Probing the evolving massive star population in Orion with kinematic and radioactive tracers

Rasmus Voss$^1$, Roland Diehl$^1$, Jorick S. Vink$^2$, Dieter H. Hartmann$^3$

1 - Max Planck institute for extraterrestrial physics; 2 - Armagh observatory; 3 - Clemson University

Orion is the nearest star-forming region to host a significant number of young and massive stars. The energy injected by these OB stars is thought to have created the Eridanus superbubble. Because of its proximity, Orion is a prime target for a detailed investigation of the interaction between massive stars and their environment.
We study the massive star population of Orion and its feedback in terms of energy and mass, in order to compare the current knowledge of massive stars with kinematic and radioactive tracers in the surrounding interstellar medium (ISM). We assembled a census of the most massive stars in Orion, then used stellar isochrones to estimate their masses and ages, and used these results to establish the stellar content of Orion's individual OB associations. From this, our new population synthesis code was utilized to derive
the history of the emission of UV radiation and kinetic energy of the material ejected by the massive stars and also to follow the ejection of the long-lived radioactive isotopes $^{26}$Al and $^{60}$Fe. To estimate the precision of our method, we compare and contrast three distinct representations of the massive stars. We compared the expected outputs with observations of $^{26}$Al gamma-ray signal and the extent of the Eridanus cavity.
We find an integrated kinetic energy emitted by the massive stars of 1.8$^{+1.5}_{-0.4}times10^{52}$ erg. This number is consistent with the energy thought to be required to create the Eridanus superbubble. We also find good agreement between our model and the observed $^{26}$Al signal, estimating a mass of $5.8^{+2.7}_{-2.5}times10^{-4}$ $M_{odot}$ of $^{26}$Al in the Orion region.
Our population synthesis approach is demonstrated for the Orion region to reproduce three different kinds of observable outputs from massive stars in a consistent manner: Kinetic energy as manifested in ISM excavation, and ionization as manifested in free-free emission, and nucleosynthesis ejecta as manifested in radioactivity gammarays. The good match between our model and the observables does not argue for considerable modifications of mass loss. If clumping effects turn out to be strong, other processes would need to be identified to compensate for their impact on massive-star outputs. Our population synthesis analysis jointly treats kinematic output and the return of radioactive isotopes, which proves a powerful extension of the methodology that constrains feedback from massive stars.

Reference: A&A
Status: Manuscript has been accepted