Star Clusters In Large Magellanic Cloud Research Articles

The dynamical importance of binary systems in young massive star clusters

Abstract Characterization of the binary fractions in star clusters is of fundamental importance for many fields in astrophysics. Observations indicate that the majority of stars are found in binary systems, while most stars with masses greater than 0.5M⊙ are formed in star clusters. In addition, since binaries are on average more massive than single stars, in resolved star clusters these systems are thought to be good tracers of (dynamical) mass segregation. Over time, dynamical evolution through two-body relaxation will cause the most massive objects to migrate to the cluster center, while the relatively lower-mass objects remain in or migrate to orbits at greater radii. This process will globally dominate a cluster’s stellar distribution. However, close encounters involving binary systems may disrupt ‘soft’ binaries. This process will occur more frequently in a cluster’s central, dense region than in its periphery, which may mask the effects of mass segregation. Using high resolution Hubble Space Telescope observations, combined with sophisticated N-body simulations, we investigate the radial distributions of the main-sequence binary fractions in massive young Large Magellanic Cloud star clusters. We show that binary disruption may play an important role on very short timescales, depending on the environmental conditions in the cluster cores. This may lead to radial binary fractions that initially decline in the cluster centers, which is contrary to the effects expected from dynamical mass segregation.

DIFFERENT DYNAMICAL AGES FOR THE TWO YOUNG AND COEVAL LMC STAR CLUSTERS, NGC 1805 AND NGC 1818, IMPRINTED ON THEIR BINARY POPULATIONS

The two Large Magellanic Cloud star clusters NGC 1805 and NGC 1818 are approximately the same chronological age (~30 Myr), but show different radial trends in binary frequency. The F-type stars (1.3 - 2.2 MSun) in NGC 1818 have a binary frequency that decreases towards the core, while the binary frequency for stars of similar mass in NGC 1805 is flat with radius, or perhaps bimodal (with a peak in the core). We show here, through detailed N-body modeling, that both clusters could have formed with the same primordial binary frequency and with binary orbital elements and masses drawn from the same distributions (defined from observations of open clusters and the field of our Galaxy). The observed radial trends in binary frequency for both clusters are best matched with models that have initial substructure. Furthermore, both clusters may be evolving along a very similar dynamical sequence, with the key difference that NGC 1805 is dynamically older than NGC 1818. The F-type binaries in NGC 1818 still show evidence of an initial period of rapid dynamical disruptions (which occur preferentially in the core), while NGC 1805 has already begun to recover a higher core binary frequency, owing to mass segregation (which will eventually produce a distribution in binary frequency that rises only towards the core, as is observed in old Milky Way star clusters). This recovery rate increases for higher-mass binaries, and therefore even at one age in one cluster, we predict a similar dynamical sequence in the radial distribution of the binary frequency as a function of binary primary mass.

Gemini/GMOS photometry of intermediate-age star clusters in the Large Magellanic Cloud

We present Gemini South GMOS g,i photometry of 14 intermediate-age Large Magellanic Cloud (LMC) star clusters, namely: NGC 2155, 2161, 2162, 2173, 2203, 2209, 2213, 2231, 2249, Hodge 6, SL 244, 505, 674, and 769, as part of a continuing project to investigate the extended Main Sequence Turnoff (EMSTO) phenomenon. Extensive artificial star tests were made over the observed field of view. These tests reveal the observed behaviour of photometric errors with magnitude and crowding. The cluster stellar density radial profiles were traced from star counts over the extent of the observed field. We adopt clus- ter radii and build colour-magnitude diagrams (CMDs) with cluster features clearly identified. We used the cluster (g,g-i) CMDs to estimate ages from the matching of theoretical isochrones. The studied LMC clusters are confirmed to be intermediate-age clusters, which range in age 9.10 < log(t) < 9.60. NGC 2162 and NGC 2249 look like new EMSTO candidates, in addition to NGC 2209, on the basis of having dual red clumps.

CONSEQUENCES OF DYNAMICAL DISRUPTION AND MASS SEGREGATION FOR THE BINARY FREQUENCIES OF STAR CLUSTERS

The massive (13,000-26,000 Msolar), young (15-30 Myr) Large Magellanic Cloud star cluster NGC 1818 reveals an unexpected increasing binary frequency with radius for F-type stars (1.3-2.2 Msolar). This is in contrast to many older star clusters that show a decreasing binary frequency with radius. We study this phenomenon with sophisticated N-body modeling, exploring a range of initial conditions, from smooth virialized density distributions to highly substructured and collapsing configurations. We find that many of these models can reproduce the cluster's observed properties, although with a modest preference for substructured initial conditions. Our models produce the observed radial trend in binary frequency through disruption of soft binaries (with semi-major axes, a > 3000 AU), on approximately a crossing time (~ 5.4 Myr), preferentially in the cluster core. Mass segregation subsequently causes the binaries to sink towards the core. After roughly one initial half-mass relaxation time (t_rh(0) ~ 340 Myr) the radial binary frequency distribution becomes bimodal, the innermost binaries having already segregated towards the core, leaving a minimum in the radial binary frequency distribution that marches outwards with time. After 4-6 t_rh(0), the rising distribution in the halo disappears, leaving a radial distribution that rises only towards the core. Thus, both a radial binary frequency distribution that falls towards the core (as observed for NGC 1818) and one that rises towards the core (as for older star clusters) can arise naturally from the same evolutionary sequence owing to binary disruption and mass segregation in rich star clusters.

Ks-BAND LUMINOSITY EVOLUTION OF THE ASYMPTOTIC GIANT BRANCH POPULATION BASED ON STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD

We present a study of Ks band luminosity evolution of the asymptotic giant branch (AGB) population in simple stellar systems using star clusters in the Large Magellanic Cloud (LMC). We determine physical parameters of LMC star clusters including center coordinates, radii, and foreground reddenings. Ages of 83 star clusters are derived from isochrone fitting with the Padova models, and those of 19 star clusters are taken from the literature. The AGB stars in 102 star clusters with log(age) = 7.3 - 9.5 are selected using near-infrared color magnitude diagrams based on 2MASS photometry. Then we obtain the Ks band luminosity fraction of AGB stars in these star clusters as a function of ages. The Ks band luminosity fraction of AGB stars increases, on average, as age increases from log(age) ~ 8.0, reaching a maximum at log(age) ~ 8.5, and it decreases thereafter. There is a large scatter in the AGB luminosity fraction for given ages, which is mainly due to stochastic effects. We discuss this result in comparison with five simple stellar population models. The maximum Ks band AGB luminosity fraction for bright clusters is reproduced by the models that expect the value of 0.7 - 0.8 at log(age) = 8.5 - 8.7. We discuss the implication of our results with regard to the study of size and mass evolution of galaxies.

Population I Cepheids and star formation history of the Large Magellanic Cloud

Population I Cepheids and star formation history of the Large Magellanic Cloud

No compelling evidence of significant early star cluster disruption in the Large Magellanic Cloud

Whether or not the rich star cluster population in the Large Magellanic Cloud (LMC) is affected by significant disruption during the first few x 10^8 yr of its evolution is an open question and the subject of significant current debate. Here, we revisit the problem, adopting a homogeneous data set of broad-band imaging observations. We base our analysis mainly on two sets of self-consistently determined LMC cluster ages and masses, one using standard modelling and one which takes into account the effects of stochasticity in the clusters' stellar mass functions. On their own, the results based on any of the three complementary analysis approaches applied here are merely indicative of the physical conditions governing the cluster population. However, the combination of our results from all three different diagnostics leaves little room for any conclusion other than that the optically selected LMC star cluster population exhibits no compelling evidence of significant disruption -- for clusters with masses, M_cl, of log(M_cl/M_sun) >= 3.0-3.5 -- between the age ranges of [3-10] Myr and [30-100] Myr, either "infant mortality" or otherwise. In fact, there is no evidence of any destruction beyond that expected from simple models just including stellar dynamics and stellar evolution for ages up to 1 Gyr. It seems, therefore, that the difference in environmental conditions in the Magellanic Clouds on the one hand and significantly more massive galaxies on the other may be the key to understanding the apparent variations in cluster disruption behaviour at early times.

The binary fractions in the massive young Large Magellanic Cloud star clusters NGC 1805 and NGC 1818

Using high-resolution data sets obtained with the Hubble Space Telescope, we investigate the radial distributions of the F-type main-sequence binary fractions in the massive young Large Magellanic Cloud star clusters NGC 1805 and NGC 1818. We apply both an isochrone-fitting approach and chi^2 minimization using Monte Carlo simulations, for different mass-ratio cut-offs, q, and present a detailed comparison of the methods' performance. Both methods yield the same radial binary fraction profile for the same cluster, which therefore supports the robustness and applicability of either method to young star clusters which are as yet unaffected by the presence of multiple stellar populations. The binary fractions in these two clusters are characterized by opposite trends in their radial profiles. NGC 1805 exhibits a decreasing trend with increasing radius in the central region, followed by a slow increase to the field's binary-fraction level, while NGC 1818 shows a monotonically increasing trend. This may indicate dominance of a more complicated physical mechanism in the cluster's central region than expected a priori. Time-scale arguments imply that early dynamical mass segregation should be very efficient and, hence, likely dominates the dynamical processes in the core of NGC 1805. Meanwhile, in NGC 1818 the behavior in the core is probably dominated by disruption of soft binary systems. We speculate that this may be owing to the higher velocity dispersion in the NGC 1818 core, which creates an environment in which the efficiency of binary disruption is high compared with that in the NGC 1805 core.

A VLT/FLAMES STUDY OF THE PECULIAR INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 1846. I. KINEMATICS

In this paper we present high resolution VLT/FLAMES observations of red giant stars in the massive intermediate-age Large Magellanic Cloud star cluster NGC 1846, which, on the basis of its extended main-sequence turn-off (EMSTO), possesses an internal age spread of ~300 Myr. We describe in detail our target selection and data reduction procedures, and construct a sample of 21 stars possessing radial velocities indicating their membership of NGC 1846 at high confidence. We consider high-resolution spectra of the planetary nebula Mo-17, and conclude that this object is also a member of the cluster. Our measured radial velocities allow us to conduct a detailed investigation of the internal kinematics of NGC 1846, the first time this has been done for an EMSTO system. The key result of this work is that the cluster exhibits a significant degree of systemic rotation, of a magnitude comparable to the mean velocity dispersion. Using an extensive suite of Monte Carlo models we demonstrate that, despite our relatively small sample size and the substantial fraction of unresolved binary stars in the cluster, the rotation signal we detect is very likely to be genuine. Our observations are in qualitative agreement with the predictions of simulations modeling the formation of multiple populations of stars in globular clusters, where a dynamically cold, rapidly rotating second generation is a common feature. NGC 1846 is less than one relaxation time old, so any dynamical signatures encoded during its formation ought to remain present.

Propiedades fundamentales de cúmulos estelares azules, compactos y de alto brillo superficial en la Nube Mayor de Magallanes

Presentamos espectros integrados en el rango óptico (3600-6800Å) de 29 cúmulos azules compactos y de alto brillo superficial de la Nube Mayor de Magallanes (NMM). Estimamos enrojecimiento a partir del método de ajuste de templates y usando mapas de extinción interestelar en la región de los cúmulos, las edades la determinamos a partir del método de ajuste de templates y de los anchos equivalentes (AEs). En este último caso, usamos calibraciones empíricas en función de la edad, junto con diagrama de diagnóstico que involucran la suma de AEs de características espectrales seleccionadas (K CaII, G band (CH), MgI, Hβ, Hγ and Hδ. El rango de edades derivadas oscila entre ~5 millones y 800 millones de años. Obtuvimos un buen acuerdo entre los resultados de los dos métodos. Los espectros obtenidos mejoran y complementan las bases de datos espectrales actualmente existente para la NMM.DOI: http://dx.doi.org/10.5377/ce.v1i1.606Ciencias Espaciales 1(1) 2009

Investigating ageing methods of Large Magellanic Cloud star clusters using integrated colours

We present an investigation of 84 star clusters in the Large Magellanic Cloud (LMC) galaxy using different broad-band photometric, age-estimation methods. Because of its intermediate distance, the LMC is uniquely positioned to compare its clusters that have previously been aged using both resolved photometry [colour–magnitude diagrams (CMDs)] of the constituent stars and unresolved methods (integrated, broad-band colour photometry). In our comparison between the published CMD ages to three similar, but different methods based on UBV integrated colours, we find poor matches. We attribute this primarily to two things. First, the UBV integrated broad-band ageing methods require matching a cluster with an expected model prediction of the cluster colours as a function of age. The biggest problem we find is that the stellar clusters in our sample do not typically lie on the model line based on their known age and extinction. That is to say, real cluster colours often do not match the model colours and can be found some distance from expected model values. The second issue, which has been previously documented in numerous studies, is the strong degeneracy between age and extinction in the UBV plane. Certainly, providing more photometric bands will reduce degeneracy between age and reddening. Better yet, if extinction can be independently determined, we show that ages from methods based on integrated colours will more closely match those obtained from CMD ages. However, the underlying issue remains. Simple stellar population models often do not accurately represent the colours of real stellar clusters due to the incomplete and stochastic sampling of the stellar mass function in low- and moderate-mass stellar clusters.

Integrated parameters of star clusters: a comparison of theory and observations

This paper presents integrated magnitudes and colours for synthetic clusters. The integrated parameters have been obtained for the whole cluster population as well as for the main-sequence (MS) population of star clusters. We have also estimated observed integrated magnitudes and colours of the MS population of galactic open clusters, Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) star clusters. It is found that the colour evolution of the MS population of star clusters is not affected by the stochastic fluctuations, however, these fluctuations significantly affect the colour evolution of the whole cluster population. The fluctuations are maximum in (V−I) colour in the age range 6.7 < log(age) < 7.5. Evolution of integrated colours of the MS population of clusters in the Milky Way, LMC and SMC, obtained in the present study is well explained by the present synthetic cluster model. The observed integrated (B−V) colours of the MS population of LMC star clusters having age ≥500 Myr seem to be distributed around the Z= 0.004 model, whereas (V−I) colours are found to be bluer than those predicted by the Z= 0.004 model. The (V−I) versus (B−V) two-colour diagram for the MS population of the Milky Way star clusters shows a fair agreement between the observations and present model, however, the diagrams for LMC and SMC clusters indicate that observed (V−I) colours are relatively bluer. Possible reasons for this anomaly have been discussed. Comparison of the synthetic (U−B) versus (B−V) relation with the observed integrated parameters of the whole cluster population of the Milky Way, LMC and SMC star clusters indicates that the majority of the bluest clusters [(B−V)0 < 0.0] follow the MS population relation. The colour evolution of young Milky Way, LMC and SMC clusters [6.5 ≤ log(age) ≤8.0] also indicates that a large number of young clusters follow the MS population relation. Therefore, in the absence of a careful modelling of stochastic effects, age determination of young star clusters by comparing their integrated colours with whole cluster synthetic colours may yield erroneous results.

VARIABLE STARS IN THE LARGE MAGELLANIC CLOUD GLOBULAR CLUSTER NGC 2257. I. RESULTS BASED ON 2007-2008B,VPHOTOMETRY

The variable stars in the Large Magellanic Cloud star cluster NGC 2257 are reinvestigated using photometry (to ~20th mag) of over 400 new B, V CCD images taken with the CTIO 0.9 m telescope on 14 nights in 2007 December and 2008 January. New period searches have been made using two independent algorithms (CLEAN, Period04); the resultant periods of most of the stars are consistent with the pulsation periods derived previously, and where there are discrepancies these have been resolved. For the B and V light curves, accurate Fourier coefficients and parameters are given. Six new variable stars have been discovered (V45-50), including a bright candidate long-period variable star showing secondary oscillations (V45) and two anomalously bright RRc stars (V48 and V50), which are shown to be brightened and reddened by nearby red giant stars. Also discovered among the previously known variable stars are three double-mode RR Lyrae stars (V8, V16, and V34) and several Blazhko variables. Archival Hubble Space Telescope images and the photometry by Johnson et al. have been used to define better the properties of the most crowded variable stars. The total number of cluster variable stars now stands at forty-seven: 23 RRab stars, four of which show Blazhko amplitude variations; 20 RRc stars, one showing clear Blazhko variations and another showing possible Blazhko variations; the three RRd stars, all having the dominant period ~0.36 day and period ratios P 1/P 0 ~0.7450; and an LPV star located near the tip of the red giant branch. A comparison of the RRd stars with those in other environments shows them to be most similar to those in IC4499.

THE STAR FORMATION HISTORY OF THE LARGE MAGELLANIC CLOUD

We present the first ever global, spatially resolved reconstruction of the star formation history (SFH) of the Large Magellanic Cloud (LMC), based on the application of our StarFISH analysis software to the multiband photometry of 20 million of its stars from the Magellanic Clouds Photometric Survey. The general outlines of our results are consistent with previously published results: following an initial burst of star formation, there was a quiescent epoch from approximately 12 to 5 Gyr ago. Star formation then resumed and has proceeded until the current time at an average rate of roughly 0.2 M☉ yr−1, with temporal variations at the factor of 2 level. The re-ignition of star formation about 5 Gyr ago, in both the LMC and Small Magellanic Cloud (SMC), is suggestive of a dramatic event at that time in the Magellanic system. Among the global variations in the recent star formation rate are peaks at roughly 2 Gyr, 500 Myr, 100 Myr, and 12 Myr. The peaks at 500 Myr and 2 Gyr are nearly coincident with similar peaks in the SFH of the SMC, suggesting a joint history for these galaxies extending back at least several Gyr. The chemical enrichment history recovered from our StarFISH analysis is in broad agreement with that inferred from the LMC's star cluster population, although our constraints on the ancient chemical enrichment history are weak. We conclude from the concordance between the star formation and chemical enrichment histories of the field and cluster populations that the field and cluster star formation modes are tightly coupled.

Multiple Stellar Populations in Three Rich Large Magellanic Cloud Star Clusters

We present deep colour-magnitude diagrams for three rich intermediate-age star clusters in the Large Magellanic Cloud, constructed from archival ACS F435W and F814W imaging. All three clusters exhibit clear evidence for peculiar main-sequence turn-offs. NGC 1846 and 1806 each possess two distinct turn-off branches, while the turn-off for NGC 1783 shows a much larger spread in colour than can be explained by the photometric uncertainties. We demonstrate that although all three clusters contain significant populations of unresolved binary stars, these cannot be the underlying cause of the observed turn-off morphologies. The simplest explanation is that each cluster is composed of at least two different stellar populations with very similar metal abundances but ages separated by up to ~300 Myr. The origin of these unusual properties remains unidentified; however, the fact that at least three massive clusters containing multiple stellar populations are now known in the LMC suggests a potentially significant formation channel.

CCD photometric and mass function study of nine young Large Magellanic Cloud star clusters

Abstract We present a CCD photometric and mass function study of nine young Large Magellanic Cloud star clusters, namely NGC 1767, 1994, 2002, 2003, 2006, SL 538, NGC 2011, 2098 and 2136. BV RI data, reaching down to V∼ 21 mag, were collected from the 3.5-m NTT/EFOSC2 in subarcsec seeing conditions. For NGC 1767, 1994, 2002, 2003, 2011 and 2136, broad-band photometric CCD data are presented for the first time. Seven of the nine clusters have ages between 16 and 25 Myr, and the other two have ages of 32 ± 4 Myr (NGC 2098) and 90 ± 10 Myr (NGC 2136). For the seven youngest clusters, the age estimates based on a recent model and the integrated spectra are found to be systematically lower (∼10 Myr) than the present estimates. In the mass range ∼2–12 M⊙, the mass function slopes for eight out of nine clusters were found to be similar, with the value of γ ranging from −1.90 ± 0.16 to −2.28 ± 0.21. For NGC 1767 the slope is flatter, with γ=−1.23 ± 0.27. Mass segregation effects are observed for NGC 2002, 2006, 2136 and 2098. This is consistent with the findings of Kontizas and colleagues for NGC 2098. The presence of mass segregation in these clusters could be an imprint of the star formation process, as their ages are significantly smaller than their dynamical evolution time. The mean mass function slope of γ=−2.22 ± 0.16 derived for a sample of 25 young (≤100 Myr) dynamically unevolved Large Magellanic Cloud stellar systems provides support for the universality of the initial mass function in the intermediate-mass range ∼2–12 M⊙.

The poorly constrained cluster disruption time-scale in the Large Magellanic Cloud

We use Monte Carlo simulations, combined with homogeneously determined age and mass distributions, based on multiwavelength photometry, to constrain the cluster formation history and the rate of bound cluster disruption in the Large Magellanic Cloud (LMC) star cluster system. We evolve synthetic star cluster systems formed with a power-law initial cluster mass function (ICMF) of spectral index a = -2 assuming different cluster disruption time-scales. For each of these cluster disruption time-scales, we derive the corresponding cluster formation rate (CFR) required to reproduce the observed cluster age distribution. We then compare, in a 'Poissonian' Χ 2 sense, model mass distributions and model two-dimensional distributions in log(mass) versus log(age) space of the detected surviving clusters to the observations. Because of the bright detection limit (M lim V ≃ -4.7 mag) above which the observed cluster sample is complete, one cannot constrain the characteristic cluster disruption time-scale for a 104 M ⊙ cluster, t dis 4 [where the disruption time-scale depends on cluster mass as t dis = t dis 4 (M cl /10 4 M ⊙ )ν, with γ ≃ 0.62], to better than a lower limit, t dis 4 > 1 Gyr. We conclude that the CFR has been increasing steadily from 0.3 clusters Myr -1 5 Gyr ago to a present rate of (20-30) clusters Myr -1 for clusters spanning a mass range of ∼100-10 7 M ⊙ . For older ages, the derived CFR depends sensitively on our assumption of the underlying CMF shape. If we assume a universal Gaussian ICMF, then the CFR has increased steadily over a Hubble time from ∼1 cluster Gyr -1 15 Gyr ago to its present value. On the other hand, if the ICMF has always been a power law with a slope close to a = -2, the CFR exhibits a minimum some 5 Gyr ago, which we tentatively identify with the well-known age gap in the LMC's cluster age distribution.

Simple stellar population models as probed by the Large Magellanic Cloud star cluster ESO 121-SC03

The presence of blue straggler stars (BSs) in star clusters has proven a challenge to conventional simple stellar population (SSP) models. Conventional SSP models are based on the evolution theory of single stars. Meanwhile, the typical locations of BSs in the colour-magnitude diagram of a cluster are brighter and bluer than the main-sequence turn-off point. Such loci cannot be predicted by single-star evolution theory. However, stars with such properties contribute significantly to the integrated light of the cluster. In this paper, we reconstruct the integrated properties of the Large Magellanic Cloud cluster European Southern Observatory (ESO) 121-SC03, the only cluster populating the well-known age gap in the cluster age distribution, based on a detailed exploration of the individual cluster stars, and with particular emphasis on the cluster's BSs. We find that the integrated light properties of ESO 121-SC03 are dramatically modified by its BS component. The integrated spectral energy distribution (ISED) flux level is significantly enhanced towards shorter wavelengths, and all broad-band colours become bluer. When fitting the fully integrated ISED of this cluster based on conventional SSP models, the best-fitting values of age and metallicity are significantly underestimated compared to the true cluster parameters. The age underestimate is similar to 40 per cent if we only include the BSs within the cluster's half-light radius and similar to 60 per cent if all BSs are included. The corresponding underestimates of the cluster's metallicity are similar to 30 and similar to 60 per cent, respectively. The populous star clusters in the Magellanic Clouds are ideal objects to explore the potential importance of BSs for the integrated light properties of more distant unresolved star clusters in a statistically robust manner, since they cover a large range in age and metallicity.

Extended star formation history of the star cluster NGC 2154 in the Large Magellanic Cloud

The colour-magnitude diagram (CMD) of the intermediate-age Large Magellanic Cloud star cluster NGC 2154 and its adjacent field has been analysed using Padova stellar models to determine the cluster's fundamental parameters and its star formation history. Deep BR CCD photometry, together with synthetic CMDs and integrated luminosity functions, has allowed us to infer that the cluster experienced an extended star formation period of about 1.2 Gyr, which began approximately 2.3 Gyr ago and ended 1.1 Gyr ago. However, the physical reality of such a prolonged period of star formation is questionable, and could be the result of inadequacies in the stellar evolutionary tracks themselves. A substantial fraction of binaries (70 per cent) seems to exist in NGC 2154.

How well do we know the age and mass distributions of the star cluster system in the Large Magellanic Cloud?

The Large Magellanic Cloud (LMC) star cluster system offers the unique opportunity to independently check the accuracy of age (and the corresponding mass) determinations based on a number of complementary techniques. Using our sophisticated tool for star cluster analysis based on broad-band spectral energy distributions (SEDs), 'AnalySED', we re-analyse the Hunter et al. LMC cluster photometry. Our main aim is to set the tightest limits yet on the accuracy of absolute age determinations based on broad-band SEDs, and therefore on the usefulness of such an approach. Our broad-band SED fits yield reliable ages, with statistical absolute uncertainties within Δlog(Age/yr) ≃ 0.4 overall. The systematic differences we find with respect to previous age determinations are caused by conversions of the observational photometry to a different filter system, thus leading to systematically inaccurate results. The LMC's cluster formation rate (CFR) has been roughly constant outside of the well-known age gap between ∼3 and 13 Gyr, when the CFR was a factor of ∼5 lower. Using a simple approach to derive the characteristic cluster disruption time-scale, we find that log(tdis4/yr) = 9.9 ± 0.1 , where tdis=tdis4(Mcl/104 M⊙)0.62 . This long characteristic disruption time-scale implies that we are observing the initial cluster mass function (CMF). We conclude that while the older cluster (sub)samples show CMF slopes that are fully consistent with the α≃−2 slopes generally observed in young star cluster systems, the youngest mass and luminosity-limited LMC cluster subsets show shallower slopes (at least below masses of a few ×103 M⊙ ), which is contrary to dynamical expectations. This may imply that the initial CMF slope of the LMC cluster system as a whole is not well represented by a power law, although we cannot disentangle the unbound from the bound clusters at the youngest ages.