The complex stellar populations in the lines of sight to open clusters in the third Galactic quadrant

Multi-color photometry of the stellar populations in five fields in the third Galactic quadrant centred on the clusters NGC 2215, NGC 2354, Haffner 22, Ruprecht 11, and ESO489SC01 is interpreted in terms of a warped and flared Galactic disk, without resort to an external entity such as the popular Monoceros or Canis Major overdensities. Except for NGC 2215, the clusters are poorly or unstudied previously. The data generate basic parameters for each cluster, including the distribution of stars along the line of sight. We use star counts and photometric analysis, without recourse to Galactic-model-based predictions or interpretations, and confirms earlier results for NGC 2215 and NGC 2354. ESO489SC01 is not a real cluster, while Haffner~22 is an overlooked cluster aged about 2.5 Gyr. Conclusions for Ruprecht~11 are preliminary, evidence for a cluster being marginal. Fields surrounding the clusters show signatures of young and intermediate-age stellar populations. The young population background to NGC~2354 and Ruprecht~11 lies 8-9 kpc from the Sun and $\sim$1 kpc below the formal Galactic plane, tracing a portion of the Norma-Cygnus arm, challenging Galactic models that adopt a sharp cut-off of the disk 12-14 kpc from the Galactic center. The old population is metal poor with an age of 2-3 Gyr, resembling star clusters like Tombaugh 2 or NGC 2158. It has a large color spread and is difficult to locate precisely. Young and old populations follow a pattern that depends critically on the vertical location of the thin and/or thick disk, and whether or not a particular line of sight intersects one, both, or none.Comment: 16 pages, 9 eps figures, in press in MNRA

Luminosity and mass functions of galactic open clusters: II. NGC 4852

e present wide field deep UBVI photometry for the previously unstudied open cluster NGC 4852 down to a limiting magnitude $I\sim24$, obtained from observations taken with the Wide Field Imager camera on-board the MPG/ESO 2.2m telescope at La Silla (ESO, Chile). These data are used to obtain the first estimate of the cluster basic parameters, to study the cluster spatial extension by means of star counts, and to derive the Luminosity (LF) and Mass Function (MF). The cluster radius turns out to be $5.0\pm1.0$ arcmin. The cluster emerges clearly from the field down to V=20 mag. At fainter magnitud es, it is completely confused with the general Galactic disk field. The stars inside this region define a young open cluster (200 million years old) 1.1 kpc far from the Sun (m-M = 11.60, E(B-V) = 0.45). The Present Day Mass Functions (PDMF) from the $V$ photometry is one of the most extended in mass insofar obtained, and can be represented as a power-law with a slope $\alpha = 2.3\pm0.3$ and (the Salpeter (1955) MF in this notation has a slope $\alpha = 2.35$), in the mass range $3.2 \leq \frac{m}{m_{\odot}} \leq 0.6$. Below this mass, the MF cannot be considered as representative of the cluster MF, as the cluster merges with the field and therefore the MF is the result of the combined effect of strong irregularities in the stellar background and interaction of the cluster with the dense Galactic field. The cluster total mass at the limiting magnitude results to be 2570$\pm$210 M$_{\odot}$.Comment: 9 pages, 10 eps figures (some degraded in resolution), accepted for publication in A&

Luminosity and mass functions of galactic open clusters II: NGC 4852

We present wide-field deep UBVI photometry for the previously unstudied open cluster NGC 4852 down to a limiting magnitude I ∼ 24, obtained from observations taken with the Wide Field Imager camera on-board the MPG/ESO 2.2 m telescope at La Silla (ESO, Chile). These data are used to obtain the first estimate of the cluster basic parameters, to study the cluster spatial extension by means of star counts, and to derive the Luminosity (LF) and Mass Function (MF). The cluster radius turns out to be 5.0 ±1.0 arcmin. The cluster emerges clearly from the field down to V = 20 mag. At fainter magnitudes, it is completely confused with the general Galactic disk field. The stars inside this region define a young open cluster (200 million years old) 1.1 kpc far from the Sun (m - M = 11.60, E(B - V) = 0.45). The Present Day Mass Functions (PDMF) from the V photometry is one of the most extended in mass obtained to date, and can be represented as a power-law with a slope α = 2.3 ± 0.3 and (the Salpeter MF in this notation has a slope α = 2.35), in the mass range 3.2 ≤ m/m⊙ ≤ 0.6. Below this mass, the MF cannot be considered as representative of the cluster MF, as the cluster merges with the field and therefore the MF is the result of the combined effect of strong irregularities in the stellar background and interaction of the cluster with the dense Galactic field. The cluster total mass at the limiting magnitude results to be 2570 ±210 M⊙.Facultad de Ciencias Astronómicas y Geofísica

Extended star formation history of the star cluster NGC 2154 in the large magellanic cloud

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

The embedded clusters DBS 77, 78, 102, and 160-161 and their link with the interstellar medium

Aims. We report a study of the global properties of some embedded clusters placed in the fourth quadrant of the Milky Way to clarify some issues related with their location into the Galaxy and their stellar formation processes. Methods. We performed BVI photometric observations in the region of DBS 77, 78, 102, 160, and 161 clusters and infrared spectroscopy in DBS 77 region. They were complemented with JHK data from VVV survey combined with 2MASS catalogue, and used mid-infrared information from GLIMPSE catalogue. We also searched for HI data from SGPS and PMN radio surveys, and previous spectroscopic stellar classification. The spectroscopic and photometric information allowed us to estimate the spectral classification of the brightest stars of each studied region. On the other hand, we used the radio data to investigate the interstellar material parameters and the continuum sources probably associated with the respective stellar components. Results. We estimated the basic physical parameters of the clusters (reddening, distance, age, and initial mass function). We searched for HII regions located near to the studied clusters and we analyzed the possible link between them. In the particular case of DBS 160-161 clusters, we identified the HI bubble B332.5-0.1-42 located around them. We found that the mechanical energy injected to the interstellar medium by the more massive stars of this couple of clusters was enough to generate the bubble.Comment: 15 pages, 14 figures, 6 tables, accepted for publication in A&

The Luminosity & Mass Function of the Trapezium Cluster: From B stars to the Deuterium Burning Limit

We use the results of a new, multi-epoch, multi-wavelength, near-infrared census of the Trapezium Cluster in Orion to construct and to analyze the structure of its infrared (K band) luminosity function. Specifically, we employ an improved set of model luminosity functions to derive this cluster's underlying Initial Mass Function (IMF) across the entire range of mass from OB stars to sub-stellar objects down to near the deuterium burning limit. We derive an IMF for the Trapezium Cluster that rises with decreasing mass, having a Salpeter-like IMF slope until near ~0.6 M_sun where the IMF flattens and forms a broad peak extending to the hydrogen burning limit, below which the IMF declines into the sub-stellar regime. Independent of the details, we find that sub-stellar objects account for no more than ~22% of the total number of likely cluster members. Further, the sub-stellar Trapezium IMF breaks from a steady power-law decline and forms a significant secondary peak at the lowest masses (10-20 times the mass of Jupiter). This secondary peak may contain as many as \~30% of the sub-stellar objects in the cluster. Below this sub-stellar IMF peak, our KLF modeling requires a subsequent sharp decline toward the planetary mass regime. Lastly, we investigate the robustness of pre-main sequence luminosity evolution as predicted by current evolutionary models, and we discuss possible origins for the IMF of brown dwarfs.Comment: 74 pages, 30 figures, AASTeX5.0. To be published in the 01 July 2002 ApJ. For color version of figure 1 and online data table see http://www.astro.ufl.edu/~muench/PUB/publications.htm

Star cluster detection with WFC/ACS in M 33 : 33 new clusters and 51 candidates

In this work we present the detection of 33 star clusters and 51 candidates in one field of the near by galaxy M 33. This study is based on WFC/ACS images available from the HST archive. Thanks to the high resolving power, we were able to confirm that two candidates previously indicated by Christian & Schommer (1982, ApJS, 49, 405) are indeed star clusters. We list the main properties for the star clusters (and candidates), along with some peculiar objects, such as background galaxies and possible HII regions.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

A Circumbinary Planet in Orbit Around the Short-Period White-Dwarf Eclipsing Binary RR Cae

By using six new determined mid-eclipse times together with those collected from the literature, we found that the Observed-Calculated (O-C) curve of RR Cae shows a cyclic change with a period of 11.9 years and an amplitude of 14.3s, while it undergoes an upward parabolic variation (revealing a long-term period increase at a rate of dP/dt =+4.18(+-0.20)x10^(-12). The cyclic change was analyzed for the light-travel time effect that arises from the gravitational influence of a third companion. The mass of the third body was determined to be M_3*sin i' = 4.2(+-0.4) M_{Jup} suggesting that it is a circumbinary giant planet when its orbital inclination is larger than 17.6 degree. The orbital separation of the circumbinary planet from the central eclipsing binary is about 5.3(+-0.6)AU. The period increase is opposite to the changes caused by angular momentum loss via magnetic braking or/and gravitational radiation, nor can it be explained by the mass transfer between both components because of its detached configuration. These indicate that the observed upward parabolic change is only a part of a long-period (longer than 26.3 years) cyclic variation, which may reveal the presence of another giant circumbinary planet in a wide orbit.Comment: It will be published in the MNRA

Luminosity and mass functions of galactic open clusters II: NGC 4852

We present wide-field deep UBVI photometry for the previously unstudied open cluster NGC 4852 down to a limiting magnitude I ∼ 24, obtained from observations taken with the Wide Field Imager camera on-board the MPG/ESO 2.2 m telescope at La Silla (ESO, Chile). These data are used to obtain the first estimate of the cluster basic parameters, to study the cluster spatial extension by means of star counts, and to derive the Luminosity (LF) and Mass Function (MF). The cluster radius turns out to be 5.0 ±1.0 arcmin. The cluster emerges clearly from the field down to V = 20 mag. At fainter magnitudes, it is completely confused with the general Galactic disk field. The stars inside this region define a young open cluster (200 million years old) 1.1 kpc far from the Sun (m - M = 11.60, E(B - V) = 0.45). The Present Day Mass Functions (PDMF) from the V photometry is one of the most extended in mass obtained to date, and can be represented as a power-law with a slope α = 2.3 ± 0.3 and (the Salpeter MF in this notation has a slope α = 2.35), in the mass range 3.2 ≤ m/m⊙ ≤ 0.6. Below this mass, the MF cannot be considered as representative of the cluster MF, as the cluster merges with the field and therefore the MF is the result of the combined effect of strong irregularities in the stellar background and interaction of the cluster with the dense Galactic field. The cluster total mass at the limiting magnitude results to be 2570 ±210 M⊙.Facultad de Ciencias Astronómicas y Geofísica

Extended star formation history of the star cluster NGC 2154 in the large magellanic cloud

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