arXiv subjects

Vinod Chandra Pathak

Publications and source records attributed to Vinod Chandra Pathak.

3 recordsLinked to original sources

arXiv2026

IPA: Morphology and Kinematics of Molecular Hydrogen Winds in Five Young Protostars across the Mass Spectrum Observed with JWST

Molecular winds may play a key role in governing angular momentum transport and accretion during the early evolution of protostars. We present the morphology and kinematic properties of the H$_2$ emission in five young, envelope-dominated, protostars across a broad bolometric luminosity range, from 0.2 to $10^4~L_{\odot}$, observed with the NIRSpec/IFU and MIRI/MRS onboard JWST as part of the Investigating Protostellar Accretion (IPA) program. A rich set of pure rotational lines of H$_2$, up to $v=0-0$ S(18), and a few ro-vibrational lines are detected in the winds, revealing bipolar structures. The H$_2$ lines show a stratified/onion-like structure morphologically and kinematically, where the lines with higher $E_{\rm up}$ show a higher degree of collimation and higher velocities. Additionally, the wind velocity scales with the $L_{\rm bol}$ of the host protostellar system. In 4 out of 5 protostars, H$_2$ emission fills the outflow cavity without showing pronounced limb brightening. We also report a tentative detection of H$_2$ wind rotation in IRAS 16253, which suggests a launch radius of $\sim4$ au and the magnetic lever arm parameter of $\sim5-10$. Taken together, these properties of the H$_2$ winds can be explained by the magnetohydrodynamic disk wind models. We detect a collimated, high-velocity H$_2$ jet toward HOPS 370, which is more evolved than the extremely young source HH 211, but is accreting at a high accretion rate. This suggests that the presence of collimated molecular jets in protostars is more closely connected to accretion rate than system age.

astro-ph.SR↗

arXiv2026

JWST/MIRI Detection of Molecular H$_2$ Winds from an Edge-on Class II Source HV Tau C

The evolution of protoplanetary disks is regulated by accretion onto the central star and mass loss through jets and winds. While atomic and ionized outflows are commonly observed, molecular winds in evolved Class II disks remain rarely detected. We characterize the spatial, thermal, kinematic, and dynamical properties of molecular hydrogen (H$_2$) emission from the nearly edge-on Class II disk HV Tau C and assess the impact of its molecular wind. We also constrain accretion using H I recombination lines detected in the same mid-infrared spectrum. Using JWST/MIRI-MRS data from the MINDS Cycle 1 GTO program, we analyze spatially resolved pure-rotational H$_2$ emission. Rotational and position-velocity diagrams constrain excitation and kinematics, from which we estimate wind properties. We detect extended H$_2$ emission tracing a wide-angled, biconical molecular wind extending beyond the near-infrared scattered-light disk, ALMA 887 $\mu$m dust continuum, and compact $^{12}$CO ($J=3$-$2$) gas disk. The H$_2$ rotational diagram requires warm ($\sim$600K) and hot ($\sim$2000K) components, similar to those in younger protostars. The gas shows outward motions of a few tens of km s$^{-1}$ and dynamical timescales of tens to hundreds of years. The inferred mass-loss rate is $\sim10^{-8}$ M$_\odot$ yr$^{-1}$, while accretion rates derived from H I lines are $10^{-10}$-$10^{-8}$ M$_\odot$ yr$^{-1}$. The accretion rate may be underestimated because of the edge-on geometry. Our results show that wide-angled molecular H$_2$ winds can persist into the Class II phase, with outflow rates comparable to some protostellar systems, suggesting that such winds may remain important for angular momentum removal, disk evolution, and dispersal. (Abstract modified; see the paper for the full version.)

astro-ph.SR↗

arXiv2025

Improving Accretion Diagnostics for Young Stellar Objects with Mid-infrared Hydrogen lines from JWST/MIRI

We present a comprehensive study of mid-infrared neutral hydrogen (H~\textsc{i}) emission lines in 79 nearby (d $<$ 200 $pc$) young stars using JWST/MIRI. We aim to identify mid-infrared H~\textsc{i} transitions that can serve as reliable accretion diagnostics in young stars, and evaluate their utility in deriving physical conditions of the accreting gas. We identify and measure 22 H~\textsc{i} transitions in the MIRI wavelength regime (5-28 $\mu m$) and perform LTE slab modelling to remove the H\textsubscript{2}O contribution from selected H~\textsc{i} transitions. We find that mid-IR H~\textsc{i} line emission is spatially compact, even for sources with spatially extended [Ne~\textsc{ii}] and [Fe~\textsc{ii}] jets, suggesting minimal contamination from extended jet. Although Pfund~$\alpha$ (H~\textsc{i}~6--5) and Humphreys~$\alpha$ (H~\textsc{i}~7--6) are the strongest lines, they are blended with H$_2$O transitions. This blending necessitates additional processing to remove molecular contamination, thereby limiting their use as accretion diagnostics. Instead, we identify the H~\textsc{i}~(8--6) at 7.502 $\mu m$ and H~\textsc{i}~(10--7) at 8.760 $\mu m$ transitions as better alternatives, as they are largely unaffected by molecular contamination and offer a more reliable means of measuring accretion rates from MIRI spectra. We provide updated empirical relations for converting mid-IR H~\textsc{i} line luminosities into accretion luminosity for 6 different H~\textsc{i} lines in the MIRI wavelength range. Moreover, comparison of observed line ratios with theoretical models shows that MIR H~\textsc{i} lines offer robust constraints on the hydrogen gas density in accretion columns, $n_\mathrm{H} = $10$^{10.6}$ to 10$^{11.2}$ cm$^{-3}$ in most stars, with some stars exhibiting lower densities ($<10^{10}$~cm$^{-3}$), approaching the optically thin regime.

astro-ph.SR↗