Tackling the FeO orange band puzzle in meteor and airglow spectra through combined astronomical and laboratory studies

Abstract

The iron oxide ‘orange arc’ bands are unambiguously detected in persistent meteor trains, meteor wakes, and clouds, as well as in the terrestrial airglow. In contrast to the majority of other astronomically important diatomic molecules, theoretical simulation of the FeO rovibronic spectra is not feasible due to the extremely condensed and strongly perturbed multiplet structure of its excited states. In this work, the time-evolution of the laser-induced breakdown spectra (LIBS) of high-purity iron recorded in air at high temperature and impact conditions is used to mimic the FeO pseudo-continuum emission observed during meteor events and the terrestrial night airglow. The relative intensity distributions in the structural continuum of the LIBS spectra are measured at 530–660 nm and a plasma temperature of 1500–6500 K. The anomalous increase of the intensity observed at 620–640 nm and temperature < 2000 K could be attributed to the emission of higher oxides of iron as explained by the conducted thermodynamic and kinetic modeling of iron burning in the atmosphere.

Laboratory modeling in laser-induced plasma to estimate the pressure in bolide wake

“…The spectra of the Benešov bolide obtained in 1991 were described in detail in several works (Borovička & Spurný 1996;Borovička & Berezhnoy 2016;Popov et al 2021) with an emphasis on different aspects. The bolide wake spectrum at an altitude of 39 km has been investigated becausee its Fe and FeO features are intense, while the Ca and CaO signals are weaker than in spectra at other altitudes (Berezhnoy et al 2018).…”

“…Experimental studies of emission spectra and laboratory simulations of their temporal evolution during meteor events are promising approaches. Meteor spectra have been compared with the spectra of laboratory plasma produced via the laser ablation of meteorites (Křivková et al 2021;Milley et al 2007;Ferus et al 2019;Popov et al 2021), high-enthalpy plasma flow systems (Drouard et al 2018;Helber et al 2019), or by arc heater (Agrawal et al 2018). West & Broida (1975) obtained chemiluminescence spectra of FeO that were later subtracted by Berezh-noy et al (2018) from Benešov bolide spectra, which enabled separation and study of the CaO contribution.…”

“…However, chemiluminescence spectra were obtained at low temperature (700 K), while the temperature estimates for bolide wake plasma are significantly higher (2000-4000 K) (Berezhnoy & Borovička 2010). Another effort by Popov et al (2021) demonstrated the applicability of laser-induced breakdown spectrometry (LIBS) to simultaneous simulations of both molecular and atomic components of meteor spectra. A less frequently studied problem is the influence of pressure on the observed spectra.…”

“…The essence of the method is to obtain LIP spectra under conditions similar to those at different meteor observation heights. It is also evident that the experiments at atmospheric pressure (Popov et al 2021) do not allow a full simultaneous reconstruction of the meteor spectrum shape for atomic and molecular features. We therefore study Fe and FeO in LIP under reduced pressure here to develop a meaningful approach for finding the plasma state that reproduces the meteor plasma at a given altitude.…”

Наблюдение Атомной Флуоресценции Кальция В Лазерно Индуцированной Плазме С Высоким Пространственным Разрешением

“…Плазменные источники широко используются в науке и технике для получения и обработки материалов [1], находят применение в медицине [2], используются для определения элементного состава самых разнообразных объектов [3,4], а также для имитации ударных процессов в верхних слоях атмосферы [5]. Все это требует создания подходящих источников плазмы, способов контроля их параметров и подробной информации о пространственном распределении частиц [6].…”