The old open clusters Saurer A, B and C revisited

We report on deep (V $\approx$ 24.0) $VI$ CCD photometry of 3 fields centered in the regions of the old open clusters Saurer A, B and C. In the case of Saurer A, which is considered one of the oldest known open cluster, we also provide a comparison field. From the analysis of the photometry we claim that Saurer A is as old as M 67 ($\approx$ 5 Gyrs), but more metal poor (Z=0.008). Moreover it turns out to be the open cluster with the largest galactocentric distance so far detected. As for Saurer B, it closely resembles NGC 2158, and indeed is of intermediate-age (1.8-2.2 Gyrs) and significantly reddened. In this case we revise both the age and the distance with respect to previous studies, but we are not able to clearly establish the cluster metal abundance. Finally, Saurer C has an age of about 2 Gyrs, but we emphasize that the precise determination of its properties is hampered by the heavy fieldstars contamination.Comment: 10 pages, 16 eps figures, in press in MNRA

The anticenter old open cluster NGC 1883: radial velocity and metallicity

Having already reported on the first photometric study of the intermediate-age open cluster NGC 1883 (Carraro et al. 2003), we present in this paper the first spectroscopic multi-epoch investigation of a sample of evolved stars in the same cluster. The aim is to derive the cluster membership, velocity and metallicity, and discuss recent claims in the literature (Tadross 2005) that NGC 1883 is as metal poor as globular clusters in the Halo. Besides, being one of the few outer Galactic disk intermediate-age open clusters known so far, it is an ideal target to improve our knowledge of the Galactic disk radial abundance gradient, that is a basic ingredient for any chemical evolution model of the Milky Way. The new data we obtained allow us to put NGC 1883's basic parameters more reliable. We find that the cluster has a mean metallicity of [Fe/H] = -0.20$\pm$0.22, from which we infer an age (650$^{+70}_{-70}$ Myr) close to the Hyades one and a Galactocentric distance of 12.3$^{+0.4}_{-0.2}$ kpc. The metal abundance, kinematics, and position make NGC 1883 a genuine outer disk intermediate-age open cluster. We confirm that in the outer Galactic disk the abundance gradient is shallower than in the solar vicinity.Comment: 8 pages, 7 eps figures (some degraded in resolution), accepted for publication in MNRA

NGC 1883: a neglected intermediate-age open cluster located in the outskirts of the Galactic disk

We report on $BVI$ CCD photometry of a field centered in the region of the open cluster NGC 1883 down to V=21. This cluster has never been studied insofar, and we provide for the first time estimates of its fundamental parameters, namely radial extent, age, distance and reddening. We find that the cluster has a radius of about 2.5 arcmin, and shows signatures of dynamical relaxation. NGC 1883 is located in the anti-center direction, and exhibits a reddening in the range E$(B-V)= 0.23-0.35$, depending on the metal abundance. It turns out to be of intermediate-age (1 billion years old), and quite distant for an open cluster. In fact it is located 4.8 kpc from the Sun, and more than 13 kpc from the Galactic center. This results makes NGC 1883 one of the most peripheral old open clusters, with important consequences for the trend of the metallicity with distance in the outer Galactic disk.Comment: 5 pages, 6 eps figures, in press in MNRA

Calculation of Contraction Coefficient under Sluice Gates and Application to Discharge Measurement

The contraction coefficient under sluice gates on flat beds is studied for both free flow and submerged conditions based on the principle of momentum conservation, relying on an analytical determination of the pressure force exerted on the upstream face of the gate together with the energy equation. The contraction coefficient varies with the relative gate opening and the relative submergence, especially at large gate openings. The contraction coefficient may be similar in submerged flow and free flow at small openings but not at large openings, as shown by some experimental results. An application to discharge measurement is also presented

A study of the two northern open clusters NGC 1582 and NGC 1663

We present CCD UBV(I)C observations obtained in the field of the previously unstudied northern open clusters NGC 1582 and NGC 1663. For the former, we also provide high-resolution spectra of the brightest stars and complement our data with Two-Micron All-Sky-Survey (2MASS) near-infrared photometry and with astrometric data from the Tycho-2 catalog. From the analysis of all these data, we argue that NGC 1582 is a very poor, quite large and heavily contaminated open cluster. It turns out to have a reddening EB-V = 0.35 +/- 0.03, to be situated 1100 +/- 100 pc from the Sun and to have an age of 300 +/- 100 Myr. On the other hand, we were not able to unambiguously clarify the nature of NGC 1663. By assuming it is a real cluster and from the analysis of its photometric diagrams, we found a color excess value EB-V = 0.20, an intermediate age value ( ~ 2000 Myr) and a distance of about 700 pc. The distribution of the stars in the region however suggests we are probably facing an open cluster remnant. As an additional result, we obtained aperture photometry of three previously unclassified galaxies placed in the field of NGC 1663 and performed a preliminary morphological classification of them.Fil: Baume, Gustavo Luis. Università di Padova; ItaliaFil: Villanova, S.. Università di Padova; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; ArgentinaFil: Carraro, Giovanni. Università di Padova; Itali

When Rational Sections Become Cyclic: Gauge Enhancement in F-theory via Mordell--Weil Torsion

We explore novel gauge enhancements from abelian to non-simply-connected gauge groups in F-theory. To this end we consider complex structure deformations of elliptic fibrations with a Mordell--Weil group of rank one and identify the conditions under which the generating section becomes torsional. For the specific case of Z2 torsion we construct the generic solution to these conditions and show that the associated F-theory compactification exhibits the global gauge group [SU(2) x SU(4)]/Z2 x SU(2). The subsolution with gauge group SU(2)/Z2 x SU(2), for which we provide a global resolution, is related by a further complex structure deformation to a genus-one fibration with a bisection whose Jacobian has a Z2 torsional section. While an analysis of the spectrum on the Jacobian fibration reveals an SU(2)/Z2 x Z2 gauge theory, reproducing this result from the bisection geometry raises some conceptual puzzles about F-theory on genus-one fibrations.Comment: 51 page