———————– YEAR 2015 ———————– 

09-12-2015, 11:00, Aula IB09, ARTOV
Dr.ssa Nazma Islam Syeda (Raman Research Institute – Indian Institute of Science)
Long term observations of X-ray binaries with All Sky Monitors: New results

Abstract:  I will describe some new studies carried out using long term light curves of X-ray binaries with various X-ray all sky monitors. 16 years of RXTE-ASM light-curves are utilised to construct multiple snapshots of X-ray Luminosity Functions (XLF) of the X-ray binaries in the Milky Way and study the effect of variability of X-ray binaries on them. Using orbital phase resolved spectroscopic measurements of the bright High Mass X-ray binary GX 301-2 with an unprecedented orbital coverage with MAXI, we examined various models about the mode of accretion on to the neutron star. Presence of an eclipse in a X-ray binary can be useful in determining orbital parameters like inclination and estimating the orbital evolution by eclipse timing method. The orbital period evolution of the eclipsing X-ray binary 4U 1700-37 was measured using long term light-curves obtained with the all sky monitors RXTE–ASM, Swift–BAT and MAXI–GSC. We have also used the mid-eclipse times and the eclipse duration measurements obtained from 10 years long X-ray light curve obtained with Swift–BAT to separately put constraints on the eccentricity of the binary system and attempted to measure any apsidal motion.
The orbital intensity profile of another X-ray binary IGR J16393-4643 created with Swift-BAT shows it to have a short eclipse, which is used to constrain the inclination of this system. With 5 years of MAXI-GSC data, we have for the first time measured long term averaged spectra of X-ray binaries and have constructed composite X-ray binary spectrum of the Milky Way. The long term averaged composite spectrum will be an useful input to realistically estimate the contribution of X-ray heating at the epoch of re-ionization. I will also describe the various payloads onboard the recently launched Indian multi-wavelength astronomy mission ASTROSAT.

30-10-2015, 11:00, Aula IB09, ARTOV
Dr.ssa Valeria Mangano (IAPS – Roma)
THEMIS Na exosphere observations of Mercury and their correlation with in-situ magnetic field measurements by MESSENGER
Abstract:  The Na exosphere of Mercury is being studied since its discovery in mid ’80s from Earth-based telescopes, and it has revealed a high dynamicity and variability. Although the processes and inter-relations characterizing the Hermean exosphere dynamics are still not thoroughly understood, the existence of a connection among the planet’s surface, exosphere, intrinsic magnetic field and the Interplanetary Magnetic Field (IMF) that drives Solar Wind ions into Mercury’s magnetosphere via magnetic reconnection, is undoubtful.
We analyzed an extended dataset of images of the exospheric Na emission, corresponding to the period from 2009 to 2013, obtained by the THEMIS ground-based telescope, in order to perform a comprehensive statistical study of the recurrent patterns and their relationship with the IMF variability. For this purpose, we take advantage of a subset (years 2011-2013) of contemporary in-situ measurements of the IMF obtained by the MAG instrument onboard the MESSENGER spacecraft.
Data seem to confirm that the mid-high latitude double peak configuration is the most common Na emission pattern, supporting the view that the solar wind ion precipitation through the polar cusps has an important role in the generation of the observed Na exospheric emission. Moreover, the lack of a statistically significant North-South asymmetry seems to disfavour the idea of an asymmetric and/or shifted magnetic dipole.
In addition, comparison with the IMF data indicates that the contribution of the IMF Bx component to the magnetic reconnection is generally weak while negative IMF Bz values are usually connected with double peaks emission and positive IMF Bz valules are more frequently associated to single peaked equatorial Na emission.

28-10-2015, 11:00, Aula IB09, ARTOV
Dr. Gianni Bernardi (SKA Africa & Rhodes University)
The South African pathway to the Square Kilometre Array)
Abstract: The Square Kilometre Array (SKA) is a radio telescope array that promises to revolutionize our knowledge of the Universe. It is currently planned and designed by a consortium of countries (including Italy) and will be built on South Africa (mid-high frequency component) and Australia (low frequency component). In South Africa the SKA will incorporate the MeerKAT pathfinder, a 64 antenna radio interferometer that will operate in the 0.5-1.6 GHz regime. MeerKAT is preceded by the engineering testbed 7-antenna Karoo Array Telescope (KAT-7) that has been successfully commissioned and has been operated in “science mode” since a few years. I will review the current status of radio astronomy development in South Africa, paving the way to the SKA and outlining opportunities for the community.

06-10- 2015, 11:30, Aula IB09, ARTOV
Dr. Robert Carlson (Jet Propulsion Laboratory California Institute of Technology Pasadena, USA)
Jupiter’s Great Red Spot: Possible chromophores from photolysis of ammonia in the presence of acetylene
Abstract: The high altitude of Jupiter’s Great Red Spot (GRS) may enhance the upward flux of ammonia (NH3) gas into the high troposphere, where NH3 molecules can be photodissociated and initiate a chain of chemical reactions with downwelling acetylene molecules (C2H2). These reactions, experimentally studied earlier by Ferris and Ishikawa (Ferris and Ishikawa, 1987; Ferris and Ishikawa, 1988), produce chromophores that absorb in the visible and ultraviolet. In this work we photolyzed mixtures of NH3 and C2H2 with methane (CH4) using ultraviolet radiation with a wavelength of 214 nm and measured the spectral transmission of the precipitated films in the visible region (400-700nm). From these transmission data we derived the imaginary indices of refraction.
Assuming that ammonia grains at the top of the GRS clouds are coated with this material we performed layered sphere and radiative calculations to predict GRS reflection spectra. Comparison of these results with reflectance spectra and true-color images of the GRS shows that the unknown GRS chromophore is spectrally consistent with the coupled NH3-C2H2 photochemical products produced in our laboratory experiments. These laboratory-produced chromophores consist of aliphatic imines, amines, and nitriles, isonitriles, and ketenimines.

07-09-2015, 11.00, Aula IB09, ARTOV
Prof. Gary Zank (University of Alabama at Huntsville, USA)
Diffusive Shock Acceleration and Reconnection Processes
Abstract: An emerging paradigm for the dissipation of magnetic turbulence is via localized small-scale reconnection processes, essentially between quasi-2D interacting magnetic islands. Charged particles trapped in merging magnetic islands can be accelerated by the electric field generated by magnetic island merging and the contraction of magnetic islands. We have derived a gyrophase-averaged transport equation for particles experiencing pitch-angle scattering and energization in a super-Alfvenic flowing plasma experiencing multiple small-scale reconnection events. A simpler advection-diffusion transport equation for a nearly isotropic particle distribution has been derived from the gyrophase-averaged transport description. The dominant charged particle energization processes are 1) the electric field induced by quasi-2D magnetic island merging, and 2) magnetic island contraction. The magnetic island topology ensures that charged particles are trapped in regions where they experience repeated interactions with the induced electric field or contracting magnetic islands. Shock waves naturally generate vertical turbulence downstream of shocks. This introduces an additional possibility or mechanism to accelerate particles distinct from classical diffusive shock acceleration (DSA). We present a new mechanism that combines DSA with particle acceleration by reconnection-related processes. We discuss the nature of the spectra and the evolution of the energetic particle intensities with distance from the shock wave. We relate our theoretical models to observations made of energetic particles at the heliospheric termination shock that cannot be explained on the basis of classical DSA.

24-06-2015, 16:00, Aula IB09, ARTOV
Dr. Andrea Tramacere (ISDC – Data Center for Astrophysics, Versoix – Ginevra)
Application of topological clustering algorithms in automatic galaxy shape classification
Abstract: We present a method based on topological clustering algorithms aimed to automatic galaxy shape classification, based on a novel combination of clustering algorithms (DBSCAN and DENCLUE). The method does not require any external tool to extract the galaxy from the CCD image.
In a first stage, we use the DBSCAN algorithm to extract the cluster of pixels belonging to the galaxy. In a second stage, we apply the DENCLUE algorithm to this cluster of pixels, obtaining a partition the initial galaxy image in sub-clusters generated from the localization of local maxima, by a kernel density estimation. Typically, elliptical galaxies are characterized by a single sub-cluster, whilst spiral ones present several sub-clusters related to different segments of arms. The arms segments are then merged, and fitted by a log-spiral analytical function, and the resulting parameters provide a sub-set of the features. Further topological and statistical features are extracted from the distribution of the sub-clusters, and from the computation of geometrical invariant moments of the pixels belonging to the contours of the galaxy, and to the sub-clusters. Finally these features are used with different classifiers, such as Random Forest.
We present results for a sample of galaxies from SDSS Stripe 82 data set, and we compare our classification results to GalaxyZoo2 ones.

11-06-2015, 11:00, Aula Comitato, ARTOV
Dr. Simone Marchi (Institute for the Science of Exploration Targets  Colorado)
Widespread mixing and burial of Earth’s Hadean crust by asteroid impacts
Abstract: In this talk I will present a new bombardment model of the Hadean Earth (4.0-4.5 billion years ago) that has been calibrated using existing lunar data and terrestrial highly siderophile elements. We find that the surface of the Hadean Earth was widely reprocessed by impacts through mixing and burial by impact-generated melt. This model may explain the absence of early terrestrial rocks. Furthermore, we will discuss an intriguing correlation between the age distribution of Hadean zircons and the impact flux, possibly indicating impacts played an important role in Hadean zircon formation. Finally, by tracking the magnitude and timing of early collisions, we find that existing oceans would have repeatedly boiled away into steam atmospheres as a result of large collisions as late as about 4 billion years ago.

03-06-2015, 11.00, Aula IB09, ARTOV
Prof. Toru Tanimori (Department of Physics, Kyoto University, Kyoto Japan)
Development of Electron Tracking Compton Camera (ETCC) for a Survey of Deep Universe by MeV gamma-rays
Abstract: ETCC with a gas Time Projection Chamber (TPC) and pixel GSO scintillators, by measuring electron tracks, provides both a strong background rejection by dE/dx of the track and clear imaging by adding the arc direction of incident gammas (SPD: Scatter Plane Deviation) with the ARM (angular Resolution Measure) direction measured in standard Compton Camera (CC). In 2006 its background rejection was revealed by SMILE-I balloon experiment with 10 cm-cubic ETCC using the dE/dx of tracks. In 2013, 30 cm-cube-ETCC has been developed to catch gammas from Crab in next SMILE-II balloon with >5 sigma detection for 4 hrs. Now its sensitivity has been improved to 10 sigma by attaining the angular resolution of the track (SPD angle) to that determined by multiple scattering of the gas. Thus, we show the ability of ETCC to give a better significance by a factor of 10 than that of standard CCs having a same detection area by electron tracking. Based on this technology, SMILE-II with 3 atm CF4 gas is expected to provide a 5 times better sensitivity than COMPTEL for one month balloon flight around the polar region, and 4 modules of 50 cm-cube ETCCs would exceed over 10^-12 erg/cm^2s^1 (1 mCrab) at 10^6 s in satellite.
To verify its performance in space, SMILE-II was irradiated by intense gammas and neutron using 140 MeV proton beam, and successfully measured both clear image of a weak RI without the efficiency deterioration under 10 times stronger radiation than that in space.
Here we summarize the performance of the ETCC and new astrophysics opened in near future by high-sensitivity observation of MeV gamma-rays.

14-05-2015, 11:00, Aula IB09, ARTOV
Dr. Yasuo Fukui  (Department of Physics Nagoya University)
How to form Spitzer bubbles: Wind bubbles or collision-created cavities
Abstract: It is generally believed that the Spitzer bubbles are formed by winds by O stars. In this scenario, the mechanism of the formation of the central O star remains unexplained. Recent CO observations of RCW120, one of the most typical Spitzer bubbles, show that RCW120 may have been formed by collision between a small cloud and a large cloud (Torii et al. 2015 ApJ in press, http://ads.nao.ac.jp/abs/2015arXiv150300070T). In this scenario, a cavity is created in the large cloud by the collision and the central O star formed by the collisional triggering illuminates the inside of the cavity, which is observable as a bubble-like infrared nebula. I will discuss the pros and cons of the cloud-cloud collision scenario and the wind bubble scenario, and the implications on star formation.

06-05-2015, 11:00, Aula IB09, ARTOV
Dr. Riccardo Claudi (INAF – Osservatorio Astronomico Padova)
Pianeti Extrasolari, HARPS-N@TNG e GAPS
Abstract: GAPS (Global Architecture for Planetary Systems) è una collaborazione che raccog,lie in se tutta o la maggior parte della comunità esoplanetaria italiana. E’ una collaborazionee aperta a nuove adesioni ed è stata sollecitata dall’INAF nel 2011 con una “open call” quando l’ente ha deciso di dedicare molte risorse all’integrazione di HARPS – N al Telescopio Nazionale Galileo. Un adeguato uso del migliore strumento al mondo per la misura di velocità radiali ha come contropartita uno sforzo non indifferente per coordinare e gestire la comunità che potenzialmene lo può usare.
La storia comincia a padova nel 2011 e poi continua a Roma nel 2012 dove questo gruppo si è costituito. GAPS comincia ufficialmente le sue osservazioni in agosto 2012, da allora ha avuto un totale di 1764 ore assegnate (1456 effettivamente osservate), distribuite nei vari sotto progetti che lo costituiscono. Lo scopo di GAPS è molteplice ed è suddiviso in diversi blocchi che permettono di capire l’architettura dei sistemi planetari: 1) studiare la frequenza di pianeti di piccola massa in funzione della massa e della metallicità delle stelle ospite e della densità dell’ambiente stellare; 2) caratterizzare i pianeti noti; 3) analizzare l’attività delle stelle ospiti ed il suo effetto sulla derivazione dei parametri planetari; 4) derivare misurazioni accurate della massa planetaria per mezzo dello studio asterosismologico delle stelle ospiti.
Dal 2012 ad oggi sono stati ottenuti molti risultati che saranno oggetto di questo seminario, non ultimo quello di aver coagulato intorno al miglior cacciatore di pianeti un’intera comunità.

29-04-2015, 11.00, Aula IB09, ARTOV
Tanmoy Chattopadhyay (Physical Research Laboratory of Ahmedabad – India)
X-ray Polarimetry Programs in Physical Research Laboratory (PRL), India
Abstract: Hard X-ray polarimetry is supposed to provide better understanding of celestial X-ray sources. Compton polarimeters when coupled with hard X-ray optics can provide sensitive polarisation measurements in hard X-rays with a broad energy band. In this regard, we are developing a focal plane hard X-ray Compton polarimeter consisting of a plastic scintillator as active scatterer surrounded by a cylindrical array of CsI scintillators read by Si Photomultipliers. Here I briefly describe the experimental results obtained from the final polarimetric configuration.
Apart from this, CdZnTe Imager (CZTI) onboard Astrosat, can also work as a potential Compton polarimeter in 100 – 300 kev range due to its multi-pixel detection capability and significant Compton efficiency in this energy range. We have experimentally verified the polarization measurement capability of CZTI modules. Astrosat is going to be launched  in 2015 end and therefore gives unique opportunity to measure polarization of few bright hard X-ray sources e.g. Crab nebula and CygX1. Prospects of hard X-ray polarimetry with CZTI, will also be discussed here briefly.

17-04-2015, 11.00, Aula Convegni, ARTOV
Dr. Claudio Maccone (International Academy of Astronautics)
“SETI and ASTROBIOLOGY: current status”
Abstract: SETI and ASTROBIOLOGY have long been regarded as two separate research fields. The growing number of discovered exoplanets of various sizes and characteristics, however, forces us to envisage some sort of CLASSIFICATION of exoplanets based on the question: *where does a newly-discovered exoplanet stand ON ITS WAY TO DEVELOP LIFE ?*
This author has tried to answer this question in a mathematical fashion by virtue of his “Evo-SETI” (standing for “Evolution and SETI”) mathematical model. The results were two papers published in the International Journal of Astrobiology, the first of which turned out to be the second most-widely read paper in the International Journal of Astrobiology in the year 2013. In this seminar the Evo-SETI mathematical model is described in mathematical detail for the benefit of researchers.

25-03-2015, 11.00,  Aula IB09, ARTOV
Prof. Jean-Claude Gerard (Université de Liège, Belgium)
Jupiter’s aurora, ultraviolet, visible and infrared views: what can we learn?
Abstract: Precipitation of energetic electrons from Jupiter’s magnetosphere into the atmosphere is a powerful process which generates a photon flux of a few 1011 to 1012 Watts. Unlike the Earth’s or Saturn’s case, aurora on Jupiter is not located near the boundary between open and closed magnetic field line. It is powered by the planet’s fast rotation which creates a global current system and accelerates electrons into the atmosphere where their collisions with H2 produce the spectacular aurora. Most of the observations on the morphology and its relation with the solar wind have been collected with the ultraviolet cameras on board the Hubble Space Telescope. These observations have also shown that changes in Io’s volcanic activity also controls to some extent the size if the aurora. Observations of the H3+ emission in the infrared have been obtained with ground-based telescopes and show similarities with their UV counterparts. Some differences are also seen, probably stemming from the sensitivity of the IR emission to the local gas temperature. The main morphological features of the Jovian aurora will be presented and the unique case so far when images were simultaneously collected in the UV and IR will be analysed. Possible reasons for differences will be discussed. We shall also describe recent work using UV spectral imaging that made it possible to remotely map the energy of the precipitated electrons. Perspectives to combine future observations collected with UVS and JIRAM on board the Juno orbiter will be discussed.

12-03-2015,  11.00, Aula IB09, ARTOV
Dr.ssa Christina Plainaki (INAF – IAPS)
A global model for Ganymede’s exosphere in view of the JUICE mission
Abstract: The interactions between Jupiter’s magnetospheric plasma and Ganymede’s icy surface are responsible for the generation of the moon’s neutral environment. Such interactions are strongly constrained by the moon’s intrinsic magnetic field determining the pattern of the ion precipitation to the icy surface. In this paper, the water and oxygen exospheres of Jupiter’s moon Ganymede are simulated through the application of a 3D Monte Carlo modeling technique that takes into consideration the combined effect on the exosphere generation of the main surface release processes (i.e. sputtering, sublimation and radiolysis) and the precipitation of the magnetospheric ions to the moon’s surface. We find that plasma precipitation occurs in a region related to the open-closed magnetic field lines (OCFB) boundary and its extent depends on the assumption used to mimic the plasma mirroring in Jupiter’s magnetosphere. In the full mirroring assumption, the primary surface sputtering mechanism at the whole polar cap of Ganymede can alone explain the observed higher albedo of this region; in the non- mirroring assumption the polar cap brightness above the OCFB ring can be explained with the action of secondary sputtering due to ionized exospheric particles re-impacting the surface. At small altitudes above the moon’s subsolar point the main contribution to the neutral environment comes from sublimated water; the spatial distribution of the directly sputtered-water molecules exhibits a close correspondence with the plasma precipitation region and extends at high altitudes, being, therefore, well differentiated from the sublimated water. The oxygen exosphere comprises two different populations: a thermal one (extending to some 100s of km above the surface) and a more energetic one consisting of more energetic oxygen molecules sputtered directly from the surface after water-dissociation by ions has taken place.
The availability to the science community of such an exospheric model could be of help during the planning of the future JUICE mission observations. The interdisciplinary study of endogenic/exogenic surface release processes– with their potential implication on the nature of the moon’s inner ocean – have as mandatory prerequisite an accurate characterization of Ganymede’s exospheric background.

20-01-2015, 11:00, Aula Convegni, ARTOV
Prof. C. T. Russell (University of California, Los Angeles)
The Dawn Discovery Mission: A Voyage in Space and Time

Abstract: Giuseppe Piazzi discovered Ceres 214 years ago. Almost exactly 2 centuries later NASA selected the Dawn mission to visit Ceres and map it completely. On the way to Ceres it studied Vesta, discovered in 1807 two centuries before Dawn’s launch.   In this talk we present a short summary of the Dawn objectives, the spacecraft, the observations made at Vesta, and the planned observations at Ceres.