Title: Well behaved class of Heintzmann's solution within $f(R,\,T)$ framework

Abstract: The primary objective of this paper is to develop a well-behaved class of Heintzmann IIa [{\em H. Heintzmann, Z. Physik 228, 489-493 (1969)}] solution in the context of $f(R,\, T)$ gravity. In the $f(R, T)$ framework, the gravitational action includes both the Ricci scalar ($R$) and the trace of the energy-momentum tensor ($T$). We chose a particular $f(R,\,T)$ model s.t. $f(R,\,T) = R+2 \chi T$, where $\chi$ is known as the coupling parameter. This solution describes a novel isotropic compact fluid sphere with positively finite central pressure and density in this extended theory of gravity. The results obtained analytically are better described by graphical representations of the physical parameters for various values of the coupling parameter $\chi$. The solution for a specific compact object, Vela X-1, with radius $\mathfrak{R} = 9.56_{-0.08}^{+0.08}$ km and mass $\mathcal{M} = 1.77 \pm 0.08~\mathcal{M}_{\odot}$ [{\em M. L. Rawls et al. ApJ, 730, 25 (2011)}], is shown here. We analyze the fundamental physical attributes of the star, which reveals the influence of the coupling parameter $\chi$ on the values of substance parameters. This helps us to make a fruitful comparison of this modified $f(R,\, T)$ gravity with the standard GR and notice that it holds good for stable compact objects. In this framework, the star under our consideration exhibits a stable structure consistent with the Heintzmann IIa {\em ansatz}. From all of our obtained graphical and numerical results, we can ultimately conclude that our reported model is physically admissible and satisfies all the physical criteria for an acceptable model.