Elenco dei seminari passati

Speaker Anmol Kumar (St. Andrews Univ.)

Titolo TBA

Abstract TBA

Titolo: Carte geografiche, tra arte e scienza (M. Coniglio, I. Chinnici)

Speaker: Ileana Chinnici (INAF)

Abstract: TBD

Speaker: Ileana Chinnici (INAF)

Titolo: Tra i segreti di un manoscritto: lo strumento misterioso

Abstrat: Un manoscritto nascosto, una lettera su E-bay, uno strumento misterioso: sono gli ingredienti di un “giallo”, illustrato in questo seminario, che ci riporterà alla fine del Settecento, tra sospetti, dubbi e test sulla affidabilità degli strumenti utilizzati dagli astronomi inglesi. Per qualche (finora) oscuro motivo, l’Osservatorio di Palermo è entrato in possesso di un importante documento relativo a tali questioni: lo studio di questo manoscritto ha rivelato l’esistenza uno strumento sconosciuto, di cui non si trova (quasi) traccia.

Speaker: Victor Almendros (INAF)

Title: Evolution of the mass accretion rate and its relationship with the stellar and disk mass from brown dwarfs to stars

Abstract:
The time evolution of the dependence of the mass accretion rate with the stellar mass and the disk mass represents a fundamental way to understand the evolution of protoplanetary disks and the formation of planets. Recent studies suggest the existence of a bimodal accretion behavior at 2-3 Myr in the relationship of the stellar mass and the mass accretion rate, which may indicate that low-mass stars evolve faster (than higher-mass stars) into lower accretion rates. We recently measured the mass accretion rate of 26 new brown dwarfs and low-mass stars in the Ophiuchus, Cha-I and Upper Scorpius star-forming regions using X-Shooter/VLT. Combining these new observations with data from the literature, we compared the relations between accretion rate and stellar/disk properties of four different star-forming regions with different ages: Ophiuchus (1 Mar), Lupus (2 Myr), Cha-I (3 Myr) and Upper Scorpius (5-12 Myr). Overall, we observe hints of a faster evolution into low accretion rates of low-mass stars and brown dwarfs. At the same time, we also found that brown dwarfs present larger Mdisk/Macc ratios than stars in Ophiuchus, Lupus and Cha-I. This apparently contradictory result may imply that the evolution of protoplanetary disks around brown dwarfs may be different than in the stellar regime.

Speaker: Ileana Chinnici (INAF)
Titolo: Le spedizioni scientifiche dell’Osservatorio di Palermo, ieri e oggi

Abstract:
Anche l’Osservatorio di Palermo, nel corso della sua lunga storia, ha organizzato o partecipato ad alcune spedizioni scientifiche; naturalmente, non sempre si è trattato di finalità vòlte a studi astronomici, ma in ogni caso le spedizioni avevano scopi scientifici. Tra quelle di carattere astronomico vanno ricordate, in particolare, la spedizione nella Sicilia sud-orientale per l’osservazione dell’eclisse totale di Sole del 1870, quella per il transito di Venere in India nel 1874, quella per le eclissi totale di Sole nelle Isole Nicobar nel 1875 e in Tunisia nel 1905. Di recente, come è noto, è stata anche organizzata una spedizione in Calabria per l’occultazione di Betelgeuse da parte dell’asteroide Leonia nel dicembre 2023. Lo scopo di questo seminario è quello di illustrare soprattutto le spedizioni storiche astronomiche (da cui sempre c’è da imparare!) e raccogliere notizie su eventuali altre spedizioni del XX secolo di cui hanno memoria i colleghi più anziani.

Speaker: Francesco Malara (UniCal)

Titolo del talk: “MHD waves and turbulence in plasmas of the solar corona”

Abstract:
“The solar corona is made of extremely tenuous plasmas having different physical conditions, e.g., temperature, density, and magnetic fields. In response to perturbations, restoring forces determined by pressure and the local magnetic field can determine the formation and propagation of magnetohydrodynamic (MHD) waves. Coronal loops sustain the propagation of different types of MHD with a broad range of periods and amplitude, with the most easily observed and studied one being the kink mode. Kink waves in loops, usually excited in impulsive events (e.g. flares) with amplitude of 4-5 Mm and periods of 3-5 min, are strongly damped within few wave periods. However, high-resolution observations from different space missions in the last decade have shown the omnipresence of so-called “decayless fluctuations”, i.e., kink oscillations with a small amplitude (< 1 Mm) and no damping. Their discovery in the solar corona has posed new questions about their driver and the mechanisms for energy transfer in the solar atmosphere. In fact, the dissipation of the fluctuation energy is one of the possible mechanisms that are believed to be resposible for the heating of the solar corona. In an extremely high Reynolds/Lundquist number plasma, such as in the corona, a key role is played by fluctuation-inhomogeneity couplings, as well as by nonlinear effects that generate a turbulent cascade. In the last few decades such effects have been studied in great detail. Here we present a numerical investigation aiming at clarifying the interplay of these two mechanims in the dissipation of Alfvén waves. We find that, in a regime representative of coronal magnetic structures, fluctuation-inhomogeneity couplings and turbulence synergically work to significantly speed up the conversion of fluctuating kinetic/magnetic energy into thermal energy. Their potential contribution to solving the coronal heating problem is emphasized, as well as the potentialities offered by the MUSE mission in studying the formation and evolution of MHD waves in the corona.”