (~ 0.2 - 0.8M ), from the MS turn off to the VLM regime, and measured, for the first time, their mass functions (MFs). We find that the fraction of MPs does not depend on the stellar mass and that their MFs have similar slopes. These findings indicate that the properties of MPs do not depend on stellar mass. In a scenario where the second generations formed in higher-density environments than the first generations, the possibility that the MPs formed with the same initial MF would suggest that it does not depend on the environment., Comment: 22 pages, 15 figures. Accepted for publication in ApJ

By means of 3D hydrodynamic simulations, we explore the effects of rotation in the formation of second-generation (SG) stars in globular clusters (GC). Our simulations follow the SG formation in a first-generation (FG) internally rotating GC; SG stars form out of FG asymptotic giant branch (AGB) ejecta and external pristine gas accreted by the system. We have explored two different initial rotational velocity profiles for the FG cluster and two different inclinations of the rotational axis with respect to the direction of motion of the external infalling gas, whose density has also been varied. For a low (10^-24 g cm^-3) external gas density, a disk of SG helium-enhanced stars is formed. The SG is characterized by distinct chemo-dynamical phase space patterns: it shows a more rapid rotation than the FG with the helium-enhanced SG subsystem rotating more rapidly than the moderate helium-enhanced one. In models with high external gas density (10^-23 g cm^-3), the inner SG disc is disrupted by the early arrival of external gas and only a small fraction of highly enhanced helium stars preserves the rotation acquired at birth. Variations in the inclination angle between the rotation axis and the direction of the infalling gas and the velocity profile can slightly alter the extent of the stellar disc and the rotational amplitude. No significant variation has been found in the timespan of our simulations when changing the inclination angle between the rotation axis and the direction of the infalling gas, while different velocity profiles can slightly alter the extent of the stellar disc and the rotational amplitude. The results of our simulations illustrate the complex link between dynamical and chemical properties of multiple populations and provide new elements for the interpretation of observational studies and future investigations of the dynamics of multiple-population GCs., Comment: 16 pages, 13 figures, accepted for publication in MNRAS

Schwannomas are rare benign tumours that arise from Schwann cells. The most known and studied is the intracranial vestibular schwannoma, even if it is not the most frequent. More often schwannomas arise from peripheral sensitive nerves, and the vagous is most involved among the cranial nerves. Intraparotid schwannomas account for just 10% of all facial involvement, so they are an extremely rare localisation. At present, there are less than 100 cases described in the literature. We performed a retrospective analysis of parotidectomy in two Italian hospitals and present two cases of intraparotid schwannoma and a review of the literature. In the first case, we performed a parotidectomy with a stripping of tumour from the nerve. In the other case, a hypoglossal-facial neurorrhaphy was performed. Follow-up was 24 months in the first (House-Brackmann II degree in temporal-ocular and III in facial-cervical branches) and 30 months in the second case (House-Brackmann III degree in both temporal-ocular and facial-cervical branches). Preoperative diagnosis of facial nerve schwannoma is a challenge; however, it is extremely important since post-operative palsy is common and often higher grade. Unfortunately, schwannoma has similar radiologic finding as more common pleomorphic adenoma and often FNAC is not helpful. Due to its rarity and benign nature, there is debate in the literature on the need for surgical removal. Wait-and-see is a valid option, but may could give problems in secondary surgery. Stripping or near-total removal can be useful in cases of limited involvement of the nerve. Neurorrhaphy can provide good functional results when facial sacrifice is needed.Schwannoma del nervo facciale intraparotideo: due casi clinici e review della letteratura.Gli schwannomi sono tumori benigni rari che prendono origine dalle cellule di Schwann. Tali cellule formano la guaina mielinica dei nervi periferici permettendo la trasmissione saltatoria, attraverso i nodi di Ranvier, del segnale neurale. Certamente quello più conosciuto e studiato è lo schwannoma vestibolare che ha origine generalmente dalla branca inferiore del nervo vestibolare. Più frequentemente, però, gli scwhannomi originano dai nervi sensitivi periferici e fra i nervi cranici il vago è quello più frequentemente interessato. Nel distretto testa-collo la localizzazione parafaringea è la più comune. Lo schwannoma del nervo facciale intraparotideo è un’evenienza molto rara che rende conto del 10% circa di tutti gli schwannomi che interessano il volto e fino a circa l’1,5% di tutti i tumori parotidei. Al momento in letteratura se ne contano meno di 100 casi. In questo studio abbiamo revisionato la casistica operatoria di due centri ospedalieri italiani riportando due casi di schwannoma del nervo facciale insieme ad una review della letteratura. Nel primo caso abbiamo eseguito una parotidectomia superficiale con dissezione smussa del tumore dalle fibre assonali realizzando una procedura molto simile alla demielinizzazione su base infiammatoria (es. sindromi demielinizzanti acute). Nel secondo caso invece, sempre dopo aver eseguito la parotidectomia, non è stato possibile salvare il nervo facciale per cui, dopo resezione, è stata praticata una neurorrafia con il nervo ipoglosso. Nell’immediato post-operatorio entrambi i pazienti hanno sviluppato una paresi facciale di grado V secondo House-Brackmann. Dopo terapia medica e riabilitativa il primo caso ha residuato un paresi di II-III grado (follow-up di 24 mesi) mentre il secondo una paresi di III (follow-up di 30 mesi). La diagnosi preoperatoria di questa neoplasia è alquanto difficoltosa, in particolare perché non esistono segni radiologici distintivi (di frequente anzi gli schwannomi sono confusi con i molto più comuni adenomi pleomorfi) e spesso anche la FNAC non consente una diagnosi. Fra le opzioni di trattamento, data la rarità e benignità, il wait-and-see può essere ritenuta una scelta valida, sebbene questa possa inficiare il risultato di un’eventuale chirurgia successiva. Al contrario la rimozione subtotale o la dissezione dalle fibre assonali possono essere utili anche se con precise limitazioni. Infine nei casi in cui la sezione del nervo è necessaria, la neurorrafia può consentire risultati soddisfacenti.

Nasal administration of Streptococcus salivarius 24SMB and Streptococcus oralis 89a has been proposed to reduce the risk of new episodes of adenoiditis, tonsillitis and acute rhinosinusitis in children.We enrolled 202 children with a recent diagnosis of recurrent upper respiratory tract infection. All the patients were treated twice daily for 7 days each month for 3 consecutive months with a nasal spray whose active agents were two specific bacterial strains: Streptococcus salivarius 24SMB and Streptococcus oralis 89a. Evaluation was performed at the end of treatment and at follow-up at 3, 6, and 12 months.Patients who completed the entire 90-day course of bacteriotherapy and the follow-up period showed a 64.3% reduction in their episodes of upper respiratory tract infections compared to the number of episodes recorded in the previous year. Treatment decreased the reported incidence of infection events by 52.4% in the first 3 months, 31.2% at 6-month follow-up, and 20.8% after 12 months. Enrolled patients tolerated the product well, and there were no dropouts.Prophylactic bacteriotherapy by administration of Streptococcus salivarius 24SMB and Streptococcus oralis 89a in children with a history of recurrent upper respiratory tract infection could reduce the number of episodes of otolaryngologic infections. Bacteriotherapy can be even more clinically important due to increasing difficulty in finding new effective antibiotic compounds. New alternative therapeutic approaches must be found with, in comparison to antibiotics, greater specificity and safety with respect to patients' native beneficial flora; lack of drug interactions; the ability to leverage complementary systemic modes of action; and drastically reduced risk of developing resistance within the patient population and the environment.

The advent of affordable parallel computers such as Beowulf PC clusters and, more recently, multicore PCs has been highly beneficial for a large number of scientists and smaller institutions that might not otherwise have access to substantial computing facilities. However, there hasn't been an analogous progress in the development and dissemination of parallel software-scientists need the expertise to develop parallel codes and must invest a significant amount of time in the development of tools even for the most common data-analysis tasks. The authors describe the Beowulf analysis symbolic interface (BASIN), a multiuser parallel data analysis and visualization framework. BASIN is aimed at providing scientists with a suite of parallel libraries for astrophysical data analysis along with general tools for data distribution and parallel operations on distributed data that lets them easily develop new parallel libraries for their specific tasks.

We investigate the evolution of the mass function of the Galactic globular cluster system (GCMF) taking into account the effects of stellar evolution, two-body relaxation, disk shocking and dynamical friction on the evolution of individual globular clusters.We have adopted a log-normal initial GCMF and we have studied in detail the dependence on the initial dispersion and mean value of the GCMF of the fraction of the initial number of clusters surviving after one Hubble time, of the final GCMF, and of the difference between the properties of the GCMF of clusters closer to the Galactic center and of those in the outer regions of the Galaxy.The initial log-normal shape of the GCMF is preserved in most cases and if a power-law in M is adopted for the initial GCMF, evolutionary processes tend to modify it into a log-normal GCMF. The difference between initial and final values of dispersion and mean value of the GCMF as well as the difference between the final values of these parameters for inner and outer clusters can be positive or negative depending on initial conditions.A significant effect of evolutionary processes does not necessarily give rise to a strong trend of the mean value of the GCMF with the galactocentric distance.The existence of a particular initial GCMF able to keep its initial shape and parameters unaltered during the entire evolution through a subtle balance between disruption of clusters and evolution of the masses of those which survive,suggested in Vesperini(1997),is confirmed. (abridged), Comment: 16 pages LaTeX(MNRAS style) 22 figures, (MNRAS in press)

I present a summary of results from various HST photometric studies of the dense central regions of Galactic globular clusters that my collaborators and I have carried out over the last 6 years. The dataset includes short exposures of 47 Tuc, M15, M3 and M13 obtained with the aberrated Planetary Camera-I (PC-I) and F555W (“V”) and F785LP (“I”) filters, as well as post-refurbishment Wide Field Planetary Camera 2 (WFPC2) snapshots of the post core collapse clusters M15, M30, and NGC 6624 in F336W (“U”), F439W (“B”), and V. Recently, a very deep, doubly oversampled PC-I U image of the core of 47 Tuc, and accompanying B and V images, have also been analyzed. In addition, we have carried out extensive checks of incompleteness and photometric error with the help of multiband image simulations that mimic the relevant characteristics of the HST PC-I and WFPC2 images: empirical point spread function, crowding effects based on a realistic density profile and stellar luminosity function (LF), noise, undersampling, A/D saturation, etc..

The relationship between diabetes mellitus (DM) and hypoacusia has been discussed since the work of Jordao, in 1857. Type II diabetes was considered a prevalent age-related medical condition, resulting in subclinical pathological changes. It was estimated that the incidence is about 9.6% of people in USA. (Cowie et al. 2006). Some studies has shown that the magnitude of hearing loss in patients with DM is related to the duration of the disease, age, and affects the auditory threshold to high frequencies. (Frisina et al. 2006). In a study of Tay HL et al. (1995) was found that there is a possible correlation between the duration of diabetes and hearing loss. The auditory system requires glucose and high-energy utilization for its complex signal processing. This suggests that the cochlea may also be a target organ for the ill effects of hyperglycemias. (Cullen and Cinnamond, 1993). Increased glucose exposure, even for short periods, initiates a metabolic cascade that could disrupt the cochlea both anatomically and physiologically (Jorgensen, 1961). Hearing depends on small blood vessels and nerves of the inner ear that are affected by high blood sugar level in diabetic patients. Outer hair cells modulate auditory reception in the inner ear: consequently, OAEs are commonly considered a useful index of cochlear function...

We present an analysis of observational data for 127 globular clusters which seems to indicate the importance of the Gurzadyan-Savvidy relaxation mechanism in driving the evolution of stellar systems.

We have studied the evolution of globular cluster systems (GCS) in elliptical galaxies with a power-law initial GCS mass function (GCMF) ($f(M) \propto M^{-\alpha}$) similar to that predicted by some theoretical studies of globular clusters formation and to that of young cluster systems observed in merging galaxies. We have carried out a survey over a large number of different host galaxies and we have considered different values for the index, $\alpha$, of the initial power-law GCMF ($\alpha=1.5,1.8,2.0$); we show the dependence of the main GCS final properties (mean mass and dispersion of the final GCMF, fraction of surviving clusters, radial gradient of the GCMF parameters) on the structure of the host galaxy and on the slope of the initial GCMF. For a subsample of host galaxies with values of effective masses and radii equal to those determined using observational data for a number of giant, normal and dwarf galaxies our results show that the relation between the final GCMF properties and those of the host galaxies as well as the dependence of the final GCMF parameters on the galactocentric distance within individual galaxies differ from those observed in old GCS: the values of the final GCS mean mass are in general smaller (4.2 < log M_final < 5.0) than those observed and the galaxy-to-galaxy dispersion of logM_final is larger than that reported by observational analyses. The results are compared with those of a companion paper in which we investigated the evolution of GCS with a log-normal initial GCMF and in which the final GCS properties were perfectly consistent with observations., Comment: 13 pages, accepted for publication in MNRAS

We study the evolution of globular cluster systems (GCS) in elliptical galaxies and explore the dependence of their main properties on the mass and the size of the host galaxy.The dependence of the evolution of the GCS mass function (GCMF), of the fraction of surviving clusters and of the ratio of the final to initial mass in clusters on the structure of the host galaxy as well as their variation with the galactocentric distance inside individual host galaxies has been thoroughly investigated.After a survey over a large number of different host galaxies we have restricted our attention to a sample of galaxies with effective masses and radii equal to those observed for dwarf,normal and giant ellipticals. We show that, in spite of large differences in the fraction of surviving clusters, the final mean masses of the GCMF in massive galaxies are very similar to each other with a small galaxy-to-galaxy dispersion;low-mass compact galaxies tend to have smaller values of the final mean mass and a larger galaxy-to-galaxy dispersion. These findings are in agreement with those of recent observational analyses. The fraction of surviving clusters increases with the mass of the host galaxy. We show that a small difference between the initial and the final mean mass and dispersion of the GCMF and the lack of a significant radial dependence of the mean mass inside individual galaxies do not necessarily imply that evolutionary processes have been unimportant in the evolution of the initial population of clusters. For giant galaxies most disruption occurs within the effective radius while for low-mass galaxies a significant disruption of clusters takes place also at larger galactocentric distances. The dependence of the results obtained on the initial mean mass of the GCMF is investigated. (abridged), 17 pages, accepted for publication in MNRAS

We study the internal response of a galaxy to an unbound encounter and present a survey of orbital parameters covering typical encounters in different galactic environments. Overall, we conclude that relatively weak encounters by low-mass interloping galaxies can cause observable distortions in the primaries. The resulting asymmetries may persist long after the interloper is evident. We focus our attention on the production of structure in dark halos and in cluster ellipticals. Any distortion produced in a dark halo can distort the embedded stellar disk, possibly leading to the formation of lopsided and warped disks. Features excited in an elliptical are directly observable and we predict that asymmetries in the morphologies of these systems can be produced by relatively small perturbers. We use these detailed results to predict the distribution of the $A$ parameter defined by Abraham et al. and the shift between the center of mass of the primary system and the position of the peak of density for a range of environments. We find that high-density, low-velocity dispersion environments are more likely to host galaxies with significant asymmetries. Our distribution for the $A$ parameter is in good agreement with the range spanned by the observed values for local galaxy clusters and for distant galaxies in the MDS and in the HDF.Finally, we propose a generalized asymmetry parameter $A(r)$ which provides detailed information on the radial structure of the asymmetry produced by the mechanism explored in our work. (abridged), 24 pages, uses emulateapj.sty, submitted to The Astrophysical Journal

I present a summary of results from various HST photometric studies of the dense central regions of Galactic globular clusters that my collaborators and I have carried out over the last 6 years. The dataset includes short exposures of 47 Tuc, M15, M3 and M13 obtained with the aberrated Planetary Camera-I (PC-I) and F555W (“V”) and F785LP (“I”) filters, as well as post-refurbishment Wide Field Planetary Camera 2 (WFPC2) snapshots of the post core collapse clusters M15, M30, and NGC 6624 in F336W (“U”), F439W (“B”), and V. Recently, a very deep, doubly oversampled PC-I U image of the core of 47 Tuc, and accompanying B and V images, have also been analyzed. In addition, we have carried out extensive checks of incompleteness and photometric error with the help of multiband image simulations that mimic the relevant characteristics of the HST PC-I and WFPC2 images: empirical point spread function, crowding effects based on a realistic density profile and stellar luminosity function (LF), noise, undersampling, A/D saturation, etc.

We investigate the stability of dense stellar clusters against relativistic collapse by approximate methods described in the previous paper in this series. These methods, together with the analysis of the fractional binding energy of the system, have been applied to sequences of equilibrium models, with cutoff in the distribution function, which generalize those studied by Zeldovich & Podurets. We show the existence of extreme configurations, which are stable all the way up to infinite values of the central redshift.

In this paper we address the issue of the origin of some observational properties of the galactic globular cluster system. After a preliminary study of some general properties of the main evolutionary processes, we investigate the evolution of systems of globular clusters located in a model of the Milky Way starting from different initial conditions. We study the role of the evolutionary processes in changing the spatial distribution and mass function of the cluster system, in establishing and/or preserving some of the observed correlations and trends between internal properties of globular clusters and between internal properties and location inside the host galaxy and we provide an estimate for the rates of core collapse and disruption of globular clusters. The initial mass function and spatial distribution of the cluster system evolve quite significantly in one Hubble time and the evolution is toward a final state similar to the observed one. If the mass function is initially taken to be a log-normal distribution similar to the one currently observed in our galaxy, its shape is not significantly altered during the entire simulation even though a significant number of clusters are disrupted before one Hubble time, which suggests that the present mass function might represent a sort of 'quasi-equilibrium' distribution., accepted for publication in MNRAS, 12 pages LaTeX (MNRAS style), 14 figures available on request from vesperin@astro.sns.it

Recent surveys of the observational properties of galactic globular clusters have shown the existence of interesting correlations and trends between structural parameters and between structural parameters and location inside the Galaxy (Chernoff & Djorgovski 1989, Djorgovski & Meylan 1994). The origin of most of these correlations is not clear yet and it is not clear to what extent they reflect the primordial conditions or the result of evolution. We have carried out a set of simulations following the evolution of the properties of a globular cluster system (mass function, spatial distribution, correlations between structural parameters) starting from given initial conditions. The evolution of each individual cluster has been followed by the same method applied by Chernoff et al. (1986) and Chernoff & Shapiro (1987). The effects of internal relaxation, disk shocking and dynamical friction have been considered. The main goal of the analysis is that of establishing the role of initial conditions and evolutionary processes in determining the present observational properties.

We investigate a population of primordial binaries during the initial stage of evolution of a star cluster. For our calculations we assume that equal mass stars form rapidly in a tidally truncated gas cloud, that $\sim10$\% of the stars are in binaries and that the resulting star cluster undergoes an epoch of violent relaxation. We study the collisional interaction of the binaries and single stars, in particular, the ionization of the binaries and the energy exchange between binaries and single stars. We find that for large $N$ systems ($N > 10^3$) even the most violent beginning leaves the binary distribution function largely intact. Hence, the binding energy originally tied up in the cloud's protostellar pairs is preserved during the relaxation process and the binaries are available to interact at later times within the virialized cluster., 37 pages, LaTeX, 12 compressed postscript figures, accepted by The Astrophysical Journal

We investigate how the core size of globular clusters in a postcollapse phase driven by primordial binaries depends upon the parameters of the distribution of the binary binding energy and the abundance of the binaries. We show that the variation of these quantites increases the plausible range for the core size.

Stability of dense stellar clusters against relativistic collapse is investigated by approximate methods, similar to the static criteria of stellar stability. The equilibrium models with Maxwellian distribution function with cutoff, studied by Zel'dovich & Podurets (ZP), have been considered. Three new methods for stability investigation are considered. The first method is based on the choice of the sequence of Maxwellian models with fixed cutoff parameter, in accordance with adiabatic conditions p cut ∼n c 1/3 . The second one is based on the consideration of the sequence of Maxwellian models with the same value of the specific entropy

The formation of Low mass X-ray binaries (LMXB) is favored within dense stellar systems such as Globular Clusters (GCs). The connection between LMXB and Globular Clusters has been extensively studied in the literature, but these studies have always been restricted to the innermost regions of galaxies. We present a study of LMXB in GCs within the central 1.5 deg2 of the Fornax cluster with the aim of confirming the existence of a population of LMXB in intra-cluster GCs and understand if their properties are related to the host GCs, to the environment or/and to different formation channels.

Globular star clusters that formed at the same cosmic time may have evolved rather differently from a dynamical point of view (because that evolution depends on the internal environment) through a variety of processes that tend progressively to segregate stars more massive than the average towards the cluster centre. Therefore clusters with the same chronological age may have reached quite different stages of their dynamical history (that is, they may have different dynamical ages). Blue straggler stars have masses greater than those at the turn-off point on the main sequence and therefore must be the result of either a collision or a mass-transfer event. Because they are among the most massive and luminous objects in old clusters, they can be used as test particles with which to probe dynamical evolution. Here we report that globular clusters can be grouped into a few distinct families on the basis of the radial distribution of blue stragglers. This grouping corresponds well to an effective ranking of the dynamical stage reached by stellar systems, thereby permitting a direct measure of the cluster dynamical age purely from observed properties., Comment: Published on the 20 December 2012 issue of Nature