arXiv subjects

A. Choudhary

Publications and source records attributed to A. Choudhary.

3 recordsLinked to original sources

arXiv2026

A Quiet Host in an Active Planet-Forming Disk: Optical Spectroscopy of WISPIT 2

WISPIT 2 is a young pre-main-sequence star hosting a multi-ringed transition disk and two directly imaged protoplanets, including the accreting WISPIT 2b, making it the closest known analogue to PDS 70. We present the first optical spectrum of its central star, obtained with HFOSC on the 2-m Himalayan Chandra Telescope, and derive its atmospheric parameters, test its youth, and constrain its accretion state. We analyse low-resolution spectra with iSpec and validate the pipeline at HFOSC resolution against Gaia FGK Benchmark Stars and K-type pre-main-sequence templates. We measure T_eff = 4551 +/- 150 K, log g = 4.32 +/- 0.18, and a low-resolution, model-dependent global metallicity [M/H] = -0.17 +/- 0.16. The surface gravity and Li I equivalent width support the pre-main-sequence nature of the host. H-alpha remains in net absorption but is partially filled by weak emission at only 1.5-2.0 sigma, approximately 1.1 dex below the expected chromospheric-noise level and therefore consistent with chromospheric activity rather than detectable accretion. We place a 95% upper limit on the stellar accretion rate of 3.6 x 10^-11 solar masses per year, below even the lowest monitored value for PDS 70 and implying a host-to-planet accretion-rate ratio below approximately 18. Both known double-protoplanet hosts therefore show strongly suppressed or undetectable stellar accretion. Larger spectroscopic samples are needed to determine whether this is common in multi-protoplanet transition disks.

astro-ph.SR↗

arXiv2025

Magnetic ground state, critical analysis of magnetization, and large magnetocaloric effect in the ferromagnetically coupled kagome lattice YCa$_3$(MnO)$_3$(BO$_3$)$_4$

We report a detailed study of the magnetic properties, critical analysis of magnetization, and magnetocaloric effect of a spin-$2$ kagome lattice YCa$_3$(MnO)$_3$(BO$_3$)$_4$. The experiments are complemented by the density functional band structure calculations. The magnetic measurements suggest a highly frustrated nature of the compound due to competing ferro- and antiferromagnetic interactions with the dominant one being ferromagnetic. It undergoes a unconventional ferromagnetic ordering at $T^* \simeq 7.8$ K and a field induced metamagnetic transition in low fields, implying spin canting. A $H$-$T$ phase diagram is constructed that features three phase regimes. Indeed, the band structure calculations reveal dominant ferromagnetic interaction along the chains that are coupled antiferromagnetically yielding a frustrated kagome geometry. This compound shows a large magnetocaloric effect with isothermal entropy change $ΔS_{\rm m} \simeq 12$ J/kg-K, adiabatic temperature change $ΔT_{\rm ad} \simeq 8.4$ K, and relative cooling power $RCP \simeq 349$ J/kg for a field change of 7 T. The critical analysis of magnetization and magnetocaloric parameters suggests that the transition is a second order phase transition and it is tricritical mean field type. Owing to it's large magnetocaloric parameters, second order phase transition, and no thermal hysteresis, YCa$_3$(MnO)$_3$(BO$_3$)$_4$ emerges as a potential rare-earth free material for magnetic refrigeration.

cond-mat.mtrl-sci↗

arXiv2019

Inertial migration of an electrophoretic rigid sphere in a two-dimensional Poiseuille flow

In this work, we analyze the inertial migration of an electrophoretic particle in a 2-D Poiseuille flow with an electric field applied parallel to the walls. For a thin electrical double layer, the particle exhibits a slip-driven electrokinetic motion along the direction of the applied electric field, which causes the particle to lead or lag the flow (depending on its surface charge). The fluid disturbance caused by this slip-driven motion is characterized by a rapidly decaying source-dipole field which alters the inertial lift on the particle. We determine this inertial lift using the reciprocal theorem. Assuming no wall effects, we derive an analytical expression for a phoretic-lift which captures the modification to the inertial lift due to electrophoresis. We also take wall effects into account and find that the analytical expression is valid away from the walls. We find that for a leading particle, the phoretic-lift acts towards the regions of high shear (i.e. walls), while the reverse is true for a lagging particle. Using an order-of-magnitude analysis, we obtain different components which contribute to the inertial force and classify them on the basis of the interactions from which they emerge. We show that the dominant contribution to the phoretic-lift originates from the interaction of slip-driven source-dipole field with the stresslet field (generated due to particle's resistance to strain in the background flow). Furthermore, to contrast the slip-driven phenomenon from a force-driven phenomenon in terms of their influence on the inertial migration, we also study a non-neutrally buoyant particle. We show that the gravitational effects alter the inertial lift primarily through the interaction of background shear with buoyancy induced stokeslet field.

physics.flu-dyn↗