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IGR J20084+3221 is a previously unclassified Galactic source first detected by INTEGRAL. Chandra observations led to possible classifications of either a magnetic Cataclysmic Variable (mCV) or high mass X-ray binary (HMXB) based on the hardness of its spectrum. Here, we report follow-up observations taken by XMM-Newton, NuSTAR and the Hale Telescope at Palomar Observatory. Based on these observations, we conclude that IGR J20084+3221 is most likely an Intermediate Polar (IP) type mCV. Timing analysis of the X-ray data found a significant peak period of P = 635.0 ± 0.4 s, which we interpret to be the spin period of the white dwarf (WD). The X-ray spectrum is well fit to an absorbed Bremsstrahlung model with components accounting for partial covering, reflection, and a fluorescent Fe-line, all typical for an IP. The optical spectrum shows clear emission lines, consistent with emission dominated by an accretion disk. We find counterparts to the source across the optical and infrared (IR) bands, and, despite uncertainties in the distance and extinction, we estimate that the source is too faint in the IR to be an HMXB. Given the evidence pointing towards an IP classification, we fit the X-ray spectrum to a post-shock region model where we find a WD mass of <inline-formula><tex-math id="TM0001" notation="LaTeX">$M=1.09^{+0.12}_{-0.11}$</tex-math></inline-formula>M<SUB>⊙</SUB>, larger than the average mass for a WD in an mCV.

It is known that the mass distribution of the known neutron stars (NSs) exhibits a bimodal pattern. The origin of this distribution remains a subject of debate. We constructed a super-Eddington accretion model for accreting NSs and investigated the mass growth and distribution of these stars using the population synthesis method. We find, in our model, the mass growth of NSs depends on the binary orbital period and the mass of the donor star. Our results can successfully account for the bimodal distribution of NS masses. The peak distribution of NS masses at around ∼1.8 M<SUB>⊙</SUB> primarily originates from NS binary systems where the donor star mass is less than ∼1.6 M<SUB>⊙</SUB> and the orbital period is shorter than 20 days; meanwhile, NS systems may undergo common envelope evolution and these NSs can account for the mass peak at 1.4 M<SUB>⊙</SUB>.

We present analysis and modeling of optical and infrared (IR) spectroscopy of the type II supernova (SN II) 2024ggi obtained with ground-based instruments and the James Webb Space Telescope (JWST) at phases of ∼265─400 days. The near- and mid-IR spectra reveal diverse iron-group emission-line morphologies, including double-peaked profiles in [Ni I] 3.119 and 11.998 μm, [Fe II] 1.644 and 17.931 μm, and [Co I] 12.255 μm, alongside Gaussian profiles in [Ni II] 1.939 μm, [Co II] 10.520 μm, and [Ni I] 7.505 and 11.304 μm. These differences imply both chemical inhomogeneity and the aspherical ionization of inner ejecta, consistent with expectations from the <SUP>56</SUP>Ni bubble effect. The modeling of double-peaked profiles supports an ejecta distribution with polar enhancements as large as ∼7 for Ni-/Co-/Fe-rich material and ∼2 for intermediate-mass elements. LTE estimates imply a stable Ni mass of M<SUB>Ni</SUB> ≍ 2.1 × 10<SUP>−3</SUP> M<SUB>⊙</SUB>, but electron densities near critical values indicate departures from LTE. Comparisons to non-LTE radiative transfer models favor a progenitor mass of ∼12─15.2 M<SUB>⊙</SUB>. We show that a simple mapping between the elemental mass distribution and projected velocity reproduces line profiles produced in a CMFGEN radiative transfer calculation. We apply this property to 3D neutrino-driven explosion simulations and predict Ni emission profiles for varying viewing angles. We find that only energetic 3D explosion models of high-mass progenitors reproduce the observed extent of Ni mixing in SN 2024ggi, conflicting with the progenitor masses inferred from radiative transfer models. These results demonstrate the utility of resolved nebular IR lines as direct probes of the 3D distribution of explosively synthesized material in core-collapse SNe.