Electronic Telegram No. 5126 Central Bureau for Astronomical Telegrams Mailing address: Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network TAU HERCULID METEORS 2022 P. Jenniskens, SETI Institute and NASA Ames Research Center, reports that a meteor outburst of tau Herculids (IAU shower 61) from the encounter with the 1995 debris of comet 73P/Schwassmann-Wachmann was observed much as anticipated (cf. CBET 5125). The global networks of the Cameras for Allsky Meteor Surveillance (CAMS) low-light video survey measured the orbit of 2244 tau Herculid meteors (cf. website URL http://cams.seti.org/FDL/ for the date of 2022 May 31). The shower peaked on May 31d04h42m +/- 25m UT (corresponding to solar longitude 69.436 +/- 0.017 deg, equinox J2000.0), with forecasts ranging from 3h52m to 5h01m UT. For visual observers, the peak zenith hourly rate was about 40 tau Herculid meteors per hour at that time (see the website of the International Meteor Organization at URL http://www.imo.net). The peak lasted from about 1h30m to 9h00m UT (solar longitude 69.30-69.61 degrees), with a duration of 3.5 hours (full-width-at-half-maximum). Meteors radiated from a median geocentric radiant at R.A. = 209.17 +/- 0.09 deg, Decl. = +28.21 +/- 0.07 deg, with a 1-sigma dispersion of 3.4 and 2.8 degrees, respectively, and geocentric velocity 12.01 +/- 0.09 km/s. The predicted values were R.A. = 209 deg, Decl. = +28 deg, with geocentric velocity 12.1 km/s, in good agreement. As expected, the shower was rich in faint meteors. The number of video-detected meteors from all CAMS networks with peak brightness from magnitude -2 to +5 in one-magnitude increments was 20, 48, 172, 380, 461, 277, 120, and 3 tau Herculids, corresponding to a magnitude-distribution index of N(m+1)/N(m) = 3.79 +/- 0.12 (where m is the magnitude). Starting on May 27, rates gradually increased leading up to this peak. The radiant of the shower shifted north and the geocentric speed increased. On May 28, seven tau Herculids radiated from R.A. = 203.3 +/- 2.1 deg, Decl. = +17.3 +/- 2.5 deg, with geocentric velocity 10.8 +/- 1.4 km/s. On May 29, twelve tau Herculids radiated from R.A. = 203.5 +/- 1.7 deg, Decl. = 20.2 +/- 2.0 deg, with geocentric velocity 11.1 +/- 0.9 km/s (cf. website URL http://www.meteornews.net). On May 30, 555 tau Herculids radiated from R.A. = 205.3 deg, Decl. = +22.9 deg, and geocentric velocity 11.2 km/s during 4h-6h UT; from R.A. = 206.8 deg, Decl. = +25.2 deg, and geocentric velocity 11.4 km/s during 16h-19h UT (perhaps the 1892 dust trail); and also from R.A. = 209.6 deg, Decl. = +28.2 deg, geocentric velocity 11.5 km/s starting at 23h UT (perhaps the 1995 debris). It is not clear at present if the 1892 and 1897 dust trails were detected. Observations to this report were contributed by CAMS California (P. Jenniskens, J. Albers, E. Egland, B. Grigsby, T. Beck, and D. Samuels, SETI Institute), LO-CAMS (N. Moskovitz, Lowell Observatory), CAMS Texas (W. Cooney), CAMS Arkansas (L. Juneau), CAMS Florida (A. Howell), CAMS Mid- Atlantic (P. Gural), CAMS BeNeLux (C. Johannink, M. Breukers, and S. Rau), CAMS Turkey (O. Unsalan, Ege University; and M. Boyukata, Yozgat Bozok University), UAE Astronomical Camera Network (M. Odeh, International Astronomical Center), CAMS Namibia (T. Hanke, E. Fahl, and R. van Wyk, H.E.S.S. Collaboration), CAMS South Africa (T. Cooper, Astronomical Society of Southern Africa), CAMS Australia (M. Towner, Curtin University), CAMS New Zealand (J. Baggaley, University of Canterbury), CAMS Chile (S. Heathcote and T. Abbott, AURA/Cerro Tololo; and E. Jehin, University of Liege), and CAMS EXOSS (M. de Cicco). D. Vida, University of Western Ontario; and D. Segon, Global Meteor Network (GMN), report that the video-based GMN observed a total of 1396 tau Herculid meteors via triangulation from multiple sites during the outburst that yielded the computation of orbits. The video cameras use Sony IMX291 sensors and (mostly) 3.6-mm f/0.9 lenses. The cameras' stellar limiting magnitudes are +6.0 +/- 0.5 at 25 frames per second. For this particular shower, the mean meteor magnitude across all systems was +6.04. The 600+ cameras are not only located in Europe, but across the globe. The full map of all cameras can be seen at URL https://tammojan.github.io/meteormap/. The peak of activity occurred at 69.42 +/- 0.02 deg (May 31d04h15m UT), and the full period of activity lasted from solar longitudes 67.1 to 71.1 deg. The observed geocentric radiant at the peak is R.A. = 208.6 +/- 0.04 deg, Decl. = 27.7 +/- 0.04 deg (equinox J2000.0), with geocentric velocity 11.4 +/- 1.0 km/s. The shower experienced a significant radiant drift of 2.83 degrees in R.A. and 4.86 degrees in Decl. (units of degrees on the sky per degree of solar longitude, relative to the peak). A slight drift of 0.33 km/s per degree of solar longitude was observed in geocentric velocity. The observed radiant dispersion (median offset from the mean radiant) is 1.2 deg. The sun-centered ecliptic plots showing the radiants are available on the GMN website via URL tinyurl.com/2p8nfyar; the full orbital data set is available at URL https://globalmeteornetwork.org/data/. A single-station flux of 11.2 +/- 0.5 x 10^-3 meteoroids per square kilometer per hour (in the atmosphere at altitude 88 km) at a limiting magnitude of +6.5 (limiting mass 0.005 g) was measured using GMN data at the peak of activity. The equivalent ZHR is 22.0 +/- 1.0 meteors per hour. A population index of r = 2.5 +/- 0.1 (differential mass index s = 2.0, where s = 2.5 log 10r + 1) was measured directly from the video data. The tau Herculid meteoroids appeared to be very fragile as compared to sporadics at the same velocities. A measured mean meteor altitude of 88 km was used in computing the flux collection areas (as noted above). A total of 14306 single-station meteors were used in the analysis. A total of 58 individual flux measurements were made during the period of activity (approximately once every 30 minutes). NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2022 CBAT 2022 June 3 (CBET 5126) Daniel W. E. Green