Abstract
Radio emission from stars can be used, for example, to study ionized winds or stellar flares. The radio emission is faint and studies have been limited to few objects. The Square Kilometer Array (SKA) brings a survey ability to the topic of radio stars. In this paper we investigate what the SKA can detect, and what sensitivity will be required for deep surveys of the stellar Milky Way. We focus on the radio emission from OB stars, Be stars, flares from M dwarfs, and Ultra Compact HII regions. The stellar distribution in the Milky Way is simulated using the Besançon model, and various relations are used to predict their radio flux. We find that the full SKA will easily detect all UltraCompact HII regions. At the limit of 10 nJy at 5 GHz, the SKA can detect 1500 Be stars and 50 OB stars per square degree, out to several kpc. It can also detect flares from 4500 M dwarfs per square degree. At 100 nJy, the numbers become about 8 times smaller. SKA surveys of the Galactic plane should be designed for high sensitivity. Deep imaging should consider the significant number of faint flares in the field, even outside the plane of the Milky Way.
Highlights
In the past few decades, improvements in the sensitivity of instrument such as the Very Large Array (VLA) have allowed the study of radio emissions from stars
We focus on the radio emission from OB stars, Be stars, and Ultra Compact HII regions for massive stars, and for M dwarfs for low-mass stars
Due to the large amount of M dwarfs in the galaxy, we only study a part of the sky (0◦ ≤ b ≤ 10◦) here
Summary
In the past few decades, improvements in the sensitivity of instrument such as the Very Large Array (VLA) have allowed the study of radio emissions from stars. Radio emission has been detected from many different kinds of stars in different evolution stages, including mass-losing stars and binaries with thermal wind, magnetically-active stars, and other main sequence stars [2]. Since it is the atmosphere that produces the radio emission, studying the radio emission can help us understand the properties of the star’s atmosphere and the environments in which those astrophysical phenomenon and stellar activities are taking place. Depending on the magnetic field strength, this mechanism produces gyrosynchrotron emission for mildly relativistic electrons and synchrotron emission for highly relativistic electrons. For stars with radio brightness temperature higher than 1012 K, there are two main kinds of coherent radiation mechanisms [1]. Its fundamental emission is best observed below 1 GHz. The second is the electron cyclotron maser emission [3,4]. It is emitted mostly at the fundamental and the second harmonic of νc (1)
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