Research

Using high-resolution (~0.2″) ALMA observations of HCN, H¹³CN and HC¹⁵N J=4–3 towards the circumbinary disk around V4046 Sgr, I fitted the hyperfine-resolved spectra simultaneously with an MCMC pipeline to derive radially resolved isotope ratios.

The ¹⁴N/¹⁵N ratio rises from ~60 at 20 au to above 500 near 76 au, revealing strong ¹⁵N enrichment in the inner, planet-forming disk. This trend is consistent with isotope-selective photodissociation of N₂ in UV-irradiated disk layers, and spans values characteristic of comets and the Earth. The ¹²C/¹³C ratio stays near ~100 at intermediate radii before falling to the local ISM value.

Status: first-author paper submitted to ApJ.

Key techniques: ALMA imaging (CASA) • hyperfine line fitting with MCMC (emcee) • radial profiles with GoFish • rotational diagrams • isotope fractionation

Ultraviolet radiation and the gas-phase carbon-to-oxygen (C/O) ratio shape the chemistry of the irradiated surface layers of disks. CN, C₂H and HCN are often used to study this chemistry, but they have rarely been compared at the same spatial resolution.

I combine new ALMA observations of CN with C₂H and HCN data from the ALMA Large Program DECO (Disk-Exoplanet C/Onnection) for about 12 disks around K- and M-type stars. For each disk I match the resolution, extract spectra on a common radial grid and fit the hyperfine structure of all three molecules with the same model. I then compare where they emit, their column densities and excitation temperatures, and look for correlations with stellar, disk and chemical properties, including the C/O ratio.

Status: first-author paper in preparation.

Key techniques: Beam matching and spectral extraction • hyperfine line fitting • column densities and excitation temperatures • correlation analysis

Research project at PUC, mentored by Prof. Gijs Mulders and Dr Pietro Curone.

Most disks in Lupus are compact in dust, but how far their gas extends is largely unknown. If dust grains drift inwards efficiently, the gas disk should be much larger than the dust disk. I calibrated and imaged ALMA Band 6 observations of CO J=2–1 towards 33 compact disks in Lupus.

CO was not detected in any of them with the short integration per source (~7 minutes). Comparing these non-detections with the CO flux expected from each disk's continuum, and accounting for beam dilution, I derived lower limits on the gas disk sizes and on the gas-to-dust size ratio. The limits are consistent with gas disks that extend beyond the dust, as expected if radial drift is efficient, and motivate deeper observations.

Key techniques: ALMA calibration and imaging (CASA) • sensitivity and beam-dilution estimates • gas and dust disk sizes

Project Fellow, CHRIST University, Bangalore, India. Paper: Detection of a new sample of Galactic white dwarfs in the direction of the Small Magellanic Cloud (A&A 690, A68).

This project demonstrated the power of combining the Ultraviolet Imaging Telescope (UVIT) and Gaia DR3 for large-scale white dwarf discovery. We identified 43 single white dwarfs (37 of them new) and derived their masses, effective temperatures and cooling ages using white dwarf evolutionary models. The study also reported new extremely low-mass white dwarf candidates and estimated the local white dwarf space density.

Key techniques: Multi-wavelength photometry (UVIT, Gaia) • spectral energy distribution fitting • stellar evolutionary models • Python

M.Sc. thesis, CHRIST University, Bangalore, India; advisor Dr Blesson Mathew. Study of disk evolution in classical Be stars using LAMOST medium-resolution spectra.

This thesis used medium-resolution (R ≈ 7500) LAMOST DR7 spectra to study disk evolution in classical Be stars. From multi-epoch data, I identified 10 stars with line-profile variability and 15 with variable Hα emission strength. Light-curve analyses gave variability periods, providing insight into disk formation and the possible role of binarity in the “Be phenomenon”.

Key techniques: LAMOST spectroscopy • time-series and periodogram analysis • disk variability • Python