arXiv subjects

Ayanabha De

Publications and source records attributed to Ayanabha De.

6 recordsLinked to original sources

arXiv2024

The 10 pc Neighborhood of Habitable Zone Exoplanetary Systems: Threat Assessment from Stellar Encounters & Supernovae

The habitability of a planet is influenced by both its parent star and the properties of its local stellar neighborhood. Potential threats to habitability from the local stellar environment mainly arise from two factors: cataclysmic events such as powerful stellar explosions and orbital perturbations induced by close stellar encounters. Among the 4,500+ exoplanet-hosting stars, about 140+ are known to host planets in their habitable zones. In this study, we use \textit{Gaia DR3} data to investigate the 10~pc stellar neighborhood of the 84 habitable zone systems (HZS) closest to the Sun. We assess the possible risks that local stellar environment of these HZS pose to their habitability. In particular, we find that HD~165155 has a high stellar density around it, making it likely to experience at least one flyby encounter within a span of 5~Gyr. We also identified two high-mass stars ($M \geq 8 M_\odot$) as potential progenitors of supernovae, which could threaten the long-term survivability of habitable zone systems HD~48265 and TOI-1227. Further, to quantify the similarity between habitable zone stars and the Sun, as well as their respective 10~pc stellar environments, we employ various astrophysical parameters to define a Solar Similarity Index (SSI) and a Neighborhood Similarity Index (NSI). Our analysis suggests that HD~40307 exhibits the closest resemblance to the solar system, while HD~165155 shows the least resemblance.

astro-ph.SR↗

arXiv2024

Demography of stellar radio population within 500 pc: A VLASS-Gaia DR3 study

In this work, we have carried out a systematic analysis of the VLASS quick look catalogs together with \textit{Gaia DR3} to identify the optical counterparts of 3~GHz radio emitters within 500~pc to obtain a homogeneous statistical sample of stellar radio sources. We have identified distinct populations of 3 GHz emitters across the \textit{Gaia DR3} color-magnitude diagram. We also present candidate sources (transient, highly variable or background artifacts) which can be confirmed by follow-up observations. A majority of the detected sources constitute main sequence G, K and M-type stars including ultra-cool dwarfs. Pinning down the origin of radio emission from these populations can help us gain further insights into the origin of stellar and planetary magnetic fields. By analyzing the variation of brightness temperature of the sources with their spectral type, we have tentatively associated possible emission mechanisms with different object types. We inspected the correlation between quiescent radio and X-ray emission for our sample that can provide crucial insights into the current understanding of the Gudel-Benz relationship, which is essential for modeling steady radio emission and coronal heating. This VLASS-\textit{\textit{Gaia DR3}} analysis acts as a pilot study for follow-up observations at multiple wavelengths to better understand stellar structure, model flaring activities and detect radio emission caused by star-planet interactions.

astro-ph.SR↗

arXiv2024

uGMRT Survey of EXoplanets Around M-dwarfs (GS-EXAM): Radio observations of GJ 1151

Coherent radio emission with properties similar to planetary auroral signals has been reported from GJ 1151, a quiescent, slow-rotating mid-M star, by the LOFAR Two-metre (120-170 MHz) Sky Survey (LoTSS). The observed {LOFAR} emission is fairly bright at 0.89 mJy with 64% circular polarization, and the emission characteristics are consistent with the interaction between an Earth-sized planet with an orbital period of 1-5 days and the magnetic field of the host star. However, no short-period planet has been detected around GJ 1151. To confirm the reported radio emission caused by the putative planet around GJ 1151 and to investigate the nature of this emission, we carried out uGMRT observations of GJ 1151 at 150, 218, and 400 MHz over 33 hours across ten epochs. No emission was detected at any frequency. While at 150 MHz and 218 MHz, non-detection could be due to the low sensitivity of our observations, at 400 MHz, the rms sensitivities achieved were sufficient to detect the emission observed with LOFAR at $\sim$ 20$σ$ level. Our findings suggest that the radio emission is highly time-variable, likely influenced by the star-planet system's phase and the host star's magnetic field. Additional observations below 170 MHz, at more frequent epochs (as the periodicity of the emission is unknown), especially during periods of high stellar magnetic field strength, are needed to confirm the emission.

astro-ph.EP↗

arXiv2023

Probability density function of the unbalanced impulse in Langevin theory of Brownian motion

This paper attempts to find a probability distribution for the white noise (rapidly fluctuating unbalanced force) in the Langevin Equation. Unbalanced force is the resultant impulse provided to the brownian particle by the colliding fluid molecules. Therefore, a probability distribution of the speed of the particles after each impact will have the same probability distribution of the white noise. Such a distribution is discovered in this work by constructing a simple model based on thermal molecules colliding with the particle from all directions. The molecules obey Maxwell-Boltzmann speed distribution law. At low temperatures, for bigger brownian particles, existence of some non-random distribution for the unbalanced impulse, in itself is an interesting result. The distribution takes a near half gaussian form at these limits. At high temperatures, for small brownian particles(e.g: pollen grains), the distribution is shown to approach uniform distribution, and hence consistent with bulk of well established theoretical assumptions and experimental results in the literature that claims the unbalanced force to be a random white noise.

cond-mat.stat-mech↗

arXiv2022

Two-stream Plasma Instability as a Potential Mechanism for Particle Escape from the Venusian Ionosphere

In this work we investigate the possibility of two-stream instability in the Venusian atmosphere to lead to momentum transfer to subsequent escape of Hydrogen and Oxygen ions from the ionosphere. We employ the hydrodynamic model and obtain the linear dispersion relation from which the two-stream instability is studied. Further the interaction of solar wind with the ions of Venus ionosphere from which the instability sets in, has been studied with the data from ASPERA-4 of Venus Express (VEX). The data supports the fact that the two-stream instability can provide sufficient energy to accelerate ions to escape velocity of the planet.

physics.plasm-ph↗

arXiv2022

Chaotic Excitations of Rogue Waves in Stable Parametric Region for Highly-Energetic Pair Plasmas

We have studied the Rogue wave existence and propagation in Ion-acoustic mode for the highly energetic case using kappa distributed electrons in accordance with the Korteweg de Vries equation that is modified KdV and extended KdV equation. We have used reductive perturbation method. We first examined the linear dispersive behaviour in Ionacoustic mode. Obtaining the Nonlinear Schrodinger equation, we simulated Rogue wave and examined dynamics of it, and its response to small perturbations. We discussed the possibility of generation of Rogue wave as well as the stability of this against various parameters like wave number, spatial and time component. This study is quite helpful for understanding some prominent points of the nonlinearity of IA waves and Rogue wave generation of the highly energetic case in space plasma also in a laboratory plasma.

physics.plasm-ph↗