3D Morpho-kinematic modeling of supernova remnants

Abstract

The subject of research of the current Thesis, was the reconstruction -for the first time- of the three dimensional (3D) Morpho-kinematic (MK) modeling of a Supernova Remnant (SNR). The innovation of this project lies in the fact that, for the first time, high resolution observational data in imaging and spectroscopy were used for the creation of a model that would reproduce both the morphology and the kinematic field of a Supernova Remnant.SNRs are these very beautiful and also complicated nebulae that remain after the massive explosion (Supernova) of certain types of stars. Their gaseous debris carry information about the properties of the progenitor star, and also manifest the attributes of the ambient circum-stellar (CSM)/ interstellar (ISM) medium. Therefore, SNRs are an ideal “laboratory” for probing the aftermaths of certain types of stars and their environment, and subsequently, to deeper understand the stellar evolution mechanisms and to decode an interstellar region.With respect to their morphology, although there are cases of spherically symmetric SNRs, however -traditionally- they illustrate a wide range of complex structures. Any deviation from symmetry implies inhomogeneity in the initial explosion conditions and/or in the CSM/ISM medium in the vicinity of the SNR. This is depicted in the velocity field of the remnant as well,as different parts of it may expand at different velocities, depending on the environment they encounter during their expansion.In order to study the morphology of a SNR, we obtain telescope images. However, the act that these images are two-dimensional (2D), is a physical restriction that prevents us from having an overall perspective of the object under study. Therefore, in order to surmount this obstacle and to obtain the now missing information in the 3rd dimension, we create 3D models of the objects. The information in the 3rd dimension that a 3D modeling provide us with,renders the 3D visualization of an object a very powerful tool in the field of investigation.In particular, a 3D Morpho-kinematic model presents i) the structure of the object and ii)its velocity field, both in three dimensions. It is a time- and distance-independent model, that presents the object at the time of its observation. Through this model, the object “reveals” itself and from the derived information we can trace back to the explosion conditions and obtain indirect evidences for the vicinity of the SNR.For the modeling we employed the astronomical software SHAPE, in which imaging and spectroscopic data are used for the reconstruction of the 3D modeling. SHAPE is already established in the field of Planetary Nebulae (PNe), where many important projects have been performed by its use. However, it had never been applied in a SNR before, due to the high degree of complexity that SNRs present (both in morphology and kinematics), and due to the large amount of observational data needed for the full covering of extended objects like SNRs.This is why, for the needs of code-learning, I first applied SHAPE code in the case of the Planetary Nebula Hb4, which was already under study.Hb4 shows an unusual kinematic behaviour as, its expelled bipolar outflows decelerate as they recede from the central star. The model helped us to clarify the nature and the morphology of these outflows and to investigate their kinematics. Furthermore, the model revealed the periodicity in the ejection of the outflows, while it also gave us clues about the characteristics of the progenitor star, and the conditions of the local ISM. The results were published in Derlopaet al. 2019, and are described in Chapter 4.After the modeling of Hb4 and having obtained experience in SHAPE, I proceeded to the much more complicated case of the modeling of a SNR, which is the first 3D Morpho-kinematic model of a SNR ever created.The selected object was the SNR VRO 42.05.01. It is a remnant of great scientific interest,whose peculiar morphology indicates a very active evolutionary history. The physical results that the model gave, contributed a lot to a more thorough interpretation of the observational data. For example, the model revealed a third component in the structure of VRO that was not obvious in the 2D data, along with the regions of two shock break-outs. The results were published in Derlopa et al. 2020, and are described in Chapter 5.Finally, it is worth mentioning that the results of a 3D MK model can be used as input information for the creation of Hydrodynamical (HD) models too. This has already been tested in the case of VRO, where the MK and the HD models acted complimentary for the interpretation of VRO properties and evolutionary history. Completing the 3D MK modeling of VRO and having in mind the very important physical results deduced from the model, we can argue that a new, valuable tool to the methods of probing SNRs has been added. Since morphology and kinematics are indissolubly linked to each other, it was showed that such a 3D visualisation can contribute to the decoding of the complexity of SNRs both in their shape and their velocity field. This opens the way for a more thorough investigation of these very interesting and complicated objects, the probing of which contributes to the understanding of stellar evolution.

Το αντικείμενο έρευνας της παρούσας Διδακτορικής διατριβής, είναι η δημιουργία τού πρώτου τρισδιάστατου (3Δ) Μορφοκινηματικού (ΜΚ) μοντέλου ενός Υπολείμματος Υπερκαινοφανούς Αστέρος (ΥΥΑ). Η πρωτοτυπία αυτής της εργασίας έγκειται στο ότι για πρώτη φορά, υψηλής ανάλυσης εικόνες και φάσματα χρησιμοποιούνται για την αναπαραγωγή τής μορφολογίας και της κινηματικής ενός ΥΥΑ. Η εργασία αυτή ήταν ιδιαίτερα απαιτητική λόγω της πολυπλοκότητας της μορφολογίας τού υπό μελέτη αντικειμένου, καθώς και των διαφορετικών ταχυτήτων των υποπεριοχών του, όπως αναλυτικά παρουσιάζονται στην εργασία. Για την μοντελοποίηση χρησιμοποιήσαμε τον αστρονομικό κώδικα SHAPE. Πρόκειται για ένα λογισμικό ήδη πολύ επιτυχημένο και καθιερωμένο στο τομέα των Πλανητικών Νεφελωμάτων, το οποίο όμως ποτέ δεν είχε εφαρμοσθεί στην περίπτωση ενός ΥΥΑ μέχρι στιγμής, κυρίως λόγω της πολυπλοκότητας σε μορφολογία και κινηματική που συνήθως τα ΥΥΑ παρουσιάζουν. Για τους λόγους αυτούς, προηγήθηκε η εφαρμογή τού SHAPE στην περίπτωση του Πλανητικού Νεφελώματος Hb4, το οποίο ήδη ήταν υπό μελέτη, ενώ στη συνέχεια πραγματοποιήθηκε η μοντελοποίηση του -κατά πολύ δυσκολότερου- ΥΥΑ VRO 42.05.01. Εκτός από την 3Δ απεικόνιση του VRO, από το μοντέλο εξαγάγαμε και φυσικά αποτελέσματα τα οποία μας βοήθησαν στο να ερμηνεύσουμε ορθότερα τα παρατηρησιακά 2Δ δεδομένα. Επίσης, τα αποτελέσματα του μοντέλου συνεισέφεραν κατά πολύ στο να απαντηθούν ανοιχτά ερωτήματα σχετικά με τα χαρακτηριστικά αυτού τού αντικειμένου καθώς και την εξελικτική του πορεία. Η μεθοδολογία και τα αποτελέσματα παρουσιάζονται αναλυτικά στην εργασία. Συνεπώς, με τη δημιουργία τού πρώτου 3Δ Μορφο-κινηματικού μοντέλου ενός ΥΥΑ, ένα νέο και ιδιαιτέρως χρήσιμο εργαλείο έρευνας προστέθηκε στον τομέα των ΥΥΑ, το οποίο μπορεί να συμβάλλει κατά πολύ στην αποκωδικοποίηση των χαρακτηριστικών αυτών των αντικειμένων. Επιπλέον, έχοντας υπ' όψιν ότι τα αντικείμενα αυτά βρίσκονται στο “μεταθανάτιο” στάδιο των αστέρων, είναι προφανές ότι η ενδελεχής έρευνά τους παρέχει σημαντική ώθηση στα μοντέλα τής αστρικής εξέλιξης.