Solar Observations with Single-Dish INAF Radio Telescopes: Continuum Imaging in the 18 – 26 GHz Range

Righini, S.; Iacolina, M. N.; Marongiu, M.; Mulas, S.; Murtas, G.; Valente, G.; Egron, E.; Bachetti, Matteo; Buffa, Franco; Concu, R.; Deiana, Gian Luigi; Guglielmino, S. L.; Ladu, A.; Loru, S.; Maccaferri, A.; Marongiu, P.; Melis, A.; Navarrini, A.; Orfei, A.; Ortu, Pierluigi; Pili, M.; Pisanu, T.; Pupillo, G.; Saba, Andrea; Schirru, Luca; Serra, G.; Tiburzi, C.; Zanichelli, A.; Zucca, Pietro; Messerotti, M.

doi:10.1007/s11207-022-02013-5

Cited by 4 publications

(8 citation statements)

References 89 publications

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“…The duration of these solar campaigns covers over five years, from 2018 to mid-2023. These solar observations are the core of the "SunDish Project" (PI: A. Pellizzoni) 4 , in collaboration with INAF and ASI (Pellizzoni et al 2019(Pellizzoni et al , 2022Plainaki et al 2020), aimed at the imaging and monitoring of the solar atmosphere.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

“…The 64-m SRT is located at 650 m elevation in Sardinia (Italy). Up to date, SRT has observed the Sun mostly at 18.8 and 24.7 GHz once a month through a seven-feed dual-polarization K-band receiver, customised for solar observations (Bolli et al 2015;Prandoni et al 2017;Pellizzoni et al 2022) and characterised by a beam size of 1.0 and 0.8 arcmin, respectively. This radio telescope is currently in the final step of an upgrade phase that includes the installation of new receivers (suitable also for solar observations) operating up to 116 GHz in the context of the National Operative Programme (Programma Operativo Nazionale-PON; Govoni et al 2021) 5 .…”

Section: Observations and Data Reductionmentioning

confidence: 99%

“…The solar maps are reconstructed from on-the-fly (OTF) scans (Prandoni et al 2017) in right ascension (RA) and declination (Dec), respectively, covering an area in the sky of 4800 × 4800 arcsec at Medicina, and 5400 × 5400 arcsec at SRT. The imaging and calibration procedures are performed using the SRT Single-Dish Imager (SDI; Egron et al 2017;Pellizzoni et al 2019Pellizzoni et al , 2022Loru et al 2019Loru et al , 2021Marongiu et al 2020Marongiu et al , 2022Mulas et al 2022). The data analysis is provided by the Python solar pipeline SUNPIT (Marongiu et al 2022).…”

Section: Observations and Data Reductionmentioning

confidence: 99%

“…In this paper, we focus on the study of the atmospheric emission through the analysis of the brightness profiles of about 300 solar images, obtained through single-dish observations from the newly appointed Medicina Gavril Grueff Radio Telescope (hereafter, Grueff Radio Telescope) and the Sardinia Radio Telescope (SRT) at the radio , over about half a solar cycle (from 2018 to mid-2023), in the frame of the SunDish project aimed at the development of solar imaging observing modes for the INAF radio telescopes (Pellizzoni et al 2022). Through this project, accurate brightness temperature, T B , profiles of the solar disk were obtained and the solar size was deeply analysed, finding that the measured solar radii, R -ranging between 959 and 994 arcsec -calculated for each observing frequency and radio telescope, are consistent with the other values reported in the literature (Marongiu et al 2024).…”

Section: Introductionmentioning

confidence: 99%

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Study of solar brightness profiles in the 18–26 GHz frequency range with INAF radio telescopes

Marongiu,

Pellizzoni,

Righini

et al. 2024

A&A

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One of the most important objectives of solar physics is to gain a physical understanding of the solar atmosphere, whose structure can also be described in terms of the density ($N$) and temperature ($T$) distributions of the atmospheric matter. Several multi-frequency analyses have shown that the characteristics of these distributions are still under debate, especially for outer coronal emission. We aim to constrain the $T$ and $N$ distributions of the solar atmosphere through observations in the centimetric radio domain. We employed single-dish observations from two of the INAF radio telescopes at the K-band frequencies ($18$ -- $26$ GHz). We investigated the origin of the significant brightness temperature ($T_B$) detected up to the upper corona (at an altitude of $ 800$ Mm with respect to the photospheric solar surface). To probe the physical origin of the atmospheric emission and to constrain instrumental biases, we reproduced the solar signal by convolving specific 2D antenna beam models. We performed an analysis of the solar atmosphere by adopting a physical model that assumes the thermal bremsstrahlung as the emission mechanism, with specific $T$ and $N$ distributions. We compared the modelled $T_B$ profiles with those observed by averaging solar maps obtained at $18.3$ and $25.8$ GHz during the minimum of solar activity (2018 -- 2020). We probed any possible discrepancies between the $T$ and $N$ distributions assumed from the model and those derived from our measurements. The $T$ and $N$ distributions are compatible (within a $25<!PCT!>$ of uncertainty) with the model up to $ 60$ Mm and $ 100$ Mm in altitude respectively. Our analysis of the role of the antenna beam pattern on our solar maps proves the physical nature of the atmospheric emission in our images up to the coronal tails seen in our $T_B$ profiles. Our results suggest that the modelled $T$ and $N$ distributions are in good agreement (within $25<!PCT!>$ of uncertainty) with our solar maps up to altitudes of $ Mm. A subsequent, more challenging analysis of the coronal radio emission at higher altitudes, together with the data from satellite instruments, will require further multi-frequency measurements.

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Section: Observations and Data Reductionmentioning

confidence: 99%

Section: Observations and Data Reductionmentioning

confidence: 99%

Section: Observations and Data Reductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Study of solar brightness profiles in the 18–26 GHz frequency range with INAF radio telescopes

Marongiu,

Pellizzoni,

Righini

et al. 2024

A&A

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“…The Cagliari Astronomical Observatory used the Medicina 32 m and Sardinia Radio Telescope (SRT) 64 m antennas for solar imaging observations and obtained approximately 170 maps of the entire solar disk in the 18-26 GHz band, with beamwidths of 2 1 and 1 5 for the 18 GHz and 26 GHz solar observations, respectively, when using the Medicina 32 m antenna. The beamwidths of the 18 GHz, 24 GHz, and 25 GHz solar observations with the SRT 64 m antenna were 1 02, 0 78, and 0 75, respectively (Prandoni et al 2017;Pellizzoni et al 2022). When correlated by two antennas (a nulling interferometer) to compensate for the quiet solar background radiation, the solar flare can be considered a point-source signal as compared to the solar disk, and the nulling interferometer can largely reduce fluctuations in the overall quiet solar flux density (Luthi et al 2005).…”

Section: Introductionmentioning

confidence: 99%

A Two-element Interferometer for Millimeter-wave Solar Flare Observations

Yu¹,

Zhang³

et al. 2023

ApJS

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In this paper, we present the design and implementation of a two-element interferometer operating in the millimeter-wave band (39.5–40 GHz) for observing solar radio emissions through nulling interference. The system is composed of two 50 cm aperture Cassegrain antennas installed on a common equatorial mount, with a separation of 230 wavelengths. The cross-correlation of the received signals effectively cancels out the quiet solar component of the high flux density (∼3000 sfu) that reduces the detection limit due to atmospheric fluctuations. The system performance is as follows: the noise factor of the analog front end in the observation band is less than 2.1 dB, system sensitivity is approximately 12.4 K (∼34 sfu) with an integration time constant of 0.1 ms (default), the frequency resolution is 153 kHz, and the dynamic range is ≥30 dB. Through actual testing, the nulling interferometer observes a quiet Sun with a low level of output fluctuations (up to 50 sfu) and has a significantly lower radiation flux variability (up to 190 sfu) than an equivalent single-antenna system, even under thick cloud cover. As a result, this new design can effectively improve observation sensitivity by reducing the impact of atmospheric and system fluctuations during observation.

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Study of solar brightness profiles in the 18–26 GHz frequency range with INAF radio telescopes

Marongiu,

Pellizzoni,

Mulas

et al. 2024

A&A

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The Sun is an extraordinary workbench, on which several fundamental astronomical parameters can be measured with high precision. Among these parameters, the solar radius $R_ odot $ plays an important role in several aspects, for instance, in evolutionary models. Moreover, it conveys information about the structure of the different layers that compose the solar interior and its atmosphere. Despite the efforts to obtain accurate measurements of $R_ odot $, the subject is still debated, and measurements are puzzling and/or lacking in many frequency ranges. We determine the mean, equatorial, and polar radii of the Sun ($R_c$, $R_ eq $, and $R_ pol $) in the frequency range $18.1$ -- $26.1$ GHz. We employed single-dish observations from the newly appointed Medicina Gavril Grueff Radio Telescope and the Sardinia Radio Telescope (SRT) in five years, from $2018$ to mid-$2023$, in the framework of the SunDish project for solar monitoring. Two methods for calculating the radius at radio frequencies were employed and compared: the half-power, and the inflection point. To assess the quality of our radius determinations, we also analysed the possible degrading effects of the antenna beam pattern on our solar maps using two 2D models (ECB and 2GECB). We carried out a correlation analysis with the evolution of the solar cycle by calculating Pearson's correlation coefficient rho in the 13-month running means. We obtained several values for the solar radius, ranging between $959$ and $994$ arcsec, and rho , with typical errors of a few arcseconds. These values constrain the correlation between the solar radius and solar activity, and they allow us to estimate the level of solar prolatness in the centimeter frequency range. Our $R_ odot $ measurements are consistent with the values reported in the literature, and they provide refined estimates in the centimeter range. The results suggest a weak prolateness of the solar limb ($R_ eq $ > $R_ pol $), although $R_ eq $ and $R_ pol $ are statistically compatible within 3sigma errors. The correlation analysis using the solar images from the Grueff Radio Telescope shows (1) a positive correlation between solar activity and the temporal variation in $R_c$ (and $R_ eq $) at all observing frequencies, and (2) a weak anti-correlation between the temporal variation of $R_ pol $ and solar activity at $25.8$ GHz.

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Solar Observations with Single-Dish INAF Radio Telescopes: Continuum Imaging in the 18 – 26 GHz Range

Cited by 4 publications

References 89 publications

Study of solar brightness profiles in the 18–26 GHz frequency range with INAF radio telescopes

Study of solar brightness profiles in the 18–26 GHz frequency range with INAF radio telescopes

A Two-element Interferometer for Millimeter-wave Solar Flare Observations

Study of solar brightness profiles in the 18–26 GHz frequency range with INAF radio telescopes

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