The Terzan 5 puzzle: discovery of a third, metal-poor component

We report on the discovery of 3 metal-poor giant stars in Terzan 5, a complex stellar system in the the Galactic bulge, known to have two populations at [Fe/H]=-0.25 and +0.3. For these 3 stars we present new echelle spectra obtained with NIRSPEC at Keck II, which confirm their radial velocity membership and provide average [Fe/H]=-0.79 dex iron abundance and [alpha/Fe]=+0.36 dex enhancement. This new population extends the metallicity range of Terzan~5 0.5 dex more metal poor, and it has properties consistent with having formed from a gas polluted by core collapse supernovae.Comment: Accepted for publication on ApJ Lette

Party organisational change in Italy (1991-2006)

This article analyses the organisational change in Italian political parties since 1990 with the aim of finding evidence in favour or against the widespread view in the literature that organisational resources, and hence power, are becoming more and more concentrated in the hands of party and/or parliamentary leaders, and that there is a corresponding decline in the territorial presence of parties. 10 The account made here of the evolution of Italian parties follows quite closely Katz and Mair’s approach by analysing separately their three organisational faces and observing their characteristics and change over time face by face. Trends in membership, finances, staff and party statutes confirm to a large extent the overall research hypothesis.This article analyses the organisational change in Italian political parties since 1990 with the aim of finding evidence in favour or against the widespread view in the literature that organisational resources, and hence power, are becoming more and more concentrated in the hands of party and/or parliamentary leaders, and that there is a corresponding decline in the territorial presence of parties. 10 The account made here of the evolution of Italian parties follows quite closely Katz and Mair’s approach by analysing separately their three organisational faces and observing their characteristics and change over time face by face. Trends in membership, finances, staff and party statutes confirm to a large extent the overall research hypothesis

Proper motions in Terzan 5: membership of the multi-iron sub-populations and first constrain to the orbit

By exploiting two sets of high-resolution images obtained with HST ACS/WFC over a baseline of ~10 years we have measured relative proper motions of ~70,000 stars in the stellar system Terzan 5. The results confirm the membership of the three sub-populations with different iron abudances discovered in the system. The orbit of the system has been derived from a first estimate of its absolute proper motion, obtained by using bulge stars as reference. The results of the integration of this orbit within an axisymmetric Galactic model exclude any external accretion origin for this cluster. Terzan 5 is known to have chemistry similar to the Galactic bulge; our findings support a kinematic link between the cluster and the bulge, further strengthening the possibility that Terzan 5 is the fossil remnant of one of the pristine clumps that originated the bulge.Comment: 25 pages, 14 figures, accepted for publication by Ap

Chemical and kinematical properties of Galactic bulge stars surrounding the stellar system Terzan 5

As part of a study aimed at determining the kinematical and chemical properties of Terzan 5, we present the first characterization of the bulge stars surrounding this puzzling stellar system. We observed 615 targets located well beyond the tidal radius of Terzan 5 and we found that their radial velocity distribution is well described by a Gaussian function peaked at =+21.0\pm4.6 km/s and with dispersion sigma_v=113.0\pm2.7 km/s. This is the one of the few high-precision spectroscopic survey of radial velocities for a large sample of bulge stars in such a low and positive latitude environment (b=+1.7{\deg}). We found no evidence for the peak at \sim+200 km/s found in Nidever et al. 2012. The strong contamination of many observed spectra by TiO bands prevented us from deriving the iron abundance for the entire spectroscopic sample, introducing a selection bias. The metallicity distribution was finally derived for a sub-sample of 112 stars in a magnitude range where the effect of the selection bias is negligible. The distribution is quite broad and roughly peaked at solar metallicity ([Fe/H]\simeq+0.05 dex) with a similar number of stars in the super-solar and in the sub-solar ranges. The population number ratios in different metallicity ranges agree well with those observed in other low-latitude bulge fields suggesting (i) the possible presence of a plateau for |b|<4{\deg} for the ratio between stars in the super-solar (0<[Fe/H]<0.5 dex) and sub-solar (-0.5<[Fe/H]<0 dex) metallicity ranges; (ii) a severe drop of the metal-poor component ([Fe/H]<-0.5) as a function of Galactic latitude.Comment: 27 pages, 9 figures, accepted for publication by Ap

Ceci n'est pas a globular cluster: the metallicity distribution of the stellar system Terzan 5

We present new determinations of the iron abundance for 220 stars belonging to the stellar system Terzan 5 in the Galactic bulge. The spectra have been acquired with FLAMES at the Very Large Telescope of the European Southern Observatory and DEIMOS at the Keck II Telescope. This is by far the largest spectroscopic sample of stars ever observed in this stellar system. From this dataset, a subsample of targets with spectra unaffected by TiO bands was extracted and statistically decontaminated from field stars. Once combined with 34 additional stars previously published by our group, a total sample of 135 member stars covering the entire radial extent of the system has been used to determine the metallicity distribution function of Terzan 5. The iron distribution clearly shows three peaks: a super-solar component at [Fe/H]$\simeq0.25$ dex, accounting for 29% of the sample, a dominant sub-solar population at [Fe/H]$\simeq-0.30$ dex, corresponding to 62% of the total, and a minor (6%) metal-poor component at [Fe/H]$\simeq-0.8$ dex. Such a broad, multi-modal metallicity distribution demonstrates that Terzan 5 is not a genuine globular cluster but the remnant of a much more complex stellar system.Comment: 29 pages, 10 figures. Accepted for publication by Ap

Eco1-dependent cohesin acetylation anchors chromatin loops and cohesion to define functional meiotic chromosome domains

Cohesin organizes the genome by forming intra-chromosomal loops and inter-sister chromatid linkages. During gamete formation by meiosis, chromosomes are reshaped to support crossover recombination and two consecutive rounds of chromosome segregation. Here, we show that meiotic chromosomes are organized into functional domains by Eco1 acetyltransferase-dependent positioning of both chromatin loops and sister chromatid cohesion in budding yeast. Eco1 acetylates the Smc3 cohesin subunit in meiotic S phase to establish chromatin boundaries, independently of DNA replication. Boundary formation by Eco1 is critical for prophase exit and for the maintenance of cohesion until meiosis II, but is independent of the ability of Eco1 to antagonize the cohesin release factor, Wpl1. Conversely, prevention of cohesin release by Wpl1 is essential for centromeric cohesion, kinetochore mono-orientation, and co-segregation of sister chromatids in meiosis I. Our findings establish Eco1 as a key determinant of chromatin boundaries and cohesion positioning, revealing how local chromosome structuring directs genome transmission into gametes