Abstract
Abstract Luminous Red Variables are most likely eruptions that are the outcome of stellar mergers. V838 Mon is one of the best-studied members of this class, representing an archetype for stellar mergers resulting from B-type stars. As result of the merger event, “nova-like” eruptions occur driving mass loss from the system. As the gas cools considerable circumstellar dust is formed. V838 Mon erupted in 2002 and is undergoing very dynamic changes in its dust composition, geometry, and infrared luminosity providing a real-time laboratory to validate mineralogical condensation sequences in stellar mergers and evolutionary scenarios. We discuss recent NASA Stratospheric Observatory for Infrared Astronomy 5–38 μm observations combined with archival NASA Spitzer spectra that document the temporal evolution of the freshly formed (within the last ≲20 yr) circumstellar material in the environs of V838 Mon. Changes in the 10 μm spectral region are strong evidence that we are witnessing a classical dust condensation sequence expected to occur in oxygen-rich environments where alumina formation is followed by that of silicates at the temperature cools.
Highlights
Luminous Red Variables (LRVs) are characterized by very high luminosities, low effective temperatures, long ( 200 day) evolution timescales of the eruption, and large eruption energies
The temporal changes observed in the the 10 μm is evidence of a “classical” dust condensation sequence expected to occur in dense oxygen-rich regions
Further synoptic study of V838 Mon in the infrared with Stratospheric Observatory for Infrared Astronomy (SOFIA) and James Webb Space Telescope (JWST) are required to explore timescales for condensation pathways, to ascertain the nature of the colder component contributing to the spectral energy distribution at wavelengths 20 μm, and to understand the spatial distribution of the circumstellar emission
Summary
Luminous Red Variables (LRVs) are characterized by very high luminosities, low effective temperatures, long ( 200 day) evolution timescales of the eruption, and large eruption energies (see Figure 1 in Kasliwal 2012) They display the presence of gas-phase AlO, SiO, SO, SO2 and occasionally H2S emission and/or absorption (Kamiński et al 2018), dusty circumstellar disks that show evidence of alumina (Al2O3), and other solid oxides (Banerjee et al 2015). Comparison of the recent SOFIA measurement of the spectral energy distribution to prior Spitzer spectra obtained almost a decade earlier suggests that in the 10 μm region we are observing signatures of a “classical” dust condensation sequence that is expected to occur in oxygen-rich environments (Tielens 1990; Karovicova et al 2013) where alumina (Al2O3) forms initially in the hot, T ∼ 1700 K dust envelope (Speck et al 2000) followed by the formation of various silicates at cooler temperatures of T ; 1200 K (Tielens et al 1998; Gail & Hoppe 2010)
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