arXiv subjects

Vladimir Bozhilov

Publications and source records attributed to Vladimir Bozhilov.

8 recordsLinked to original sources

arXiv2026

A Catalog of Homogeneously Derived Stellar Parameters for Spectroscopic Survey Stars

Uniformly derived stellar parameters are vital for exoplanet demographic studies because they directly influence the inferred planetary masses, radii, and bulk densities. This study presents a new homogeneous catalog of physical stellar parameters for 5533 single stars observed by the HARPS, HIRES, and CARMENES radial-velocity (RV) surveys. Stellar parameters are determined using a Bayesian framework with two independent sets of stellar evolutionary models: MIST and PARSEC, using published spectroscopic parameter estimates and catalog values as priors. The resulting stellar effective temperatures, masses, radii, and surface gravities are compared and evaluated for consistency with stellar parameters listed in major exoplanet catalogs. While our estimates show consistency with those listed in external catalogs, we identify method-dependent differences in stellar masses for low-mass and pre-main-sequence stars, as well as G and K giants, where isochrone-based solutions may be affected by age-mass degeneracies. For low-mass stars such as M-dwarfs, the catalog provides masses derived from established mass-luminosity empirical relations, which tend to be more reliable. This catalog provides the largest uniformly derived stellar reference sample for Doppler survey targets and also illustrates the applicability and limitations of stellar-parameter homogenisation methods for future RV exoplanet demographics studies.

astro-ph.SR↗

arXiv2026

A Warm Massive Pair of Planets around TOI-1232 Revealed with Transit-timing Variations and Doppler Spectroscopy

TOI-1232 is a G-dwarf star with a mass of $1.06_{-0.06}^{+0.07} M_\odot$, a radius of $1.07\pm 0.05 R_\odot$, and slightly higher metallicity than solar of Fe/H = $0.18 \pm 0.05$. The star hosts a transiting warm Jovian-mass planet, TOI-1232 b, with an orbital period of $P_{b} = 14.256_{-0.001}^{+0.001}$ days, identified with data from multiple sectors of the $\textit{TESS}$ space telescope. The $\textit{TESS}$ light curve of TOI-1232 is complex, as it is contaminated by a background eclipsing binary with a period of $1.37$ days. The TOI-1232 b was firmly confirmed by ground-based transit follow-up campaigns from Las Cumbres, Hazelwood, Brierfield, and ASTEP observatories.Additionally, the $\textit{TESS}$ transits of TOI-1232 b exhibit strong transit timing variations (TTVs) with a super-period of $235.5 \pm 0.7$ days and a semi-amplitude of 27 minutes. Radial velocity (RV) follow-up with the FEROS spectrograph confirms the planetary nature of the transiting candidate, while a self-consistent $N$-body analysis of RVs and TTVs pinpoints the presence of a second outer Saturn-mass companion, TOI-1232 c with a period of $P_{c} = 30.356_{-0.012}^{+0.010}$ days. The TOI-1232 warm-giant system is particularly important due to the evidence of two massive planets that reside near the 2:1 commensurability but are not locked in a mean motion resonance (MMR). Thanks to $\textit{TESS}$, we have revealed a handful of these rare systems. Hence, TOI-1232 is an important addition to understanding the formation and dynamical evolution of such compact, massive, warm giant planets.

astro-ph.EP↗

arXiv2026

Long-period magnetic activity in the K dwarf GJ 1137 and a new super-Earth on a 9-day orbit

Aims: We investigate long-term radial velocity (RV) variability in the K-dwarf star GJ 1137 (HD 93083, HIP52521), a known Saturn-mass exoplanet host, and assess the role of stellar activity in shaping the observed signals. Methods: We analyse 13 years of archival high-precision spectroscopic observations obtained with the High Accuracy Radial velocity Planet Searcher spectrograph (HARPS). We performed an extensive spectroscopic analysis of the stellar activity indicators and applied an RV modelling approach, incorporating Keplerian fits, Gaussian process regression as a proxy for stellar activity, and other stellar activity diagnostics. Furthermore, we refined the orbital parameters and the minimum mass of the known exoplanet GJ 1137 b and searched for additional planetary candidates in the system. Results: We detect a long-period RV signal that, if interpreted as planetary, would suggest the presence of a Jovian analogue companion. However, our spectroscopic activity analysis provides strong evidence that this variability is induced by the star's long-term magnetic cycle ( Pcyc = 5870+(480)-(350) days) rather than by an orbiting planet. The signal is detected in both full width at half maximum (FWHM) of the crosscorrelation function and the chromospheric activity index log R'Hk. We measure the stellar rotation period to Prot = 32.3+(1.2)-(1.3) d and identify a significant short-period RV signal, which we attribute to a Super Earth with a period of 9.6412+(12)-(11) d and a minimum mass of 5.12+(0.70)-(0.69) Earth masses, making GJ 1137 a multiple-planet system.

astro-ph.EP↗

arXiv2023

A 2:1 Mean-Motion Resonance Super-Jovian pair revealed by TESS, FEROS, and HARPS

We report the discovery of a super-Jovian 2:1 mean-motion resonance (MMR) pair around the G-type star TIC 279401253, whose dynamical architecture is a prospective benchmark for planet formation and orbital evolution analysis. The system was discovered thanks to a single transit event recorded by the Transiting Exoplanet Survey Satellite (TESS) mission, which pointed to a Jupiter-sized companion with poorly constrained orbital parameters. We began ground-based precise radial velocity (RV) monitoring with HARPS and FEROS within the Warm gIaNts with tEss (WINE) survey to constrain the transiting body's period, mass, and eccentricity. The RV measurements revealed not one but two massive planets with periods of 76.80$_{-0.06}^{+0.06}$ days and 155.3$_{-0.7}^{+0.7}$ days, respectively. A combined analysis of transit and RV data yields an inner transiting planet with a mass of 6.14$_{-0.42}^{+0.39}$ M$_{\rm Jup}$ and a radius of 1.00$_{-0.04}^{+0.04}$ R$_{\rm Jup}$, and an outer planet with a minimum mass of 8.02$_{-0.18}^{+0.18}$ M$_{\rm Jup}$, indicating a massive giant pair. A detailed dynamical analysis of the system reveals that the planets are locked in a strong first-order, eccentricity-type 2:1 MMR, which makes TIC 279401253 one of the rare examples of truly resonant architectures supporting disk-induced planet migration. The bright host star, $V \approx$ 11.9 mag, the relatively short orbital period ($P_{\rm b}$ = 76.80$_{-0.06}^{+0.06}$ d) and pronounced eccentricity (e =0.448$_{-0.029}^{+0.028}$) make the transiting planet a valuable target for atmospheric investigation with the James Webb Space Telescope (JWST) and ground-based extremely-large telescopes.

astro-ph.EP↗

arXiv2019

All-sky Medium Energy Gamma-ray Observatory: Exploring the Extreme Multimessenger Universe

The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class mission concept that will provide essential contributions to multimessenger astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity in the 200 keV to 10 GeV energy range with a wide field of view, good spectral resolution, and polarization sensitivity. Therefore, AMEGO is key in the study of multimessenger astrophysical objects that have unique signatures in the gamma-ray regime, such as neutron star mergers, supernovae, and flaring active galactic nuclei. The order-of-magnitude improvement compared to previous MeV missions also enables discoveries of a wide range of phenomena whose energy output peaks in the relatively unexplored medium-energy gamma-ray band.

astro-ph.IM↗

arXiv2019

Supermassive black holes at high redshifts

MeV blazars are the most luminous persistent sources in the Universe and emit most of their energy in the MeV band. These objects display very large jet powers and accretion luminosities and are known to host black holes with a mass often exceeding $10^9 M_{\odot}$. An MeV survey, performed by a new generation MeV telescope which will bridge the entire energy and sensitivity gap between the current generation of hard X-ray and gamma-ray instruments, will detect $>$1000 MeV blazars up to a redshift of $z=5-6$. Here we show that this would allow us: 1) to probe the formation and growth mechanisms of supermassive black holes at high redshifts, 2) to pinpoint the location of the emission region in powerful blazars, 3) to determine how accretion and black hole spin interplay to power the jet.

astro-ph.HE↗

arXiv2018

Photopolarimetrical Study of Blazar-type AGN OJ287 in 2012-2015 with the 2m RCC Telescope at NAO Rozhen

We present the results of a photopolarimetric study of the blazar OJ287 in the period November 2012-January 2015. Observations were conducted using the Focal Reductor FoReRo-2 of the 2-meter RCC telescope of the National Astronomical Observatory (NAO) Rozhen. The observed change of the position angle (P.A.) corresponds to mean rotation of the plane of polarization of 6.23 deg/day, in good agreement with previous measurements. An indication of a correlation between the change of brightness in R-band and the change in the degree of polarization is also observed.

astro-ph.GA↗

arXiv2010

The Entropy Principle and the Influence of Sociological Pressures on SETI

We begin with the premise that the law of entropy could prove to be fundamental for the evolution of intelligent life and the advent of technological civilization. Building on recent theoretical results, we combine a modern approach to evolutionary theory with Monte Carlo Realization Techniques. A numerical test for a proposed significance of the law of entropy within the evolution of intelligent species is performed and results are compared with a neutral test hypothesis. Some clarifying aspects on the emergence of intelligent species arise and are discussed in the framework of contemporary astrobiology.

physics.pop-ph↗