CCD Washington photometry of four poorly studied open clusters in the two inner quadrants of the galactic plane

Complementing our Washington photometric studies on Galactic open clusters (OCs), we now focus on four poorly studied OCs located in the first and fourth Galactic quadrants, namely BH 84, NGC 5381, BH 211 and Czernik 37. We have obtained CCD photometry in the Washington system $C$ and $T_1$ passbands down to $T_1$ $\sim$ 18.5 magnitudes for these four clusters. Their positions and sizes were determined using the stellar density radial profiles. We derived reddening, distance, age and metallicity of the clusters from extracted $(C-T_1,T_1)$ color-magnitude diagrams (CMDs), using theoretical isochrones computed for the Washington system. There are no previous photometric data in the optical band for BH 84, NGC 5381 and BH 211. The CMDs of the observed clusters show relatively well defined main sequences, except for Czernik 37, wherein significant differential reddening seems to be present. The red giant clump is clearly seen only in BH 211. For this cluster, we estimated the age in (1000$^{+260}_{-200}$) Myr, assuming a metallicity of $Z$ = 0.019. BH 84 was found to be much older than it was previously believed, while NGC 5381 happened to be much younger than previously reported. The heliocentric distances to these clusters are found to range between 1.4 and 3.4 kpc. BH 84 appears to be located at the solar galactocentric distance, while NGC 5381, BH 211 and Czernik 37 are situated inside the solar ring.Comment: 30 pages, 9 figures, 10 table

Spectral evolution of star clusters in the Large Magellanic Cloud: I. Blue concentrated clusters in the age range 40-300 Myr

Integrated spectroscopy of a sample of 17 blue concentrated Large Magellanic Cloud (LMC) clusters is presented and its spectral evolution studied. The spectra span the range ~3600-6800A with a resolution of ~14A FWHM, being used to determine cluster ages and, in connection with their spatial distribution, to explore the LMC structure and cluster formation history. Cluster reddening values were estimated by interpolation, using the available extinction maps. We used two methods to derive cluster ages: (i) template matching, in which line strengths and continuum distribution of the cluster spectra were compared and matched to those of template clusters with known astrophysical properties, and (ii) equivalent width (EW) method, in which new age/metallicity calibrations were used together with diagnostic diagrams involving the sum of EWs of selected spectral lines (KCaII, G band (CH), MgI, Hdelta, Hgamma and Hbeta). The derived cluster ages range from 40Myr (NGC2130 and SL237) to 300Myr (NGC1932 and SL709), a good agreement between the results of the two methods being obtained. Combining the present sample with additional ones indicates that cluster deprojected distances from the LMC center are related to age in the sense that inner clusters tend to be younger. Spectral libraries of star clusters are useful datasets for spectral classifications and extraction of parameter information for target star clusters and galaxies. The present cluster sample complements previous ones, in an effort to gather a spectral library with several clusters per age bin.Comment: 13 pages, 22 figures. Accepted for publication in A&

Faint, Large-scale H-Alpha Filaments in the Milky Way

During the initial data reduction of the Wisconsin H-Alpha Mapper (WHAM) H-Alpha Sky Survey, we have discovered several very long (~30--80 deg) filaments superimposed on the diffuse H-Alpha background. These features have no clear correspondence to the other phases of the interstellar medium revealed by 21 cm, X-ray, IR, or radio continuum surveys, and they have no readily identifiable origin or source of ionization. In this letter, the data for two of these faint (I_{H-Alpha} = 0.5--1.5 R) structures are presented. The first is an 80 deg-long, 2 deg-wide arch that extends nearly perpendicular to the Galactic plane at l = 225 deg and attains a maximum latitude of +51 deg near l = 240 deg. Where this feature appears to meet the Galactic plane near l = 225 deg, it is directly above the H II region surrounding CMa R1/OB1. A second filament consists of a ~25--30 deg-long arc spanning l = 210--240 deg at b = +30 deg to +40 deg. Both features have measurable velocity trends with position. However, they have rather constant intensities along their entire lengths, ranging from 0.5--1.5 R (EM = 1--3 cm^{-6} pc) with no obvious trends.Comment: 9 pages, 3 figures; Figure 1 is full color PostScript. Accepted for publication by ApJ Letters. More information on the WHAM project can be found at http://www.astro.wisc.edu/wham

Ca II triplet spectroscopy of small magellanic cloud red giants. II. abundances for a sample of field stars

We have obtained metallicities of ∼360 red giant stars distributed in 15 Small Magellanic Cloud (SMC) fields from near-infrared spectra covering the Ca II triplet lines using the VLT + FORS2. The errors of the derived [Fe/H] values range from 0.09 to 0.35 dex per star, with a mean of 0.17 dex. The metallicity distribution (MD) of the whole sample shows a mean value of [Fe/H] = -1.00 ± 0.02, with a dispersion of 0.32 0.01, in agreement with global mean [Fe/H] values found in previous studies. We find no evidence of a metallicity gradient in the SMC. In fact, on analyzing the MD of each field, we derived mean values of [Fe/H] = -0.99 ± 0.08 and [Fe/H] = -1.02 ± 0.07 for fields located closer and farther than 4° from the center of the galaxy, respectively. In addition, there is a clear tendency for the field stars to be more metal-poor than the corresponding cluster they surround, independent of their positions in the galaxy and of the clusters' age. We argue that this most likely stems from the field stars being somewhat older and therefore somewhat more metal-poor than most of our clusters. © 2010. The American Astronomical Society.Fil: Parisi, Maria Celeste. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Geisler, Doug. Universidad de Concepción; ChileFil: Grocholski, A. J.. University of Florida; Estados Unidos. Space Telescope Science Institute; Estados UnidosFil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: Sarajedini, A.. University of Florida; Estados Unido

Photometric observations and Coravel radial velocities of red giant candidates in open clusters

Presentamos fotometrıa fotoelectrica multicolor de alta precision y velocidades radiales (VRs) Coravel para una muestra de candidatas a gigantes rojas (GRs) en nueve cumulos abiertos galacticos. Encontramos que aproximadamente el 82 % de las estrellas analizadas son GRs de los cumulos, de acuerdo a criterios fotometricos, en excelente acuerdo con los resultados inferidos a partir de las VRs Coravel. Se determinan excesos de color E(B − V ), temperaturas efectivas y metalicidades para las gigantes de los cumulos. Una nueva binaria espectroscopica fue descubierta entre las GRs de NGC 2482.We present high precision multicolour photoelectric photometry together with Coravel radial-velocity data for a sample of red giant (RG) candidates in nine Galactic open clusters. Nearly 82% of the analized stars are found to be cluster RGs from photometric criteria, in excellent agreement with the Coravel membership probabilities. E(B − V ) colour excesses, effective temperatures and metallicities are derived for the cluster giants. A new spectroscopic binary was discovered among the RGs of NGC 2482.Fil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; ArgentinaFil: 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: Mermilliod, J. C.. Ecole Polytechnique Federale de Lausanne; FranciaFil: Palma, T.. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentin

Radial Velocities of Six OB Stars

We present new results from a radial velocity study of six bright OB stars with little or no prior measurements. One of these, HD 45314, may be a long-period binary, but the velocity variations of this Be star may be related to changes in its circumstellar disk. Significant velocity variations were also found for HD 60848 (possibly related to nonradial pulsations) and HD 61827 (related to wind variations). The other three targets, HD 46150, HD 54879, and HD 206183, are constant velocity objects, but we note that HD 54879 has H$\alpha$ emission that may originate from a binary companion. We illustrate the average red spectrum of each target.Comment: Accepted for publication in PASP July 2007 issu

Ages and metallicities of five intermediate-age star clusters projected towards the Small Magellanic Cloud

Colour-magnitude diagrams are presented for the first time for L32, L38, K28 (L43), K44 (L68) and L116, which are clusters projected onto the outer parts of the Small Magellanic Cloud (SMC). The photometry was carried out in the Washington system $C$ and $T_1$ filters allowing the determination of ages by means of the magnitude difference between the red giant clump and the main sequence turnoff, and metallicities from the red giant branch locus. The clusters have ages in the range 2-6 Gyr, and metallicities between $-1.65<$ [Fe/H] $<-1.10$, increasing the sample of intermediate-age clusters in the SMC. L116, the outermost cluster projected onto the SMC, is a foreground cluster, and somewhat closer to us than the Large Magellanic Cloud. Our results, combined with those for other clusters in the literature, show epochs of sudden chemical enrichment in the age-metallicity plane, which favour a bursting star formation history as opposede to a continuous one for the SMC.Comment: 12 pages, 11 Postscript figures. MNRAS, in pres

A Spitzer Study of Debris Disks In The Young Nearby Cluster NGC 2232: Icy Planets Are Common Around ~ 1.5--3 Solar-Mass Stars

We describe Spitzer IRAC and MIPS observations of the nearby 25 Myr-old open cluster NGC 2232. Combining these data with ROSAT All-Sky Survey observations, proper motions, and optical photometry/spectroscopy, we construct a list of highly probable cluster members. We identify 1 A-type star, HD 45435, with definite excess emission at 4.5--24 micron indicative of debris from terrestrial planet formation. We also identify 2--4 late-type stars with possible 8 micron excesses, and 8 early-type stars with definite 24 micron excesses. Constraints on the dust luminosity and temperature suggest that the detected excesses are produced by debris disks. From our sample of B and A stars, stellar rotation appears correlated with 24 micron excess, a result expected if massive primordial disks evolve into massive debris disks. To explore the evolution of the frequency and magnitude of debris around A-type stars, we combine our results with data for other young clusters. The frequency of debris disks around A-type stars appears to increase from ~ 25% at 5 Myr to ~ 50--60% at 20--25 Myr. Older A-type stars have smaller debris disk frequencies: ~ 20% at 50--100 Myr. For these ages, the typical level of debris emission rises from 5--20 Myr and then declines. Because 24 micron dust emission probes icy planet formation around A-type stars, our results suggest that the frequency of icy planet formation is eta(i) > 0.5--0.6. Thus, most A-type stars (approx. 1.5--3 Msun) produce icy planets.Comment: 51 pages, 14 figures, accepted for publication in The Astrophysical Journa

Multicolour photometry and Coravel observations of stars in the southern open cluster IC 2488

We preseent new UBV photoelectric observations of 119 stars in the field of the southern open cluster IC 2488, supplemented by DDO and Washington photometry and Coravel radial velocities for a sample of red giant candidates. Nearly 50% of the stars sampled - including three red giants and one blue straggler - are found to be probable cluster members. Photometric membership probabilities of the red giant candidates show good agreement with those obtained from Coravel data. A mean radial velocity of (-2.63 +/- 0.06) km/s is derived for the cluster giants. The reddening across the cluster is found to be E(B-V) = 0.24 +/- 0.04. IC 2488, located at a distance of (1250 +/- 120) pc from the Sun and 96 below the Galactic plane, is most probably not related to the planetary nebulae ESO 166-PN21. A metal abundance 0.10 +/- 0.06 relative to the Sun is determined from DDO data of the red giant members, in good agreement with the metallicity values derived from five independent Washington abundance indices. An age of 180 Myr is determined from the fitting of isochrones computed with convective overshooting for Z = 0.019. The isochrone for log t = 8.25 reproduces remarkably well not only the morphology of the upper main sequence but also the observed red giant pattern.Fil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: 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: Lapasset Gomar, Emilio. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mermilliod, J. C.. Universite de Lausanne; Suiz