arXiv subjects

L. Dolla

Publications and source records attributed to L. Dolla.

13 recordsLinked to original sources

arXiv2026

Coordinated Coronagraphic Observations from Proba-3 and Aditya-L1: Investigating CME Energetics in the Inner Corona

Constraining the plasma properties and energetics of coronal mass ejections (CMEs) in the inner corona is essential for understanding their early evolution, yet remains challenging because of limited observations. We investigate the mass and density evolution, and energy partitioning of two CMEs observed on 2025 September 14 and 16, and assess the potential of coordinated Proba-3/ASPIICS and Aditya-L1/VELC observations to constrain CME energetics in the low corona. We present the first coordinated observations of CMEs obtained simultaneously by Proba-3/ASPIICS and Aditya-L1/VELC. Using ASPIICS white-light observations, we estimate the CME mass, volume, number density, and the evolution of kinetic, thermal, and magnetic energies. Magnetic energies are estimated from observed CME properties using observationally constrained, physically motivated assumptions. Simultaneous VELC Fe XIV 5303 Angstorm observations provide independent estimates of the emission measure, electron number density, thermal energy, and CME lateral extent. The two events exhibit markedly different energy partitioning in the low corona. For the 14 September CME, the kinetic and magnetic energies are comparable, while the thermal energy remains nearly two orders of magnitude smaller, indicating limited plasma heating. In contrast, the 16 September CME exhibits a substantial thermal-energy enhancement, with thermal energy eventually becoming comparable to kinetic energy. For both CMEs, the estimated magnetic energy remains comparable to or exceeds the kinetic energy over the observed height. Our results demonstrate the scientific potential of synergetic ASPIICS and VELC observations for constraining CME mass, density, and energetics in the inner corona, providing new observational constraints on the early evolution of CMEs.

astro-ph.SR↗

arXiv2026

Diffraction in the ASPIICS coronagraph: observations and modeling

Context: ASPIICS is a giant-baseline visible light solar coronagraph, which relies on the millimetric positioning performance of the precision formation flying Proba-3 mission of the European Space Agency. Proba-3 was launched on 5 Dec 2024, and since then ASPIICS observes the solar corona with the field of view (1.1-3) R_sun. Aims: Diffraction, in particular diffraction of solar disk light on the external occulter, is known to provide a major source of straylight in coronagraphs. We aim to analyze diffracted light visible in ASPIICS images, compare it with the analytical-numerical diffraction model reported earlier, and fine-tune the model. Methods: We compare diffraction effects visible in ASPIICS data with simulated diffraction images; in particular, we compare the geometrical properties and the radiometric signal. The properties of the diffraction described in previous works suggest how to fine-tune the model in order to achieve a better correspondence with the observations. Results: Early ASPIICS observations, where diffraction is pronounced, fully confirm all the qualitative properties of diffracted light suggested by the model. After fine-tuning of the model we see quantitative correspondence of the level of 30\% -- 50\%, depending on the configuration. Conclusions: The performed analysis allows (a) to validate our analytical-numerical model and justify the assumptions, and (b) to estimate the contribution of the diffracted light in the ASPIICS images. In the majority of the field of view the diffracted light is two orders of magnitude below the coronal signal.

astro-ph.IM↗

arXiv2025

Observing the solar corona from a formation-flying mission. First results of Proba-3/ASPIICS

We report the first results from observations of the solar corona by the ASPIICS coronagraph aboard the Proba-3 mission. ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun) is a giant coronagraph consisting of the telescope mounted aboard one of the mission's spacecraft and the external occulter placed on the second spacecraft. The two spacecraft separated by around 144 m fly in a precise formation up to 5.5 hours at a time, which allows coronal observations in eclipse-like conditions, i.e. close to the limb (typically down to 1.099 Rs, occasionally down to 1.05 Rs) and with very low straylight. ASPIICS observes quasi-stationary structures, such as coronal loops, streamers, quiescent prominences, and a variety of dynamic phenomena: erupting prominences, coronal mass ejections, jets, slow solar wind outflows, coronal inflows. In particular, weak, widespread and persistent small-scale outflows and inflows between 1.3 and 3 Rs are observed at a high spatial (5.6 arcsec) and temporal (30 s) resolution for the first time, expanding the range of scales at which the variable slow solar wind is observed to form.

astro-ph.SR↗

arXiv2025

Height-dependent thermal properties of extreme-ultraviolet campfires in the quiet Sun

Small-scale impulsive energy-release events are widely considered a key ingredient of quiet-Sun coronal heating. We quantified the thermal-energy content of extreme-ultraviolet (EUV) campfires, examined their impulsive heating characteristics, and investigated how their properties vary with atmospheric height. We analysed 1,468 campfires from an observing sequence on 30 May 2020 with Solar Orbiter/EUI HRIEUV at 174 A. Temperatures and emission measures were adopted from SDO/AIA diagnostics, and geometric uncertainties were explored using multiple volume models. Statistical properties were characterised using cumulative distribution functions and maximum-likelihood techniques and compared with Solar Orbiter/STIX microflares and SDO/AIA nanoflare-like events. Campfire durations show a clear dependence on height: short-duration events occur at all heights, whereas longer-lived brightenings are preferentially associated with chromospheric layers. Emitting volumes and thermal energies, by contrast, show no comparable height dependence. Background-subtracted thermal energies span approximately 10^20-10^24 erg, with rare events reaching approximately 5 x 10^24 erg. The statistically robust power-law regime extends over approximately 10^22-10^24 erg. Directly detected campfires contribute a sub-percent fraction of the canonical quiet-Sun heating requirement; approximate corrections for the detection threshold and DEM completeness could raise this contribution to a value of order a few percent. EUV campfires extend the flare energy distribution towards lower energies and provide height-resolved constraints on impulsive heating in the quiet Sun. The height dependence of event durations, combined with broadly invariant energy and volume distributions, indicates that atmospheric stratification primarily modulates cooling and dissipation timescales rather than the characteristic energy scale.

astro-ph.SR↗

arXiv2025

The ASPIICS solar coronagraph aboard the Proba-3 formation flying mission. Scientific objectives and instrument design

We describe the scientific objectives and instrument design of the ASPIICS coronagraph launched aboard the Proba-3 mission of the European Space Agency (ESA) on 5 December 2024. Proba-3 consists of two spacecraft in a highly elliptical orbit around the Earth. One spacecraft carries the telescope, and the external occulter is mounted on the second spacecraft. The two spacecraft fly in a precise formation during 6 hours out of 19.63 hour orbit, together forming a giant solar coronagraph called ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun). Very long distance between the external occulter and the telescope (around 144 m) represents an increase of two orders of magnitude compared to classical externally occulted solar coronagraphs. This allows us to observe the inner corona in eclipse-like conditions, i.e. close to the solar limb (down to 1.099 Rs) and with very low straylight. ASPIICS will provide a new perspective on the inner solar corona that will help solve several outstanding problems in solar physics, such as the origin of the slow solar wind and physical mechanism of coronal mass ejections.

astro-ph.SR↗

arXiv2022

Prominence eruption observed in He II 304 {\AA} up to $>6 R_\sun$ by EUI/FSI aboard Solar Orbiter

We report observations of a unique, large prominence eruption that was observed in the He II 304 {\AA} passband of the the Extreme Ultraviolet Imager/Full Sun Imager telescope aboard Solar Orbiter on 15-16 February 2022. Observations from several vantage points (Solar Orbiter, the Solar-Terrestrial Relations Observatory, the Solar and Heliospheric Observatory, and Earth-orbiting satellites) were used to measure the kinematics of the erupting prominence and the associated coronal mass ejection. Three-dimensional reconstruction was used to calculate the deprojected positions and speeds of different parts of the prominence. Observations in several passbands allowed us to analyse the radiative properties of the erupting prominence. The leading parts of the erupting prominence and the leading edge of the corresponding coronal mass ejection propagate at speeds of around 1700 km/s and 2200 km/s, respectively, while the trailing parts of the prominence are significantly slower (around 500 km/s). Parts of the prominence are tracked up to heights of over $6 R_\sun$. The He II emission is probably produced via collisional excitation rather than scattering. Surprisingly, the brightness of a trailing feature increases with height. The reported prominence is the first observed in He II 304 {\AA} emission at such a great height (above 6 $R_\sun$).

astro-ph.SR↗

arXiv2022

Automatic detection of small-scale EUV brightenings observed by the Solar Orbiter/EUI

Context. Accurate detections of frequent small-scale extreme ultraviolet (EUV) brightenings are essential to the investigation of the physical processes heating the corona. Aims. We detected small-scale brightenings, termed campfires, using their morphological and intensity structures as observed in coronal EUV imaging observations for statistical analysis. Methods. We applied a method based on Zernike moments and a support vector machine classifier to automatically identify and track campfires observed by Solar Orbiter/Extreme Ultraviolet Imager (EUI) and SDO/AIA. Results. This method detected 8678 campfires (with length scales between 400 km and 4000 km) from a sequence of 50 High Resolution EUV telescope (HRIEUV) 174{\AA} images. From 21 near co-temporal AIA images covering the same field of view as EUI, we found 1131 campfires, 58% of which were also detected in HRIEUV images. In contrast, about 16% of campfires recognized in HRIEUV were detected by AIA. We obtain a campfire birthrate of 2*10-16m-2s-1. About 40% of campfires show a duration longer than 5 s, having been observed in at least two HRIEUV images. We find that 27% of campfires were found in coronal bright points and the remaining 73% have occurred out of coronal bright points. We detected 23 EUI campfires with a duration greater than 245 s. We found that about 80% of campfires are formed at supergranular boundaries, and the features with the highest total intensities are generated at network junctions and intense H I Lyman-{\alpha} emission regions observed by EUI/HRILya. The probability distribution functions for the total intensity, peak intensity, and projected area of campfires follow a power law behavior with absolute indices between 2 and 3. This self-similar behavior is a possible signature of self-organization, or even self-organized criticality, in the campfire formation process.

astro-ph.SR↗

arXiv2021

Stereoscopy of extreme UV quiet Sun brightenings observed by Solar Orbiter/EUI

The 3D fine structure of the solar atmosphere is still not fully understood as most of the available observations are taken from a single vantage point. The goal of the paper is to study the 3D distribution of small-scale brightening events ("campfires") discovered in the EUV quiet Sun by the Extreme Ultraviolet Imager (EUI) aboard Solar Orbiter. We used a first commissioning data set acquired by the EUI's High Resolution EUV telescope on 30 May 2020 in the 174 {\AA} passband and we combined it with simultaneous data taken by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory in a similar 171 {\AA} passband. The two-pixel spatial resolution of the two telescopes is 400 km and 880 km, respectively, which is sufficient to identify the campfires in both data sets. The two spacecraft had an angular separation of around 31.5 degrees (essentially in heliographic longitude), which allowed for the 3D reconstruction of the campfire position. These observations represent the first time that stereoscopy was achieved for brightenings at such a small scale. Manual and automatic triangulation methods were used to characterize the campfire data. The height of the campfires is located between 1000 km and 5000 km above the photosphere and we find a good agreement between the manual and automatic methods. The internal structure of campfires is mostly unresolved by AIA; however, for a particularly large campfire, we were able to triangulate a few pixels, which are all in a narrow range between 2500 and 4500 km. The low height of EUI campfires suggests that they belong to the previously unresolved fine structure of the transition region and low corona of the quiet Sun. They are probably apexes of small-scale dynamic loops heated internally to coronal temperatures. This work demonstrates that high-resolution stereoscopy of structures in the solar atmosphere has become feasible.

astro-ph.SR↗

arXiv2021

Stereoscopic Measurements of Coronal Doppler Velocities

The Solar Orbiter mission, with an orbit outside the Sun Earth line and leaving the ecliptic plane, opens up opportunities for the combined analysis of measurements obtained by solar imagers and spectrometers. For the first time, different space spectrometers will be located at wide angles to each other, allowing three-dimensional (3D) spectroscopy of the solar atmosphere. The aim of this work is to prepare the methodology to facilitate the reconstruction of 3D vector velocities from two stereoscopic LOS Doppler velocity measurements using the Spectral Imaging of the Coronal Environment (SPICE) onboard the Solar Orbiter and the near-Earth spectrometers, while widely separated in space. We develop the methodology using the libraries designed earlier for the STEREO mission but applied to spectroscopic data from the Hinode mission and the Solar Dynamics Observatory. We use well-known methods of static and dynamic solar rotation stereoscopy and the methods of EUV stereoscopic triangulation for optically thin coronal EUV plasma emissions. We develop new algorithms using analytical geometry in space to determine the 3D velocity in coronal loops. We demonstrate our approach with the reconstruction of 3D velocity vectors in plasma flows along "open" and "closed" magnetic loops. This technique will be applied to an actual situation of two spacecraft at different separations with spectrometers onboard (SPICE versus the Interface Region Imaging Spectrograph (IRIS) and Hinode imaging spectrometer) during the Solar Orbiternominal phase. We summarise how these observations can be coordinated.

astro-ph.SR↗

arXiv2021

Extreme UV quiet Sun brightenings observed by Solar Orbiter/EUI

The goal of this paper is to study the smallest brightening events observed in the EUV quiet Sun. We use commissioning data taken by the EUI instrument onboard the recently launched Solar Orbiter mission. On 2020 May 30, EUI was situated at 0.556AU from the Sun. Its HRIEUV telescope 17.4nm passband reached an exceptionally high two-pixel spatial resolution of 400km. The size and duration of small-scale structures is determined in the HRIEUV data, while their height is estimated from triangulation with the simultaneous SDO/AIA data. This is the first stereoscopy of small scale brightenings at high resolution. We observed small localised brightenings ("campfires") in a quiet Sun region with lengthscales between 400km and 4000km and durations between 10 and 200s. The smallest and weakest of these HRIEUV brightenings have not been observed before. Simultaneous HRILYA observations do not show localised brightening events, but the locations of the HRIEUV events correspond clearly to the chromospheric network. Comparison with simultaneous AIA images shows that most events can also be identified in the 17.1nm, 19.3nm, 21.1nm, and 30.4nm passbands of AIA, although they appear weaker and blurred. DEM analysis indicates coronal temperatures peaking at log(T)~6.1-6.15. We determined the height of a few campfires, which is between 1000 and 5000km above the photosphere. We conclude that "campfires" are mostly coronal in nature and are rooted in the magnetic flux concentrations of the chromospheric network. We interpret these events as a new extension to the flare/microflare/nanoflare family. Given their low height, the EUI "campfires" could be a new element of the fine structure of the transition region/low corona: apexes of small-scale loops that are internally heated to coronal temperatures.

astro-ph.SR↗

arXiv2020

The Solar Orbiter Science Activity Plan: translating solar and heliospheric physics questions into action

Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument suites, the coordination and planning of the operations are essential to address the following four top-level science questions: (1) What drives the solar wind and where does the coronal magnetic field originate? (2) How do solar transients drive heliospheric variability? (3) How do solar eruptions produce energetic particle radiation that fills the heliosphere? (4) How does the solar dynamo work and drive connections between the Sun and the heliosphere? Maximising the mission's science return requires considering the characteristics of each orbit, including the relative position of the spacecraft to Earth (affecting downlink rates), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. Furthermore, since each orbit's science telemetry will be downloaded over the course of the following orbit, science operations must be planned at mission level, rather than at the level of individual orbits. It is important to explore the way in which those science questions are translated into an actual plan of observations that fits into the mission, thus ensuring that no opportunities are missed. First, the overarching goals are broken down into specific, answerable questions along with the required observations and the so-called Science Activity Plan (SAP) is developed to achieve this. The SAP groups objectives that require similar observations into Solar Orbiter Observing Plans (SOOPs), resulting in a strategic, top-level view of the optimal opportunities for science observations during the mission lifetime.

astro-ph.SR↗

arXiv2012

Time delays in quasi-periodic pulsations observed during the X2.2 solar flare on 2011 February 15

We report observations of quasi-periodic pulsations (QPPs) during the X2.2 flare of 2011 February 15, observed simultaneously in several wavebands. We focus on fluctuations on time scale 1-30 s and find different time lags between different wavebands. During the impulsive phase, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) channels in the range 25-100 keV lead all the other channels. They are followed by the Nobeyama RadioPolarimeters at 9 and 17 GHz and the Extreme Ultra-Violet (EUV) channels of the Euv SpectroPhotometer (ESP) onboard the Solar Dynamic Observatory (SDO). The Zirconium and Aluminum filter channels of the Large Yield Radiometer (LYRA) onboard the Project for On-Board Autonomy (PROBA2) satellite and the SXR channel of ESP follow. The largest lags occur in observations from the Geostationary Operational Environmental Satellite (GOES), where the channel at 1-8 {\AA} leads the 0.5-4 {\AA} channel by several seconds. The time lags between the first and last channels is up to 9 s. We identified at least two distinct time intervals during the flare impulsive phase, during which the QPPs were associated with two different sources in the Nobeyama RadioHeliograph at 17 GHz. The radio as well as the hard X-ray channels showed different lags during these two intervals. To our knowledge, this is the first time that time lags are reported between EUV and SXR fluctuations on these time scales. We discuss possible emission mechanisms and interpretations, including flare electron trapping.

astro-ph.SR↗

arXiv2008

Solar off-limb line widths: Alfven waves, ion-cyclotron waves, and preferential heating

Alfven waves and ion-cyclotron absorption of high-frequency waves are frequently brought into models devoted to coronal heating and fast solar-wind acceleration. Signatures of ion-cyclotron resonance have already been observed in situ in the solar wind (HELIOS spacecrafts) and, recently, in the upper corona (UVCS/SOHO remote-sensing results). We propose a method to constrain both the Alfven wave amplitude and the preferential heating induced by ion-cyclotron resonance, above a partially developed polar coronal hole observed with the SUMER/SOHO spectrometer. The instrumental stray light contribution is first substracted from the spectra. By supposing that the non-thermal velocity is related to the Alfven wave amplitude, it is constrained through a density diagnostic and the gradient of the width of the Mg X 625 A line. The temperatures of several coronal ions, as functions of the distance above the limb, are then determined by substracting the non-thermal component to the observed line widths. The effect of stray light explains the apparent decrease with height in the width of several spectral lines, this decrease usually starting about 0.1-0.2 Rs above the limb. This result rules out any direct evidence of damping of the Alfven waves, often suggested by other authors. We also find that the ions with the smallest charge-to-mass ratios are the hottest ones at a fixed altitude and that they are subject to a stronger heating, as compared to the others, between 57" and 102" above the limb. This constitutes a serious clue to ion-cyclotron preferential heating.

astro-ph↗