arXiv subjects

Ö. Adebali

Publications and source records attributed to Ö. Adebali.

3 recordsLinked to original sources

arXiv2026

Forward modeling solar spectra onto Doppler images of λ And

By using the Doppler images of λ And, we aim to investigate whether surface temperature information can be reversed to create its activity parameters, by feeding a toy model with solar spectra, based on the surface images. At the same time, we examine whether spot contributions alone are sufficient to explain the observed activity modulation of the RS CVn star λ And while quantifying the differences with the actual observations of this star that are obtained simultaneously with the Doppler images we use. Due to a lack of publicly available starspot models for its stellar type, we adopt observed solar spectra as the only available approximation of λ And's spots. These spectra are injected into sequence of full disk temperature map derived from Doppler imaging that represent a full stellar rotation. Using this approach, we show that even with simplified assumptions the spectral behavior of λ And can be qualitatively reproduced. Toy models such as the one presented in this work procure an additional dimension, providing a relation between the surface structures and chromospheric emissions. It also helps to develop a further understanding for the heating mechanisms of these active giants through comparative techniques, where in this case the spot activity seemingly modulates the chromospheric signal and can explain the bulk of its variations over a rotation.

astro-ph.SR↗

arXiv2025

Surface image and activity-corrected orbit of the RS CVn binary HR 7275: Disentangling activity tracers

Quantifying stellar parameters and magnetic activity for cool stars in double-lined spectroscopic binaries (SB2) is not straightforward, as both stars contribute to the observed composite spectra and are likely variable. Disentangled component spectra allow a detailed analysis of a component's magnetic activity. We aim at separating the spectra of the two stellar components of the HR\,7275 SB2 system. Our further aim is a more accurate orbital solution by cleaning the observed radial velocities (RV) from activity perturbations of the spotted primary ("RV jitter") and obtain a surface image of this component. The Doppler image of the primary shows two large cool spots of size $\approx$20\% of the visible hemisphere plus three smaller spots, each still $\approx$13\% in size. In total, HR\,7275a exhibited an impressive spottedness of $\approx$40\%\ of its entire surface in May-June 2022. The RV is modulated by the rotation of the primary with maximum amplitudes of 320\,\ms\ and 650\,\ms\ for two different modulation behaviors during the 250\,d of our observations. This jitter is primarily caused by the varying asymmetries of the apparent disk brightness due to the cool spots. Its removal resulted in roughly ten times higher precision of the orbital elements. Our snapshot magnetic-field measurements reveal phase-dependent (large-scale) surface fields between +0.6$\pm$2.0\,G at phase 0.1 and $-$15.2$\pm$2.7\,G at phase 0.6, indicating a complex magnetic morphology related to the location of the photospheric spots. We also obtain a logarithmic lithium abundance of 0.58$\pm$0.1 for HR\,7275a, indicating considerable mixing, and 0.16$^{+0.23}_{-0.63}$ for HR\,7275b, which is an extremely low value. }

astro-ph.SR↗

arXiv2025

First Doppler image and starspot-corrected orbit for $λ$ Andromedae: A multifaceted activity analysis

We quantify the effect of starspots for the orbital elements of the spotted RS CVn binary $λ$ Andromedae ($λ$ And) and present an empirical correction. The aim is to obtain a more precise orbital solution that can be used to better study the system's severe orbital-rotational asynchronism. Phase-resolved high-resolution optical spectra were recorded over the course of 522 days in 2021-2022. We employed two facilities with medium and high resolution spectroscopy for the multiple activity analyses. Doppler imaging is used to reconstruct $λ$ And's starspots with a high resolution (R= 250 000) and high signal-to-noise ratio spectra. Optimized cross-correlation functions were used to measure precise radial velocities at a level of a few ten's of m/s. The spot-corrected radial velocities enable, on average, a threefold increase in precision of the individual orbital elements. The residual velocity jitter with a full range of 500 m/s is modulated by the rotation period of $λ$ And of 54.4$\pm$0.3 days. Our logarithmic gravity from spectrum synthesis of 2.8$\pm$0.2 together with the interferometrically determined stellar radius suggest a most-likely mass of the primary of $\approx$1.4 Msun. The small orbital mass function then implies a secondary mass of just $\approx$0.1 Msun, which is appropriate for an L-class brown dwarf. The Doppler image reconstructs a dominating cool spot with an umbral temperature difference of $\approx$1000 K with respect to the photosphere of 4660 K and is likely surrounded by a moat-like velocity field. Three more weaker spots add to the total surface spottedness, which is up to 25% of the visible surface. Seven optical chromospheric tracers show rotational modulation of their emission line fluxes in phase with the cool spots. This surface configuration appears to have been stable for the 522 days of our observations.

astro-ph.SR↗