Yazar "Sonbas, E." seçeneğine göre listele

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  • [ X ]
    Öğe
    A Combined TESS and Ground-based Study of Transit Timing Variations in HAT-P-16, TOI-1516 and TOI-2046 Systems
    (Iop Publishing Ltd, 2025) Sonbas, E.; Kaplan, K.; Tanriver, M.; Keskin, A.; Dhuga, K.; Bulut, A.; Gogus, E.
    We present new results for the hot Jupiters HAT-P-16b, TOI-1516b, and TOI-2046b, based on photometric observations collected using both space- and ground-based facilities. Ground-based data were collected in the 2020-2024 time span with the 0.6 m telescope (ADYU60) located at the Adiyaman University Application and Research Center (Adiyaman, T & uuml;rkiye) and the 1.0 m telescope at the T & uuml;rkiye National Observatory (TUG, T & uuml;rkiye). Through a combination of fits to our ground-based data, the midtransit times data from TESS, and additional data taken from the literature, we present an updated linear ephemeris for each system. Transit timing variations (TTVs) were analyzed using linear, orbital decay, and apsidal precession models. The resulting BIC(Delta BIC) values indicate that the orbital decay model is statistically favored for HAT-P-16b and TOI-1516b, while the constant period model is preferred for TOI-2046b. False alarm probabilities (FAPs) were computed to assess the significance of any periodic signals. TOI-1516b displays a strong TTV signal with a FAP (of 0.0001) well below the 0.01 threshold, suggesting a likely dynamical origin that warrants further investigation. The higher FAP value (0.0055) for HAT-P-16b suggests that the case of a possible presence of an additional body in the system is less convincing. In contrast, the much higher FAP value (0.0196) for TOI-2046b implies that there are no statistically significant TTVs.
  • [ X ]
    Öğe
    Optical counterparts of ULXs in NGC 1672
    (Oxford Univ Press, 2022) Allak, S.; Akyuz, A.; Sonbas, E.; Dhuga, K. S.
    In this work, we deploy archival data from Hubble Space Telescope, Chandra, XMM-Newton, and Swift-XRT, to probe the nature of nine candidate ultraluminous X-ray sources (ULXs) in NGC 1672. Specifically, our study focuses on using the precise source positions obtained via improved astrometry based on Chandra and Hubble Space Telescope observations to search for and identify potential optical counterparts for these ULXs. Unique optical counterparts are identified for two of the ULX candidates, i.e. X2 and X6; for three of the candidates, i.e. X1, X5, and X7, we found two potential counterparts for each source within the respective error radii. No optical counterparts were found for the remaining four sources. The spectral energy distribution of X2 is fitted to a blackbody spectrum with a temperature of similar to 10(4) K and the spectral class of the source is determined to be B7-A3, a supergiant donor star. We used colour-magnitude diagrams to investigate ages of the counterparts. Of all the sources studied, X9 exhibits the most variability whereby the X-ray flux varies by a factor of similar to 50 over a time period spanning 2004-2019, and also traces a partial q-curve-like feature in the hardness-intensity diagram, hinting at possible spectral transitions.