Physics Of Extreme Massive Stars

In the frame of this POEMS project, I had a second secondment in Brussels, visiting our colleague Dr. Alex Lobel at the Royal Observatory of Belgium (ROB).

We started our flight from Prague on Sept. 16th 2023. This time the secondment was for just 9 days and was to “finish” the one I started in 2020 that was interrupted by the COVID-19 pandemic.

This time we found a small but comfortable flat in the Uccle quarter, it was quite expensive but it satisfied all our requirements. This time our daughter did not go to the school as in 2020, but we visited it once to thank the director for receiving Sofia in 2020.

Adapting to life in Brussels was very easy, we were able to buy our monthly ticket for public transportation and we recognized the trams and buses that took us to the observatory in a very simple and fast way.

In this “second” secondment at the observatory, the adaptation was very simple and working with Alex was smooth as usual. There was a common space to have lunch and share with them, and the atmosphere was very calm too.

During this stay, we walked a lot around Brussels, considering that this was in summer/autumn and not in winter as in 2020. We found this time the Brussels to be much more colorful.

Finally, the most important thing is that working with Alex was a pleasure. He is a very nice and pleasant person and we were able to have long and interesting conversations on the subject of winds of massive stars. During this stay we managed to find some interesting new results, which we hope to publish in the near future. Also, my PhD student, Daniela Turis, was at ROB working with Alex.

In this secondment, we had the opportunity to share a nice evening with our families as seen in this picture.

I appreciate the opportunity this Marie Curie project gave me to visit the Royal Observatory of Belgium and share the very pleasant and productive research stay with these colleagues.

During this secondment, I participated in the International Summer School on Stellar Winds and Outflows at Harachov, where I worked on the project supervised by Dr. Lydia Cidale (UNLP) and Dr. Andrea Torres: “Fitting synthetic Hα line-profiles to observations”. During this school, I had the opportunity to interact with and learn from several distinguished experts in the field.

After the school, I spent 6 weeks in the stellar department of the Astronomical Institute in Ondřejov, Czech Republic. There, I worked on the analysis of 67 observations of the star P Cyg using the APPEL code to later study the variability of its parameters.

I also had the opportunity to collaborate with Matias Ruiz, Julieta Sanchez and Peter Nemeth, on the analysis of the equivalent widths of different spectral lines from synthetic models. For that purpose, I used ISOSCELES grid and a study the isocontours of two observed stars and constrained successfully some stellar parameters.

Furthermore, I attended a seminar at the Masaryk University in Brno and joined the regular journal club in the Institute. Here, I also contributed with a seminar talk where I showed my Ph.D. work on the wind momentum luminosity relationship and discussed my results with some experts in the area. I also presented the effort and teamwork I put into my secondment highlighting my contributions.

Finally, during the weekends I visited many different places with my Latin-American colleagues, including nearby countries and some local castles. It was another rewarding period thanks to the POEMS project and its members.

During the first two weeks of my stay, I attended the International Summer School on Stellar Winds and Outflows held in Harrachov. The school provided a comprehensive overview of stellar astrophysics, and I had the privilege of participating in a series of lectures that covered a wide range of topics, as well as hands-on workshops involving various computational tools.

This school concluded with a mini research project that allowed us to apply our newly acquired knowledge. It was a rewarding experience to put theory into practice and share experiences with other participants from diverse backgrounds.

Following the summer school, I traveled to the Stellar Department of the Astronomical Institute in Ondřejov to continue my work on stellar winds, where I also shared a wonderful time with new friends.

During this period, I worked on creating synthetic spectral models using the FASTWIND, CMFGEN and TLUSTY codes, focusing on massive O-type stars in the UV range, under the guidance of Peter Nemeth. This job provided me the opportunity to further deepen my experience using the TLUSTY code. The underlying results have led to tighter estimates for rotational velocities and mass-loss rates, and have confirmed the efficacy of using clumping models, in comparison to previous studies. These results will be very useful in the framework of my doctoral research, allowing me to establish a solid foundation for my future studies.

Furthermore, I actively participated in various seminars held at the institute, with one in particular being led by PhD. Julieta Sanchez in Brno.

Additionally, on some weekends, I had the opportunity to explore neighboring countries. I visited Poland, Austria, and Germany with the company of friends, and explored cities like Kutná Hora and Brno here in Czechia, immersing myself in various cultures and experiencing European lifestyle. These trips not only enriched my cultural understanding but also broadened my personal horizons.

Connecting and interacting with other professionals, along with the opportunity to appreciate the diversity of European cultures, was a truly transformative experience, and I am grateful for the knowledge and connections I have gained during this journey. Thank you everyone!

The two main objectives of my visit to Czech Republic, as planned by my advisor Marcelo Borges from Observatório Nacional, were attending POEMS’ summer school of Stellar Winds and Outflows, which spanned from 3 to 15 of September in Harrachov, followed by my secondment at Ondrejov’s Astronomical Institute’s Stellar Department under the supervision of Michaela Kraus until September 30th.

I arrived in Prague on August 30th, just a couple of days before the beginning of the summer school, so I had the privilege to explore the city and visit many of the touristic spots it had to offer: Prague castle, Charles bridge, the old town hall, the observatory tower, Vysehrad castle, the Jewish quarter and a plethora of museums and expositions. On the day before the school started, I met some other schoolmates and we traveled to Harrachov together by bus (none of us speaks Czech, but fortunately we did not get lost!).

For the next weekdays, we would wake up in the morning, have our breakfast at the hotel’s restaurant and head to the seminar room where we would have our lectures until late afternoon, taking a rest only for lunch and coffee breaks. For the first week, some of the topics were: Radiative Transfer, Introduction to Hydrodynamics, Radiation-Driven Winds, Mass Loss Recipes, TLUSTY, SYNSPEC, ROTIN and CMFGEN softwares.

We had the days off during weekends. On Saturday, we all went hiking on the nearby hills close to the border with Poland; we ended up walking longer than intended, since the cable car to the top was not operating that day, but everything went well and no one was left behind! On Sunday, I decided to accompany some of the schoolmates for a very quick visit to Wroclaw, in Poland.

The next week started and we had the last batch of lectures, for instance: Stellar Winds And Magnetospheres, Astronomical Data Archives For Stellar Spectroscopy, Winds And Outflows From Massive Pre-Main Sequence Stars, Mass-Loss Activity Of Yellow Hypergiants, Winds Of LBV’s And Cool Hypergiants. After that, we were given the assignment of forming groups and choosing one of the project topics proposed by the lecturers to work on, and with their help we would need to present our results to everyone in the form of a short lecture. I worked with Bharti Arora and Suryani Guha as group mates, having Olga Maryeva as our supervisor, and we analyzed the clumping effect in O-type star spectra using CMFGEN. In the end, we successfully finished the task and we were awarded with the school certificate.

The school was over, so me and other secondment students along with Astronomical Institute researchers moved to Ondrejov by car. For us students, the following workdays consisted basically of walking from our dormitory to the institute early in the morning and working on our individual research until late afternoon; while for weekends and holidays, we had our day off, and in my case I would usually spend the day in Prague, considering how small and quiet Ondrejov is. During my time in the institute, I worked under the supervision of Michaela Kraus on B[e] star spectra which exhibited CO lines, a topic of quite importance to my Ph.D research on stars in Transition Phase. The spectra were observed with the GEMINI Observatory’s IGRINS spectograph, obtained by my advisor, Marcelo Borges. Michaela taught me how to use her own CO Code to fit the stellar parameters of the simulated spectra with the observed one.

Then my secondment came to an end on September 30th as planned, and after saying goodbye to all my research fellows I took my flight back to Brazil. I’m really thankful for all the new friends from all over the world I made during my stay in the Czech Republic, and for all the academic and personal experience acquired from this unique opportunity.

I have been visiting the Tartu Observatory, University of Tartu in Estonia in the framework of the POEMS project for two months. Firstly, I obtained skills on working with Linux operating system and then I learned about the processing of spectral materials in the Linux operating system through the IRAF program. IRAF is a product of the National Optical Astronomy Observatories and was developed for the astronomical community.

We also had discussions with Tõnis Eenmäe from Department of Stellar Physics, about processing photometric observational data. He gave me very important information about the depths of photometry and showed me the practical methods of processing photometric observational data through various programs.

During my visit, I also had the chance to participate in the “Stellar spectroscopy workshop” held at the Tartu Observatory. On the first day of the 2-day workshop, lectures on stellar spectroscopy were heard, and on the next day, all participants were involved in practical work. The workshop is financed by the EU Horizon Europe Twinning project EXOHOST and UK Research and Innovation.

In addition, during my visit I gave a seminar: “Photometric variability of Wolf-Rayet type star HD191765”. I also participated regularly in astroseminars that take place at Tartu Observatory.

During these two months, every weekend I visited different places of interest in Estonia. One of the most unforgettable places I visited was the Pärnu city. The city sits off the coast of Pärnu Bay, an inlet of the Gulf of Riga, which is a part of the Baltic Sea. Walking along the shores of the Baltic Sea in autumn was a wonderful feeling. I also visited University of Tartu Pärnu College and tasted various dishes from Estonian cuisine, listened to Estonian music and got acquainted with Estonian culture and traditions. In addition, I also went to the town of Elva, which is located near the observatory. Although it is a small town, it has a magnificent forest and lake view.

At the end, I would like to thank the entire staff of the Tartu Observatory for their hospitality during this visit, especially Dr. Anna Aret. I hope to see you all again!

Our secondment in ASU was divided into two parts: Ondrejov and Harrachov.

The first part started with us arriving to the Prague Airport on August 16th 2023, where Michaela Kraus was waiting for us and with a van from ASU we went to Leonora Villa in Ondrejov.

In the following picture (left) we are in the office we had at ASU. The atmosphere there was very pleasant, and I had the chance to use the coffee machine.

We were a bit surprised by the weather (upper right picture). We were in the middle of the summer with temperatures about 13° Celsius, but as you see in the picture we were "prepared". The next picture was taken in front of the 2-meter telescope dome which we also had a pleasure to visit.

The two weeks in Ondrejov went by very quickly. We prepared the slides for the summer school and I gave a talk about the solar wind introducing the Lambert-W function.

Our baggages were very heavy and with the help of Peter Nemeth, we could "send" them to Harrachov which was the second part of our secondment.

On September 3rd, Julieta Sanchez, kindly offered to take us in her car to Harrachov, to the skycentrum Hotel where the International Summer School on Stellar Winds was held. The place was very nice, surrounded by the national Park. The day after we started the 2-weeks summer school with ca. 24 attendants.

During the following weekend we, as almost all of the participants, went to a trip in the neighborhood, around 20 km from Harrachov. Over there we were frustrated because the cable car was not working, and we had to go to the summit on foot. However, in the end the view was so beautiful that everything about the "climbing on foot" was forgotten.

We had an excellent time in Harrachov and enjoyed the level of commitment of all the students.

In the last day, all the lecturers went to a "camaraderie" dinner, as seen in the following picture.

Then on September 16th, we rented a car and went early in the morning to Prague airport and flew to Brussels.

I visited the Stellar Department of the Astronomical Institute in Ondřejov, Czech Republic (9 May - 8 July 2023). There, I collaborated with Dr. Michaela Kraus and under her supervision, continued the development of the code I have been writing to generate synthetic spectra of diatomic molecules present in circumstellar disks. The calculation of synthetic spectra is crucial for identifying the presence of specific molecules in circumstellar disks and deriving various physical and dynamic parameters of the disk. During my stay, I made the necessary changes to the code to enable calculations for molecules with energy levels with semi-integer rotational quantum numbers and degenerate rovibrational energy levels, thereby increasing the number of molecules for which we can calculate spectra from the initial 6 to over 50. Additionally, together with Dr. Michaela Kraus, we analyzed the results obtained with the code and discussed the methodology for using these synthetic spectra and comparing them with observations from various researchers members of POEMS. I presented the results of this code to the researchers of the Stellar Department in a talk titled "Modeling of Diatomic Molecules in Circumstellar Disks," and I hope to publish them soon and start utilizing the code with the observations.

Furthermore, I attended a Python course taught by Tomasz Różański, which took place at the beginning of my stay. I also participated in the department's regular activities, such as seminars, journal clubs, discussion meetings, as well as various social activities.

During the weekends, I had the opportunity to visit Prague several times and learn more about the history and architecture of this marvelous city, particularly the aspects related to astronomy, which is strongly associated with the time when Tycho Brahe and Johannes Kepler were in the city.

Thanks to POEMS, I have had the experience of working alongside people from different nationalities and witnessing different approaches to everyday challenges. I hope that several collaborations can be established in the near future. Finally, I must express my gratitude for the hospitality of Michaela and all the members of the group, who have always been willing to make my stay as pleasant as possible.

Recently I spent two wonderful autumn months at the La Plata National University. It was a bright, interesting, memorable and, of course, fruitful trip in terms of both scientific communication and personal gains.

During the secondment I started to study three interesting stars with the B[e] phenomenon. Infrared data for them were collected by Argentinian colleagues, while optical spectra were obtained at the telescopes in Czech Republic and Estonia. And now it's time to put everything together and publish the results. Stars with the B[e] phenomenon is a new field for me, thus regular meetings and discussions with the colleagues - Prof. Lydia Cidale, Dr. Maria Arias and Dr. Andrea Torres - were very useful and helped me a lot. During the visit I also gave a talk titled “Unveiling new LBVs in modern sky surveys” at the University seminar.

I really liked the observatory itself and its atmosphere. The observatory is an old building, with a courtyard paved with white stone. You may feel that the observatory not only conducts modern exploration of the Universe, but also carefully preserves the memory. Dr. Yael Aidelman and Prof. Roberto Gamen showed me the collection of historical photographic plates. I was amazed and happy to see the plates with spectra of WR stars that the famous researcher of these objects, Virpi Niemelä, acquired. The observations logbooks, which kept records of observations performed a hundred years ago, aroused my delight.

In addition, it was interesting to see by my own eyes the tapes with data from the first ever space-borne ultraviolet observatory – IUE, the International Ultraviolet Explorer. Reels of tapes with recorded data on the shelves create the right mood and inspire new research. Memorial plaques on the observatory’s walls are reminders of the difficult years in the history of Argentina.

Besides the science, the secondment to UNLP gave me the opportunity to see the amazing nature of Argentina, its incredible lakes, the Perito Moreno glacier and the Iguazu Falls.

I would like to thank Lydia, Lorena, Andrea and Maria and their families for the hospitality and responsiveness, for helping me in solving everyday problems and for organization of common activities! Many thanks to Matias, Aldana, Yanina, Yael, Paula and Rodolfo with whom we shared the office! I also want to thank the people I met at the UNLP during this visit, who made my stay so much warmer. I hope to see you all again!

During my last visit to La Plata National University (10 November 2022-11 January 2023), I initiated two projects. The first project aimed to understand the interplay between stellar oscillations and mass loss during the stellar evolution of Galactic B supergiant stars. The second project focused on Be stars in clusters and the study of their pulsations and the Be phenomena for different cluster ages.

During this secondment (1 April - 2 June 2023) I worked in tight collaboration with Prof. Lydia Cidale and Lic. Matias Diaz Ruiz on the Galactic B supergiants project, addressing the referee report for the paper I submitted to Galaxies for a Special Issue in which Prof. Lydia Cidale and Prof. Michaela Kraus are editors. In this paper, we successfully employed the code developed by Dr. Peter Nemeth during his secondment at the University of Valparaiso in Chile, in collaboration with Dr. Elisson S.G. de Almeida, to retrieve the stellar and wind parameters as well as the CNO mass fractions for the selected objects. We performed a careful analysis of TESS light curves for the 3 selected B-Supergiants with Lic. Matias Diaz Ruiz finding one rotational splitting in one of these objects and low frequencies modes possibly related to strange modes. The discussions with Prof. Lydia Cydale on the spectroscopy of these objects were also extremely useful in understanding how different wind parameters affect their spectra.

Additionally, I continue working on the stellar photometric variability of Be stars in different clusters with Dr. Yanina Cochetti. We worked with the LightKurve package to retrieve the light curve of the selected objects from the TESS Target Pixel Files (TPF). We implemented different codes, such as TESS-Localize, to identify the sources of variabilities within the TPF. We faced major complications mainly due to the crowded TPF for most of the clusters and will be difficult to perform statistical studies on the stellar variability and its connection with the Be phenomenon in these stars. But we won’t give up and I will continue addressing this project with stellar interior and pulsation theoretical models.

Beyond these research activities, I attended seminars and meetings to organize the upcoming POEMS School in September. I could enjoy the beautiful fall in La Plata and share nice moments with my colleagues, among them the awarding of the master's degree of Matias Ruiz Diaz. I am looking forward to continuing these collaborations within POEMS project!

During a one-month research visit to the University of Valparaíso, Chile, I had the pleasure of collaborating with Dr. Alejandra Christen and her PhD student Gunther Avila from the Institute of Statistics, as well as with PhD student Vitalii Checha from the University of Tartu. The primary objective of our visit was to gain insights into various methods for analyzing unevenly spaced time series.

Throughout our stay, we learned to use Weighted Wavelet Z-Transform (WWZ) method, frequency analysis with Lomb-Scargle and Generalized Lomb-Scargle (GLS) periodograms, and Phase Dispersion Minimization (PDM) technique. We applied these methods to conduct frequency analysis of spectroscopic time series data of the blue supergiant rho Leo, which was obtained with the 1.5-m telescope at Tartu Observatory during 2017-2023.

In addition to our work with Dr. Christen and Mr. Avila, we engaged in fruitful discussions with Prof. Michel Curé and Dr. Catalina Arcos. We shared and discussed the results of modeling the echelle spectra of rho Leo using the FASTWIND code, which was conducted in collaboration with Dr. Ignacio Araya during our visit to the University Mayor. Moreover, we explored the application of the hydrostatic NLTE model atmosphere code TLUSTY for modeling blue supergiants. Dr. Catalina Arcos also introduced us to the multi-fitting tool MUFIN, which works well for determining parameters of hot main sequence stars. However, this tool, based on the standard grid of TLUSTY model atmospheres, is not ideally suited for the analysis of supergiant stars.

I am sincerely grateful to our Chilean colleagues for their warm welcome and generous sharing of knowledge. This remarkable opportunity to advance my research would not have been possible without their gracious hospitality and collaboration.

Beyond the enriching academic experiences, my memories of Valparaiso itself are deeply cherished. Its colorful houses climbing from the coast to the mountains, adorned with stunning street art at every turn, created an atmosphere unlike any other. The overwhelming views of the magnificent ocean further added to the city's charm, making this research visit a truly unforgettable experience.

During my collaboration with Professor Alejandra Christen and Gunther Avila from the Statistical Institute, who specializes in the statistical analysis of periodic processes, our main objective was to identify potential periodicity in our spectral data, specifically in the stellar pulsations of star rho Leonis. To achieve this, I utilized data series with radial velocity spanning several years of observations. Given that pulsations are not inherently periodic, finding the periods proved to be a non-trivial task. However, through our joint efforts, we explored numerous powerful statistical methods for analyzing periodic processes.

Moreover, I had the privilege of collaborating with Michel Cure and Catalina Arcos, with whom I discussed the physics of stellar pulsation and their influence on spectra.

I am genuinely grateful to Alejandra, Michel, and Catalina for their warm hospitality, the time they dedicated to our collaboration, and the memorable tour in Valparaiso.

I lived in a good area of the city - near the university, very close, so you could walk there. I was also very lucky with the apartment - there was a gorgeous view from the windows.

I visited the University of La Plata, in Argentina, during the period March 26 - May 25, 2023 in the frame of POEMS project. I collaborated with Prof. Lydia Cidale who is specialized in the physics of hot stars, and quickly adapted my science plans to meet those of the group. In particular, I investigated the variability properties of a list of OB-type stars, for which the group in La Plata has been conducting high-resolution spectroscopy with CASLEO telescope throughout the latest years. My direct goal was to extract the frequencies from the multi-periodic signal of the stars that is related to pulsations, rotation and binarity. The available spectra will further allow to join the photometric activity to the kinematics of the photosphere and to wind/mass-loss diagnostics.

The working sample of my study was retrieved from the database of the TESS survey. The satellite has been providing the community with high-cadence photometry with unprecedented accuracy that allows to resolve relative amplitudes as low as few thousandths of the stellar light. I devoted time in extracting the light curves using own-built masks and cleaning the data from the systematics. Frequencies were then extracted using state-of-the-art tools throughout a process known as pre-whitening. I conducted statistics that associate the periodic pattern with the spectral type of the stars from the literature. Refined statistics are currently explored upon the inclusion of accurate spectroscopic temperatures from CASLEO. In addition, fit of the spectral energy distribution will enable to measure luminosities and to identify the location of the stars on the evolutionary diagram. The results from the different methods will be presented in an upcoming article, to be submitted in a high-impact journal (Kourniotis et al. in prep.). My research visit ended with a review talk titled as "Yellow hypergiants: a missing piece in the late massive-star evolution", where our up-to-date knowledge on this rare stellar type was discussed.

Thanks to POEMS, a fruitful collaborative study has been initiated with the aim to address open questions on the massive star physics. The exchange of knowledge and sharing of techniques is integral part of research activity. Supportive actions such as POEMS has made it possible and I am grateful for being given this opportunity. Moreover, I am grateful to the host researcher Lydia Cidale for our discussions and her kind and warm hospitality. Highlight of the trip was a visit to the iconic landmark of Argentina, the glacier in El Calafate in the area of Patagonia; an adventure of those that you need to travel to the other side of the world in order to experience.

I visited the University Mayor with Vitalii Checha, a PhD student at the University of Tartu who is studying the variability of B-type supergiant stars. During the visit, we collaborated with Dr. Ignacio Araya to use the FASTWIND code for modelling the spectra of Rho Leonis, a B-type supergiant star. Our objective was to obtain a theoretical spectrum that would accurately match the observed spectra of our object at a quiet epoch, and determine the corresponding atmospheric and wind parameters. We used echelle spectra from the HARPS-N spectrograph, which were accessible via the ESO Archive Science Portal. The resulting model profiles of the Halpha and He I 6678 A lines will be used to gather information about the formation of variable asymmetric structures in the star's wind, based on spectral monitoring with the Tartu Observatory’s 1.5-m telescope. Wind influence on the shape of He I line, as well as the Si III triplet (4552, 4567, 4574 A), may essentially affect the results of pulsation analysis.

I delivered two talks about Tartu Observatory and the research conducted in the Department of Stellar Physics. The first talk took place at Universidad de Santiago de Chile on April 14, 2023, the second talk was given at Universidad Mayor on April 21, 2023

During the weekends, we took trips to the Andes mountains and marveled at the breathtaking wonders of the Chilean landscape. Although it was very hot in Santiago, with temperatures exceeding 30 degrees Celsius, the 15-degree drop in temperature at night was quite shocking.

I am grateful to Dr. Ignacio Araya for his warm hospitality and valuable collaboration. I also appreciate the modern office he provided us with at the Huechuraba campus of the Universidad Mayor, which not only offered comfortable amenities but also an exceptional view overlooking Santiago. The stunning view added to the overall enjoyment of our stay.

During my collaboration with physicist Ignacio Araya, who specializes in theoretical modeling of stellar atmospheres, our main objective was to find a theoretical spectrum that matched well with our observed spectra. I used both our own spectra and high-resolution (HARPS) spectra. For better fitting with the theoretical model, a lot of spectral lines were used (Si III triplet, Si IV, He I, hydrogen Balmer lines). This also involved determining the key stellar parameters of our objects. Our work yielded theoretical profiles of spectral lines that can be compared with observational data.

Thanks to a colleague Dr. Anna Aret, who is also a physicist, I had the opportunity to visit the Chilean Andes mountains and appreciate the breathtaking views they offer. Additionally, the climate of the Santiago Valley caught my attention: despite it being autumn, there were a significant number of clear days with very dry and warm air.

I express my sincerest gratitude to Ignacio for his unwavering care and attention towards me. It was a pleasure to work with him. Furthermore, he provided me with a very good working environment and frequently drove me to and from the office in his car.

I arrived at the observatory in Tõravere on a snowy day. Anna Aret told me that, according to Estonian beliefs, the old man in the sky that controls the weather was showing me what he could do. And certainly, he can make a lot of snow!

I have been working in the observatory for two months. One of the tasks I did was to work with Algol's spectroscopic data. I made the reduction of some of the spectra previously taken in the Balmer's jump region and analysed them using the BCD method. On the other hand, I revised the data taken in Argentina (CASLEO observatory) and selected some examples with different instrumental configurations that would be used to improve the POEMS database. I also had the opportunity to know the telescopes and join an observing night, and attend a day of presentations given by the different departments in the observatory. That included one by Anni Kasivok about the POEMS project. Finally, by the end of my stay, I gave a seminar on my recent work about IR spectroscopy of Be stars with the hdust code.

During those two months, I could be part of the life of the observatory. Eating in the canteen, attending seminars and meetings, and walking around the neighbourhood were part of the routine. I also had the incredible good luck of catching very intense northern lights. I had never seen it before, and it was an amazing experience! The photos have been taken by Veronika Mitrokhina, who was observing that night.

When there were no more traces of snow, and the dark nights started to dilute, it was time to return home. I really enjoyed seeing how the weather changed in those two months, and I am very thankful to all the people in the Department of Stellar Physics who welcomed me.

I was invited by Dr. Michaela Kraus to work for two months in Ondřejov. During this period, I worked on topics related to the molecular environment of symbiotic systems and B[e] stars, and also on photospheric CO absorption bands.

Firstly, I analyzed a high-resolution infrared spectrum (R∼45 000) of the symbiotic star BI Cru. The aim of the project is to model the CO emission in the H- and K-band, using the code developed by Michaela Kraus to derive physical parameters of the circumstellar disk such as density and temperature, as well as information on its kinematics.

On the other hand, this secondment was really enriching since it prompted the study in the H-band of nine symbiotic systems, eight of which had already been previously analyzed in the K-band with SOAR/OSIRIS (R∼3000). This process was completed thanks to the link Michaela Kraus created with Michalis Kourniotis’s work. Using synthetic spectra generated with MARCS model atmospheres, I estimated the effective temperature and performed a spectral classification for the cool companion of the symbiotic star. All this work has been written into an article submitted to the journal Galaxies for publication in the Special Issue: Theory and Observation of Active B-Type Stars.

Apart from this, I attended the monthly Journal Club in Ondřejov and the Seminar in the Stellar Physics Department. Also, I gave a talk about the work I have been doing with Dr. Lydia Cidale, titled “Resolving HD327083”, at the same seminar.

Regarding the experience of living two winter months in Ondřejov, I had only one concern: not to slip on the snowy roads! But every time that concern appeared, it was quickly dismissed. I really enjoyed walking up the road on the hill to get to the Institute, with the only accompanist the wind singing through the trees or the sound of my footsteps on the snow. Every day, walking through the deep silence of the forest brought this phrase in my mind: "Enjoy the silence", just like the name of the song... so I can sum up my stay in Ondřejov as a “Depeche Mode Experience”.

Here I leave some photos that I took, where you can see the beauty of the landscape and imagine the soft sound of the wind.

As I mentioned before, my stay in Ondřejov was enjoyable and very productive. I want to thank all the members of the Stellar Department, especially Michaela Kraus and Tiina Liimets, who organized my arrival at the Institute with great warmth. I would also like to thank Mauricio Cabezas, who shared his office with me, for his kindness and camaraderie.

I stayed in Ondrejov for two months. During this period, I worked on topics related to the database ISOSCELES (Grid of stellar atmosphere and hydrodynamic models for massive stars), the first grid of synthetic data for massive stars that involve both the m-CAK hydrodynamics (instead of the generally used beta-law) and the NLTE radiative transport. Currently, we use this grid to derive the physical parameters from massive stars.

These topics are mainly:

• Work on the manuscript about ISOSCELES. This work included improving some line spectral fittings, developing a way to estimate the best-fitting parameters’ uncertainties, testing the algorithm that finds the most suitable model, and writing the manuscript.


• Improve and expand the ISOSCELES grid. This included planning new Fastwind models using its latest version (this version contains lines in the UV range), updating Hydwind code (now available the version 3.3 with the corresponding manual), preparing the scripts to execute a new ISOSCELES grid with other metallicities (LMC and SMC) with the latest versions of Hydwind and Fastwind.
  
  

I also participated in the monthly journal clubs, one in Prague and the other in Ondrejov (where I presented a paper). In addition, I gave a talk about my research titled “Massive stars and their hydrodynamic wind regimes” at the seminar at the Stellar Department

I had a wonderful stay in Ondrejov. I remember arriving at night with very heavy rain, and in the morning, I woke up with a beautiful view; everything was snowy. Also, I will always remember the fantastic sunsets from my window.

I tried every day a variety of Czech dishes at the canteen. Moreover, I attended the Institute's Christmas lunch and the Stellar Department's Christmas party. Also, I spent New Year's Eve in Ondrejov with people from the POEMS team. It was a fantastic night. First, we met at Dr Tiina Liimets’ home, and then we saw the fireworks near the old radiotelescope.

Overall, my stay was enjoyable. I want to thank every Stellar Department member, especially Dr Michaela Kraus, who organised my arrival and every aspect of my visit. I would also like to thank Dr Tiina Liimets, who shared her office with me.

During my stay at La Plata National University, I worked mainly with Dr. Lydia Cidale and Dr. Yanina Cochetti on two different projects involving B supergiant stars. The first project is a collaboration with Dr. Peter Nemeth from ASU, Matías Ruíz Díaz from La Plata National University and Dr. Elisson Saldanha da Gama de Almeida from the University of Valparaíso in which we combine the analysis of the spectra with CMFGEN and TESS light curves with numerical simulations of the evolution, internal structure and oscillation of B supergiant stars at different evolutionary stages to explore the physical parameters involved in the evolution of these objects. For this project, I had constant scientific discussions with Dr. Cidale with whom we analyzed and interpreted the frequencies derived from the TESS light curves with different methods (Fourier and Wavelet transforms) for a set of B supergiant stars. Additionally, I started a collaboration with Dr. Cochetti and Dr. Aidelman (from La Plata National University) to study stellar oscillations in several cluster members with the aim to detect and analyse a possible relationship between stellar oscillations and the Be phenomena for different cluster ages. We worked side-by-side with Dr. Cochetti developing scripts to download the target pixel file from TESS, creating the light curves and analysing the periodograms for every cluster. We expect to move forward in this project for my next secondment on April 2023.

Additionally, I attended scheduled seminars organized by the Faculty of Astronomical and Geophysical Sciences and the on-line POEMS meeting. I participated, as well, in a workshop for Argentinean female astronomers living in different countries aimed to support, help and exchange experiences about living and working abroad.

I’m really grateful for the warm welcome I received from my former colleagues. It was great to see them again after difficult times during the pandemic. I could enjoy the Argentinean food again and the happy atmosphere during the football world cup championship. Summarizing, it was fantastic and I’m looking forward to coming back soon!

On 31/10/2022 I started my 3-months stay in Göttingen. During my stay I worked at the Institute for Astrophysics of the Georg August Universität with Prof. Dr. Wolfgang Glatzel and my colleague Aldana Alberici Adam (also from UNLP and a member of the POEMS collaboration).

One of the main objectives of the visit was to learn about stellar pulsations, both their underlying physics and the best numerical methods to calculate the pulsation modes. To this end, Dr. Glatzel gave a series of lectures, a more detailed and extensive version of the lectures he presented in La Plata, Argentina, during the Pulsations Along the Stellar Evolution School organized by POEMS in 2019. In parallel to these classes we analyzed the theoretical pulsation modes of a set of supergiant B stars that have light curves observed by Transiting Exoplanet Survey Satellite (TESS) and for which we have a vast collection of spectra, in order to compare the observed photometric and spectroscopic variability with the latest calculated models. Unfortunately, 3 months were not enough time to develop a robust and reliable strategy to carry out this plan, but we will soon have the first results.

Few days before the end of my secondment I observed (in remote mode) the spectra of about 10 blue supergiant B stars during 5 nights from 20/01/2023 to 25/01/2023 with the 2.15 m telescope Jorge Sahade located at the CASLEO observatory in Argentina. Some of those stars have been observed in the same period by TESS so we will have simultaneous light curves to our spectra.

During that time I got to know a lot about Germany, its culture, its forests and its history. I visited several cities such as Berlin, Hamburg, Munich, etc., its museums, cathedrals and squares, enjoying its landscapes and its food.

On 27/01/2023 I said goodbye to Germany and Europe. It was an amazing experience and I’m looking forward to applying all the knowledge I acquired.

My stay in Göttingen (Germany) was 3 months. During that time I was able to work with Dr. Wolfgang Glatzel at the Institute of Astrophysics of the Georg-August-University of Göttingen.

The main purpose of my visit was to train me in the theory of stellar pulsations. During the months of November and December 2022, I attended with my colleague Matías Ruíz Díaz (who is also part of the POEMS group) to the theoretical classes given by Prof. Glatzel. He explained us the theory behind his code for modeling stellar pulsations and we saw practical examples of how to interpret his results. In January I started working with Dr. Glatzel on the modeling of a group of supergiant B stars, looking for non-adiabatic linear pulsations. The purpose of this work is to compare the theoretical results obtained from the models with the results from a photometric periodicity analysis to determine periods and quasi-periods, which could be associated with pulsation and/or binary phenomena. For this, light curves obtained by TESS and analysis tools such as the WaveletComp and Period04 packages were used. In addition, the theoretical pulsation modes will be compared with the observationally detected frequencies, which will allow us to estimate a theoretical mass for these stars. In the future, we will be able to compare the theoretical mass with the mass derived from photometric or spectroscopic techniques in order to discuss the mass discrepancy problem. The results of this work will be published in an article called "Variability in B-type supergiant stars: theoretical and photometric analysis for period detection", with the collaboration of Dr. Lydia Cidale and Dr. Alejandra Christen.

Also during my stay I was working on a paper called "Design of synthetic light curves of pulsating binary stars to compare the efficiency in the detection of periodicities" together with Dr. Lydia Cidale, Dr. Alejandra Christen and a colleague from the University of Valparaíso, Gunther Avila. In this paper we propose a simulation design of pulsating binary stars to study how the different simulated phenomena are reproduced in a scalogram, using wavelet analysis, and in a Fourier periodogram. This paper is about to be submitted to the journal Galaxies.

During the weekends I was able to visit different cities in Germany, such as Hamburg, Berlin, Munich, and Erfurt. My experience during this stay was great! It was my first time in Europe and I improved my English level a lot. Germany is a very beautiful country and the people are very friendly. I want to thank the POEMS project for allowing me to do this training, especially Dr. Wolfgang Glatzel, for his patience and kindness all the time. I also want to thank the people I met at the Institute during this visit, who made my stay so much warmer. I hope to see you all again!

I visited Valparaiso for a two-month secondment to learn about a variety of tools used in quantitative massive star spectroscopy. The main aim of my visit was to develop a wrapper code for the CMFGEN model atmosphere program and apply wind models in an existing iterative spectral fitting procedure. This task was performed under the supervision of Prof. Michel Curé and I worked closely together with Dr. Elisson de Almeida. We were able to complete the task and at the end of my visit, we started a publication based on the results from the new method for 3 B-type supergiant stars.

Beyond the major work with CMFGEN, I have also learned about:

• self-consistent hydrodynamic wind velocity structures and their calculations with the HYDWIND code from Prof. Michel Curé.


• calculation of massive star spectra with the FASTWIND code from Dr. Ignacio Araya.


• radiative force calculations with the LOCUS code from Dr. Felipe Figueroa.
  
  

Once these codes will be applied concurrently, they will provide a deeper understanding of massive star atmospheres, and the details of mass loss, and offer a method to model massive stars self-consistently with a reduced number of free parameters.

I have given introductory classes and discussed some practicalities regarding the hydrostatic NLTE model atmosphere code Tlusty.

The Institute for Astrophysics of the University of Valparaíso (UV) is also hosting strong research on evolved and compact stars. I had regular meetings with Dr. Maja Vuckovic and Larissa Amaral to discuss the current topics in hot subdwarf and white dwarf research.

Besides work the two-month stay allowed me to explore Valparaíso, Vina del Mar, and Concon. The bay has many historical and natural landmarks, as well as plenty of cultural events. The miradors of Valparaíso offer beautiful views over the Pacific, showing different colors every time one visits, and require just a short walk from the office.

Seeing the turn of the seasons from spring to summer, November was the best time to visit, when the entire town has dressed in flowers. The waves, grills, and cafes of Vina. The sand dunes of Concon and the uncountable number of hills and colorful homes of Valparaíso, the elevators, the ocean breeze, and the hospitality of the town and its residents are there to welcome visitors or secondees. I am looking forward to visiting again and continuing our collaboration.

When I arrived in Prague, I immediately left for Turnov to participate in the POEMS workshop from September 28 to October 4, 2022, to discuss new results and strategies to motivate more substantial collaboration with our POEMS team. My talk was about the different methods and problems for deriving stellar parameters. As a result of this meeting, interesting new topics emerged that are now pillars of our future work.

During my two-month visit to ASU, I could share and discuss methods, results and new developments with my colleagues and students. In addition, I worked closely with Dr Michaela Kraus on 55 Cyg. The IR lines of this object show spectroscopic oscillations on a different time scale. The perturbations show cycles of 11-12 days and 19-25 days; the latter is similar to that we found from optical data (22.5 days) taken between 2009 and 2013. From the NIR observations taken in 2015, we derived a higher mean mass-loss rate (almost by a factor of 2) than the one obtained in 2013. Interestingly, we also found that the profile shape of the Hu14 line sets constraints on the mass loss. In addition, we discovered the NIR Mg II doublet in emission, suggesting the presence of a circumstellar ring or shell. A second work deals with the evolutionary status of HD 327083. Our group obtained an orbital period of ~107 days and derived the orbital parameter of this star. We rule out the star is a B[e] supergiant, although it is a hot evolved object. With Dr Michaela Kraus, we rediscussed the CO fittings to our high-resolution spectra and the model parameters. I also discussed joint research work with Dr Catalina Arcos, Dr Julieta Sánchez Arias and the graduate students Lorena Mercanti, Matias Ruiz Diaz, and Natalia Machuca. We modelled spectra of the P Cygni star, the S73 supergiant, and other blue supergiants to find a link between the mass-loss rate and their pulsations. I also had exciting discussions with other team members and learned new codes and tricks.

On October 12, the Argentina Ambassador invited Matias and me to visit the Embassy in Prague. We were happy to share with them the scientific goals of our visit to ASU and our progress.

We had a good time at the “Pietro” Restaurant. Also, we celebrated many birthday parties and au revoir meetings with our colleagues, organizing picnics and grilled sausages in the forest.

During the weekends, I visited the “Hrad Valdštejn”, the incredible Czech paradise in Turnov, the impressive Sedlec Ossuary in Kutná Hora, and the wonderful Prague city. In addition, I enjoyed the trekking activities around the ASU forest and the unexpected snow of mid-November that suddenly changed the landscape. I was delighted by this visit and happy to meet my dear colleagues again after the long pandemic. I thank the POEMS team for this fulfilling interaction and splendid time together.

In the first month of my scientific visit, I participated in spectrum reduction classes with IRAF on the example of spectra obtained with the 1.5 m telescope AZT-12 of the Tartu Observatory with a long-slit spectrograph in the Cassegrain focus, providing spectral resolution of R~100 to 12000. The classes were conducted 5 days a week under the guidance of the head of the Department of Stellar Physics, Associate Professor Anna Aret.

In the second month of my scientific visit, I engaged in IRAF reduction of spectra with Dr. Anna Aret and Tõnis Eenmäe obtained with the 2 m telescope of Shamakhy Astrophysical observatory by using a fibre echelle spectrograph ShAFES, in spectral range λ3700-9000Å, with spectral resolution R=28000 and R=56000.

During my visit, I participated in scientific seminars and meetings of the Tartu Observatory. In particular, I had a seminar on "Non-stationary processes in supergiant stars of spectral class B and A" at the Tartu Observatory scientific seminar.  

I can mention that my scientific mission was very successful thanks to the friendly and business-like staff of the Tartu Observatory, especially Dr. Anna Aret. I also enjoyed the peaceful nature of Tartu city, colorful autumn and snowy winter scenery.

During this exquisite visit, I worked modeling observational data of massive stars observed with FEROS spectrograph. I found their stellar and wind parameters using the synthetic spectrum that best fit the data. For this purpose, I used the ISOSCELES grid of models (hosted on the servers of the Universidad de Valparaíso) and the code I developed for my master thesis to find the hydrodynamical model that most resembles the observational data using a chi-square test.

I also attended scheduled seminars and the POEMS Workshop 2022, in Turnov, and contributed with the talk “Hydrodynamical solutions in spectral analysis”.

One of the most enriching opportunities was to learn from other visitors with whom I also collaborated and had the most enjoyable times. I worked with Professor Lydia Cidale in the study of a specific wind parameter; with the doctoral student Matias Ruiz, to study two stars observed with CASLEO; and with Lorena Mercanti, for the same purpose of finding models for the star P-Cyg observed in multiple epochs.

In the last week, I manage to write two programs to read Olya Maryeva's grid of synthetic models, created with CMFGEN code and hosted in ASU servers, and to compare these models with observational data. The code can find the model that best resembles the spectrum of a given star.

Finally, I had the opportunity to visit Prague, several times, and enjoy the beauty of this country in terms of nature and urbanism. I thank all my colleagues for making me part of this amazing group and for the amazing experience, I can't wait to come back!

During the first month, I worked with frames from photometric observations of the Cyg X-1 star. Since the second month, IRAF classes have been held five days a week under the leadership of Dr. Anna Aret. I had a seminar on my dissertation work during my visit.

I enjoyed the quiet environment of the Tartu observatory and looked forward to seeing the deer and squirrel every day. Friendly co-workers helped me master the place faster.  

I spent the weekends walking around the city, enjoying the peaceful nature and delicious food. I visited Tallinn and was amazed at how to the city has preserved its past so well. I hope to be able to come here again in the future.

I was at the Tartu Observatory of the Estonian Republic from 01 September to 28 November in the framework of Horizon 2020. During the visit, I discussed the investigation of massive stars in collaboration with astronomers from Tartu Observatory and Shamakhy Astrophysical Observatory (ShAO). The results of the spectral investigation of star beta Lyr were discussed. These results were reported at the Tartu Observatory seminar.

During the visit, I was acquainted with the telescopes of the Tartu Observatory and the methods of processing and obtaining spectral and photometric observations at this observatory. The opportunity for simultaneous observation of massive stars at Tartu Observatory and ShAO telescopes was discussed. During the visit I also discussed visits from ShAO to Tartu and from Tartu to ShAO during the 2023-2024 years. 

At weekends I visited Tartu museums and the old Struve observatory. This observatory was very impressive. I was also at one of the oldest universities in Europe, Tartu University. On weekends I spent my free time, mainly in the nature. The nature of Estonia is very nice.

My visit to Ondrejov started on 02/09/2022 and ended on 31/10/2022. The aim of the visit was to model spectra of B supergiant stars with a P Cygni profile in spectral lines sensitive to the stellar wind, in particular H𝛼. For this task I have a large archive of spectra taken with the Reosc spectrograph in Echelle mode at the Casleo observatory (San Juan, Argentina) by Dr Maximiliano Haucke, Dr Lydia Cidale and myself, from 2006 to 2022. The range of most of these spectra is from 4200 to 6650 Angstroms. The tool of choice is Fastwind, which in addition to the lines most affected by the wind allows modelling lines of photospheric elements such as Helium and Silicon. This is important because some of the stellar parameters I want to measure are not affected by the wind. For this task I found a lot of help from Dr. Cidale and Dr. Kraus, who helped me to understand how the changes in specific parameters affect some specific line profiles and how Fastwind works. Also Natalia Machuca Arroyo helped me by using her code to find the best fits in the ISOSCELES (GrId of Stellar AtmOSphere and HydrodynamiC ModELs for MassivE Stars) to compare the results

At the end of my stay I started measuring periods from TESS lightcurves of three B supergiants with WaveletComp and Period04, in order to compare the measured periods with those predicted by theoretical models. This is a work in progress under the direction of Dr. Sánchez Arias and collaboration of Drs. Nemeth, de Almeida, Haucke and Kraus.

During my visit the POEMS workshop at Turnov, Czech Republic, took place. I contributed to the workshop with two presentations: the first was a practical demonstration of the WaveletComp package for measuring periods in light curves of supergiant B stars, and the second was a short reduction recipe of observations taken with the CASLEO Observatory's Reosc spectrograph. The questions and advice I received from those who attended these presentations allowed me to resolve my own doubts and devise strategies to improve my skills in both areas.

On a personal note, this was an excellent first experience overseas. The Czech Republic is a beautiful country, with an inescapable importance for the history of astronomy. I was able to enjoy beautiful landscapes and historical sites together with my friends from the Stellar Department.

We also enjoyed, together with Dr Lydia Cidale, a fruitful meeting with the Argentinean ambassador in the Czech Republic, Mr Roberto Salafia, who was interested in the state of the POEMS collaboration and the contribution of UNLP researchers to it.

Last but not least I would like to thank all the nice people I met, they made me feel very comfortable on my first trip to Europe. Looking forward to seeing you again!

I spent 2 months at the Ondřejov Astronomical Institute working mainly with Dr. Michaela Kraus on the topic of B[e] stars. I learned about the physics behind this kind of star and the information that we can obtain from measurements over the emission lines. The main idea of my secondment was to study the input models and their respective outputs calculated with the code HDUST. To do this, first I reproduced the model of the main sequence B[e] star studied before with this code (Carciofi et al. 2010), to check if the setting options in the code were working properly. After that, I studied how to use different dust grains and composition models to affect the spectral energy distribution obtained. All models were performed by setting a bi-modal wind model (a high-velocity wind at the stellar pole and a low velocity and high mass-loss rate at the stellar equator) for the gas structure followed by a dust ring. The input parameters were varied to study how affect the observed hydrogen emission lines. With this information, I created several models to study the disk of the B[e] S73. This was done also in collaboration with Dr. Lydia Cidale from UNLP, who was also doing her secondment at ASU.

I also collaborated with the PhD student Lorena Mercalli from UNLP, determining the stellar radius of the star P-cygni by using the multi-fitting tool MUFIN (Arcos et al. 2018).

During my secondment, I participated as a listener in the regular scientific seminars at ASU, and also presented a recent paper on massive stars in the monthly Journal Club organized by Dr. Julieta Sanchez. I did a seminar about my main research topic on Be stars and I participated in the POEMS working workshop in Turnov, presenting talks about the use of the code HDUST, the tool MuFIN, and the TESS pipeline.  

Finally, I enjoyed the beautiful environment around the institute and spend almost all my weekends hiking around the town and eating pizza at Pietro's restaurant. I visited Prague (castle, Charles's bridge, and downtown) and the amazing church made of bones in Kutná Hora.

I have been visiting the Stellar Physics Department of the Astronomical Institute in Ondřejov in the frame of the POEMS project for three months. There I worked with the group Physics of Hot Stars on the investigation of stellar winds and circumstellar disks of B[e] supergiants. This research forms part of my PhD project. One primary task in my research consists in the fit of synthetic line profiles to observed spectra. So far, I focused on a small selection of supergiants and luminous blue variable stars. The exchange with the members of the institute and fellow guest researchers allowed me the implementation of different methods and the development of new tools that complement the code I use for the line profile modelling. For example, during my secondment, I learned a method for constraining the stellar radius (a fundamental input parameter for our model) based on different observational data sets with Dr. Catalina Arcos.

Another activity during my visit has been the development of a program for calculating Ca II populations. This code can be used in the program that considers the presence of a stellar wind or can be incorporated into existing codes that assume the presence of circumstellar rings. Preliminary results suggest that both features, the stellar wind and disk, have to be included in order to explain the line profiles observed in one of the B[e] supergiants I work with. The intensive and fruitful interaction I had with the head of the project and the local group, Dr. Michaela Kraus has been very valuable to promote my research activities.

In addition, I participated in the POEMS workshop in Turnov. This workshop extended over four working days with presentations and demonstrations of tools and codes. Towards the end of my stay in Ondřejov, I presented a seminar with the title: "Research activities within the framework of POEMS and PhD projects". Furthermore, I joined Dr. Olga Maryeva in an observation session with the Perek 2 m telescope. I attended the lecture given by M.Sc. Mauricio Cabezas on Data Reduction of echelle spectra using IRAF, within the framework of the Workshop on Observational Techniques 2022 organized by the ASU Stellar Physics Department. Spectrum analysis is an important part for my research and PhD activities.  

I am very grateful for the warm reception and permanent support, for all the shared knowledge and for this great opportunity to advance with my research, to get to know the culture and nature in Czech Republic and to build personal bonds.

During my second secondment to University of Valparaiso (UV) I explored possibilities to create data processing pipelines for CASLEO REOSC Echelle spectrograph and also other Echelle spectrographs (ShAO, ASU, coming TO one) and found a couple of promising and customizable codes for that. Most of the time I worked on the programs to submit raw observational data properly into the POEMS database, having accent on CASLEO data - because UNLP has large amount of Echelle spectra from that observatory. That work was almost finished.

In addition, I participated regularly in astrophysics seminars that take place every Friday at UV.

During my three month stay in Valparaiso, I worked with Prof. Michel Curé in the field of winds of massive stars. In the first month, I followed the book on Stellar Winds by H. Lamers and J. Cassinelli and learned the basic (mCAK) theory of radiation driven winds. Then, through various papers by M. Curé, et al. I learned about the new omega and delta slow wind solutions for massive stars. Through the second month, I simulated these winds using the stationary code HYDWIND and the time evolutionary code ZEUS3D. The aim was to obtain various quantities like the stellar mass loss rate, the terminal velocity, and the variation of the hydrodynamic quantities with distance and time. Finally, in the third month, we tried to simulate these winds with the 3D MHD code FARGO3D, and study the interaction regions of the winds with the interstellar medium, which is still in progress.

I also presented a review talk in the Institute of Physics and Astronomy seminar at the University of Valparaiso titled “Astrospheres: Stellar Wind Bubbles as Borders to the Interstellar Medium,” in which I discussed various old and new models of the heliosphere and trying to establish a connection of the same with the observations of the Voyager spacecraft.

During the weekends, I enjoyed the scenic beauty and the culture of Valparaiso and traveled to a few cities nearby. I loved my stay in Valparaiso, and am looking forward to future collaborations.

During my second visit to the Astronomical Institute in Ondřejov, Czech Republic, I continued the work initially started during my stay there in 2019. This work is devoted to study the photometric and spectral behavior of the young massive star WW Vul of the Ae/Be Herbig type, which is still pre-main-sequence object. Since my first visit, a lot of photometric data were accumulated with FRAM (collaborative effort between ASU and FZU) and Mini-MegaTORTORA telescopes. I thank Sergey Karpov who maintains the archives of both of these telescopes and performed observations on FRAM telescope. Light curves and their possible variations are constructed using photometric data. The color–magnitude dependence, the “bluing” effect, and other features of the behavior of the star WW Vul have been studied. For study of spectral variability of WW Vul public archival data were used, besides spectral material obtained at ShAO.

Moreover, I took part in regular observations at the 2-meter Perek telescope of ASU, joining the observing nights with Olga Maryeva. The spectra of other young massive stars were also obtained within the framework of the POEMS program. It was a useful experience for my further work, and data obtained during the observations will be essential for future studies.

It was interesting for me to visit Charles University to attend the "Ph.D. student annual conference" and to see how the future astronomers of Europe start their careers. As part of this visit, I not only enriched myself with knowledge of various aspects of astronomy, but also visited the city of Prague and other attractions of the Czech Republic. I would especially like to thank Michaela Kraus and Olga Maryeva for including me both into the scientific and free time activities.