arXiv subjects

Oren Ironi

Publications and source records attributed to Oren Ironi.

3 recordsLinked to original sources

arXiv2026

IK Pegasi and the Double-merger Path to Type Ia Supernovae

Recent Gaia astrometry has revealed thousands of main-sequence + white-dwarf binaries (MS+WD) at separations of ~0.1-10 au, including a subset hosting unusually massive (>~0.8 Msun) WDs. We argue that s-process enrichment in the non-degenerate companion provides a powerful diagnostic for identifying WDs that formed via mergers in hierarchical triple systems. For a massive WD, standard single-star evolution requires a massive (>~4 Msun) progenitor, yet such progenitors produce negligible s-process yields. We define IK Peg-type systems as those exhibiting this mass-yield tension: barium-enhanced companions orbiting WDs too massive to have descended from efficient s-process producers. The well-known system IK Peg exemplifies this class. Applying this framework to published spectroscopic data reveals several additional candidates, and we estimate that a few dozen such systems should exist in the current Gaia sample. If these systems trace inner-binary mergers in primordial triples, they represent observable intermediate stages toward eventual Type Ia supernovae via the double-merger pathway, as predicted by recent population-synthesis models.

astro-ph.SR↗

arXiv2025

The initial-to-final mass relation of white dwarfs in intermediate-separation binaries

We examine the applicability of the initial-to-final mass relation (IFMR) for white dwarfs (WDs) in intermediate-separation binary systems (approximately 1 AU), using astrometric binaries identified in open clusters from Gaia DR3. A careful analysis of the astrometric orbits and spectral energy distributions isolates 33 main-sequence (MS) stars with highly likely WD companions. By combining cluster age estimates, dynamically measured WD masses, and, where available, WD cooling temperatures, we derive progenitor masses for 26 WD candidates. Our analysis suggests the presence of two distinct WD populations: (i) low-mass WDs, likely shaped by binary interactions during the progenitor's red-giant phase; and (ii) "spender" WDs, which experienced higher-than-expected mass loss and have progenitor masses above the IFMR predictions. The rest of the candidates, referred to as the "others", represent systems with inconclusive formation mechanisms. We suggest that at least some of these systems might be hierarchical triples, where the companion to the MS is a double WD or a double-WD merger product. However, follow-up studies are required to determine the nature of each case. These results highlight significant deviations from the IFMR derived for isolated WDs, emphasizing the role of binary evolution. Follow-up observations, particularly in the far-ultraviolet, are crucial for refining these findings and advancing our understanding of mass transfer processes and binary evolution pathways.

astro-ph.SR↗

arXiv2024

HighSpec: A High-Resolution Spectrograph for the MAST Telescope Array

We present the updated design of HighSpec, a high-resolution $\mathcal{R} \sim 20,000$ spectrograph designed for the Multi Aperture Spectroscopic Telescope (MAST). HighSpec offers three observing modes centered at the Ca II H&K, Mg b triplet, and H$α$ lines. Each mode is supported by a highly optimized ion-etched grating, contributing to an exceptional instrument peak efficiency of $\gtrsim85\%$ for the two latter bands ($\gtrsim55\%$ for the Ca II H&K band). Optimizing throughput over wavelength coverage ($Δλ=10-17$ nm), HighSpec enables the precise measurement of spectral lines from faint targets. This approach is especially relevant for stellar object studies, specifically of WDs, which are intrinsically faint and have few spectroscopic lines. Each observing mode was tailored to target spectral features essential for WD research. Its integration with MAST, an array of 20 custom-designed telescopes that can function as a single large telescope (equivalent to a $2.7$ m telescope in collecting area) or multiplexing over the entire sky, provides unique adaptability for extensive and effective spectroscopic campaigns. Currently in its final assembly and testing stages, HighSpec's on-sky commissioning is scheduled for 2025.

astro-ph.IM↗