# Stellar work

Photos and diagrams courtesy of Victor Ramirez Delgado | Video by Jeffrey C. Chase

## UD’s Ramirez Delgado studies the wobble of red giants

Editor’s note: Research, community service, internships and study abroad typically make summers memorable for many University of Delaware students. While the coronavirus (COVID-19) pandemic sidetracked some of these activities, UD students continued with hundreds of remarkable projects remotely. Check out our series of profiles and stories, which also are being highlighted on the Summer Spotlight website.

Victor Ramirez Delgado is a physics major and a student in the Honors College from Caracas, Venezuela. He has a concentration in astronomy, a minor in mathematics and is on track to graduate from UD in spring 2021.

Q: What are you studying and with whom?

Ramirez Delgado: I am studying the radial velocity variations of the star Gamma Draconis with the objective of developing a mathematical model to describe it. Gamma Dra is a red giant star, about 1.7 times the mass of our sun and 600 times brighter, located 154.3 light years away from Earth. My project focuses on studying its radial velocity, which is a measure how much it moves with respect to our point of reference here on Earth. It is one of the methods most used by astronomers to detect planets orbiting other stars, known as exoplanets or extrasolar planets. Ultimately, the goal is to develop a mathematical model — using a machine learning algorithm called Gaussian process regression — to analyze the data we have on the star and determine what is causing its changing radial velocity. I have been studying this star at UD since the fall of 2019 with my mentor, Sarah Dodson-Robinson, associate professor of physics and astronomy.

Q: What inspired this project?

Ramirez Delgado: The inspiration to study this star comes from the fact that it was previously reported to have a planet, with a mass of around 10 times the mass of Jupiter, orbiting around it. However, after further investigation it was determined that the signals present in the radial velocity of Gamma Dra were coming from stellar variability, instead of coming from a planet. This stellar variability is associated with changes in brightness due to the star’s internal activity; natural processes like the star’s rotation, the magnetic activity at the surface and other factors can contribute to the stellar variability measured. The signals coming from these sources are an issue when trying to detect planets around a star, because they can masquerade a planet that does not exist due to their periodic behavior. Gamma Dra is not the only star where the detection of what appears to be a planet is caused by the activity on the star’s surface. My advisor, Dr. Dodson-Robinson, along with a group of students and faculty at UD studied the similar case of Kapteyn’s Star. The work that I have done is based on many aspects of the principles and methodology they used. Finally, another main source of inspiration comes from the idea that by being able to develop a mathematical model for this star, we could learn much more about the unpredictable nature of stellar activity present on other red giant stars.

Victor Ramirez Delgado is a physics major from Caracas, Venezuela. He has a concentration in astronomy, a minor in mathematics and is on track to graduate from UD in spring 2021.

Ramirez Delgado: I have always been interested in astrophysics and I am hoping to go to graduate school to follow my goal of getting a Ph.D. in this area. Therefore, this project has been a great introduction to the type of work that I could be doing in the future. I think my main source of interest in this area comes from my curiosity for learning more about space and the laws of nature that rule our world and the rest of our universe. It is incredible to realize that there is an unimaginable number of stars, galaxies and mysteries out there, and all we need to do to see them is to look up at the sky. Most important, I think it is fascinating that through centuries of studies we have made such great progress on learning about the universe, while also finding more and more questions that we still have no means to answer. Since the topic of my project is based around finding extrasolar planets, it deeply relates to finding how common it is to find planets around stars, which naturally raises the question about how probable it would be for life to develop in these planets. Overall, the objective of answering these types of questions is one of my sources of inspiration and I am extremely grateful that the work that I do can contribute to this cause.

Q: How has COVID-19 shaped your plans for this project? Is flexibility something that comes easily for you?

Ramirez Delgado: I think the whole situation caused by COVID-19 changed a lot of how I was expecting to work on this project. I was expecting to work on campus and have weekly in-person meetings with my professor, as well as presenting my progress in this project to the American Astronomical Society meeting. Once circumstances changed, I had to move all of my plans online. Thankfully, all of the work I do can be done with just a laptop since we are using measurements that we already had at our disposal. My adviser and I have done all our meetings over Zoom, which has not been too much of an issue. Finally, the talk that I gave to the American Astronomical Society was also done using Zoom, which was the hardest thing for me so far. I enjoy doing presentations in person by being able to directly look at the audience and it is also easier to ask questions. To make sure things would go as smoothly as possible, I prepared the slides days in advance, checked that everything worked on Zoom and practiced the presentation many times. At the end I was pleased that everything worked and that my first talk went very well, even when it happened during these chaotic times.

Q: What are the possible real-world applications for your study?

Ramirez Delgado: The findings on this project can be a great tool to confirm extrasolar planet discoveries around red giant stars. If the model we used can describe the behavior of stellar activity, it might tell us more about how often and how strong the activity in the surface of Gamma Dra occurs. Therefore, it could be possible to use similar models in other red giant stars to subtract the noise caused by these effects, and what remains would be mostly signals that are caused by the motion of a planet around the star. These would greatly improve the effectiveness of the radial velocity method, allowing us to ease the discovery of new exoplanets and confirm previous possible planet detections.

Q: How would you explain your work to a fifth grader or someone’s grandparent?

Ramirez Delgado: I would start with the basics. First, the stars that we see in our night sky are very much like our sun. Some are orbited by planets, just as our sun is orbited by the Earth and the other seven planets in our solar system. We can find out if those stars are orbited by planets by looking at the star’s “colors,” known as spectral lines, to see if the star “wobbles.” When a star moves, its spectral lines shift positions based on our point of view. When the star moves toward us, the colors become “bluer” and when it moves away from us, they become “redder.” With this information we can determine how much it wobbles, and that wobbling can be caused by a planet.

Astronomers can detect “wobbles” in a star’s motion by analyzing the rainbow of light produced as it moves toward or away from us. Sometimes wobbles are caused by natural processes on the surface of the star. Sometimes they are caused by the gravitational tug of an orbiting planet.

I am studying the star Gamma Draconis, a red giant star that is almost twice as heavy as our sun and more than 40 times larger. We previously thought that a planet bigger than Jupiter was causing the wobbling on Gamma Dra, but it turns out that what appeared to be a planet was caused by the star itself. The surface of a star is filled with activity, because of the high temperatures and events that happen inside of it. These events happen naturally and since the star is so far away from us, we do not know how to differentiate whether the changes on the spectral lines come from a planet or from an event at its surface. Therefore, I use the data on Gamma Dra and a computer program to describe what is happening on the surface of the star. This could help us get rid of all the noise that comes from a star when we look for planets around other stars like Gamma Dra.

Q: What advice would you give younger kids (middle school or high school) with similar interests?

Ramirez Delgado: I would advise them to follow what they are passionate about and to not get discouraged by what other people think. Back when I was in Venezuela, people could not understand the idea that I wanted to be a physicist. In my country most people didn’t see a career like physics as a successful path because of the lack of opportunities for the natural sciences. In my country there is not a vision of the importance of the natural sciences and how all the research that is done in these areas can change people’s lives for the best. However, I was certain of what I wanted to do and the things I wanted to accomplish. My message to any student that is interested in physics, astronomy or any career in general, is that I encourage you to continue doing what you enjoy and to put all of your effort on it. The path will not always be straightforward and there will be times when things seem to be going nowhere, but trust me when I tell you that as long as you keep your conviction and you keep your vision of what you want to achieve, you will find the means to always move forward. I believe that as long as you keep your mind open to learn something new and to keep asking the questions that fill you with curiosity to understand our world, you will come to understand why you should follow your passion for science.

Q: Have the changes required by the pandemic changed your perspective on anything? Would you share an example or two

Ramirez Delgado: The whole situation has taught some important lessons about being able to adapt to unexpected situations and how to deal with the uncertainty of not knowing what will happen in the future. I think about how before COVID-19 hit the United States, I had many expectations of things I wanted to do during the semester and during the summer. I thought about the many times I would hang out with my friends, about doing research on campus and making the most of my time before the start of my senior year. Unfortunately, once the pandemic arrived in the U.S., all those plans changed to a spring semester with classes online, to spending months of lockdown at home with my parents and to living with the uncertainty of not knowing when and under what conditions I will go back to UD. Although things did not go as I imagined, that is not a reason to throw in the towel. I just learned that I had to adapt to this new situation and make it as manageable as possible, without forgetting the goals I want to accomplish. This situation took the whole world by surprise and the issues that we are experiencing in the U.S. are happening in most countries. I see this new perspective as a reminder that if we want to overcome the challenges we are facing right now, we must show solidarity for each other and work together to bring out our best in a time of struggle.

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