Icarus 239 (2014) 273–280

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Icarus

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Orbit and emission spectroscopy of a-Capricornid fireballs

http://dx.doi.org/10.1016/j.icarus.2014.06.0050019-1035/� 2014 Elsevier Inc. All rights reserved.

⇑ Corresponding author.E-mail addresses: madiedo@cica.es, jmmadiedo@gmail.com (J.M. Madiedo).

José M. Madiedo a,⇑, Josep M. Trigo-Rodríguez b, José L. Ortiz c, Alberto J. Castro-Tirado c,Jesús Cabrera-Caño a

a Departamento de Física Atómica, Molecular y Nuclear, Facultad de Física, Universidad de Sevilla, 41012 Sevilla, Spainb Institute of Space Sciences (CSIC-IEEC), Campus UAB, Facultat de Ciències, Torre C5-parell-2ª, 08193 Bellaterra, Barcelona, Spainc Instituto de Astrofísica de Andalucía, CSIC, Apt. 3004, Camino Bajo de Huetor 50, 18080 Granada, Spain

a r t i c l e i n f o a b s t r a c t

Article history:Received 9 December 2013Revised 3 June 2014Accepted 6 June 2014Available online 20 June 2014

Keywords:MeteoritesCometsMeteors

Seven double-station a-Capricornid bolides with absolute magnitudes ranging from �6 to �10 are ana-lyzed. These events were imaged between 2011 and 2013 in the framework of the continuous fireballmonitoring and meteor spectroscopy campaign developed by the SPanish Meteor Network (SPMN). Theiratmospheric trajectory is calculated, together with the orbit in the Solar System of the progenitor mete-oroids and the tensile strength of these particles. Their emission spectra are also discussed, and the rel-ative abundances of the main rock-forming chemical elements contained in these meteoroids areestimated. An overabundance of Mg with respect to the expected value for chondritic materials isinferred for most of these particles, although the spectra also reveal differences in the composition ofa-Capricornid meteoroids that allow us to derive information about the parent body of this stream.

� 2014 Elsevier Inc. All rights reserved.

1. Introduction

The a-Capricornid meteoroid stream gives rise to an annual dis-play of meteors from about July 19 to August 18, with a maximumactivity around the end of July and a zenithal hourly rate (ZHR) of�10 h�1 (Jenniskens, 2006). Recently, Jenniskens and Vaubaillon(2010) identified the Jupiter Family Comet 169P/NEAT (=2002EX12) as the parent body of this stream. Its perihelion distance(q = 0.61 AU) and short orbital period (about 4.2 yr) suggest a rapidsublimation of volatiles from this cometary nucleus. However,recent observations of this object, with activity confined to the per-iod around perihelion, indicate that 169P is a dying comet (Kasugaet al., 2010).

Although most a-Capricornid meteors are faint, this stream alsopresents a population of large (cm-sized) meteoroids that producesvery bright bolides which often exhibit a characteristic terminalflare. Thus, for instance, the brightest event recorded in 2006 bythe SPanish Meteor Network SPMN was a fireball with an absolutemagnitude of �12 ± 2 associated with this meteor shower (Trigo-Rodríguez et al., 2007a). Unfortunately these a-Capricornid bolidesare rare and, so, a continuous fireball monitoring simultaneouslyperformed from several observing stations is fundamental in orderto get additional information about the orbits and physical param-eters of these meteoroids. Meteor spectroscopy is of particular

interest, as the emission spectra obtained during the ablation ofthese particles in the atmosphere provide helpful informationabout the composition of these meteoroids and about the natureof their parent body (Trigo-Rodríguez et al., 2007b, 2009;Madiedo et al., 2013a, 2013b, 2014). Thus, for instance, Borovickaand Weber (1996) analyzed the emission spectrum produced dur-ing the terminal flare of a mag. �5 a-Capricornid fireball. Theyobtained the following abundances relative to Fe: Na/Fe = 0.04,Mn/Fe = 0.003, Cr/Fe = 0.001, Mg/Fe = 3, and Ca/Fe = 0.001. Theseresults suggest an overabundance (by a factor of about 3) of Mgin 196P/NEAT when compared to CI or CM chondrites (Jessbergeret al., 1988; Rietmeijer, 2002a; Trigo-Rodríguez et al., 2003;Lodders, 2003). However, additional a-Capricornid spectra wouldbe necessary before drawing conclusions about this topic. In thiscontext, we present here the analysis of seven of a-Capricornidfireballs registered over Spain. Their absolute magnitude rangesfrom �10.0 ± 0.5 to �6.0 ± 0.5. We also discuss the emission spec-trum recorded for these events during the ablation of the progen-itor meteoroids in the atmosphere and the implications that fromthe inferred meteoroid chemical information can be derived forthe nature of the parent body of this meteoroid stream.

2. Observations and methodology

Fig. 1 shows composite images of the fireballs discussed in thiswork. As can be noticed, all of them exhibited at least one flare

Fig. 1. Composite image of the a-Capricornid fireballs imaged on (a) July 22, 2011 at 0h13m56.6s ± 0.1s UTC (SPMN220711); (b) July 25, 2012 at 1h40m19.5s ± 0.1s UTC(SPMN250712); (c) July 27, 2012 at 23h54m00.0s ± 0.1s UTC (SPMN270712); (d) July 28, 2012 at 22h17m12.6s ± 0.1s UTC (SPMN280712), (e) July 18, 2013, at21h33m31.9 ± 0.1s UTC (SPMN180713), (f) July 26, 2013, at 2h52m05.4s ± 0.1s UTC (SMPN260713), (g) July 29, 2013, at 22h04m36.7s ± 0.1s UTC (SPMN290713).

274 J.M. Madiedo et al. / Icarus 239 (2014) 273–280

along their atmospheric path. Most of them show the above-men-tioned terminal flare which is characteristic of the a-Capricornids.To image these events we have employed an array of high-sensitiv-ity CCD video cameras (models 902H and 902H Ultimate fromWatec Co., Japan) operating from the meteor observing stationslisted in Table 1. The video cameras are equipped with a 1/200 Sonyinterline transfer CCD image sensor with their minimum lux ratingranging from 0.01 to 0.0001 lux at f1.4. Aspherical lenses areemployed. Their focal length ranges from 6 to 25 mm and the field

Table 1Geographical coordinates of the meteor observing stations involved in this work.

Station # Station name Longitude (W) Latitude (N) Alt. (m)

1 Sevilla 05�5805000 37�2004600 282 El Arenosillo 06�4305800 37�0601600 403 La Hita 03�1100000 39�3400600 6744 Huelva 06�5601100 37�1501000 255 Sierra Nevada 03�2300500 37�0305100 2896

of view covered by each device ranges from 62 � 50� to 14 � 11�.In this way, different areas of the sky can be monitored by everycamera and point-like star images are obtained across the entirefield of view. These cameras generate interlaced imagery accordingto the PAL video standard, at a rate of 25 frames per second andwith a resolution of 720 � 576 pixels. They are arranged in sucha way that the common atmospheric area monitored by neighbor-ing observing stations is maximized. A more detailed description ofthese systems can be found elsewhere (Trigo-Rodríguez et al.,2007b; Madiedo and Trigo-Rodríguez, 2008; Madiedo et al.,2010). For meteor spectroscopy we employed transmission diffrac-tion gratings (500 or 1000 lines/mm, depending on the device)attached to the optics of these CCD video devices. We do notemploy additional image intensifying devices. In this way, wecan obtain the emission spectrum of meteors brighter than magni-tude �3/�4 (Madiedo et al., 2013a, 2013b, 2013c).

With the configuration of our experimental setup the times offireball passage were known with an accuracy of 0.1 s. Meteor

Table 2Trajectory and radiant data (J2000) for the a-Capricornid fireballs analyzed here.

SPMN code Date Time (UTC) ± 0.1 s Mv ± 0.5 Hb (km) He (km) ag (�) dg (�) V1 (km s�1) Vg (km s�1) Vh (km s�1)

220711 July 22, 2011 0h13m56.6s �10.0 97.7 ± 0.5 75.6 ± 0.5 301.8 ± 0.04 �10.5 ± 0.05 25.7 ± 0.2 23.2 ± 0.2 36.5 ± 0.2250712 July 25, 2012 1h40m19.5s �7.0 101.5 ± 0.5 80.0 ± 0.5 303.1 ± 0.2 �9.93 ± 0.04 25.6 ± 0.2 23.2 ± 0.2 37.3 ± 0.2270712 July 27, 2012 23h54m00.0s �8.5 100.7 ± 0.5 76.8 ± 0.5 303.2 ± 0.1 �11.4 ± 0.02 24.5 ± 0.2 21.8 ± 0.2 37.5 ± 0.2280712 July 28, 2012 22h17m12.6s �7.5 98.9 ± 0.5 76.6 ± 0.5 303.5 ± 0.3 �14.2 ± 0.1 24.6 ± 0.2 21.7 ± 0.2 37.6 ± 0.2180713 July 7, 2013 21h33m31.9s �8.0 108.2 ± 0.5 78.1 ± 0.5 302.4 ± 0.3 �10.1 ± 0.1 27.5 ± 0.3 24.8 ± 0.3 36.4 ± 0.3260713 July 26, 2013 2h52m05.4s �7.5 102.4 ± 0.5 77.2 ± 0.5 300.0 ± 0.2 �10.0 ± 0.1 24.4 ± 0.3 22.0 ± 0.3 37.6 ± 0.3290713 July 29, 2013 22h04m36.7s �6.0 103.3 ± 0.5 75.9 ± 0.5 305.3 ± 0.2 �10.7 ± 0.1 24.2 ± 0.3 21.2 ± 0.3 36.8 ± 0.3

Table 3Orbital elements (J2000) for the bolides discussed in the text.

SPMN code a (AU) e i (�) X (�) x (�) q (AU)

220711 2.15 ± 0.04 0.751 ± 0.006 7.7 ± 0.1 118.7179 ± 10�4 276.0 ± 0.1 0.534 ± 0.002250712 2.50 ± 0.07 0.775 ± 0.007 7.6 ± 0.1 122.3494 ± 10�4 271.1 ± 0.4 0.563 ± 0.003270712 2.65 ± 0.08 0.767 ± 0.008 5.9 ± 0.1 125.1428 ± 10�4 264.2 ± 0.2 0.619 ± 0.003280712 2.60 ± 0.20 0.770 ± 0.010 3.8 ± 0.1 126.0276 ± 10�4 264.1 ± 0.9 0.610 ± 0.010180713 2.13 ± 0.08 0.775 ± 0.009 8.9 ± 0.2 116.2133 ± 10�4 282.0 ± 0.2 0.479 ± 0.005260713 2.70 ± 0.12 0.770 ± 0.010 7.3 ± 0.1 123.1062 ± 10�4 263.8 ± 0.4 0.620 ± 0.004290713 2.28 ± 0.09 0.730 ± 0.010 6.0 ± 0.1 126.7363 ± 10�4 266.9 ± 0.4 0.608 ± 0.003

J.M. Madiedo et al. / Icarus 239 (2014) 273–280 275

positions were measured by hand in each video frame in order toobtain, for each recording station, the equatorial coordinates ofthe apparent position of these events along their apparent trajec-tory in the night sky (Trigo-Rodríguez et al., 2009; Madiedo et al.,2013c). These astrometric measurements are then employed tocalculate the atmospheric trajectory and radiant position of thefireballs by means of the AMALTHEA software (Trigo-Rodríguezet al., 2009; Madiedo et al., 2011a), which follows the planes inter-section method (Ceplecha, 1987). Once the atmospheric path isdetermined, the orbital elements of the corresponding meteoroidsare obtained by following the procedure described in Ceplecha(1987).

To analyze the photometric behavior of these fireballs, the evo-lution of magnitudes along each trajectory was determined bydirect comparison of the brightness level of the pixels of themeteor trail and those of nearby stars. However, for the brightestphase of these events a different approach was employed. Sincethese bolides were much luminous than these stars during thebrightest portion of their atmospheric trajectory, a previous cali-bration of our cameras with bright sources in a laboratory wasemployed to obtain the corresponding magnitudes. In this way,the visual magnitudes were determined with an uncertainty ofabout 0.5 magnitudes.

The atmospheric trajectory parameters of the a-Capricornidfireballs analyzed here are summarized in Table 2. Their SPMNcode was assigned after the corresponding recording date. Theirabsolute magnitude Mv ranges from �6.0 ± 0.5 to �10.0 ± 0.5. Thebeginning (Hb) and ending (He) heights of these events are alsoindicated. The final height reached by these events is higher than75 km above the ground level. The radiant and orbital data(J2000) obtained from the analysis of these bolides are summa-rized in Table 3.

3. Results

Events SPMN220711, SPMN250712, SPMN280712 andSPMN260713 were recorded from stations #1 and 2 in Table 1,and bolides SPMN180713 and 290713 were recorded from stations#1 and 5. Fireball SPMN270712 was imaged from stations #1 and3, and the first half of its atmospheric path was also imaged fromstation #4. All these observations were taken into account for dataanalysis. The light curves obtained from each recording station forthese fireballs are shown in Fig. 2. As can be noticed, the maximum

brightness of these bolides was reached during the second half oftheir atmospheric path. This is typical of meteor events producedby compact meteoroids (Murray et al., 1999; Campbell et al.,2000). In addition, these a-Capricornids exhibited a bright flareat the end of their atmospheric trajectory as a consequence ofthe sudden catastrophic disruption of the parent meteoroids. How-ever, the photometric behavior of events SMPN260713 andSPMN290713 is somewhat different, since these bolides exhibit aprevious flare which is brighter than the terminal one.

The emission spectra recorded for the fireballs analyzed hereprovide an insight into the chemical nature of the progenitor mete-oroids, but also about the parent body of the a-Capricornid mete-oroid stream. The spectrum of events SPMN220711, SPMN250712,SPMN280712 and SPMN260713 was recorded from station #2 inTable 1. For fireball SPMN270712 the spectrum was imaged fromstation #3, and for bolides SPMN180713 and SPMN290713 it wasrecorded by one spectrograph operating at station #5. The identi-fication of the chemical elements and multiplets producing themain emission lines in these video spectra was performed withthe CHIMET software (Madiedo et al., 2011b, 2013a). This applica-tion processes video sequences containing meteor spectra, so thateach frame is previously deinterlaced, dark-subtracted and flat-fielded. Then, the signal is calibrated in wavelength by identifyingtypical lines appearing in the spectrum and corrected by takinginto account the spectral efficiency of the recording device. Theresult can be seen in Fig. 3, where multiplet numbers are givenaccording to Moore (1945). Most lines correspond to Fe-I multi-plets that are widely distributed along the signal, which is typicalfor meteor spectra (see e.g. Trigo-Rodríguez et al., 2003). The linesfrom Ca I-2 (422.6 nm) and the H and K lines of ionized calcium (at396.8 and 393.3 nm, respectively) have been also identified,although these appear blended with several Fe I lines. As can benoticed, the contribution of the Mg I-2 triplet at 516 nm is moreimportant than that of the Na I-1 doublet at 588.9 nm, except forevents SPMN260713 and SPMN290713.

4. Discussion

4.1. Tensile strength and meteoroid mass

The aerodynamic strength S at which the break-up of the pro-genitor meteoroids took place can be calculated by means of theequation given by Bronshten (1981):

Fig. 2. Light curves (absolute magnitude vs. time) obtained from each recording station for the a-Capricornid bolides discussed in the text: (a) SPMN220711, (b)SPMN250712, (c) SPMN270712, (d) SPMN280712, (e) SPMN180713, (f) SMPN260713, (g) SPMN290713.

276 J.M. Madiedo et al. / Icarus 239 (2014) 273–280

S ¼ qatm � v2 ð1Þ

where v is the velocity of the meteoroid at the disruption point andqatm the atmospheric density at the height where the fracture took

place. This density can be calculated, for instance, by means of theUS standard atmosphere model (U.S. Standard Atmosphere, 1976).This aerodynamic strength can be used as an estimation of the ten-sile strength of the meteoroid (Trigo-Rodríguez and Llorca, 2006,

Fig. 3. Calibrated emission spectra recorded for the a-Capricornid fireballs analyzed here, where intensity is expressed in arbitrary units: (a) SPMN220711, (b) SPMN250712,(c) SPMN270712, (d) SPMN280712, (e) SPMN180713, (f) SMPN260713, (g) SPMN290713.

J.M. Madiedo et al. / Icarus 239 (2014) 273–280 277

Table 4Tensile strength estimated for the a-Capricornid fireballs exhibiting a final flare as aconsequence of the sudden disruption of the meteoroid.

SPMNcode

Height(km)

Velocity(km s�1)

Aerodynamic pressure(dyn cm�2)

220711 79.5 ± 0.5 25.0 ± 0.6 (1.0 ± 0.4) � 105

250712 84.6 ± 0.5 24.9 ± 0.6 (4.4 ± 0.4) � 104

270712 79.3 ± 0.5 23.8 ± 0.6 (1.0 ± 0.4) � 105

280712 80.1 ± 0.5 24.1 ± 0.6 (9.0 ± 0.4) � 104

180713 80.2 ± 0.5 24.0 ± 0.6 (8.9 ± 0.4) � 104

260713 82.6 ± 0.5 23.9 ± 0.6 (5.8 ± 0.4) � 104

290713 79.2 ± 0.5 23.7 ± 0.6 (1.0 ± 0.4) � 105

Table 5Preatmospheric photometric mass and diameter (by assuming a bulk density of2.1 g cm�3) for the meteoroids producing the a-Capricornid fireballs discussed in thetext, together with the estimated ejection velocity (Vej) of these particles from Comet169P/NEAR.

SPMN code Mass (g) Diameter (cm) Vej (m s�1)

220711 210 ± 20 5.7 ± 0.2 5.8 ± 0.1250712 10 ± 1 2.1 ± 0.1 9.5 ± 0.1270712 115 ± 11 4.7 ± 0.2 6.4 ± 0.1280712 25 ± 2 2.9 ± 0.1 8.1 ± 0.1180713 140 ± 15 5.0 ± 0.2 6.2 ± 0.1260713 190 ± 20 5.5 ± 0.2 5.9 ± 0.1290713 50 ± 6 3.5 ± 0.2 7.3 ± 0.1

Table 6Computed elemental abundances relative to Fe derived for the fireballs analyzed inthe text. The abundances inferred for other Solar System undifferentiated materialsare also indicated (Jessberger et al., 1988; Rietmeijer and Nuth, 2000; Rietmeijer,2002a).

Object Mg ± 0.08 Na ± 0.009 Ca ± 0.005 T (K)

SPMN220711 0.70 0.031 0.021 4000SPMN250712 2.63 0.039 0.005 3900SPMN270712 2.78 0.035 0.009 3900SPMN280712 2.20 0.029 0.009 3900SPMN180713 2.12 0.050 0.028 4000SPMN260713 2.29 0.030 0.010 3600SPMN290713 2.14 0.029 0.013 37001P/Halley 1.93 0.193 0.121 –IDPs 1.34 0.135 0.076 –CI chondrites 1.17 0.066 0.078 –CM chondrites 1.23 0.041 0.085 –

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2007). The values obtained for the fireballs analyzed in this workare summarized in Table 4, together with the corresponding heightsand velocities. According to this analysis, these meteoroids exhib-ited their brightest flare under an average dynamic pressure of(8.3 ± 0.4) � 104 dyn cm�2, which is in good agreement with thevalues obtained by Trigo-Rodríguez and Llorca (2006, 2007) forother relatively-low-strength meteoroids with a cometary origin(between (6.0 ± 0.3) � 104 to (9.0 ± 0.2) � 104 dyn cm�2).

The initial (photometric) mass mp of the parent meteoroids canbe estimated from the light curves shown in Fig. 2 by using thewell-known equation:

mp ¼ 2Z te

tb

Ip=ðsv2Þdt ð2Þ

Thus, we have computed the initial mass of the meteoroids asthe total mass lost during the ablation of these particles betweenthe beginning of the luminous phase and the terminal point ofthe atmospheric path. The integration limits, tb and te, are the timescorresponding to the beginning and the end of the luminous phase,respectively. Ip is the measured luminosity of the fireball, which isrelated to the absolute magnitude M by means of

M ¼ �2:5 logðIpÞ ð3Þ

For the estimation of the luminous efficiency (s), whichdepends on velocity, we have employed the equations given byCeplecha and McCrosky (1976). The calculated values of the initialphotometric mass and diameter for each fireball are listed inTable 5. These masses range from 210 ± 20 g for the mag. �10.0SPMN220711 event to 10 ± 1 g for the mag. �7.0 SPMN100712bolide. According to Babadzhanov and Kokhirova (2009), the bulkdensity of a-Capricornid meteoroids is 2.1 g cm�3. So, if we assumespherical shapes, the diameter of the particles producing the fire-balls listed in Table 2 ranged from 5.7 ± 0.2 to 2.9 ± 0.1 cm (Table 5).Although even meter-sized meteoroids with a cometary origin arecompletely destroyed at high altitude in the atmosphere (Madiedoet al., 2014), meteoroids within this mass range may pose animportant threat for artificial satellites. Jenniskens andVaubaillon (2010) proposed a dramatic increase in the ZHR of thisshower during the 23rd and 24th centuries from the current valueof about 10 h�1 to a peak of around 2200 h�1. Thus, if this is accom-panied by an important increment in the number of cm-sized a-Capricornid meteoroids reaching the Earth, this would alsoincrease dramatically the potential danger for artificial satellites.

According to Jenniskens and Vaubaillon (2010), most of themass in the a-Capricornid meteoroid stream came from a massivebreakup of the parent body instead of being produced by normalcomet activity from water vapor drag (Whipple, 1951). However,by assuming a dynamical age for this stream of about 5000 yr,Kasuga et al. (2010) showed that the a-Capricornid stream is theproduct of steady disintegration of the parent comet at everyreturn. In fact, the meteoroids that produced the fireballs studiedhere could be produced by the disruption of the parent body, buttheir origin is also compatible with the scenario proposed byKasuga et al. (2010). Thus, we have calculated the ejection velocity(Vej) of these meteoroids from the nucleus of Comet 169P/NEATduring the perihelion passage by using the equation proposed byJones (1995):

Vejðm s�1Þ ¼ 20:3 � R1=2c �m�1=6 � q�1=3 � r�1:038 ð4Þ

Here Rc is the radius of the cometary nucleus in km and r its helio-centric distance at perihelion, expressed in AU. The density q andthe mass m of the meteoroids are given, respectively, in km m�3

and kg. For this calculation we have considered an average valuer = 0.6 AU.

The effective radius of the nucleus (Rc) was found to be of about2.3 km (Kasuga et al., 2010). The resulting ejection velocitiesobtained for each meteoroid are listed in Table 5. These velocitieswere compared with the escape velocity Vesc from the nucleus ofComet 169P, which is given by the well-known formula

Vesc ¼

ffiffiffiffiffiffiffiffiffiffiffiffiffi2GMc

Rc

sð5Þ

The mass of the comet Mc was considered be of about 9.7 � 1013 kg(Jenniskens and Vaubaillon, 2010). According to this, the escapevelocity yields Vesc = 2.4 m s�1. So, since the calculated velocitiesshown in Table 5 are higher than this value, these meteoroids couldhave been released from their parent comet by vapor drag.

4.2. Emission spectra

It is worth mention that no early release of Na or any otherpeculiarities were found in the emission spectra imaged for thesefireballs. The early release of Na has been reported, for example,in some Leonid meteors (Borovicka et al., 1999), a behavior that

J.M. Madiedo et al. / Icarus 239 (2014) 273–280 279

has been related, for instance, to Na being present in a moderatelyvolatile host phase (Rietmeijer, 2002b).

From these spectra we can obtain an insight into the chemicalnature of the parent meteoroids. We have employed a model toestimate from these spectra the averaged temperature of themeteor plasma and the relative abundances with respect to Fefor Na, Mg and Ca. For this purpose we have followed the techniquedescribed in Borovicka (1993). The results are listed in Table 6. Wehave expressed the abundances with respect to Fe. These showthat, although the Na abundances fit relatively well the expectedvalues for chondritic materials, these meteoroids are not chon-dritic. Specifically, except for SPMN220711, these meteoroids areMg-rich, with elemental abundances for this element higher by afactor of about 2–3 with respect to the chondritic value. This isin agreement with the result obtained from the a-Capricornidspectrum analyzed by Borovicka and Weber (1996). One possibilityfor this Mg enrichment may be caused by a high content in the par-ent comet (and so also in a-Capricornid meteoroids) of forsteriticolivine and Mg-rich pyroxene, as has also been reported for cometHale Bopp (Wooden et al., 1999) and were found in Comet 81P/Comet Wild 2 (Zolensky et al., 2008). Primitive carbonaceous chon-drite components and silicate vapor condensation experimentssuggest that Mg-rich components are characteristic of primitiveamorphous condensates. For example, Rietmeijer (2002a) con-cluded that the condensed amorphous dust was Mg-rich. Ourobservations are showing Mg abundances higher than identifiedin IDPs (except for SPMN220711). However, the differences foundfor the Mg abundance for event SPMN220711 also reveal a diver-sity in the composition of particles within the a-Capricornidstream. This, in turn, would imply inhomogeneities in the compo-sition of the parent comet at the cm-level. On the other hand, thederived Ca abundances are clearly lower than expected for chon-dritic materials, but this can be explained on the basis of the incom-plete evaporation of this element during ablation (Trigo-Rodríguezet al., 2003, 2004).

5. Conclusions

We have analyzed seven a-Capricornid bolides with absolutemagnitudes ranging from �6.0 to �10.0. From this we haveextracted the following conclusions:

(1) These bolides did not penetrate the atmosphere below75 km above the ground level. The tensile strengths of theprogenitor meteoroids were found to be typical for other rel-atively-low-strength meteoroids with a cometary origin.

(2) The preatmospheric mass of the meteoroids producing theseevents ranged from 210 ± 20 to 10 ± 1 g. These cm-sized par-ticles may imply a threat for artificial satellites, although thecurrent impact rate of these meteoroids is low.

(3) Although according to previous studies a massive disruptionof the parent body could explain the origin of these largemeteoroids, the alternative scenario in which these cm-sizedparticles were released by vapor drag during perihelion pas-sage of the progenitor comet cannot be discarded.

(4) The emission spectra obtained for these events indicate thatthe progenitor meteoroids are Fe-poor with respect to thechondritic value. In addition, six of these particles exhibitedan overabundance of Mg by a factor of about 2–3 withrespect to the expected value for chondritic materials. Thiscould be associated to a likely high content of forsteritic oliv-ine and Mg-rich pyroxene in Comet 169P/NEAT, as has alsobeen reported for comet Hale Bopp. Nevertheless, the exis-tence of a population of a-Capricornid meteoroids with amuch lower Mg-content in our sample reveals inhomogene-ities in the parent comet at the cm-scale.

Acknowledgments

The meteor stations involved in this research have been fundedby the first author. We also acknowledge support from the SpanishMinistry of Science and Innovation (Projects AYA2009-13227 andAYA2011-26522). We thank the AstroHita Foundation for its contin-uous support in the operation of the meteor observing stationlocated at La Hita Astronomical Observatory.

References

Babadzhanov, P.B., Kokhirova, G.I., 2009. Densities and porosities of meteoroids.Astron. Astrophys. 495, 353–358.

Borovicka, J., 1993. A fireball spectrum analysis. Astron. Astrophys. 279, 627–645.Borovicka, J., Weber, M., 1996. An alpha-Capricornid meteor spectrum. J. Int. Meteor

Org. 24, 30–32.Borovicka, J., Štork, R., Bocek, J., 1999. First results from video spectroscopy of 1998

Leonid meteors. Meteorit. Planet. Sci. 34, 987–994.Bronshten, V.A., 1981. The Physics of Meteoritic Phenomena. Geophysics and

Astrophysics Monographs, Reidel, Dordrecht.Campbell, M.D. et al., 2000. Image-intensified video results from the 1998 Leonid

shower: I. Atmospheric trajectories and physical structure. Meteorit. Planet. Sci.35, 1259–1267.

Ceplecha, Z., 1987. Geometric, dynamic, orbital and photometric data onmeteoroids from photographic fireball networks. Bull. Astron. Inst. Czech. 38,222–234.

Ceplecha, Z., McCrosky, R.E., 1976. Fireball end heights – A diagnostic for thestructure of meteoric material. J. Geophys. Res. 81, 6257–6275.

Jenniskens, P., 2006. Meteor Showers and their Parent Comets. CambridgeUniversity Press.

Jenniskens, P., Vaubaillon, J., 2010. Minor planet 2002 EX12 (=169P/NEAT) and theAlpha Capricornid shower. Astron. J. 139, 1822–1830.

Jessberger, E.K., Christoforidis, A., Kissel, J., 1988. Aspects of the major elementcomposition of Halley’s dust. Nature 332, 691–695.

Jones, J., 1995. The ejection of meteoroids from comets. Mon. Not. R. Astron. Soc.275, 773–780.

Kasuga, T., Balam, D.D., Wiegert, P.A., 2010. Comet 169P/NEAT(=2002 EX12): Theparent body of the a-Capricornid meteoroid stream. Astron. J. 140, 1806–1813.

Lodders, K., 2003. Solar System abundances and condensation temperatures of theelements. Astrophys. J. 591, 1220–1247.

Madiedo, J.M., Trigo-Rodríguez, J.M., 2008. Multi-station video orbits of minormeteor showers. Earth, Moon, Planets 102, 133–139.

Madiedo, J.M., Trigo-Rodríguez, J.M., Ortiz, J.L., Morales, N., 2010. Robotic systemsfor meteor observing and Moon impact flashes detection in Spain. Adv. Astron.2010, 1–5.

Madiedo, J.M., Trigo-Rodríguez, J.M., Lyytinen, E., 2011a. Data Reduction andControl Software for Meteor Observing Stations Based on CCD Video Systems.NASA/CP-2011-216469, p. 330.

Madiedo, J.M., Toscano, F.M., Trigo-Rodríguez, J.M., 2011b. Software tools for theanalysis of video meteors emission spectra. EPSC-DPS Joint Meeting 2011.Abstract #Vol. 6, EPSC-DPS2011-72.

Madiedo, J.M. et al., 2013a. The 2011 October Draconids outburst – II. Meteoroidchemical abundances from fireball spectroscopy. Mon. Not. R. Astron. Soc. 433,571–580.

Madiedo, J.M., Trigo-Rodríguez, J.M., Williams, I.P., Ortiz, J.L., Cabrera, J., 2013b. TheNorthern v-Orionid meteoroid stream and possible association with thepotentially hazardous Asteroid 2008XM1. Mon. Not. R. Astron. Soc. 431,2464–2470.

Madiedo, J.M. et al., 2013c. On the activity of the c-Ursae Minorids meteoroidstream in 2010 and 2011. Mon. Not. R. Astron. Soc. 431, 1678–1685.

Madiedo, J.M., Ortiz, J.L., Trigo-Rodríguez, J.M., et al., 2014. Icarus 233, 27–35.Moore, C.E., 1945. In: A Multiplet Table of Astrophysical Interest. Princeton

University Observatory, Princeton, NJ. Contribution No. 20.Murray, I.S., Hawkes, R.L., Jenniskens, P., 1999. Airborne intensified charge-coupled

device observations of the 1998 Leonid shower. Meteorit. Planet. Sci. 34, 949–958.

Rietmeijer, F., 2002a. The earliest chemical dust evolution in the solar nebula. Chem.Erde 62, 1–45.

Rietmeijer, F., 2002b. Shower meteoroids: Constraints from interplanetary dustparticles and Leonid meteors. Earth, Moon, Planets 88, 35–58.

Rietmeijer, F., Nuth, J.A., 2000. Collected extraterrestrial materials: Constraints onmeteor and fireball compositions. Earth, Moon, Planets 82 (83), 325–350.

Trigo-Rodríguez, J.M., Llorca, J., 2006. The strength of cometary meteoroids: Clues tothe structure and evolution of comets. Mon. Not. R. Astron. Soc. 372, 655–660.

Trigo-Rodríguez, J.M., Llorca, J., 2007. Erratum: The strength of cometarymeteoroids: Clues to the structure and evolution of comets. Mon. Not. R.Astron. Soc. 375, 415.

Trigo-Rodríguez, J.M., Llorca, J., Borovicka, J., Fabregat, J., 2003. Chemicalabundances determined from meteor spectra: I. Ratios of the main chemicalelements. Meteorit. Planet. Sci. 38, 1283–1294.

Trigo-Rodríguez, J.M., Llorca, J., Borovicka, J., Fabregat, J., 2004. Spectroscopy of aGeminid Fireball: Its similarity to cometary meteoroids and the nature of itsparent body. Earth, Moon, Planets 95, 375–387.

280 J.M. Madiedo et al. / Icarus 239 (2014) 273–280

Trigo-Rodríguez, J.M. et al., 2007a. Spanish meteor network: 2006 continuousmonitoring results. WGN 35, 13–22.

Trigo-Rodríguez, J.M. et al., 2007b. Asteroid 2002NY40 as a source of meteorite-dropping bolides. Mon. Not. R. Astron. Soc. 382, 1933–1939.

Trigo-Rodríguez, J.M. et al., 2009. Observations of a very bright fireball and its likelylink with Comet C/1919 Q2 Metcalf. Mon. Not. R. Astron. Soc. 394, 569–576.

U.S. Standard Atmosphere, 1976. NOA-NASA-USAF, Washington.

Whipple, F.L., 1951. A comet model. II. Physical relations for comets and meteors.Astrophys. J. 113, 464.

Wooden, D.H. et al., 1999. Silicate mineralogy of the dust in the inner coma ofComet C/1995 01 (Hale–Bopp) pre- and postperihelion. Astrophys. J. 517, 1034–1058.

Zolensky, M. et al., 2008. Comparing Wild 2 particles to chondrites and IDPs.Meteorit. Planet. Sci. 43, 261–272.