National Astronomy Meeting Poster Exhibition

We investigate a new method to obtain the plasma parameters of solar prominences observed in the Mgii h&k spectral lines by comparing line profiles from the IRIS satellite to a bank of profiles computed with a one-dimensional non-LTE radiative transfer code. Using a grid of 1007 one dimensional non-LTE radiative transfer models, some including a prominence-corona transition region (PCTR), we carry out a novel method to match computed spectra to observed line profiles while accounting for line core shifts not present in the models. The prominence observations were carried out by the IRIS satellite on 19th April 2018.

The models are able to recover satisfactory matches in areas of the prominence where single line profiles are observed. Large values of ionisation degree are found by the procedure. These are found in areas where the line of sight crosses mostly plasma from the PCTR, correlating with high mean temperatures and correspondingly no Hα emission.

The models were unable to recover satisfactory fits in the regions where we see Hα emission. This is due to the complex line shapes manifesting from many unresolved independently moving threads. This issue might be solved in future by increasing the microturbulent velocities in the models to simulate these unresolved movements.

The plasma dynamics at frequencies comparable with collisional frequency between various species has to be described in multifluid framework, where collisional interaction between particles is an important ingredient. In our study, we will assume that charged particles are strongly coupled, meaning that they form a single fluid that interacts with neutrals, therefore we will employ a two-fluid model. Here, we aim to investigate the evolutionary equation of slow sausage waves propagating in a gravitationally stratified flux tube in the two-fluid solar atmosphere in a strongly ionized limit using an initial value analysis. Due to the collisional interaction between massive particles (ions and neutrals), the governing equations are coupled. Solutions are sought in the strongly ionized limit and the density ratio between neutrals and charged particles is a small parameter. This limit is relevant to the upper part of the chromosphere. Our results show that slow sausage waves associated with charged particles propagate such that their possible frequency is affected by a cut-off due to the gravitational stratification. In contrast, for neutral acoustic waves the cut-off value applies on their wavelength and only small wavelength waves are able to propagate. Slow modes associated with neutrals are driven by the collisional coupling with ions.

In this work, we applied POD and DMD techniques to identify the dominant MHD wave modes in sunspot umbrae. The sunspot intensity time series employed in this study were acquired using the Hydrogen-Alpha Rapid Dynamics camera at the Dunn Solar Telescope (DST). The POD technique was used to find modes that are spatially orthogonal, whereas the DMD technique identifies temporal orthogonality. It was found that the combined POD and DMD approaches can be successfully used for MHD modes detection. With the DKIST era now upon us, these same techniques can be applied to much higher resolution data, allowing us to probe the fine structure of sunspot umbrae with local helioseismology.

Robustly inferring the properties of a dark matter subhalo in a strong lensing image requires marginalizing over uncertainties in the main lens mass and source light distributions. This is an extremely difficult problem due to the high dimensionality of lensing observations. Here we present a new multi-stage method for performing subhalo inference that combines the strengths of parametric lensing models and simulation-based inference (SBI), a tool that leverages neural networks to directly obtain marginal posteriors from observations. In the first stage, we use our novel Gaussian process-inspired lensing model to closely fit an observation, obtaining approximate posteriors for all model parameters. We use the obtained posteriors to generate variations of the target image with different subhalo realizations. In the second stage we train a targeted inference network on these images to produce precision posteriors for the subhalo's parameters using the technique of neural likelihood-to-evidence estimation. The final inference is performed by applying the trained network to the original observation of interest. We present results of a mock analysis showing we can accurately reconstruct a subhalo's position and mass in a realistic, high-resolution observation, marginalizing over more than 100,000 lens and source parameters. The whole analysis can be performed rapidly using a single graphical processing unit and scales rather favorably (linearly) with models complexity.

The SuperWASP Variable Stars project on the Zooniverse asks citizen science volunteers to classify light curves in order to identify candidate variable stars. Volunteers are presented with folded lightcurve plots, generated from archive data collected by the SuperWASP exoplanet search. The volunteers classify each plot by its shape, choosing one of: pulsator; EA/EB (detached eclipsing binaries); EW (contact eclipsing binaries); rotator; unknown (miscellaneous periodic shapes); or junk (no periodic shape). In its first two years, the project received 1 million volunteer classifications from 4,500 users. We are now preparing the first release of aggregated classifications from the project, containing 148,522 candidate variable stars. This will be published online via an open-access website called VeSPA: The SuperWASP Variable Star Photometry Archive. VeSPA will allow volunteers to interactively explore and download the results of the project, as well as providing a catalogue of variable star candidates for professional astronomers to use. Users will be able to look up objects by ID and perform cone searches, and filter on parameters such as variable star type, period length, and magnitude. Results will be available to download in CSV format, and raw (unfolded) photometric data will be available in FITS format.

Magnetosheath jets are localised high-dynamic pressure pulses originating at Earth’s bow shock and propagating earthward through the magnetosheath. Jets can influence magnetospheric dynamics upon interacting with the magnetopause; however a significant fraction dissipate before reaching it. Using a database of 13,096 jets observed by the THEMIS spacecraft and associated upstream solar wind conditions from OMNI from 2008 to 2018, we statistically determine how upstream solar wind conditions control the likelihood of jets forming at the bow shock, and how they affect the jets’ likelihood of propagating to the magnetopause. We see that these two effects are separate, but when combined, the observations indicate that jets are approximately 12 times more likely to reach and impact the magnetopause during low IMF cone angle conditions, and 5 times more likely during high solar wind speeds. On the other hand, solar wind plasma beta and dynamic pressure display no net effect on magnetopause impacts. Our results suggest that jet impact rates may have a solar cycle dependence as well as vary during the passage of solar wind transients. In addition, we study the properties of near-magnetopause jets to further investigate their potential influence on magnetospheric processes.

It is critical to determine the solar disk's radiation in Mg II lines, e.g. to evaluate the radiation incident on solar chromospheric structures such as spicules or prominences, and to comprehend the radiation emitted by these structures in these lines. The aim of this project is to investigate the spatial and temporal variability of the Mg II h&k (2803.53 and 2796.35, respectively) lines in solar observations. Additionally, we seek to derive information on the spectral features of the Mg II h&k lines in the quiet sun at the centre of the sun. We present a novel approach for automatically determining the positions of k1v, k2v, k3, k2r, and k1r, as well as h1v, h2v, h3, h2r, and h1r, in the line profiles obtained by IRIS at the quiet sun centre. In this poster, we will address the variation in the spectral characteristics of the Mg II h&k lines in the quiet sun at the sun centre.

MUSE is the most modern instrument to obtain data with the integral-field spectroscopy technique in the optical range, its high spectral and spatial resolution allows to recover more information than any other IFS instruments. To explore and exploit the information that MUSE provides, we present the code pyHIIExplorerV2 to detect clumpy regions of Halpha maps (candidates to HII regions) and extract as much spectroscopic information as possible (for both the underlying stellar populations and emission lines). Simultaneously during the detection and extraction of the clumpy regions, pyHIIExplorerV2 builds a diffuse ionized gas model (DIG). The construction of DIG will allow us to decontaminate the information of the HII regions candidates.

We analyze solar events associated with flares: gradual - M3.7 on March 7, 2011 and impulsive - X6.9 on August 9, 2011. These flares were accompanied by HXR and MW radiation, sustained > 100 MeV gamma radiation, CME with a velocity of ~ 2000 km /s. Estimates of the magnitude and duration of acceleration for CME were obtained from the condition of stitching the assumed uniformly accelerated and observed uniform motion. These estimates indicate that the CME should have accelerated significantly longer than the estimated minimum time. The obtained mean values and duration of CME acceleration do not contradict CME acceleration in two phases - impulsive and prolong, as was directly observed in the events of May 13, 2013 [Gou et al. 2020] and September 10, 2017 [Gopalswamy et al., 2018]. In the cases considered the largest bursts of HXR and MW radiation can be observed both before and during the CME impulsive acceleration (X6.9 flare on August 9, 2011), and after it (M3.7 flare on March 7, 2011). ). This shows that the acceleration processes of charged particles in flares do not depend on the magnitude of the CME acceleration. The CME velocity is high in the corona and interplanetary space, most likely, was determined by a long acceleration on March 7, 2011, but a long deceleration on August 9, 2011.

In this talk I present lensing results from the cross correlation of the VST ATLAS quasar catalogue with galaxy and galaxy cluster catalogues. We also detect strong Quasar - Planck CMB lensing. The quasar-galaxy cross-correlation allows us to fit models to our data to calculate the galaxy bias as a test of the ΛCDM model. We also fit halo models to our data in order to calculate galaxy cluster halo masses and predict velocity dispersions. The Quasar-CMB cross-correlations provide a direct measurement of the quasar bias and quasar host halo masses. We shall also consider the possibility of searching for dark matter haloes using quasar variability data from quasar catalogues from VST ATLAS, KiDS and ultimately the Vera Rubin LSST. We aim to present results from a pilot study using quasar variability data from a new CTIO DECam survey.