# UV spectroscopy of artificial meteors (200–400 nm)

J. Vaubaillon, N. Rambaux, S. Loehle, P. Matlovič, J. Tóth, Jean-François

Mariscal

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J. Vaubaillon, N. Rambaux, S. Loehle, P. Matlovič, J. Tóth, et al., UV spectroscopy of artificial meteors (200–400 nm). Icarus, 2024, 410 (March), pp.115906. 10.1016/j.icarus.2023.115906. insu-04327909

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UV spectroscopy of artificial meteors (200–400 nm)

J. Vaubaillon, N. Rambaux, S. Loehle, P. Matlovič, J. Tóth,
J.F. Mariscal

PII: S0019-1035(23)00485-2

DOI: https://doi.org/10.1016/j.icarus.2023.115906

Reference: YICAR 115906

To appear in: *Icarus*

Received date : 31 March 2023

Revised date : 27 November 2023

Accepted date : 28 November 2023

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Please cite this article as: J. Vaubaillon, N. Rambaux, S. Loehle et al., UV spectroscopy of artificial meteors (200–400 nm). *Icarus* (2023), doi: https://doi.org/10.1016/j.icarus.2023.115906.

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Highlights

UV spectroscopy of artificial meteors (200-400 *nm*)

J. Vaubaillon,N. Rambaux,S. Loehle,P. Matlovič,J. Tóth,J. F. Mariscal

* First UV measurements of artificial meteors in the band [200-400] nm.

* Strong emission lines between 220 and 330 nm.

* Fe, Mg, Si detected in all tested samples but not C.
# UV spectroscopy of artificial meteors (200-400 nm)

J. Vaubaillon<sup>a</sup>, N. Rambaux<sup>a</sup>, S. Loehle<sup>b</sup>, P. Matlovič<sup>c</sup>, J. Tóth<sup>c</sup> and J. F. Mariscal<sup>d</sup>

<sup>a</sup>IMCCE, Observatoire de Paris, PSL, Sorbonne Université, 77 Av. Denfert Rochereau, Paris, 75014, France

<sup>b</sup>High Enthalpy Flow Diagnostics Group, Institute of Space Systems, University of Stuttgart, Pfaffenwaldring 29, 70569 Stuttgart, Germany

<sup>c</sup>Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia

<sup>a</sup>LATMOS, 11, boulevard D'Alembert, 78280 Guyancourt, France.

## ABSTRACT

The high energy of meteoroid entering the Earth atmosphere presumably results in UV radiation. However, ground-based observations are impaired by the atmospheric absorption below 400 nm. Artificial meteors are produced in a high enthalpy wind tunnel, and observed with a [200 - 400] nm fiber-fed spectrometer in order to analyse for the first time the UV emission of meteors. Similarly to visible observations, several atomic lines of Fe and Mg are detected. Contrary to observations in the visible wavelength range, Si is also clearly detected in all tested samples. Carbon is not detected in atomic lines. As the strongest emission lines are detected between 220 and 330 nm, we recommend that future meteor dedicated space-based UV instruments focus on this particular wavelength interval.

## 1. Introduction

Natural meteors occur when a meteoroid enters the Earth atmosphere. Remote observations are routinely performed from the ground thanks to dedicated camera networks. Most of these cameras are industrial, high sensitivity, visible band cameras. The meteor phenomenon happens because of the extremely high entering velocity of the meteoroids (usually between 11 and 72 km/s). Given the energy involved in the process, ionisation, disintegration, melting and fragmentation process may occur (for a full review, see Popova et al., 2019). All of these phenomena are accompanied with emission, usually detected in the visible band. Imaging as well as spectroscopy are used to infer the dynamical origin (from the trajectory and orbit), the chemical composition (from the spectrum) and the tensile strength (from any light curve spike) of the initial meteoroid (for a full review, see Koten et al., 2019). We focus here on the spectroscopy, allowing us to infer the composition of the meteoroid.

Most meteor spectroscopy devices make the most of existing low light sensors to measure spectra in the visible band (see e.g. Matlovič et al., 2022). Observations in the near-IR range are more rare (Taylor et al., 2007). However, given the high energy of the meteor phenomenon, UV radiation is expected. The scientific interest of the UV band for meteor analysis was foreseen by e.g. Achal et al. (1986); Nuth et al. (2008). However, ground-based observations in the UV band (typically from 200 to 400 nm) are impaired by the Earth atmospheric absorption. As a consequence, many ground-based UV observations of meteors are restricted to the 300 - 400 nm band (Almoznino and Topaz, 1998; Abe et al., 2005; Kasuga et al., 2005; Abe et al., 2011). Only two space-based serendipitous detections of meteors below 300 nm were performed in the past during the exceptional meteor shower outburst (Carbary et al., 2003; Jenniskens et al., 2002). More recently, the possibility to directly detect organic material falling in our atmosphere from a space platform and in UV wavelength was raised by Rambaux et al. (2014). The design of any future device dedicated to UV observation of meteors is therefore also impaired by our limited knowledge of the typical features in meteor UV spectra in the 200 - 400 nm band.

In order to fully characterize the UV emission of meteors, a wind tunnel experiment was performed and UV spectra of real meteorite samples were acquired. We present in section 2 the experimental setup, the results in section 3, followed by a conclusion in section 4.

<footnote>*Corresponding author
ORCID(s):</footnote>
UV Meteor

## 2. Experiment setup

The overall experimental campaign is fully described in Tóth (2023) and references therein. All the details regarding the wind tunnel setup as well as the campaign are described in Loehle et al. (2021, 2023). For clarification purposes, we recall key elements relevant for the present paper.

### 2.1. Wind tunnel and Meteorite samples

Meteorite samples are introduced in a high enthalpy wind tunnel flow, which simulates the physical conditions of a spherical 34.8 mm diameter meteoroid entering Earth's atmosphere at an altitude of 80 km of altitude with a velocity of 11.7 km/s. Optical instruments are installed outside the wind tunnel and record the artificial meteor. In this paper we focus on the UV spectroscopy measurements. For this purpose, a UV-transparent quartz window was installed on the side of the wind tunnel. Figure 1 shows the general setup scheme and highlights the location of the UV instrument. Figure 2 shows the instrumental setup at the wind tunnel.

<figure><img src="image_3.png" /><figcaption>Figure 1: Overall view of the experiment (from Loehle et al., 2021).</figcaption></figure>

The meteorite samples were 1-cm diameter shaped cylinders mounted to a copper holder which connected the sample to a water-cooled wind tunnel probe which lasts the flow heating. However, some of them were different from the ideal shape due to difficulties in machining or high risk in destroying it while machining the outer form. The meteorite samples observed with the UV spectrometer are described in table 1. A high-temperature ceramic glue (hereafter GLU - described in Tóth (2023)) was used to fix small meteorite to the wind tunnel sample handler.

### 2.2. UV Spectrometer

We used a Hamamatsu C9404CAH optical fiber spectrometer. It has a 1 nm resolution over the [200; 400] nm spectral range. The sensor is a back-thinned CCD, having 1024 pixels and 16 bits capabilities. Figure 3 shows the
UV Meteor

<figure><img src="image_4.png" /><figcaption>**Figure 2:** Instrumental setup at the wind tunnel: Collection optics are mounted directly to the window flange (on the right side in black), the fiber (orange) is connected to the spectrometer with the readout to a laptop computer (on the left side)</figcaption></figure>

**Table 1**

List of meteorite samples for which N-UV spectra were taken during the third MetSpec campaign (Tóth, 2023). The weight percentage compositions in Fe, Si and Mg are taken from Grigat et al. (2023).

<table><thead><tr><th>Name</th><th>Code</th><th>Type</th><th>Fe</th><th>Si</th><th>Mg</th></tr></thead><tbody><tr><td>North West Africa 869</td><td>NWA1R</td><td>L3-6</td><td>22</td><td>18</td><td>15</td></tr><tr><td>Kosice</td><td>KOS</td><td>H5</td><td>29</td><td>17</td><td>14</td></tr><tr><td>Mincy</td><td>MIN</td><td>mesosiderite</td><td>11</td><td>22</td><td>11</td></tr><tr><td>Mocs</td><td>MOC</td><td>L5-6</td><td>22</td><td>18</td><td>15</td></tr><tr><td>NWA 11303</td><td>LUN</td><td>Lunar</td><td>3</td><td>20</td><td>2</td></tr><tr><td>Lance</td><td>LAN</td><td>CO3.5</td><td>25</td><td>16</td><td>14</td></tr><tr><td>Tissint</td><td>TIS</td><td>Martian</td><td>15</td><td>22</td><td>10</td></tr><tr><td>Eagle</td><td>EAG</td><td>Enstatite EL6</td><td>23</td><td>20</td><td>14</td></tr><tr><td>Glue</td><td>GLU</td><td>Glue</td><td>-</td><td>N.A.</td><td>-</td></tr></tbody></table>

spectral response of the instrument. The spectrometer is fed by an optical fiber (200 µm, NA = 0.22), matched by a numerical aperture NA = 0.22 optics aligned towards the meteorite sample. For all experiments, the minimal (10 ms) exposure time was set. However, the signal was saturated for the NWA1R and KOS3 samples, so a careful selection of the unsaturated frame was performed for the analysis. We added an aperture and a neutral density filter in front of the main lens in order to reduce the incoming light and avoid pixel saturation. The aperture limited the flux to 1/3, and the density to another 1/10. This proved to allow us to acquire unsaturated spectra. With a 10 ms exposure time, it takes 20 s to acquire 1000 spectra, so the average fps is 50 fps, for an estimated dead time of 10 ms.
<figure><img src="image_5.png" /><figcaption>**Figure 3:** Spectral responses of the spectrometer sensor (provided by the manufacturer)</figcaption></figure>

**2.3. Calibrations**

Dark frames are taken in absence of any signal, and a master dark is computed and subtracted from the raw data. The spectrum of the plasma present in the wind tunnel before the introduction of the sample were recorded and the averaged spectral value subtracted from the meteorite spectra.

The spectral calibration is performed using Mercury-Argon lamp (Ocean Optics HG-1) in order to calibrate the wavelength axis of the spectrometer.

For the intensity calibration, the Deuterium lamp is positioned at the location of the meteorite sample to be acquired. Then, a spectra is acquired (see Fig. 6). Figure 4 shows the calibration data provided by the manufacturer.

<figure><img src="image_6.png" /><figcaption>**Figure 4:** Calibration data of the Deuterium lamp for the lamp positioned at a distance to the detector of 300 mm (provided by the manufacturer).</figcaption></figure>

As can be seen, there is no intensity value provided below 200 nm. In practice, atomic lines were detected mostly above 230 nm as seen in tab. 2. All calibration measurements were taken with and without the neutral filter in position
UV Meteor

in order to correct the corresponding spectra (i.e. taken with or without the filter). The corresponding measured spectra of the Mercury-Argon lamp and the Deuterium lamp are shown in Fig 5 and 6. The intensity data of the Deuterium lamp is provided by the manufacturer as irradiance data (in W.m⁻².nm⁻¹) with a distance between lamp and detector of 300 mm. For the present investigation this data was translated to irradiance by taking into account the distance of 1310 mm and an opening angle of 90°(= π).

The calibration of the ADU of the spectra taken during a meteorite exposition is then translated into radiance by calculating the calibration factor K, which is

$$ K = \frac{\text{spectra(Deuteriumlamp)}}{\text{measurement(Deuteriumlamp)}} \quad \text{in} \quad \frac{\text{W/m}^2/\text{nm/sr}}{\text{counts/ms}} \quad (1) $$

All measured spectra (in ADU) have to be multiplied by the calibration factor K resulting in absolute quantitative radiance data. This is the eventually resulting data as plotted in Figs. 8- 16.

<figure><img src="image_7.png" /><figcaption>Figure 5: Mercury-Argon lamp calibration spectrum.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Figure 6: Deuterium lamp calibration spectrum.</figcaption></figure>
# 3. Results and discussion

## 3.1. Generalities

Given the instrument spectral response provided by the manufacturer (fig 4, the signal below 200 nm is not considered here. During the very first experiment, saturation was detected during the steady regime (once the sample is in its nominal centerline position with respect to the plasma jet), and only a few spectra could be exploited (see e.g. fig. 9). With the aperture and neutral density filter, full time resolved spectra were recorded. The contribution of the wind tunnel plasma proves to be negligible compared to the meteorite signal, as can be seen in Fig. 7. Overall, the evolution of the spectra with time shows very little variation in terms of identified atomic lines. However, the relative intensity of the lines changes over time: see e.g. fig. 8 compared to 9. The spectrum shown in fig. 8 was taken at the very start of the experiment, whereas that shown in fig. 9 was taken towards the end of the experiment (and corresponds to the maximum emission of the sample). A Thorough examination shows that fig. 8 was taken 0.11 s after the sample was in position, which corresponds to the heating phase (Leiser, this issue et al., 2023). Strong emission lines in the [230 - 310] nm band are observed for all tested samples. From past experiments in the N-UV, strong Fe lines near 380-400 nm, i.e. near the visible, were expected. However, they do not appear as strong compared to other lines detected here. Fe lines in the UV (<350 nm) might therefore be much stronger than in the N-UV (>380 nm) and visible band.

<figure><img src="image_9.png" /><figcaption>**Figure 7:** Raw KOS3 time-averaged UV-spectrum (uncorrected from instrument spectral response curve) "average" is the time-average signal recorded while the meteorite was in position. "plasma" is the time-averaged signal recorded before the sample moved into position. "average-plasma" is the difference between the two. The contribution of the wind tunnel plasma is negligible compared to the meteorite spectrum (ADU in log scale).</figcaption></figure>

An overview of the meteorite temperatures studied by various techniques within our experiment is provided in Leiser, this issue et al. (2023). For the formation of the observed spectra, the temperature of the plasma consisting of the evaporating meteorite material and heated surrounding air plays the major role. Preliminary estimates of the plasma temperatures in our experiments by Pisarčíková (2023), obtained from fitting and modelling of the visible range Echelle spectra, show that these temperatures typically range from 4600 to 6000 K (preliminary results). These values are well representative of the main temperature component also observed in meteor observations (Borovicka, 1994). However, the high temperature component, observed for fast and bright fireballs, and associated with temperatures over 10000 K is likely not achieved in our experiments. Interestingly, Pisarčíková (2023) did observe some lines which are typically assumed to belong to the high temperature component in our visible range spectra - specifically the lines of N I, O I (from the generated plasma) and H I (likely from the meteorite). We assume that this is caused by an alternative excitation process of these abundant atoms besides the thermal excitation.
UV Meteor

**3.2. Detected species**

Figures 8 to 16 show the reduced spectra for all the tested meteorite samples, sorted by decreasing Fe weight percentage (see also tab 1). As expected from the measured temperature (Leiser et al., 2023), no thermal black body radiation is seen in the data. The full list of identified species is provided in table 2. Atomic emission lines of Fe I, Fe II, Mg I, Mg II are clearly detected. These species are commonly also detected in the visible band (Matlovič et al., 2022; Pisarčíková, 2023; Leiser et al., 2023). The emission of Fe II ion is usually only notable in visible spectra of fast and bright fireballs. The LAN and NWA1R meteorites have similar Fe and Mg weight percentage (data available in Leiser et al., 2023).

Emission of neutral silicon (Si I) was detected in all of the samples, in contrast to the visible spectra of most meteors (Borovicka, 1994) and meteorites tested during this and the previous experiments (Drouard et al., 2018; Leiser et al., 2023). It is worth mentioning that the only visible line of Si I in natural meteors is around 390.55 nm (technically in the N-UV band). The detection of Si by Borovicka (1994) was performed for a fireball (i.e. very bright meteor) and is still quite exceptional and unusual in natural meteor observations. This Si I line is however very often not detected due to the typically low resolution of meteor spectrographs, where the line is blended by much stronger surrounding Fe I lines or the Ca II doublet. Also, for some spectrographs, this lines is at the edge of the spectral sensitivity limit. Therefore, the detection of Si I in meteor spectra is very rare. We observed the Si I 390.55 nm line in most meteorite spectra within our MetSpec campaigns. However the line is usually also much fainter compared to the surrounding Fe I lines. This line is only dominant for silicate rich and Fe-poor meteorite types (e.g. the Aubrite). Therefore, its efficient detection in UV observations at other wavelengths could be of great benefit to help identify the meteorite type associated to a natural meteor.

As pointed out, in the visible band, only silicate rich meteorites such as the Aubrite Norton County displayed significant Si I emission (Matlovič et al., 2022, using the data from the 2019 campaign only; technically, 390.55 nm is in the N-UV band), while Si is mostly detected only in ionized form in faster, usually cometary meteors. Since glue was sometimes used to hold the samples (Tóth, 2023), a contamination by this component may be suspected. However, as outlined by Tóth (2023), the contribution of the glue to the signal has always been negligible. We conclude that Si can indeed be detected in N-UV band, contrary to the observations in the visible band where it was only apparent in silicate-rich samples.

No Carbon line was detected at the expected wavelengths. Theoretically, a relatively strong line of C I could be observed at around 247.8 nm with excitation at around 7.68 eV, which is feasible at the assumed plasma conditions. However the C content of the tested meteorites is low enough to make it challenging to be detected, especially because of the closeby Fe I lines. The best candidate for the detection of C I is the carbonaceous meteorite Lance (Fig. 8), but even here the identification was not clear from the surrounding Fe I lines. The CN band near 385-390 nm, which was detected in the visible spectra of carbonaceous and some achondritic meteorites (Pisarčíková, 2023) was not recognized in the N-UV data, also likely due to the low C content of the studied samples. Although C cannot be directly detected in the samples tested here, it might still be searched for in the form of CN in natural meteors.

**4. Conclusion**

UV spectra (200-400 nm) of meteors from real meteorites in a ground testing facility have been successfully acquired. Such data cannot be taken from the ground because of the absorption in the atmospheric air. The spectra show many emission lines in the [220 ; 330] nm wavelength interval. Similarly to the visible band, Fe and Mg are detected. Si seems to be easier to detect in the [200 ; 300] nm wavelength interval than in the visible. Although the detection of Carbon would have been of tremendous interest for exo-biology studies, gaseous carbon was not detected. Rather than attempting direct carbon detection, the detection of CN could serve as a useful proxy for detecting carbon, as suggested by Pisarčíková (2023).

Future space borne devices dedicated to the observation of meteors may provide complementary data to identify the composition of incoming meteoroids. As most atomic lines are detected between 220 to 330 nm, we recommend future devices to focus on this particular band.

**Acknowledgements**

We are thankful to the High Enthalpy Flow Diagnostics Group (HEFDiG) at the Institute of Space Systems, University of Stuttgart for their invaluable support during the experimental campaigns. This work was supported by
UV Meteor

the ESA contract No. 4000128930/19/NL/SC, the Slovak Research and Development Agency grant APVV-16-0148, the Slovak Grant Agency for Science grant VEGA 1/0218/22. J. Vaubaillon was supported by CNES, the French space agency, in the framework of the MALBEC project. We thank Ludovic Ferrière from the Natural History Museum Vienna for providing meteorite samples used in the experiments.

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<figure><img src="image_10.png" /><figcaption>Figure 8: Calibrated KOS3 UV spectrum (see also fig. 9).</figcaption></figure>

<table><caption>Table 2: Detected species in the N-UV spectra. λ: wavelength in nm. Diff: difference between theoretical and measured value. A '-' in the 3rd column indicates that the elements is not identified.</caption><thead><tr><th>λ</th><th>Diff</th><th>Element</th></tr></thead><tbody><tr><td>216.558</td><td>0.119</td><td>FeI</td></tr><tr><td>221.137</td><td>0.037</td><td>SiI</td></tr><tr><td>230.081</td><td>0.264</td><td>FeI</td></tr><tr><td>231.73</td><td>0.000</td><td>-</td></tr><tr><td>234.461</td><td>0.033</td><td>FeII</td></tr><tr><td>234.733</td><td>0.078</td><td>FeII</td></tr><tr><td>236.09</td><td>0.061</td><td>FeII</td></tr><tr><td>238.25</td><td>0.046</td><td>FeII</td></tr><tr><td>239.595</td><td>0.032</td><td>FeII</td></tr><tr><td>240.399</td><td>0.044</td><td>FeII</td></tr><tr><td>242.537</td><td>0.000</td><td>-</td></tr><tr><td>243.07</td><td>0.445</td><td>SiI</td></tr><tr><td>243.336</td><td>0.179</td><td>SiI</td></tr><tr><td>244.133</td><td>0.000</td><td>-</td></tr><tr><td>244.929</td><td>0.000</td><td>-</td></tr></tbody><tfoot><tr><td colspan="3">Continued on next page</td></tr></tfoot></table>
<table><caption>Table 2 – continued from previous page</caption><thead><tr><th>λ</th><th>Diff</th><th>Element</th></tr></thead><tbody><tr><td>246.253</td><td>0.012</td><td>FeI</td></tr><tr><td>247.045</td><td>0.245</td><td>FeI</td></tr><tr><td>248.099</td><td>0.121</td><td>FeI</td></tr><tr><td>248.889</td><td>0.075</td><td>FeI</td></tr><tr><td>249.677</td><td>0.000</td><td>-</td></tr><tr><td>251.51</td><td>0.078</td><td>SiI</td></tr><tr><td>252.294</td><td>0.009</td><td>FeI</td></tr><tr><td>253.338</td><td>0.487</td><td>SiI</td></tr><tr><td>256.197</td><td>0.057</td><td>FeII</td></tr><tr><td>257.492</td><td>0.000</td><td>-</td></tr><tr><td>258.525</td><td>0.063</td><td>FeII</td></tr><tr><td>259.815</td><td>0.022</td><td>FeII</td></tr><tr><td>260.588</td><td>0.121</td><td>FeII</td></tr><tr><td>261.102</td><td>0.085</td><td>FeII</td></tr><tr><td>262.386</td><td>0.181</td><td>FeII</td></tr><tr><td>262.899</td><td>0.070</td><td>FeII</td></tr><tr><td>266.479</td><td>0.000</td><td>-</td></tr><tr><td>267.753</td><td>0.000</td><td>-</td></tr><tr><td>271.054</td><td>0.387</td><td>FeII</td></tr><tr><td>271.814</td><td>0.089</td><td>FeI</td></tr><tr><td>272.572</td><td>0.182</td><td>FeII</td></tr><tr><td>274.34</td><td>0.020</td><td>FeII</td></tr><tr><td>274.592</td><td>0.056</td><td>FeII</td></tr><tr><td>275.347</td><td>0.227</td><td>FeII</td></tr><tr><td>276.605</td><td>0.000</td><td>-</td></tr><tr><td>279.365</td><td>0.188</td><td>MgII</td></tr><tr><td>280.116</td><td>0.155</td><td>MgII</td></tr><tr><td>281.116</td><td>0.000</td><td>-</td></tr><tr><td>283.112</td><td>0.000</td><td>-</td></tr><tr><td>285.102</td><td>0.111</td><td>MgI</td></tr><tr><td>288.077</td><td>0.081</td><td>SiI</td></tr><tr><td>293.499</td><td>0.191</td><td>FeI</td></tr><tr><td>294.48</td><td>0.308</td><td>FeI</td></tr><tr><td>295.215</td><td>0.179</td><td>FeI</td></tr><tr><td>296.437</td><td>0.089</td><td>FeI</td></tr><tr><td>296.926</td><td>0.084</td><td>FeI</td></tr><tr><td>298.145</td><td>0.000</td><td>FeI</td></tr><tr><td>299.119</td><td>0.324</td><td>FeI</td></tr><tr><td>299.848</td><td>0.247</td><td>FeI</td></tr><tr><td>300.577</td><td>0.237</td><td>FeI</td></tr><tr><td>301.789</td><td>0.260</td><td>FeI</td></tr><tr><td>303.481</td><td>0.258</td><td>FeI</td></tr><tr><td>304.446</td><td>0.314</td><td>FeI</td></tr><tr><td>305.409</td><td>0.500</td><td>FeI</td></tr><tr><td>309.722</td><td>0.000</td><td>-</td></tr><tr><td>344.307</td><td>0.081</td><td>FeI</td></tr><tr><td>356.768</td><td>0.230</td><td>FeI</td></tr><tr><td>357.169</td><td>0.159</td><td>FeI</td></tr><tr><td>358.366</td><td>0.246</td><td>FeI</td></tr><tr><td>372.032</td><td>0.038</td><td>FeI</td></tr></tbody><tfoot><tr><td colspan="3">Continued on next page</td></tr></tfoot></table>
UV Meteor

<table><caption>Table 2 – continued from previous page</caption><thead><tr><td>λ</td><td>Diff</td><td>Element</td></tr></thead><tbody><tr><td>373.466</td><td>0.020</td><td>FeI</td></tr><tr><td>374.531</td><td>0.025</td><td>FeI</td></tr><tr><td>381.548</td><td>0.036</td><td>FeI</td></tr><tr><td>382.043</td><td>0.000</td><td>FeI</td></tr><tr><td>382.537</td><td>0.051</td><td>FeI</td></tr></tbody></table>
<figure><img src="image_11.png" /><figcaption>**Figure 9:** Calibrated KOS3 UV spectrum, taken during maximum emission. The raw signal for λ >~ 265 nm was saturated, preventing the exploitation of this part of the spectrum.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Figure 10: Calibrated LAN UV spectrum.**</figcaption></figure>
<figure><img src="image_13.png" /><figcaption>**Figure 11: Calibrated NWA1R UV spectrum.**</figcaption></figure>
<figure><img src="image_14.png" /><figcaption>**Figure 12:** Calibrated MOC UV spectrum.</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>Figure 13: Calibrated EAG UV spectrum.</figcaption></figure>
<figure><img src="image_16.png" /><figcaption>Figure 14: Calibrated TIS UV spectrum.</figcaption></figure>
UV Meteor

<figure><img src="image_17.png" /><figcaption>Figure 15: Calibrated MIN UV spectrum.</figcaption></figure>
UV Meteor

<figure><img src="image_18.png" /><figcaption>Figure 16: Calibrated LUN UV spectrum.</figcaption></figure>
**Declaration of interests**

X The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

<figure><img src="image_19.png" /></figure>

☐ The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: