arXiv subjects

Yassine Damerdji

Publications and source records attributed to Yassine Damerdji.

3 recordsLinked to original sources

arXiv2026

Magnetic Activity Cycles and Rotation in Planet-hosting and Non-hosting Solar-type Stars

We analyze periodicities in radial velocity (RV) measurements and magnetic activity indicators (S-index and BIS) for 767 Gaia RV standard stars to distinguish between stellar activity and planetary signals. Significant RV periods were detected in only 359 of these stars. Rotation and magnetic cycle periods are identified through iterative periodogram analysis. Among stars with confirmed planets, $28.2\%$ exhibit RV signals that coincide with activity indicators, compared to $21.3\%$ among stars without planets; however, statistical tests show this difference is not statistically significant. Several RV signals previously attributed to planets, such as those in HIP7240, HIP28460, and HIP48331, are instead likely caused by stellar activity, emphasising the importance of using multiple diagnostics to assess RV variability. We report rotation periods in 125 stars, including 30 new estimates, and detect magnetic activity cycles in 127 stars, 95 of which are new. We further investigate the relationship between rotation and magnetic cycle periods in the context of stellar dynamo theory. The full sample reveals a continuous distribution in the $P_{\rm rot}/P_{\rm cyc}$, Rossby number diagram, lacking the classical division into active and inactive branches and instead showing a negative slope, in contrast to some earlier studies. Interestingly, stars with planetary companions exhibit a steeper trend (slope of $-1.049 \pm 0.078$) compared to non-hosts ($-0.654 \pm 0.056$), suggesting that the presence of planets may subtly influence the host star's magnetic behaviour.

astro-ph.SR↗

arXiv2025

Magnetic activity and differential rotation of HIP12653

We present a spectroscopic and photometric study of HIP12653 to investigate its magnetic cycle and differential rotation. Using HARPS archival spectra matched with MARCS-AMBER theoretical templates, we derive the stellar parameters (Teff, logg, FeH, and vsini) of the target. The S-index, an activity indicator based on the emission of the CaII H&K lines, is fitted to determine the magnetic cycle and rotation periods. We refine the magnetic cycle period to 5799.20 \pm 0.88 d and suggest the existence of a secondary, shorter cycle of 674.6922 \pm 0.0098 d, making HIP12653 the youngest star known to exhibit such a short activity cycle. During the minimum activity phase, a rotation period of 4.8 d is estimated. This is notably different from the 7-day period obtained when measurements during minimum activity are excluded, suggesting that these two periods are rotation periods at different latitudes. To explore this hypothesis, we introduce a novel light curve fitting method that incorporates multiple harmonics to model different spot configurations. Applied to synthetic light curves, the method recovers at least two rotation periods close to the true input values in 92.1% of cases. The inferred rotation shear shows a median deviation of 0.0011 \pm 0.0003 and a standard deviation of 0.0177 \pm 0.0002 from the true value. Applying this approach to TESS photometric data from 2018 to 2023, we detect three distinct rotation periods, 4.8 d, 5.7 d, and 7.7 d, (along with a signal at 3.75 d interpreted as its first harmonic), consistent with spots located at different latitudes. Assuming a solar-like differential rotation, we estimate an inclination of 34.0 \pm 1.8^\circ and a rotational shear of α= 0.38 \pm 0.01. These results confirm the 4.8-d period and demonstrate that differential rotation can be constrained by tracking rotation period changes across different phases of the magnetic cycle.

astro-ph.SR↗

arXiv2006

Continuous optical monitoring during the prompt emission of GRB 060111B

We present the time-resolved optical emission of GRB 060111B during its prompt phase, measured with the TAROT robotic observatory. This is the first time that the optical emission from a gamma-ray burst has been continuously monitored with a temporal resolution of a few seconds during the prompt gamma-ray phase. The temporal evolution of the prompt optical emission at the level of several seconds is used to provide a clue to the origin of this emission. The optical emission was found to decay steadily from our first measure, 28s after the trigger, in contrast to the gamma-ray emission, which exhibits strong variability at the same time. This behaviour strongly suggests that the optical emission is due to the reverse shock.

astro-ph↗