arXiv subjects

Ahmed Daassou

Publications and source records attributed to Ahmed Daassou.

4 recordsLinked to original sources

arXiv2025

Responses of AdS black holes to the collective influence of quintessence and string cloud

This research paper explores the interplay between quintessence and a cloud of strings, focusing on their influence on critical points, behaviors, and fractional-order phase transitions in AdS black holes. We analyze the thermodynamic properties of AdS black holes surrounded by quintessence and a cloud of strings, with particular attention to the effects of thermal fluctuations on their thermodynamics. Using critical conditions, we derive approximate analytical expressions for the critical points applicable to all types of these black holes. We further study the impact of the quintessence parameter and the intensity of the cloud of strings on critical behaviors, employing three-dimensional visualizations to depict these effects for different values of $ω_q$. Our results show how these factors affect the locations of phase transitions and the regions where both phases coexist. In addition, we examine fractional-order phase transitions, which reveal significant transformations in the black hole system.

hep-th↗

arXiv2023

Another Shipment of Six Short-Period Giant Planets from TESS

We present the discovery and characterization of six short-period, transiting giant planets from NASA's Transiting Exoplanet Survey Satellite (TESS) -- TOI-1811 (TIC 376524552), TOI-2025 (TIC 394050135), TOI-2145 (TIC 88992642), TOI-2152 (TIC 395393265), TOI-2154 (TIC 428787891), & TOI-2497 (TIC 97568467). All six planets orbit bright host stars (8.9 <G< 11.8, 7.7 <K< 10.1). Using a combination of time-series photometric and spectroscopic follow-up observations from the TESS Follow-up Observing Program (TFOP) Working Group, we have determined that the planets are Jovian-sized (R$_{P}$ = 1.00-1.45 R$_{J}$), have masses ranging from 0.92 to 5.35 M$_{J}$, and orbit F, G, and K stars (4753 $<$ T$_{eff}$ $<$ 7360 K). We detect a significant orbital eccentricity for the three longest-period systems in our sample: TOI-2025 b (P = 8.872 days, $e$ = $0.220\pm0.053$), TOI-2145 b (P = 10.261 days, $e$ = $0.182^{+0.039}_{-0.049}$), and TOI-2497 b (P = 10.656 days, $e$ = $0.196^{+0.059}_{-0.053}$). TOI-2145 b and TOI-2497 b both orbit subgiant host stars (3.8 $<$ $\log$ g $<$4.0), but these planets show no sign of inflation despite very high levels of irradiation. The lack of inflation may be explained by the high mass of the planets; $5.35^{+0.32}_{-0.35}$ M$_{\rm J}$ (TOI-2145 b) and $5.21\pm0.52$ M$_{\rm J}$ (TOI-2497 b). These six new discoveries contribute to the larger community effort to use {\it TESS} to create a magnitude-complete, self-consistent sample of giant planets with well-determined parameters for future detailed studies.

astro-ph.EP↗

arXiv2019

Qatar Exoplanet Survey: Qatar-8b, 9b and 10b --- A Hot Saturn and Two Hot Jupiters

In this paper we present three new extrasolar planets from the Qatar Exoplanet Survey (QES). Qatar-8b is a hot Saturn, with Mpl = 0.37 Mjup and Rpl = 1.3 Rjup, orbiting a solar-like star every Porb = 3.7 days. Qatar-9b is a hot Jupiter with a mass of Mpl = 1.2 Mjup and a radius of Rpl = 1 Rjup, in a Porb = 1.5 days orbit around a low mass, Mstar = 0.7 Msun, mid-K main-sequence star. Finally, Qatar-10b is a hot, Teq ~ 2000 K, sub-Jupiter mass planet, Mpl = 0.7 Mjup, with a radius of Rpl = 1.54 Rjup and an orbital period of Porb = 1.6 days, placing it on the edge of the sub-Jupiter desert.

astro-ph.EP↗

arXiv2014

An analytical model for the 0.33 - 7.85 micron transmission spectrum of HD189733b : Effect of stellar spots

In this paper an analytical theory is used to complete the transmission spectrum of HD189733b from near-ultraviolet to infrared (0.33 - 7.85 $μm$). The model suggests a new approach which take into account the quantity of light transmitted through the planetary atmosphere and the thermal emissions from the night side of the planet, to describe the transmission spectrum of HD189733b in photometric study. The availability of measures in different wavelengths has allowed us to validate our model with more efficiency. We found an agreement between our transmission spectrum model of HD189733b and data from the infrared to the UV. The model predicts a value of $R_p /R_\star$ $= 0.1516$ at $7.3 μm$, which is a low value compared to all observations at different wavelengths. We interpreted this value by a fluorescence emission from sulphur dioxide ($SO_2$). Therefore, the likely presence of these molecules in the atmosphere of HD 189733b. The second objective of this paper is to study the effect of starspots on the transmission spectrum of this hot-Jupiter. To reach this goal, we developed an analytical theory considered as an extension of the approach proposed by Berta et al. (2011). The model shows clearly that the unocculted spots would significantly increase the transit radius ratio at visible and near-ultraviolet wavelengths, while having a minimal impact at infrared wavelengths. Therefore, the wavelength dependence of the spots effect has been clearly shown by this new model. At the end of this paper, we reported the way in which this model can provide an estimation of the percentage of the unocculted spots area relative to stellar disk area for an observation of HD189733 performed in a given epoch and at a given wavelength.

astro-ph.EP↗