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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/223635
Search and study of massive runaway stars in the Milky Way and impact on high-energy binaries
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[eng] Massive stars are ubiquitous in many astrophysical phenomena. A significant fraction of massive stars are runaways, displaying high velocities with respect to their environment. Due to their formation scenarios, runaway stars play a relevant role in cluster and binary physics. However, the relative contribution of runaway formation scenarios, their role in massive binary evolution, and their relation with binary products hosting compact objects (COs) are not well constrained. In particular, some of these binaries with CO can be high-energy sources. Although some studies have been conducted in the Magellanic Clouds, the massive runaway star population in the Milky Way remains poorly explored. The Data Release 3 (DR3) of the Gaia mission of the European Space Agency (ESA) has provided data with unprecedented astrometric precision, allowing us to derive accurate distances and proper motions that are key to identify runaway stars in the Milky Way.
The central aim of this thesis is to improve the understanding of the massive runaway star population in the Milky Way. A secondary aim is to study their connection with high-energy binaries. To achieve these objectives, we developed a novel and self-consistent method to identify runaway stars which avoids the use of velocity thresholds, in contrast to previous works. This allows us to detect runaway stars as well as walkaway stars. The characterization of the runaway stars was done with Gaia-DR3 data, complemented with multiwave- length archival data, dedicated radio observations, and high-resolution IACOB spectroscopic information.
We identified 106 and 69 O- and Be-type Galactic massive runaway stars, with half of them being new discoveries. We characterized their spatial and velocity distributions in the Galaxy. We found higher velocities and runaway fractions for the O-type stars, in agreement with predictions for dynamical ejections from clusters. This work resulted in the compilation of two runaway catalogs, including precise distance and velocity estimates. In addition, we studied the interaction of these runaway stars with the interstellar medium (ISM) using WISE data, discovered new stellar bow shocks and bubbles, and derived ISM densities around them. Radio searches around these bow shocks resulted in no new detections, although the results obtained served to model the nature of their potential radio emission.
We conducted a large and unprecedented observational study of O-type runaway stars in the Milky Way in space and rotational velocities, as well as in binarity classifications, obtained in a homogeneous way. To this end, we combined our runaway star catalogs with IACOB spectroscopic data. We found that most runaway stars appear to be single, confirming theoretical expectations, while most are slow rotators. The trends observed in the investigated parameter space were used to identify potential imprints of the runaway ejection mecha- nisms in the studied Galactic runaway population, offering valuable constraints on models about runaway origins.
We found an interesting sample of runaway binary systems, some of which are high-mass X-ray binaries (HMXBs) or gamma-ray binaries. In particular,
we find an overabundance of runaways among the known gamma-ray bina- ries. Within the O-type runaway star sample, we identified some runaway single-lined spectroscopic binary systems, with half of them being HMXBs or candidates to host black holes. The latter exhibit similar properties to the HMXBs within our investigated parameter space. Altogether, these runaway binary systems represent a rich sample for potentially hosting COs.
We also searched for very-high-energy (VHE) gamma-ray emission from the HMXB Cygnus X-3 with the MAGIC Telescopes. We analyzed the largest VHE data set and found no significant emission. We provided the most stringent constraints on the VHE flux to date, which could offer insights into the system properties.
In conclusion, this thesis has deepened the knowledge of massive runaway stars in our Galaxy. It provides robust runaway star classifications, new empir- ical constraints on runaway formation mechanisms, and interesting runaway binaries potentially hosting COs, which could eventually show high-energy emission. Since massive runaway stars are crucial to many astrophysical phe- nomena, all catalogs compiled in this thesis are openly published to broaden the research impact beyond its immediate scope.
Future larger catalogs of massive stars and Gaia DR4 will enable a more comprehensive study of runaway stars, which could allow the discovery of new high-energy binaries through multiwavelength studies, and potentially refine the observed trends, binary evolution models, and ultimately, the understanding of massive binary interaction.
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CARRETERO CASTRILLO, María del mar. Search and study of massive runaway stars in the Milky Way and impact on high-energy binaries. [consulta: 2 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/223635]