Interferometric Observations of the Quiet Sun at 20 and 25 MHz in May 2014

Melnik, V. N.; Шепелев, В. А.; Poedts, Stefaan; Dorovskyy, V. V.; Браженко, А. И.; Rücker, H. O.

doi:10.1007/s11207-018-1316-3

Cited by 8 publications

(11 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It was shown that the polar and equatorial sizes of the Sun increased with decreasing of frequency following the power law with indexes -0.27 and -0.26 respectively. In addition, these dependences appeared to be very close to the plasma frequency dependence on the distance in undisturbed corona model by Baumbach-Allen [46]. The effective brightness temperature of the solar thermal radio emission was found to be equal to 5 2 10  K, which is several times smaller in magnitude than the kinetic plasma temperature.…”

Section: S R supporting

confidence: 75%

Exploration of the Solar Decameter Radio Emission With the Utr-2 Radio Telescope

Melnik

Konovalenko

Dorovskyy

et al. 2021

Radio phys. radio astron.

Self Cite

View full text Add to dashboard Cite

Purpose: The overview of the scientifi c papers devoted to the study of the solar decameter radio emission with the world’s largest UTR-2 radio telescope (Ukraine) published for the last 50 years. Design/methodology/approach: The study and analysis of the scientifi c papers on both sporadic and quiet (thermal) radiation of the Sun recorded with the UTR-2 radio telescope at the decameter wavelength range. Findings: The most signifi cant observational and theoretical results of the solar radio emission studies obtained at the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine for the last 50 years are given. Conclusions: For the fi rst time, at frequencies below 30 MHz, the Type II bursts, Type IV bursts, S-bursts, drift pairs and spikes have been recorded. The dependences of these bursts parameters on frequency within the frequency band of 9 to 30 MHz were obtained. The models of their generation and propagation were suggested. Moreover, for the fi rst time the fi ne time-frequency structures of the Type III bursts, Type II bursts, Type IV bursts, U- and J-bursts, S-bursts, and drift pairs have been observed due to the high sensitivity and high time-frequency resolutions of the UTR-2 radio telescope. The super-fi ne structure of Type II bursts with a “herringbone” structure was identifi ed, which has never been observed before. New types of bursts were discovered: “caterpillar” bursts, “dog-leg” bursts, Type III bursts with decay, Type III bursts with changing drift rate sign, Type III-like bursts, Jb- and Ub-bursts, etc. An interpretation of the unusually high drift rates and drift rates with alternating signs of the Type III-like bursts was suggested. Based on the dependence of spike durations on frequency, the coronal plasma temperature profi le at the heliocentric heights of 1.5–3RS was determined. Usage of the heliographic and interferometric methods gave the possibility to start studies of the spatial characteristics – sizes and locations of the bursts emission sources. Thus, it was shown that at the decameter band, the Type III burst durations were defi ned by the emission source linear sizes, whereas the spike durations were governed by the collision times in the source plasma. It was experimentally proved that the effective brightness temperatures of the sources of solar sporadic radio emission at the decameter band may reach values of 1014–1015 K. In addition, it was found that the radii of the quiet Sun at frequencies 20 and 25 MHz are close to the distances from the Sun at which the local plasma frequency is equal to the corresponding observed frequency of radio emission in the Baumbach–Allen model. Key words: UTR-2; Sun; decameter radio emission; radio bursts; corona

show abstract

Section: S R supporting

confidence: 75%

Exploration of the Solar Decameter Radio Emission With the Utr-2 Radio Telescope

Melnik

Konovalenko

Dorovskyy

et al. 2021

Radio phys. radio astron.

Self Cite

View full text Add to dashboard Cite

show abstract

“…Both the E-W and N-S radii are significantly larger than the result of Melnik et al (2018). The trend of radius frequency to high frequency is consistent with Mercier & Chambe (2015) and Sharma & Oberoi (2020).…”

Section: Size Of the Sun In Low Frequencysupporting

confidence: 71%

“…The size measured by this method can ignore extended solar radio emission below the half-power level. The Gaussian fitting method assumes the radio source to have a Gaussian-like flux distribution, and fits it with a Gaussian function in UV visibility (Melnik et al 2018) or image space (Ramesh et al 2006). The size of the radio Sun is thus determined by the FWHM of the fitted Gaussian.…”

Section: Size Of the Sun In Low Frequencymentioning

confidence: 99%

“…Vocks et al (2018) inferred a scale height temperature of 2.2 × 10 6 K with multifrequency interferometry imaging observation of the quiet Sun using the LOw Frequency ARray (LOFAR) telescope's Low Band Array (LBA). Melnik et al (2018) performed interferometric imaging of the quiet Sun with the Ukrainian T-shaped Radio telescope of the second modification (UTR-2). They found brightness temperatures of 5.1 × 10 5 and 5.7 × 10 5 K at 20 and 25 MHz, respectively.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Imaging of the Quiet Sun in the Frequency Range of 20–80 MHz

Zhang

Zucca

Kozarev

et al. 2022

ApJ

View full text Add to dashboard Cite

Radio emission of the quiet Sun is considered to be due to thermal bremsstrahlung emission of the hot solar atmosphere. The properties of the quiet Sun in the microwave band have been well studied, and they can be well described by the spectrum of bremsstrahlung emission. In the meter-wave and decameter-wave bands, properties of the quiet Sun have rarely been studied due to the instrumental limitations. In this work, we use the LOw Frequency ARray telescope to perform high quality interferometric imaging spectroscopy observations of quiet Sun coronal emission at frequencies below 90 MHz. We present the brightness temperature spectrum and the size of the Sun in the frequency range of 20–80 MHz. We report on dark coronal regions with low brightness temperatures that persist with frequency. The brightness temperature spectrum of the quiet Sun is discussed and compared with the bremsstrahlung emission of a coronal model and previous quiet Sun observations.

show abstract

“…Thus knowing one of these two parameters we can define another one. From the current state of available observation facilities, such as interferometric observations with UTR-2 radio telescope (Dorovskyy, et al, 2018;Melnik, et al, 2018) or tiedarray imaging realized at LOFAR station (Reid and Kontar, 2017;Gordovskyy et al, 2019) it seems more realistic to define the height of the loop as well as its deviation from the normal direction. This will enable us to yield the temperature of the confined plasma, which is difficult to measure by other means at such heights.…”

Section: Analysis and Discussionmentioning

confidence: 99%

Solar Type U Burst Associated with a High Coronal Loop

et al. 2020

Self Cite

View full text Add to dashboard Cite

An inverted U burst with equally developed ascending and descending branches observed by Giant Ukrainian Radio Telescope (GURT) on 18 April 2017 in meter wavelengths band is discussed. This U burst was attributed to the high coronal loop above the limb active region NOAA 12651. Under the assumption that, associated with the burst, the coronal loop confines isothermal plasma stratified according to a Boltzmann density relation, the geometrical and physical parameters of the loop were estimated. According to our model coronal loops may contain plasma which is up to 20 times denser than the surrounding coronal plasma. In general the proposed model gives the relation between the plasma temperature and the height of the loop in such a way that under the given parameters of the associated U burst, higher loops contain cooler plasma and vice versa. An alternative method of coronal loop height determination was suggested. Assuming that the observed U burst and the preceding Type III burst were generated by the same exciter we define the height of the loop from the delay of the former with respect to the latter at certain frequency. We show that defining of coronal loops heights by another independent method, e.g. interferometric or tied-array imaging may solve the uncertainty of the inside-the-loop plasma temperature determination. Keywords Radio bursts: dynamic spectrum • Meter-wavelengths and longer (m, dkm, hm, km) • Type III • Corona: structures most common for metric and decametric bands (Suzuki and Dulk, 1985; Dorovskyy, et al., 2010;Reid and Kontar, 2017). More detailed and extended analysis made by Leblanc and Hoyos (1985) showed that U bursts turning frequencies most often occur in frequency range 25-30 MHz.

show abstract

Interferometric Observations of the Quiet Sun at 20 and 25 MHz in May 2014

Cited by 8 publications

References 23 publications

Exploration of the Solar Decameter Radio Emission With the Utr-2 Radio Telescope

Exploration of the Solar Decameter Radio Emission With the Utr-2 Radio Telescope

Imaging of the Quiet Sun in the Frequency Range of 20–80 MHz

Solar Type U Burst Associated with a High Coronal Loop

Contact Info

Product

Resources

About