We develop the equation of state (EOS) of protoneutron stars (PNSs) at various stages of evolution by varying entropy per baryon $S$, using the Korea-IBS-Daegu-SKKU density functional model. With finite values for both temperature and density, we systematically investigate the influence of nucleon effective mass on the EOS of PNSs, for different values of isoscalar effective mass ${\mu }_S^{*}$. For high entropy values, we aim to replicate conditions of failed core-collapse supernovae forming black holes. At each stage of evolution, structural and nonradial oscillation (fundamental $f$-mode and first pressure $p_1$-mode) properties are computed under isentropic conditions by varying ${\mu }_S^{*}$. We focus on the effects of $S$ and ${\mu }_S^{*}$ on the oscillation frequencies $f_f$ and $f_{p_1}$, adopting complete general relativistic formalism and Cowling approximation. Thermal effects reduce the values of $f_f$ and $f_{p_1}$ of PNSs compared to those of cold NSs; consequently the detection of the former gets facilitated. For high-mass PNSs, this reduction is more pronounced for $f_{p_1}$ than $f_f$. Moreover, lower values of ${\mu }_S^{*}$ reduce $f_f$ and $f_{p_1}$ further. Universality of mass-scaled angular frequency (${\omega }_{f}M$) with compactness ($C$) and tidal deformability ($\mathrm{\Lambda }$) are obtained as nonlinear fits that shift upwards (downwards) in the ${\omega }_{f}M-C$ (${\omega }_{f}M-\mathrm{\Lambda }$) plane for increasing values of $S$. For fixed $S$, the universality is also retained for variation of ${\mu }_S^{*}$. $S$ shows a stronger correlation than ${\mu }_S^{*}$ with the structural and oscillation properties of (P)NSs. The strength of the correlation of $S$ is more prominent with $f_{p_1}$ than $f_f$ while the trend is opposite for ${\mu }_S^{*}$. These findings suggest that detection of oscillation frequencies by upcoming GW detectors, could potentially indicate the evolutionary stage of a star during its transition from supernova to cold NS.

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• Nuclear astrophysics
• Nuclear density functional theory
• Nuclear matter in neutron stars