arXiv subjects

C. M. Dutra

Publications and source records attributed to C. M. Dutra.

17 recordsLinked to original sources

arXiv2004

Discovery of three optical open clusters in the Galaxy

We report the discovery of three optical open clusters in the Milky Way. Two clusters are in Scutum (Cluster1 at l=18.44 degrees and b=-0.42 degrees, and Cluster2 at l=19.60 degrees and b=-1.02 degrees), thus projected not far from the Galactic center direction, and the other is in Canis Major (Cluster3 at l=235.61 degrees and b=-4.10 degrees), near the anti-center direction. Cluster3 is less populous than Clusters 1 and 2, but presents evidence of being a physical system. The objects were found optically by inspecting maps obtained from the Guide Star Catalogue and images from the Digitized Sky Survey. No previous identification of cluster has been reported in each area so far. The analysis was carried out with 2MASS photometry in J and H. For Cluster1 we derive an age of 25 Myr, a reddening E(B-V)=2.18 and a distance from the Sun 1.64kpc; for Cluster2, age of 500Myr, E(B-V)=0.91 and distance 2.19kpc; finally for Cluster3, age 32-100Myr, E(B-V)=0.94 and distance of 3.93kpc. Luminosity and mass functions are derived for Clusters1 and 2 which, in turn, allowed us to estimate their observed masses as 147 and 89 solar masses, respectively. Estimated total masses, by extrapolating the mass functions to 0.08 solar mass, amount to 382 and 614 solar masses, for the two clusters. Cluster3 has an observed mass of 55 solar masses. The present results indicate that further searches in the optical might still reveal new open clusters, and more so in infrared bands.

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arXiv2003

NTT infrared imaging of star cluster candidates towards the central parts of the Galaxy

We address the issue whether the central parts of the Galaxy harbour young clusters other than Arches, Quintuplet and the Nuclear Young Cluster. A large sample of centrally projected cluster candidates has been recently identified from the 2MASS J, H and Ks Atlas. We provide a catalogue of higher angular resolution and deeper images for 57 2MASS cluster candidates, obtained with the near-IR camera SOFI at the ESO NTT telescope. We classify 10 objects as star clusters, some of them deeply embedded in gas and/or dust clouds. Three other objects are probably star clusters, although the presence of dust in the field does not exclude the possibility of their being field stars seen through low-absorption regions. Eleven objects are concentrations of stars in areas of little or no gas, and are classified as dissolving cluster candidates. Finally, 31 objects turned out to be the blend of a few bright stars, not resolved as such in the low resolution 2MASS images. By combining the above results with other known objects we provide an updated sample of 42 embedded clusters and candidates projected within 7 degrees. As a first step we study Object 11 of Dutra & Bica (2000) projected at approximately 1 degree from the nucleus. We present H and Ks photometry and study the colour-magnitude diagram and luminosity function. Object 11 appears to be a less massive cluster than Arches or Quintuplet, and it is located at a distance from the Sun d=8 kpc, with a visual absorption Av=15.

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arXiv2003

On the calibration of the COBE/IRAS dust emission reddening maps

In this work we study the spectral properties (3600 - 6800 A) of the nuclear region of early-type galaxies at low (|b|<25, intermediate (including surroundings of the Magellanic Clouds) and high (South Polar Cap) Galactic latitudes. We determine the E(B-V) reddening values of the galaxies by matching their continuum distribution with respect to those of reddening-free spectral galaxy templates with similar stellar populations. We also compare the spectroscopic reddening value of each galaxy with that derived from 100 micron dust emission (E(B-V)_{FIR}) in its line of sight, and we find that there is agreement up to E(B-V)=0.25. Beyond this limit E(B-V)_{FIR} values are higher. Taking into account the data up to E(B-V) \approx 0.7, we derive a calibration factor of 0.016 between the spectroscopic E(B-V) values and Schlegel et al.'s (1998) opacities. By combining this result with an A_K extinction map built within ten degrees of the Galactic centre using Bulge giants as probes (Dutra et al. 2003), we extended the calibration of dust emission reddening maps to low Galactic latitudes down to |b|=4 and E(B-V)= 1.6 (A_V \approx 5). According to this new calibration, a multiplicative factor of approximately 0.75 must be applied to the COBE/IRAS dust emission reddening maps.

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arXiv2003

New infrared star clusters in the Northern and Equatorial Milky Way with 2MASS

We carried out a survey of infrared star clusters and stellar groups on the 2MASS J, H and K_s all-sky release Atlas in the Northern and Equatorial Milky Way (350 < l < 360, 0 < l < 230). The search in this zone complements that in the Southern Milky Way (Dutra et al. 2003a). The method concentrates efforts on the directions of known optical and radio nebulae. The present study provides 167 new infrared clusters, stellar groups and candidates. Combining the two studies for the whole Milky Way, 346 infrared clusters, stellar groups and candidates were discovered, whereas 315 objects were previously known. They constitute an important new sample for future detailed studies.

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arXiv2003

New infrared star clusters in the southern Milky Way with 2MASS

We carried out a 2MASS J, H and K_s survey of infrared star clusters in the Milky Way sector 230$^{\circ}$ $< \ell <$ 350$^{\circ}$. This zone was the least studied in the literature, previously including only 12 infrared clusters or stellar groups with $|b|<$ 10$^{\circ}$, according to the recent catalogue by Bica et al. (2003). We concentrated efforts on embedded clusters, which are those expected in the areas of known radio and optical nebulae. The present study provides 179 new infrared clusters and stellar groups, which are interesting targets for detailed future infrared studies. The sample of catalogued infrared clusters and stellar groups in the Galaxy is now increased by 63%.

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arXiv2002

A Catalogue of infrared star clusters and stellar groups

We compiled a catalogue of infrared star clusters in the Galaxy, which are most of them embedded. It condenses the growing literature information. We also include in the sample infrared stellar groups which are less dense than star clusters, such as those embedded in the dark clouds Taurus-Auriga and Chamaleon I. We provide galactic and equatorial coordinates, angular dimensions, different designations and related objects such as nebulae. A total of 189 infrared clusters and 87 embedded stellar groups are included. A fraction of 25 % of the embedded clusters are projected close to each other in pair or triplet systems, indicating that multiplicity plays an important role in star cluster formation.

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arXiv2002

Extinction within 10 degrees of the Galactic Centre using 2MASS

We extract J and K_s magnitudes from the 2MASS Point Source Catalog for approximately 6 million stars with 8 < K_s < 13 in order to build an A_K extinction map within 10 degrees of the Galactic centre. The extinction was determined by fitting the upper giant branch of (K_s, J-K_s) colour-magnitude diagrams to a dereddened upper giant branch mean locus built from previously studied Bulge fields. The extinction values vary from A_K=0.05 in the edges of the map up to A_K=3.2 close to the Galactic centre. The 2MASS extinction map was compared to that recently derived from DENIS data. Both maps agree very well up to A_K=1.0. The 2MASS extinction values were also compared to those obtained from dust emission in the far infrared using DIRBE/IRAS. Several systematic effects likely to bias this comparison were addressed, including the presence of dust on the background of the bulk of 2MASS stars used in the extinction determination. For the region with $3^{\circ}<|b|<5^{\circ}$, where the dust contribution on the far side of the Galaxy is $\approx$ 5%, the two extinction determinations correlate well, but the dust emission A_K values are systematically higher than those from 2MASS. A calibration correction factor of 76% for the DIRBE/IRAS dust emission extinction is needed to eliminate this systematic effect. Similar comparisons were also carried out for the $1^{\circ}<|b|<3^{\circ}$ and $|b| < 0.5^{\circ}$ strips. An asymmetry relative to the Galactic plane is observed in the dust maps, roughly in the sense that A_K values are 60% smaller in the south than in the north for $1^{\circ}<|b|<5^{\circ}$. This asymmetry is due to the presence of foreground dust clouds mostly in the northern region of the Bulge.

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arXiv2002

A catalogue of dust clouds in the Galaxy

In this study 21 catalogues of dust clouds in the Galaxy were cross-identified by taking into account available properties such as position, angular dimensions, opacity class and velocity. An initial list of $\approx$6500 entries was condensed into a cross-identified all-sky catalogue containing 5004 dust clouds. In particular, the transition zone between high and low Galactic latitude studies was also cross-identified. The unified catalogue contains 525 high-latitude clouds. The catalogue deals primarily with optical dark nebulae and globules, but it includes as well substantial information from their molecular counterparts. Some previously uncatalogued clouds were detected on optical images and FIR maps. Finally, we address recent results and prospective work based on NIR imaging, especially for clouds detected in the 2MASS $K_s$ Atlas.

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arXiv2001

Low-extinction windows in the inner Galactic Bulge

We built K band extinction maps in the area of two candidate low-extinction windows in the inner Bulge: W0.2-2.1 at (l,b) = (0.25o,-2.15o), and W359.4-3.1 at (l,b) = (359.40o,-3.10o). We employed JHKs photometry from the 2MASS Point Source Catalog. Extinction values were determined by fitting the upper giant branch found in the present 2MASS Ks x J-Ks diagrams to a de-reddened bulge stellar population reference giant branch. We tested the method on the well known Baade's and Sgr I windows: the 2MASS mean extinction values in these fields agreed well with those of previous studies. We confirm the existence of low-extinction windows in the regions studied, as local minima in the A_K maps reaching A_K values about 2 standard deviations below the mean values found in the neighbouring areas. Schlegel et al.'s (1998) FIR extinction maps, which integrate dust contributions throughout the Galaxy, are structurally similar to those derived with 2MASS photometry in the two studied windows. We thus conclude that the dust clouds affecting the 2MASS and FIR maps in these directions are basically the same and are located on foreground of the bulk of bulge stars. However, the A_K absolute values differ significantly. In particular, the FIR extinction values for W359.4-3.1 are a factor ~1.45 larger than those derived from the 2MASS photometry. Possible explanations of this effect are discussed. The lower Galactic latitudes of the low-extinction windows W359.4-3.1 and W0.2-2.1, as compared to Baade's Window, make them promising targets for detailed studies of more central bulge regions.

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arXiv2001

New infrared star clusters and candidates in the Galaxy detected with 2MASS

A sample of 42 new infrared star clusters, stellar groups and candidates was found throughout the Galaxy in the 2MASS J, H and especially K$_S$ Atlases. In the Cygnus X region 19 new clusters, stellar groups and candidates were found as compared to 6 such objects in the previous literature. Colour-Magnitude Diagrams using the 2MASS Point Source Catalogue provided preliminary distance estimates in the range 1.0 $<$ d$_{\odot}$ $<$ 1.8 kpc for 7 Cygnus X clusters. Towards the central parts of the Galaxy 7 new IR clusters and candidates were found as compared to 61 previous objects. A search for prominent dark nebulae in K$_S$ was also carried out in the central bulge area. We report 5 dark nebulae, 2 of them are candidates for molecular clouds able to generate massive star clusters near the Nucleus, such as the Arches and Quintuplet clusters.

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arXiv2001

Open clusters or their remnants: B and V photometry of NGC 1901 and NGC 1252

Photometry in the B and V bands is presented for the southern stellar groups NGC 1901 and NGC 1252. NGC 1901 is often described as an open cluster while NGC 1252 consists of a concentration of about 20 stars centered approx 20' north of the original New General Catalogue coordinates, and at the southwest edge of the large region previously assigned to this object in the literature. NGC 1901 has a clear main sequence and shares similarities with the Hyades. We derive a reddening value E(B-V) = 0.04, a distance from the Sun d = 0.45 kpc (Z = -0.23 kpc) and an age 0.6 +/- 0.1 Gyr. NGC 1901 is conclusively a physical system, dynamically comparable to or more evolved than the Hyades. The colour- magnitude diagram of NGC 1252 suggests a turnoff and main sequence, and a total of 12 probable members. We simulated the Galactic field colour-magnitude diagram in the same direction and found it to be a poor match to NGC 1252, suggesting that NGC 1252 is not a field fluctuation. Isochrone fitting to the probable members is consistent with E(B-V) = 0.02, a distance from the Sun d = 0.64 kpc (Z = -0.46 kpc) and an age 3 +/- 1 Gyr. NGC 1252 cannot be ruled out as a physical group with the available data. If so, evidence is found that it is not a classical open cluster, but rather an open cluster remnant.

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arXiv2001

Background galaxies as reddening probes throughout the Magellanic Clouds

We study the spectral properties in the range 3600 Å- 6800 Åof the nuclear region of galaxies behind the Magellanic Clouds. The radial velocities clarified the nature of the objects as background galaxies or extended objects belonging to the Clouds. For most galaxies behind the main bodies of the LMC and SMC, radial velocities were measured for the first time. In the present sample typical LMC background galaxies are nearby (4000 < V(km/s) < 6000), while SMC's are considerably more distant (10000 < V(km/s) < 20000). We determine the reddening in each line of sight by matching a reddening-free galaxy template with comparable stellar population. For the LMC main body we derive a combined Milky Way and internal reddening value E(B-V)$_{MW+i}$ = 0.12$\pm$0.10, while for the SMC E(B-V)$_{MW+i}$ = 0.05$\pm$0.05. By subtracting Milky Way reddening values for galaxies projected onto the surroundings of each Cloud, we estimate average internal reddening values $Δ$E(B-V)$_i$ = 0.06 and 0.04, respectively for the main bodies of the LMC and SMC. The Clouds are optically thin, at least in the directions of the studied background galaxies which are often difficult to be identified as such on ESO/SERC sky survey images. Nevertheless, more reddened zones may occur where it is difficult to identify galaxies.

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arXiv2000

Dissolving star cluster candidates

We present a list of 34 neglected entries from star cluster catalogues located at relatively high galactic latitudes ($|b| >$ 15$^{\circ}$) which appear to be candidate late stages of star cluster dynamical evolution. Although underpopulated with respect to usual open clusters, they still present a high number density contrast as compared to the galactic field. This was verified by means of (i) predicted model counts from different galactic subsystems in the same direction, and (ii) Guide Star Catalog equal solid angle counts for the object and surrounding fields. This suggests that the objects are physical systems, possibly star clusters in the process of disruption or their fossil remains. The sample will be useful for followup studies in view of verifying their physi cal nature.

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arXiv2000

New star clusters projected close to the Galactic Centre

We carried out a systematic search for new star clusters in a field of 5$^{\circ} \times5^{\circ}$ centred close to the Galactic Nucleus using the infrared JHK$_s$ 2MASS Survey archive. In addition we searched for embedded clusters in the directions of HII regions and dark clouds for $|\ell|\le4^{\circ}$. As a result we present a list of 58 IR star clusters or candidates. We provide positions, sizes and reddening estimated from 100 $μ$m dust emission. Their angular distribution together with previously catalogued objects in the region and possible relation with star forming complexes are also discussed.

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arXiv2000

Morphologies and ages of star cluster pairs and multiplets in the Small Magellanic Cloud

An isophotal atlas of 75 star cluster pairs and multiplets in the Small Magellanic Cloud is presented, comprising 176 objects. They are concentrated in the SMC main body. The isophotal contours were made from Digitized Sky Survey images and showed relevant structural features possibly related to interactions in about 25% of the sample. Previous N-body simulations indicate that such shapes could be due to tidal tails, bridges or common envelopes. The diameter ratio between the members of a pair is preferentially in the range 1 - 2, with a peak at 1. The projected separation is in the range ~ 3 - 22 pc with a pronounced peak at ~ 13 pc. For 91 objects it was possible to derive ages from Colour-Magnitude Diagrams using the OGLE-II photometric survey. The cluster multiplets in general occur in OB stellar associations and/or HII region complexes. This indicates a common origin and suggests that multiplets coalesce into pairs or single clusters in a short time scale. Pairs in the SMC appear to be mostly coeval and consequently captures are a rare phenomenon. We find evidence that star cluster pairs and multiplets may have had an important role in the dynamical history of clusters presently seen as large single objects.

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arXiv2000

Foreground and background dust in star cluster directions

This paper compares reddening values E(B-V) derived from the stellar content of 103 old open clusters and 147 globular clusters of the Milky Way with those derived from DIRBE/IRAS 100 micron dust emission in the same directions. Star clusters at |b|> 20 show comparable reddening values between the two methods, in agreement with the fact that most of them are located beyond the disk dust layer. For very low galactic latitude lines of sight, differences occur in the sense that DIRBE/IRAS reddening values can be substantially larger, suggesting effects due to the depth distribution of the dust. The differences appear to arise from dust in the background of the clusters consistent with a dust layer where important extinction occurs up to distances from the Plane of ~ 300 pc. For 3 % of the sample a significant background dust contribution might be explained by higher dust clouds. We find evidence that the Milky Way dust lane and higher dust clouds are similar to those of several edge-on spiral galaxies recently studied in detail by means of CCD imaging.

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arXiv1999

Updating the census of star clusters in the Small Magellanic Cloud

Surveys using CCD detectors are retrieving bright and faint cataloged clusters and revealing new ones in the Magellanic Clouds. This paper discusses the contribution of the OGLE Survey to the overall census of star clusters in the SMC. A detailed cross-identification indicates that the new objects in the SMC OGLE catalog are 46. The increase in the number of cataloged clusters is ~ 7%, the total sample being ~ 700. This updated census includes embedded clusters in HII regions and a density range attaining loose systems.

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