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ABSTRACT: It is currently widely accepted that open star clusters and stellar
associations result from the evolution of embedded star clusters. Parameters
such star formation efficiency, time-scale of gas removal and velocity
dispersion can be determinants of their future as bound or unbound systems.
Finding objects at an intermediate evolution state can provide constraints to
model the embedded cluster evolution. In the HII region IC1396, Trumpler 37 is
an extended young cluster that presents characteristics of an association. We
employed the Two Micron All Sky Survey (2MASS) photometry to analysing its
structure and stellar content, and determining its astrophysical parameters. We
also analysed 11 bright-rimmed clouds in IC1396 in order to search for young
infrared star clusters, and the background open star cluster Teutsch 74, to
verify whether it has any contribution to the observed stellar density profile
of Trumpler 37. The derived parameters and comparison with template objects
from other studies lead us to conclude that Trumpler 37, rather than as a star
cluster, will probably emerge from its molecular cloud as an OB association.
01/2012;
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J Borissova,
R Kurtev,
S Folkes,
É Artigau,
V Ivanov,
D Minniti,
P Lucas,
F Penaloza,
S Sale, E Bica, [......],
M Hempel,
M Zoccali,
I Toledo,
D Geisler,
C Moni Bidin,
A Ahumada,
R Barba,
R Grijs,
A Jordán,
G Baume
01/2012: pages 101;
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R. K. Saito,
M. Hempel,
D. Minniti,
P. W. Lucas,
M. Rejkuba,
I. Toledo,
O. A. Gonzalez,
J. Alonso-Garcia,
M. J. Irwin,
E. Gonzalez-Solares, [......],
J. Stead,
A. W. Stephens,
M Tamura,
C. Tappert,
M. A. Thompson,
E. Valenti,
L. Vanzi,
N. A. Walton,
W. Weidmann,
A. Zijlstra
[show abstract]
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ABSTRACT: The ESO Public Survey VISTA Variables in the Via Lactea (VVV) started in
2010. VVV targets 562 sq. deg in the Galactic bulge and an adjacent plane
region and is expected to run for ~5 years. In this paper we describe the
progress of the survey observations in the first observing season, the
observing strategy and quality of the data obtained. The observations are
carried out on the 4-m VISTA telescope in the ZYJHKs filters. In addition to
the multi-band imaging the variability monitoring campaign in the Ks filter has
started. Data reduction is carried out using the pipeline at the Cambridge
Astronomical Survey Unit. The photometric and astrometric calibration is
performed via the numerous 2MASS sources observed in each pointing. The first
data release contains the aperture photometry and astrometric catalogues for
348 individual pointings in the ZYJHKs filters taken in the 2010 observing
season. The typical image quality is ~0.9-1.0". The stringent photometric and
image quality requirements of the survey are satisfied in 100% of the JHKs
images in the disk area and 90% of the JHKs images in the bulge area. The
completeness in the Z and Y images is 84% in the disk, and 40% in the bulge.
The first season catalogues contain 1.28x10^8 stellar sources in the bulge and
1.68x10^8 in the disk area detected in at least one of the photometric bands.
The combined, multi-band catalogues contain more than 1.63x10^8 stellar
sources. About 10% of these are double detections due to overlapping adjacent
pointings. These overlapping multiple detections are used to characterise the
quality of the data. The images in the JHKs bands extend typically ~4 mag
deeper than 2MASS. The magnitude limit and photometric quality depend strongly
on crowding in the inner Galactic regions. The astrometry for Ks=15-18 mag has
rms ~35-175 mas.
11/2011;
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ABSTRACT: We investigate the effect that the usually large errors associated with ground-based proper motion (PM) components have on the determination of a star cluster’s velocity dispersion (σv). Rather than histograms, we work with PM distribution functions (PMDFs), taking the 1σ uncertainties formally into account. In this context, a cluster’s intrinsic PMDF is broadened by the error distribution function (eDF) that, given the average error amplitude, has a width usually comparable to the cluster PMDF. Thus, we apply a Richardson–Lucy (RL) deconvolution to the PMDFs of a set of relatively nearby and populous open clusters (OCs), using the eDFs as point spread functions. The OCs are NGC 1039 (M 34), NGC 2477, NGC 2516, NGC 2682 (M 67) and NGC 7762. The deconvolved PMDFs are approximately Gaussian in shape, with dispersions lower than the observed ones by a factor of 4–10. NGC 1039 and 2516, the nearest OCs of the sample, have deconvolved σv compatible with those of bound OCs of mass ∼103 M⊙. NGC 2477 and 2682 have deconvolved PMDFs with a secondary bump, shifted towards higher average velocities, which may be an artefact of the RL deconvolution when applied to asymmetric profiles. Alternatively, it may originate from cluster merger, large-scale mass segregation or, least probably, binaries.
Monthly Notices of the Royal Astronomical Society 07/2011; 415(1):313 - 322. · 4.90 Impact Factor
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J Borissova,
C Bonatto,
R Kurtev,
J R A Clarke,
F Peñaloza,
S E Sale,
D Minniti,
J Alonso-García,
E Artigau,
R Barbá, [......],
M Hempel,
V D Ivanov,
M S N Kumar,
P Lucas,
F Mauro,
C Moni Bidin,
M Rejkuba,
R K Saito,
M Tamura,
I Toledo
[show abstract]
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ABSTRACT: Context. VISTA Variables in the Vía Láctea (VVV) is one of the six ESO Public Surveys operating on the new 4-meter Visible and Infrared Survey Telescope for Astronomy (VISTA). VVV is scanning the Milky Way bulge and an adjacent section of the disk, where star formation activity is high. One of the principal goals of the VVV Survey is to find new star clusters of different ages. Aims. In order to trace the early epochs of star cluster formation we concentrated our search in the directions to those of known star formation regions, masers, radio, and infrared sources. Methods. The disk area covered by VVV was visually inspected using the pipeline processed and calibrated KS-band tile images for stellar overdensities. Subsequently, we examined the composite JHKS and ZJKS color images of each candidate. PSF photometry of 15 × 15 arcmin fields centered on the candidates was then performed on the Cambridge Astronomy Survey Unit reduced images. After statistical field-star decontamination, color-magnitude and color-color diagrams were constructed and analyzed. Results. We report the discovery of 96 new infrared open clusters and stellar groups. Most of the new cluster candidates are faint and compact (with small angular sizes), highly reddened, and younger than 5 Myr. For relatively well populated cluster candidates we derived their fundamental parameters such as reddening, distance, and age by fitting the solar-metallicity Padova isochrones to the color-magnitude diagrams.
Astronomy and Astrophysics 07/2011; 532. · 4.59 Impact Factor
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J. Borissova,
J. R. A. Clarke,
C. Bonatto,
A. N. Chené, E. Bica,
R. Kurtev,
D. Minniti,
F. Peñaloza,
M. Catelan,
P. Lucas,
S. E. Sale,
F. Mauro,
C. Moni Bidin,
D. Geisler,
V. D. Ivanov,
G. L. Baume
[show abstract]
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ABSTRACT: We are reporting the discovery of 156 new infrared open clusters and stellar groups in the Vista Variables in the Via Lactea (VVV) ESO Large Public Survey area.
Scientific Meeting in Honor of Anthony F. J. Moffat, held at Auberge du Lac Taureau, St-Michel-Des-Saints, Québec, Canada,; 07/2011
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ABSTRACT: We investigate five embedded clusters (ECs) and the extended stellar group itself of the prominent H ii region NGC 2174 (Sh2-252), which presents scarce and heterogeneous information coming from the optical and infrared. Considering the discrepant values of distance and age, the clusters and the H ii region appear to be physically unrelated. The analysis is based on field-star-decontaminated 2MASS photometry, which allows sampling of the pre-main sequence (PMS). We find that Sh2-252A, C, E, NGC 2175s and Teu 136 are small ECs (radius within 1.0–2.3 pc) characterized by a similar age (∼5 Myr), reddening (AV∼ 1), distance from the Sun (d⊙∼ 1.4 kpc) and low mass (60–200 M⊙). This age is consistent with the H ii region, the presence of O and B stars still in the main sequence (MS) and the dominance (≳95 per cent by number) of PMS stars in the colour–magnitude diagrams (CMDs). NGC 2175 is not a star cluster, but an extended stellar group that encompasses the ECs Sh2-252 A and C. It contains ∼36 per cent of the member stars (essentially PMS) in the area, with the remaining belonging to the two ECs. CMDs of the overall star-forming region and the ECs provide d⊙= 1.4 ± 0.4 kpc for the NGC 2174 complex, consistent with the value estimated for the physically related association Gem OB1. Our uniform approach shows that NGC 2174 and its related ECs (except, perhaps, for Teu 136) are part of a single star-forming complex. CMD similarities among the ECs and with the overall region suggest a coeval (to within ±5 Myr) star-forming event extending for several Myr. At least four ECs originated in the event, together with the off-cluster star formation that probably gave rise to the scattered stars of NGC 2175.
Monthly Notices of the Royal Astronomical Society 07/2011; 414(4):3769 - 3776. · 4.90 Impact Factor
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ABSTRACT: We investigate the nature of 14 embedded clusters (ECs) related to a group of
four H II regions Sh2-235, Sh2-233, Sh2-232, and Sh2-231 in the giant molecular
cloud G174 + 2.5. Projected towards the Galactic anticentre, these objects are
a possible example of the collect and collapse scenario. We derive
astrophysical parameters (age, reddening, distance, core and cluster radii) for
the ECs and investigate the relationship among their parameters. Parameters are
derived with field decontaminated 2MASS colour-magnitude diagrams (CMDs) and
stellar radial density profiles (RDPs). The CMDs of these young clusters are
characterised by a poorly-populated main sequence and a significant number of
pre-main sequence stars, affected by differential reddening. The ECs are KKC
11, FSR 784, Sh2-235 E2, Sh2-235 Cluster, Sh2-233SE Cluster, BDSB 73, Sh2-235B
Cluster, BDSB 72, BDSB 71, Sh2-232 IR, PCS 2, and the newly found clusters CBB
1 and CBB 2. We were able to derive fundamental parameters for all ECs in the
sample. Structural parameters are derived for FSR 784, Sh2-235 Cluster and
Sh2-235E2.
05/2011;
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ABSTRACT: Context. Poorly-populated star clusters may have photometric and structural properties not much different from aster-isms, to the point that, in some cases, widely-used databases present conflicting classifications. Aims. We investigate the nature of a sample of challenging targets that have been classified either as star clusters or asterisms in different studies. A few objects are studied for the first time. Methods. The analysis employs 2MASS photometry, field-star decontamination, to enhance the intrinsic colour-magnitude diagram (CMD) morphology, and colour-magnitude filters, for high contrast stellar radial density profiles (RDPs). Results. Based on properties derived from field-star decontaminated CMDs, and structural parameters from RDPs, we find that Pismis 12, IC 1434, Juchert 10, Ruprecht 30, NGC 3519, Herschel 1, Mayer 1, and Muzzio 1 are open clusters with ages within 5 Myr -1.3 Gyr. Ruprecht 129, 130, 140, and 146 are borderline cases, being rather poorly-populated, with evolutionary sequences and RDPs suggesting star clusters. Dolidze 39, BH 79, and Ruprecht 103, have CMDs and RDPs typical of asterisms. Conclusions. When a low stellar population is associated with a dense field contamination and/or important differential reddening, only a thin line separates star clusters and asterisms. These cases require specific analytical tools to establish their nature.
05/2011;
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ABSTRACT: The dynamical processes that lead to open cluster disruption cause its mass to decrease. To investigate such processes from the observational point of view, it is important to identify open cluster remnants (OCRs), which are intrinsically poorly populated. Due to their nature, distinguishing them from field star fluctuations is still an unresolved issue. In this work, we developed a statistical diagnostic tool to distinguish poorly populated star concentrations from background field fluctuations. We use 2MASS photometry to explore one of the conditions required for a stellar group to be a physical group: to produce distinct sequences in a colour–magnitude diagram (CMD). We use automated tools to (i) derive the limiting radius; (ii) decontaminate the field and assign membership probabilities; (iii) fit isochrones; and (iv) compare object and field CMDs, considering the isochrone solution, in order to verify the similarity. If the object cannot be statistically considered as a field fluctuation, we derive its probable age, distance modulus, reddening and uncertainties in a self-consistent way. As a test, we apply the tool to open clusters and comparison fields. Finally, we study the OCR candidates DoDz 6, NGC 272, ESO 435 SC48 and ESO 325 SC15. The tool is optimized to treat these low-statistic objects and to separate the best OCR candidates for studies on kinematics and chemical composition. The study of the possible OCRs will certainly provide a deep understanding of OCR properties and constraints for theoretical models, including insights into the evolution of open clusters and dissolution rates.
Monthly Notices of the Royal Astronomical Society 02/2011; 412(3):1611 - 1626. · 4.90 Impact Factor
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D Minniti,
J ~J Clariá,
R ~K Saito,
M Hempel,
P ~W Lucas,
M Rejkuba,
I Toledo,
O ~A Gonzalez,
J {Alonso-Garc'i}a,
M ~J Irwin, [......],
A ~C Schröder,
M Smith,
L Sodré Jr,
A ~W Stephens,
N ~A Walton,
A ~A Zijlstra,
M Tamura,
C Tappert,
M ~A Thompson,
L Vanzi
Boletin de la Asociacion Argentina de Astronomia La Plata Argentina. 01/2011; 54:265-276.
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J Borissova,
J ~R ~A Clarke,
C Bonatto,
A -N Chené, E Bica,
R Kurtev,
R Barbá,
D Minniti,
F Peñaloza,
M Catelan,
P ~W Lucas,
F Mauro,
C Moni Bidin,
D Geisler,
V ~D Ivanov,
G Baume,
C Feinstein
Boletin de la Asociacion Argentina de Astronomia La Plata Argentina. 01/2011; 54:277-280.
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ABSTRACT: We derive fundamental, structural and photometric parameters of 15 overlooked Ruprecht (hereafter Ru) star clusters by means of Two-Micron All-Sky Survey photometry and field-star decontamination. Ru 1, 10, 23, 26, 27, 34, 35, 37, 41, 54, 60, 63, 66 and 152 are located in the third Galactic quadrant, while Ru 174 is in the first. With the constraints imposed by the field-decontaminated colour–magnitude diagrams and stellar radial density profiles (RDPs), we derive ages in the range 400 Myr – 1 Gyr, except for the older Ru 37, with ∼3 Gyr. Distances from the Sun are within 1.5 ≲ d⊙ (kpc) ≲ 8.0. The RDPs are well-defined and can be described by a King-like profile for most of the radial range, except for Ru 23, 27, 41, 63 and 174, which present a conspicuous stellar density excess in the central region. The clusters dwell between (or close to) the Perseus and Sagittarius-Carina arms. We derive evidence in favour of cluster size increasing with distance to the Galactic plane (ZGP), which is consistent with a low frequency of tidal stress associated with high-|ZGP| regions. The clusters are rather faint even in the near-infrared, with apparent integrated J magnitudes within 6.4 ≲mJ≲ 9.8, while their absolute magnitudes are −6.6 ≲MJ≲−2.6. Extrapolation of the relation between MV and MJ, derived for globular clusters, suggests that they are low-luminosity optical clusters, with −5 ≲MV≲−1.
Monthly Notices of the Royal Astronomical Society 09/2010; 407(3):1728 - 1738. · 4.90 Impact Factor
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ABSTRACT: Embedded clusters are formed in molecular clouds where massive stars can produce HII regions. The detailed embedded-open cluster evolutionary connection as well as the origin of associations are yet to be unveiled. There appears to be a high infant mortality rate among embedded clusters and the few survivors evolve to open clusters. We study the colour-magnitude diagrams and structure of the star clusters related to the Sh2-132 HII region using the 2MASS database. Cluster fundamental and structural parameters are determined via MS and PMS isochrones and stellar radial density profiles. We report the discovery of four clusters. One of them is projected a few diameters away from the optical cluster Teutsch\,127 and appears to be deeply embedded, seen only in the infrared. Evidence is found that we are witnessing the dynamical transition from an embedded to an open cluster. An additional cluster is also close to Teutsch\,127 and might be associated with a bow-shock. We also study the CMD and structure of the open cluster Berkeley\,94 in Sh2-132 and a new cluster which is projected in the outskirts of the complex. Finally, we searched for star clusters around the two known Wolf-Rayet stars in the complex. One of them appears to be related to a compact cluster. Finally, the present analyses suggest early dynamical evolution for young star clusters. Comment: 12 pages, 20 figures, 6 tables
06/2010;
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ABSTRACT: We investigate the degree of spatial correlation among extended structures in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). To this purpose, we work with subsamples characterized by different properties such as age and size, taken from the updated catalogue of Bica et al. or gathered in the present work. The structures are classified as star clusters or non-clusters (basically, nebular complexes and their stellar associations). The radius distribution functions follow power laws (dN/dR∝R−α) with slopes and maximum radius (Rmax) that depend on object class (and age). Non-clusters are characterized by α≈ 1.9 and Rmax≲ 472 pc, while young clusters (age ≲10 Myr) have α≈ 3.6 and Rmax≲ 15 pc and old ones (age ≳600 Myr) have α≈ 2.5 and Rmax≲ 40 pc. Young clusters present a high degree of spatial self-correlation and, especially, correlate with star-forming structures, which does not occur with the old ones. This is consistent with the old clusters having been heavily mixed up, since their ages correspond to several LMC and SMC crossing times. On the other hand, with ages corresponding to fractions of the respective crossing times, the young clusters still trace most of their birthplace structural pattern. Also, small clusters (R < 10 pc), as well as small non-clusters (R < 100 pc), are spatially self-correlated, while their large counterparts of both classes are not. The above results are consistent with a hierarchical star formation scenario for the LMC and SMC.
Monthly Notices of the Royal Astronomical Society 03/2010; 403(2):996 - 1008. · 4.90 Impact Factor
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ABSTRACT: We present flux-calibrated integrated spectra for 7 star clusters belonging to the Small Magellanic Cloud in the optical range (≈3600–7000 Ä), obtained at CASLEO (Argentina). Three out of the 7 clusters were not previously studied so their ages and reddening values are determined for the first time in the current study. Using the equivalent widths of selected spectroscopic lines and comparing the cluster spectra with template spectra of known properties, we derive foreground interstellar reddening and age. The clusters are in the (5–300) Myr age range and their E (B – V) colour excesses were in all cases smaller than 0.12. The present data also contribute to enlarge the cluster spectral library at the metallicity level of the Small Magellanic Cloud. The buildup of such database, which also includes Galactic and Large Magellanic Cloud clusters, is a long-term project that we have been developing and which has proved to be useful in the analysis of stellar populations of extragalactic systems (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Astronomische Nachrichten 03/2010; 331(3):323 - 329. · 1.01 Impact Factor
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ABSTRACT: Teutsch 145 and Teutsch 146 are shown to be open clusters (OCs) orbiting well inside the solar circle, a region where several dynamical processes combine to disrupt most OCs on a time-scale of a few 108 yr. BVI photometry from the GALILEO telescope is used to investigate the nature and derive the fundamental and structural parameters of the optically faint and poorly known OCs Teutsch 145 and 146. These parameters are computed by means of field-star-decontaminated colour–magnitude diagrams and stellar radial density profiles (RDPs). Cluster mass estimates are made based on the intrinsic mass functions (MFs). We derive the ages 200+100−50 and 400 ± 100 Myr, and the distances from the Sun d⊙= 2.7 ± 0.3 and 3.8 ± 0.2 kpc, respectively, for Teutsch 145 and 146. Their integrated apparent and absolute magnitudes are mV≈ 12.4 and 13.3 and MV≈−5.6 and −5.3. The MFs (detected for stars with m≳ 1 M⊙) have slopes similar to Salpeter's initial mass function. Extrapolated to the H-burning limit, the MFs would produce total stellar masses of ∼1400 M⊙, typical of relatively massive OCs. Both OCs are located deep into the inner Galaxy and close to the Crux–Scutum arm. Since cluster-disruption processes are important, their primordial masses must have been higher than the present-day values. The conspicuous stellar density excess observed in the innermost bin of both RDPs might reflect the dynamical effects induced by a few 108 yr of external tidal stress.
Monthly Notices of the Royal Astronomical Society 02/2010; 402(3):1685 - 1692. · 4.90 Impact Factor
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D. Minniti,
P. W. Lucas,
J. P. Emerson,
R. K. Saito,
M. Hempel,
P. Pietrukowicz,
A. V. Ahumada,
M. V. Alonso,
J. Alonso-García,
J. I. Arias, [......],
M. R. Schreiber,
A. C. Schröder,
M Smith,
L. Sodré Jr,
M Soto,
M Tamura,
C. Tappert,
M. A. Thompson,
I. Toledo,
M. Zoccali
[show abstract]
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ABSTRACT: We describe the public ESO near-IR variability survey (VVV) scanning the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high. The survey will take 1929 hours of observations with the 4-metre VISTA telescope during five years (2010-2014), covering ~10^9 point sources across an area of 520 deg^2, including 33 known globular clusters and ~350 open clusters. The final product will be a deep near-IR atlas in five passbands (0.9-2.5 microns) and a catalogue of more than 10^6 variable point sources. Unlike single-epoch surveys that, in most cases, only produce 2-D maps, the VVV variable star survey will enable the construction of a 3-D map of the surveyed region using well-understood distance indicators such as RR Lyrae stars, and Cepheids. It will yield important information on the ages of the populations. The observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, INTEGRAL, WISE, Fermi LAT, XMM-Newton, GAIA and ALMA for a complete understanding of the variable sources in the inner Milky Way. This public survey will provide data available to the whole community and therefore will enable further studies of the history of the Milky Way, its globular cluster evolution, and the population census of the Galactic Bulge and center, as well as the investigations of the star forming regions in the disk. The combined variable star catalogues will have important implications for theoretical investigations of pulsation properties of stars. Comment: accepted for publication in New Astronomy
12/2009;
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ABSTRACT: To study the evolution of binary star clusters we have imaged 7 systems in the Small Magellanic Cloud with SOAR 4-m telescope using B and V filters. The sample contains pairs with well-separated components (d < 30 pc) as well as systems that apparently merged, as evidenced by their unusual structures. By employing isochrone fittings to their CMDs we have determined reddening, age and metallicity and by fitting King models to their radial stellar density profile we have estimated core radius. Disturbances of the density profile are interpreted as an evidence of interaction. Circunstances as distances between components and their age difference are addressed in terms of the timescales involved to access the physical connection of the system. In two cases the age difference is above 50 Myr, which suggests chance alignment, capture or sequential star formation. Comment: 4 pages, 1 figure. To appear in online version of Proc. IAU Symp. 266 (Star clusters), eds. R. de Grijs and J. Lepine
09/2009;
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ABSTRACT: NGC 6522 has been the first metal-poor globular cluster identified in the bulge by W. Baade. Despite its importance, very few high resolution abundance analyses of stars in this cluster are available in the literature. The bulge metal-poor clusters may be important tracers of the early chemical enrichment of the Galaxy. The main purpose of this study is the determination of metallicity and elemental ratios in individual stars of NGC 6522. High resolution spectra of 8 giants of the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with the FLAMES+GIRAFFE spectrograph. Multiband V,I,J,Ks} photometry was used to derive effective temperatures as reference values. Spectroscopic parameters are derived from FeI and FeII lines, and adopted for the derivation of abundance ratios. The present analysis provides a metallicity [Fe/H] = -1.0+-0.2. The alpha-elements Oxygen, Magnesium and Silicon show [O/Fe]=+0.4, [Mg/Fe]=[Si/Fe]= +0.25, whereas Calcium and Titanium show shallower ratios of [Ca/Fe]=[Ti/Fe]=+0.15. The neutron-capture r-process element Europium appears to be overabundant by [Eu/Fe]=+0.4. The neutron-capture s-elements La and Ba are enhanced by [La/Fe]=+0.35 and [Ba/Fe]=+0.5. The large internal errors, indicating the large star-to-star variationin the Ba and Eu abundances, are also discussed. The moderate metallicity combined to a blue Horizontal Branch (BHB), are characteristics similar to those of HP~1 and NGC 6558, pointing to a population of very old globular clusters in the Galactic bulge. Also, the abundance ratios in NGC 6522 resemble those in HP 1 and NGC 6558. The ultimate conclusion is that the bulge is old, and went through an early prompt chemical enrichment. Comment: 18 pages, 16 figures. Astronomy & Astrophysics, accepted
08/2009;
