arXiv subjects

Tirupati Kumara Sridharan

Publications and source records attributed to Tirupati Kumara Sridharan.

4 recordsLinked to original sources

arXiv2026

A Cyanopolyyne-rich but COM-poor Massive Protostar: The First Hot Carbon Chain Chemistry Source G28.28-0.36

We present molecular emission line data from the massive young stellar object (MYSO) G28.28-0.36 (G28.28) obtained with the Atacama Large Millimeter/submillimeter Array Band 3. Cyanopolyynes (HC$_3$N and HC$_5$N) and three complex organic molecules (COMs; CH$_3$OH, CH$_3$CN, and CH$_3$CHO) are detected from the MYSO G28.28. In addition, strong emission regions of cyanopolyynes are identified between G28.28 and a nearby ultracompact H II region. The HC$_5$N emission is coincident with the dust continuum peak, where an excitation temperature of 100 K is derived from CH$_3$CN. These results suggest that the Hot Carbon Chain Chemistry (HCCC) mechanism produces cyanopolyynes in the hot region around G28.28. We find that G28.28 exhibits a unique chemical feature: cyanopolyynes are abundant, but COMs are deficient, unlike the other MYSOs studied previously. These results imply that G28.28 is a counterpart of the Warm Carbon Chain Chemistry (WCCC) low-mass source L1527. G28.28 is the first HCCC source identified so far.

astro-ph.GA↗

arXiv2026

The ngVLA Band-4 Water Vapor Radiometry Concept

The ngVLA has adopted a standalone system with a $\sim$~1.5 m diameter antenna and associated ambient temperature receiver and electronics at each antenna as its baseline design for water vapor radiometer (WVR). The WVR is intended to decrease calibration overheads for tropospheric phase correction for the high frequency bands (5 \& 6; 30.5-116 GHz) to levels lower than feasible with fast switched reference gain calibration. In this memo, we present an alternative concept utilizing the standard Band-4 science receivers and the main antennas. This would require the Band-4 feed to be placed between those of Bands 5 \& 6 resulting in a beam offset of 0.8 deg, similar to the beam size of the standalone 1.5 m antenna. The main benefits of the Band-4 WVR concept are: (1) sensing water vapor in a region more representative of the Band 5 \& 6 science beams in the lower layers of the troposphere, in the near-field of the 18 m antenna, than the 1.5 m antenna (2) significantly relaxing the stability requirements due to the lower receiver temperature of the standard Band-4 cryogenic receiver and (3) eliminating the procurement, deployment, and maintenance of a large number of standalone units. Given these advantages, it is recommended that the details and the pros and cons of Band-4 WVR implementation compared a standalone system be carefully considered.

astro-ph.IM↗

arXiv2025

Preliminary Baseline Antenna Design for the Black Hole Explorer (BHEX) Mission

The Black Hole Explorer (BHEX) mission extends the submillimeter Very-Long-Baseline Interferometry (VLBI) to space. The preliminary baseline design of a shaped axial-symmetric displaced-axis dual-reflector antenna for the BHEX is presented. The main goal of the antenna design optimization is to maximize aperture efficiency given the geometric and mechanical constraints of a space-borne antenna.

astro-ph.IM↗

arXiv2025

Origin of the IRAS Vela Shell: New Insights from 3D Dust Mapping

The IRAS Vela Shell (IVS) is a structure of enhanced FIR emission located towards the Gum Nebula, a prominent region of $\rm Hα$ emission in the local Milky Way shaped by various galactic stellar feedback over the past several million years. We constrain the 3D spatial geometry of the IVS using a parsec-resolution 3D dust map and contextualize it within the broader Gum Nebula. Our analysis reveals a dense, bowl-like IVS structure below the Galactic plane, with a more diffuse component above. We obtain a total shell mass of $5.1_{-2.4}^{+2.4}\times 10^{4}\;\rm M_{\odot}$ and, incorporating previous studies on shell expansion, a momentum of $6.0_{-3.4}^{+4.7}\times 10^{5}\;\rm M_{\odot}\;km\; s^{-1}$. We find a spatial correlation between the morphology of the dust-traced IVS and the Gum Nebula's $\rm Hα$ emission when projected onto the sky. We quantify contributions of feedback from stellar winds, an expanding HII region, and supernovae to the IVS formation, finding that stellar winds are subdominant. Our momentum analysis shows that both an HII region and supernova feedback could drive the shell's expansion. Using astrometric constraints from Gaia and Hipparcos, we trace back nearby feedback sources and find that the massive stars $\gamma2$ Velorum and $ζ$ Puppis are currently within the IVS, producing enough ionizing luminosity to form an HII region of comparable size. Alternatively, if the IVS' momentum is primarily driven by supernovae, $1-2$ events would be required. We also identify several young massive clusters that could have hosted supernovae within the past 3 Myr.

astro-ph.GA↗