arXiv subjects

Manuel Luna

Publications and source records attributed to Manuel Luna.

At least 19 recordsLinked to original sources

arXiv2026

Automatic detection of solar filament oscillations I: Multi-scale spectral pipeline

Solar filament oscillations provide important diagnostics of prominence magnetic structure and stability, but their detection in long H\alpha archives has traditionally relied on visual inspection, manually placed slits, and time--distance diagrams. We present an automatic pipeline for detecting spatially coherent filament oscillations in GONG H\alpha image sequences. The method combines image preprocessing and coalignment, deep-learning-based filament detection and segmentation, multi-scale spatial averaging, Lomb--Scargle spectral analysis, convolutional-neural-network background estimation, empirical calibration of significance thresholds, and clustering of candidate detections in period and space. Only oscillations supported across at least four spatial scales are retained, reducing sensitivity to local pixel-scale intensity fluctuations. The pipeline recovers several events from the manual GONG catalog of Luna et al. (2018), including the 1 January 2014 oscillation with a period of approximately 76 min. Applied to the first two weeks of January 2014, it identifies 91 oscillatory events, compared with 22 non-duplicate events in the corresponding manual catalog, with detected periods ranging from about 20 to 126 min. It also detects previously unreported oscillations, including an event on 13 January 2014 with a period of approximately 86 min that is independently confirmed using a conventional time--distance diagram. These results demonstrate that automated filament segmentation, multi-scale spectral analysis, and calibrated significance testing can provide a reproducible and scalable alternative to manual slit-based searches. The pipeline substantially increases detection sensitivity while preferentially selecting coherent filament-scale oscillations, enabling future statistical studies over extended GONG intervals and across the solar cycle.

astro-ph.SR↗

arXiv2024

Study of the excitation of large amplitude oscillations in a prominence by nearby flares

Large amplitude oscillations commonly occur in solar prominences, triggered by energetic phenomena such as jets and flares. On March 14-15, 2015, a filament partially erupted in two stages, leading to oscillations in different parts. This study explores longitudinal oscillations from the eruption, focusing on the mechanisms behind their initiation, with special attention to the large oscillation on March 15. The oscillations and jets are analyzed using the time-distance technique. For flares and their interaction with the filament, we analyze AIA channels and use the DEM technique. Initially, a jet fragments the filament, splitting it into two segments. One remains in place, while the other detaches and moves. This causes oscillations in both segments: (a) the position change causes the detached segment to oscillate with a period of $69 \pm 3$ minutes; (b) the jet flows cause the remaining filament to oscillate with a period of $62 \pm 2$ minutes. In the second phase, on March 15, another jet seemingly activates the detached filament eruption, followed by a flare. A large longitudinal oscillation occurs in the remnant segment with a period of $72 \pm 2$ minutes and velocity amplitude $73 \pm 1 \, \mathrm{km s^{-1}}$. During the oscillation trigger, bright field lines connect the flare with the filament, appearing only in the AIA 131$\r{A}$ and 94$\r{A}$ channels, indicating the presence of hot plasma. DEM analysis confirms this, showing plasma around 10 MK pushing the prominence from its southeastern side, displacing it along the field lines and starting the oscillation. From this, the flare -- not the preceding jet-triggers the oscillation. The hot plasma flows into the filament channel. We explain how flares trigger large oscillations in filaments by proposing that post-flare loops reconnect with the filament channel's magnetic field.

astro-ph.SR↗

arXiv2024

Future Prospects for Partially Ionised Solar Plasmas: the Prominence Case

Partially ionised plasmas (PIP) constitute an essential ingredient of our plasma universe. Historically, the physical effects associated with partial ionisation were considered in astrophysical topics such as the interstellar medium, molecular clouds, accretion disks and, later on, in solar physics. PIP can be found in layers of the Sun's atmosphere as well as in solar structures embedded within it. As a consequence, the dynamical behaviour of these layers and structures is influenced by the different physical effects introduced by partial ionisation. Here, rather than considering an exhaustive discussion of partially ionised effects in the different layers and structures of the solar atmosphere, we focus on solar prominences. The reason is that they represent a paradigmatic case of a partially ionised solar plasma, confined and insulated by the magnetic field, constituting an ideal environment to study the effects induced by partial ionisation. We present the current knowledge about the effects of partial ionisation in the global stability, mass cycle and dynamics of solar prominences. We revise the identified observational signatures of partial ionisation in prominences. We conclude with prospects for PIP research in prominences, proposing the path for advancing in the prominence modelling and theory and using new and upcoming instrumentation.

astro-ph.SR↗

arXiv2024

Modeling of Condensations in Coronal Loops Produced by Impulsive Heating

We present the results of models of impulsively heated coronal loops using the 1-D hydrodynamic Adaptively Refined Godunov Solver (ARGOS) code. The impulsive heating events (which we refer to as "nanoflares") are modeled by discrete pulses of energy along the loop. We explore the occurrence of cold condensations due to the effective equivalent of thermal non-equilibrium (TNE) in loops with steady heating, and examine its dependence on nanoflare timing and intensity and also nanoflare location along the loop, including randomized distributions of nanoflares. We find that randomizing nanoflare distributions, both in time/intensity and location, diminishes the likelihood of condensations as compared to distributions with regularly occurring nanoflares with the same average properties. The usual criteria that condensations are favored for heating near loop footpoints and with high cadences are more strict for randomized (as opposed to regular) nanoflare distributions, and for randomized distributions the condensations stay in the loop for a shorter amount of time. That said, condensations can sometimes occur in cases where the average values of parameters (frequency or location) are beyond the critical limits above which condensations do not occur for corresponding steady, non-randomized values of those parameters. These properties of condensations occurring due to randomized heating can be used in the future to investigate diagnostics of coronal heating mechanisms.

astro-ph.SR↗

arXiv2024

Producing C-S-H gel by reaction between silica oligomers and portlandite: A promising approach to repair cementitious materials

Impregnation treatments are one of the alternatives to protect concrete-based building and monuments from weathering degradation. However, it is important to consider the chemical compatibility of the reaction products with the building material. The impregnation product studied here consists of a silica oligomer able to polymerize, by a simple sol-gel process, inside the pore structure of concrete. In this work, we investigate the ability of this impregnation treatment to produce C-S-H gel in contact with cement paste. A complete characterization of the reaction products demonstrated that the silanol groups from silica oligomers react with the portlandite present in the cement paste generating a material with the chemical, structural and morphological features of CS-H gel. Simultaneously, the 29Si NMR results indicate that the Si-O units are incorporated into the existing C-S-H, increasing its chain length. These results open the way for a simple concrete structures repairing procedure.

cond-mat.mtrl-sci↗

arXiv2023

Numerical simulations of prominence oscillations triggered by external perturbations

Several energetic disturbances have been identified as triggers of the large-amplitude oscillations (LAOs) in prominences. However, the mechanisms for LAOs excitation are not well understood. We aim to study these mechanisms, performing time-dependent numerical simulations in 2.5D and 2D setups using magnetohydrodynamic (MHD) code MANCHA3D. Two types of disturbances are applied to excite prominence oscillations, such as a perturbation associated with an eruption and the waves caused by an artificial energy release. In the simulation with the eruption, we obtain that it does not produce LAOs in the prominence located in its vicinity. While the erupting flux rope rises, an elongated current sheet forms behind it, which becomes unstable and breaks into plasmoids. The downward-moving plasmoids cause perturbations in the velocity field by merging with the post-reconnection loops. This velocity perturbation propagates in the surroundings and perturbs the nearby prominence. The analysis of the oscillatory motions of the prominence plasma reveals the excitation of small-amplitude oscillations (SAOs), which are a mixture of longitudinal and vertical oscillations. In the simulation with a distant artificial perturbation, a fast-mode shock wave is produced, and it gradually reaches two flux rope prominences at different distances. This shock wave excites vertical LAOs and longitudinal SAOs with similar amplitudes, periods, and damping times in both prominences. Finally, in the experiment with the external triggering of LAOs in a dipped arcade prominence model, we find that, although the vector normal to the front of a fast-mode shock wave is parallel to the spine of the dipped arcade well before the contact, this wave does not excite longitudinal LAOs. When the wave front approaches the prominence, it pushes the dense plasma down, establishing vertical LAOs.

astro-ph.SR↗

arXiv2023

Interaction of solar jets with filaments: Triggering of large-amplitude filament oscillations

Large-amplitude oscillations (LAOs) are often detected in filaments. Using multiwavelength observations, their origin can be traced back to the interaction with eruptions and jets. We present two different case studies as observational evidence in support of 2.5D MHD numerical experiments that show that the LAOs in the filament channels can be initiated by solar jets. In the two studied events, we can identify a quadrupolar configuration with an X-point at the top of the parasitic region suggestive of a classical null-point. A reconnection flow emanates from this structure leading to a jet that propagates along the filament channel. In both cases we can identify the quiescent and eruptive phases of the jet. The triggered LAOs have periods of around 70-80 minutes and are damped after a few oscillations. The minimum magnetic field intensity inferred with seismology for the filament turns out to be around 30 Gauss. We conclude that the two case studies are consistent with the recent numerical model of Luna and Moreno-Insertis (2021), in which the LAOs are initiated by jets. The relationship between the onset of the jet and filament oscillations is straight-forward for the first case and less for the second case. In the second event, although there is some evidence, we cannot rule out other possibilities such as activity unrelated to the null-point or changes in the magnetic structure of the filament. Both jets are associated with very weak flares which did not launch any EUV wave. Therefore the role of EUV waves for triggering the filament oscillations can be eliminated for these two case.

astro-ph.SR↗

arXiv2022

Automatic detection technique for solar filament oscillations in GONG data

Solar filament oscillations have been known for decades. Now thanks to the new capabilities of the new telescopes, these periodic motions are routinely observed. Oscillations in filaments show key aspects of their structure. A systematic study of filament oscillations over the solar cycle can shed light on the evolution of the prominences. This work is a proof of concept that aims to automatically detect and parameterise such oscillations using H$α$ data from the GONG network of telescopes. The proposed technique studies the periodic fluctuations of every pixel of the H$α$ data cubes. Using the FFT we compute the power spectral density (PSD). We define a criterion to consider whether it is a real oscillation or whether it is a spurious fluctuation. This consists in considering that the peak in the PSD must be greater than several times the background noise with a confidence level of 95\%. The background noise is well fitted to a combination of red and white noise. We applied the method to several observations already reported in the literature to determine its reliability. We also applied the method to a test case, which is a data set in which the oscillations of the filaments were not known a priori. The method shows that there are areas in the filaments with PSD above the threshold value. The periodicities obtained are in general agreement with the values obtained by other methods. In the test case, the method detects oscillations in several filaments. We conclude that the proposed spectral technique is a powerful tool to automatically detect oscillations in prominences using H$α$ data.

astro-ph.SR↗

arXiv2021

Large-amplitude longitudinal oscillations in solar prominences simulated with different resolutions

Large-amplitude longitudinal oscillations (LALOs) in solar prominences have been widely studied in the last decades. However, their damping and amplification mechanisms are not well understood. In this study, we investigate the attenuation and amplification of LALOs using high-resolution numerical simulations with progressively increasing spatial resolutions. We performed time-dependent numerical simulations of LALOs using the 2D magnetic configuration that contains a dipped region. After the prominence mass loading in the magnetic dips, we triggered LALOs by perturbing the prominence mass along the magnetic field. We performed the experiments with four values of spatial resolution. In the simulations with the highest resolution, the period shows a good agreement with the pendulum model. The convergence experiment revealed that the damping time saturates at the bottom prominence region with improving the resolution, indicating the existence of a physical reason for the damping of oscillations. At the prominence top, the oscillations are amplified during the first minutes and then are slowly attenuated. The characteristic time suggests more significant amplification in the experiments with the highest spatial resolution. The analysis revealed that the energy exchange between the bottom and top prominence regions is responsible for the attenuation and amplification of LALOs. The high-resolution experiments are crucial for the study of the periods and the damping mechanism of LALOs. The period agrees with the pendulum model only when using high enough spatial resolution. The results suggest that numerical diffusion in simulations with insufficient spatial resolution can hide important physical mechanisms, such as amplification of oscillations.

astro-ph.SR↗

arXiv2021

Large-amplitude prominence oscillations following the impact by a coronal jet

Observational evidence shows that coronal jets can hit prominences and set them in motion. The impact leads to large-amplitude oscillations (LAOs) of the prominence. In this paper we attempt to understand this process via 2.5D MHD numerical experiments. In our model, the jets are generated in a sheared magnetic arcade above a parasitic bipolar region located in one of the footpoints of the filament channel (FC) supporting the prominence. The shear is imposed with velocities not far above observed photospheric values; it leads to a multiple reconnection process, as in previous jet models. Both a fast Alfvénic perturbation and a slower supersonic front preceding a plasma jet are issued from the reconnection site; in the later phase, a more violent (eruptive) jet is produced. The perturbation and jets run along the FC; they are partially reflected at the prominence and partially transmitted through it. There results a pattern of counter-streaming flows along the FC and oscillations of the prominence. The oscillations are LAOs (with amplitude above $10~\mathrm{km\, s^{-1}}$) in parts of the prominence both in the longitudinal and transverse directions. In some field lines, the impact is so strong that the prominence mass is brought out of the dip and down to the chromosphere along the FC. Two cases are studied with different heights of the arcade above the parasitic bipolar region, leading to different heights for the region of the prominence perturbed by the jets. The obtained oscillation amplitudes and periods are in general agreement with the observations.

astro-ph.SR↗

arXiv2020

Numerical simulations of large-amplitude oscillations in flux-rope solar prominences

Context. Large-amplitude oscillations (LAOs) of the solar prominences are very spectacular but poorly understood phenomena. These motions have amplitudes larger than $10 {\mathrm{\, km \,s^{-1}}}$ and can be triggered by the external perturbations, e.g., Moreton or EIT waves. Aims. Our aim is to analyze the properties of large-amplitude oscillations using realistic prominence models and the triggering mechanism by external disturbances. Methods. We perform time-dependent numerical simulations of LAOs using a magnetic flux rope model with two values of the shear angle and the density contrast. We study the internal modes of the prominence using the horizontal and vertical triggering. In addition, we use the perturbation that arrives from outside in order to understand how such external disturbance can produce LAOs. Results. The period of longitudinal oscillations and its behavior with height show good agreement with the pendulum model. The period of transverse oscillations remains constant with height, suggesting a global normal mode. The transverse oscillations typically have shorter periods than the longitudinal oscillations. Conclusions. The periods of the longitudinal and transverse oscillations show only weak dependence on the shear angle of the magnetic structure and the prominence density contrast. The external disturbance perturbs the flux rope exciting oscillations of both polarizations. Their properties are a mixture of those excited by purely horizontal and vertical driving.

astro-ph.SR↗

arXiv2019

Simultaneous longitudinal and transverse oscillations in filament threads after a failed eruption

Longitudinal and transverse oscillations are frequently observed in the solar prominences and/or filaments. These oscillations are excited by a large scale shock wave, impulsive flares at one leg of the filament threads, or due to any low coronal eruptions. We report simultaneous longitudinal and transverse oscillations in the filament threads of a quiescent region filament. We observe a big filament in the north-west of the solar disk on $6^{th}$ July 2017. On $7^{th}$ July 2017 it starts rising around 13:00 UT. Then we observe a failed eruption and subsequently, the filament threads start to oscillate around 16 UT. We observe both transverse and longitudinal oscillations in a filament thread. The oscillations damp down and filament threads almost disappear. We place horizontal and vertical artificial slits on the filament threads to capture the longitudinal and transverse oscillations of the threads. Data from Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO) is used to detect the oscillations. We find the signatures of large amplitude longitudinal oscillations (LALOs). We also detect damping in LALOs. In one thread of the filament, we observe large amplitude transverse oscillations (LATOs). Using the pendulum model we estimate the lower limit of magnetic field strength and radius of curvature from the observed parameter of LALOs. We show the co-existence of two different wave modes in the same filament threads. We estimate magnetic field from LALOs and hence suggest a possible range of the length of the filament threads using LATOs.

astro-ph.SR↗

arXiv2019

The Role of Asymmetries in Thermal Non-Equilibrium

Thermal non-equilibrium (TNE) is a fascinating situation that occurs in coronal magnetic flux tubes (loops) for which no solution to the steady-state fluid equations exists. The plasma is constantly evolving even though the heating that produces the hot temperatures does not. This is a promising explanation for isolated phenomena such as prominences, coronal rain, and long-period pulsating loops, but it may also have much broader relevance. As known for some time, TNE requires that the heating be both (quasi) steady and concentrated at low coronal altitudes. Recent studies indicate that asymmetries are also important, with large enough asymmetries in the heating and/or cross-sectional area resulting in steady flow rather than TNE. Using reasonable approximations, we have derived two formulae for quantifying the conditions necessary for TNE. As a rough rule of thumb, the ratio of apex to footpoint heating rates must be less than about 0.1, and asymmetries must be less than about a factor of 3. The precise values are case dependent. We have tested our formulae with 1D hydrodynamic loop simulations and find a very acceptable agreement. These results are important for developing physical insight about TNE and assessing how widespread it may be on the Sun.

astro-ph.SR↗

arXiv2019

Fundamental Transverse Vibrations of the Active Region Solar Corona

Some high-resolution observations have revealed that the active-region solar corona is filled with myriads of thin strands even in apparently uniform regions with no resolved loops. This fine structure can host collective oscillations involving a large portion of the corona due to the coupling of the motions of the neighbouring strands. We study these vibrations and the possible observational effects. Here we theoretically investigate the collective oscillations inherent to the fine structure of the corona. We have called them fundamental vibrations because they cannot exist in a uniform medium. We use the T-matrix technique to find the normal modes of random arrangements of parallel strands. We consider an increasing number of tubes to understand the vibrations of a huge number of tubes of a large portion of the corona. We additionally generate synthetic time-distance Doppler and line broadening diagrams of the vibrations of a coronal region to compare with observations. We have found that the fundamental vibrations are in the form of clusters of tubes where not all the tubes participate in the collective mode. The periods are distributed over a wide band of values. The width of the band increases with the number of strands but rapidly reaches an approximately constant value. The frequency band associated with the fine structure of the corona depends on the minimum separation between strands. We have found that the coupling between the strands is of large extent. The synthetic Dopplergrams and line-broadening maps show signatures of collective vibrations, not present in the case of purely random individual kink vibrations. We conclude that the fundamental vibrations of the corona can contribute to the energy budget of the corona and they may have an observational signature.

astro-ph.SR↗

arXiv2018

Self-Similar Approach for Rotating Magnetohydrodynamic Solar and Astrophysical Structures

Rotating magnetic structures are common in astrophysics, from vortex tubes and tornados in the Sun all the way to jets in different astrophysical systems. The physics of these objects often combine inertial, magnetic, gas pressure and gravitational terms. Also, they often show approximate symmetries that help simplify the otherwise rather intractable equations governing their morphology and evolution. Here we propose a general formulation of the equations assuming axisymmetry and a self-similar form for all variables: in spherical coordinates $(r,θ,ϕ)$, the magnetic field and plasma velocity are taken to be of the form: ${\bf B}={\bf f}(θ)/r^n$ and ${\bf v}={\bf g}(θ)/r^m$, with corresponding expressions for the scalar variables like pressure and density. Solutions are obtained for potential, force-free, and non-force-free magnetic configurations. Potential-field solutions can be found for all values of~$n$. Non-potential force-free solutions possess an azimuthal component $B_ϕ$ and exist only for $n\ge2$; the resulting structures are twisted and have closed field lines but are not collimated around the system axis. In the non-force free case, including gas pressure, the magnetic field lines acquire an additional curvature to compensate for an outward pointing pressure gradient force. We have also considered a pure rotation situation with no gravity, in the zero-$β$ limit: the solution has cylindrical geometry and twisted magnetic field lines. The latter solutions can be helpful in producing a collimated magnetic field structure; but they exist only when $n<0$ and $m<0$: for applications they must be matched to an external system at a finite distance from the origin.

astro-ph.SR↗

arXiv2018

GONG Catalog of Solar Filament Oscillations Near Solar Maximum

We have catalogued 196 filament oscillations from the GONG $Hα$ network data during several months near the maximum of solar cycle 24 (January - June 2014). Selected examples from the catalog are described in detail, along with our statistical analyses of all events. Oscillations were classified according to their velocity amplitude: 106 small-amplitude oscillations (SAOs), with velocities $<10\mathrm{\, km \; s^{-1}}$, and 90 large-amplitude oscillations (LAOs), with velocities $>10\mathrm{\, km \; s^{-1}}$. Both SAOs and LAOs are common, with one event of each class every two days on the visible side of the Sun. For nearly half of the events we identified their apparent trigger. The period distribution has a mean value of 58$\pm$15 min for both types of oscillations. The distribution of the damping time per period peaks at $τ/P=1.75$ and $1.25$ for SAOs and LAOs respectively. We confirmed that LAO damping rates depend nonlinearly on the oscillation velocity. The angle between the direction of motion and the filament spine has a distribution centered at $27^\circ$ for all filament types. This angle agrees with the observed direction of filament-channel magnetic fields, indicating that most of the catalogued events are longitudinal (i.e., undergo field-aligned motions). We applied seismology to determine the average radius of curvature in the magnetic dips, $R\approx89$ Mm, and the average minimum magnetic-field strength, $B\approx16$ G. The catalog is available to the community online, and is intended to be expanded to cover at least 1 solar cycle.

astro-ph.SR↗

arXiv2016

Damping of prominence longitudinal oscillations due to mass accretion

We study the damping of longitudinal oscillations of a prominence thread caused by the mass accretion. In this model we considered a thin curved magnetic tube filled with the plasma. The parts of the tube at the two sides of the thread are filled with hot rarefied plasma. We assume that there are flows of rarefied plasma toward the thread caused by the plasma evaporation at the magnetic tube footpoints. Our main assumption is that the hot plasma is instantaneously accommodated by the thread when it arrives at the thread, and its temperature and density become equal to those of the thread. Then we derive the system of ordinary differential equations describing the thread dynamics. We consider linear and nonlinear oscillation. The nonlinearity reduces the damping time, however this reduction is small. The damping time is inversely proportional to the accretion rate. We also obtain that the oscillation periods decrease with time. However even for the largest initial oscillation amplitude considered in our article the period reduction does not exceed 20%. We conclude that the mass accretion can damp the motion of the threads rapidly. Thus, this mechanism can explain the observed strong damping of large-amplitude longitudinal oscillations. In addition, the damping time can be used to determine the mass accretion rate and indirectly the coronal heating.

astro-ph.SR↗

arXiv2015

Damped transverse oscillations of interacting coronal loops

Damped transverse oscillations of magnetic loops are routinely observed in the solar corona. This phenomenon is interpreted as standing kink magnetohydrodynamic waves, which are damped by resonant absorption owing to plasma inhomogeneity across the magnetic field. The periods and damping times of these oscillations can be used to probe the physical conditions of the coronal medium. Some observations suggest that interaction between neighboring oscillating loops in an active region may be important and can modify the properties of the oscillations compared to those of an isolated loop. Here we theoretically investigate resonantly damped transverse oscillations of interacting non-uniform coronal loops. We provide a semi-analytic method, based on the T-matrix theory of scattering, to compute the frequencies and damping rates of collective oscillations of an arbitrary configuration of parallel cylindrical loops. The effect of resonant damping is included in the T-matrix scheme in the thin boundary approximation. Analytic and numerical results in the specific case of two interacting loops are given as an application.

astro-ph.SR↗