Browsing by Author "Pilecki, Bogumił"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    In-depth Investigation of a Type II Cepheid in a Binary System
    (2025) Oyarce Leal, María Laura; Catelan, Márcio; Pilecki, Bogumił; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
    Type II Cepheids are old, low-mass variable stars that are essential for mapping old stellar populations, thanks to their greater brightness compared to RR Lyrae. They play a key role in calibrating cosmic distances. OGLE-GD-T2CEP-0178, a type II Cepheid located in the Galactic disk, is part of an eclipsing binary system, which allows its mass to be directly measured and to study its evolutionary status.The main goal of this thesis was to determine the masses of OGLE-GD-T2CEP-0178 and its companion and to characterize the binary system. Spectroscopic data obtained with HARPS and photometric data from six surveys in different bands were used. Through light and radial velocity curves modeling with PHOEBE, the physical parameters of each component and the key orbital parameters of the system were derived.The results reveal that the binary system (P_orb=81.72 days) is composed of a type II Cepheid with a pulsation period of P_puls=3.833 days, a mass of M_ cep=1.16 +- 0.09 Msun and a radius of R_cep=14.12 +- 1.73 Rsun, along with a more massive companion of M_ comp=5.5 +- 0.3 Msun. The system also has a disk with a radius of R_disk=174 +- 42 Rsun. The complexity of the system suggests that some companion parameters could be underestimated.These results support the hypothesis that the current Cepheid underwent a past mass transfer event during which it lost part of its hydrogen envelope. As a consequence, the Cepheid's pulsation properties may have been affected. To confirm this scenario, a detailed binary evolution analysis must be performed to understand how mass transfer shaped the system's current configuration.
  • Thumbnail Image
    Item
    Properties of RR Lyrae variables in binary systems: towards a first-time mass measurement
    (2022) Hajdu, Gergely; Pietrzyński, Grzegorz; Catelan, Marcio; Jurcsik, Johanna; Karczmarek, Paulina; Pilecki, Bogumił; Thompson, Ian
    Despite their general usefulness as distance indicators and tracers of old stellar populations, several properties of RR Lyrae variable stars remain poorly understood. Crucially, the most basic stellar parameter, the stellar mass, has never been measured for any member of this class. We performed a new search for RR Lyrae variables in binary systems, looking for the light travel-time effect in the long-term light curves obtained by the OGLE project toward the Galactic bulge, finding 87 high-confidence candidates. The distributions of the inferred properties of these binary systems are quite peculiar: no system has a binary period below 1000d, and their frequency peaks between 3000 and 4000d; their eccentricities are strongly concentrated around 0.27; and their mass functions are apparently trimodal. Supposing an isotropic inclination distribution, and a mass of 0.65 times solar for a typical RR Lyrae, these three modes point to typical companion masses of ~0.6, ~0.2 and ~0.067 solar masses. These can be attributed to a combination of main sequence and white dwarf, red dwarf, and brown dwarf companions, respectively. As RR Lyrae variables are evolved from (close to) solar mass, Population II main sequence stars, their binary parameters provide a unique glimpse into the binary properties of the old stellar population. These properties seem to be wildly different from those of Population I binaries. The difference in the distribution of binary periods can be explained tentatively by binary stellar evolution and selection effects. However, the distribution of eccentricities, and especially the trimodal companion mass distribution is in stark contrast to Population I binary parameters of solar-type stars, requiring further observations to confirm, and theoretical efforts to explain them. Finally, the observed binary properties inform us on the prospects of both finding and RR Lyrae variable in an eclipsing binary system, as well as on the possibility of obtaining an astrometric mass measurement using observations of the Gaia satellite....