Observation of the α Carinid meteor shower 2020 unexpected outburst
Juan Sebastian Bruzzone, Robert Weryk, Diego Janches, Carsten Baumann, Gunter Stober, Jose Luis Hormaechea
DDraft version March 1, 2021
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Observation of the α Carinid meteor shower 2020 unexpected outburst.
Juan Sebastian Bruzzone,
1, 2
Robert J. Weryk,
3, 2
Diego Janches, Carsten Baumann, Gunter Stober, andJose Luis Hormaechea
6, 7 Department of Physics, Catholic University of America, 620 Michigan Ave., N.E. Washington, DC 20064, USA ITM Physics Laboratory,NASA/Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt MD 20771, USA Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu HI 96822, USA Deutsches Zentrum f¨ur Luft- und Raumfahrt, Institut f¨ur Solar-Terrestrische Physik, Neustrelitz, Germany Institute of Applied Physics & Oeschger Center for Climate Change Research, Microwave Physics, University of Bern, Bern, Switzerland Facultad de Ciencias Astronomicas y Geof´ısicas, Universidad Nacional de La Plata, Argentina Estaci´on Astronomica Rio Grande, Rio Grande, Tierra del Fuego, Argentina (Received January 15, 2021; Revised February 21, 2021; Accepted February 23, 2021)
ABSTRACTWe present observations of the sudden outburst of the α Carinid meteor shower recorded with the SouthernArgentina Agile MEteor Radar-Orbital System (SAAMER-OS) near the South Toroidal sporadic region. Theoutburst peaked between 21 UT and 22 UT on October 14, 2020 and lasted 7 days (199 ◦ ≤ λ (cid:12) ≤ ◦ ) witha mean Sun-centered geocentric ecliptic radiant of λ g − λ (cid:12) = 271 ◦ . β g = − ◦ .
4, and a geocentric speed of33.3 km s − . Assuming a mass index value of s = 2 .
0, we compute a peak 24 hour-average flux of 0.029 met.km − hr − to a limit of 9th magnitude, which is equivalent to a zenithal hourly rate (ZHR) of 5.7, andcomparable to other established showers with similar mass indices. By further estimating the peak fluxes forother typical mass index values, we find that the outburst likely never exceeded a maximum ZHR of ∼ a = 3 . ± . q (cid:39) e = 0 . ± . i = 55 ◦ . ± ◦ . ω = 1 ◦ ± ◦ , Ω = 21 ◦ .
7, and are similarto those derived for two previous shower outbursts observed with SAAMER-OS at high southern eclipticlatitudes. Using the D (cid:48) criterion did not reveal a parent object associated with this shower in the knownobject catalogues. INTRODUCTIONThe Solar System, like other planetary systems (i.e. β Pictoris, Burrows et al. 1995; Fomalhaut, Kalas et al. 2005),contains a circumsolar second-generation dusty disk known as the Zodiacal Dust Cloud (ZDC) populated by debris fromasteroid collisions and the breakup and activity of comets and interstellar medium grains (Jenniskens 2006, Nesvornyet al. 2010). Dedicated radar and optical meteor surveys probe the dust content in the inner solar system via detectionof meteoroid ablation high in Earth’s atmosphere providing a reliable way to examine the dissemination of materialpopulating the ZDC (Baggaley 2002; Brown et al. 2010; Janches et al. 2015; Jenniskens et al. 2011). Observations ofthe influx of material at Earth’s atmosphere reveal two populations clearly distinguishable in the distribution of theZDC: the sporadic background sources which comprise of dynamically-evolved sub mm-sized meteoroids and micron-size dust grains largely affected by radiation pressure, and meteor showers, streams of younger and larger meteoroidsthat in principle could be linked dynamically to parent bodies, namely asteroids and comets, due to their similarity inorbital elements (Jenniskens 2006).Surveying, identifying, and studying the meteoroid population is highly relevant, both scientifically and from anoperational standpoint. Collisions with 1 µg − g meteoroids moving at average relative speeds in excess of 30 kms − could constitute a risk to satellite operations and present a safety concern for manned space missions in low orbit.For example, showers like the Daytime Arietids (ARI), the Geminids (GEM) and the Quadrantids (QUA) attain Corresponding author: J.S. [email protected] a r X i v : . [ a s t r o - ph . E P ] F e b Bruzzone et al. fluxes for 0.3-cm-equivalent particles near the limits for pressure vessel perforation (Moorhead et al. 2019). All-skymeteor surveys capable of conducting uninterrupted observations and delivering timely reports of sudden changesin meteor activity are thus highly desirable. Furthermore, recording long-term seasonal variations of the sporadicbackground provide constraints to meteoroid stream models (McNamara et al. 2004). Meteor orbit radars currently inoperation like the Canadian Meteor Orbit Radar (CMOR, Webster et al. 2004; Brown et al. 2008) and the SouthernArgentina Agile MEteor Radar Orbital System (SAAMER-OS, Janches et al. 2015) aim to address these objectivesby continuously monitoring the sub-mm sized meteoroid population (10 − kg − − kg) to collect a large quantity ofmeteoroid orbit and flux datasets to characterize meteor showers and sporadic sources (Brown & Jones 1995; Brownet al. 2010; Bruzzone et al. 2015; Campbell-Brown & Brown 2015; Janches et al. 2015; Pokorn´y et al. 2014, 2017).Sudden changes in meteor shower activity are not unusual, and in some cases, may be dramatic. For instance, showerslike the Leonids (LEO) or the Draconids (DRA) can produce storms with levels of activity thousand of times higherthan normal (Kronk 2014). On the other hand, some shower outbursts can be relatively mild enough to only raise theflux slightly above the radar detection threshold making observations of it possible for the first time. Recent examplesof abrupt outbursts include the unexpected Draconid (DRA) meteor storm on October 8, 2012 (Ye et al. 2014) andtwo shower outbursts detected at austral latitudes: the Volantids shower (VOL) outburst ( β = − ◦ .
7) in late 2015(Jenniskens et al. 2016; Younger et al. 2016; Pokorn´y et al. 2017), and the β Tucanid / δ Mensid outburst ( β = − ◦ . α Carinidshower on the night of October 13-14, 2020, recording 130 orbits with the Cameras for Allsky Meteor Surveillance(CAMS; Jenniskens et al. 2011). The α Carinid is a high-latitude southern shower, α g = 103 ◦ . δ g = − ◦ , v g = 30 . − , and first reported in Jenniskens et al. (2018) based on 121 orbits with CAMS. In this work, we report theunpredicted outburst of the α Carinid shower as detected by SAAMER-OS, peaking on October 14, 2020 ( λ (cid:12) = 201 ◦ ).In Section 2 we describe the radar and the daily shower monitoring methodology. We provide results and characterizethe outburst radiants, orbits and fluxes in Sections 3.1 and 3.2. Lastly, conclusions and final remarks are presented inSection 4. INSTRUMENTATION AND DATA ANALYSISSAAMER-OS is a VHF all-sky multi-station backscatter meteor orbit radar hosted by the Estaci´on Astron´omica RioGrande (EARG) in Rio Grande, Tierra del Fuego, Argentina (Janches et al. 2015). Here we present a brief overview ofthe system and refer the reader to Janches et al. (2020) for a more in-depth review of the hardware and data analysiscapabilities. SAAMER-OS is a SKiYMET radar system (Hocking et al. 1997), comprised of a main site (SAAMER-C;53 ◦ .
786 S, 67 ◦ .
751 W) and four remote stations: SAAMER-S (53 ◦ .
852 S, 67 ◦ . W ) located at approximately 7 kmsouth of the SAAMER-C; SAAMER-N (53 ◦ .
682 S, 67 ◦ .
871 W) at 13 km northwest of the central station; SAAMER-W(53 ◦ .
828 S, 67 ◦ .
842 W) approximately 7 km southwest of SAAMER-C and SAAMER-E (53 ◦ .
772 S, 67 ◦ .
727 W), atroughly 4 km northeast of main site. The main site hosts the 64 kW (peak power) transmitter with a single three-crosselement Yagi transmitting antenna, and the five three-element crossed yagi receiving antenna interferometer array(Hocking et al. 1997; Jones et al. 1998). At the main site, meteors are detected as backscatter echoes from meteortrails a few km in length (Kaiser & Singer 1956) with average interferometric errors less than 0 ◦ .
5. SAAMER-OStransmits 32.55 MHz pulses with a repetition frequency of 625 Hz, and employs a 7-bit Barker code to achieve aspatial resolution of 1.5 km. Each remote station is equipped with an identical single three-element crossed Yagireceiving antenna to detect the slightly forward scattered signals off the meteor trails. The time delays between thedetection of meteors at the main site and the each remote site allows for the determination of the meteoroid speedand its trajectory. SAAMER-OS currently employs an empirical meteor deceleration correction to better estimate thetrue out-of-atmosphere meteoroid speed (Bruzzone et al. 2020). SAAMER-OS’s software suite for event detection,correlation and orbit computation is similar to the one employed in CMOR (Weryk & Brown 2012) and runs in parallelto the SKiYMET’s standard software routines (SKYCORR; Hocking et al. 2001). Daily detection counts can exceed10,000 meteoroid orbits (Janches et al. 2020), to a limiting radio magnitude of +9.0, equivalent to meteoroids of mass10 − kg (or 300 µ m in diameter) at 30 km s − (Verniani 1973).The SAAMER-OS data reduction pipeline employs a 3-D wavelet transform algorithm that is well suited to thedaily detection of meteor shower radiants. This method was first used by the Advanced Meteor Orbit Radar (AMOR;Baggaley et al. 1994; Galligan & Baggaley 2002), which operated near Christchurch, New Zealand, to probe forclustering of meteor radiants. Since then, it has been applied by other meteor radar surveys (Brown et al. 2008, 2010;Bruzzone et al. 2015; Pokorn´y et al. 2017; Schult et al. 2018), and more recently, it has been applied to radar and n Unexpected Outburst of the α Carinid Meteor Shower λ g − λ (cid:12) , β g , v g ). Meteoroids that belong to a specific shower concentrate in radiantspace and time with a characteristic spread in angular coordinates and speed that differs from the sporadic meteorbackground. For a given radiant distribution, the wavelet transform returns a list of wavelet coefficients ( W c ) that serveas a metric for clustering in radiant space enhancing the presence of showers. The wavelet transform can be furtheroptimized to amplify the presence of meteor showers by adjusting the wavelet kernel scale dimensions to resemblethe shower’s natural spread in radiant space (Bruzzone et al. 2015). In this way, meteor showers can be effectivelyseparated from the activity of the sparse sporadic meteor background. For SAAMER-OS, we adopt the wavelet kernelscale parameters σ a = 2 . ◦ and σ v = 15% derived in Pokorn´y et al. (2017). For the analysis of SAAMER-OS dailyobservations, the wavelet-based algorithm is evaluated for λ g − λ (cid:12) ∈ [0 ◦ , ◦ ) and β g ∈ ( − ◦ , ◦ ] at 0 . ◦ v g ∈ [10 km s − , 80 km s − ] at 5% steps, while advancing at 1 ◦ steps in λ (cid:12) . For each day, this procedure returnsa list of W c for which each individual entry is compared to its yearly median and standard deviation. Those entriesthat exceed 3 times the total standard deviation above the yearly median, σ , are stored and used in a global maximasearch. We proceed to identify a shower core candidate as the radiant returning the maximum in W c . Each shower coreidentified is cross referenced with a compiled list of known meteor showers (Brown et al. 2010; Pokorn´y et al. 2017).When the location of a core candidate is within 3 ◦ and 15% in v g of a shower in the reference list, a match is recordedand the candidate is labeled with the shower IAU code in a radiant density map. Radiants in the map are color-codedby the number of adjacent radiants within 2 . ◦ α Carinid outburst and repeat the wavelet-based analysis at 0 . ◦ λ g − λ (cid:12) , β g ) and1.5% in v g to secure a more precise radiant position and speed. We then follow Bruzzone et al. (2020) to track theoutburst progression with time by linking the shower core radiants at each degree in solar longitude. RESULTS AND DISCUSSION
Figure 1.
SAAMER-OS daily radiant density plot in Sun-centered geocentric ecliptic coordinates on October 14 2020. TheSouthern Taurids (STA) is labeled on the map while the α Carinid outburst is labeled as shower candidate ID-0.
Wavelet-based activity profile and orbits
Figure 1 shows the radiant density plot with meteor detections over a 24 hr-period on October 14 2020 in Sun-centeredgeocentric ecliptic coordinates. The wavelet-based analysis pipeline labels the position of the Southern Taurids as STA,and the α Carinid outburst as candidate ID-0 as it does not match with any known shower in our reference catalog.The procedure returns the radiant location for the outburst at λ g − λ (cid:12) = 271 ◦ .
04 ( α g = 98 ◦ . β g = − ◦ . δ g = − ◦ . v g = 33 . − achieving a maximum W c = 1358 on October 14, 2020 ( λ (cid:12) = 201 ◦ ) with a Bruzzone et al. strong detection of 16 . σ based on 1352 meteors. The wavelet analysis identifies the outburst activity for six consecutivedays (199 ◦ ≤ λ (cid:12) < ◦ ) starting on October 12 through October 17, 2020. The radiant position and speed measuredwith SAAMER-OS agree with the mean values from 130 optical meteors reported by Jenniskens (2020) ( α g = 98 ◦ . δ g = − ◦ . v g = 32 . − ) with a difference of 0 . ◦ and 0.9 km s − respectively. Such a difference in radiantposition and speed between SAAMER-OS and CAMS video observations is in agreement with mean values found fora selection of 20 established meteor showers in Bruzzone et al. (2020). Figure 2 shows the annual activity profiles bycomputing W c at λ g − λ (cid:12) = 271 . ◦ , β g = − . ◦ and v g = 33 . − while advancing at 1 ◦ steps in λ (cid:12) for 2017through 2020. A horizontal dashed line indicates the 3 σ level above the median W c of 51.4 for 2020. The profilesconfirm the absence of this shower in past years with SAAMER-OS data, and its sudden appearance in 2020. Theinsert in Figure 2 displays the hourly meteoroid flux between 0 UT October 12 and 0 UT October 18 2020. Fluxestimates with SAAMER-OS are corrected for observational biases by adjusting the observed meteor rates by theradar response function (RRF, Ceplecha et al. 1998; Galligan & Baggaley 2004) and the variation of the radar effectivecollecting area with time. Meteor rates are estimated using a 3 ◦ -radius aperture centered in the outburst radiantpositions returned by the wavelet transform. We measure a peak hourly 9 mag-flux of 0.097 met. km − hr − down toa limiting mass of 1 . × − kg. The peak activity ranged between 21 UTC and 22 UTC on October 14, λ (cid:12) (cid:39) . ◦ ,roughly 1 ◦ apart of the time of peak activity at λ (cid:12) = 200 . ◦ ± . ◦ for optical detections reported by Jenniskens(2020). We further elaborate on SAAMER-OS’ collecting area and meteoroid flux estimates in 3.2. The geocentricecliptic radiant positions, geocentric speed, and orbital elements derived with the wavelet analysis are listed in Table1. We employ 10,000 iterations in a Monte Carlo procedure to draw orbital element uncertainties from the errors inradiant position and speed. We follow Bruzzone et al. (2020) to estimate the error in the outburst radiant positionas the angular separation of the wavelet radiant position and the position of peak radiant density at λ (cid:12) = 201 ◦ . Onthe same date, we adopt the error in the outburst speed as the standard error of the outburst mean geocentric speed.The errors in the outburst radiant position and speed are 0 . ◦ and 0 .
09 km s − respectively. The orbital elementsderived with SAAMER-OS closely resemble those obtained by Jenniskens (2020) with video observations. Employingthe D (cid:48) criterion (Drummond 1981) to look for potential parents for this outburst from the Minor Planet Center OrbitDatabase results in no clear parent object of the α Carinid meteor shower.
Figure 2.
Wavelet coefficient (
W c ) profiles at 1 ◦ steps in λ (cid:12) for 2017 through 2020. W c values are estimated at the radiantposition and speed of the outburst during the peak at λ (cid:12) = 201 ◦ . The horizontal dashed line marks the 3 σ level above theannual median W c for 2020. The insert shows the hourly flux from 0 UTC October 12 through 0 UTC October 18, 2020 for amass index value of 2, times of very low and zero meteor flux indicate reduced radar detectability of meteors when the showerradiant is close to the local zenith. In addition to the outburst reported here, two more sudden outbursts have been detected with SAAMER-OS southof the South Toroidal region: the Volantids outburst on December 31, 2015 (Bruzzone et al. 2020): λ (cid:12) = 280 ◦ , n Unexpected Outburst of the α Carinid Meteor Shower λ g − λ (cid:12) = 304 ◦ . β g = − . v g = 30 . − , and the β Tucanid / δ Mensid in March 12, 2020 (Janches et al.2020), λ (cid:12) = 352 ◦ , λ g − λ (cid:12) = 305 . ◦ . β g = − . v g = 30 . − . Radiant and orbital elements are listed inTable 1. All three outburst orbits resemble those of a short period comet, but display similarly higher inclinations thanexpected for Jupiter-family comets. The orbits share similar shape, size, and inclination; however their orientationsdiffer and both ω and Ω display more scatter. The orbits are close to several important Mean Motion Resonances(MMR) with Jupiter, especially to the 2:1, 5:3, 8:5 and 7:3 at e = 0 . i = 55 ◦ (Gallardo 2020) and differ fromthose at the South and North Toroidal regions: a ∼ e ∼ . i ∼ ◦ − ◦ (Campbell-Brown 2008; Jancheset al. 2015). Furthermore, the duration of these outburst may indicate they are part of relatively younger streams asopposed to the older sporadic meteoroids comprising the Toroidal ring which likely evolved from long period comet-type objects (Pokorn´y et al. 2014). We note however, that the duration for these outbursts (between two and sevendays) suggest fairly evolved streams as opposed to very young ones such as the Camelopardalids. Janches et al. 2020report asteroid (248590) 2006 CS ( a = 2 .
91 au, e = 0 . i = 52 ◦ .
3, Ω = 172 ◦ . ω = 346 ◦ .
4) as a promising parentcandidate ( D (cid:48) = 0 . β Tucanid / δ Mensid shower outburst. The latter may suggest that the three detectedoutbursts could have originated from a short-period object. However, further analysis including dynamical simulationswill be needed to properly address the origin of these outbursts.
Table 1.
Meteor shower outburst observed with SAAMER-OS.Object λ g − λ (cid:12) (deg) β g (deg) v g (km s − ) a(au) q(au) e i(deg) ω (deg) Ω (deg) α Carinid 271 . − . . ± . . ± . . ± .
02 55 . ± . ±
173 21.7 β Tucanid / δ Mensid 305 . − . . . ± . . ± .
001 0 . ± .
01 50 . ± . . ± . − . . ± . . ± .
001 0 . ± .
04 49 . ± . . ± . Estimating SAAMER-OS’ collecting area and meteoroid fluxes
In order to estimate meteoroid fluxes with SAAMER-OS, a measure of the radar collecting area and a correctionfor observational biases is needed. The meteoroid flux Φ, can be estimated by dividing the debiased meteor rate Σby the radar collecting area A (Campbell-Brown 2004; Campbell-Brown & Brown 2015; Bruzzone et al. 2015). Biasesaffecting radar observations are numerous and pertain to the specific radar system parameters, the interaction of thescattered waves within the atmosphere, and the inherent scattering mechanism of radio waves by free electrons (cf.Ceplecha et al. 1998; Galligan & Baggaley 2004, 2005). Such biases include the initial trail radius effect, in whichthe observability of meteors occurring higher in the atmosphere is reduced due to the increase of the mean free pathwith height, resulting in the attenuation of the echo amplitude for large trail widths due to destructive interference.Other effects include Faraday rotation, the change of the polarization plane of the radar wave as it passes throughthe ionosphere; the diffusion of meteor trails during formation and the decay time of established meteor trails. Thecombination of these effects result in a decrease in the meteor rates for any radar system. To correct for observationalbiases we make use of the derivation of SAAMER-OS’ RRF in Janches et al. (2015) and refer the reader to thatstudy for an in-depth description and derivation of correction factors for this system. We model the transmittingand receiving antennas with a NEC-2D code to determine the beam patterns. We find that the total gain and beampatterns for the antennas are the same and well described by a smooth function on elevation alone and proceed tofit it with a nine-order polynomial. The peak gain is 8.8 dB at the zenith ( z = 0 ◦ ) with the -3 dB point at z = 79 ◦ .Correction for Faraday rotation is not necessary since SAAMER-OS receiving antennas are cross-Yagis and thus thesystem receives both linear polarizations and is not sensitive to this effect (Janches et al. 2015). To estimate the radarcollecting area, we use the methodology in Kaiser (1960); Brown & Jones (1995) and Brown et al. (1998) as a guide.The collecting area is a strip of space that is perpendicular to the meteor radiant and has a width given by the meanvertical trail length, which describes the altitude range in which ablation occurs. The length of the strip is the lengthof the echo line which extends from horizon to horizon. In practice, the echo line is truncated out to a limiting rangefor the radar. For the vertical trail height, we use the empirical relation with mass index s reported in Brown et al.(1998) from TV observations of faint meteors by Flemming et al. (1993). Values of s below 2.0 indicate that thereis more mass in larger particles, where the opposite holds for values larger. In general, values for showers are in the1 . − . s = 2 . Bruzzone et al. estimates in this work. However, we also include fluxes for a list of s values and leave the development of a method todetermine specific shower mass indices with SAAMER-OS for a future study.We parameterize the echo line as a function of its elevation φ , weighted by the antenna gain, and obtain the lengththrough numeric integration. Since the vertical trail length is only dependent on s , the collecting area A ( z, h, s ) can befound by multiplying the echo line length by the vertical trail length. Following Campbell-Brown (2004); Campbell-Brown & Brown (2015) and Bruzzone et al. (2015), we set h = 100 km. After some algebra (see Baumann 2012), thecollecting area A ( z, h, s ) can be expressed as: A ( z, h, s ) = 2 (cid:90) π/ ( G ( φ ) cos z ) s − R E cos φ R E R E + h sin φ (cid:114) − (cid:16) R E R E + h cos φ (cid:17) − dφ sin z (cid:16) .
15 + 14 . e − s . (cid:17) , (1)where G ( φ ) = (cid:112) G Tx ( φ ) G Rx ( φ ) is the radar gain pattern, z the radiant zenith distance, R E is Earth’s radius, h isthe meteor height, s is the mass index, and φ the echo line elevation. Here G Tx and G Rx are the radar transmit andreceive antenna gain powers, which in this case are identical.Outburst fluxes are estimated at one hour intervals within a 6 ◦ × ◦ window centered on the position of wavelet-basedoutburst radiants for each day from October 12 through October 17 2020. Windows are partitioned in 0 . ◦ steps andthe debiased meteor rates and collecting area computed. Hourly fluxes are then determined by finding the ratio Σ : A .Hourly α Carinid fluxes in Figure 2 are determined as the total sum of fluxes in the window within 3 ◦ from the positionof the wavelet radiants. The shower daily flux is computed from the averaged hourly fluxes where we subtract theequivalent sporadic background averaged over 15 consecutive days before October 12, and 15 days after October 17,2020. To help the comparison with results from visual observers, we follow Koschack & Rendtel (1990) and adjust theflux to a +6.5 limiting magnitude, Φ +6 . , usingΦ +6 . = Φ +9 . × (6 . − . s − / . , (2)and estimate the zenithal hourly rates (ZHR) with ZHR ( r ) = 37200 km × Φ +6 . × (cid:32) ( r − . − . . r − . (cid:33) , (3)where r = 10 ( s − / . is the population index. Figure 3 displays the average meteoroid fluxes for the outburst, beforesporadic flux subtraction, and sporadic background fluxes. The dashed line indicates the 30 day-median sporadic flux.After background subtraction, we record a peak average flux, Φ +9 . = 0 .
029 meteoroids km − hr − , down to a +9limiting magnitude, on October 14, 2020. The peak flux corresponds to a ZHR max of approximately 5.7 at r = 2 . r values:Southern and Northern Taurids (ZHR max = 5, r = 2 . (cid:15) Perseids (ZHR max = 5, r = 2 . max = 6, r = 2 . α Capricornids (ZHR max = 4, r = 2 .
5) and γ Normids (ZHR max = 4, r = 2 .
4) (Rendtel2014). Instead of displaying a fixed s value, in general the shower mass index drops as the Earth intersects the coreof the stream where larger particles are located (Blaauw et al. 2011a). For this reason, we include peak flux estimatesfor a list of mass index values typical for showers in Table 2. The wide range in ZHR values reflects the sensitivityof shower fluxes with mass index. Our flux estimates suggest that the outburst flux likely never rises above the levelseen in showers like the η − Aquariids, ZHR max = 50 −
80, adopting s = 1 . max = 189 at s = 1 .
75 (Bruzzone et al. 2015).We revisit archival observations of the previous β Tucanid shower outburst detected with SAAMER-OS on March12, 2020 (Janches et al. 2020), and apply the procedure developed here to estimate the average peak flux. We finda maximum 9-magnitude flux for the β Tucanid shower of 0.01 met. km − hr − at s = 2 . max slightly above 2. CONCLUSIONSWe reported radar observations of an unexpected outburst of the α Carinid meteor shower recorded with theSouthern Argentina Agile MEteor Radar Orbital System (SAAMER-OS). Our wavelet-based analysis returned the n Unexpected Outburst of the α Carinid Meteor Shower Figure 3. α Carinid 24hr-average fluxes with SAAMER-OS with s = 2 .
0. Fluxes associated with the shower by the wavelet-based transform displayed in blue with background fluxes in grey. The dashed line marks the 30 day-median background fluxof 0.00415 met. km − hr − Table 2. α Carinid fluxes for various mass index values following the procedure outlined in Section 3.2. s Φ +9 Φ +6 . ZHR1.65 2.24e-2 5.33e-3 43.81.70 2.25e-2 4.89e-3 31.11.75 2.52e-2 4.50e-3 22.71.80 2.60e-2 4.12e-3 16.81.85 2.68e-2 3.78e-3 12.61.90 2.75e-2 3.47e-3 9.61.95 2.83e-2 3.17e-3 7.42.00 2.90e-2 2.90e-3 5.72.05 3.00e-2 2.66e-3 4.42.10 3.04e-2 2.43e-3 3.52.15 3.11e-2 2.23e-3 2.72.20 3.18e-2 2.04e-3 2.2 shower radiant location south of the South Toroidal ring at λ g − λ (cid:12) = 271 ◦ . β g = − ◦ . v g = 33 . − during the peak at λ (cid:12) = 201 ◦ on October 14, 2020. The wavelet-based technique unequivocally confirms thesudden appearance of the outburst in 2020 rising 16 times the total standard deviation above the annual median. Theoutburst lasted for approximately 6 days starting on October 12 through October 17, 2020. The radiant location, speedand period of observation agree with those reported with video observations by Jenniskens (2020). We measured a9-magnitude peak hourly flux of 0.09 meteoroids km − hr − , assuming s = 2, down to a limiting mass of 1 . × − kgbetween 21 UTC and 22 UTC on October 14. To compute fluxes we debiased the observed meteor rates and estimatedthe radar collecting area at one hour intervals. The 6 magnitude-equivalent peak average daily flux corresponds to aZHR of approximately 6, comparable to other known meteor showers at similar s values. We computed peak averagefluxes for several mass index values to derive probable ZHR estimates returning limits between 2 and 44 approximately.The latter suggest that α Carinid fluxes remain well below those recorded for strong showers like the Daytime Arietidsor Geminids. Based on 1352 events during the peak, the orbital elements resemble those of a short-period object: a = 3 . ± . q (cid:39) e = 0 . ± . i = 55 ◦ . ± ◦ . ω = 1 ◦ ± ◦ , Ω = 21 ◦ .
7. Comparably, two other australshower outbursts previously recorded with SAAMER-OS, the β Tucanid / δ Mensid and the Volantids (VOL), haveorbits with shape, size and inclination similar to the α Carinid. Our search for a parent object using the D (cid:48) criterion(Drummond 1981) did not reveal any clear candidate. While the duration suggests the shower is not as old as the Bruzzone et al.
Arietids or Taurid streams (thousands to tens of thousands of years), the significant spread in nodal crossing mayindicate a fairly evolved stream. ACKNOWLEDGEMENTSJ.S.B. and D.J.’s work is supported by the NASA SSO and ISFM Programs and the NASA NESC. RJW was sup-ported through NASA grant 80NSSC18K0656. SAAMER’s operation is supported by NASA SSO, NESC assessmentTI-17-01204, and NSF grant AGS-1647354. The authors appreciate the invaluable support of Carlos Ferrer, GerardoConnon, Luis Barbero and Leandro Maslov with the operation of SAAMER.REFERENCES n Unexpected Outburst of the α Carinid Meteor Shower9