Is the galactic disk older than the halo?

Aim of this study is to infer the age of the Galactic Disk by means of the ages of old open clusters, and comment on some recent claims that the Galactic Disk can be older than the Halo. To this purpose, we analyze the Color-Magnitude Diagrams (CMDs) of six very old clusters, namely NGC 188, NGC 6791, Collinder 261, Melotte 66, Berkeley 39 and Berkeley 17, and determine their ages. For each cluster we use the most recent photometric and spectroscopic data and metallicity estimates. The ages are derived from the isochrone fitting method using the stellar models of the Padua library (Bertelli et al . 1994, Girardi et al. 1999). We find that the ages of these clusters fall in the range 4 to 9-10 Gyr: Melotte 66 is the youngest whereas NGC 6791 and Berkeley 17 have ages of about 9-10 Gyr. Previous estimates for Berkeley 17 indicated an age as old as 12 Gyr, almost falling within the range of classical globular clusters. In our analysis, this cluster is always very old but perhaps somewhat younger than in previous studies. However we call attention on the fact that the above ages are to be taken as provisional estimates, because of the many uncertaintes still affecting stellar models in the mass range 1.0 to 1.5 Mo. Despite this drawback of extant theory of stellar structure, if NGC 6791 and Berkeley 17 set the limit to the age of the Galactic Disk, this component of the Milky Way can be as old as 9-10 Gyr, but surely younger than the Galactic Halo, at least as inferred from recent determinations of the age of globular clusters. Finally, it is worth recalling that open clusters can only provide a lower limit to the age of the Galactic Disk, while other indicators - like White Dwarfs - are perhaps more suited to this task.Comment: 16 pages, 11 figure, accepted for publication in MNRA

Near-infrared photometry of the young open clusters NGC 1893 and Berkeley 86

We present photometry in the J and K near-infrared bands for two regions centered on the young open clusters NGC 1893 and Berkeley 86. We study 700 stars down to K = 17 in the field of NGC 1893, and about 2000 stars in the field of Berkeley 86 down to K$\sim$ 16.5, for which near-infrared photometry was insofar not available. Coupling J-K data with UBV photometry taken from literature, we produce reddening corrected colour-magnitude diagrams. We find that our data are consistent with previous determinations: the clusters are roughly coeval with an age between 4 and 6 million years. The mean reddening (measured as E(J-K)) values turn out to be 0.35 and 0.50 for NGC 1893 and Berkeley 86, respectively.Using colour-colour plots we discuss the presence of candidate pre-main sequence stars showing infrared excess. Candidates are found in both cluster regions, confirming the young age of these clusters.Comment: 9 pages, 12 figures, Astronomy & Astrophysics Main Journal Accepte

Community core detection in transportation networks

This work analyses methods for the identification and the stability under perturbation of a territorial community structure with specific reference to transportation networks. We considered networks of commuters for a city and an insular region. In both cases, we have studied the distribution of commuters' trips (i.e., home-to-work trips and viceversa). The identification and stability of the communities' cores are linked to the land-use distribution within the zone system, and therefore their proper definition may be useful to transport planners.Comment: 8 pages, 13 figure

Effect of Cutting Size and Basal Heat on Rooting of Micromeria fruticulosa Stem Cuttings

Micromeria fruticulosa (Bertol.) Grande is a small pulviniform shrub, belonging to the Labiates, and characterized by twisted stems and pink-purple flowers. Endemic to Campania and Sicily (Italy), M. fruticulosa grows from sea level to 600 m altitude. This specie might be considered an excellent native plant for landscape purposes in Mediterranean areas because of its long flowering period, extending from November to June, and its tolerance to heat and drought. The exploitation of wild plants for ornamental purposes implies knowledge on the factors influencing the propagation methods. Root development of stem cuttings of M. fruticulosa was investigated in relation to basal heat and cutting size. Softwood terminal cuttings of a clone grown in Sicily were trimmed to two sizes: short (3 cm) or long (6 cm) length. Propagation was performed in unheated greenhouse covered with clear polyethylene and external 70% shade-cloth. To verify the rooting response to basal heat, half of the cuttings were placed on a basal heated bench (22 ± 2 °C constant temperature) while the remaining were placed on an unheated bench. Acclimatized rooted cuttings were thereafter transplanted into each plastic pot (diameter 16 cm). Plants were thereafter transplanted in the open field and were evaluated for their ornamental value. Basal heat promoted earlier rooting and positively affected adventitious root formation. Six cm long cuttings exposed to basal heat exhibited the best development in terms of number and length of adventitious roots. Flowering plants derived from 6 cm long cuttings exposed to basal heat showed the highest number of flowering branches and flowers per plant

The intermediate-age open cluster NGC 2158

We report on $UBVRI$ CCD photometry of two overlapping fields in the region of the intermediate-age open cluster NGC 2158 down to V=21. By analyzing Colour-Colour (CC) and Colour-Magnitude Diagrams (CMD) we infer a reddening $E_{B-V}= 0.55\pm0.10$, a distance of $3600 \pm 400$ pc, and an age of about 2 Gyr. Synthetic CMDs performed with these parameters (but fixing $E_{B-V}=0.60$ and $[{\rm Fe/H}]=-0.60$), and including binaries, field contamination, and photometric errors, allow a good description of the observed CMD. The elongated shape of the clump of red giants in the CMD is interpreted as resulting from a differential reddening of about $\Delta E_{B-V}=0.06$ across the cluster, in the direction perpendicular to the Galactic plane. NGC 2158 turns out to be an intermediate-age open cluster with an anomalously low metal content. The combination of these parameters together with the analysis of the cluster orbit, suggests that the cluster belongs to the old thin disk population.Comment: 11 pages, 12 figures, in press in MNRA

Effect of Cutting Size and Basal Heat on Rooting of Micromeria fruticulosa Stem Cuttings

Micromeria fruticulosa (Bertol.) Grande is a small pulviniform shrub, belonging to the Labiates, and characterized by twisted stems and pink-purple flowers. Endemic to Campania and Sicily (Italy), M. fruticulosa grows from sea level to 600 m altitude. This specie might be considered an excellent native plant for landscape purposes in Mediterranean areas because of its long flowering period, extending from November to June, and its tolerance to heat and drought. The exploitation of wild plants for ornamental purposes implies knowledge on the factors influencing the propagation methods. Root development of stem cuttings of M. fruticulosa was investigated in relation to basal heat and cutting size. Softwood terminal cuttings of a clone grown in Sicily were trimmed to two sizes: short (3 cm) or long (6 cm) length. Propagation was performed in unheated greenhouse covered with clear polyethylene and external 70% shade-cloth. To verify the rooting response to basal heat, half of the cuttings were placed on a basal heated bench (22 ± 2 °C constant temperature) while the remaining were placed on an unheated bench. Acclimatized rooted cuttings were thereafter transplanted into each plastic pot (diameter 16 cm). Plants were thereafter transplanted in the open field and were evaluated for their ornamental value. Basal heat promoted earlier rooting and positively affected adventitious root formation. Six cm long cuttings exposed to basal heat exhibited the best development in terms of number and length of adventitious roots. Flowering plants derived from 6 cm long cuttings exposed to basal heat showed the highest number of flowering branches and flowers per plant

Improved Propagation and Growing Techniques for Oleander Nursery Production

In the first trial, we examined rooting of stem cuttings in relation to number of nodes and indole-3-butyric acid (IBA) treatment in several Nerium oleander clones grown in Sicily. In a second trial, we tested the effect of different forcing dates and shading on oleander plants for gardens and natural landscapes. Three- and four-node cuttings, ranging in length from 10 to 14 cm, were significantly superior to two-node cuttings (8–10 cm long) in terms of rooting percentage and number of roots per cutting. The application of IBA improved rooting percentage and root number as compared to untreated control. Irrespective of IBA, rooting percentages ranged from 94% in clone 1 to 52% in clone 4. Shaded plants forced in October were significantly higher than those forced in November and in December. Beginning of flowering was delayed in unforced plants. Plants forced in October flowered significantly sooner (first decade of March) than unforced ones (first decade of May) and reached complete flowering almost two months earlier (last week of March).Shading had little effect on plants forced in October and in November as compared to unshaded plants in terms of start of flowering, but it slightly hastened beginning of flowering of December forced plants as compared to their unshaded counterparts