arXiv subjects

Yasir Abdul Qadir

Publications and source records attributed to Yasir Abdul Qadir.

6 recordsLinked to original sources

arXiv2026

Investigation of Transit Timing and an Optical Transmission Spectrum of the Hot Jupiter WASP-11 b

WASP-11~b/HAT-P-10~b is an inflated hot Jupiter, which has a low density that makes it a good target for atmospheric studies using the transmission spectroscopy technique. In this work, we present 31 new transit light curves of WASP-11~b/HAT-P-10~b, obtained through the SPEARNET network. These data were analyzed along with previously published ground-based observations and space-based data from \texttt{TESS}. We refine the planetary parameters of WASP-11~b/HAT-P-10~b and perform a transit timing analysis using data spanning 16 years. The updated ($O-C$) diagram shows no significant evidence of orbital decay. The TTV analysis reveals no significant signals indicative of additional planets. Atmospheric analysis using multi-band optical observations indicates a strong Rayleigh scattering slope in the transmission spectra, which may originate from the planetary atmosphere itself or be influenced by contamination such as stellar activity or light from the companion star.

astro-ph.EP↗

arXiv2026

The Transit Timing and Transmission Spectrum of Hot Jupiter WASP-43 b from a decade of Multi-band Transit Follow-up Observations

We present a new set of 35 transit light curves of the hot Jupiter WASP-43~b, obtained through the SPEARNET network. These datasets were analyzed together with previously published ground-based observations, as well as space-based data from \emph{TESS}, \emph{HST}, and \emph{JWST}, to refine the planetary parameters of WASP-43~b. A total of 188 mid-transit times, measured with \texttt{TransitFit}, were analyzed for potential timing variations. The transit timing variations do not show any significant evidence of orbital decay. Atmospheric retrievals using \emph{HST}/WFC3 G141 transmission spectra suggest that higher-temperature solutions are associated with higher water abundances. However, when these data are combined with observations from ground-based telescopes, \emph{TESS}, and \emph{JWST}, the increased modeling complexity across the broad wavelength baseline presents significant challenges for atmospheric characterization. These results highlight that high-precision, multi-instrument datasets will be necessary to break existing degeneracies in the atmospheric modeling of this target in the future.

astro-ph.EP↗

arXiv2025

High-precision broadband linear polarimetry of early-type binaries. V. The Binary System HD 165052 in Open Cluster NGC 6530

This study continues our investigation of early-type binaries using high-precision broad-band polarimetry, focusing on HD 165052, a massive O+O-type binary in the young cluster NGC 6530. Our aim was to monitor linear polarization variations and independently determine the orbital period through polarization data analysis. By examining the phase-locked Stokes parameters, we estimated the orbital inclination at about 55+5/-55 deg, and the orientation at 148+20/-22 deg. The binary's rotation direction is clockwise. Using the Dipol-2 polarimeter with the 60 cm KVA and Tohoku T60 telescopes, we achieved polarization measurement accuracy around 0.01 percent in the B, V, and R passbands. Period analysis identified a strong periodic signal with a cycle of about 1.48 days, corresponding to half of the orbital period of about 2.96 days. The second Fourier harmonics suggest a symmetric scattering geometry, likely due to electron scattering in interacting stellar winds. Our estimates indicate a mass-loss rate of approximately 3.5 x 10^(-7) solar masses per year. Observations of neighboring stars in NGC 6530 revealed complex interstellar polarization behaviors within the cluster, enhancing our understanding of its polarimetric environment.

astro-ph.SR↗

arXiv2023

High-precision broadband linear polarimetry of early-type binaries IV. Binary system of DH Cephei in the open cluster of NGC 7380

DH Cephei is a prominent O+O-type binary system in the NGC 7380 open cluster. Our high-precision multi-band polarimetry demonstrates synchronous linear polarization variations with the orbital period. Using Stokes parameters, we derived the binary system's orbital inclination, orientation, and rotation direction. To estimate interstellar polarization, we observed neighboring stars in NGC 7380. Utilizing Dipol-2 polarimeter and T60 telescope, we measured linear polarization in the $B$, $V$, and $R$ bands with $\sim$0.003% accuracy. Lomb-Scargle period search revealed a dominant frequency at 1.055 d, corresponding to half of the 2.11 d orbital period. The $B$ passband showed a non-periodic component, while the $V$ passband provided reliable values for inclination ($46^{\circ}+11^{\circ}/-46^{\circ}$) and orbital orientation ($Ω= 105^{\circ} \pm 55^{\circ}$). Using these values, we estimated a mass loss of $\sim$$3.4 \times 10^{-7}M_{\rm \odot} ; \rm yr^{-1}$. The binary system's rotation on the sky is clockwise. Polarimetric observations of neighboring stars indicate interstellar dust causing cluster star polarization.

astro-ph.SR↗

arXiv2023

High-precision broadband linear polarimetry of early-type binaries III. AO Cassiopeiae revisited

The fact that the O-type close binary star system AO~Cassiopeiae exhibits variable phase-locked linear polarization has been known since the mid-1970s. In this work, we re-observe the polarization arising from this system more than 50 years later to better estimate the interstellar polarization and to independently derive the orbital parameters, such as inclination, $i$, orientation, $Ω$, and the direction of the rotation for the inner orbit from the phase-folded polarization curves of the Stokes $q$ and $u$ parameters. The Dipol-2 polarimeter was used to obtain linear polarization measurements of AO~Cassiopeiae in the $B$, $V$, and $R$ passbands with the T60 remotely controlled telescope at an unprecedented accuracy level of $\sim$0.003\%. We have obtained the first proper quantification of the interstellar polarization in the direction heading towards AO~Cas by observing the polarization of three neighboring field stars. We employed a Lomb-Scargle algorithm and detected a clear periodic signal for the orbital period of AO~Cas. The standard analytical method based on a two-harmonics Fourier fit was used to obtain the inclination and orientation of the binary orbit. Our polarimetric data exhibited an unambiguous periodic signal at 1.76 days, thus confirming the orbital period of the binary system of 3.52 days. Most of the observed polarization is of interstellar origin. The de-biased values of the orbital inclination are $i = 63^{\circ} +2^{\circ}/ -3^{\circ}$ and orientation of $Ω= 29^{\circ} (209^{\circ}) \pm 8^{\circ}$. The direction of the binary system rotation on the plane of the sky is clockwise.

astro-ph.SR↗

arXiv2022

Optical polarization signatures of black hole X-ray binaries

Polarimetry provides an avenue for probing the geometry and physical mechanisms producing optical radiation in many astrophysical objects, including stellar binary systems. We present the results of multiwavelength (BVR) polarimetric studies of a sample of historical black hole X-ray binaries, observed during their outbursts or in the quiescent (or near-quiescent) state. We surveyed both long- and short-period systems, located at different Galactic latitudes. We performed careful analysis of the interstellar polarization in the direction on the sources to reliably estimate the intrinsic source polarization. Intrinsic polarization was found to be small (< 0.2 per cent) in sources observed in bright soft states (MAXI J0637-430 and 4U 1957+115). It was found to be significant in the rising hard state of MAXI J1820+070 at the level of 0.5 per cent and negligible in the decaying hard state and during its failed outbursts, while Swift J1357.2-0933 showed its absence in the rising hard state. Three (XTE J1118+480, V4641 Sgr, V404 Cyg) sources observed during quiescence show no evidence of significant intrinsic polarization, while MAXI J1820+070 is the only black hole X-ray binary which showed substantial (> 5 per cent) intrinsic quiescent-state polarization with a blue spectrum. The absence of intrinsic polarization at the optical wavelengths puts constraints on the potential contribution of non-stellar (jet, hot flow, accretion disc) components to the total spectra of quiescent black hole X-ray binaries.

astro-ph.HE↗