arXiv subjects

Katarzyna Kruszynska

Publications and source records attributed to Katarzyna Kruszynska.

3 recordsLinked to original sources

arXiv2026

Expanding the SPISEA Stellar Population Synthesis Software to the Substellar Regime

We present an extension of the SPISEA stellar population synthesis framework that adds brown dwarfs to the existing range of stellar mass objects, enabling physically consistent modeling of brown dwarfs within synthetic star clusters. Previous versions of SPISEA included limited substellar support, relying on outdated initial mass functions and incomplete atmospheric and evolutionary coverage below the hydrogen-burning limit. This was addressed through the implementation of a modern substellar initial mass function based on robust observational constraints, the introduction of merged atmospheric grids that smoothly transition between stellar and brown dwarf regimes, and the construction of unified evolutionary tracks spanning the lowest-mass brown dwarf objects through massive stars at solar metallicity. The updated framework was validated by comparing simulated color-magnitude diagrams to observational data from the Pleiades, Upper Scorpius, and M44 clusters using Gaia, UKIDSS, and 2MASS photometry. The new models allow for generation of user-specified isochrones and clusters that reproduce observed stellar behaviors while enabling realistic population synthesis in the brown dwarf regime. This work extends SPISEA's applicability to substellar science cases, including young cluster studies and microlensing simulations, and provides a foundation for future incorporation of planetary-mass objects and non-solar metallicities.

astro-ph.IM↗

arXiv2025

Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. IV. Lens Mass and Distance Measurements

As part of the Galactic Bulge Time Domain Survey (GBTDS), the Nancy Grace Roman Galactic Exoplanet Survey (RGES) will use microlensing to discover cold outer planets and free-floating planets unbound to stars. NASA has established several science requirements for the GBTDS to ensure RGES success. A key advantage of RGES is Roman's high angular resolution, which will allow detection of flux from many host stars. One requirement specifies that Roman must measure the masses and distances of 40% of detected planet hosts with 20% precision or better. To test this, we simulated microlensing events toward the GBTDS fields and used Fisher matrix analysis to estimate light curve parameter uncertainties. Combining these with Roman imaging observables (lens flux, relative lens-source proper motion), we estimated the achievable precision of lens mass and distance measurements. Using pyLIMASS, a publicly available code for estimating lens properties, we applied this analysis to 3,000 simulated events. Assuming the Cassan et al. (2012) exoplanet mass function, we find that >40% of host stars meet the required 20% precision threshold, confirming that the GBTDS can satisfy the mission requirement. We validated our approach by comparing our inferred lens masses and distances to empirical measurements from detailed image-constrained light curve modeling of historical microlensing events with Hubble and Keck follow-up imaging. Our results agree within roughly 1 sigma, demonstrating that both approaches yield consistent and reliable mass and distance estimates, and confirming the robustness of our simulations for Roman-era microlensing science.

astro-ph.EP↗

arXiv2024

Gaia22dkvLb: A Microlensing Planet Potentially Accessible to Radial-Velocity Characterization

We report discovering an exoplanet from following up a microlensing event alerted by Gaia. The event Gaia22dkv is toward a disk source rather than the traditional bulge microlensing fields. Our primary analysis yields a Jovian planet with M_p = 0.59^{+0.15}_{-0.05} M_J at a projected orbital separation r_perp = 1.4^{+0.8}_{-0.3} AU, and the host is a ~1.1 M_sun turnoff star at ~1.3 kpc. At r'~14, the host is far brighter than any previously discovered microlensing planet host, opening up the opportunity of testing the microlensing model with radial velocity (RV) observations. RV data can be used to measure the planet's orbital period and eccentricity, and they also enable searching for inner planets of the microlensing cold Jupiter, as expected from the ''inner-outer correlation'' inferred from Kepler and RV discoveries. Furthermore, we show that Gaia astrometric microlensing will not only allow precise measurements of its angular Einstein radius theta_E, but also directly measure the microlens parallax vector and unambiguously break a geometric light-curve degeneracy, leading to definitive characterization of the lens system.

astro-ph.EP↗