Established meteor shower activity periods and orbits

The CAMS dataset of 111233 orbits collected in the period 2010-2013 has been checked to verify the online data of the IAU meteor shower list. The activity periods for all meteor streams detected in CAMS data has been derived from the solar longitudes of the individual orbits that were associated with the meteor stream. For meteor showers that were absent in the CAMS data, mainly daylight meteor streams, CMOR data has been used to complete the information. To make future associations easier and to avoid mixing up shower data, the official naming and IAU code with the orbital elements are listed in this contribution.

1 Introduction

Some CAMS-tools need a meteor shower list as reference to associate single station meteors with active radiants. So far a list has been used based on the IMO Shower Calendar. As this source proved to be rather incomplete and not up-to-date, the author prepared a new reference list based on the IAU meteor shower list on request of Pete Gural, the CAMS software engineer. In order to double check the data in the published online version of the IAU meteor shower list, the original sources were consulted. Most of the currently established meteor showers (status as January 2017) have data based on recently published CAMS data (Jenniskens et al., 2016) and CMOR data (Brown et al., 2008, 2010). For a few cases that were not covered by either CAMS or CMOR, the historic data was provided by Peter Jenniskens.

Going through the official online list and the references, a number of inconsistencies were noticed which required clarification. For the CAMS data the most efficient checkup was to use the dataset made public on the NASA SETI-CAMS website. The CAMS dataset lists 111233 orbits obtained in 2010–2013. The orbits were extracted for each meteor shower and the median value has been calculated for a number of parameters. This way the inconsistencies between the online IAU list and the published references could be verified and corrected.

Regarding the CMOR data, Peter Brown provided a working list with up-to-date CMOR results which allowed to check this data too.

The survey of all the data resulted in some extra information that is not published in the online IAU Shower list. Since this extra information is definitely useful for anyone working on this topic, we share the data in this contribution. Although the information is available online, it may be practical to have the data printed on paper.

2 Activity periods for all meteor showers

The IAU Meteor shower list provides only the solar longitude valid for the orbital elements. In most cases this solar longitude is the median value of all solar longitudes of the individual orbits. In some cases this solar longitude was replaced by the solar longitude derived from the time of the observed maximum activity which is not necessarily the same as the median value. Nothing is mentioned about the activity period of the meteor showers in the IAU list.

Since CAMS collected many orbits for most of the established meteor showers, we have a reliable idea about the interval in solar longitude during which orbits could be identified for most established meteor showers. Since the criteria to associate an orbit with some meteor shower are very strict this method is far more rigorous than the assumptions based on statistics from single station meteor observations. The shower identification in the dataset we use has been done by Dr. Peter Jenniskens and the method used has been described in a recently published paper (Jenniskens et al., 2016).

In Table 1 the activity periods are listed as derived mainly from the original CAMS dataset or the CMOR working list. Data based on CAMS is indicated with ‘C’, data from CMOR with ‘R’ and the few cases with older historic data with ‘H’. In most cases the number of orbits is statistical significant, but be aware that for some established meteor showers only few orbits have been collected by CAMS. The number of orbits is given in the last column of Table 1. The data is based on this number of orbits available and should not be interpreted in a restrictive way, but rather as the time span during which the orbits were collected in the above mentioned datasets. It is very likely that orbits will be identified in the future collected at solar longitudes before or after the current time span.

The value λ_ʘ-m is the median value for all orbits, unless observations allowed determining the solar longitude of the maximum activity in a more precise way.  λ_ʘ-b is the integer value of the solar longitude at which the earliest orbit has been recorded and λ_ʘ-e the integer value of the solar longitude after the solar longitude of the last orbit, e.g. if the last λ_ʘ was 26.3° then λ_ʘ-e was set as 27°.

For some showers which are labelled as daylight stream we used CAMS data where possible. Some of these showers produced enough meteors for CAMS to derive a relevant orbit. Most daylight streams were documented from CMOR data only. In cases with CMOR data for nighttime streams, the absence of CAMS data is most likely due to the fact that CMOR detects data from many more faint meteors while CAMS detects meteors in the fireball range up to magnitude +5.0. Showers that produce mainly meteors fainter than +5.0 will not easily show up in CAMS data.

Table 1 – The activity periods in solar longitude for all 112 established meteor showers. The radiant position valid at λ_ʘ-m is given together with the radiant drift Δα and Δδ and the geocentric velocity V_g. Column N indicates the source for the data, ‘C’ stands for CAMS, ‘R’ for CMOR and ‘H’ for historic data, the number of orbits on which the data has been based is mentioned.

3 Orbits for all showers

Checking for the activity period of each shower offered an easy bonus to have the orbital elements checked again based on the original dataset. The results are listed in Table 2. The median value has been calculated for each orbital element. Table 2 is complementary to Table 1 and can be compared using the IAU code. The values for λ_ʘ-m and V_g are displayed in Table 2 as well. The number of orbits available and listed under N in Table 1 should be observed to consider the relevance of the orbit for the stream. Many of these minor showers will benefit from additional orbits collected since 2013.

During past 10 years the video meteor networks such as CAMS allowed to discover or to confirm many different meteor showers. Many of these shower names are not familiar at all to most amateurs. The IAU code provides a short unique identification, but still the multiple new minor meteor showers risk to confuse amateurs and even professional meteor workers. Such a situation occurred with the prediction of a possible shower activity from a radiant not listed among the established meteor showers, but which by mistake got announced as a possible enhanced activity of the December φ-Cassiopeiids (DPC – 446). Both activity period and radiant position were wrong, but in spite of this obvious erroneous name association, the mistake remained unnoticed until some amateur claimed having observed activity long after the predicted date. This weird story caused even more confusion about the discrepancies of the predicted radiant and the December φ-Cassiopeiids data.

To make it easy to check the radiant data, names, IAU codes and orbital data, both tables in this contribution may help to avoid such confusing situations in the future. It can be handy to have this shower list at hand, with the activity periods, radiant, geocentric velocity and the orbital elements in a single document.

Table 2 – The orbital elements for all 112 established meteor showers.

4 Conclusion

The large number of newly discovered and confirmed minor meteor showers should be further monitored to improve the statistical significance of the orbital data. The currently available data listed in this contribution may be helpful for meteor workers to check future shower associations.

Although the radar and video meteor data allowed to complete a lot of formerly missing data such as reliable orbital elements for minor showers, future data will definitely require a regular revision of the data listed in this contribution.

Acknowledgment

The author thanks Peter Brown for providing the recent CMOR data and Peter Jenniskens for providing the historic data for a number of meteor streams.

References

Brown P., Weryk R. J., Wong D. K. and Jones J. (2008). “A meteoroid stream survey using the Canadian Meteor Orbit Radar. I. Methodology and radiant catalogue”. Icarus, 195, 317–339.

Brown P., Wong D. K., Weryk R. J. and Wiegert P. (2010). “A meteoroid stream survey using the Canadian Meteor Orbit Radar. II: Identification of minor showers using a 3D wavelet transform”. Icarus, 207, 66–81.

Jenniskens P., Nénon Q., Albers J., Gural P. S., Haberman B., Holman D., Morales R., Grigsby B. J., Samuels D. and Johannink C. (2016). “The established meteor showers as observed by CAMS”. Icarus, 266, 331–354.