arXiv subjects

Simranpreet Kaur

Publications and source records attributed to Simranpreet Kaur.

7 recordsLinked to original sources

arXiv2026

Discovering and Characterising Exoplanets and Ultracool Dwarfs with the Square Kilometre Array

The majority of the Solar System planets are sources of bright radio emission, driven by energetic electrons trapped within each planet's magnetic field. Detection of this emission from exoplanets provides a unique opportunity to characterise their magnetic fields, which is key to determining the atmospheric evolution of exoplanets. However, a conclusive detection of radio emission from an exoplanet remains at large, primarily due to a lack of sensitivity at low radio frequencies. On the other hand, planet-like radio signatures have been detected on objects called ultracool dwarfs (UCDs) for over two decades. UCDs are of comparable sizes to Jupiter, but are more massive. They also possess similar interior structures to Jupiter, the region where magnetic fields are generated. Therefore, UCDs are ideal targets to study to advance our understanding of how magnetic fields manifest at planetary scales. In this Chapter, we outline the revolutionary role that the Square Kilometre Array will play in the study of exoplanets and UCDs. We anticipate that it will facilitate the first detection of radio emission from giant exoplanets with strong magnetic fields, and will deliver thousands of detections of UCDs within a few hundred parsecs. Combined with very long baseline interferometry, we also expect that astrometric monitoring will enable the detection of planets of a few Earth masses orbiting nearby radio-emitting UCDs. These findings will open a new window into how planets form and evolve in extrasolar systems.

astro-ph.EP↗

arXiv2026

Searching for radio emission from stellar wind-magnetosphere interaction or co-rotation breakdown in brown dwarfs

With the improvements in radio interferometry sensitivity, the quest for coherent radio emission from exoplanets and ultra-cool dwarfs, which is indicative of their magnetic fields, has gained significant momentum in recent years. We investigated the relatively unexplored possibility of radio emission from wide-orbit brown dwarf companions, which may radiate through rapid rotation, as in isolated ultra-cool dwarfs, or via interactions between their extended magnetospheres and the host star's wind. We analysed $\sim 60$ hours of Upgraded Giant Metrewave Radio Telescope and Karl G. Jansky Very Large Array data for a set of well-characterized systems previously unobserved at 0.3-2 GHz. The targets include companions orbiting the G-type stars HD 26161 and BD-004475, the K-type HD 153557A and $\nu$ Oph, and the M dwarfs GJ 3626 and 2MJ01225093-2439505. No detections were obtained with 3$\sigma$ upper limits down to $\sim 25\,\mu$Jy/beam in Stokes V in the best cases. The light-curve analysis also revealed no evidence of short ($\gtrsim$ minutes), intense ($\gtrsim$ mJy) radio bursts. The upper limits provide tentative constraints on model parameters. However, the effects of model uncertainties, limited observational coverage, and intrinsic variability or beaming of the emission must be considered. The improvement in sensitivity of the next-generation radio interferometers will likely allow to go below the expected flux range over a much larger range of free parameters.

astro-ph.SR↗

arXiv2025

Polarized, variable radio emission from the scallop-shell binary system DG CVn

DG CVn is an eruptive variable star and represents the closest member of the known sample of complex periodic variables, or scallop-shell stars. Over the years, this M dwarf binary system has shown significant flaring activity at a wide range of frequencies. Here, we present a detailed analysis of $\sim 14$ hours of radio observations of this stellar system, taken with the Karl G.Jansky Very Large Array at band L, centered at 1.5 GHz. In both $7$-hour long observations, we have found a quiescent, weakly polarized component, that could be ascribable to the incoherent, gyro-synchrotron emission coming from the magnetosphere surrounding one or both stars, along with multiple $\sim90\%$ right-circularly polarized bursts, some of which last for a few minutes, while others being longer, $\gtrsim$ 30 minutes. Some of these bursts show a drift in frequency and time, possibly caused due to beaming effects or the motion of the plasma responsible for the emission. We assess the possible modulation of burst frequency with the primary and secondary periods, and discuss the properties of these bursts, favoring electron cyclotron maser over plasma emission as the likely underlying mechanism. We compare DG CVn's dynamic spectrum to other young M dwarfs and find many similarities. A dedicated proper radio/optical simultaneous follow-up is needed to monitor the long-term variability, increase the statistics of bursts, in order to test whether the co-rotating absorbers detected in optical can drive the observed radio emission, and whether the occurrence of radio bursts correlates with the rotational phase of either stars.

astro-ph.SR↗

arXiv2025

Rossby number regime, convection suppression, and dynamo-generated magnetism in inflated hot Jupiters

Hot Jupiters (HJs) are commonly thought to host the strongest dynamo-generated magnetic fields among exoplanets, up to one order of magnitude larger than Jupiter. Thus, they have often been regarded as the most promising exoplanets to display magnetic star-planet interaction signals and magnetically-driven coherent radio emission, which unfortunately remains elusive, despite many diversified observational campaigns. In this work, we investigate the evolution of the internal convection and dynamo properties of HJs via one-dimensional models. We explore the dependency on orbital distance, planetary and stellar masses, and types of heat injection. We employ one-dimensional evolutionary models to obtain internal convective structures. Specifically, we obtain the Rossby number $\mathrm{Ro}$ as a function of planetary depth and orbital period, after showing that tidal synchronization is likely valid for all HJs. When the heat is applied uniformly, the convective layers of almost all HJs remain in the fast rotator regime, $\mathrm{Ro} \lesssim 0.1$, except possibly the most massive planets with large orbital distances (but still tidally locked). We recover magnetic field strengths for inflated HJs by applying well-known scaling laws for fast rotators. When strong heat sources are applied mostly in the outer envelope and outside the dynamo region, as realistic Ohmic models predict, convection in the dynamo region often breaks down. Consequently, the heat flux and the derived surface magnetic fields can be greatly reduced to or below Jovian values, contrary to what is commonly assumed, thus negatively affecting estimates for coherent radio emission, and possibly explaining the failure in detecting it so far.

astro-ph.EP↗

arXiv2024

Hints of auroral and magnetospheric polarized radio emission from the scallop-shell star 2MASS J05082729$-$2101444

Scallop-shell stars, a recently discovered class of young M dwarfs, show complex optical light curves that are characterized by periodic dips as well as other features that are stable over tens to hundreds of rotation cycles. The origin of these features is not well-understood. 2MASS J05082729$-$2101444 is a $\sim$25 Myr old scallop-shell star that was identified using TESS data; it has a photometric period of 6.73h that has been attributed to rotation. Of the $\sim$50 recently confirmed scallop-shell stars, it is one of the few detected at radio frequencies between 1 and 8 GHz. We observed this rare system with the upgraded Giant Meterwave Radio Telescope at 575--720 MHz, covering 88% of the photometric period in each of the two observations scheduled almost a month apart in 2023. We detected $\sim$millijansky emission from the target in both epochs, with a significant circular polarization fraction: $|V/I|\sim$20--50%. The 3.5-min phase-folded light curves reveal unique variability in circular polarization, showing an $\sim$hour-long helicity reversal in both epochs, similar in amplitude, length, and (possibly) phase. These results suggest two emission components: The first is a persistent, moderately polarized component possibly ascribable to gyro-synchrotron emission driven by centrifugal breakout events. The second is a highly polarized, short burst-like component, likely due to an electron cyclotron maser (ECM), indicative of auroral emission and potentially responsible for the helicity reversal. To explain this, we discuss the different origins of the plasma responsible for the radio emission, including the possibility that the occulting material is acting as a plasma source. Future coordinated multifrequency radio and optical observations can further constrain the underlying scenario, as well as the magnetic geometry of the system, if we assume an ECM-like auroral emission.

astro-ph.SR↗

arXiv2024

Variable, circularly polarized radio emission from the Young Stellar Object [BHB2007]-1: another ingredient of a unique system

The young stellar object [BHB2007]-1 has been extensively studied in the past at radio, millimeter, and infrared wavelengths. It shows a gap in the disk and previous observations claimed the possible emission from a forming sub-stellar object, in correspondence to the disk gap. Here, we analyze a set of 8 Karl Jansky Very Large Array (VLA) observations at 15 GHz and spread over a month. We infer a slowly variable emission from the star, with a $\sim 15 \text{-} 20\%$ circular polarization detected in two of the eight observations. The latter can be related to the magnetic fields in the system, while the unpolarized and moderately varying component can be indicative of free-free emission associated with jet induced shocks or interaction of the stellar wind with dense surrounding material. We discard any relevant short flaring activities when sampling the radio light curves down to 10 seconds and find no clear evidence of emission from the sub-stellar object inferred from past observations, although deeper observations could shed further light on this.

astro-ph.SR↗

arXiv2020

Roles of Blackbody Friction Forces in the Rb and Cs Atom Interferometers

Atom interferometry is amongst the most advanced technologies that provides very high-precision measurements. There can exist a number of obscure forces that can interfere with the atoms used in this instrument. In the present work, we are probing possible roles of one such important forces, known as ``blackbody friction force (BBFF)'', that may affect the precisions in the measurements made using atom interferometers based on the Rb and Cs atoms. The BBFF can be generated on atoms due to the black-body radiations emitted by the stray electromagnetic fields present in the experimental set-up and other metallic shielding. The strength of the BBFF can be calculated by integrating the complex parts of the dynamic polarizabilities of atoms, which show varying behaviour at the resonant and non-resonant transitions in the above atoms. Our analyses suggest that the off-resonant atomic transitions make significant contributions to the BBFF at low temperatures in the Rb and Cs atom interferometers. Present study also advocates that it is imperative to carry out the integration over a wide spectrum of frequencies for correct evaluation of the BBFF; specially at higher temperatures.

physics.atom-ph↗