Results of spectral observations of meteor showers and sporadic meteors from October 2018 until May 2020

By Takashi Sekiguchi

 

Abstract: I present a survey of 1596 spectra obtained from October 2018 until May 2020. Meteor spectra that include sporadic meteors as well as members of minor and major meteor showers. These meteors are in the absolute magnitude range from +2.6 to −8. The overall spectrum type for sporadic meteors showed mostly similar distributions. In addition, the Quadrantids, the Perseids, and the Geminids could be analyzed more in detail than other major meteor showers. The Quadrantids and the Geminids could be classified into four types. The types of other major meteor showers differed depending upon the meteor stream. Even minor meteor showers with three or more spectra showed differences. Na Free and Na Poor were observed in the Quadrantids and Geminids and Southern δ-Aquariids and several minor meteor showers. An Fe content rate with more than 50% is considered to be intermediate with Irons, we have several suspected Iron meteoroids and minor meteor shower parent bodies.

 

1 Introduction

Borovička et al. (2005) published a survey of the spectra of 97 sporadic meteors. The luminous intensity was obtained in high-sensitivity video, mainly in the magnitude range from +3 to 0. The spectra were classified into seven categories according to the relative line intensities of Mg, Na, and Fe. Moreover, three different populations of meteoroids without Na were identified. Vojáček et al. (2015) presented a catalog of 84 video spectra of both sporadic and shower meteors obtained for meteors from magnitude +2 to –3.5. This is representative in the sense that it includes everything as a catalog of observed sporadic meteors as well as major meteor showers.

This study was started by an investigation of what can be obtained from a large amount of spectral data with many cameras compared to the studies made by Borovička et al. and Vojáček et al. Major and minor meteor shower as well as sporadic meteor results are considered for future research.

 

2 Observing equipment

The equipment to register spectra consists of a color SONY alpha 7s camera with a 50 mm f 1.4 lens with a transmission diffraction grating film of 500 lines per mm as spectrometer. From 2018 October 01 until 2019 December 03 Standard definition (SD) was used and from 2019 December 03 to May 2020 full high definition (FHD) was used. Furthermore, seven black and white cameras were used, four Watecs Neptune 100+ with CBC 6 mm lenses, one with a 12 mm f 0.8 lens, two Watecs 902H2U with CBC lenses of 6 mm and 8 mm with f 0.8. Some cameras had a spectrometer, from 2018 December 18 until 2020 May these used SD. From the observations so far, the resolution for Fe is rather poor in SD. In FHD, the resolution increased and Fe became clearly visible (Figure 1).

 

 

3  Observing and orbital calculation software

The author uses the software UFOCaptureV2, UFOCaptureHD2, UFOAnalyzer V2 and UFOOrbitV2 (http://sonotaco.com/). These programs identify identical events and perform the triangulation calculations for the SonotaCo net’s meteor data. Since each observing person has different conditions such as cameras and weather, there are variations in accuracy. For simultaneous events from three or more points, the orbit is determined based on the best fit solution.

 

4  Spectral analysis software

The Japanese version of the spectral analysis software Rspec (https://www.rspec-astro.com/) has been used. In each spectrum analysis, a triangular diagram is created with the peak ratios including rotation, tilt correction, background correction and sensitivity correction. There may be a difference of about 5 to 10% when comparing without sensitivity correction, also in the peak area ratio. This time, I am applying the sensitivity correction because I use many cameras. Most of them measure the whole path, but some of them include only a part of the emission point with either the part of the extinction point or the part with the explosion point.

Saturated meteors are measured in the unsaturated area.

 

5  Triangular diagrams

The software CKTriangle (https://clikington-saito.com/CKTriangle/CKTriangle.html) is used to create the triangular or ternary diagrams for the 1596 spectral observations of October 2018 to May 2020 captured by eight cameras. The distribution of Na (5892 Å), Mg (5182 Å) and Fe (5269–5441 Å) is displayed by a triangle diagram. I refer for the classification to the article by Borovička et al. (2005):

• Iron meteoroids are these where the Na line is missing and the Mg line is much fainter than in normal spectra. Given that most of the light is emitted by Fe atoms (e.g. Figure 2).
• Na-free meteoroids are defined as those without the Na line but not classified as Irons. They fall into the region close to the left edge of the ternary diagram.
• Na-rich meteoroids are these dominated by the Na line. The Na/Mg and Na/Fe ratios are obviously higher than expected for chondritic meteoroids.
• Normal meteoroids are mainstream meteoroids lying near the expected position for chondritic bodies in the Mg–Na–Fe diagram or with somewhat lower Fe intensity.
• Na-poor meteoroids are mainstream meteoroids with the Na line significantly weaker than expected for the given velocity but still well visible.
• Enhanced-Na meteoroids are defined as those with the Na line obviously brighter than expected for the given meteor velocity but not so dominant as in Na-rich meteoroids.
• Fe-poor meteoroids are mainstream meteoroids having the expected Na/Mg ratio but with Fe lines too faint to be classified as Normal meteoroids. In this paper, Normal types with iron content of 20% or less are classified as Fe poor.

 

Figure 2 – The triangle diagram displaying the relative line intensities of Na, Mg and Fe. The triangle (top) is for the 1596 spectra, obtained from October 2018 until May 2020 for this work. The triangle (bottom) is taken from Vojáček et al. (2015).

 

The 1596 meteor spectra include sporadic meteors and members of minor and major meteor showers. These meteors are in the absolute magnitude range from +2.6 to −8. There are many Normal types. There are only few Na rich meteoroids and Irons. Compared to the paper by Vojáček et al. (2015), there are many, about 50 to 80%, of the spectra of meteors with Na enhanced, Na rich, Fe poor and Fe contents. The distribution trends are similar (Figure 2). Examples of spectrograms are given in Figure 3.

 

726 meteor spectra were obtained for sporadic meteors. Like for all meteors, there are many Normal types among these sporadics. Twenty-one Irons were analyzed. Nearly 25 meteors with 50% or more Fe are present, and there are many intermediate meteors in which the Fe component can be seen at the start of the light emission. In addition, the distribution of sporadic meteors is similar to the distribution of all meteors, except for some meteor showers. Therefore, we believe that this distribution is reliable (Figure 4).

The type differs depending on the meteor shower. The Quadrantids (QUA#010) and the Geminids (GEM#004) spectra can be divided into four types. These are Na free meteoroids, Normal meteoroids, Na-poor meteoroids and Fe poor meteoroids. The Perseids (PER#007) are Normal meteoroids and Fe-poor meteoroids.

The Geminids had a different type of distribution from year to year (http://sonotaco.jp/forum/viewtopic.php?t=4555), probably due to the difference in the dust trail distribution.

The Geminids have a higher proportion of Na free and Na poor meteoroids compared to the Quadrantids. (Figure 5).

 

 

 

A concentration can be seen in the Normal type. The σ-Hydrids (HYD#016), α-Capricornids (CAP#001), Ursids (URS#015) and η-Aquariids (ETA#031) are Normal meteoroids. The Coma Berenicids (COM#020), April Lyrids (LYR#006), Orionids (ORI#008) and the December Monocerotids (MON#019) are Normal meteoroids and Fe poor meteoroids. The Southern δ-Aquariids (SDA#005) were observed as Na free meteoroids, Na poor meteoroids and Normal meteoroids. The κ-Cygnids (KCG#012) are Normal meteoroids and Na enhanced meteoroids. The Leonids (LEO#013) are Normal meteoroids and have a higher Fe content than the others. Northern Taurids (NTA#017) and Southern Taurids (STA#002) cover a wider area than any other meteor showers. Most of them were Normal type, but no Irons (Figure 6).

 

 

 

The minor showers cover a wider area than the major meteor showers. There are many Normal and Fe poor meteoroids everywhere. The January χ-Ursae Majorids (XUM#341) stream has mostly Na free meteoroids and Na poor meteoroids. The November Orionids (NOO#250) stream has mostly Fe poor meteoroids and Na poor meteoroids. The α-Cancrids (ACC#266) stream has mostly Na poor meteoroids and one Iron. The December α-Draconids (DAD#334) stream has Na free meteoroids and Na poor meteoroids and one Iron. The h-Virginids (HVI#343) stream has mostly Enhanced-Na meteoroids. The σ-Leonids (SLE#136) stream has about half, from 40% to nearly 50%, of Fe. The ρ-Geminids (RGE#094) and α-Hydrids (AHY#331) streams contain mostly Normal meteoroids. The September ε-Perseids (SPE#208) shower has Normal meteoroids and Fe poor meteoroids. The ο-Leonids (OLE#515) stream consists of Na poor meteoroids (Figure 7).

59 Iron meteoroids in which the Fe content was determined to be 50% or more, were identified from the graph of Mr. Maeda’s classification (Figure 8). The areas N6 and N7 appear denser in the classification than in the study by Borovička (2005) (Figure 9).

 

 

6 Percentage of classification compared to Mr. Maeda

Normal meteoroids represent about half in both pie charts shown in Figure 10. Other types are slightly different, but this is assumed to be due to the observation period, the cameras, the lenses, etc. In this paper, the number of cases in N6 and N7 are larger and smaller for N1 because we used mainly lenses with a shorter focal length than Maeda, so there are many low speed fireball cases and less faint meteors can be captured. In addition, it seems that Mr. Maeda has a better resolution, so the difference in the number of Iron meteoroids is more apparent (Figure 10).

 

 

 

 

Figures 11 and 12 as a whole tend to show many Normal meteoroids for most of the meteor streams. Both SPO, GEM#004 and SDA#005 are very similar. The other streams are similar in the sense that these contain many Normal meteoroids, but differences can be seen for some types. Therefore, it can be concluded that there is a difference in composition depending on the meteor stream (Figures 11 and 12). The major meteor showers show mainly Normal meteoroids, but minor meteor showers display a clear difference in composition depending on the meteor showers (Figure 13).

 

 

The minor meteor showers XUM#341, OLE#515 and ACC#266 had a N0 + N1 ratio close to 70% (see Figure 14). In the major meteor showers, the Geminids, (GEM#004), the Southern δ-Aquariids (SDA#005) and the Quadrantids (QUA#010) have values of 30 to 40%. These meteor showers may be depleted of Na. Except for the QUA#010 and ACC#266, the perihelion distance q is 0.2 A.U. or less, which are Sun-approaching orbits. ACC#266 has a high value of two thirds for N0 + N1, one third are iron meteoroids, and the perihelion distance q is about 0.4 to 0.6 A.U. (Figure 14).

 

 

7 Radiant point distribution

The radiants of major and minor meteor showers appear as a number of concentrations. This can be seen at different positions for most of the velocity classes. (Figure 15).

 

 

8 Measured Na/Mg line intensity ratio

The Na/Mg line intensity ratio in function of the geocentric velocity v_g has been plotted in Figure 16. The overall trend changes with the same slope until about 30 km/sec, comparable to the result of Borovička (2005) and Vojáček (2015). Above 30 km/sec, there is no effect on the Na ratio visible in function of the velocity. It is the composition itself that changes. This graph also shows that the Quadrantids (QUA#010) with v_g = 41 km/s, the Geminids (GEM#004) with v_g = 34 km/s and the Southern δ-Aquariids (SDA#005) with v_g = 41 km/s have a large amount of Na free meteoroids and Na poor meteoroids (Figure 16).

 

 

According to Maeda’s classification, each type can be clearly seen separately. The lower the speed, the more Na rich. The fact that a little higher speed can be seen is probably due to the difference in composition. There are a few numbers where the velocity is around 50 km/sec. There are only few Irons and all have a low velocity (Figure 17).

 

 

9 Measured O/Mg line intensity ratio

The O/Mg line intensity ratio in function of the geocentric velocity v_g (Vojáček et al., 2015) has been plotted in Figure 18, based upon 802 meteors obtained with a black and white camera. The proportion of O increased as the velocity increased, and the tendency is similar to the results obtained by Vojáček et al. (2015). The number of Na enhanced meteoroids and Na rich meteoroids is larger at velocities below 25 km/sec (Figure 18).

 

10  Relationship between meteor emission altitude and velocity

The tendency that the height of the beginning of light emission becomes lower as the speed becomes slower can be well seen in Figure 19. Looking by type, most of the iron meteoroids and the Na-free meteoroids start to ablate at lower heights than all other types. Na rich meteoroids and Na enhanced meteoroids are most common for meteors slower than 30 km/sec. Normal meteoroids can be seen throughout the entire distribution. Fe poor meteoroids are mainly found among medium-speed and high-speed meteors.

 

 

11  Meteoroid orbits

The geocentric and heliocentric orbits are known for all 1523 meteors from double-station observations. This had been achieved for almost a year ago or more. Many orbit calculations were possible not only for sporadic meteors but also for the major and minor meteor showers. The distribution for each orbital element is displayed in Figure 20. Peaks can be explained by the presence of a large contribution by some major showers.

 

 

12 Relationship with orbital elements

In this section we consider the relationship with the orbital elements. The Tisserand parameter relative to Jupiter can be computed from;

 

Where ????_???? = 5.2 A.U. is the semimajor axis of Jupiter, a is the semimajor axis of the meteoroid and e is the eccentricity of the meteoroid. Five classes of meteoroid orbits were defined by Borovička et al. (2005):

• (SA) Sun-approaching orbits with q< 0.2 AU. Orbits with small perihelion distances are defined as a separate class.
• (ES) ecliptic shower orbits: Members of ecliptic meteor showers. For example, the Taurid meteors derived from the comet 2P/Encke and other showers with orbits close to the boundary between asteroids and Jupiter family comets.
• (HT) Halley-type orbits: T_J< 2 or 2 < T_J < 3 and
  i > 45◦.
• (JF) Jupiter-family orbits: 2 < T_J < 3 and i< 45◦ and Q > 4.5 AU.
• (A-C) Asteroidal-chondritic orbits: T_J> 3 or Q < 4.5 AU.

Most of the Na rich meteoroids are sporadic meteors with mainly Asteroidal-chondritic orbits. Many Na enhanced meteoroids are often sporadic meteors with Asteroidal-chondritic orbits. In addition, some meteors with ecliptic shower obits were recorded. Other types are in general widespread. For Normal meteoroids and Fe poor meteoroids, the Halley-type orbits are often seen, more than the Asteroidal-chondritic orbits (Figure 21).

 

 

 

When q is 0.3AU or less, the numbers decrease for all types. Na rich, Na enhanced, Normal and Fe poor meteoroids are concentrated in the range of 0.3 – 1 A.U. Most of the meteoroids with Sun-approaching orbits with q < 0.2 AU are Na poor and Na free meteoroids (Figure 22).

Looking at Na rich meteoroids, it can be seen that the number decreases as q decreases and the amount of Na becomes less (Figure 23).

 

 

 

There is a split between the Jupiter-family orbits and the Halley-type orbits at an inclination i ~ 45° (Figure 24).

The number of spectra that can be obtained will change depending on the observation period. Irons are often slow, fainter meteors, not present between solar longitude 70° to 240°. This is probably due to bad weather and poor transparency of the sky (Figure 25).

 

 

The number of spectra that can be obtained will change depending on the observation period. Irons are often slow, fainter meteors, not present between solar longitude 70° to 240°. This is probably due to bad weather and poor transparency of the sky (Figure 25).

Most of the Na free meteoroids and Na poor meteoroids have a mass less than 5 g. Masses of above 100 g are mostly Normal meteoroids (Figure 26).

 

 

 

Looking at the overall relationship of the Tisserand parameter T_J and KB, the air density calculated from the altitude approximation (Ceplecha, 1988; Rudawska et al., 2016), we see many A types in Figure 27. There are few D types and Jupiter family comets. Irons are mostly asteroidal and A types. Na free meteoroids and Na poor meteoroids are often A types. Na rich meteoroids and Na enhanced meteoroids have less C and D types. Normal meteoroids and Fe poor meteoroids are considered to be mainly Halley cometary types and appear as a concentration of meteor showers (Figure 27).

Looking at the overall relationship between the Tisserand, parameter T_j and PE (Ceplecha, 1988; Rudawska et al., 2016), there are many types II–IIIB and few types I. Na poor meteoroids have a lot of II and IIIA types. Na-free meteoroids and Fe-poor meteoroids are mostly II–IIIB types. Normal meteoroids and Na-enhanced meteoroids appear numerous as IIIA and IIIB types. Irons are mostly type IIIA (Figure 28).

 

 

 

13 Irons

I compared the Irons with the results of other researchers. First, the luminous intensity distribution is compared. There is a difference in the range captured by the type of camera and lens. My devices use multiple short focal length lenses which are brighter. Still, there are many faint meteors (Figure 29).

 

 

Regarding the relationship between the observed velocity and the luminosity, we see many faint meteors (magnitude –1 to +4) with low velocities v_o within the range 10–30 km/sec (Figure 30).

Regarding the relationship between the observed velocity v_o and the ablation altitude, Irons display a similar tendency for H_b in function of v_o, but the Fe 50–80% has no correlation. This is probably because the covered range is too wide (Figure 31).

 

The relationship between the Tisserand parameter Tj and the inclination i (Vojáček et al., 2015) shows that most of the Fe 50–80% group belong to the Asteroidal-chondritic class (A-C) and Jupiter-family orbits (JF). There were three Halley-type orbits (HT). Irons had two Halley-type orbits (Figure 32).

 

 

 

 

 

Table 1 – Orbital elements of meteoroids classified as Irons compared to the orbits of the parent bodies.

 

Table 2 – Orbital elements for XUM#341, OLE#515, ACC#266, HVI#343 and NOO#250, first the orbit for this study, compared with the reference orbit given by the IAU and compared with the orbit of the candidate parent body.

 

The Fe 50–80% group has two Sun-approaching orbits (q < 0.2 A.U.). A concentration appears at 0.6 < q < 1.1 A.U. Irons had two Sun-approaching orbits. There is a lot of scatter. Except for the two meteoroids with Q > 10, it is very similar to the distribution for Irons obtained from other analyzes. Therefore, it is considered that the Fe50–80% group is related to Irons (Figure 33).

I investigated the parent bodies of the Irons. V-1 and V-2 in Table 1 are taken from Vojáček et al. (2015). Table 1 compares the orbits with their possible parent bodies, for S-1 to S-4 the association seems to be certain. From S-5 to S-15, D_SH is 0.2 or less, which are good candidates (Southworth and Hawkins,1963). S-16 is supposed to be a Quadrantid, but there are errors on the velocity, etc., so it is a weak candidate only. Among the Irons, there was almost not a single one with the same orbit. Although some similar orbits are present, these cannot be identified as a meteor shower (Table 1 and Figure 34).

 

 

14 Five minor meteor showers

We investigated the mean orbits of XUM#341, OLE#515, ACC#266, HVI#343 and NOO#250 and parent candidates for the five minor meteor showers shown in Figures 7 and 14. As shown in Table 2, the ACC#266 and HVI#343 meteor shower are in very good agreement with the IAU mean orbit and the parent body. As for the other three, the average orbits are in good agreement, but it is possible that these are the closest candidates for the parent body, which may have changed due to perturbation, etc. The OLE#515 and the NOO#250 meteor showers have the perihelion distance q < 0.2 A.U. which are Sun–approaching orbits (Table 2 and Figure 35).

 

 

15 Conclusions

The shower meteors and the sporadic meteors showed almost the same distribution. In addition, the Quadrantids, Perseids and Geminids could be analyzed in greater detail than the other major meteor showers. Quadrantids and Geminids could be classified into four types. Other major meteor shower types varied from shower to shower. Differences were also seen in minor meteor showers with more than three spectra. Na Free and Na Poor meteoroids have been observed in Quadrantids, Geminids and Southern δ-Aquariids and some minor meteor showers. The comet derived meteors have a heterogeneous composition, but most of the Halley–type orbits are Na–free, Na–poor, and Fe–poor meteors. Among the orbits of the Jupiter–family orbits, there are many Na–rich and Na–enhanced meteors. Many of the Normal types have a large mass. An Iron meteoroid with an Fe content of more than 50% was captured. There are some Irons with minor meteor shower association and parent body candidates. There were two Iron meteoroids in a typical orbit approaching the Sun.

 

Acknowledgment

We would like to thank the SonotaCo network for providing orbital calculation data for this study. We would also like to thank Paul Roggemans and Masahiro Koseki for their proofreading and advice.

References

Borovička J., Koten P., Spurný P., Boček J., Štork R. (2005). “A survey of meteor spectra and orbits: evidence for three populations of Na–free meteoroids”. Icarus, 174, 15–30.

Ceplecha Z. (1988).  “Earth’s influx of different populations of sporadic meteoroids from photographic and television data”. Bulletin of the Astronomical Institutes of Czechoslovakia, 39, 221–236.

Maeda Koji and Fujiwara Yasunori (2016). “Meteor spectra using high definition video camera” In Roggemans A. and Roggemans P., editors, Proceedings International Meteor Conference, Egmond, the Netherlands, 2–5 June 2016. pages 167–170.

Rudawska Regina, Tóth Juraj, Kalmančok Dušan, Zigo Pavol, Matlovič Pavol (2016). “Meteorspectra from AMOS videosystem” Planetary and Space Science, 123, 25–32.

Southworth R. R. and Hawkins G. S. (1963). “Statistics of meteor streams”. Smithson. Contrib. Astrophys., 7, 261–286.

Vojáček V., Borovička J., Koten P., Spurný P., Štork R. (2015). “Catalogue of representative meteor spectra”. Astronomy & Astrophysics, 580, A67,1–31.