The distance to the young open cluster Westerlund 2

A new X-ray, UBVRIc, and JHKs study of the young cluster Westerlund 2 was undertaken to resolve discrepancies tied to the cluster's distance. Existing spectroscopic observations for bright cluster members and new multi-band photometry imply a reddening relation toward Westerlund 2 described by EU–B/EB–V = 0.63 + 0.02 EB–V. Variable-extinction analyses for Westerlund 2 and nearby IC 2581 based upon spectroscopic distance moduli and ZAMS fitting yield values of RV = AV/EB–V= 3.88 ± 0.18 and 3.77 ± 0.19, respectively, and confirm prior assertions that anomalous interstellar extinction is widespread throughout Carina. The results were confirmed by applying the color-difference method to UBVRIcJHKs data for 19 spectroscopically observed cluster members, yielding RV = 3.85 ± 0.07. The derived distance to Westerlund 2 of d = 2.85 ± 0.43 kpc places the cluster on the far side of the Carina spiral arm. The cluster's age is no more than τ ∼ 2 × 106 yr as inferred from the cluster's brightest stars and an X-ray (Chandra) cleaned analysis of its pre-main-sequence demographic. Four Wolf-Rayet stars in the cluster core and surrounding corona (WR20a, WR20b, WR20c, and WR20aa) are very likely cluster members, and their inferred luminosities are consistent with those of other late-WN stars in open clusters. The color-magnitude diagram for Westerlund 2 also displays a gap at spectral type B0.5 V with associated color spread at higher and lower absolute magnitudes that might be linked to close binary mergers. These features, in conjunction with the evidence for mass loss from the WR stars, may help to explain the high flux of γ-rays, cosmic rays, and X-rays from the direction toward Westerlund 2.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Gestion opérationnelle des transports d’eau dans les canaux et les rivières

Après une présentation générale historique des canaux d'irrigation, de leur importance stratégique et des évolutions récentes, nous définissons de manière plus précise les systèmes hydrauliques à surface libre auxquels nous nous intéressons dans cet article. Nous présentons leurs spécificités qui rendent leur gestion essentielle mais délicate. Nous précisons ensuite ce que nous appelons concrètement "gestion", avec différentes nuances, dont la gestion opérationnelle, et nous utilisons des concepts issus de la gestion industrielle pour mieux l'analyser. Enfin, parmi ces concepts nous détaillons celui des "machines" permettant de mettre en ½uvre cette gestion opérationnelle. / After a historical overview of irrigation canals, their strategic importance and recent trends, we define more precisely the free surface hydraulic systems we analyse in this article. We see that they have features that make their management difficult but essential. Then, we define more precisely what we call "management", with different levels, including "operational management", and we use concepts from production management to better analyze it. Finally, we detail one of these concepts: the "devices" used to implement the operational management

The intermediate-age open clusters Ruprecht 4, Ruprecht 7 and Pismis 15

We report on BVI CCD photometry to V = 22.0 for three fields centred on the region of the Galactic Star clusters Ruprecht 4, Ruprecht 7 and Pismis 15 and on three displaced control fields. Ruprecht 4 and Pismis 15 have never been studied before, and we provide, for the first time, estimates of their fundamental parameters, namely, radial extent, age, distance and reddening. Ruprecht 7 (Berkeley 33), however, was studied by Mazur, Kaluzny & Krzeminski. We find that the three clusters are all of intermediate age (0.8-1. 3 Gyr), and with a metallicity close to or lower than solar.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

The intermediate-age open clusters Ruprecht 61, Czernik 32, NGC 2225 and 2262

We present the first BVI CCD photometry to V = 22.0 of four fields centred on the region of the southern Galactic star clusters Ruprecht 61, Czernik 32, NGC 2225 and 2262 and of four displaced control fields. These clusters have never been studied before, and we provide for the first time estimates of their fundamental parameters, specifically radial extent, age, distance and reddening. We find that the four clusters are all of intermediate age (around 1 Gyr), close to the Sun and possess lower than solar metal abundance.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

A photometric study of the old open clusters Berkeley 73, Berkeley 75 and Berkeley 25

CCD BVI photometry of the faint open clusters Berkeley 73, Berkeley 75 and Berkeley 25 are presented. The two latter are previously unstudied clusters to our knowledge. While Berkeley 73 is found to be of intermediate-age (about 1.5 Gyr old), Berkeley 75 and Berkeley 25 are old clusters, with ages greater than 3.0 Gyr. We provide also estimates of the clusters size. All these clusters lie far away from the Galactic Center, at R GC ≥ 16 kpc, and quite high on the Galactic plane, at |Z ⊙ | ≥ 1.5 kpc. They are therefore important targets to probe the properties of the structure of the Galaxy in this direction, where the Canis Major over-density has been discovered to be located.Facultad de Ciencias Astronómicas y Geofísica

The intermediate-age open clusters Ruprecht 61, Czernik 32, NGC 2225 and 2262

We present the first BVI CCD photometry to V = 22.0 of four fields centred on the region of the southern Galactic star clusters Ruprecht 61, Czernik 32, NGC 2225 and 2262 and of four displaced control fields. These clusters have never been studied before, and we provide for the first time estimates of their fundamental parameters, specifically radial extent, age, distance and reddening. We find that the four clusters are all of intermediate age (around 1 Gyr), close to the Sun and possess lower than solar metal abundance.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

The intermediate-age open clusters Ruprecht 61, Czernik 32, NGC 2225 and NGC 2262

We present the first $BVI$ CCD photometry to $V=22.0$ of 4 fields centered on the region of the southern Galactic star clusters Ruprecht~61, Czernik~32, NGC 2225 and NGC 2262 and of 4 displaced control fields. These clusters were never studied before, and we provide for the first time estimates of their fundamental parameters, namely radial extent, age, distance and reddening. We find that the four clusters are all of intermediate age (around 1 Gyr), close to the Sun and possess lower than solar metal abundance.Comment: 10 pages, 14 figures, in press in MNRA

The distance to the young open cluster Westerlund 2

A new X-ray, UBVRIc, and JHKs study of the young cluster Westerlund 2 was undertaken to resolve discrepancies tied to the cluster's distance. Existing spectroscopic observations for bright cluster members and new multi-band photometry imply a reddening relation toward Westerlund 2 described by EU–B/EB–V = 0.63 + 0.02 EB–V. Variable-extinction analyses for Westerlund 2 and nearby IC 2581 based upon spectroscopic distance moduli and ZAMS fitting yield values of RV = AV/EB–V= 3.88 ± 0.18 and 3.77 ± 0.19, respectively, and confirm prior assertions that anomalous interstellar extinction is widespread throughout Carina. The results were confirmed by applying the color-difference method to UBVRIcJHKs data for 19 spectroscopically observed cluster members, yielding RV = 3.85 ± 0.07. The derived distance to Westerlund 2 of d = 2.85 ± 0.43 kpc places the cluster on the far side of the Carina spiral arm. The cluster's age is no more than τ ∼ 2 × 106 yr as inferred from the cluster's brightest stars and an X-ray (Chandra) cleaned analysis of its pre-main-sequence demographic. Four Wolf-Rayet stars in the cluster core and surrounding corona (WR20a, WR20b, WR20c, and WR20aa) are very likely cluster members, and their inferred luminosities are consistent with those of other late-WN stars in open clusters. The color-magnitude diagram for Westerlund 2 also displays a gap at spectral type B0.5 V with associated color spread at higher and lower absolute magnitudes that might be linked to close binary mergers. These features, in conjunction with the evidence for mass loss from the WR stars, may help to explain the high flux of γ-rays, cosmic rays, and X-rays from the direction toward Westerlund 2.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat