R. Paladino

Further identification of ROSAT all-sky survey sources in Orion

We report on the identification of 22 ROSAT All-Sky Survey (RASS) X-ray sources distributed in the general direc- tion of the Orion star-forming region. The X-ray sample contains sources from the ROSAT bright source catalogue and from previous detections. The optical identifications are based on intermediate-resolution spectroscopy and UBV Johnson photom- etry using a 1m-class telescope. The strengths of the Hα ,N a D2 and lithium lines for the stellar counterparts are evaluated applying the spectral subtraction technique, using templates of the same spectral type. Radial velocities of the optical coun- terparts are also reported. Thirteen of the optical counterparts show the lithium absorption line in their spectra and have radial velocities consistent with the Orion star forming region. Four of these objects can be classified as new bona-fide T Tauri stars.

New low-mass pre-main sequence spectroscopic binaries in Orion

We report the results of a high-resolution spectroscopic monitoring campaign on low-mass pre-main sequence spectroscopic binaries, discovered recently in the general direction of the Orion star-forming region, based on ROSAT all-sky survey X-ray observations. Also included in the present study are two binaries recognized in the course of optical follow-up observations of X-ray sources in a selected sky strip crossing the Orion SFR perpendicular to the galactic plane. Orbital elements for the six double-lined spectroscopic binaries are derived from the analysis of the radial velocities of the components. The orbital periods span from 3 to 47 days. In addition, through a matching of the binary composite spectrum with synthetic binary spectra, we estimate spectral types and luminosity ratios for the components and derive lithium abundances for individual binary components. Using the estimated stellar parameters combined with kinematical information and lithium abundance determinations, we examine the evolutionary status of the objects. We then use the minimum masses derived from the solution of the spectroscopic orbits for the systems of conrmed PMS nature to make comparisons with current theoretical pre-main sequence evolutionary tracks, and attempt to set constraints on some of the most frequently used models.

Improved fundamental parameters for the low-mass pre-main sequence eclipsing system RX J0529.4+0041

We report new photometric observations and a new determination of the fundamental stellar parameters for the low-mass pre-main sequence eclipsing system RX J0529.4+0041A based on high-precision, near-IR (

Correlation of the radio continuum, infrared, and CO molecular emissions in NGC 3627

\it JHK

Multifrequency polarimetry of a complete sample of PACO radio sources

) differential photometry obtained using adaptive optics at the ESO-La Silla 3.6 m telescope, and

Sardinia Radio Telescope observations of Abell 194. The intra-cluster magnetic field power spectrum

\it UBV(RI)_{\rm C}

Radio spectral index images of the spiral galaxies NGC 0628, NGC 3627, and NGC 7331

CCD photometry performed with the OIG camera at TNG. The new photometric data, in combination with already published photoelectric photometry and solution of the radial velocity curve, yield a more precise determination of the absolute dimensions and masses as well as of other basic physical properties of the components.

Polarization of extragalactic radio sources: CMB foregrounds and telescope calibration issues

Aims. We present new radio observations of two regions of the spiral galaxy NGC 3627, including new radio continuum observations at 1.4 GHz with the Very Large Array, and also new observations in the CO line, taken with the Plateau de Bure interferometer. Comparing these observations with archival Spitzer and Hα data we study the correlation of the radio continuum (RC), infrared-8 μm, and CO emissions at a spatial resolution of 100 pc. Methods. We compare the point-by-point variations of the RC, CO, and 8 μm brightnesses in two distinct regions of 2 kpc × 2 kpc in size of NGC 3627. We also present a three-dimensional fit of the observed data. Results. We examined scale much lower than the electron diffusion scale, where a breakdown of the correlations would be expected. However, no evidence for such correlation breakdown has been found. The RC emission follows the distribution of CO well, and the widths of several structures, measured along slices across them, are comparable. Furthermore, we found that down to a spatial scale of 100 pc, the radio continuum emission is correlated with dust emissions at 4.5, 5.8, and 8 μm, which trace different dust temperatures. We present a new perspective, a three-dimensional representation, with which to visualize and study the RC-CO-24 μm and RC-CO-8 μm correlations. We fit the observed data with a three-dimensional line, obtaining a rms of 0.25 dex. Conclusions. The observed correlation enhances the complexity of the electrons diffusion, losses, and injection mechanisms, and of their connection to star formation processes described by molecular and dust emissions. We plan to further investigate this connection using spatially resolved spectral index studies at low radio frequencies where the thermal emission component is seemingly negligible.

Characterization of polarimetric and total intensity behaviour of a complete sample of PACO radio sources in the radio bands

We present high sensitivity polarimetric observations in 6 bands covering the 5.5-38 GHz range of a complete sample of 53 compact extragalactic radio sources brighter than 200 mJy at 20 GHz. The observations, carried out with the Australia Telescope Compact Array (ATCA), achieved a 91% detection rate (at 5 sigma). Within this frequency range the spectra of about 95% of sources are well fitted by double power laws, both in total intensity and in polarisation, but the spectral shapes are generally different in the two cases. Most sources were classified as either steep- or peaked-spectrum but less than 50% have the same classification in total and in polarised intensity. No significant trends of the polarisation degree with flux density or with frequency were found. The mean variability index in total intensity of steep-spectrum sources increases with frequency for a 4-5 year lag, while no significant trend shows up for the other sources and for the 8 year lag. In polarisation, the variability index, that could be computed only for the 8 year lag, is substantially higher than in total intensity and has no significant frequency dependence.

Observations of the galaxy cluster CIZA J2242.8+5301 with the Sardinia Radio Telescope

Aims. We study the intra-cluster magnetic field in the poor galaxy cluster Abell 194 by complementing radio data, at different frequencies, with data in the optical and X-ray bands.Methods. We analyzed new total intensity and polarization observations of Abell 194 obtained with the Sardinia Radio Telescope (SRT). We used the SRT data in combination with archival Very Large Array observations to derive both the spectral aging and rotation measure (RM) images of the radio galaxies 3C 40A and 3C 40B embedded in Abell 194. To obtain new additional insights into the cluster structure, we investigated the redshifts of 1893 galaxies, resulting in a sample of 143 fiducial cluster members. We analyzed the available ROSAT and Chandra observations to measure the electron density profile of the galaxy cluster.Results. The optical analysis indicates that Abell 194 does not show a major and recent cluster merger, but rather agrees with a scenario of accretion of small groups, mainly along the NE−SW direction. Under the minimum energy assumption, the lifetimes of synchrotron electrons in 3C 40 B measured from the spectral break are found to be 157 ± 11 Myr. The break frequency image and the electron density profile inferred from the X-ray emission are used in combination with the RM data to constrain the intra-cluster magnetic field power spectrum. By assuming a Kolmogorov power-law power spectrum with a minimum scale of fluctuations of Λmin = 1 kpc, we find that the RM data in Abell 194 are well described by a magnetic field with a maximum scale of fluctuations of Λmax = (64 ± 24) kpc. We find a central magnetic field strength of ⟨ B0 ⟩ = (1.5 ± 0.2) μG, which is the lowest ever measured so far in galaxy clusters based on Faraday rotation analysis. Further out, the field decreases with the radius following the gas density to the power of η = 1.1 ± 0.2. Comparing Abell 194 with a small sample of galaxy clusters, there is a hint of a trend between central electron densities and magnetic field strengths.Key words: galaxies: clusters: general / galaxies: clusters: individual: Abell 194 / magnetic fields / large-scale structure of Universe