A Pathway to EMU: the SCORPIO Project

Abstract

We are entering a golden age for radio astronomy. There are several new interferometers upcoming, whose characteristics, in terms of sensitivity, frequency coverage, angular and temporal resolution, field of view, will permit unprecedented deep observations. The most outstanding ones among them will be the Square Kilometre Array (SKA) and its precursors, such as the Australian SKA Pathfinder (ASKAP) and MeerKAT. Several surveys will be carried out, in continuum and spectral line. In particular we will have as continuum surveys the Evolutionary Map of the Universe (EMU), to be carried out with ASKAP, the MeerKAT International GigaHertz Tiered extra-galactic Exploration Survey (MIGHTEE) and the MeerKAT High Frequency Galactic Plane Survey (Meer-GAL), both to be carried out with MeerKAT. All this surveys will observe large regions of the sky at high sensitivity, providing a huge increase in known object. This thesis focuses on radio stars and the science that can be carried out with the new radio interferometers. Even if, in general, stars emit in radio a small fraction of their luminosity, at these wavelengths it is possible to trace different phenomena that is not possible to study by other means. Furthermore the Galaxy is optically thin in radio, then we can observe stars in the GP that we could not observe in the optical frequencies. Unfortunately, due to the faintness of stars in radio, the number of currently known radio stars is limited to a small sample. Furthermore, they have all been observed directly, not discovered in a blind survey. We want to know how many radio stars to expect from the new surveys and, to do that, we worked on two different approaches. In the theoretical approach, described in Chapter 3 of the thesis, we estimate the number of stars that belong to those spectral type that incorporates radio emitting classes, such as Magnetic Chemically Peculiar (MCP) stars, OB stars, Flare stars and RS CVn stars from the Besancon model (Robin et al., 2003), and, from this information, from the probability of a certain spectral type star to be a radio emitter, we estimate the total number of stars detected at different sensitivities. As reported in the conclusions, we expect about 250 000 stars in EMU and about 50 000 000 with SKA-1. For the observational approach, we started the Stellar Continuum Originating from Radio Physics In Ourgalaxy (SCORPIO). SCORPIO is a blind survey of a five square degree region of the Galactic Plane, carried out with ATCA at 2.1 GHz and designed with two major goals, a scientific and a technical one. First of all, we wanted to know how may stars per square degree we can detect in a blind survey and to collect as much information as possible about the radio emission. Secondly, we wanted to know how to address the issues that comes from a blind survey on a area of the Galactic Plane, such as issues due to the complex structures present in the GP; issues due to the presence of variable sources; issues due to the diffuse emission that dominate the GP; issues regarding the identification of different populations. The work on the SCORPIO project is described in Chapters 4, 5 and 6 of this thesis. In Chapter 4 we focused on the data reduction, analysing each step from the raw data to the final image. In Chapter 5 we described a way to discriminate the source classes, studying their emission mechanism through their spectral indices. We found out, comparing our work to the ATLAS survey, that, in the SCORPIO field, about 20 sources per square degree with a flux density greater than 1 mJy are Galactic. In Chapter 6 we show all the different images created during the process, showing their importance in the study of specific physical properties. We also described the H ii regions and the radio stars found in the field. On Chapter 7 we do a summary and present the results accomplished in the thesis and the planned future work.