Dr. Gautham Sabhahit<br>

Dr. Gautham Sabhahit

Stellar Astrophysicist

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A list of all the posts and pages found on the site. For you robots out there, there is an XML version available for digesting as well.

Pages

Posts

portfolio

publications

Maximum black hole mass across cosmic time

Authors: Jorick S. Vink, Erin R. Higgins, Andreas A. C. Sander, Gautham N. Sabhahit

Published in Monthly Notices of the Royal Astronomical Society, 2021

  • gravitational waves
  • stars: black holes
  • stars: evolution
  • stars: massive
  • stars: mass-loss
  • stars: winds, outflows

NASA ADS | DOI

Mass-loss implementation and temperature evolution of very massive stars

Authors: Gautham N. Sabhahit, Jorick S. Vink, Erin R. Higgins, Andreas A. C. Sander

Published in Monthly Notices of the Royal Astronomical Society, 2022

We present a mass-loss framework tailored to studying the evolution of very massive stars at Galactic and LMC-like metallicities. We apply the concept of a model-independent anchor point - the so-called transition mass-loss rate - in young massive clusters within these two galaxies, specifically the Arches cluster near the Galactic Center and the Tarantula Nebula in the LMC. The concept of the transition mass-loss rate is straightforward: it is an analytical expression derived from fundamental principles of wind hydrodynamics that predicts the mass-loss rate of stars in spectral morphological transition between O-type stars with absorption-dominated spectra to WNh-type Wolf–Rayet stars with hydrogen-rich, emission-dominated spectra. For these transitional “slash” stars, both the wind efficiency and wind optical depth are roughly unity. The key advantage of using the transition mass-loss rate is that it is far less model-dependent and more accurate than traditional mass-loss diagnostics based on underlying atmosphere models which are heavily plagued by clumping uncertainties and can suffer from uncertainties more than an order of magnitude.

For inlists and runstars for the MESA implementation, See MESA inlists and runstars here

  • stars: evolution
  • stars: massive
  • stars: mass-loss
  • stars: winds, outflows

NASA ADS | DOI

X-Shooting ULLYSES: Massive stars at low metallicity. I. Project description

Authors: Jorick S. Vink, A. Mehner, P. A. Crowther, A. Fullerton, M. Garcia, F. Martins, N. Morrell, L. M. Oskinova, N. St-Louis, A. ud-Doula, A. A. C. Sander, H. Sana, J. -C. Bouret, B. Kubátová, P. Marchant, L. P. Martins, A. Wofford, J. Th. van Loon, O. Grace Telford, Y. Götberg, D. M. Bowman, C. Erba, V. M. Kalari, M. Abdul-Masih, T. Alkousa, F. Backs, C. L. Barbosa, S. R. Berlanas, M. Bernini-Peron, J. M. Bestenlehner, R. Blomme, J. Bodensteiner, S. A. Brands, C. J. Evans, A. David-Uraz, F. A. Driessen, K. Dsilva, S. Geen, V. M. A. Gómez-González, L. Grassitelli, W. -R. Hamann, C. Hawcroft, A. Herrero, E. R. Higgins, D. John Hillier, R. Ignace, A. G. Istrate, L. Kaper, N. D. Kee, C. Kehrig, Z. Keszthelyi, J. Klencki, A. de Koter, R. Kuiper, E. Laplace, C. J. K. Larkin, R. R. Lefever, C. Leitherer, D. J. Lennon, L. Mahy, J. Maíz Apellániz, G. Maravelias, W. Marcolino, A. F. McLeod, S. E. de Mink, F. Najarro, M. S. Oey, T. N. Parsons, D. Pauli, M. G. Pedersen, R. K. Prinja, V. Ramachandran, M. C. Ramírez-Tannus, G. N. Sabhahit, A. Schootemeijer, S. Reyero Serantes, T. Shenar, G. S. Stringfellow, N. Sudnik, F. Tramper, L. Wang

Published in Astronomy and Astrophysics, 2023

  • stars: atmospheres
  • stars: early-type
  • stars: winds, outflows
  • stars: evolution
  • methods: observational
  • galaxies: dwarf

NASA ADS | DOI

Very massive stars and pair-instability supernovae: mass-loss framework for low metallicity

Authors: Gautham N. Sabhahit, Jorick S. Vink, Andreas A. C. Sander, Erin R. Higgins

Published in Monthly Notices of the Royal Astronomical Society, 2023

This work is a follow-up to the high-metallicity (Galactic and LMC-like) mass-loss framework for very massive stars presented in Sabhahit et al. (2022). Unlike in the Galaxy and the LMC, where young, massive clusters allow us to apply a model-independent transition mass-loss rate, for SMC-like and lower metallicity environments, we must rely on a more theoretical approach to determine this transition point. We use the hydrodynamical branch of the PoWR atmosphere code to parameterize the transition and introduce a novel framework for implementing a mass-loss prescription tailored to studying VMS evolution at low metallicity. With this new framework, we can predict the metallicity threshold below which pair-instability supernovae are expected to occur in the Universe.

For inlists and runstars for the MESA implementation, See MESA inlists and runstars here

  • stars: evolution
  • stars: massive
  • stars: mass-loss
  • stars: winds, outflows

NASA ADS | DOI

Stellar wind yields of very massive stars

Authors: Erin R. Higgins, Jorick S. Vink, Raphael Hirschi, Alison M. Laird, Gautham N. Sabhahit

Published in Monthly Notices of the Royal Astronomical Society, 2023

  • stars: massive
  • stars: evolution
  • stars: abundances
  • stars: mass-loss
  • stars: interiors
  • nuclear reactions, nucleosynthesis, abundances

NASA ADS | DOI

Stellar expansion or inflation?

Authors: Gautham N. Sabhahit, Jorick S. Vink

Published in Astronomy and Astrophysics, 2025

This paper explores the differences between two very distinct phenomena that can result in a rapid increase in stellar radius over short timescales. The expansion of a stellar envelope beyond the Main Sequence in intermediate and massive stars has been documented for decades, whereas the concept of strong radial inflation as a star approaches its local Eddington limit is a more recent development. In this work, we elucidate the differences between these two phenomena through illustrative examples showing detailed internal structure.

  • stars: black holes
  • stars: evolution
  • stars: interiors
  • stars: massive
  • stars: mass-loss

NASA ADS | DOI

A new mass estimate method with hydrodynamical atmospheres for very massive WNh stars

Authors: Gautham N. Sabhahit, Jorick S. Vink, Andreas A. C. Sander, Matheus Bernini-Peron, Paul A. Crowther, Roel R. Lefever, Tomer Shenar

Published in Astronomy and Astrophysics, 2025

We present the first-ever hydrodynamical wind modelling of two very massive star systems in the Tarantula Nebula, using the PoWR atmosphere code. The first system, R144, is a binary composed of two WNh stars, while the second, R136a1, is the current record holder for the most massive known star in the Local Group. We utilize the next-generation hydrodynamical capabilities of PoWR to simultaneously empirically derive and theoretically predict wind properties for both systems. By coupling wind hydrodynamics with atmosphere modelling, we can also predict a mass of 233 Msun for R136a1.

  • stars: atmospheres
  • binaries: spectroscopic
  • stars: massive
  • stars: mass-loss
  • stars: winds, outflows
  • stars: Wolf-Rayet

NASA ADS | DOI

Hydrodynamical mass-loss rates for Very Massive Stars. II. New theoretical mass-loss predictions at solar metallicity (Z = 0.02)

Authors: Gautham N. Sabhahit, Jorick S. Vink, Andreas A. C. Sander

Published in arXiv e-prints, 2026

This work presents the largest grid to date of hydrodynamically consistent wind-atmosphere models, covering a wide range of stellar parameters relevant to O and WNh stars. We independently confirm an upturn in the mass-loss rate as the wind transitions from optically thin to optically thick, where photons undergo multiple interactions with spectral lines and, on average, transfer momentum to the wind more than once before escaping. The predicted mass-loss rates, terminal wind velocities, and ionising photon flux counts can be used in stellar-evolution models and to study the mechanical and ionising feedback from massive and very massive stars in young clusters.

  • stars: atmospheres
  • stars: massive
  • stars: mass-loss
  • stars: winds, outflows
  • stars: Wolf-Rayet

NASA ADS | DOI

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