Osservatorio Astronomico di Roma

Oumuamua, the first asteroid coming from another planetary system
2017-11-30 11:45 - 12:45 (Europe/Rome) | Aula Gratton
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 | OAR Monte Porzio Catone – aula Gratton, Via Frascati 33, Roma, RM, 00136, Italia

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.

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.

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.

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.

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.

Observations of Fast Outflows in Active Galactic Nuclei
2017-10-24 11:45 - 12:45 | 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 primitive small bodies: from the origin of the solar system to the origin of life
2017-10-17 11:45 - 12:45 | Aula Gratton
The so-called “primitive” small bodies (carbonaceous asteroids, centaurs, comets, trans-Neptunian objects) have formed in the water- and organic-rich outer regions of the protoplanetary disk. They carry information on a number of evolutionary processes which have taken place since the solar system formation, and, in particular, they are considered as the most probable source of terrestrial prebiotic material.
In this talk, I will present the results of a 30-night observing programme carried out at the ESO-NTT in 2015-2017, the first-ever spectroscopic survey dedicated to the “small” (up to a few hundred meters) near-Earth asteroids (NEAs). Noteworthy, smaller asteroids could deposit prebiotic material on the early Earth in a more efficient way, without massive water vaporization and destruction of organic molecules as in the case of larger impacts.
I will also discuss about the ongoing sample return missions from primitive NEAs Ryugu and Bennu, that will be reached in 2018 by the Hayabusa 2 (JAXA) and OSIRIS-REx (NASA) spacecrafts, respectively. Such missions will be fundamental to assess if the organic compounds contained in primitive asteroids can indeed be associated with the formation of life on Earth.
Finally, I will report about a long-term observational programme aimed to investigate the composition and cometary activity of centaurs, a transitional population between the trans-Neptunian regions and the inner solar system. It is to be reminded that the impact of Centaur-like objects might have significantly contributed to the delivery of noble gases and amino-acids to the early Earth.

L'utilità della Scienza inutile
2017-10-10 11:30 - 12:30 | Aula Gratton
Se i risultati scientifici finanziati con i soldi dei contribuenti sono “beni pubblici”, è utile o addirittura etico spendere miliardi per cercare una particella elementare? O per andare a visitare un satellite di Giove o cercare l’acqua su Marte? O per osservare una galassia ai confini dell’Universo? In altre parole, è utile finanziare la ricerca di base? E se sì, con che risorse? E per fare quale tipo di ricerca?
La competizione è diventata una delle maggiori forze trainanti per la ricerca. Ma siamo sicuri che il modello “competition-driven science” sia davvero quello migliore?
Di più, sta cambiando il concetto stesso di conoscenza? Siamo sicuri che sia ancora valido e applicabile oggi il “metodo scientifico” introdotto da Galileo più di 400 anni fa?
Le risposte a tutte queste domande non sono scontate, anzi, possono contenere molte sorprese non tutte piacevoli o rassicuranti, risposte tra le quali cercheremo di orientarci usando un punto di vista non sempre convenzionale.
La presentazione, in Italiano, è aperta a tutto il personale, anche ai non specialisti del settore.

First black holes: observability and growth
2017-10-03 11:45 - 12:45 | Aula Gratton
The first black hole seeds ​likely ​formed when the Universe was younger than 500 Myr​ old.
​They play​ an important role ​in​ the growth of early (z=7) supermassive black holes. While ​much ​progress ha​s​ been made in understanding their formation and growth, their observational signatures remain largely unexplored. As a result, ​we are yet to ​detect ​these​ sources. ​We​ present a novel photometric method to identify black hole seed candidates in deep multi-wavelength surveys. The method relies on infrared and X-ray observations and selects​ the only two objects with a robust X-ray detection found in the CANDELS/GOODS-S survey with a photometric redshift z>6. To date, these selected objects represent the most promising black hole seed candidates, possibly formed via the direct collapse black hole scenario. While this result is based on the best photometric observations of high-z sources available to date, additional ​gains are​ expected from deeper spectroscopic and X-ray data. For this reason, ​we ​explore the role ​that ​JWST ​will play in the ​detect​on of ​the first black holes​ in ​the ​U​niverse.
Moreover, we present a novel probabilistic model for black hole growth: our results have important implications for the conditions that facilitate efficient black hole growth, particularly at early cosmic epochs. By bringing in a precise definition of “growth probability”, our finding clearly demonstrates quantitatively the generally-accepted concept that the super-massive black holes that we observed at z=7 are the “luckiest” members of the ensemble of high-z black holes. Our formalism has significant and broad ​consequences​ for upcoming observations of high-redshift quasars.

Appetite comes with eating: EXTraS PASTA & SOPA @ OAR
2017-09-26 11:45 - 12:45 | Aula Gratton
Data mining of public archives is a powerful tool in modern astronomy and it is expected to be more and more important in the near future since the size and number of experiments is rapidly increasing . Focus is put on the millions of objects falling by chance in the field of view of astronomical observations and left mostly ignored. In the EXTraS project we tapped into the poorly studied sources included in the 3XMM catalog, characterizing their variability with unprecedented detail. The products of the EXTraS project has been published in on-line catalogues open to the whole scientific community. At OAR, in particular, we searched for periodic variability of near 1.5 M timeseries. The main results of my work will be briefly shown.
Additionally, with the newly developed pipelines PASTA (Pulsation Accelerated Search for Timing Analysis) and SOPA (Searchfor Orbital Periods with Acceleration) we aim to dig even deeper into this huge amount of data by means of CINECA supercomputer facilities. I will tell you about these projects, some of their results and the prospectives of Data Mining and Big Data automatic analysis at the OAR.

The evolution of protoplanetary disks and their host stars
2017-09-13 11:45 - 12:45 | Aula Gratton
The origins of our own planetary system was set when the sun was still young and surrounded by a circumstellar disk. Although the evolutionary sequence of star formation is now well charted, the physical phenomena that drive these changes are still poorly understood. These differences determine whether and what types of planets will form, around stars of different masses and in different environments. In this talk, I will discuss how recent and upcoming observations of protoplanetary disks in nearby star forming regions are revealing the disk evolution, including inferences of ongoing planet formation. I will also discuss expected improvements in the age dating of young stars, which will form the foundation for piecing together the sequences of disk evolution.

talk by Orlagh Creevey
2017-07-11 11:45 - 12:45 | Aula Gratton

Probing the Dark Halo of the Milky Way
2017-07-04 11:45 - 12:45 | Aula Gratton
The Local Group, the regime in which detailed star-by-star studies can be done, is becoming a major testbed for the cold dark matter-based model of the Universe. Critical to these tests is a better estimate of the total Milky Way halo mass. The most reliable means by which to constrain the properties of the Milky Way dark halo is through assessing the 6-D phase space distributions of tracers of its gravitational potential. This requires accurate proper motions (tangential velocities) in addition to generally known radial velocities for field stars, streams, and satellite galaxies widely distributed throughout the halo. In turn, these measurements allow us to investigate the past histories of these tracers, and thus the accretion history of the Milky Way. I will discuss some novel approaches we have been developing to obtain proper motions for a variety of tracers in the Milky Way halo, including streams, globular clusters, and satellite galaxies, to definitively constrain the Milky Way’s dark halo mass, shape and distribution. These techniques involve space-based imagers (HST), wide-field ground-based imagers, as well as imagers equipped with adaptive optics systems. I will also discuss the future prospects for this work, and the trade-off between Gaia, space missions (JWST, WFIRST, EUCLID), and ELTs.
