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High resolution spectroscopy, providing constraints on plasma motions and temperatures, is a powerful means to investigate the structure of accretion streams in Classical T Tauri stars (CTTS). In particular the accretion-shock region, where the accreting material is heated to temperatures of a few million degrees, can be probed by X-ray spectroscopy. MHD models predict that this hot post-shock plasma should have an inward bulk motion, with v_post ~ 100 km/s, with respect to the surrounding stellar atmosphere. To verify this prediction we searched for a Doppler shift in the deep Chandra/HETG observation of the CTTS TW Hya, perfectly suited for this task because of the excellent S/N and spectral resolution of the dataset, and because of the ideal target inclination. This test should allow us to constrain definitively the nature of this X-ray emitting plasma component in CTTS, and infer constraints on the accretion stream geometry. We searched for a Doppler shift in the X-ray emission from TW Hya by measuring the position of a selected sample of emission lines. To check the absolute wavelength calibration of the Chandra gratings, and to check whether or not bulk motions with respect to the photosphere are observed in coronal plasma, we also analyzed a sample of Chandra/HETG spectra of non-accreting active stars. We found that the soft part of the X-ray spectrum of TW Hya is significantly red-shifted by ~40 km/s with respect to the known radial velocity of the stellar photosphere. Conversely no X-ray redshift is observed in the X-ray emission of non-accreting active stars. The evidence that the X-ray emitting plasma on TW Hya is moving inward with respect to the stellar surface definitively confirms that it originates in the post-shock region, at the base of the accretion stream, and not in coronal structures. The observed radial velocity indicates that the base of the accretion stream on TW Hya is located at low latitudes on the stellar surface. Moreover the observed velocity of the soft X-ray emitting plasma is very similar to the velocity of the narrow component of the CIV resonance doublet at 1550 A, suggesting that they both originate from the same post-shock regions, that the hypothesis of free-fall regime in the accretion streams holds, and that complex magnetic field geometries, as that of TW Hya, allow low latitude accretion spots.
The Carte du Ciel project is considered the mother of all astrometric enterprises. It was conceived at the end of 19th century and was aimed at photographing the entire sky vault, to produce a catalogue of stars up to magnitude 11 and a chart containing stars up to magnitude 14.. This international endeavour was promoted by Paris Observatory in 1887: 18 observatories from both hemispheres participated in it, more or less successfully. This talk will illustrate how the project was originated and developed, why it remained partially inachieved and what was its impact on the astrometric missions which preceded the current GAIA mission.
Star-Planet Interaction (SPI) is a broad phenomenological term which encompasses a variety of physical effects relevant for the evolution of extra-solar planetary systems, in particular for those hosting giant gas planets in close orbits around their parent star. While theoretical expectations of SPI are abundant, observational signatures are still elusive with current instrumentation and adopted observing strategies. I will review the state of the art on the matter, and possible future developments that may help us for a better characterization of exoplanets and their abitability conditions.
I will talk about two new possibilities to analyse the observational data on non-thermal emission of cosmic rays accelerated in supernova remnants (SNRs). The first one is related to the polarization images of SNRs. In fact, the polarized radio emission has been mapped with great detail in several Galactic supernova remnants, but has not yet been exploited to the extent it deserves. We have developed a method to model maps of the Stokes parameters for shell-like SNRs during their Sedov evolution phase. The second result bases on the time-dependent particle acceleration and relates the temporal evolution of the radio spectral index of SNR in the aftermath of the explosion to the gamma-ray spectrum at later stages. As a test case, we apply our method to describe gamma-rays from IC443; as a proxy of the IC443 parent supernova we consider SN1987A.
It is debated whether the long and intense flares observed on the PMS stars in Orion involve single and very long magnetic channels or much flatter loop arcades. This question is important because the long flaring channels may be so long as to connect the star to the circumstellar disk. In this work a new method solves the question …. (suspence is left on purpose).
of young stellar objects around V1818 Ori. This is a follow up devoted to explore the eastern edge of a ring of dust around Kappa Ori(a B0 V star) that embeds groups of YSOs to the west of the star itself. My preliminary analysis shows that also the group of V1818 Ori belongs to the Kappa Ori cluster at 250 pc and is unrelated to the Mon R2 region to which it has been associated so far.
8 giugno ore 11.00 Seminario D. Coero Borga e S. Parisini La struttura di Comunicazione dell’INAF
Come sapete da maggio 2016 l’Inaf ha formalizzato una nuova struttura dedicata alla comunicazione. Com’è organizzata? Chi ci lavora? Cosa si intende per press release, news, conferenza stampa, embargo, comunicato congiunto, virgolettato e cose simili? A chi serve? E, soprattutto, perché parlano di qualunque cosa tranne che delle mie ricerche? Nel corso della prima parte di questo incontro, dedicata a tutti ma in particolare a ricercatrici e ricercatori (precari e non, dai laureandi agli associati già in pensione) tenteremo di soddisfare queste e altre curiosità e dubbi su due dei quattro compiti della struttura di comunicazione: ufficio stampa e Media Inaf. E di raccogliere i vostri suggerimenti. L’obiettivo è migliorare la comunicazione interna, riducendo al minimo i fraintendimenti e cercando di rendere il più possibile serene – magari perfino divertenti – le occasioni d’interazione con noi.
8 giugno ore 14.30 Seminario D. Coero Borga e S. Parisini Utilizzo di videocamera per la produzione di materiale multimediale
Il pomeriggio è dedicato ad una parte più tecnica – rivolta a chiunque ne abbia voglia ma in particolare a chi è interessato a produrre materiale multimediale (perlopiù video) per l’ufficio stampa, Media Inaf e Inaf-Tv – durate la quale daremo qualche rudimento sulle riprese video e faremo qualche simulazione d’intervista. Simulazioni che non verranno messe in rete, promesso: dunque massimo relax e nessun dress code.
Classical T Tauri stars are bright in the soft X-ray and far UV bands, because of large amounts of plasma at T~105-106 K, associated with the accretion-shock regions. Inspecting the emission from the shock region is important since it can potentially reveal fundamental properties of the accretion-stream material (i.e. geometry/density/velocity/abundances). However, the precise location of these hot plasmas (pre-shock? post-shock? different shock regions with different temperatures?) is still unclear. To constrain location and properties of these accretion-related hot plasmas, X-rays and UV observations are needed. The next XMM call (deadline 6 October 2017) offers the possibility to investigate this issue. I would like to discuss with you the opportunity to propose a joint XMM+HST program, focused on TW Hya, to perform time-resolved high-resolution spectroscopy on time scales down to 15 ks, simultaneously in the X-ray and UV bands. Correlated or uncorrelated variability of plasmas at 105 and 106 K will indicate whether or not they are located in the same accretion-shock regions. That will provide important constraints on the physical properties of the accretion streams in CTTS.