HD 129590: A Binary System with an Exocomet Belt

Abstract

HD 129590 is a stellar system with a directly imaged debris disk located in the Scorpius–Centaurus association, approximately 420 light years away. With an estimated age of 15 Myr, young systems like HD 129590 have been ideal for studying the development and evolution of exocomets and planetary disks at early epochs of star formation, at a time when such structures are just emerging. Consequently, previous literature has afforded attention to the system's debris disk as part of such efforts. However, in focusing on the debris disk, the internal, as well as orbital, stellar parameters remain uncertain. In this thesis, the properties of the HD 129590 system are investigated in order to shed more light on the stellar components. This is achieved through the analysis of archival high-resolution spectra taken via the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph over different time intervals. Visual inspection of the spectra illustrate that the stellar system under investigation is in fact a binary system composed of two stars. The spectra thus display the characteristics of double-lined spectroscopic binaries. To characterise the orbits of the binary stars, double Voigt profiles are fitted over a selection of lines, whose peak positions enable the extraction of the radial velocities of the stars at different epochs. Over these radial velocity measurements, Keplerian orbits are fitted, thereby extracting the orbital parameters for the two stars. The results reveal a highly eccentric system, with a period of approximately 23 days, and a median mass ratio q=1.001 ± 7%. To characterise the internal properties of the two stars, the pySME software is utilised. Through the software, approximately 30 segments within a roughly 1000 Å spectral region are fit for each star in order to obtain parameters such as effective temperature, surface gravity, metallicity, and projected equatorial radial velocity. The results suggest stars on the boundary between a G-type star and an F-type star, with effective temperatures around 6400 K with uncertainties. Finally, a discussion is had with regards to the limitations of the project, as well as to future work that can be performed to better understand this system.

Popular Abstract

Have you ever wondered what stars are made of? How could we even tell? It's not like we can just send a spaceship to collect a sample of the Sun, bring it back to Earth, and study it under a microscope. Thankfully, even if we could, we don't need to go through all of that. Instead, we can study something which is in practically infinite abundance, and readily available to us. That something is starlight. Studying the light from a star in order to determine its properties bears the name of stellar spectroscopy.

Spectroscopy has had its emergence relatively recently. Its beginning as a modern method of scientific investigation can be traced to the scientific revolutions of the 1600s, when light was first split into constituent components by Isaac Newton in 1672. This revealed that white light is a combination of colors. This combination of colors gave birth to the "visible spectrum", a spectrum of colors emerging from the separation of visible light. Sometime later in 1814, the German Joseph von Fraunhofer discovered narrow dark streaks at seemingly irregular intervals running across the spectrum of the Sun, appropriately named "Fraunhofer lines". About half a century later, Gustav Kirchhoff and Robert Bunsen provided the explanation for those mysterious lines. By comparing them with emission lines from laboratory samples, it was revealed that these lines are caused when atoms and molecules from the atmospheres of these stars absorb light from the star, hence more generally these dark features are referred to as "absorption" features.

To the study of the stars, the observations of Kirchhoff and Bunsen were crucial. Light is absorbed at certain wavelengths thanks to the internal structure of atoms and molecules. Light, as electromagnetic radiation, can be thought of as a wave, similar to sound. Light at different wavelengths carries different energies. At the same time, atoms contain electrons in different orbitals, different orbits around the atomic nucleus. But these electrons are not fixed, they may migrate to different orbitals, provided that enough energy is put into them to make that jump. In the atmospheres of stars, such transfers of energy can occur when the light of the star intersects atoms in the stellar atmosphere, leading to the atom's absorption of the photon of light. These absorption energies and wavelengths depend, thus, on individual atoms, allowing us to identify the presence or absence of elements in a star. Furthermore, the abundance of an element can also be measured. The more abundant an element, the deeper and darker the absorption line will be, since there will be more atoms to absorb at that particular wavelength.\\

While normally an element would produce absorption features at certain wavelengths, different properties of the star impact the way the feature appears. For example, if a star were to be moving towards the observer, the emitted light, and therefore its spectrum, would be compressed, while if it was moving away it would be stretched, according to the Doppler effect. This translates into the absorption lines moving to lower or higher wavelengths depending on whether the star is moving towards you or away from you, respectively. Putting together all this, through spectroscopy we can analyse fundamental properties of stars, their orbital parameters such as velocities and period, as well as their internal properties such as temperature and mass.

In this project, I look at multiple high-resolution spectra collected with the HARPS spectrograph for the HD 129590 system. This is a young stellar system, relatively close by, with an imaged protoplanetary disk, which is all the gas, dust, and debris left over from the formation of the stellar system, and which then is in gravitational orbit around the system. From such a disk, it could be that one day planets, perhaps like the Earth, will form, or have already just formed. But to know if this fascinating scenario is worth entertaining, we must investigate first the properties of the system. To that end, I first look at the spectra to confirm the binary nature of the system, where HD 129590 is a pair of stars, embraced in a gravitational dance. As they dance around in their orbits opposite of each other, the Doppler effect splits every spectral line in two, enabling the identification of the binary. This line splitting further enables the calculation of the radial velocities of the two stars from the wavelength shift, which I use to characterise the orbital system of the binary stars. Lastly, I fit synthetic spectra of model stars over the observed spectra to see which models match best with the data, enabling me to determine the effective temperatures, metallicities and elemental abundances of my two stars.

In the long run, describing the properties of the stars in the system will enable deeper study of the system as a whole, with its protoplanetary disk, and how such disks may evolve under the influence of their stars. Crucially, since planets are thought to emerge from such disks, young systems like HD 129590 are ideal. Their age enables astronomers to study systems at ages at which planets are thought to first develop, bridging a gap not just in general knowledge, but in the knowledge of our own system. Understanding such young systems can offer clues as to the Solar System's own evolution, and perhaps to the birth of our own planet Earth, and the subsequent emergence of life therein.

• author: Slaniceanu, Sofia
• supervisor: Aline Novais; Jens Hoeijmakers
• organization: Department of Physics; Astrophysics
• course: FYSK04 20261
• year: 2026
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: HD 129590, Binary stars, Spectroscopic binaries, Stellar spectroscopy, pySME
• report number: 2026-EXA255
• other publication id: 2026-EXA255
• language: English
• id: 9240944
• date added to LUP: 2026-06-19 17:46:01
• date last changed: 2026-06-19 17:46:01