arXiv subjects

Joaquín A. Barraza-Jorquera

Publications and source records attributed to Joaquín A. Barraza-Jorquera.

3 recordsLinked to original sources

arXiv2026

Direct detections of white dwarfs in four WD+dM post-common envelope binaries within 20 pc

Characterising post-common envelope binaries (PCEBs) containing a white dwarf and a main-sequence companion is essential for improving theories of binary evolution. This paper presents the first direct spectroscopic confirmations of the white dwarf components in four PCEB systems within 20 pc of the Sun: G 203-47, GJ 207.1, LHS 1817, and Wolf 1130. To detect the white dwarfs we obtained near-UV spectroscopy from STIS on the Hubble Space Telescope, fitting with white dwarf models and M dwarf proxy spectra. We provide estimates of the white dwarf effective temperatures, which range from approximately 5300 K to 6300 K. We compare these parameters to those determined from modelling with photometry alone, and find a 5 - 8 per cent discrepancy, due to emission features. Notably, 27 years after its initial detection, we confirm the presence of a white dwarf in G 203-47, which is the ninth closest white dwarf to the Sun. Using Swift XRT data, we find that despite the 14.9-day orbital period of G 203-47, it is not tidally locked, possessing a rotation period likely exceeding 100 days, and making it a rare example of a long-period PCEB formed via a brief common envelope interaction. We update the local white dwarf space density to (5.2 $\pm $0.4) $\times$ 10$^{-3}$ pc$^{-3}$, and compare our results to models from the Binary Populations and Spectral Synthesis (BPASS) framework, finding a good agreement with the predicted and observed numbers of PCEBs within 20 pc.

astro-ph.SR↗

arXiv2026

A modest change in magnetic braking at the fully convective boundary explains cataclysmic variable evolution

Context. For decades, reproducing the orbital period distribution of non-magnetic Cataclysmic Variables (CVs) seemed to require a drastic decrease, usually termed disruption, of angular momentum loss through magnetic braking at the fully convective boundary, which argued for a change in the dynamo mechanism operating in fully and partially convective stars. However, recent studies showed that the magnetic braking prescription traditionally used in CV evolution theory is clearly outdated as saturation, that is, a weak period dependence for rapidly rotating stars, is not included. Aims. Here we test an updated version of a saturated magnetic braking prescription that has been developed to explain the spin-down of single stars in the context of CV evolution. This prescription contains a boosting and a disruption parameter that represent the change in the strength of magnetic braking at the fully convective boundary. Methods. We performed state of the art MESA simulations for CVs with the revised saturated magnetic braking prescription. Results. As in previous studies, we found that magnetic braking needs to be stronger in close binaries than in single stars and that, in contrast to what is observed in single stars, magnetic braking needs to be reduced at the fully convective boundary. However, in contrast to previous studies of CV evolution, only a moderate disruption by a factor of 2 - 3 is sufficient to explain key features of the CV orbital period distribution and the measured mass-radius relation for CV donors. Conclusions. The relatively small decrease of the efficiency of magnetic braking at the fully convective boundary might have implications for our understanding of dynamo models for fully and partially convective stars.

astro-ph.SR↗

arXiv2025

Further evidence of saturated, boosted, and disrupted magnetic braking from evolutionary tracks of cataclysmic variables

Angular momentum loss through magnetic braking drives the spin-down of low-mass stars and the orbital evolution of various close binary systems. Current theories for magnetic braking, often calibrated for specific types of systems, predict angular momentum loss rates that differ by several orders of magnitude. A unified prescription would provide valuable constraints on the relationship between angular momentum loss, stellar dynamos, and magnetic activity. Recent studies have shown that a saturated, boosted, and disrupted (SBD) magnetic braking prescription can explain the observed increase in the fraction of close white dwarf plus M-dwarf binaries at the fully convective boundary, the period distribution of main-sequence binaries, and the mass distribution of close M-dwarf companions to hot subdwarfs. To analyze whether this prescription also applies to related binaries, we investigated the evolution of cataclysmic variables (CVs) using the SBD magnetic braking model. We implemented the SBD prescription into the stellar evolution code MESA and simulated CV evolution, testing different values for the boosting and disruption parameters over a range of stellar properties. Our model reproduces the observed mass transfer rates and donor mass-radius relation with good accuracy. The evolutionary tracks match the observed boundaries of the orbital period gap and the period minimum for values of boosting and disruption slightly smaller but still consistent with those derived from detached binaries. Angular momentum loss through SBD magnetic braking can explain not only detached binaries but also cataclysmic variables, making it the only current prescription suitable for multiple types of close binary stars. Further testing in other systems is needed, and the semi-empirical convective turnover times currently used for main-sequence stars should be replaced with self-consistent values.

astro-ph.SR↗