Observations of Fast Outflows in Active Galactic Nuclei
2017-10-24 11:45 - 12:45 (Europe/Rome) | Aula Gratton
The presence of outflows in many Active Galaxies has been firmly established through X-ray spectroscopy over the last two decades.
These outflows range from the low velocity warm absorbers commonly seen in many Seyfert galaxies, through to the
so called ultra fast outflows, where the outflow velocities can reach a significant fraction of c.
Ultra fast outflows were first discovered in 2003, from the presence of highly blue-shifted absorption lines from the X-ray spectra of quasars and AGN. The observational evidence for fast outflows will be reviewed, as well as their wider properties and potential for feedback into the host galaxies of AGN. New data from large programs on the fast outflows, such as PDS 456 and PG 1211+143, will be shown, the former showing a fast wide angle outflow, while both AGN show highly variable outflows which may respond to the ionising continuum.
The evidence for fast soft X-ray absorption as well as the possible driving mechanisms of the winds will also be discussed.

The first CEMP-no star in the Sculptor dwarf spheroidal galaxy
2017-10-31 11:45 - 12:45 | Aula Gratton
The origin of carbon-enhanced metal-poor (CEMP) stars and their possible
connection with the chemical elements produced by the first stellar
generation is still highly debated. Recently, the first CEMP-no star in
the Sculptor dwarf spheroidal was discovered at an iron abundance of
[Fe/H] = 8722;2.03 ± 0.10. Since Sculptor is one of the best studied
dwarf galaxies in the Local Group, it is surprising that until now, only
one CEMP-no star has been found in this galaxy. The available observations
suggest that the fraction of CEMP stars in Sculptor is lower than in the
Galactic halo. To understand this apparent discrepancy between different
environments, I will discuss the CEMP-no fraction in Sculptor, and other
dwarf galaxies in general.

The BH mass - galaxy scaling relations in the local Universe: what is the role of type 2 AGN?
2017-11-07 11:45 - 12:45 | Aula Gratton
Coevolutionary models that link the growth of supermassive black holes (BHs) and of their host galaxies are based on the observations of tight scaling relations between the BH mass and some properties of the host bulge. These relations have been calibrated thanks to the direct measurements of the BH mass in local galaxies and are extremely important, used to measure BH masses at high redshift and to determine the distribution of accreted mass, i.e. the black hole mass function.
However, these relations seem to be biased in favour of the more massive BHs, due to a bias in the resolution of the BH sphere of influence. Hence, there is urgent need to explore the full distribution of BH masses, accumulating sources below 1e+7 solar masses.
I here present the results from a systematic study performed using deep NIR (VLT and LBT) spectroscopy of a sample of ~40 type 2 active galactic nuclei (AGN), drawn from the complete SWIFT/BAT 70-month hard (14-195 keV) X-ray catalogue. Thanks to our new virial relation based on unbiased physical quantities, i.e. hard X-ray luminosity and Paβ emission line FWHM, we have been able to measure for the first time in a virial way the supermassive black hole masses of type 2 AGN, whose values have been up today estimated using indirect proxies (e.g. from scaling relations). With direct virial masses for type 2 AGN, we discuss, for the first time, if the BH-host galaxy scaling relations hold for type 2 AGN, thus putting a missing piece to the AGN/galaxy co-evolution puzzle.

Main Sequence Multiple Populations in Large Magellanic Cloud Globular Clusters
2017-11-14 11:45 - 12:45 | Aula Gratton
Six Large Magellanic Cloud (LMC) globular clusters (GCs) (NGC 1466, NGC 1841, NGC 2210, NGC 2257, Hodge 11, and Reticulum) have been analyzed for multiple stellar populations with the Hubble Space Telescope (GO-14164). This is the first such study for ancient (ages > 13 Gyr) clusters in the LMC. We find that five out of the six GCs examined show evidence for multiple populations in the main sequence. One cluster (Hodge 11) shows irregularities in its horizontal branch that may indicate the presence of a 0.1 dex internal helium abundance spread.

Fibrillar Structures in the Solar Chromosphere
2017-11-21 11:45 - 12:45 | Aula Gratton
I present observations of dynamic, slender bright fibrils seen in high-quality narrow-band Ca II H images from the SuFI instrument onboard the SUNRISE balloon-borne solar observatory. We have shown that these slender Ca II H fibrils (SCFs) map magnetic fields in the low solar chromosphere derived from magnetostatic extrapolation of the photospheric field obtained with SUNRISE/IMaX and SDO/HMI. Our analysis reveals the prevalence of both kink and sausage waves in the SCFs, propagating at high-frequencies (up to 30 mHz), with speeds on the order of 9-15 km/s. The estimated energy flux (~ 15 kW/m^2) carried by the observed waves is marginally enough to heat the chromosphere (and perhaps the corona). Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere.
Furthermore, I present observations of fibrillar structures through the mid-to-high solar chromosphere from coordinated observations of an active region with the Interface Region Imaging Spectrograph (IRIS) explorer and the Atacama Large Millimeter/submillimeter Array (ALMA). This provides us with temperature distributions of the entire field of view at multiple chromospheric heights, and in particular, of the fibrillar structures. A detail comparison between fibrillar structures simultaneously observed at several millimetre and ultraviolet bands of, e.g., ALMA 1.3 mm as well as IRIS Mg II h & k, Si IV, C II, and O I has provided us with new insights into the nature of these thread-like structures.

The other 95%: insights from strong gravitational lensing
2017-11-28 11:45 - 12:45 | Aula Gratton
In the standard cosmological model ninety-five percent of the energy content of the universe consists of dark energy and dark matter. Even though their abundance seems well determined, very little is known about their fundamental nature. I will describe how we can learn about the physics of the dark sector by studying in detail its gravitational effect on the trajectories of photons as they travel across the universe, a phenomenon known as strong gravitational lensing. In the first part of the talk, I will use strong gravitational lenses with a time variable background source to measure the expansion rate of the universe (Hubble constant) to 3.8% precision. This result is completely independent of the local distance ladder and the cosmic microwave background, and thus provides a new opportunity to understand whether the tension between the two arises from systematic uncertainties or may be indicative of new physics. In the second part of the talk I will describe how strong lensing can be used to detect the presence of dark subhalos independent of their stellar content. This measurement tests a fundamental prediction of the cold dark matter model, i.e. that galaxies should be surrounded by large numbers of dark satellite subhalos. Proof that such satellites do not exist would force a revision of the model in favor of more exotic alternatives like warm dark matter. I will conclude by discussing the exciting future of strong lensing as a tool for cosmology, in light of the huge numbers of strong lenses that are being discovered in the current generation of wide field astronomical surveys.

Oumuamua, the first asteroid coming from another planetary system
2017-11-30 11:45 - 12:45 | OAR Monte Porzio Catone – aula Gratton, Via Frascati 33, Roma, RM, 00136, Italia
The discovery of 1I/’Oumuamua, the first interstellar object found
transiting in our Solar System, provided astronomers with an extremely
unusual new target, and with a few surprises. We will briefly present
the discovery story and the unique properties of this new temporary
visitor of our Solar System.

Oumuamua, the first asteroid coming from another planetary system
2017-11-30 11:45 - 12:45 | Aula Gratton

Mass loss of AGB stars and RSG in the Magellanic Clouds
2017-12-05 11:45 - 12:45 | Aula Gratton
I will discuss recent work that I am involved in regarding the determination of
the mass-loss rates (MLRs) of a significant sample of Asymptotic Giant Branch stars and
Red Supergiants in the Magellanic Clouds. This mostly involves modelling the
spectral energy distributions to obtain dust MLRs, but we also used ALMA to detect CO emission
in a few LMC objects. I will also discuss possible ways forward in this field

High contrast imaging and the search for young exo-planets
2017-12-12 11:45 - 12:45 | Aula Gratton
High contrast imaging has enormously progressed in the last twenty years, thanks to the development of extreme AO, efficient coronagraph, and various differential imaging techniques. The two frontier instruments are GPI at Gemini South and SPHERE at VLT. We are now routinely achieving contrast of better than 10^5 with a record of 4×10^6 at separations below 0.5 arcsec, This has allowed the discovery and characterization of about a dozen young planets, of a couple of dozens of brown dwarfs, and direct detection of several tens disks in scattered light. These data open new windows on the very early phases of planet formation, when disks are still present. Both theory and data indicate that while clearly planets form in the late phase of the protostellar disks, the relation between disk and planets is very complex. Also, the spectra we are obtaining for the young planets indicate systematic differences between young and old objects with similar temperature. I will briefly present the technological and scientific aspects of this very new and exciting science

Dust Production from Evolved Stars in the Local Group
2017-12-19 11:45 - 12:45 | Aula Gratton
Infrared observations of nearby galaxies and the Milky Way show that there are two main sources of ISM dust: the winds of evolved stars and supernovae ejecta. However, the total dust contribution from evolved stars relative to supernovae, and how it changes with metallicity, is less certain. Infrared photometric and spectroscopic Spitzer Surveys of the Large and Small Magellanic Clouds (LMC, SMC): Surveying the Agents of Galaxy Evolution (SAGE) resulted in the discovery of thousands of evolved stars. Here, I will describe how the composition and quantity of dust produced by these stars depends on metallicity. I will also discuss how the mid-IR stellar populations of the Magellanic Clouds can be used as a template for potential observations with JWST, and how we have applied this to our observing programs of Local Group galaxies and SN1987A with JWST

Microlensing
2018-01-09 11:45 - 12:45 | Aula Gratton
I will review the microlensing and pixel lensing techniques and show how they play a
fundamental role in the searches for galactic dark matter, in the study of the galactic structure and in
detecting planets around faint stars whose cahacteristics are in general not accessible to other methods.
We show that dedicated and well planned experiments would even allow to detect more exotic objects
as primordial massive black holes (if any) in nearby galaxies and/or to put strong constraints on
their existence.

Not all stars are the Sun: rethinking the Mixing Length
2018-01-12 11:45 - 12:45 | Aula Gratton
Characterizing heat transport in stars is notoriously complicated, and the task of reproducing the physics involved with high precision on stellar evolutionary timescales is a long-standing problem in stellar modeling. For this reason, convection in 1-D stellar evolution codes is addressed primarily through a framework known as mixing length theory (MLT). In this simplified picture, the efficiency of convective heat transport is encapsulated by the mixing length parameter alpha_{MLT}, measured in pressure scale heights.
While it is well understood that our nearest star is not a valid representation of stars in general, it remains the standard procedure to calibrate alpha_{MLT} according to solar specifications, and then to apply this value in any stellar model, regardless of mass or composition. However, there has been growing evidence that the use of a solar-calibrated mixing length is not always appropriate.
In this study, we investigate the scope of validity of a solar-calibrated mixing length over a range of evolutionary phases and input physics for very metal-poor stars, and find that the solar-calibrated mixing length is widely ineffective at reproducing the observed properties of such stars.

Rossby number calculations for fully convective stars
2018-01-16 11:45 - 12:45 | Aula Gratton
The Rossby number is a quantity that gauges the relative importance of
rotation in astrophysical flows. In particular, it plays a significant role
in mean-field, alpha-Omega dynamo models as it is directly related to the
“dynamo number” which, in turn, measures the efficiency of the magnetic field
generation. From an observational standpoint, the Rossby number has been
widely used to correlate either coronal or chromospheric magnetic activity of
low-mass stars with their rotation. A fundamental problem with this
rotation-activity relationship is the determination of the convective turnover
time tau_c, on which the Rossby number depends, and that can be obtained
from some empirical relations or from stellar models. The ATON stellar
evolution code has been used in the near past to calculate Rossby numbers
for solar-type stars and now, in view of the recent discovery of fully
convective stars in the non-saturated region of the rotation-activity
relationship, is being used to extend those calculations to very low mass
stars.

Deep, multi-band photometry of low-mass stars to reveal young clusters: a blind study of the NGC 2264 region
2018-01-23 11:45 - 12:45 | Aula Gratton
The LSST survey will provide multi-epoch, multi-wavelength (u,g,r,i,z,y) mapping of the Southern Hemisphere, with a single-visit depth of r~24.5 and a gain of three magnitudes by the end of the program. This unprecedented spatial coverage will enable detection of young, pre-main sequence stars and stellar clusters down to distances of 5-10 kpc. A crucial and challenging step for spatial analyses of large stellar populations is measuring the extinction Av of individual objects. Multi-color photometry on a (r-i, g-r) or (i-J, r-i) diagram offers a direct solution to this issue for M-type stars: indeed, while the color locus of early-type (< K7) stars on these diagrams is parallel to the reddening vector, the color locus traced by M-type stars is tilted with respect to the reddening vector, which enables a straightforward and empirical measurement of their Av. By investigating the correlation between extinction and spatial properties of M-type stars in a given field, it is therefore possible to reconstruct the structure of the region and probe the nature of its population. In this study, we test the method on the NGC 2264 field. We selected a 2°x2° area centered on the NGC 2264 cluster, and collected the available r,i,J photometry from existing large-scale surveys (notably Pan-STARRS and UKIDSS). Then, assuming no prior knowledge on the nature of stars in the field, we used the (i-J, r-i) diagram to identify and deredden M-type stars in the sample, and the (r-i, r) + (RA, Dec) diagrams to investigate the nature and spatial distribution of stars as a function of their Av. We derived a non-uniform distribution of Av across the region, and could distinguish between a diffuse field population and a clustered stellar population toward the center of the field. An a posteriori comparison between the inferred spatial density map of the clustered population and the literature census of the NGC 2264 cluster enabled us to assess the performance of the method and its predictive capability.
