Arcetri Astrophysical Observatory

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Arcetri hosts the fifth edition of the Galaxy Evolution and Environment conference series

The "Galaxy Evolution and Environment" (GEE) is a series of conferences that aims to bring together the astronomical community in Italy working in this field to share updates and highlights from ongoing projects and stimulate new ideas and collaborative efforts. This tradition started in 2009 in Bologna and has been repeated every two years (Milano, Padova, Naples).

banner GEE5

The fifth edition of GEE has been co-organized by Stefano Zibetti and Anna Gallazzi from the Arcetri Astrophysical Observatory together with Bianca Poggianti (Padova Astronomical Observatory) and Angela Iovino (Brera Astronomical Observatory), the two lead organizers of the GEE series. The GEE5 meeting has been funded by INAF and by the Arcetri Astrophysical Observatory and hosted by the Department of Physics and Astronomy of the University of Florence at the "Garbasso" historical building on the Arcetri hill.

The meeting has seen the participation of about 60 astronomers working in Italy and a few coming from abroad, with a significant contribution by PhD students and young researchers.  The program of the GEE5 aimed at discussing recent advances and ongoing efforts on galaxy evolution and environment from the joint perspectives of observations and of simulations and theory. The topics of the various sessions covered: the evolution of galaxy populations in clusters and in the field, the gas and dust in nearby and high-redshift galaxies as tracers of star formation and feedback, clusters and BCGs and their redshift evolution. Several people from the Arcetri Astrophysical Observatory gave talks on each of these topics: Anna Gallazzi, Stefano Zibetti, Leslie Hunt, Simone Bianchi, Mirko Curti, Giovanni Cresci, Matilde Mingozzi, Giacomo Venturi, Paolo Tozzi. Infos and presentations are available online at the GEE5 webpage.

The merger of two neutron stars opens the era of multimessenger astronomy

 

On August 17 at 12:41:04 UT the two LIGO and the Virgo gravitational wave interferometers detected the merging of two neutron stars, which occurred in the lenticular galaxy NGC 4993 at a distance of 40 Mpc (see Fig. 1). Two seconds later the Fermi satellite saw a short gamma-ray burst.

Figure 1: Artist view of a neutron star merger (Credit: NASA/Swift/Dana Berry).

This simultaneity and the coincidence of the position of the signals indicated that this was a single event; within minutes astronomers had turned their telescopes to the source, to capture for the first time the electromagnetic counterpart of an object detected in gravitational waves. Ultimately more than 70 observing facilities both ground- and space-based were used to study the electromagnetic counterpart, and verify the existence of a "kilonova" that had never before been clearly detected. INAF astronomers led many of the followup studies (see MediaINAF), and four scientists from the Arcetri Astrophysical Observatory were also involved. 

In particular Leslie Hunt participated in the study of optical and near-infraredspectra obtained with Xshooter at the VLT (Pian et al. 2017, see the Figure 2), Viviana Casasola collaborates with the team which observed the source in the radio with SRT (Aresu et al. 2017), Sperello di Serego Alighieri contributed to the optical polarimetry of the source obtained with FORS2 at the VLT (Covino et al. 2017), and Marco Padovani, who took part to the follow-up with gamma rays (HESS collaboration, 2017).

gw

Figure 2: Optical-IR spectra of the neutron stars merger obtained on consecutive days, as indicated on the right (Credit: Pian et al. 2017).

The globular cluster anti-correlation as seen by the Gaia-ESO Survey

A group of researchers led by Elena Pancinopart of theGaia-ESO Survey consortium, have recently published on A&A a work (Pancino et al. 2017) based on the fourth internal release (iDR4)  data on globular clusters (GCs).  Their work was a science demonstration case of the quality of the derived atmospheric parameters and abundance ratios for relatively metal-poor stars. They also present for the first time data for NGC 5927, which is one of the most metal-rich globular clusters studied in the literature so far, with [Fe/H]=−0.39±0.04 dex; this cluster was included to connect with the open cluster regime in the Gaia-ESO Survey internal calibration.

Elena Pancino and her collaborators have studied the shape of the Mg-Al anti-correlation, which is extremely important for understanding the still unexplained multiple population phenomenon in globular clusters (see Figure 1).

The anti-correlation is thought to be produced by the hotter reactions in the CNO hydrogen burning cycle, that require at least 80 million degrees to operate and therefore cannot be produced within the low-mass stars we observe today.

They thus studied the dependency of the Mg-Al anti-correlation extension with metallicity, present-day mass, and age of the clusters, using Gaia-ESO data in combination with a large set of homogenized literature measurements. They found a dependency with both metallicity and mass, which is evident when fitting for the two parameters simultaneously (see Figure 2), but we did not find significant dependency with age. They confirm that the Mg-Al anti-correlation is not seen in all clusters, but disappears for the less massive or most metal-rich clusters.

fig MgAl

Figure 1: The Mg-Al anticorrelation in Galactic globular clusters observed by the Gaia-ESO survey. Each panel represents one of the GCs in iDR4 dataset, with large cyan symbols representing UVES high-resolution measurements, and large magenta ones representing GIRAFFE medium resolution ones. The smaller symbols in the background represent previous literature measurements. The GCs are sorted by metallicity, with NGC 4833 at [Fe/H]=-1.92~dex and NGC 5927 at [Fe/H]=-0.39 dex: it appears clearly that higher metallic.

fig ext

Figure 2: Behaviour of the extent of the Mg-Al anticorrelation in GCs as a function of mass and metallicity. The extent is represented by two indicators: the standard deviation  σ[Al/Ma] and the maximum variation Δ[Fe/H]. Points are coloured with mass in the left panels (yellow is less massive and orange more massive) and with metallicity in the right panels (blue is less metal-rich and red is more metal-rich). As can be seen, the Mg-Al anticorrelation extension changes with the mass and the metallicity of GCs, to the point of disappearing for the less massive and/or more metal-rich GCs.

Thanks to the wide variety of checks and applications done by the group of Elena Pancino on globular clusters, we can firmly conclude that Gaia-ESO iDR4 data already meet the requirements set by the main survey goals and that they can be also used to the metal poor stellar populations, including a detailed study of globular clusters. 

References:

The Gaia-ESO Survey. Mg-Al anti-correlation in iDR4 globular clusters, Pancino, E.; Romano, D.; Tang, B.; Tautvaišienė, G.; Casey, A. R.; Gruyters, P.; Geisler, D.; San Roman, I.; Randich, S.; Alfaro, E. J, et al., 2017, A&A, 601, 112