Tor Vergata Astrophysics Seminars

Temperature and mass estimates of simulated galaxy clusters through X-ray analysis: cosmological implications

Clusters of galaxies represent a powerful tool for investigating cosmological parameters.The fundamental quantity entering theoretical models is the cluster mass, but its high-precision measurement is still precluded. From the X-ray analysis, it is possible to calculate it, assuming some models that describe the distribution and the status of the intra cluster gas and of the dark matter. Studing the dynamical distribution of both gas and dm, we showed that the models usually fail in estimating the true mass and that the discrepancy seen in theoretical analysis increases even more for the X-ray observed clusters. Another way to derive the mass comes indirectly from the X-ray temperature, which - under appropriate assumptions- is related to the cluster mass through the M-T scaling relation. In this case it is necessary to calibrate the X-ray temperature function (XTF) using simulations and to compare observed and simulated data. For this purpose we built the software package "X-MAS" (X-ray MAp Simulator), devoted to simulate X-ray observations of galaxy clusters obtained from hydro-N-body simulations, and we investigate the tricky problem of temperature definition in simulations.

Phase diversity applied to coronagraphic imaging of exo-planets

The main problem in imaging an Exo-Planet is the suppression of light from the star.  One proposed imaging system will use a telescope, coronagraph, and a Lyot stop.  However, imperfections in the optics will cause the image to have speckles which will mask a planet.  In this talk we review the phase diversity imaging method.  Then we show how it can be used to reduce the speckles in a coronagraphic imager to reveal the planet.

Solar irradiance variations induced by small magnetic elements: structure identification, proxies and applications

Sunspots, faculae and the magnetic network contribute to solar irradiance variations. The contribution due to faculae and the network is of basic importance, but suffers from considerable uncertainty. We study the radiative properties of these small magnetic elements along the rising phase of solar cycle 23, from 1996 to 2001, determining their contrasts as a function of heliocentric angle, magnetogram signal and solar cycle phase. To achieve this, we analyze near-simultaneous full disk images of photospheric continuum intensity and line-of-sight magnetic field provided by the MDI instrument on board the SOHO spacecraft.  By sorting the magnetogram signal into different bins we are able to distinguish between the contrasts of different magnetic features, finding that the center-to-limb variation (CLV) of the contrast changes strongly with magnetogram signal. The contrast CLV of these small magnetic elements is independent of time when measured along the rising phase of solar cycle 23. In addition, we will talk about the use of proxies when no suitable magnetograms are available, and their possible applications for the validation of meridional circulation models.

The binary inspiral of compact objects and the oscillations of massive  black holes are strong sources of gravitational waves for the planned  NASA-ESA Laser Interferometer Space Antenna (LISA). These waves can be  used to carry out various tests of Einstein's general relativity. I will  discuss the theoretical uncertainties and experimental limitations we must face, and the physics we can learn.

When the polarimetric sensitivity and the angular resolution are  high enough, magnetic fields show up almost everywhere on the solar surface.  These ubiquitous quiet Sun magnetic fields seems to contain far more magnetic flux and magnetic energy than all active regions, even at solar maximum. Therefore, they may be a key ingredient needed to understand the solar magnetism. I will summarize our present understanding of these magnetic fields, partly based on recent observations, and partly based on numerical simulations of magneto convection.

I will start by reviewing the current knowledge about the primordial Universe currently provided by the most recent analysis of combined CMB, SN1a luminosity distances and large scale structure survey data. I will then discuss how the direct detection of a stochastic background of gravitational radiation can yield unique information about the Early Universe and the physics beyond the Standard Model and the current constraints on such type of gravitational waves resulting from the recent analysis of the S3 LIGO data. In the last part of the talk I will describe how space-based gravitational detectors can provide complementary - with respect to CMB experiments - information about the physics of the primordial Universe.

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