Anomalous Microwave Emission in HII Regions: Is it Really Anomalous? The Case of RCW 49

The detection of an excess of emission at microwave frequencies with respect to the predicted free–free emission has been reported for several Galactic H ii regions. Here, we investigate the case of RCW 49, for which the Cosmic Background Imager tentatively (~3σ) detected Anomalous Microwave Emission (AME) at 31 GHz on angular scales of 7'. Using the Australia Telescope Compact Array, we carried out a multi-frequency (5, 19, and 34 GHz) continuum study of the region, complemented by observations of the H109α radio recombination line. The analysis shows that: (1) the spatial correlation between the microwave and IR emission persists on angular scales from 3farcm4 to 0farcs4, although the degree of the correlation slightly decreases at higher frequencies and on smaller angular scales; (2) the spectral indices between 1.4 and 5 GHz are globally in agreement with optically thin free–free emission, however, ~30% of these are positive and much greater than −0.1, consistent with a stellar wind scenario; and (3) no major evidence for inverted free–free radiation is found, indicating that this is likely not the cause of the Anomalous Emission in RCW 49. Although our results cannot rule out the spinning dust hypothesis to explain the tentative detection of AME in RCW 49, they emphasize the complexity of astronomical sources that are very well known and studied, such as H ii regions, and suggest that, at least in these objects, the reported excess of emission might be ascribed to alternative mechanisms such as stellar winds and shocks

Auroral radio emission from low-mass stars

It is now a well-established fact that also very low mass stars harbor planetary systems. These stars represent the large majority of our nearby stars but, despite their proximity, their low optical luminosity makes it difficult to apply the usual methods for exoplanet search. An effective probe for the environment of these stars is the auroral radio emission. This kind of emission is well understood for those stars whose magnetic field can be approximated as a dipole. In these cases the radio emission has a peculiar signature in time and in polarization. The presence of a planet nearby the star triggers or perturbs this emission leading to a predictable modulation. We present the case study of the ultra-cool dwarf TVLM 513-46546, for which we take advantage of VLA observations at 4.9 and 8.4 GHz. We reproduce the cyclic circularly-polarized pulses of the star using a 3D model of the auroral radio emission from the stellar magnetosphere. To take into account the possible deviation from the dipolar symmetry, the model simulates a magnetosphere shaped like an offset-dipole. To reproduce the timing and pattern of the observed pulses we explored the space of parameters controlling the auroral beaming pattern and the magnetosphere geometry. Our model explains the observed anomalies of the radio emission at 8.4 GHz as a possible interaction of the star with an external body, like in the case of the interaction between Jupiter and Io

A massive nebula around the Luminous Blue Variable star RMC143 revealed by ALMA

The luminous blue variable (LBV) RMC143 is located in the outskirts of the 30~Doradus complex, a region rich with interstellar material and hot luminous stars. We report the $3\sigma$ sub-millimetre detection of its circumstellar nebula with ALMA. The observed morphology in the sub-millimetre is different than previously observed with HST and ATCA in the optical and centimetre wavelength regimes. The spectral energy distribution (SED) of RMC143 suggests that two emission mechanisms contribute to the sub-mm emission: optically thin bremsstrahlung and dust. Both the extinction map and the SED are consistent with a dusty massive nebula with a dust mass of $0.055\pm0.018~M_{\odot}$ (assuming $\kappa_{850}=1.7\rm\,cm^{2}\,g^{-1}$). To date, RMC143 has the most dusty LBV nebula observed in the Magellanic Clouds. We have also re-examined the LBV classification of RMC143 based on VLT/X-shooter spectra obtained in 2015/16 and a review of the publication record. The radiative transfer code CMFGEN is used to derive its fundamental stellar parameters. We find an effective temperature of $\sim 8500$~K, luminosity of log$(L/L_{\odot}) = 5.32$, and a relatively high mass-loss rate of $1.0 \times 10^{-5}~M_{\odot}$~yr$^{-1}$. The luminosity is much lower than previously thought, which implies that the current stellar mass of $\sim8~M_{\odot}$ is comparable to its nebular mass of $\sim 5.5~M_{\odot}$ (from an assumed gas-to-dust ratio of 100), suggesting that the star has lost a large fraction of its initial mass in past LBV eruptions or binary interactions. While the star may have been hotter in the past, it is currently not hot enough to ionize its circumstellar nebula. We propose that the nebula is ionized externally by the hot stars in the 30~Doradus star-forming region.Comment: Paper accepted by A&A on 09/05/2019 and in proof stage. Second comments by referee are included in this versio

The SKA dish local monitoring and control system user interface

The Square Kilometre Array (SKA) project is responsible for developing the SKA Observatory, the world's largest radiotelescope ever built: eventually two arrays of radio antennas - SKA1-Mid and SKA1-Low - will be installed in the South Africa's Karoo region and Western Australia's Murchison Shire, each covering a different range of radio frequencies. In particular SKA1-Mid array will comprise 133 15m diameter dish antennas observing in the 350 MHz-14 GHz range, each locally managed by a Local Monitoring and Control (LMC) system and remotely orchestrated by the SKA Telescope Manager (TM) system. Dish LMC will provide a Graphical User Interface (GUI) to be used for monitoring and Dish control in standalone mode for testing, TM simulation, integration, commissioning and maintenance. This paper gives a status update of the LMC GUI design involving users and tasks analysis, system prototyping, interface evaluation, provides details on the GUI prototypes being developed and technological choices and discuss key challenges in the LMC UI architecture, as well as our approaches to addressing them. In the GUI design task we have adopted a Usage-Centered Design (UCD) approach based on the early involvement of users whose feedback is being iteratively considered in analysis phases, as well as in design and evaluation. An IFML based user interaction modeling approach has been adopted

Probing the magnetosphere of the M8.5 dwarf TVLM 513-46546 by modelling its auroral radio emission. Hint of star exoplanet interaction?

In this paper, we simulate the cyclic circularly polarized pulses of the ultracool dwarf TVLM 513-46546, observed with the Very Large Array at 4.88 and 8.44 GHz on 2006 May, by using a three-dimensional model of the auroral radio emission from the stellar magnetosphere. During this epoch, the radio light curves are characterized by two pulses left-hand polarized at 4.88 GHz, and one doubly peaked (of opposite polarizations) pulse at 8.44 GHz. To take into account the possible deviation from the dipolar symmetry of the stellar magnetic-field topology, the model described in this paper is also able to simulate the auroral radio emission from a magnetosphere shaped like an offset dipole. To reproduce the timing and pattern of the observed pulses, we explored the space of parameters controlling the auroral beaming pattern and the geometry of the magnetosphere. Through the analysis of the TVLM 513-46546 auroral radio emission, we derive some indications on the magnetospheric field topology that is able to simultaneously reproduce the timing and patterns of the auroral pulses measured at 4.88 and 8.44 GHz. Each set of model solutions simulates two auroral pulses (singly or doubly peaked) per period. To explain the presence of only one 8.44 GHz pulse per period, we analyse the case of auroral radio emission limited only to a magnetospheric sector activated by an external body, like the case of the interaction of Jupiter with its moons

Status of the Local Monitor and Control System of SKA Dishes

The Square Kilometer Array (SKA) project aims at building the world's largest radio observatory to observe the radio sky with unprecedented sensitivity and collecting area. In the SKA1 phase of the project, two dish arrays are to be built, one in South Africa (SKA1-Mid) and the other in Western Australia (SKA1-Survey). Each antenna will be provided with a local monitor and control system, enabling remote operations to engineers and to the Telescope Manager system. In this paper we present the current status of the software system being designed to monitor and control the dish subsystem. An overview of the dish instrumentation is reported, along with details concerning the software architecture, functional interfaces, prototyping and the evaluated technologies

Radio detection of nebulae around four luminous blue variable stars in the Large Magellanic Cloud

The nebulae associated with four luminous blue variables (LBVs) in the Large Magellanic Cloud (LMC) have been observed at 5.5 and 9GHz using the Australia Telescope Compact Array, and radio emission has been detected for first time in sources R127, R143, S61 and S119. The radio maps of the nebulae have an angular resolution of ∼1.5arcsec and a sensitivity of 1.5-3.0 × 10-2mJybeam-1 and show a very similar morphology to that observed in Hα. This similarity permits us to assume that the Hα emission is not affected by strong intrinsic extinction due to dust within the nebulae. We estimate the masses of ionized gas in the LBV nebulae and find values consistent with those measured in Galactic LBVs. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS