Context. T Tauri stars are surrounded by dust and gas disks. As material reservoirs from which matter is accreted onto the central star and planets are built, these protoplanetary disks play a central role in star and planet formation.
Aims: We aim at spatially resolving at sub-astronomical unit (sub-au) scales the innermost regions of the protoplanetary disks around a sample of T Tauri stars to better understand their morphology and composition.
Methods: Thanks to the sensitivity and the better spatial frequency coverage of the GRAVITY instrument of the Very Large Telescope Interferometer, we extended our homogeneous data set of 27 Herbig stars and collected near-infrared K-band interferometric observations of 17 T Tauri stars, spanning effective temperatures and luminosities in the ranges of ~4000-6000 K and ~0.4-10 L_⊙, respectively. We focus on the continuum emission and develop semi-physical geometrical models to fit the interferometric data and search for trends between the properties of the disk and the central star.
Results: As for those of their more massive counterparts, the Herbig Ae/Be stars, the best-fit models of the inner rim of the T Tauri disks correspond to wide rings. The GRAVITY measurements extend the radius-luminosity relation toward the smallest luminosities (0.4-10 L_⊙). As observed previously, in this range of luminosities, the R ∝ L^1∕2 trend line is no longer valid, and the K-band sizes measured with GRAVITY appear to be larger than the predicted sizes derived from sublimation radius computation. We do not see a clear correlation between the K-band half-flux radius and the mass accretion rate onto the central star. Besides, having magnetic truncation radii in agreement with the K-band GRAVITY sizes would require magnetic fields as strong as a few kG, which should have been detected, suggesting that accretion is not the main process governing the location of the half-flux radius of the inner dusty disk. The GRAVITY measurements agree with models that take into account the scattered light, which could be as important as thermal emission in the K band for these cool stars. The N-to-K band size ratio may be a proxy for disentangling disks with silicate features in emission from disks with weak and/or in absorption silicate features (i.e., disks with depleted inner regions and/or with large gaps). The GRAVITY data also provide inclinations and position angles of the inner disks. When compared to those of the outer disks derived from ALMA images of nine objects of our sample, we detect clear misalignments between both disks for four objects.
Conclusions: The combination of improved data quality with a significant and homogeneous sample of young stellar objects allows us to revisit the pioneering works done on the protoplanetary disks by K-band interferometry and to test inner disk physics such as the inner rim morphology and location.

GTO programs with run IDs: 0103.C-0347, 0102.C-0408, 0101.C-0311, 0100.C-0278, and 099.C-0667.

We examine the particle acceleration mechanism in the Mpc-scale bridge between Abell 399 and Abell 401 and assess in particular if the synchrotron emission originates from first-order or second-order Fermi re-acceleration. We use deep (~40 hours) LOw-Frequency ARray (LOFAR) observations from Abell 399 and Abell 401 and apply improved direction-dependent calibration to produce deep radio images at three different resolutions at 144 MHz. With a point-to-point analysis we find in the bridge trends between the radio emission from our new maps and X-ray emission from an XMM Newton observation. By analyzing our observations and results, we argue that second-order Fermi re-acceleration is currently the most favoured process to explain the emission from the radio bridge, where past AGN activity may be responsible for the supply of fossil plasma needed for in-situ re-acceleration. The radio halos from Abell 401 and Abell 399 are also consistent with a second-order Fermi re-acceleration model.

We present the detection of 68 sources from the most sensitive radio survey in circular polarisation conducted to date. We used the second data release of the 144 MHz LOFAR Two-metre Sky Survey to produce circularly polarised maps with a median noise of 140 µJy beam⁻¹ and resolution of 20″ for ≈27% of the northern sky (5634 deg²). The leakage of total intensity into circular polarisation is measured to be ≈0.06%, and our survey is complete at flux densities ≥1 mJy. A detection is considered reliable when the circularly polarised fraction exceeds 1%. We find the population of circularly polarised sources is composed of four distinct classes: stellar systems, pulsars, active galactic nuclei, and sources unidentified in the literature. The stellar systems can be further separated into chromospherically active stars, M dwarfs, and brown dwarfs. Based on the circularly polarised fraction and lack of an optical counterpart, we show it is possible to infer whether the unidentified sources are likely unknown pulsars or brown dwarfs. By the completion of this survey of the northern sky, we expect to detect 300±100 circularly polarised sources.

V-LoTSS catalogue is only available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/670/A124

Radio galaxies in clusters of galaxies are a prominent reservoir of magnetic fields and of non-thermal particles, which become mixed with the intracluster medium. We review the observational and theoretical knowledge of the role of these crucial ingredients for the formation of diffuse radio emission in clusters (radio halos, relics, mini halos) and outline the open questions in this field.

Context. Clusters of galaxies are known to be turbulent environments, whether they are merging systems where turbulence is injected via the conversion of gravitational potential energy into the intracluster medium (ICM), or whether they are relaxed systems in which small-scale core sloshing is occurring within the potential well. In many such systems, diffuse radio sources associated with the ICM are found: radio haloes and mini-haloes.
Aims: Abell 2142 is a rich cluster undergoing an extreme episode of core sloshing, which has given rise to four cold fronts and a complex multi-component radio halo. Recent work revealed that there are three primary components to the halo that spans a distance of up to around 2.4 Mpc. The underlying physics of particle acceleration on these scales is poorly explored, and requires high-quality multi-frequency data with which to perform precision spectral investigation. We aim to perform such an investigation.
Methods: We used new deep MeerKAT L-band (1283 MHz) observations in conjunction with LOFAR HBA (143 MHz) data as well as X-ray data from XMM-Newton and Chandra to study the spectrum of the halo and the connection between the thermal and non-thermal components of the ICM.
Results: We confirm the presence of the third halo component, detecting it for the first time at 1283 MHz and confirming its ultra-steep spectrum nature, as we recovered an integrated spectrum of α_{H3, total} = −1.68 ± 0.10. All halo components follow power-law spectra with increasingly steep spectra moving towards the cluster outskirts. We profiled the halo in three directions, finding evidence of asymmetry and spectral steepening along an axis perpendicular to the main axis of the cluster. Our investigation of the thermal non-thermal connection shows sub-linear correlations that are steeper at 1283 MHz than 143 MHz, and we find evidence of different connections in different components of the halo. In particular, we find both a moderate anti-correlation (H1, the core) and positive correlation (H2, the ridge) between the radio spectral index and X-ray temperature.
Conclusions: Our results are broadly consistent with an interpretation of turbulent (re-)acceleration following an historic minor cluster merger scenario in which we must invoke some inhomogeneities. However, the anti-correlation between the radio spectral index and X-ray temperature in the cluster core is more challenging to explain; the presence of three cold fronts and a generally lower temperature may provide the foundations of an explanation, but detailed modelling is required to study this further.

The full-field MeerKAT image is available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/686/A44

Dal 5 dicembre 2019 OA@INAF è aperto all'immissione dei RAPPORTI TECNICI. Prima di fare una submission o una review si prega di seguire attentamente le istruzioni riportate nel Manuale d'uso per l'inserimento dei rapporti tecnici in OA@INAF [versione aggiornata al 24.5.2021].
Dal 24 febbraio 2020 i ricercatori possono inserire i prodotti della ricerca. Prima di procedere, si raccomanda un'attenta lettura delle Istruzioni per l'inserimento dei prodotti della ricerca nel repository OA@INAF [versione aggiornata al 15.5.2020].

A causa di un bug di ADS che espone una lista di autori e una di ORCID non coerenti fra loro, il recupero delle pubblicazioni e il loro legame con gli autori non è possibile. Pertanto, fino a risoluzione del bug, il pregresso (fino al 2014) non sarà più importato come inizialmente previsto.

Le pubblicazioni indicizzate in ADS dal 2015 al 2019 verranno recuperate a blocchi di anni. I ricercatori troveranno nel workspace le submissions da completare con i metadati mancanti e il full text. Perché questo sia possibile, è necessario aver fatto il claim delle pubblicazioni in ADS con il proprio ORCID. Chi non ha fatto il claim non troverà nulla.. Per gli anni dal 2016 in poi le submissions da completare andranno a finire solo nel workspace del primo autore INAF, a cui spetterà il compito di completare l'inserimento nel repository.

Ciò che non è indicizzato in ADS o non viene recuperato a causa del bug potrà essere inserito nel modo semi-automatico, con ricerca per ID (DOI, ORCID, ADSBibCode).

Il repository inserisce automaticamente tutte le pubblicazioni presenti nel SitoDocente che ciascuno ha in LoginMIUR. Perché possano essere prese in considerazione per la VQR 2015-2019 è necessario, al momento del caricamento del full text, selezionare SI nel menu a discesa in corrispondenza dell'etichetta MIUR