arXiv subjects

Eduardo Bica

Publications and source records attributed to Eduardo Bica.

At least 55 records · Page 3Linked to original sources

arXiv2009

Astrophysical parameters of 14 open clusters projected close to the Galactic plane

Astrophysical parameters (\textit{age, reddening, distance, core and cluster radii}) of 14 open clusters (OCs) projected close to the Galactic plane are derived with 2MASS photometry. The OCs are Be 63, Be 84, Cz 6, Cz 7, Cz 12, Ru 141, Ru 144, Ru 172, FSR 101, FSR 1430, FSR 1471, FSR 162, FSR 178 and FSR 198. The OCs Be 63, Be 84, Ru 141, Ru 144, and Ru 172 are studied in more detail than in previous works, while the others have astrophysical parameters derived for the first time. The open clusters of the sample are located at $d_\odot=1.6-7.1$ kpc from the Sun and at Galactocentric distances $5.5-11.8$ kpc, with age in the range 10 Myr to 1.5 Gyr and reddening $E(B-V)$ in the range $0.19-2.56$ mag. The core and cluster radii are in the range $0.27-1.88$ pc and $2.2-11.27$ pc, respectively. Cz 6 and FSR 198 are the youngest OCs of this sample, with a population of pre-main sequence (PMS) stars, while FSR 178 is the oldest cluster.

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arXiv2009

Pfleiderer2: identification of a new globular cluster in the Galaxy

We provide evidence that indicate the star cluster Pfleiderer 2, which is projected in a rich field, as a newly identified Galactic globular cluster. Since it is located in a crowded field, core extraction and decontamination tools were applied to reveal the cluster sequences in B, V and I Color-Magnitude Diagrams (CMDs). The main CMD features of Pfleiderer 2 are a tilted Red Giant Branch, and a red Horizontal Branch, indicating a high metallicity around solar. The reddening is E(B-V)=1.01. The globular cluster is located at a distance from the Sun d$_{\odot}$ = 16$\pm$2 kpc. The cluster is located at 2.7 kpc above the Galactic plane and at a distance from the Galactic center of R$_{\rm GC}$=9.7 kpc, which is unusual for a metal-rich globular cluster.

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arXiv2009

The nature of the young and low-mass open clusters Pismis5, vdB80, NGC1931 and BDSB96

We investigate the nature of 4 young and low-mass open clusters (OCs) located in the $2^{nd}$ and $3^{rd}$ quadrants with near-IR 2MASS photometry (errors $<0.1$ mag). After field decontamination, the colour-magnitude diagrams (CMDs) display similar morphologies: a poorly-populated main sequence (MS) and a dominant fraction of pre-MS (PMS) stars somewhat affected by differential reddening. Pismis 5, vdB 80 and BDSB 96 have MS ages within $5\pm4$ Myr, while the MS of NGC 1931 is $10\pm3$ Myr old. However, non-instantaneous star formation is implied by the wider ($\sim20$ Myr) PMS age spread. The cluster masses derived from MS + PMS stars are low, within $\sim60-180 \ms$, with mass functions (MFs) significantly flatter than Salpeter's initial mass function (IMF). Distances from the Sun are within $1.0-2.4$ kpc, and the visual absorptions are in the range $\aV=1.0-2.0$. From the stellar radial density profiles (RDPs), we find that they are small ($\rc\la0.48$ pc, $\rl\la5.8$ pc), especially Pismis 5 with $\rc\approx0.2$ pc and $\rl\approx1.8$ pc. Except for the irregular and cuspy inner regions of NGC 1931 and Pismis 5, the stellar RDPs follow a King-like profile. At $\sim10$ Myr, central cusps - which in old clusters appear to be related to advanced dynamical evolution - are probably associated with a star-formation and/or molecular cloud fragmentation effect. Despite the flat MFs, vdB 80 and BDSB 96 appear to be typical young, low-mass OCs. NGC 1931 and especially Pismis 5, with irregular RDPs, low cluster mass and flat MFs, do not appear to be in dynamical equilibrium. Both may be evolving into OB associations and/or doomed to dissolution in a few $10^7$ yr.

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arXiv2009

On the possible generation of the young massive open clusters Stephenson2 and BDSB122 by Omega Centauri

A massive objects such as a globular cluster passing through the disk of a galaxy can trigger star formation. We test the hypothesis that the most massive globular cluster in the Galaxy, $ω$ Centauri, which crossed the disk approximately $24\pm2$ Myr ago, may have triggered the formation of the open clusters Stephenson 2 and BDSB 122. The orbits of $ω$ Centauri, Stephenson 2 and BDSB 122 are computed for the three-component model of Johnston, Hernquist & Bolte, which considers the disk, spheroidal and halo gravitational potentials. With the re-constructed orbit of $ω$ Centauri, we show that the latest impact site is consistent, within important uncertainties, with the birth-site of the young massive open clusters BDSB 122 and Stephenson 2. Within uncertainties, this scenario is consistent with the time-scale of their backwards motion in the disk, shock wave propagation and delay for star formation. Together with open cluster formation associated to density waves in spiral arms, the present results are consistent with the idea that massive globular clusters as additional progenitors of open clusters, the massive ones in particular.

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arXiv2009

Probing the age and structure of the nearby very young open clusters NGC 2244 and NGC 2239

The very young open cluster (OC) NGC 2244 in the Rosette Nebula was studied with field-star-decontaminated 2MASS photometry, which shows the main-sequence (MS) stars and an abundant pre-MS (PMS) population. Fundamental and structural parameters were derived with colour-magnitude diagrams (CMDs), stellar radial density profiles (RDPs) and mass functions (MFs). Most previous studies centred NGC 2244 close to the bright K0V star 12 Monocerotis, which is not a cluster member. Instead, the near-IR RDP indicates a pronounced core near the O5 star HD 46150. We derive an age within 1--6 Myr, an absorption $\aV=1.7\pm0.2$, a distance from the Sun $\ds=1.6\pm0.2$ kpc ($\approx1.5$ kpc outside the Solar circle), an MF slope $χ=0.91\pm0.13$ and a total (MS+PMS) stellar mass of $\sim625 \ms$. Its RDP is characterised by the core and cluster radii $\rc\approx5.6\arcmin$ ($\approx2.6$ pc) and $\rl\approx10\arcmin$ ($\approx4.7$ pc), respectively. Departure from dynamical equilibrium is suggested by the abnormally large core radius and the marked central stellar excess. We also investigate the elusive neighbouring OC NGC 2239, which is low-mass ($m_{MS+PMS}\approx301 \ms$), young ($5\pm4$ Myr) rather absorbed ($\aV=3.4\pm0.2$), and located in the background of NGC 2244 at $\ds=3.9\pm0.4$ kpc. Its RDP follows a King-like function of $\rc\approx0.5\arcmin\approx0.5$ pc and $\rl\approx5.0\arcmin\approx5.6$ pc. The MF slope, $χ=1.24\pm0.06$, is essentially Salpeter's IMF. NGC 2244 is probably doomed to dissolution in a few $10^7$ yr. Wide-field extractions and field-star decontamination increase the stellar statistics and enhance both CMDs and RDPs, which is essential for faint and bright star clusters.

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arXiv2008

Investigating the age and structure of the infrared old open clusters LK1, LK10, FSR1521 and FSR1555

(Abridged) - The combination of several mass-decreasing processes may critically affect the structure of open clusters (OCs), to the point that most dissolve into the field in a time-scale shorter than $\approx1$ Gyr. In this paper we focus on 4 candidate old star clusters, namely, LK 1, LK 10, FSR 1521, and FSR 1555. To analyse the target clusters we construct near infrared colour-magnitude diagrams (CMDs) and derive stellar radial density profiles (RDPs). The CMDs are constructed using 2MASS \jj, \hh, and \ks bands, and the intrinsic morphologies of the target OCs within these diagrams are revealed by applying a field-star decontamination algorithm. Fundamental parameters are estimated with Padova isochrones built for the 2MASS filters. We derive extinctions to the objects within the range $3.4\le\aV\le8.9$, which makes them suitable for the near-infrared analysis, ages within $1.0 - 2.0$ Gyr, and distances from the Sun within $1.4 - 4.5$ kpc. These distances, in conjunction with the positions in the sky, place the present 4 OCs close to the solar circle ($\la0.6$ kpc). For LK 10 our photometry reaches a depth $\approx3$ mags below the main sequence turn off, from which we derive a relatively steep mass function slope ($χ=2.4\pm0.4$) when compared to the Salpeter value ($χ=1.35$). LK 10 is a rather massive old OC, with a mass within $1360\le m(\ms)\le4400$, for stars in the observed magnitude range and the extrapolation to $0.08 \ms$, respectively. The mass estimated in the restricted magnitude range for the remaining, more distant OCs is within $260\le m(\ms)\le380$. However, similarity with the CMD morphology and red clump of LK 10 suggests that they may be as massive as LK 10.

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arXiv2008

The old Galactic open clusters FSR1716 and Czernik23

Open clusters older than $\sim4$ Gyr are rare in the Galaxy. Affected by a series of mass-decreasing processes, the stellar content of most open clusters dissolves into the field in a time-scale shorter than $\sim1$ Gyr. In this sense, improving the statistics of old objects may provide constraints for a better understanding of the dynamical dissolution of open clusters. Isochrone fits indicate that FSR 1716 is more probably an old ($\sim7$ Gyr) and absorbed ($\aV=6.3\pm0.2$) open cluster, located $\approx0.6$ kpc inside the Solar circle in a contaminated central field. However, we cannot rule out the possibility of a low-mass, loose globular cluster. Czernik 23 is shown to be an almost absorption-free open cluster, $\sim5$ Gyr old, located about 2.5 kpc towards the anti-centre. In both cases, Solar and sub-Solar ($[Fe/H]\sim-0.5$) metallicity isochrones represent equally well the stellar sequences. Both star clusters have a low mass content ($\la200 \ms$) presently stored in stars. Their relatively small core and cluster radii are comparable to those of other open clusters of similar age. These structural parameters are probably consequence of the several Gyrs of mass loss due to stellar evolution, tidal interactions with the disk (and bulge in the case of FSR 1716), and possibly giant molecular clouds. Czernik 23, and especially FSR 1716, are rare examples of extreme dynamical survivors. The identification of both as such represents an increase of $\approx10%$ to the known population of open clusters older than $\sim4$ Gyr in the Galaxy.

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arXiv2008

Investigating the borderline between a young star cluster and a small stellar association: a test case with Bochum1

Usually, a loose stellar distribution can be classified as an OB stellar group, an association, or a young open cluster. We make use of comparisons with the typical OB association Vul OB1. In the present paper we discuss the nature of Bochum 1, a typical example of an object affected by the above classification problem.The field-decontaminated CMD of Bochum 1 presents main sequence (MS) and pre-main sequence (PMS) stars. We report two new small angular-size, compact young clusters and one embedded cluster in the area of Bochum 1. Vul OB1 harbours the young open cluster NGC 6823 and the very compact embedded cluster Cr 404. The Vul OB1 association includes the H II region Sh2-86, and its stellar content is younger ($\approx3$ Myr) than that of Bochum 1 ($\approx9$ Myr), which shows no gas emission. Bochum 1 harbours one of the newly found compact clusters as its core. The RDP of Bochum 1 is irregular and cannot be fitted by a King-like profile, which suggests important erosion or dispersion of stars from a primordial cluster. Similarly to Bochum 1, the decontaminated CMD of NGC 6823 presents conspicuous MS and PMS sequences. Taken separately, RDPs of MS and PMS stars follow a King-like profile. The core shows an important excess density of MS stars that mimics the profile of a post-core collapse cluster. At such young age, it can be explained by an excess of stars formed in the prominent core. The present study suggests that Bochum 1 is a star cluster fossil remain that might be dynamically evolving into an OB association. Bochum 1 can be a missing link connecting early star cluster dissolution with the formation of low-mass OB associations.

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arXiv2008

A general catalogue of extended objects in the Magellanic System

We update the SMC, Bridge, and LMC catalogues of extended objects that were constructed by members of our group from 1995 to 2000. In addition to the rich subsequent literature for the previous classes, we now also include HI shells and supershells. A total of 9305 objects were cross-identified, while our previous catalogues amounted to 7900 entries, an increase of $\approx12%$. We present the results in subcatalogues containing 1445 emission nebulae, 3740 star clusters, 3326 associations, and 794 HI shells and supershells. Angular and apparent size distributions of the extended objects are analysed. We conclude that the objects, in general, appear to respond to tidal effects arising from the LMC, SMC, and Bridge. Number-density profiles extracted along directions parallel and perpendicular to the LMC bar, can be described by two exponential-disks. A single exponential-disk fits the equivalent SMC profiles. Interestingly, when angular-averaged number-densities of most of the extended objects are considered, the profiles of both Clouds do not follow an exponential-disk. Rather, they are best described by a tidally-truncated, core/halo profile, despite the fact that the Clouds are clearly disturbed disks. On the other hand, the older star clusters taken isolately, distribute as an exponential disk. The present catalogue is an important tool for the unambiguous identification of previous objects in current CCD surveys and to establish new findings.

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arXiv2008

Structures in surface-brightness profiles of LMC and SMC star clusters: evidence of mergers?

The LMC and SMC are rich in binary star clusters, and some mergers are expected. It is important to characterize single clusters, binary clusters and candidates to mergers. We selected a sample of star clusters in each Cloud with this aim. Surface photometry of 25 SMC and 22 LMC star clusters was carried with the ESO Danish 1.54 m telescope. 23 clusters were observed for the first time for these purposes. We fitted Elson, Fall and Freeman (1987, EFF) profiles to the data, deriving structural parameters, luminosities and masses. We also use isophotal maps to constrain candidates to cluster interactions.} {The structural parameters, luminosities and masses presented good agreement with those in the literature. Three binary clusters in the sample have a double profile. Four clusters (NGC 376, K 50, K 54 and NGC 1810) do not have companions and present as well important deviations from EFF profiles. The present sample contains blue and red Magellanic clusters. Extended EFF profiles were detected in some blue clusters. We find evidence that important deviations from the body of EFF profiles might be used as a tool to detect cluster mergers.

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arXiv2008

Exploring FSR open cluster candidates within $|Δ\ell|=20^\circ$ of the Galactic anticentre

We investigate the nature of a sample of star cluster candidates detected as stellar overdensities towards the Galactic anticentre. Taken from the catalogue of Froebrich, Scholz, and Raftery (FSR), the sample contains 28 star cluster candidates located within $|Δ\ell|=20^\circ$ of the anticentre. These are all the candidates in that sector classified by FSR with a high probability of being star clusters. Our main goals are to determine the fraction of such candidates that are unknown star clusters, to derive their astrophysical parameters, and to investigate the relationship of cluster parameters with position in the Galaxy. When photometric and radial distribution properties are considered together, an important fraction of the stellar overdensities with a fluctuation level $\ga3σ$ are shown to be star clusters. Thus, catalogues of star cluster candidates, coupled to the present kind of study, are an important source for identifying unknown open clusters. Such efforts affect the understanding of the star-formation rate, cluster dynamical evolution, and Galactic structure, among others.

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arXiv2008

Discovery of an open cluster with a possible physical association with a planetary nebula

We report the discovery of a new open cluster (OC) in the Galaxy at $\ell=167.0^\circ$ and $b=-1.0^\circ$. Its field includes the planetary nebula (PN) PK 167-0.1. We study the possible associations of the PN/OC pairs NGC 2818/NGC 2818A, NGC 2438/M 46 (NGC 2437), PK 6+2.5/NGC 6469, as well as of the PN PK 167-0.1 with New Cluster 1. The analyses are based on near-infrared colour-magnitude diagrams (CMDs) and stellar radial density profiles (RDPs). NGC 6469 is located in a heavily contaminated bulge field. The CMD morphology, especially for the latter two cases, is defined with a field star decontamination algorithm applied to the 2MASS \jj, \hh, and \ks photometry. Field decontamination for the OCs NGC 2818A and M 46 produced better defined CMDs and more accurate cluster parameters than in the literature. Those pieces of evidence point to M 46 as physically associated with the PN NGC 2438. The same occurs for the OC NGC 2818A and the PN NGC 2818, however previous radial velocity arguments indicate that they are not associated. The OC NGC 6469 does not appear to be associated with the PN PK 6+2.5, which probably belongs to the bulge. Finally, the distance of the OC New Cluster 1 is consistent with a physical association with the PN PK 167-0.1.

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arXiv2007

A populous intermediate-age open cluster and evidence of an embedded cluster among the FSR globular cluster candidates

We study the nature of the globular cluster (GC) candidates FSR 1603 and FSR 1755 selected from the catalogue of \citet{FSRcat}. Their properties are investigated with 2MASS field-star decontaminated photometry, which is used to build colour-magnitude diagrams (CMDs), and stellar radial density profiles (RDPs). FSR 1603 has the open cluster (OC) Ruprecht 101 as optical counterpart, and we show it to be a massive intermediate age cluster (IAC). Relevant parameters of FSR 1603 are the age $\approx1$ Gyr, distance from the Sun $\ds\approx2.7$ kpc, Galactocentric distance $\dgc\approx6.4$ kpc, core radius $\rc\approx1.1$ pc, mass function slope $χ\approx1.8$, observed stellar mass (for stars with mass in the range $\rm 1.27 \ms\leq m\leq2.03 \ms$) $\mObs\approx500 \ms$, and a total (extrapolated to $\rm m=0.08 \ms$) stellar mass $\mTot\approx2300 \ms$. FSR 1755, on the other hand, is not a populous cluster. It may be a sparse young cluster embedded in the H II region Sh2-3, subject to an absorption $\aV\approx4.1$, located at $\ds\approx1.3$ kpc. Important field-star contamination, spatially-variable heavy dust obscuration, even in \ks, and gas emission characterise its field. A nearly vertical, sparse blue stellar sequence shows up in the CMDs.

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arXiv2007

Probing FSR star cluster candidates in bulge/disk directions with 2MASS colour-magnitude diagrams

We analyse 20 star cluster candidates projected mostly in the bulge direction ($|\ell|<60^\circ$). The sample contains all candidates in that sector classified by \citet{FSRcat} with quality flags denoting high probability of being star clusters. Bulge contamination in the colour-magnitude diagrams (CMDs) is in general important, while at lower Galactic latitudes disk stars contribute as well. Properties of the candidates are investigated with 2MASS CMDs and stellar radial density profiles (RDPs) built with field star decontaminated photometry. To uncover the nature of the structures we decontaminate the CMDs from field stars using tools that we previously developed to deal with objects in dense fields. We confirm in all cases excesses in the RDPs with respect to the background level, as expected from the method the candidates were originally selected. CMDs and RDPs taken together revealed 6 open clusters, 5 uncertain cases that require deeper observations, while 9 objects are possibly field density fluctuations.

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arXiv2007

Structural parameters of star clusters: relations among light, mass and star-count radial profiles and the dependence on photometric depth

Structural parameters of model star clusters are measured in radial profiles built from number-density, mass-density and surface-brightness distributions, assuming as well different photometric conditions. Star clusters of different ages, structure and mass functions are modelled by assuming that the radial distribution of stars follows a pre-defined analytical form. Near-infrared surface brightness and mass-density profiles result from mass-luminosity relations taken from a set of isochrones. Core, tidal and half-light, half-mass and half-star count radii, together with the concentration parameter, are measured in the three types of profiles, which are built under different photometric depths. While surface-brightness profiles are almost insensitive to photometric depth, radii measured in number-density and mass-density profiles change significantly with it. Compared to radii derived with deep photometry, shallow profiles result in lower values. This effect increases for younger ages. Radial profiles of clusters with a spatially-uniform mass function produce radii that do not depend on depth. With deep photometry, number-density profiles yield radii systematically larger than those derived from surface-brightness ones. In general, low-noise surface-brightness profiles result in uniform structural parameters that are essentially independent of photometric depth. For less-populous star clusters, those projected against dense fields and/or distant ones, which result in noisy surface-brightness profiles, this work provides a quantitative way to estimate the intrinsic radii by means of number-density profiles built with depth-limited photometry.

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arXiv2007

FSR1767 - a new globular cluster in the Galaxy

The globular cluster (GC) nature of the recently catalogued candidate FSR 1767 is established in the present work. It results as the closest GC so far detected in the Galaxy. The nature of this object is investigated by means of 2MASS colour-magnitude diagrams (CMDs), the stellar radial density profile (RDP) and proper-motions (PM). The properties are consistent with an intermediate metallicity ($\feh\approx-1.2$) GC with a well-defined turnoff (TO), red-giant branch (RGB) and blue horizontal-branch (HB). The distance of FSR 1767 from the Sun is $\ds\approx1.5$ kpc, and it is located at the Galactocentric distance $\rgc\approx5.7$ kpc. With the space velocity components $(V,W)=(184\pm14,-43\pm14)\rm km s^{-1}$, FSR 1767 appears to be a Palomar-like GC with $\mv\approx-4.7$, that currently lies $\approx57$ pc below the Galactic plane. The RDP is well represented by a King profile with the core and tidal radii $\rc=0.24\pm0.08$ pc and $\rt=3.1\pm1.0$ pc, respectively, with a small half-light radius $\rh=0.60\pm0.15$ pc. The optical absorption is moderate for an infrared GC, $A_V=6.2\pm0.3$, which together with its central direction and enhanced contamination explains why it has so far been overlooked.

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arXiv2007

Old open clusters in the inner Galaxy: FSR1744, FSR89 and FSR31

We establish the nature and derive fundamental and structural parameters of the recently catalogued objects FSR1744, FSR89 and FSR31. This work intends to provide clues to constrain the Galactic tidal disruption efficiency, improve statistics of the open cluster parameter space, and better define their age-distribution function inside the Solar circle. Properties of the objects are investigated by means of 2MASS colour-magnitude diagrams and stellar radial density profiles built with field star decontaminated photometry. Diagnostic-diagrams for structural parameters are used to help disentangle dynamical from high-background effects affecting such centrally projected open clusters. FSR1744, FSR89 and FSR31 are Gyr-class OCs located at Galactocentric distances 4.0 - 5.6kpc. Compared to nearby OCs, they have small core and limiting radii. With respect to the small number of OCs observed in the inner Galaxy, the emerging scenario in the near-infrared favours disruption driven by dynamical evolution rather than observational limitations associated with absorption and/or high background levels. Internally, the main processes associated with the dynamical evolution are, e.g. mass loss by stellar evolution, mass segregation and evaporation. Externally they are, e.g. tidal stress from the disk and bulge, and interactions with giant molecular clouds. FSR1744, FSR89 and FSR31 have structural parameters consistent with their Galactocentric distances, in the sense that tidally induced effects may have accelerated the dynamical evolution.

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arXiv2007

Open clusters in dense fields: the importance of field-star decontamination for NGC5715, Lynga4, Lynga9, Trumpler23, Trumpler26 and Czernik37

Star clusters projected onto dense stellar fields require field star decontamination to confirm their nature and derive intrinsic photometric and structural fundamental parameters. The present work focusses on the OCs or candidates NGC5715, Lynga4,9, Trumpler23,26 and Czernik37 which are projected against crowded bulge and/or disc fields. We develop a CMD field star decontamination algorithm based on 2MASS data, and respective uncertainties, to detect cluster star excesses over the background. On the other hand, colour-magnitude filters are used to build stellar radial density profiles and mass functions. The results convey compelling evidence that Ly9 and Cz37 are intermediate-age open clusters, and their fundamental parameters are measured for the first time. Tr23 is a particularly challenging object, since besides high background level, its field presents variable absorption in near-IR bands. We confirm it to be an intermediate-age open cluster. These OCs are located 0.9 - 1.6kpc within the Solar Circle, with ages similar to that of the Hyades. Structurally, they are well described by King profiles. In all cases, core and limiting radii are significantly smaller than those of nearby OCs outside the Solar circle. We test the effect of background levels on cluster radii determinations by means of simulations. They indicate that for central clusters, radii may be underestimated by about 10--20%, which suggests that the small sizes measured for the present sample reflect as well intrinsic properties related to dynamical evolution effects. The objects probably have been suffering important tidal effects that may have accelerated dynamical evolution, especially in Cz37, the innermost object.

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