On the stellar content of the open clusters Melotte 105, Hogg 15, pismis 21 and Ruprecht 140

CCD observations in the B, V and I passbands have been used to generate colour-magnitude diagrams reaching down to V = 19 mag for two slightly characterized (Melotte 105 and Hogg 15) and two almost unstudied (Pismis 21 and Ruprecht 140) open clusters. The sample consists of about 1330 stars observed in fields of about 4'x4'. Our analysis shows that neither Pismis 21 nor Ruprecth 140 are genuine open clusters since no clear main sequences or other meaningful features can be seen in their colour-magnitude diagrams. Melotte 105 and Hogg 15 are open clusters affected by E(B-V) = 0.42 +/- 0.03 and 0.95 +/- 0.05, respectively. Their distances to the Sun have been estimated as 2.2 +/- 0.3 kpc and 2.6 +/- 0.8 kpc, respectively, while the corresponding ages estimated from empirical isochrones fitted to the main sequence cluster sequences are approximately 350 Myr and 300 Myr, respectively. The present data are not consistent with the membership of the WN6 star HDE 311884 to Hogg 15.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

The apparent overdensity of open clusters in the Canis Major overdensity

The exciting debate on the existence and nature of the relatively recent discovery of the so-called Canis Major (CMa) overdensity is re-examined here based on the positions, reddenings, ages and metallicities of Galactic open clusters (OCs). The data used to carry out the current study were taken from the recently updated version of the Dias et al.'s 1776 OC catalogue. We found that only Tombaugh 2 is physically located within the main body of CMa. Even if we take into account the whole sample of catalogued OCs with unknown distances, it is statistically expected that only one additional OC could be found within the CMa region. Since the CMa overdensity appears to be quite transparent to dust, only a few OCs in that zone could have been missed. Both metallicity and age distributions of OCs located in the Galactic outer disc, including Tombaugh 2 and those projected on to CMa, are in good agreement with the paradigm of a main dispersion of age and metallicity values. There are only marginal indications for a radial abundance variation. We conclude that CMa does not contain a significant population of OCs which share its properties. This result does not favour the dwarf galaxy scenario. © 2008 The Authors. Journal compilation © 2008 RAS.Fil: Piatti, Andres Eduardo. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Claria Olmedo, Juan Jose. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentin

NGC2587: a sparse open cluster projected on to a populous star field

We present CCD photometry in the Johnson U, B and V and Kron–Cousins I passbands for the open cluster NGC 2587. The sample consists of 4406 stars reaching down to V∼ 21.0. We developed a new method to clean statistically the colour–magnitude diagrams. NGC 2587 appears to be a sparse, relatively bright open cluster, with a few tens of members projected on to a populous star field. The comparatively bright F7/8 II type star HD 70927, located close to the cluster centre, seems not to be a member. Our analysis suggests that NGC 2587 is slightly younger than the Hyades and probably of solar metallicity. A cluster radius of roughly 8 arcmin was estimated from the radial stellar density profile. From 18 probable cluster members with measured proper motions, we derive the following mean values for NGC 2587: μα=−4.3 ± 3.6 mas yr−1 and μδ=−2.5 ± 3.4 mas yr−1. Adopting the theoretical metal content Z= 0.02, which provides the best global fit, we derive a cluster age of 500+60−50. Simultaneously, colour excesses E(B−V) = 0.10 and E(V−I) = 0.15 and an apparent distance modulus of V−MV= 12.50 are obtained. The interstellar extinction in the cluster direction is found to follow the normal law. NGC 2587 is located at a distance of (2.70 ± 0.70) kpc from the Sun and ∼9.8 kpc from the Galactic centre.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. European Southern Observatory; Chil

Sobre la aparente sobredensidad de cúmulos abiertos en la región de la supuesta galaxia enana en Canis Major

We examine the nature of the Canis Major (CMa) stellar overdensity based on the fundamental parameters of the open clusters (OCs) projected in that region. We find only one OC physically located within CMa and estimate that we could statistically find only one additional OC in that zone. Both age and metallicity distributions of OCs show very good agreement with a general dispersion paradigm in the outer disk, with only a marginal evidence of a radial metallicity gradient. These results allow us to conclude that CMa is not a dwarf galaxy accreted by the Milky Way, as some authors have suggested.Examinamos la naturaleza de la sobredensidad estelar en Canis Major (CMa) en base a las propiedades fundamentales de los cumulos abiertos (CAs) galacticos. Encontramos un solo CA fısicamente localizado dentro de CMa y estimamos estadısticamente que podrıamos encontrar solo un CA mas en esta region. Tanto las distribuciones de edad como de metalicidad de los CAs muestran muy buen acuerdo con el paradigma de una dispersion general en el disco exterior, con solo una evidencia marginal de un gradiente radial de abundancia metalica. Estos resultados nos permiten concluir que la sobredensidad estelar en CMa no es una galaxia enana acretada por la Vıa Lactea.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Integrated spectral properties of 7 galactic open clusters

This paper presents flux-calibrated integrated spectra in the range 3600 - 9000 Å for 7 concentrated, relatively populous Galactic open clusters. We perform simultaneous estimates of age and foreground interstellar reddening by comparing the continuum distribution and line strengths of the cluster spectra with those of template cluster spectra with known parameters. For five clusters these two parameters have been determined for the first time (Ruprecht 144, BH 132, Pismis 21, Lyngå11 and BH 217), while the results here derived for the remaining two clusters (Hogg 15 and Melotte 105) show very good agreement with previous studies based mainly on colour-magnitude diagrams. We also provide metallicity estimates for six clusters from the equivalent widths of CaII triplet and TiO features. The present cluster sample improves the age resolution around solar metal content in the cluster spectral library for population synthesis. We compare the properties of the present sample with those of clusters in similar directions. Hogg 15 and Pismis 21 are among the most reddened clusters in sectors centered at l = 270° and l = 0°, respectively. Besides, the present results would favour an important dissolution rate of star clusters in these zones.Fil: Ahumada, Andrea Veronica. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Claria Olmedo, Juan Jose. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Bica, Eduardo. Universidade Federal do Rio Grande do Sul; BrasilFil: Piatti, Andres Eduardo. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentin

The relatively young and metal-poor Galactic open cluster NGC 2194

We present CCD VIKC photometry down to V≈ 21 mag in the field of the rich open cluster NGC 2194, which is projected towards the Galactic anticentre direction. We measured V magnitudes and V−I colours for a total of 2515 stars in a field of 13.6 × 13.6 arcmin2. These data are supplemented with CCD photometry in the C, M and T1 filters of the Washington system and photoelectric CMT1T2 photometry of 20 red giant candidates. Based on the best fits of isochrones computed by the Geneva and Padova groups to the (V, V−I) colour–magnitude diagram, we derive a colour excess E(V−I) = 0.75, a cluster distance of 3.2 kpc and an age of 400 Myr. Five independent Washington abundance indices yield a mean cluster metallicity of [Fe/H]=−0.27 ± 0.06, which is compatible with the existence of both a radial and Z gradient in the Galactic disc. NGC 2194 is a relatively young open cluster, whose deficiency in metal content can be accounted for by the fact that it was born not only far from the Galactic centre in the outer disc, but also at a relatively high Z value.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Primer análisis fotométrico CCD UBVI del cúmulo abierto comparativamente brillante NGC2587

Using CCD UBVIKC images obtained at Cerro Tololo Observatory (Chile) we show that NGC 2587 is a solar metallicity open cluster, somewhat younger than the Hyades, located at ∼ 9.8 kpc from the Galactic center in a direction in which the interstellar extinction follows the normal law. Using previously published kinematic data we determine the mean cluster’s proper motion. Recently, this paper has been extensively published in MNRAS, 397, 1073 (2009).Usando imagenes CCD UBVIKC obtenidas en el Observatorio de Cerro Tololo (Chile), mostramos que NGC 2587 es un cumulo abierto de metalicidad solar, algo mas joven que las Hyades, ubicado a ∼ 9.8 kpc del centro galactico en una direccion en la cual la extincion interestelar sigue la ley normal. Usando datos cinematicos previamente publicados determinamos el movimiento propio medio de NGC 2587. Recientemente, este trabajo ha sido publicado in extenso en MNRAS, 397, 1073.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Photometric and kinematic study of the Galactic open cluster NGC 2309

We have obtained CCD UBVIKC photometry for NGC 2309, a relatively poor open cluster (OC) projected onto a rich star field in Monoceros. Probable cluster members have been identified for the first time from sound photometric criteria. We have derived the angular radius and the fundamental cluster parameters. The resulting reddening and distance values place this object among the relatively most reddened and distant known OCs projected towards the direction of NGC 2309. A detailed version of this work can be seen in PASP, 122, 288 (2010).Hemos obtenido fotometría CCD UBVIKC para NGC 2309, un cúmulo abierto (CA) relativamente pobre en estrellas proyectado sobre un campo estelar densamente poblado en Monoceros. Probables miembros del cúmulo han sido identificados por vez primera vez a partir de s´olidos criterios fotométricos. Hemos derivado el radio angular y los parámetros fundamentales del cúmulo. Los valores resultantes del enrojecimiento y la distancia muestran que NGC 2309 es uno de los CAs conocidos relativamente m´as enrojecidos y distantes proyectados en la dirección de NGC 2309. Una versión detallada del trabajo puede verse en PASP, 122, 288 (2010).Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

First estimates of the fundamental parameters of the relatively bright Galactic open cluster NGC 5288

In this paper we present charge-coupled device (CCD) images in the Johnson B and V and Kron–Cousins I passbands for the previously unstudied open cluster NGC 5288. The sample consists of 15 688 stars reaching down to V ∼ 20.5. The cluster appears to have a relatively small but conspicuous nucleus and a low-density extended coronal region. Star counts carried out in 25 × 25 pixel2 boxes distributed throughout the whole observed field allowed us to estimate the angular core and corona radii as ∼1.3 and 6.3 arcmin, respectively. Our analysis suggests that NGC 5288 is moderately young and probably more metal-rich than the Sun. Adopting the theoretical metal content Z = 0.040, which provides the best global fit, we derive an age of 130+40 −30 Myr. Simultaneously, we have obtained colour excesses E(B − V) = 0.75 and E(V − I) = 0.95 and an apparent distance modulus V − MV = 14.00. The law of interstellar extinction in the cluster direction is found to be normal. NGC 5288 is located at 2.1 ± 0.3 kpc from the Sun beyond the Carina spiral feature and ∼7.4 kpc from the Galactic Centre. The cluster metallicity seems to be compatible with the cluster position in the Galaxy, given the recognized radial abundance gradient in the disc. For the first time, in this paper we determine the basic parameters for the open cluster NGC 5381, situated in the same direction as NGC 5288. This determination was reached by using CCD VI data published almost a decade ago by Pietrzy´nski et al. (1997) for NGC 5381. The properties of some open clusters aligned along the line of sight of NGC 5288 are examined. The properties of clusters of similar ages to NGC 5288 are also looked into. Evidence is presented that these did not form mainly along the spiral arms but rather in the thin Galactic disc (Z ∼ ±100 pc).Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

On the physical nature of six galactic open cluster candidates

Presentamos fotometría CCD UBVIKC en la región de los candidatos a cúmulos abiertos (CAs), previamente no estudiados, Haffner 3, Haffner 5, NGC 2368, Haffner 25, Hogg 3 y Hogg 4. Nuestro análisis demuestra que ninguno de estos objetos son CAs genuinos dado que no se distinguen en sus diagramas color-magnitud y color-color claras secuencias principales u otras características típicas de los CAs. Recuentos estelares realizados dentro y fuera de las regiones de estos objetos no s´olo favorecen estos resultados sino que también sugieren que los mismos no son remanentes de CAs. Una versión detallada del trabajo puede verse en New Astronomy, 16, 161 (2011).We present CCD UBVIKC photometry in the fields of the unstudied open cluster (OC) candidates Haffner 3, Haffner 5, NGC 2368, Haffner 25, Hogg 3 and Hogg 4. Our analysis shows that none of these objects are genuine OCs since no clear main sequences or other typical features can be seen in their colour-magnitude and colour-colour diagrams. Star counts performed within and outside the OC candidate fields not only support these results but also suggest that these objects are not OC remnants. A detailed version of this work can be seen in New Astronomy, 16, 161 (2011).Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin