16th Conference of Hel.A.S

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Session: Stars, Planets and the Interstellar Medium

Name: Dr. Stavros Akras (IAASARS/NOA)
Coauthors: No coauthors were included.
Type: Oral
Title: Do we really comprehend Planetary Nebulae?
Abstract:
Planetary nebulae (PNe) are expanding shells of gas ejected by evolved stars. The structure of this gas can be explained by the dissociation/ionization/excitation processes of molecular and atomic gas illumated by an intense UV stellar radiation field. The overall picture of PNe depicts a highly ionized gas close to the central UV sources (central stars), and a lower ionized gas further out until it becomes neutral, atomic and even further molecular. However, this picture is broken by the presence of low-ionization structures (LISs) embedded in the nebula, and they should not be there. The recent discoveries of molecular hydrogen gas in these structures has confirmed that we still miss pieces from the puzzling nature of PNe. In this talk, I will start with a brief presentation of what we have learn about LISs over the last 30 years and then I will discuss the latest discoveries that have raised new questions. The big question in the field of PNe and more general in stellar evolution is "Are LISs mini-photodissocation regions?"
Name: Dr. Konstantina Anastasopoulou (INAF - Palermo)
Coauthors: No coauthors were included.
Type: Oral
Title: The EWOCS view of the unique population of Wolf-Rayet stars in Westerlund 1
Abstract:
Wolf-Rayet (WR) stars are the latest stage in the evolution of very massive stars, before they finally explode as supernovae (SN) or possibly gamma-ray bursts. They exhibit dense and powerful stellar winds, that along with their ultimate death as core-collapse SN, dominate the feedback to the local interstellar medium in star-forming galaxies. Studying in more detail the properties of the short-lived WR phase, will advance our understanding on star-formation processes and will test stellar evolutionary predictions. The best laboratory to study the WR phase, is the massive star cluster Westerlund 1. It is the closest massive star cluster to the Sun, and it contains an impressive large sample of coeval massive stars including one of the largest population (24) of WR stars. With a very deep Chandra survey (1Ms; as part of the Extended Westerlund One Chandra Survey; EWOCS) we are able to unravel the X-ray properties of the entire WR population, extract spectral information for more 2/3 of them, and retrieve insights on their X-ray production mechanism. We discuss these results in the context of different spectral subtypes of WR stars, as well as binarity, since several of them show signs of colliding-wind X-ray binaries.
Name: Dr. Tsiaras Angelos (INAF - Arcetri)
Coauthors: No coauthors were included.
Type: Oral
Title: Towards population studies of exoplanets in the era of JWST and Ariel
Abstract:
In the last 15 years, significant progress has been made in the field of atmospheric characterisation of exoplanets, utilising the most advanced instruments both on the ground and in space. Today, we are entering an era of very exiting prospects for the field of exoplanet characterisation. The James Webb Space Telescope (JWST) has successfully started operations, while ESA's M4 mission, Ariel, has been adopted and is planned to fly in 2029. This era will be characterised by the large volume of data that will be delivered from the new observatories. In my talk I will discuss the challenges we have to face in order to analyse the large data volume expected in the next decade: catalogues, open-source codes and follow-up observations. I will present a next-generation pipeline for the analysis of exoplanet spectroscopic observations, together with the first implementation on JWST data from the ERS program and a comparison between the HST and JWST results. Finally, I will present the progress in the ExoClock project, a pro-am collaboration with the aim of following up transiting exoplanets and contributing in preparation of the Ariel observations.
Name: Mr. Kostas Antoniadis (National Observatory of Athens / NKUA)
Coauthors: Bonanos Alceste (National Observatory of Athens)
Yang Ming (Chinese Academy of Sciences)
de Wit Stephan (National Observatory of Athens / NKUA)
Zapartas Emmanouil (National Observatory of Athens)
Munoz-Sanchez Gonzalo (National Observatory of Athens / NKUA)
Maravelias Grigoris (National Observatory of Athens)
Tramper Frank (KU Leuven)
Christodoulou Evangelia (National Observatory of Athens / NKUA)
Type: Poster
Title: The mass-loss rates of Red Supergiants in the Large Magellanic Cloud
Abstract:
The mass loss in the case of massive stars can affect many areas of astrophysics, such as the ionising radiation, the wind feedback, stellar remnants, and supernovae. The mass-loss mechanism of Red Supergiants (RSGs), which are cool massive stars with strong winds, is still poorly understood. Atmospheric turbulence, pulsations that lift the gas to a few stellar radii and radiation pressure on the newly formed dust in the circumstellar environment contribute to this mechanism. Evolutionary models have shown that high mass-loss rates can affect the fate of RSGs. Various empirical prescriptions scaled with luminosity have been derived in literature providing different results with significant dispersion. We studied the largest sample of RSG candidates (~5000 in the Large Magellanic Cloud), till now, to provide a better understanding of the mass-loss rate relation with luminosity, and hence the underlying physical mechanism. The dust formed in the circumstellar environment appears as infrared excess in the spectrum, making the availability of mid-infrared photometry significant to derive the properties of the dust shell. We used photometry in around 40 bands, ranging from ultraviolet to mid-infrared, and we fitted the Spectral Energy Distributions (SEDs) with models generated by the radiative transfer code DUSTY. We expanded this work to lower metallicity environments, 250 RSGs in NGC 6822, for which we discuss our first results. After deriving the luminosities from the SEDs and estimating stellar and circumstellar dust parameters from the best-fit models, such as the effective temperature, dust temperature, and optical depth, we derived the mass-loss rates. We found a power-law relation of the mass-loss rate with luminosity for targets with logL>4 Lo. A roughly constant mass-loss rate is found for lower luminosity targets. Finally, we compare our results with the empirical prescriptions in the literature.
Name: Mr. Dimitrios Athanasopoulos (National & Kapodistrian Univ. of Athens)
Coauthors: Gazeas Kosmas (NKUA)
Avdellidou Chrysa (University of Leiceste)
Hanus Josef (Charles University)
van Belle Gerard (Lowell Observatory)
Ferrero Andrea (Bigmuskie Observatory)
Bonamico Roberto (BSA Observatory)
Delbo Marco (OCA)
Rivet Jean-Pierre (OCA)
Conjat Matthieu (OCA)
Apostolovska Gordana (Ss. Cyril and Methodius University in Skopje)
Todorović Nataša (Belgrade Astronomical Observatory)
Bebekovska Elena Vchkova (Ss. Cyril and Methodius University in Skopje)
Novakovic Bojan (University of Belgrade)
Sioulas Nick (NOAK Observatory)
Type: Oral
Title: Ancient Asteroids: An observing campaign reveals the spin states of asteroids that belong to the most ancient collisional families of our Solar System
Abstract:
The first moments of our Solar System are determined by the gas phase of the protoplanetary disk, where the first ~100 kilometer-size solid bodies, the planetesimals, were formed. Only a few of them accreted by mutual collisions or enough mass via pebble accretion to form planets, the rest of them were removed during the violent phases of planetary migration and instability, while a few leftover are still present today in the solar system as dwarf planets or even smaller bodies. The small bodies of the inner Solar System formed an asteroid belt, whose original state is a crucial problem of planetary science. In the Main Asteroid Belt, the new asteroids stay relatively close (in terms of orbital element space) to the parent asteroid as a result to form clusters in it, the so-called asteroid collisional families. Traditional identification methods, like Hierarchical Clustering Methods, are unable to recognise Gyr- and older asteroid families, whose the family members are very dispersed by the Yarkovsky effect. A novel technique takes the advantage of the diurnal searching for the signature of the size dependent dispersion of family members operated by the Yarkovsky effect, in order to identify the most ancient collisional families of the Solar System. The method has already successfully identified two primordial families which likely formed before the giant planet orbital instability and could be as old as the Solar System and an ancient one that is ~3 Gyr-old. There is evidence from observations and theoretical evolution models that there are more old families to be. The reliability of these V-shape families has been independently tested. The observing campaign “Ancient Asteroids” initiated a Pro-Am collaboration in order to collect photometric observations for the members of these families. The obtained lightcurves from all the involved participants will be combined with data available in the literature, as well as with sparse data from space missions (Gaia, TESS, etc) and global sky surveys (ZTF, ATLAS, ASAS-SN, etc). The observations revealed the spin state of the members verifying their family membership. Further analysis of these data shown the evolutional characteristics of these collisional families, leading to a better understanding of the first stages of the evolution of the asteroid belt and the Solar System.
Name: Ms. Stella Avgousti (National & Kapodistrian Univ. of Athens)
Coauthors: Bonanos Alceste (National Observatory of Athens)
Maravelias Grigoris (National Observatory of Athens & FORTH)
Type: Poster
Title: Variable massive stars in the Andromeda galaxy using the Gaia Data Release 3
Abstract:
Massive stars, although rare, are of key importance for understanding the evolution of the Universe and are the progenitors of supernovae, gamma-ray bursts and even gravitational-wave events. An important parameter of massive stars is their mass loss rate, which has a significant impact on their evolution. Despite its importance, mass loss from massive stars and especially episodic mass loss, is poorly understood. Spectroscopy is an important tool to derive stellar properties, but is a time-consuming process. Instead, the availability of large datasets from photometric surveys, provide data for thousands of sources. Hence, a machine-learning tool has been developed, within the ASSESS project (http://assess.astro.noa.gr/), to automate the classification process of evolved massive stars. Using the machine-learning classifier, which is based on mid-IR (Spitzer) and optical (Pan-STARRS) photometry, we have obtained spectral classification of about 1.1M sources in 25 nearby galaxies. Our study focuses on massive stars in the Andromeda galaxy, for which we have predictions for ~800K sources. We used the Gaia Andromeda Photometric Survey (GAPS), which provides a significant coverage of the galaxy and offers spectral types and photometric time series. By performing a cross-match between the sources from GAPS (~1.2M sources) and our Spitzer catalogue (~800K sources) we identified approximately 26K common sources. For those we calculated the median absolute deviation to analyze the variability, to identify new variables and constrain the spectral class predictions. We plan to verify our results about the variable stars using the published data products from Gaia DR3. In total the GAPS will help us validate the performance of our machine-learning classifier and gain a deeper understanding of the nature of these objects when variability is considered. Our findings could also be used to refine the machine-learning model and improve its accuracy in classifying massive stars.
Name: Dr. Alceste Bonanos (National Observatory of Athens)
Coauthors: Maravelias Grigoris (NOA, IA-FORTH)
Yang Ming (National Astronomical Observatories, Chinese Academy of Sciences, China)
Tramper Frank (KU Leuven, Belgium)
de Wit Stephan (NOA, NKUA)
Zapartas Emmanouil (NOA)
Antoniadis Konstantinos (NOA, NKUA)
Christodoulou Evangelia (NOA, NKUA)
Munoz-Sanchez Gonzalo (NOA, NKUA)
Type: Oral
Title: Results of the ASSESS project: Episodic Mass Loss in Evolved Massive Stars: Key to Understanding the Explosive Early Universe
Abstract:
Episodic mass loss is not understood theoretically, neither accounted for in state-of-the-art models of stellar evolution, which has far-reaching consequences for many areas of astronomy. We present the status and results of the ERC-funded ASSESS project (2018-2024), which aims to determine whether episodic mass loss is a dominant process in the evolution of the most massive stars, by conducting the first extensive, multi-wavelength survey of evolved massive stars in the nearby Universe. It hinges on the fact that mass-losing stars form dust and are bright in the mid-infrared. We aim to derive physical parameters of ~1000 dusty, evolved massive stars in ~25 nearby galaxies and estimate the amount of ejected mass, which will constrain evolutionary models, and quantify the duration and frequency of episodic mass loss as a function of metallicity. The approach involves selecting dusty, luminous targets from existing multi-band photometry of nearby galaxies. We present an overview of the spectroscopic survey, the machine-learning classifier for evolved massive stars, the modeling that is underway and the mass-loss rate of red supergiants determined in the Small Magellanic Cloud. The emerging trend for the ubiquity of episodic mass loss, if confirmed, will be key to understanding the explosive early Universe and will have profound consequences for low-metallicity stars, reionization, and the chemical evolution of galaxies.
Name: Mr. Konstantinos Bouvis (NTUA-IASARS)
Coauthors: No coauthors were included.
Type: Poster
Title: Exploring the Physical Properties of Planetary Nebula NGC 3132 with MUSE, JWST and SPITZER data.
Abstract:
Imaging spectroscopy, also known as integral field spectroscopy, is a valuable tool for analyzing extended ionized nebulae like planetary nebulae (PNe), H II regions, galaxies. PNe are the remnants of low to intermediate-mass stars (1-8 M_⊙) that have expelled their outer layers. In this study, a two-dimensional spectroscopic analysis has been performed on the PN NGC 3132 using data from the MUSE. NGC 3132 was chosen for the early observing phase of the JWST, and multiple stellar system were discovered as well as significant molecular hydrogen emissions. Additionally, archival data from the Spitzer telescope were combined with JWST images to examine the radial distribution of near-infrared emission line ratios and IRAC colors. The average electron temperature of NGC 3132 was found close to, 9500 K, while the electron density ranges from 500 to 900 cm^-3. Chemical composition variations in this nebular gas are ruled out. The radial analysis of optical and infrared lines shows a strong correlation between the c(Hβ) and emission lines, indicating the presence of significant amounts of dust that prevent molecular hydrogen dissociation. The physical and chemical properties of the nebula are mapped and compared to the predictions of a 3D photoionization model in order to constrain its physical characteristics.
Name: Mr. Savvas Chanlaridis (IA-FORTH & Univ. of Crete)
Coauthors: No coauthors were included.
Type: Oral
Title: Thermonuclear and Electron-Capture Supernovae from Stripped-Envelope Stars
Abstract:
Neutron stars (NSs) are the compact remnants of massive stars formed in supernova explosions. Their properties depend sensitively on the properties of fundamental physical laws, the evolution of their progenitors, and the physical characteristics of the explosion. In our group we focus on novel numerical modelling to study the formation, evolution, and properties of NSs originating from a so-called electron-capture supernova (ECSN). The latter are produced when intermediate-mass stars with degenerate oxygen-neon (ONe) cores explode. Due to the properties of the explosion, ECSN are thought to produce low-mass/low-velocity NSs, which are crucial for explaining the formation of gravitational-wave sources, such as those recently seen by Advanced LIGO and Virgo. In this talk, I will try to illuminate the thus-far illusive stellar mass limits that separate white dwarfs, thermonuclear explosions, and NSs by investigating how sensitive these transition masses are to input physics uncertainties, for instance, composition, convective overshooting, mass-loss rate, and binary interactions. To this end, I will focus on a novel and seemingly universal mechanism, identified by our group, that allows ONe cores to disrupt in thermonuclear explosions instead of producing ECSN. This mechanism may result in a significant paradigm shift, as it produces explosions that are observationally similar to Type Ia supernovae (SNe-Ia), and it suppresses NS formation with consequences on their observed mass distribution.
Name: Ms. Evangelia Christodoulou (NOA / NKUA)
Coauthors: Bonanos Alceste (National Observatory of Athens)
Munoz Sanchez Gonzalo (National Observatory of Athens)
de Wit Stephan (National Observatory of Athens)
Maravelias Grigoris (National Observatory of Athens)
Garcia Alvarez David (Instituto de Astrofisica de Canarias)
Antoniadis Kostas (National Observatory of Athens)
Type: Poster
Title: Near Infrared Spectroscopy of red supergiants in NGC 6822, IC 10 & WLM with EMIR
Abstract:
Near Infrared Spectroscopy of red supergiants in NGC 6822, IC 10 & WLM with EMIR The role of episodic mass loss in the evolution of massive stars remains largely unknown and thus it is not included in the stellar models. The ASSESS project is conducting an optical survey in the nearby Universe (12 galaxies with Z ~ 0.1 to 1.5 Zo) searching for evolved massive stars, primarily targeting those with infrared excess (i.e. circumstellar dust) which reveals mass loss. The results of this survey in the northern hemisphere have led to the secure spectral classification of twelve red supergiants (RSGs) in NGC 6822 and IC 10 (Ζ= 0.32 Zo and 0.45 Zo). Follow up spectroscopy has been acquired in the J-band for eight of them using the EMIR detector at the Grand Telescope of the Canarias. Also, we observed one target from the literature (WLM 14), expanding our metallicity range to 0.14 Zo, as we aim to study mass loss in the low metallicity regime. Such observations are needed because the effective temperature (Teff) measured from atomic lines in the J-band is more accurate than the one estimated using the TiO bands present in the optical spectra, as the latter form at larger radii and lower temperatures. Improved Teff estimations lead to more robust estimations of mass loss. We aspire to calibrate the temperature scale of RSG at low metallicities and use it to obtain mass loss measurements for the rest of our sample (~ 130 RSGs) for which infrared spectroscopy is not feasible. I will present initial results from the analysis of these observations.
Name: Prof. Eleftheria-Pan. Christopoulou (University of Patras)
Coauthors: No coauthors were included.
Type: Oral
Title: Discovery of star systems at the merger limit by large astronomical sky surveys.
Abstract:
The mass ratio of a contact binary system evolves towards smaller values due to mass transfer, magnetic braking, and thermal oscillations until it reaches a minimum value threshold. Then the system undergoes tidal instability (Darwin instability) and is driven to a merger of its components, during which it suddenly flashes as a red nova. I will present methods for detecting new candidate systems from large modern surveys, which in combination with photometric observations, both space and ground-based at different wavelengths, and sophisticated analysis lead to the extraction of their physical parameters in order to study them statistically. Why only one such system has been observed to date? Can we consider also ultrashort period contact systems (with periods below the period cut-off ) as progenitors of red novae?
Name: Prof. Michael Contadakis (Aristotle University of Thessaloniki)
Coauthors: No coauthors were included.
Type: Poster
Title: Starquakes on the Flare stars.
Abstract:
Flare stars have been subjected to extending research for many decades at the Stefanion Observatory. Apart of the spectacular flaring phenomena, the results of the analysis of the one colour (B) observations of the Stefanion Observatory at any stage of their activity (quiescence, weak flares, strong flares),indicate that: (1) Transient high frequency oscillations occur during the flare event and during the quiet-star phase as well; (2) The Observed frequencies range between 0.0005Hz (period 33min) and 0.3 Hz (period 3s) not rigorously bounded.. It is interesting that transient oscillations appear also far apart from the observed flares, during the quiet state of the stars, as a result of the general magnetic activity of the star. This fact led us to examine the existence of starquakes on Flare stars. Thus we examine the power spectrum of the Flare stars and we find that they resample that of the solar like oscillation spectra i.e the sunquake spectra. Our tentative analysis of our observations shows that we observe starquakes on Flare stars similar to that of a red subgiant.

Co-authors:J.H. Seiradakis², S.J. Avgoloupis², Ch. Papantoniou¹
¹Department of Surveying and Geodesy, Aristotle University of Thessaloniki, GR-54124, Thessaloniki, Greece
²Session of Astronomy, Astrophysics and Mechanics, Department of Physics, Scool of Sciences, Aristotle University of Thessaloniki, GR-54124, Thessaloniki, Greece.
Keywords: Flare stars-Starquakes, Discrete Fourier Transform analysis -Brownian Walk noise
Name: Dr. Sophia Derlopa (National Observatory of Athens / IAASARS)
Coauthors: Akras Stavros (National Observatory of Athens / IAASARS)
Boumis Panos (National Observatory of Athens / IAASARS)
Amram Philippe (Aix Marseille Univ, CNRS, CNES, LAM, France)
Chiotellis Alexandros (National Observatory of Athens / IAASARS)
Mendes de Oliveira Claudia (Departamento de Astronomia, Instituto de Astronomia, Brazil)
Type: Oral
Title: Planetary Nebula NGC 2818: 3D morphology and new detected structures
Abstract:
Planetary Nebulae (PNe) of highly complicated morphology denote a very active evolutionary history during the transition from a spherically symmetric AGB envelope to the Planetary Nebula formation. In this category belongs the bipolar PN NGC 2818, which is accompanied by fragmentations, a bulk of cometary knots and complex filamentary structures. In this talk I present the results of the 3D Morpho-kinematic (MK) modeling of NGC 2818. For its reconstruction, long-slit echelle spectra were employed in conjunction with Fabry-Perot imaging spectroscopy for the first time in a PN project. The interpretation of the outcomes shed light on the physical mechanisms that created this PN, while new structures of the nebula that come to light for the first time are also discussed.
Name: Dr. Georgios Dimitriadis (Trinity College Dublin)
Coauthors: No coauthors were included.
Type: Oral
Title: The mass puzzle of "Super-Chandrasekhar" SNe Ia
Abstract:
For a long time there was general consensus that Type Ia Supernovae (SNe Ia) originate from Carbon-Oxygen White Dwarfs (CO WDs) that explode at the very latest when approaching what is known as the Chandrasekhar-mass stability limit (~1.4 solar masses). This fundamental property of the degenerate matter denotes the mass where the degeneracy pressure of the relativistic electron gas loses against the self-gravity of the WD, leading to a collapse. This theoretical paradigm was challenged with the discovery of the prototype SN 2003fg, a transient with enormous luminosity, broad light curve and low kinetic energy, implying a "Super-Chandrasekhar" (SC) mass progenitor. High-cadence and/or untargeted transient surveys performed in recent years have started to discover more members of this intriguing SN Ia subclass, allowing for sample studies while additionally revealing an intrinsic diversity in the population. However, the initial question remains: Do these peculiar events trully result from a SC scenario or alternative channels need to be invoked? What kind of binary configurations and explosion mechanisms can simultaneously explain their main properties and their intrinsic diversity? And, finally, are there observables that can act as a smoking gun for pointing to the correct answer? In this talk, I will focus on two recent SC SNe Ia, 2020esm and 2021zny, that were discovered particularly early and were densely monitored with a variety of ground- and space-based facilities. I will present their main photometric and spectroscopic properties, being similar to the siblings of their subclass, and highlight their unique characteristics: A nearly pure carbon/oxygen atmosphere during the first days after the explosion of SN 2020esm and a flux excess for the first ~ 1.5 days and prominent oxygen emission lines at nebular epochs of SN 2021zny. All our observations are in accordance with a progenitor system of two CO WDs that undergo a merger event, with the disrupted secondary WD ejecting carbon-rich circumstellar material prior to the primary WD detonation. Finally, I will conclude with a preview of ongoing peculiar SNe Ia studies, including SC SNe Ia, that may shed additional light on the nature of these enigmatic events.
Name: Ms. Zoi Filiou (National & Kapodistrian Univ. of Athens)
Coauthors: No coauthors were included.
Type: Poster
Title: Astrochemical and astrobiological applications of Laser Induced Breakdown Spectroscopy (LIBS)
Abstract:
Filiou Zoi1, Iliadou Anastasia2, Chondrokouki Maria3, Stavrakakis Hector-Andreas3,4, Antonopoulou-Athera Niki3, Gazeas Kosmas1, Papadopoulos Pantelis2, Chatzitheodoridis Elias3,4 1Section of Astrophysics, Astronomy and Mechanics, Department of Physics, National & Kapodistrian University of Athens, GR-15784, Zografos, Athens, Greece 2Department of Physics, Aristotle University of Thessaloniki, University Campus, Thessaloniki, 54124, Greece 3Department of Geological Sciences, School of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, 15772, Greece 4Network of Researchers on the Chemical Evolution of Life (NoRCEL), Leeds, UK Abstract Laser Induced Breakdown Spectroscopy (LIBS) is a spectroscopy technique that is used to define the chemical composition of materials. It is based on high-power laser pulses of short duration that hit the sample and can sublimate or evaporate it. Subsequently, the vapor gets ionized forming plasma which emits characteristic spectrum based on the sample’s chemical composition. The emission spectrum can offer qualitative and has been used in geology for the detection of major and trace elements to classify rocks and shed light on their geologic origin formation. In 2012, it became a part of the scientific equipment of the “Curiosity” rover that landed on Mars, since this experimental set-up stands out for its flexibility. Especially for a qualitative characterization, LIBS maintains both the advantages of high sensitivity and fast response without the need for sample preparation. This is ideal for deep space exploration, planetary surface analysis as it is currently happening on Mars and space object recognition. Specifically, the recognition of asteroids and meteorites can be beneficial for the calculation of their mass and as a result the prediction of their trajectory along with a better understanding of the chemical and physical procedures that the object went through during its lifetime. In our lab, we develop a LIBS instrument, which we use in the fields of geology and planetary sciences for the detection of trace elements and we aim at astrobiological and astrochemical applications. To explore the capabilities of LIBS in astrochemistry, we are investigating the possibility of detecting deuterium to hydrogen ratios (D/H), as well as elements of low atomic number elements, such as lithium (Li). Lithium could hold key information about a star’s history or planet-harbouring if combined with the trend of metal-rich stars being orbited by giant planets and models about accretion of planetesimals or entire planets. The D/H ratio on the other hand, can provide information about the origin of water on celestial bodies and their atmospheres. Most of the above studies are based on the development and testing of LIBS on meteorites, or reference minerals and rocks which are also used to calibrate the technique for quantification purposes. The same methods are investigated on terrestrial rocks and minerals (i.e., phengitic muscovite, garnet, Na-clinopyroxene and Na-amphibole), to define their geological evolution in various geotectonic environments, in which Li also plays an important role as a signature of these processes. By this contribution, we expect that we will provide insights into the capabilities of LIBS in use for space missions, but also to enhance the quantification capabilities of the technique.
Name: Prof. Anastasios Fragkos (University of Geneva)
Coauthors: No coauthors were included.
Type: Oral
Title: Unravelling the astrophysical origin of gravitational-wave sources.
Abstract:
The first detection of gravitational waves from coalescing binary black holes by LIGO allowed for the first time the direct observation of stellar-mass black holes, while the simultaneous gravitational-wave and electromagnetic signal from the merger of two neutron stars provided the first direct evidence for the origin of short gamma-ray bursts. Eight years later, we have now entered the era of gravitational-wave source population studies. These gravitational wave source populations, complemented by a half-a-century-long history of indirect observations of accreting compact objects in X-ray binaries, can now give us a more complete picture of the formation and evolution of binary stellar systems containing compact objects. At the same time, they also revealed weaknesses in the theories of stellar and binary evolution and compact object formation. In this talk, I will briefly review the current observed sample of gravitational-wave detections and their astrophysical implications and discuss the different formation pathways that have been proposed in the literature to explain the properties of the observed populations. I will then highlight results from recent studies that aim at exploring how different physical processes taking place during the evolution of binary stars, leave their signatures in the properties of gravitational-wave sources and compare these predictions with the currently observed sample of GW sources, as well as other potential electromagnetic counterparts or precursors.
Name: Mr. Dionysios Gakis (University of Patras)
Coauthors: Poultourtzidis Efthymios (Aristotle University of Thessaloniki)
Pantelidou Georgia (Freie Universität Berlin)
Kokori Anastasia (University College London)
Tsiaras Angelos (University College London)
Bewersdorff Leon (Fairborn Institute)
Iliadou Anastasia (Aristotle University of Thessaloniki)
Lekkas Georgios (University of Ioannina)
Sidiropoulos Chrysostomos (University of Ioannina)
Type: Poster
Title: Transit Timing Variations in exoplanetary systems through the ExoClock Project
Abstract:
The ExoClock project is a platform that monitors the ephemerides of transiting exoplanets, with the purpose to provide a verified list of them for the upcoming ESA's M4 mission, Ariel, scheduled for launched in 2029. The project also offers a useful service for the wider working community, since it can give valuable information about the best timings for future observations. To this end, a large dataset of individual transits has been examined, including observations with space telescopes (Kepler, K2, TESS), ground-based observations and mid-time values from literature. This poster will emphasize on the latter aspect and will discuss the opportunities provided by ExoClock to utilize the project’s database for further research. More specifically, we search for non-linear patterns in planetary ephemerides and combine them with other physical properties (like possible resonances) for a number of exoplanetary systems. A fundamental Transit Timing Variations (TTVs) analysis of those has been performed and the results will be presented. These results include the estimation of the non-linear terms along with the underlying uncertainties. Additionally, as ExoClock is a pro-am collaboration, this work will also highlight the contribution of the amateur astronomers to the observations and the power of collaborative work produced by volunteers.
Name: Ms. Margarita Gega (National & Kapodistrian Univ. of Athens)
Coauthors: No coauthors were included.
Type: Oral
Title: Detection of potential maar craters on planet Mars using HRSC/MEx data
Abstract:
Detection of potential maar craters on planet Mars using HRSC/MEx data Gega M.1, O. Sykioti2 and I.A. Daglis1,3 1 Department of Physics, National and Kapodistrian University of Athens, Athens, Greece 2 Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, Athens, Greece 3 Hellenic Space Center, Athens, Greece Αbstract In this study, we aim to detect potential maar craters on the surface of planet Mars. A maar crater is a small surficial feature corresponding to a particular type of volcanic crater, which is created by a violent explosion that occurs as magma moves up toward the surface and hits groundwater or a body of surface water. Typically, magma that contains enough gas to erupt explosively forms a cinder cone, as debris accumulates around the volcano's vent. But if abundant water exists in the region of the volcano, the magma interacts with the water, causing highly explosive eruptions that build a maar rather than a cinder cone. The study of maar craters provides information about the geophysical activities that have developed below the Martian surface and are considered as indicators of the existence of water in the past. Studying the maar craters would also help to better identify potential landing sites for future missions. For our study we have obtained data from the High Resolution Stereo Camera (HRSC) from ESA’s Mars Express mission (MEx), and we have calculated the morphological characteristics such as diameter, perimeter and area of 245 craters on the Martian surface. The number of craters resulted after keeping in the data catalog only those craters that can be classified as potential Maar craters and then classifying them based on their shape. We then investigated the relation of their density and geographical distribution between the north and south hemispheres. Finally, we used existing global mineral maps from the hyperspectral OMEGA/MEx data in order to characterize their general surface composition and to investigate whether these potential maar craters contain hydrated minerals. This work is part of the BSc thesis of the leading author, who is an under-graduate student in the Department of Physics of the National Kapodistrian University of Athens.
Name: Prof. Paul Kalas (UC Berkeley, Univ. of Crete & FORTH)
Coauthors: No coauthors were included.
Type: Oral
Title: New HST detections of complex outer structure for the dusty debris disks surrounding seven young planetary systems using STIS coronagraphy
Abstract:
Resolved images of dusty debris disks trace the physical location of solid material orbiting a star and may be dynamically perturbed by the gravitational influence of planets in the system. Here we used the HST/STIS coronagraph to survey ten young (10-25 Myr) planetary systems where prior near-infrared adaptive-optics observations discovered debris disks within two arcseconds of each star. The STIS optical observations are sensitive to the outer portions of each disk, and we detect seven of the these beyond two arcseconds radius. Unexpectedly, several systems have complex morphologies that were not evident in the ground-based images. We show how these new findings lend support to a recent dynamical model where debris disk dust is produced by a catastrophic impact between two planetesimals followed by the rearrangement of small grains due to radiation forces.
Name: Mr. Anastasis Karagiannis (National & Kapodistrian Univ. of Athens)
Coauthors: No coauthors were included.
Type: Poster
Title: Characterizing Hα emitters from the S-PLUS survey, combining photometric from GALEX, GAIA and SDSS data
Abstract:
The era of Big Data astronomy/astrophysics has begun, and the combination of photometric data from different surveys provide a unique pool of information for the characterization or identification of various sources. Hα emitters are sources of particular high interest as they cover a wide range of classes from planetary nebulae, symbiotic stars, cataclysmic variable, young stellar objects, star-forming galaxies, QSO, among others. The identification and characterization of Hα emitters in publicly available photometric surveys is essential for understanding better the underlying physical processes that regulate the emission of Hα line and for studying stellar and galaxy evolution. Observed and modeled colors based on the GALEX, GAIA and SDSS surveys for main sequence stars, white dwarfs, binary systems, galaxies and QSOs have been used in order to explore the origin of Hα emitters found in the SPLUS survey. Machine learning algorithms have also been employed to look for the colors that better distinguish UV and non-UV source.
Name: Prof. Theodora Karalidi (Univ. of Central Florida)
Coauthors: No coauthors were included.
Type: Oral
Title: Seeing the giants in 2D and 3D
Abstract:
Imaged exoplanets and brown dwarfs share a number of properties: from their size to their temperature, gravity and even clouds that form in their atmospheres. Time-resolved observations of brown dwarfs with Spitzer and the Hubble Space Telescope (HST) allowed us to study the variable cloud conditions in these atmospheres in a few pressure layers. Ground-based high spectral resolution observations with Keck and other Very Large Telescopes (VLTs) gave us insights in the cloud variability at different pressures. These observations paved the way for the characterization of clouds on imaged exoplanets in the James Webb Space Telescope (JWST) and Extremely Large Telescopes (ELTs) era. In this talk we will discuss how we use time resolved observations to study giant imaged atmospheres and constrain their structure in 2D and 3D. We will see how ground-based observations, in tandem with HST and Spitzer observations, allowed us to study the approximate-3D structure of some atmospheres and how the larger wavelength coverage of JWST will allow us to study imaged atmospheres in 3D. We will see how the large informational content of JWST time-resolved observations necessitates the creation of new tools for the characterization of these atmospheres. Finally, we will see how polarimetry complements flux observations and how it will help break degeneracies that flux-only observations have, allowing us to accurately characterize giant imaged atmospheres in the JWST and ELTs era.
Name: Ms. Lydia Konstantinou (National Technical University of Athens)
Coauthors: No coauthors were included.
Type: Poster
Title: NGC 3242 and the enigmatic nature of its Low Ionization Structures: A MUSE perspective
Abstract:
A planetary nebula (PN) is formed when low-to-intermediate mass stars expel their outer envelopes to the Interstellar Medium during the AGB phase. The UV radiation from the central star ionises the gas, leading to homogeneous nebular structures. However, in some PNe, we observe distinct small-scale structures with a lessened degree of ionisation level. These low-ionisation structures (LISs) are embedded in the PNe, and although there are some theoretical scenarios about their origin, their nature is poorly understood. My study is focused on NGC 3242, a multiple shell PN that contains a pair of LISs. The preliminary results of a 2D spectroscopic analysis of MUSE (Multi Unit Spectroscopic Explorer) via the SATELLITE code have shown that the electron temperature decrease moving outwards, while the electron density is slightly higher at the inner parts of the nebula. Additionally, my analysis confirms that NGC 3242 is a low-ionisation PN and that there is no significant chemical variation. Lastly, the thorough examination of MUSE data has led to the identification of the [C I] λ8727 emission line emitted only from the LISs. This unforeseen result supports the scenario of a photoevaporating dense molecular gas.
Name: Dr. Maria Kopsacheili (ICE-CSIC)
Coauthors: No coauthors were included.
Type: Oral
Title: Study of Supernova Remnants using IFU data
Abstract:
Study of Supernova Remnant (SNR) demographics and their physical properties (density, temperature, shock velocities) is very important in order to understand their role in galaxies. Many photometric and spectroscopic studies of SNRs, have been carried out in our Galaxy but also in extragalactic environments. The most common means for the SNR identification in the optical regime, is the use of the flux ratio of the [S II] (λλ6717, 6731) to Hα (λ6563) emission lines. However, this diagnostic is biased against low excitation SNRs. For this reason, we have developed new diagnostics that combine 2 and 3 emission line ratios along with a Support Vector Machine model, that efficiently differentiate SNRs from HII regions. These diagnostics recover up to 35% of the SNRs that we miss using the traditional diagnostic tool, which is very important in order to obtain more complete samples of SNRs (i.e. SNRs of different physical properties) and consequently to more efficiently explore the feedback processes to the host galaxy. We present the application of these diagnostics on a nearby galaxy using Integral Field Unit (IFU) data, that not only provide the necessary emission lines, but also the opportunity to study the properties of SNRs and their environment. Hence, we present the distribution of their shock velocity, pre-shock density, shock excitation, and we explore correlations between those and the properties of their environment. For this galaxy, we also present new X-ray SNRs, counterparts of recently-identified optical ones.
Name: Dr. Maria Kopsacheili (ICE-CSIC)
Coauthors: Huussein-Bassia Issa (University of Crete)
Kopsacheili Maria (Institute of Space Sciences, Barcelona)
Leonidaki Ioanna (University of Crete/Institute of Astrophysics)
Zezas Andreas (University of Crete/Institute of Astrophysics)
Type: Poster
Title: A systematic analysis of the physical parameters of Galactic SNRs
Abstract:
We present a meta-analysis of the physical parameters of Galactic Supernova Remnants based on a systematic literature review. We use data for 64 SNRs with published information (mainly from optical observations) regarding their shock or expansion velocity, density and temperature, based on a variety of methods and tracers. We also have further information on individual regions of 34 objects, providing a picture of the variation of the physical parameters within an object. We quantify this variation and we also discuss the effect of the different tracers on the diversity of the estimated values. We explore the correlations between the physical parameters of SNRs (such as velocity, density and excitation parameters) as a function of their age and type, providing for the first time a picture of the overall trends of the properties of the SNR population within our Galaxy. Comparison of the derived correlations with SNR evolution models shows very good agreement.
Name: Dr. Grigoris Maravelias (National Observatory of Athens & FORTH)
Coauthors: Bonanos Alceste (National Observatory of Athens)
de Wit Stephan (National Observatory of Athens, National & Kapodistrian Univ. of Athens)
Tramper Frank (KU Leuven)
Munoz-Sanchez Gonzalo (National Observatory of Athens, National & Kapodistrian Univ. of Athens)
Zapartas Manos (National Observatory of Athens)
Christodoulou Evangelia (National Observatory of Athens, National & Kapodistrian Univ. of Athens)
Antoniadis Konstantinos (National Observatory of Athens, National & Kapodistrian Univ. of Athens)
Bonfini Paolo (Ballista Technologies)
Yang Ming (National Astronomical Observatories, Chinese Academy of Sciences)
Type: Oral
Title: Investigating the populations of dusty evolved stars in various metallicities with machine learning
Abstract:
Although our knowledge on stellar evolution has improved dramatically over the last decades, both regarding single and binary evolutionary models, we still lack pieces of the puzzle. Mass loss is a key property to understand and characterize stellar evolution in particular beyond the main-sequence, as it determines the immediate environment around the source as well as its final fate. Unfortunately, there is a mismatch between the observational and theoretical values (derived from models). Even worse, the episodic mass loss in evolved massive stars, although definitely present observationaly, is not included in the models. Therefore, its importance of its role is currently undetermined. A major hindrance is the lack of large samples of classified stars. In the framework of the ASSESS project, we attempted to address this by applying machine-learning techniques to IR (Spitzer) and optical (Pan-STARRS) photometry, coupled with Gaia astrometry to detect foreground sources. Using color indices as features we utilized an ensemble approach (combining the probabilities from three different algortihms, Support Vector Machines, Random Forest, and Multilayer Perceptron). The three supervised algorithms were trained on M31 and M33 sources with known spectral classification, and we grouped the sources into Blue/Yellow/Red Supergiants, Luminous Blue Variables, classical Wolf-Rayet stars, B[e] Supergiants, and a class for outliers (e.g. background galaxies, AGNs). We then applied the ensemble classifier to about one million Spitzer point sources from 25 galaxies, spanning a range of 1/15 to ~3 Zsolar. Only a tiny fraction (~0.5%) of these sources have spectral classification. We delivered relatively reliable classifications for ~30% of the Spitzer point sources, and, therefore, providing the most numerous catalog of massive evolved stars compiled for these galaxies to-date. Equipped with spectral classifications we investigated the occurrence of these classes and ratios with respect to metallicity environments.
Name: Dr. Grigoris Maravelias (National Observatory of Athens & FORTH)
Coauthors: de Wit Stephan (National Observatory of Athens, National & Kapodistrian Univ. of Athens)
Bonanos Alceste (National Observatory of Athens)
Tramper Frank (KU Leuven)
Munoz-Sanchez Gonzalo (National Observatory of Athens, National & Kapodistrian Univ. of Athens)
Christodoulou Evangelia (National Observatory of Athens, National & Kapodistrian Univ. of Athens)
Type: Poster
Title: New B[e] supergiants and candidate Luminous Blue Variables in nearby galaxies from the ASSESS project
Abstract:
Mass loss is one of the key parameters that determine stellar evolution. Despite the progress we have achieved over the last decades we still cannot match the observational derived values with theoretical predictions. Even worse, there are certain phases, such as the B[e] supergiants (B[e]SGs) and the Luminous Blue Variables (LBVs), where significant mass is lost through episodic or outburst activity. This leads to various structures around them that permit dust formation, making these objects bright IR sources. The ASSESS project aims to determine the role of episodic mass, by examining large numbers of cool and hot objects (such as B[e]SGs/LBVs). For this, we initiated a large observing campaign to obtain spectroscopic data for ∼1000 IR selected sources in 27 nearby galaxies. Within this project we successfully identified 6 B[e] supergiants and 5 Luminous Blue Variables of which 5 and 3, respectively, are new discoveries. We used spectroscopic, photometric and light curve information to better constrain the nature of the reported objects. We particularly note the presence of B[e]SGs at metallicity environments as low as 0.14Z⊙.
Name: Mr. Gonzalo Munoz-Sanchez (National Observatory of Athens / NKUA)
Coauthors: Bonanos Alceste (National Observatory of Athens)
de Wit Stephan (National Observatory of Athens / NKUA)
Boutsia Konstantina (The Carnegie Institution for Science)
Antoniadis Konstantinos (National Observatory of Athens / NKUA)
Type: Poster
Title: A luminous RSG in the LMC with a bow shock?
Abstract:
Episodic mass loss in evolved massive stars is an unresolved question. Specifically, in the Red Supergiant (RSG) phase, important physical processes such as mass loss, the mechanisms behind it, and the role of metallicity remain uncertain. Not understanding these processes has large implications in a variety of fields, from theoretical evolutionary models and stellar population synthesis to building proper RSG models to obtain accurate and reliable physical properties. To shed some light on the discussion, we introduce the community to one of the most luminous and extreme RSGs in the LMC. Through medium-resolution spectroscopy with MagE (Baade telescope, Las Campanas, Chile) we have detected spectral variability in [W60]B90, among the three epochs obtained. In addition to the photometric variability and the near and mid-IR excess, the evidence suggests that it might be experiencing an unstable phase in its life with a period of enhanced mass loss. Moreover, we have confirmed shocked material in its immediate surroundings. After using Gaia DR3 to compute its peculiar velocity we verified that it is moving towards the shocked region. Hence [W60]B90 can be considered a strong candidate to be the first RSG with a bow shock outside the Milky Way (and the fourth RSG in general). Direct detection of the bow shock would be crucial to understand the interaction between star-ISM in a subsolar metallicity environment and may open a new horizon to estimate its previous mass loss and compare it with the current status of this unique star.
Name: Ms. Sofia Palafouta (National & Kapodistrian Univ. of Athens)
Coauthors: No coauthors were included.
Type: Poster
Title: Low mass ratio eclipsing binaries as red nova progenitors.
Abstract:
Eclipsing binaries that have a large difference in the mass values of their components and high fill-out factors are exceedingly rare, with only a few dozen known to date. These systems have the potential to become red novae and pose a challenge to existing theoretical models of stellar evolution, as they merge around critical mass ratio values of 0.07 and 0.09, when they become overcontact. It is believed that they follow the Darwinian instability model during the merging process and may be the progenitors of FK Com-type and Blue Straggler stars. This study examines the physical and orbital parameters of W UMa-type binaries in their final state of evolution, while considering the various dynamical structures and gravitational phenomena involved. By analyzing a robust sample of photometric and spectroscopic data, valuable information can be obtained about the orbital and physical characteristics of these systems. When combined with the predicted critical mass ratio values for each system, it becomes possible to compile an extensive list of stellar merger candidates, which could help establish a method for predicting red nova events.
Name: Dr. George Pantolmos (CNRS/IPAG)
Coauthors: Zanni Claudio (INAF/Observatory of Turin)
Bouvier Jerome (CNRS/IPAG)
Type: Oral
Title: The stable and unstable accretion regimes: Implications for the stellar rotation
Abstract:
In this talk, I will present the outcome of three-dimensional simulations studying the interaction between a magnetized solar-mass protostar and its surrounding accretion disk. The standard picture of magnetospheric accretion suggests that the disk gas reaches the stellar surface through accretion funnels or curtains, the so-called stable accretion regime. Three-dimensional models are able to capture the intrinsically non-axisymmetric interchange (or magnetized Rayleigh-Taylor) instability that can develop at the magnetospheric boundary. Previous works have shown that this instability results in the formation of equatorial accretion tongues, which penetrate the stellar magnetosphere, further affecting the stellar photometric variability. This is the unstable accretion regime. The critical parameter, which characterises both the accretion state (stable or unstable) and the angular-momentum transport in the star-disk system, is the ratio between the disk truncation radius and the system co-rotation radius (where the disk rotation rate matches the stellar rotation rate). I will present a new scaling that predicts the disk truncation radius from the system global parameters such as the mass accretion rate, stellar mass and radius, magnetic field strength. In addition, I will demonstrate that stable accretion is a key ingredient for a stellar spin-down, with a spin-down timescale of about one Myr and thus, it can explain the observed slow rotation of classical T Tauri stars (i.e., class II low-mass young stellar objects). Finally, I will discuss how the observed variability in T Tauri stars, likely linked with the accretion state, can provide insights on the rotational-evolution state of the central object (spin-down or spin-up).
Name: Dr. Tatiana Pavlidou (University of Vienna)
Coauthors: No coauthors were included.
Type: Oral
Title: Linking the Class 0 and Hot Corino populations of the Perseus Molecular Cloud Complex
Abstract:
Class 0 sources represent the earliest and the coldest phase of the star formation process. They are thought to be the new-born protostars still deeply embedded in their parent cloud. Hot corinos are compact (~100 AU), hot (~100K) and dense (~10^7 cm^(-3)) envelopes abundant in complex organic molecules (COMs) and are associated with low-mass Class 0 sources. In this talk I will present the first results from a set of photometric criteria using Herschel and Spitzer data. I will focus on the Perseus molecular cloud complex in which the youngest population of stars is recovered by these criteria. I will present evidence that this population might coincide with the population of hot corinos which can support these photometric characteristics as criteria for hot corino candidates in general.
Name: Dr. Danae Polychroni (INAF - Trieste)
Coauthors: No coauthors were included.
Type: Poster
Title: Birth and destruction in protoplanetary disks: dust production by planetesimal collisions
Abstract:
Dust plays a central role in the chemical evolution of protoplanetary disks and is the source material from which planetary bodies form. Coagulation into planetesimals and planets is expected to steadily decrease the dust abundance in disks over time. However, recent surveys point to the median dust content of disks increasing from 1 to 2 Myr in nearby star-forming regions. Furthermore, resolved observations of HD 163296 reveal unexpected regions of high dust concentration across its extension. Building on our insight on the collisional evolution of small bodies from the Solar System, we show that such unexpected behaviours of the dust stem from the planet formation process. The early formation of massive planets dynamically stirs the nearby planetesimals and causes high-velocity impacts between them, resulting in the production of second-generation dust. This collisional production naturally explains the rise in the dust population observed in disks with ages between 1 and 2 Myr, suggesting this is the characteristic timescale of giant planet formation. The appearance of second-generation dust also explains the spatial distribution of dust observed in older disks like HD 163296. By sustaining the dust population over time, this collisional rejuvenation process acts to extend the duration of the planet formation process and the chemical evolution of disks.
Name: Dr. Ioanna Psaradaki (University of Michigan)
Coauthors: No coauthors were included.
Type: Oral
Title: Mineralogy of interstellar dust in the X-ray regime
Abstract:
Interstellar dust is an important ingredient of the interstellar medium (ISM) of galaxies. High-resolution X-ray spectroscopy is a powerful tool for studying interstellar dust mineralogy. X-ray absorption fine structures (XAFS) are oscillatory modulations observed near the X-ray photoelectric absorption edges, and their shape is the ultimate footprint of the dust chemical composition, size and lattice structure. In this presentation I will demonstrate the newest laboratory measurements of XAFS from astrophysical dust templates in the O K and Fe L photoabsorption edges (Psaradaki et al. 2020,2021), and their application to high-resolution X-ray spectra of a sample of bright Galactic X-ray sources. I will present recent results (Psaradaki et al. 2022) on dust mineralogy in the diffuse regions in our Galaxy using XMM-Newton/RGS and Chandra/HETGS observations. This study gave the most comprehensive view of the silicate mineralogy in the diffuse regions of ISM, through the X-ray energy band. We found that the Mg-rich amorphous pyroxene dust composition (Mg0.75Fe0.25SiO3), and metallic iron represents the bulk of the dust chemistry in the diffuse ISM. Finally, I will discuss the prospects of studying the dust grain chemistry in denser regions of the ISM through the new X-ray Imaging and Spectroscopy mission, XRISM, which will be launched in the summer of 2023.
Name: Ms. Sofia Savvidou (MPIA, Heidelberg)
Coauthors: No coauthors were included.
Type: Oral
Title: A giant solution to the disc mass budget problem of planet formation
Abstract:
Planet formation is directly linked to the birthing environment that protoplanetary discs provide. The disc properties determine if a giant planet forms and how it evolves. The number of exoplanet and disc observations is ever-increasing, however, it is still not possible to directly link these two populations, therefore a deep theoretical understanding of how planets form is crucial. Giant planets are not the most common exoplanets, but their presence in a disc can have significant consequences for the evolution of the disc itself, the forming planetary system, and it also offers more chances of observational features in the disc structure. We perform numerical simulations of planet formation via pebble and gas accretion, including migration, in a viscously evolving protoplanetary disc, with dust growing, drifting, and evaporating at the icelines. We discuss the most favorable conditions for giant planet formation, however, we conclude that there is no specific initial parameter that leads to giant planet formation, but it is mainly the outcome of a combination of beneficial and non-limiting factors. This also implies that the diversity of the exoplanet systems is the product of the intrinsic diversity of the protoplanetary discs and it is crucial to take advantage of the increasing number and quality of observations to constrain the disc population properties and ultimately planet formation theories. Additionally, we present how the disc dust mass evolves in our models after a giant has formed and compare this with the dust mass we would estimate for these discs through observations. We conclude that there is no disc mass budget problem and the discrepancy between the mass estimates of the observed discs and the observed exoplanets is a product of the underlying assumptions.
Name: Dr. Raphael Skalidis (Caltech)
Coauthors: No coauthors were included.
Type: Oral
Title: Estimating the magnetic field strength in the interstellar medium
Abstract:
A large scale magnetic field permeates the interstellar medium (ISM) of our Galaxy. The ISM magnetic field strength is notoriously difficult to measure, and for this reason there is a longstanding debate about its dynamical importance in the star formation process. The magnetic field strength can be directly measured, with the Zeeman effect, only in a limited number of cases. For this reason, indirect methods have been developed for estimating the magnetic field strength. The most widely accessible methods are based on dust polarization. Dust polarization probes directly the plane-of-the-sky magnetic field morphology, but not its strength. These indirect magnetic field strength estimation methods are based on the energy balance of incompressible turbulence. Observations, however, indicate that turbulence in the ISM is highly compressible, hence the assumptions of the existing methods are incompatible with the observations. In this thesis, we propose a novel method for estimating the magnetic field strength from dust polarization based on the energetics of compressible turbulence. We assess the accuracy of the proposed method with synthetic data produced from a suite of numerical simulations. We find that with the proposed method an accuracy better than a factor of two can be achieved.
Name: Dr. Aris Tritsis (EPFL)
Coauthors: No coauthors were included.
Type: Oral
Title: Can we observe the ion-neutral drift velocity in molecular clouds?
Abstract:
Given the low ionization fraction of molecular clouds, ambipolar diffusion is thought to be an integral process in star formation. However, chemical and radiative-transfer effects, observational challenges, and the fact that the ion-neutral drift velocity is inherently very small render a definite detection of ambipolar diffusion extremely non-trivial. I studied the ion-neutral drift velocity in a suite of chemodynamical, non-ideal magnetohydrodynamic (MHD), 2-dimensional axisymmetric simulations of prestellar cores where I altered the temperature, cosmic-ray ionization rate, visual extinction, mass-to-flux ratio and chemical evolution. Subsequently, I performed a number of non-local thermodynamic equilibrium (non-LTE) radiative-transfer calculations considering various idealized and non-idealized scenarios in order to assess which factor (chemistry, radiative transfer and/or observational difficulties) is the most challenging to overcome in our efforts to detect the ion-neutral drift velocity. I found that temperature has a significant effect in the amplitude of the drift velocity with the coldest modeled cores (T = 6 K) exhibiting drift velocities comparable to the sound speed. Against all odds, I found that, in idealized scenarios (where two species are perfectly chemically co-evolving) the drift velocity "survives" radiative-transfer effects and can be observed. However, I found that observational challenges and chemical effects can significantly hinder our view of the ion-neutral drift velocity. Specifically, I found that the pairs of HCN and HCO+, and NH3 and N2H+, previously used in observational studies of ambipolar diffusion, exhibit significantly different abundance distributions within the modeled clouds and are thus not suitable for probing the ion-neutral drift velocity. Finally, I propose that HCN and HCNH+, being chemically co-evolving, could be used in future observational studies aiming to measure the ion-neutral drift velocity.
Name: Mr. Alexandros Tsouros (IA-FORTH & Univ. of Crete)
Coauthors: Edenhofer Gordian (Max Planck Institute for Astrophysics)
Enßlin Torsten (Max Planck Institute for Astrophysics)
Mastorakis Michalis (Institute of Astrophysics - FORTH)
Pavlidou Vasiliki (Institute of Astrophysics - FORTH)
Type: Oral
Title: 3D Galactic Magnetic Field Reconstruction Using Local Measurements
Abstract:
The Galactic magnetic field (GMF) is pivotal to our understanding of cosmology and high-energy astrophysics. Comprehensive knowledge of its 3D structure is vital for correcting the impact of the Galaxy on the observed polarisation of the cosmic microwave background (CMB). However, our understanding of this structure remains limited due to the scarcity of local measurements and the dependence on line-of-sight (LoS) integrated observations. In this talk, we introduce an innovative method for 3D reconstruction of the GMF using principles of Information Field Theory and Bayesian inference. Upcoming stellar optopolarimetric surveys, such as PASIPHAE, along with Gaia data on stellar parallaxes, are expected to provide local measurements of the GMF in the near future. We simulate these anticipated sparse and local GMF measurements to reconstruct the GMF in regions of the Galaxy where local data can be obtained. This approach presents a promising avenue for unravelling the intricate local structure of the GMF and assessing its influence on various astrophysical processes. To evaluate this method, we will investigate its applicability in high-energy astrophysics, specifically by tracing the propagation of ultra-high energy cosmic rays (UHECRs). Lastly, we will offer an outlook on forthcoming data and advancements that will further bolster our ability to reconstruct the GMF and comprehend its implications for the field.
Name: Dr. Manos Zapartas (National & Kapodistrian Univ. of Athens)
Coauthors: Bonanos Alceste (NOA)
de Wit Stephan (NOA)
Antoniadis Kostas (NOA)
Muñoz Sanchez Gonzalo (NOA)
Christodoulou Evangelia (NOA)
Maravelias Grigoris (NOA)
Fragos Tassos (University of Geneva)
Type: Oral
Title: Investigating the effect of mass loss of Red Supergiants in the Small Magellanic Cloud
Abstract:
Massive stars play an important role in astrophysics, shaping their environment during their life, and through their explosive deaths. However one of their main properties, their mass loss mechanism during the late stages of their evolution as Red Supergiants (RSGs) is still poorly understood and constrained, especially at low metallicities. Recently, Yang et al. (2023) provided an empirical prescription of mass loss during the RSG phase, based on the most complete and clean sample so far in the Small Magellanic Cloud (SMC). We investigate the effect of this new mass-loss rate prescription, as well as others from literature, on stellar evolutionary models, using MESA code (e.g., Paxton et al. 2011). We have implemented these prescriptions in grids of single star models of SMC metallicity, that were generated with the population synthesis code POSYDON (Fragos et al. 2023). We compare the theoretically predicted surface properties of the RSGs with the observed ones, including their luminosity functions and their position in the Hertzsprung-Russell diagram. We find that the suggested high mass-loss rate of Yang et al. leads to extreme stripping of the envelope of the RSGs, leaving only a thin Hydrogen-rich layer above their cores, driving them to the hotter temperatures before their eventual death in a core-collapse event.