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

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.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Optical photometry and spectral classification in the field of the open cluster NGC 6996 in the North America Nebula

We present and discuss broad band CCD UBV(I)c photometry and low resolution spectroscopy for stars in the region of the open cluster NGC 6996, located in the North America Nebula. The new data allow us to tightly constrain the basic properties of this object. We revise the cluster size, which in the past has been significantly underestimated. The width of the Main Sequence is mainly interpreted in terms of differential reddening, and indeed the stars' color excess EB-V ranges from 0.43 to 0.65, implying the presence of a significant and evenly distributed dust component. We cross-correlate our optical photometry with near infrared photometry from 2MASS, and by means of spectral classification we are able to build extinction curves for an handful of bright members. We find that the reddening slope and the total to selective absorption ratio Rv toward NGC 6996 are anomalous. Moreover the reddening-corrected colors and magnitudes allow us to derive estimates for the cluster distance and age, which turn out to be 760 ± 70 pc (V0 - Mv = 9.4 ± 0.2) and ∼350 Myr, respectively. Based on our results, we suggest that NGC 6996 is located in front of the North America Nebula, and does not seem to have any apparent relationship with it.Facultad de Ciencias Astronómicas y Geofísica

NGC 2401: A template of the Norma-Cygnus Arm's young population in the Third Galactic Quadrant

Based on a deep optical CCD (UBV(RI)_C) photometric survey and on the Two-Micron All-Sky-Survey (2MASS) data we derived the main parameters of the open cluster NGC 2401. We found this cluster is placed at 6.3 $\pm$ 0.5 kpc (V_O - M_V = 14.0 \pm 0.2) from the Sun and is 25 Myr old, what allows us to identify NGC 2401 as a member of the young population belonging to the innermost side of the extension of the Norma-Cygnus spiral--arm in the Third Galactic Quadrant. A spectroscopic study of the emission star LSS 440 that lies in the cluster area revealed it is a B0Ve star; however, we could not confirm it is a cluster member. We also constructed the cluster luminosity function (LF) down to $V \sim 22$ and the cluster initial mass function (IMF) for all stars with masses above M \sim 1-2 M_{\sun}. It was found that the slope of the cluster IMF is $x \approx 1.8 \pm 0.2$. The presence of a probable PMS star population associated to the cluster is weakly revealed.Comment: 10 paginas, 11 eps figures, accepted for publication in MNRA

Optical photometry and spectral classification in the field of the open cluster NGC 6996 in the North America Nebula

We present and discuss broad band CCD $UBV(I)_C$ photometry and low resolution spectroscopy for stars in the region of the open cluster NGC 6996, located in the North America Nebula. The new data allow us to tightly constrain the basic properties of this object. We revise the cluster size, which in the past has been significantly underestimated. The width of the Main Sequence is mainly interpreted in terms of differential reddening, and indeed the stars' color excess $E_{B-V}$ ranges from 0.43 to 0.65, implying the presence of a significant and evenly distributed dust component. We cross-correlate our optical photometry with near infrared from 2MASS, and by means of spectral classification we are able to build up extinction curves for an handful of bright members. We find that the reddening slope and the total to selective absorption ratio $R_V$ toward NGC 6996 are anomalous. Moreover the reddening corrected colors and magnitudes allow us to derive estimates for the cluster distance and age, which turn out to be $760 \pm 70 pc$ ($V_{0}-M_{V} = 9.4 \pm 0.2$) and $\sim 350$ Myr, respectively. Basing on our results, we suggest that NGC 6996 is located in front of the North America Nebula, and does not seem to have any apparent relationship with it.Comment: 19 pages, 12 eps figures, in press in A&

Orbital period analyses for two cataclysmic variables: UZ Fornacis and V348 Puppis inside the period gap

Four new CCD eclipse timings of the white dwarf for polar UZ Fornacis and six updated CCD mid-eclipse times for SW-Sex-type nova-like V348 Puppis are obtained. Detailed O-C analyses are made for both cataclysmic variables (CVs) inside the period gap. Orbital period increases at a rate of 2.63(±0.58) × 10-11 s s -1 for UZ For and 5.8(±1.9) × 10-12 s s -1 for V348 Pup, respectively, are discovered in their new O-C diagrams. However, conservative mass transfer from the secondary to the massive white dwarf cannot explain the observed orbital period increases for both CVs, which are regarded as part of modulations at longer periods. Moreover, the O-C diagram of UZ For shows a possible cyclical change with a period of 23.4(±5.1) yr. To explain the observed cyclical period changes in UZ For, both mechanisms of magnetic activity cycles in late-type secondaries and the light travel-time effect are regarded as probable causes. Not only does the modulation period of 23.4 yr obey the empirical correlation between Pmod and Ω, but also the estimated fractional period change δP/P ~ 7.3 × 10-7 displays a behaviour similar to that of CVs below the period gap. On the other hand, a calculation for the light travel-time effect implies with a high confidence level that the tertiary component in UZ For may be a brown dwarf, when the orbital inclination of the third body is larger than 16°.Facultad de Ciencias Astronómicas y Geofísica

Orbital period analyses for two cataclysmic variables: UZ Fornacis and V348 Puppis inside the period gap

Four new CCD eclipse timings of the white dwarf for polar UZ Fornacis and six updated CCD mid-eclipse times for SW-Sex-type nova-like V348 Puppis are obtained. Detailed O-C analyses are made for both cataclysmic variables (CVs) inside the period gap. Orbital period increases at a rate of 2.63(±0.58) × 10-11 s s -1 for UZ For and 5.8(±1.9) × 10-12 s s -1 for V348 Pup, respectively, are discovered in their new O-C diagrams. However, conservative mass transfer from the secondary to the massive white dwarf cannot explain the observed orbital period increases for both CVs, which are regarded as part of modulations at longer periods. Moreover, the O-C diagram of UZ For shows a possible cyclical change with a period of 23.4(±5.1) yr. To explain the observed cyclical period changes in UZ For, both mechanisms of magnetic activity cycles in late-type secondaries and the light travel-time effect are regarded as probable causes. Not only does the modulation period of 23.4 yr obey the empirical correlation between Pmod and Ω, but also the estimated fractional period change δP/P ~ 7.3 × 10-7 displays a behaviour similar to that of CVs below the period gap. On the other hand, a calculation for the light travel-time effect implies with a high confidence level that the tertiary component in UZ For may be a brown dwarf, when the orbital inclination of the third body is larger than 16°.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 highly polarized open cluster Trumpler 27

We have carried out multicolor linear polarimetry (UBVRI) of the brightest stars in the area of the open cluster Trumpler 27. Our data show a high level of polarization in the stellar light with a considerable dispersion, from $P = 4$ to $P = 9.5$. The polarization vectors of the cluster members appear to be aligned. Foreground polarization was estimated from the data of some non-member objects, for which two different components were resolved: the first one associated with a dust cloud close to the Sun producing $P_{\lambda max}=1.3$ and $\theta=146$ degrees, and a second component, the main source of polarization for the cluster members, originated in another dust cloud, which polarizes the light in the direction of $\theta= 29.5$ degrees. From a detailed analysis, we found that the two components have associated values $E_{B-V} < 0.45$ for the first one, and $E_{B-V} > 0.75$ for the other. Due the difference in the orientation of both polarization vectors, almost 90 degrees (180 degrees at the Stokes representation), the first cloud ($\theta \sim 146$ degrees) depolarize the light strongly polarized by the second one ($\theta \sim 29.5$ degrees).Comment: 12 Pages, 6 Figures, 2 tables (9 Pages), accepted for publication in A

Influence of Canal Geometry and Dynamics on Controllability

This paper presents the results of the Task Committee on Canal Automation Algorithms with regard to the influence of canal properties on the controllability of irrigation canals. While the control provided by individual algorithms was not evaluated, studies were performed to illustrate inherent hydraulic limitations—the inability of canal pools to recover rapidly from disturbances or flow perturbations. Studies were performed in nondimensional form to develop a better understanding of how pool properties influence pool response. Three such studies were performed. First, nondimensional backwater curves were developed for a range of canal conditions. The second study involved the propagation of waves initiated at the upstream end of a canal pool, as this is influenced by downstream boundary conditions. Finally, the response of pools to downstream withdrawals was examined in terms of their sluggish recovery even when the correct flow change is applied upstream. These results will help in understanding how canal properties influence the ability of operators to effectively control a canal either manually or automatically, and should influence future design practices