Chemical properties of distant Milky Way halo stars from current and future spectroscopic surveys
2016-12-20 11:45 - 12:45 (Europe/Rome) | Aula Gratton
The study of elemental abundances of long-lived individual stars is one of the pillars of Galactic Archaeology, as a powerful way for retrieving information on the stars birth environment.
Through this approach, it has already been established that the inner Milky Way halo cannot have formed solely from the disruption of satellite galaxies experiencing as low an initial star formation rate as in the surviving Milky Way satellites.
However, the growing observational evidence for a dual nature of the Milky Way stellar halo raises the question of whether the elemental abundances of inner halo stars can be considered as representative of the whole Milky Way halo and if the inner and outer halo were formed through different dominant mechanisms.
In this talk I will present our investigation of the
chemical properties of the outer Milky Way halo, based on abundances of large samples of distant halo stars, both from SDSS-DR13
and proprietary spectroscopic campaigns at VLT, Magellan and HET. I will conclude with a
discussion of the prospects that future Galactic Archaeology surveys such as with the WHT/WEAVE spectrograph will open up for the study of the Milky Way halo properties.

Radial metallicity gradients of disk galaxies: The emission-line probes
2017-01-10 11:45 - 12:45
The metallicity of stellar and interstellar probes thorough disk galaxies, including our own, is distributed non-uniformly, showing typically shallow radial metallicity gradients where the metallicity decreases radially, inside out. Ultimately, the chemical evolution models need to be constrained by observations to determine the existence and extent of gradient slope and evolution, which in turn are linked to the formation and evolution of the galaxy.
The use of emission-line probes to test metallicity gradients takes advantage of the brightness of the nebular emission lines, and of the fact that the two major nebular probes, planetary nebulae (PNe) and HII regions, probe different epochs since galaxy formation. The limitation is that direct abundances are within observational reach only in the Local Universe. On the Galactic side, additional complications are added to the problem by the uncertainty of the PN distance scale.
In this talk I review the radial metallicity gradients background and main observational results, the latest direct metallicity gradient determinations in the Galaxy and beyond, the Gaia solution to the PN distance problem, and the foreseen advances of this field with the next generation of observational capabilities.

Sensing the Universe in colour; Kinetic Inductance Detectors for optical and near-IR astronomy
2017-01-17 11:45 - 12:45
I will describe the ongoing work in the development of Microwave Kinetic Inductance Detectors (MKIDs) for optical and infra-red astronomy. These super-conducting devices represent an important step towards the development of the ‘ultimate detector’; one that can measure the position, energy and arrival time of a photon. I will describe the operating principles of the devices and their current status. I will present the current MKID-based optical/IR instruments and show results from recent science demonstration runs. Finally, I will discuss the future promise of the technology and highlight some of the areas of astronomical instrumentation where they could have a transformational impact and our program at Oxford to exploit these devices.

Protoplanetary disk evolution: the key to planet formation
2017-01-24 08:00 - 17:00
The evolution of protoplanetary disks in young stellar clusters is regulated by the interplay of various physical processes, such as accretion and winds, and by the interactions with other stars in the cluster. Accretion and winds are best studied spectroscopically. Instruments like the VLT/X-Shooter spectrograph allow us to observe simultaneously the signatures of the accretion process, such as the UV-excess and the emission lines, together with lines tracing winds and outflows, such as helium lines and forbidden lines. At the same time, these spectra allow us to robustly derive the physical parameters of the central objects, such as their temperature and their mass. These processes relate to the disk mass and size, which can nowadays be studied with ALMA. Finally, the coming Gaia data releases will open the field to new studies of dynamical evolution of stars in young clusters by means of kinematical modelling.
I will report on the stellar, accretion, and wind properties derived with X-Shooter of the complete samples of low-mass stars in the Lupus and Chamaeleon star forming regions, and discuss the dependence of stellar and accretion parameters with the disk properties obtained with ALMA surveys in these regions. I will present the results of the study of some peculiar dipping young stars recently discovered. Finally, I will show how we can use Gaia data to study young clusters and the effect of interactions on the evolution of disks.

The mystery of Fast Radio Bursts: are we closer to the solution?
2017-01-27 11:45 - 12:45
With the recent firm localization of the host galaxy of the Fast Radio
Burst FRB 121102, the solution to the mystery of these peculiar signals
might be getting closer. FRB 121102 is, however, the only one showing
repeating pulses, leaving open the possibility that more classes, hence
different progenitors, of FRBs exist. In this talk I will give, following
the timeline of their observational milestones, an overview of FRBs. I
will presenting their main observational features, some of the many
theoretical models suggested to explain their characteristics, and some
possible use of FRBs as cosmological probes.

Sterile Neutrinos as Dark Matter: From Production to Predictions
2017-01-31 11:45 - 12:45
Sterile neutrinos with masses of a few keV are very
well-motivated Dark Matter candidates. However, even though they have the
perfect properties for that job, it is unclear how to produce them in the
early Universe. In this talk, I will mainly focus on how to make this
production happen in the early Universe. While several proposals exist in
the literature, the production aspect unfortunately suffers from several
incorrect or at least oversimplified statements (e.g., that keV sterile
neutrino Dark Matter would usually be ‘warm’). I will make an attempt to
explain parts of the issues and how to resolve them, which ultimately
leads to means to distinguish the different mechanisms via their impact on
cosmic structure formation. While lab experiments are not well-suited to
probe this type of Dark Matter candidate, cosmology and astrophysics
provide the tools to do so. The whole talk is supposed to be more
pedagogical than technical, so I will avoid heavy formula whereever
possible.

High-contrast imaging observations of exoplanets: current status and future
2017-02-07 11:45 - 12:45
Thanks to notable advancements in adaptive optics combined with
coronagraphic observational strategies, high-contrast imaging techniques
are rapidly progressing in the current years. The exploration of the
sub-stellar regime via direct imaging, hampered so far by technical limitations, is starting to provide us with a powerful tool, thanks to the advent of new-generation instruments, such as e.g., GPI or ScEXAO. SPHERE at VLT is a new facility that combining extreme adaptive optics with coronagraphy, dual-band imaging, and integral field spectroscopy has recently started its operations and aims at revealing relatively massive exoplanets at few tenths of arcsecond separations and contrasts better than 10^6. In this contribution I will present recent results obtained with SPHERE in the framework of the exoplanet detection and characterisation. Moreover, I will present a new system for coronagraphy with high-order adaptive optics that will be operating at LBT by the end of 2018: SHARK. This system will provide coronagraphic observations from visual to NIR bands, granting a very powerful tool that is not currently available for any other instrument in the world. Finally, I will discuss the employment of a brand-new technique that combines high-contrast imaging with high-dispersion spectroscopy, allowing in principle to reach contrasts down to 10^10. In the era of E-ELT, this will open the way to investigating earth-like planets in the habitable zones of their parent stars.

A main sequence for quasars
2017-02-14 14:30 - 15:30
The last 15 years have seen a major step forward in the analysis of optical UV spectroscopic data of large quasar samples. Multivariate statistical approaches have proved to be especially helpful, as they have led to the definition of systematic trends (first and second eigenvector derived from Principal Component Analysis) in observed properties that are the basis of physical and dynamical modeling of quasar structure. In this talk I will discuss the empirical correlates of the so-called quasar “main sequence” associated with the quasar eigenvector 1, its governing physical parameters, as well as luminosity effects associated with the second eigenvector. I will also briefly discuss quasars in a segment of the main sequence which includes the strongest FeII emitters. These sources show a small dispersion around a well-defined Eddington ratio value, a property which makes them potential “Eddington standard candles”.

The challenge of massive black hole binary coalescence; from galaxy formation to gravitational waves
2017-02-21 11:45 - 12:45
I will review recent progress in understanding how a pair of massive black holes can evolve from galactic scale separations, kpc and above, to milliparsec separations, where gravitational wave emission takes over
and leads to signals that should be detected by the Laser Interferometer
Space Antenna (LISA). I will show how, contrary to common belief, the
orbital decay of massive black holes in gaseous environments can be
less efficient and more stochastic than in stellar backgrounds, where
the only two processes at play are dynamical friction and 3-body
encounters with passings stars. Novel supercomputer simulations that attempt to study orbital decay in realistic galactic hosts show that coalescence timescales
can become very short, about 10 Myr, in high redshit massive galaxies that are on their way to become quenched spheroids, but can be longer than a
Gyr in massive star forming gas-rich disks as those observed at z > 1.
Hosts of LISA black holes are expected to have a different nature. The complex interplay between
the physical properties of galactic nuclei and the orbital decay process
poses a huge challenge to computational model, but at the same time
holds the promise for LISA and other gravitational wave detection
experiments to become a powerful probe of galaxy formation and evolution.

AGB dust production: what we learn from the Local Group galaxies
2017-02-28 11:45 - 12:45
Asymptotic giant branch (AGB) stars are among the most important gas and dust polluters of the Universe. The composition and the amount of dust produced in the winds of AGB stars is strongly correlated with the evolution of the central object. Detailed knowledge of the physical structure and chemical composition Is an essential ingredient to estimate the impact of these stars in the evolution history of their host environment.
A new release of AGB+dust models were developed in the last years to this scope. Their application in characterizing the AGB population and its contribution to the dust budget in the MCs, as well as in dwarf galaxies of the Local Group will be discussed in this talk.

From the first stars to the first quasars
2017-03-07 11:45 - 12:45
Observations of the most luminous quasars at redshift z>6 reveal the existence of numerous supermassive black holes (SMBHs, > 10^9 Msun) already in place about twelve billion years ago. The growth of these first SMBHs is still a major challenge for theoretical models. If it starts from black hole (BH) remnants of Population III stars (light seeds with mass ~100 Msun), it requires super-Eddington accretion. An alternative route is to start from heavy seeds formed by the direct collapse of gas on to a ~10^5 Msun BH. In addition, the interstellar medium (ISM) of the galaxies hosting these quasars are observed to be chemically mature systems, with metallicities Z>Zsun and dust masses >10^8 Msun, similar to that of more evolved, local galaxies. The connection between the rapid growth of the SMBHs and the fast chemical evolution of the host galaxy is one of the most puzzling issues for theoretical models.
I will present the results of our cosmological, data constrained semi-analytic model in which we investigate the relative role of light and heavy seeds as BH progenitors of the first SMBHs, self-consistently following the evolution of the chemical properties (metals and dust abundance) in the host galaxies ISM.

Highly Ionized X-ray Absorbers in AGNs and their Energetic: the case of NGC 4051
2017-03-14 11:45 - 12:45
Highly ionized absorbers are found in 50% of type 1 Seyferts and QSOs. They presence, along our line of sight, imprints a number of absorption lines from highly ionized metals in the far UV and X-ray spectral bands, like FeX-XVII, CIV-VI, OVI-OVIII, NeVII-X, etc. These absorption lines are always detected blue-shifted compared to the host galaxy reference system, which implies that the ionized material is being ejected from the nucleus and driven outwards, possibly by the AGN radiation pressure. Outflow velocities span a wide range, from few hundreds to few thousands km/s in the so called Narrow-Absorption Line (NAL) and/or Warm Absorber objects, to non negligible fractions of the speed of light in UV Broad Absorption Line (BAL) or X-ray Ultra-Fast Outflows (UFOs). These outflows are believed to be photo-ionized by the central source and their energetic depends on their mass outflow rate which, in turn, depends on the volume density n_e of the material, which is difficult to measure because degenerate with the square of the distance R of the absorber from the photo-ionizing source.
In this talk, after a brief overview of the phenomenon, I will show how time-evolving photo-ionization works and how it can be used to break the degeneracy between the absorber volume density n_e and its distance R from the central engine. I will then present the particularly fortunate case of NGC 4051 and show the puzzling results of the analysis performed here at OAR of the long 2009 XMM-Newton monitoring of this source.

Dwarf Galaxies - Fossils of Galaxy Evolution
2017-03-21 11:45 - 12:45
Dwarf galaxies are the most common type of galaxy in the Universe and
include the most dark-matter-dominated objects known. They offer
intriguing insights into evolutionary processes at low halo masses
and low metallicities. Moreover, as survivors of a once much more
numerous population of building blocks of larger galaxies, they are
key to understanding very early star formation processes. The Local
Group and particularly the Milky Way’s dwarf galaxy entourage offer
us the unique possibility to compare in detail dwarf and Galactic
populations. This is an important step towards quantifying the
magnitude and time scales of dwarf contributions to the build-up of
the Milky Way and allows us to test predictions of cosmological
theories and hierarchical structure formation

The AGB-Supernovae mass transition
2017-03-27 09:00 - 2017-03-31 18:00

The dust mass in Cassiopeia A from spatially resolved Herschel photometry
2017-04-04 11:45 - 12:45
The large reservoirs of dust observed in some high redshift galaxies have been hypothesised to originate from dust produced by supernovae from massive stars. Theoretical models predict that core-collapse supernovae (CCSN) can be efficient dust producers (0.1-1 Msun) potentially responsible for most of the dust production in the early Universe. Observational evidence for this dust production efficiency is however currently limited to only a few CCSN remnants (e.g., SN1987A, Crab Nebula) that confirm this scenario.
We revisit the dust mass produced in Cassiopeia A (Cas A), a ~330-year old O-rich Galactic supernova remnant (SNR) embedded in a dense interstellar foreground and background. We present the first spatially resolved analysis of Cas A based on Spitzer and Herschel infrared and submillimetre data at a common resolution of ~0.6 arcmin for this 5arcmin diameter remnant following a careful removal of contaminating line emission and synchrotron radiation. We fit the dust continuum from 17 to 500 micron with a four-component interstellar medium (ISM) and supernova (SN) dust model.
We find a concentration of cold dust in the unshocked ejecta of Cas A and derive a mass of 0.3-0.5 Msun of silicate grains freshly produced in the SNR. For a mixture of 50% of silicate-type grains and 50% of carbonaceous grains, we derive a total SN dust mass between 0.4 Msun and 0.6 Msun. These dust masses estimates are higher than from most previous studies of Cas A and support the scenario of supernova dominated dust production at high redshifts. Our resolved analysis shows that the cold SN dust component is mainly distributed interior to the reverse shock of Cas A, suggesting that part of the newly formed dust has already been destroyed by the reverse shock. We furthermore derive an interstellar extinction map which towards Cas A gives average values of AV=6-8 mag, up to a maximum of AV=15 mag.
