Abstract: Last year’s surprise activity from the delta Mensid meteor shower in the southern hemisphere was repeated this year on March 12 and 13, 2021. The delta Mensids displayed strong activity in CAMS low-light video data in the period between March 12 10h and March 13 06h UTC. The possible parent body is asteroid-looking object 2006 CS. In 2020, the shower continued to be active for two weeks after the outburst, until March 26, with good detections on March 20-22.
The delta Mensids (DME#130) were first detected by visual observers in the southern hemisphere and received their shower number in Jenniskens (2006). The shower was confirmed from low-light video observations by the CAMS New Zealand network (Jenniskens et al., 2018). In 2020, the shower showed strong activity in SAAMER southern hemisphere radar data, peaking on March 12 at 9h30m UTC (Janches et al., 2020a). Janches et al. (2020b) identified a possible source for the activity: now asteroid-looking object 2006 CS (asteroid 248590). The asteroid moves in a Jupiter-family comet orbit with Tisserand parameter TJ = 2.44. Jupiter-family comets have TJ values between 2 and 3.
In video observations that year, the shower was also well detected in the period March 20-22 (see website http://cams.seti.org/FDL/ for dates of 2020-03-20 to 22), and it is interesting to check if any activity can be recorded this year on those days.
2 The 2021 activity
Southern hemisphere “Cameras for Allsky Meteor Surveillance” (CAMS) networks detected strong activity from the delta Mensid meteor stream (IAU shower 130) in the brief interval between March 12 10h and 13 06h UTC, 2021, corresponding to solar longitudes 351.77-352.57 degrees (equinox J2000.0). 29 meteors were triangulated. Outside this interval, the rate of detections was only around 1 meteor per day from what may be an annual shower. Based on 2020 observations, that annual shower is ongoing and indeed more shower members were triangulated in the recent days immediately following March 13. These radiants can be seen on the CAMS data visualization website for the date of 2021 March 13 (Figure 1).
The 29 Delta Mensid meteors were detected by CAMS Namibia (T. Hanke, E. Fahl, and R. van Wyk, with the H.E.S.S. Collaboration), CAMS Chile (S. Heathcote and T. Abbott, AURA/Cerro Tololo; and E. Jehin, University of Liege), CAMS Australia (M. Towner, Curtin University, with support of L. Toms and C. Redford), CAMS New Zealand (J. Baggaley, University of Canterbury; and N. Frost, Mount John Observatory, with support from I. Crumpton and C. and L. Duncan), and CAMS South Africa (T. Cooper, Astronomical Society of Southern Africa; and P. Mey, South African Radio Astronomy Observatory).
The radiant and orbit data obtained in 2021 are compared to older data in Table 1. The results are in good agreement with 2020 results from CAMS data (cf. Janches et al., 2020a).
Table 1 – Median orbital elements for the delta Mensids (equinox J2000.0).
|Jenniskens (2006)||Jenniskens et al. (2018)||CAMS 2020||CAMS 2021|
|λʘ||356.7°||358.4°||352.40 ± 0.08°||352.26 ± 0.05°|
|αg||58°||75.6°||61.4 ± 3.8°||62.2 ± 4.9°|
|δg||–80°||–78.9°||–76.7 ± 0.7°||–77.4 ± 1.1°|
|vg||33 km/s||34.8 km/s||31.0 ± 2.4 km/s||30.9 ± 1.6 km/s|
|a||3.2 a.u.||7.01 a.u.||3.4 a.u.||3.0 a.u.|
|q||0.982 a.u.||0.992 a.u.||0.976 ± 0.005 a.u.||0.977 ± 0.004 a.u.|
|e||–||0.859||0.700 ± 0.030||0.679 ± 0.094|
|ω||345.6°||352.8°||342.9 ± 2.3°||343.8 ± 2.5°|
|Ω||177.1°||178.4°||172.40 ± 0.08°||172.26 ± 0.22°|
|i||56.1°||56.5°||50.8 ± 1.1°||51.1 ± 2.0°|
The shower peaked at solar longitude 352.26 ± 0.05 degrees with a full-width-at-half-maximum of about 0.5 degrees in solar longitude. In 2020, the shower peaked at solar longitude 352.40 ± 0.08 degrees (cf. Janches et al., 2020a) and continued to be detected until March 26.
CAMS detected the shower particularly well March 20-22, 2020. Those dates fall over a weekend this year, and during a first quarter Moon. If this activity repeats this year, then southern hemisphere meteor observers may have a chance to see some meteors from this unusual high southern declination shower after midnight, weather permitting.
Janches D., Bruzzone J. S., Weryk R. J., Hormaechea J. L., Brunini C., Wiegert P., Jenniskens P. (2020a). “Delta Mensid meteor shower 2020”. CBET 4772. D. W. E. Green (ed.), IAU Central Bureau for Astronomical Telegrams. 1 pp.
Janches D., Bruzzone J. S., Weryk R. J., Hormaechea J. L., Wiegert P., Brunini C. (2020b). “Observations of an unexpected meteor shower outburst at high ecliptic southern latitude and its potential origin”. Astrophysical Journal Letters 895, L25-31.
Jenniskens P. (2006). Meteor Showers and their Parent Comets, ISBN 0521853494. Cambridge, UK: Cambridge University Press, 2006. page 701.
Jenniskens P., Baggaley J., Crumpton I., Aldous P., Pokorny P., Janches D., Gural P. S., Samuels D., Albers J., Howell A., Johannink C., Breukers M., Odeh M., Moskovitz N., Collison J. and Ganjuag S. (2018). “A survey of southern hemisphere meteor showers”. Planetary Space Science, 154, 21–29.