arXiv subjects

Ahlam Alqasim

Publications and source records attributed to Ahlam Alqasim.

4 recordsLinked to original sources

arXiv2025

Investigating the eccentricity distribution of transiting, long-period giant planets

Eccentric giant planets are predicted to have acquired their eccentricity through two major mechanisms: the Kozai-Lidov effect or planet-planet scattering, but it is normally difficult to separate the two mechanisms and determine the true eccentricity origin for a given system. In this work, we focus on a sample of 92 transiting, long-period giant planets (TLGs) as part of an eccentricity distribution study for this planet population in order to understand their eccentricity origin. Using archival high-contrast imaging observations, public stellar catalogs, precise Gaia astrometry, and the NASA Exoplanet Archive database, we explored the eccentricity distribution correlation with different planet and host-star properties of our sample. We also homogeneously characterized the basic stellar properties for all 86 host-stars in our sample, including stellar age and metallicity. We found a correlation between eccentricity and stellar metallicity, where lower-metallicity stars ([Fe/H] <= 0.1) did not host any planets beyond e > 0.4, while higher-metallicity stars hosted planets across the entire eccentricity range. Interestingly, we found no correlation between the eccentricity distribution and the presence of stellar companions, indicating that planet-planet scattering is likely a more dominant mechanism than the Kozai-Lidov effect for TLGs. This is further supported by an anti-correlation trend found between planet multiplicity and eccentricity, as well as a lack of strong tidal dissipation effects for planets in our sample, which favor planet-planet scattering scenarios for the eccentricity origin.

astro-ph.EP↗

arXiv2023

TOI-733 b: a planet in the small-planet radius valley orbiting a Sun-like star

We report the discovery of a hot ($T_{\rm eq}$ $\approx$ 1055 K) planet in the small planet radius valley transiting the Sun-like star TOI-733, as part of the KESPRINT follow-up program of TESS planets carried out with the HARPS spectrograph. TESS photometry from sectors 9 and 36 yields an orbital period of $P_{\rm orb}$ = $4.884765 _{ - 2.4e-5 } ^ { + 1.9e-5 }$ days and a radius of $R_{\mathrm{p}}$ = $1.992 _{ - 0.090 } ^ { + 0.085 }$ $R_{\oplus}$. Multi-dimensional Gaussian process modelling of the radial velocity measurements from HARPS and activity indicators, gives a semi-amplitude of $K$ = $2.23 \pm 0.26 $ m s$^{-1}$, translating into a planet mass of $M_{\mathrm{p}}$ = $5.72 _{ - 0.68 } ^ { + 0.70 }$ $M_{\oplus}$. These parameters imply that the planet is of moderate density ($ρ_\mathrm{p}$ = $3.98 _{ - 0.66 } ^ { + 0.77 }$ g cm$^{-3}$) and place it in the transition region between rocky and volatile-rich planets with H/He-dominated envelopes on the mass-radius diagram. Combining these with stellar parameters and abundances, we calculate planet interior and atmosphere models, which in turn suggest that TOI-733 b has a volatile-enriched, most likely secondary outer envelope, and may represent a highly irradiated ocean world - one of only a few such planets around G-type stars that are well-characterised.

astro-ph.EP↗

arXiv2022

A New Method to Determine X-ray Luminosity Functions of AGN and their Evolution with Redshift

Almost all massive galaxies today are understood to contain supermassive black holes (SMBH) at their centers. SMBHs grew by accreting material from their surroundings, emitting X-rays as they did so. X-ray Luminosity Functions (XLFs) of Active Galactic Nuclei (AGN) have been extensively studied in order to understand the AGN population's cosmological properties and evolution. We present a new fixed rest-frame method to achieve a more accurate study of the AGN XLF evolution over cosmic time. Normally, XLFs are constructed in a fixed observer-frame energy band, which can be problematic because it probes different rest-frame energies at different redshifts. In the new method, we construct XLFs in the fixed rest-frame band instead, by varying the observed energy band with redshift. We target a rest-frame 2$-$8 keV band using XMM-Newton and HEAO 1 X-ray data, with 7 observer-frame energy bands that vary with redshift for $0 < z < 3$. We produce the XLFs using two techniques; one to construct a binned XLF, and one using a Maximum Likelihood (ML) fit, which makes use of the full unbinned source sample. We find that our ML best-fit pure luminosity evolution (PLE) results for both methods are consistent with each other, suggesting that performing XLF evolution studies with the high-redshift data limited to high-luminosity AGN is not very sensitive to the choice of fixed observer-frame or rest-frame energy band, which is consistent with our expectation that high-luminosity AGN typically show little absorption. We have demonstrated the viability of the new method in measuring the XLF evolution.

astro-ph.GA↗

arXiv2022

HD 20329b: An ultra-short-period planet around a solar-type star found by TESS

We used TESS light curves and HARPS-N spectrograph radial velocity measurements to establish the physical properties of the transiting exoplanet candidate found around the star HD 20329 (TOI-4524). We performed a joint fit of the light curves and radial velocity time series to measure the mass, radius, and orbital parameters of the candidate. We confirm and characterize HD 20329b, an ultra-short-period (USP) planet transiting a solar-type star. The host star (HD 20329, $V = 8.74$ mag, $J = 7.5$ mag) is characterized by its G5 spectral type with $\mathrm{M}_\star= 0.90 \pm 0.05$ M$_\odot$, $\mathrm{R}_\star = 1.13 \pm 0.02$ R$_\odot$, and $\mathrm{T}_{\mathrm{eff}} = 5596 \pm 50$ K; it is located at a distance $d= 63.68 \pm 0.29$ pc. By jointly fitting the available TESS transit light curves and follow-up radial velocity measurements, we find an orbital period of $0.9261 \pm (0.5\times 10^{-4})$ days, a planetary radius of $1.72 \pm 0.07$ $\mathrm{R}_\oplus$, and a mass of $7.42 \pm 1.09$ $\mathrm{M}_\oplus$, implying a mean density of $ρ_\mathrm{p} = 8.06 \pm 1.53$ g cm$^{-3}$. HD 20329b joins the $\sim$30 currently known USP planets with radius and Doppler mass measurements.

astro-ph.EP↗