Research Projects
Formation and Evolution of subdwarf B stars
Subdwarf B stars (sdBs) are a well-known class of hot, low-mass stars thought to be formed through interactions in stellar binary systems. As such, their different formation channels and characteristics of the predicted populations depend on the initial set of assumptions that describe relevant physical processes (common envelope episodes, angular momentum loss during mass transfer, etc). My research focuses on trying to find the best possible configuration in order to better predict the observed sdB sample by using the rapid population synthesis code COMPAS. I have noticed that yet another key component is usually poorly described and constrained: the hydrogen-rich remnant in the outer layers of sdBs. While not playing a big role in the orbital evolution, it does significantly affect the atmospheric properties and, therefore, observables such as effective temperature and surface gravity. To bridge the gap between the simplified prescriptions used in BPS codes, I use detailed models built by using MESA.
Related publications: Rodriguez-Segovia, Ruiter & Seitenzahl 2024
Deep Drilling with DECam
This research project is in the context of my involvement in the optical imaging survey of four deep drilling fields (DDFs) with the Dark Energy Camera (DECam) on the 4-m Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO) as a Co-I. Thousands of images per field and 5 to 6 images per night per filter in g, r, i, and/or z are become publicly available.
Prof. Márcio Catelan’s group and I have focused on the analysis of Variable Stars in these fields, particularly during undergraduate and Masters students’ research projects. I have been in charge of processing and managing these data for Prof. Márcio ever since the beginning of this project, which has led to my involvement in several different projects. Most notably, the research led by Karina Baeza-Villagra has recently led to the creation and publication of updated RR Lyrae light curve multiband templates that greatly improve what was previously available in the literature, potentially helping to inform the next generation of multiband classifiers that will be required to fully realize Rubin/LSST’s potential.
While we have explored several different topics using these data, we have focused on a single DDF so far. This, combined with the great amount of images, means that the dataset still holds great potential for future work.
Related publications: Baeza-Villagra et al. 2025, Graham et al. 2023
Period Change Rates in LMC Cepheids
The period-change rate (PCR) of pulsating variable stars is a useful probe of changes in their interior structure, and thus of their evolutionary stages. In this project we derive PCRs for Classical Cepheids pulsating in their fundamental mode, by taking advantage of the long time baseline afforded by the Digital Access to a Sky Century @ Harvard (DASCH) light curves, combined with additional CCD data from more recent surveys. We provide an unprecedented sample of 1303 LMC classical Cepheids with accurate PCRs, the largest for any single galaxy, including the Milky Way. The derived PCRs are largely compatible with theoretically expected values as computed by our team using the Modules for Experiments in Stellar Astrophysics code. Interestingly, we find five long-period (longer than 50 days) sources that display period changes that are incompatible with evolutionary changes. Additionally, two first-crossing Cepheid candidates are identified owing to their fast change rates, which hints at them being Hertzsprung gap stars.
While this project was part of my undergraduate thesis and is no longer my main focus of research, I do re-visit these methods from time to time whenever I find interesting sources with plenty of photometric data available. Also, data for the SMC should now be available in DASCH, which can also be explored.
Related publications: Rodriguez-Segovia et al. 2022, Espinoza-Arancibia et al. 2022