- Email: [email protected]
1854 L1 (Klinkerfues) and the ε-Eridanids
Advances in Space Research 39 (2007) 612–615 www.elsevier.com/locate/asr
Dust trail evolution applied to long-period comet C/1854 L1 (Klinkerfues) and the e-Eridanids Jeremie Vaubaillon a
a,*
, Peter Jenniskens
b
Institut de Me´canique Ce´leste et de Calcul des E´phe´me´rides, 75014 Paris, France b The SETI Institute, 515 N. Whisman Rd., Mountain View, CA 94043, USA
Received 24 June 2005; received in revised form 1 November 2005; accepted 14 November 2005
Abstract In recent years, meteor outbursts and storms have greatly increased the likelihood of detection for meteor spectrographs with a small field of view. The successful prediction of the Leonid storms has made the deployment of new spectrographic techniques possible. Here, we apply a prediction model developed for the Leonid storms to the evolution of dust ejected from comet C/1854 L1 (Klinkerfues) in an effort to determine whether the 1981 outburst of e-Eridanids may have been caused by this comet, and if so to predict future returns. We also investigated the possible link to comet C/962 B2. We find that the 1981 outburst may be explained as a Filament component (10–100 year old dust trails) from comet C/1854 L1, if that comet has an orbital period P 127 years. 2007 Published by Elsevier Ltd on behalf of COSPAR. Keywords: Meteor; Comet; Klinkerfues; Celestial mechanics
1. Introduction In 1981, observer Murray Gayski of the Western Australian Meteor Society reported high activity from the constellation of Eridanus in the night of September 10/11 (Fig. 1). Wood (1981) writes about GayskiÕs observation: Into his third hour which began at 14:00 UT, he started noticing fast bright trained yellow-orange meteors streaking out of Eridanus, which at this time was low on the eastern horizon. There was a near-full Moon. The meteors had an average magnitude of +1.2 (r = 2.0) were mostly yellow or orange in color, and 44% left a brief train. Three 1-h counts were reported starting at 14:00 UT (September 10): 3, 11 and 34 meteors, with no meteors seen in the 3 h prior when the radiant was below the horizon. * Corresponding author. Present address: Department of Physics and Astronomy, University of Western Ontario, London, Ont., Canada N6A 3K7. E-mail address: [email protected] (J. Vaubaillon).
0273-1177/$30 2007 Published by Elsevier Ltd on behalf of COSPAR. doi:10.1016/j.asr.2005.11.001
Wood (1981) associated the event with long-period or Halley-type comet C/1854 L1 (Klinkerfues), comet 1854 III, not to be confused with comet C/1853 L1 (1853 III) Klinkerfues. The theoretical radiant is at RA = 54, Dec. = 16 on September 10, for a relative velocity of 39.2 km/s. During the return in 1854, it just barely reached naked eye brightness. The comet was intrinsically bright, with H10 = +6.0 (D 4.8 km), making this a good candidate for a meteor shower parent. However, the miss distance is a large +0.011 AU. Moreover, the outburst occurred a day before passing the comet node, more than the usual discrepancy for the 1-revolution dust trails of long-period comets (Lyytinen and Jenniskens, 2003). The outburst was also not as sharp as that expected for a 1-revolution old long-period comet dust trail, lasting for several hours at least. Finally, there is an annual shower active from a radiant near the star e-Eridanus, referred to as the p-Eridanids to discriminate from the e-Eridanid outburst. Rates are about ZHR = 1.5/h at ko = 167 (Jenniskens, 1994). It is possible that some p-Eridanids are sporadic apex shower meteors, but if not, then there is a dense stream just outside Earth orbit.
J. Vaubaillon, P. Jenniskens / Advances in Space Research 39 (2007) 612–615
Fig. 1. The e-Eridanid outburst as reported by Murray Gayski. The stream profile may have been as broad as suggested by the dashed line, or as narrow as indicated by the gray area.
All these observations suggest to us that the parent comet is of Halley-type, rather than a long-period comet. Comet C/1854 L1 Klinkerfues (1854 III) is one of those long-period comets not well enough observed to reveal whether they are of Halley-type or long-period. Observations in 1854 only span a period of two months in June and July, when the comet was near perihelion. An orbit was calculated by Winnecke and Page (1856) who found no significant deviation from a parabolic orbit over the period that the comet was observed: Die Bahn la¨sst nicht die geringste Abweichung von der Parabel mit Sicherheit erkennen, wodurch die Anfangs vermuthete Identita¨t dieses Cometen mit dem von 960 umgestossen wird, ein Resultat, zu dem shon fru¨her Oudemans durch Betrachtungen anderer Art ebenfalls gelangt ist. Winnecke and Pape therefore dismissed the possible identity of comet C/962 B1 as the same object, following an opinion expressed by Jean Abraham Chretien Oudemans at Leiden Observatory (without providing a reference). Here, we studied the dust generated by comet Klinkerfues and its subsequent planetary perturbations to reveal if the 1981 e-Eridanid outburst could have had its source at this comet, whether this comet is of Halley-type or a long-period comet, and how the event may be related to comet C/962 B2. 2. Methodology The model used here is the one developed by Vaubaillon et al. (2005). It is based on the dirty snowball model of a comet (Whipple, 1950). Meteoroid streams are created by the ejection of the particles by water vapor drag from the sunlit hemisphere of the cometary nucleus. The ejection velocity is computed from the model developed by Crifo and Rodionov (1997), as soon as the nucleus reaches a heliocentric distance rh less than 3 AU (q < rh < 3 AU). It depends on the size of the meteoroids, the angle of ejection
613
from the sub-solar point and the physical parameters of the cometary nucleus. These parameters were arbitrary set, since there is obviously no available observation to exploit. The radius of the body is chosen as 1 km, for a Bond Albedo of 0.04, and a fraction of active area of 0.3 (typical values for an average comet of this kind). Once released, the meteoroids endure the gravitation of the Sun and the nine planets, as well as the Moon. In addition, non-gravitational forces are taken into account (radiation pressure and Poynting-Robertson effect). This model is applied in a massive numerical simulation, involving 5 size bins of meteoroids. The radii considered here are in the size bins: [0.1;0.5], [0.5;1], [1;5], [5;10] and [10;100] mm, for a density of 1000 kg/m3. Ten thousand (104) particles were simulated per size bin, for a total of 5 · 104 particles per perihelion passage. Trying several solutions of the orbital elements of the comet, the total number of simulated particle is 7.5 · 105 particles. The program was run on 5–50 parallel processors of an IBM SP3 located at CINES (France). In order to know the timing of a possible meteor shower, the nodes of the particles were saved, but only if they are close enough to the Earth. Even with such an amount of particles, it is very unlikely that any simulated meteoroid would hit the Earth itself. Therefore, we have to set a space criterion to select the particles in a region much larger than the path of the planet. This criterion is usually a function of the relative velocity of the comet and the Earth (see Vaubaillon et al., 2005 for further details). As this quantity is unknown, we choose a space criterion (diameter of the spatial region in the ecliptic plane) of 0.46 AU, corresponding to a hypothetical relative velocity of 40 km/s, and a time criterion (length of the spatial region along the dust trail) of 20 days. These are considered particles passing in the vicinity of the Earth. A further analysis of the node of these individual meteoroids examines how close they really are, and whether to consider them as impacting the planet or not. This also allows us to have a look at the influence of the selection criterion. Results show that these criteria are not critical, because of the stability and inclination of the orbit. The position and velocity of the meteoroids were regularly saved in order to understand the behavior of the stream. 3. Results First, we confirmed that the observations in 1854 permit an elliptic orbit for this comet. The comet was observed near perihelion only, and over too short an arc to make a significant distinction between parabolic and elliptic orbits of Halley-type with period P 100–250 years. Next, we considered the possibility that C/962 B1 could be the same object. From the two descriptions in the Chinese chronicles, comet C/962 B1 was estimated to be similarly intrinsically bright, with an uncertain H10 +2.5 (Vsekhsvyatskij, 1964). Matching a different number of orbits between 962 and 1854, solutions with N = 4–9 would make this a Halley-type comet with few recent returns. We discovered that N = 7 (or P 127
614
J. Vaubaillon, P. Jenniskens / Advances in Space Research 39 (2007) 612–615
years) would have had the comet come back in 1981, when Gayski observed the outburst. Halley-type comets such as 55P/Tempel-Tuttle and 109P/Swift-Tuttle are known to have most intense shower activity in the years when the comet is near perihelion, because the dust does not disperse as rapidly along the comet orbit as with long-period comets (from large range in orbital periods) or Jupiter-family comets (from large perturbations by Jupiter). We then integrated back the orbit of Klinkerfues until 961 AD, by permitting a range of initial velocities at perihelion, to find the orbit with close to matching perihelion time (Fig. 1). The resulting orbit is: C/1854 L1 C/962 B2
T
a (AU)
q
i(, J2000)
x
Node
961 Dec. 27.0 (UT) 961 Dec. 28.0 (UT)
23.258 Inf.
0.6659 0.63
108.569 119
75.631 85
349.394 362
The inclination is the most significant discrepancy between the calculated orbit of C/1854 L1 in 962 AD and the orbit derived from observations (Hasegawa, 1979; Kronk, 1999). It is significant that the inclination does not change much from planetary perturbations over time. When plotting the calculated positions of the comet in 961 AD, it appears higher in the sky (by 10 to 20) than was reported by the three accounts from China. No close encounters with planets occurred that could account for the difference. Oudemans may have been right, and the association of Klinkerfues and C/962 B2 remains uncertain. Starting with the position of comet Klinkerfues in 1854, we integrated a series of comet orbit solutions, for a range of semi-major axis close to a = 25 AU, backward in time. The planetary perturbations on these orbits, results in surprisingly modulated dispersion of solutions and would mimick the shape of a dust trail for large grains with no significant radiation pressure. The distribution of orbital elements remains in a narrow range of elements (Fig. 2) and the spatial distribution remains much confined (Fig. 3). The large-scale loops are due to the perturbations of Jupiter, while the small excursions are due to encounters with the Earth. Only after 7 orbits does the distribution become more dispersed to form a filament, much as observed for the dust ejected from 55P/Tempel-Tuttle with shorter semi-major axis a 10 AU. Based on a study of the Monocerotids, our earlier assumption that many of the large grains would have been
Fig. 3. One-revolution dust trail of a long-period comet back at aphelion (no radiation pressure). Case of an a = 50 AU comet in the orbit of C/ 1854 L1 (Klinkerfues).
Fig. 4. The spatial distribution of dust after 1.5 revolutions for an initial a = 68 AU comet orbit solution, for a range of radiation pressures.
ejected in hyperbolic orbits because of radiation pressure (Jenniskens et al., 1997) does not pan out by the models. Instead, most larger meteoroids responsible for visible meteors are ejected in bound orbits. Fig. 4 shows the a = 68 AU trail 1.5 orbits after ejection in 1030 AD.
Fig. 2. The distribution of orbital elements semi-major axis (a, in AU) and eccentricity (e) for different solutions of the orbit of comet C/1854 L1 integrated backward in time, centered the orbit of C/1854 L1 during the 1854 return for different values of the semi-major axis.
J. Vaubaillon, P. Jenniskens / Advances in Space Research 39 (2007) 612–615
615
with the program created by Neslusan et al. (1998) and for a semi-major axis a 25 AU, is at RA = 64.2, Dec. = 6.6, but considerably less certain given the orbit and therefore perhaps consistent with the observed value. However, in that case the comet has not been seen since 962 AD, which means that it is either in a long-period orbit or intrinsically faint. Both conditions argue against an association with the broad 1981 e-Eridanid outburst. The next outburst of this shower is expected only around the time of the next return of comet C/1854 L1 to perihelion, which is about 127 years after AD 1981, in about AD 2108. Acknowledgements Fig. 5. Particles are close to the orbit of the Earth but do not cross it. The same situation is found in the late 70Õs until the late 90Õs.
This means that the peculiar magnitude distribution (with a high-mass cut-off) measured for the a-monocerotids dust trail by Jenniskens et al. (1997) is not due to large grains being lost during ejection, but must come on account of the larger grains not being able to disperse far enough along the comet dust trail all the way out to where Earth encounters the meteoroids. If so, this implies that the meteoroid distribution can determine where the parent comet is in its orbit. Until now, the parent of the a-monocerotid shower has not been discovered. We subsequently investigated the possibility that dust ejected by comet 1854 L1 in a prior return could have caused the 1981 outburst. We find that the meteoroid orbits evolved from ejection during the 1854 return have nodes in the next return in 1981 that are systematically outside of Earth orbit with a closest encounter 1.4 days after the observed peak, at September 12.1 UT instead of September 10.68 UT (Fig. 5). We conclude that the 1981 outburst was not caused by a recent dust trail crossing. This, in fact, is consistent with the relatively long duration of the shower. Due to the high inclination, Earth would have crossed a recent dust trail in less than an hour. That leaves open the possibility that the 1981 outburst was similar to the Leonid fireball shower of 1998, the Filament component of 10–100 orbits old ejecta (Asher et al., 1999; Jenniskens and Betlem, 2000). In the case of 55P/Tempel-Tuttle, the 1998 Fireball shower peaked 0.75 days before the younger dust trails were encountered. This situation is similar. The type of dispersion found in the Filament component is generated only after more than 10 revolutions in the case of C/1854 L1. Even after 7 revolutions, only some parts of the dust trail start to catch up on each other (Fig. 3). It is not so likely that the 1981 meteors derived from comet C/962 B2, if in a manner unrelated to comet C/ 1854 L1. The theoretical radiant of C/962 B2 computed
The Leonid Multi-Instrument Aircraft Campaign was supported by NASAÕs Astrobiology and Planetary Astronomy Programs and by the US Air Force. We thank CINES (Montpellier, France) for their support in parallel computation and L. Neslusan for providing his program. J.V. acknowledges support for this work from NASAÕs Planetary Astronomy program and the hospitality of the SETI Institute while working on this project. References Asher, D.J., Bailey, M.E., EmelÕyanenko, V.V. Resonant meteoroids from comet Tempel-Tuttle in 1933: the cause of the unexpected Leonid outburst in 1998. MNRAS 304, L53–L56, 1999. Crifo, J.F., Rodionov, A.V. The dependence of the circumnuclear coma structure on the properties of the nucleus. Icarus 127, 319–353, 1997. Jenniskens, P. Meteor stream activity I. The annual streams. Astron. Astrophys. 287, 990–1013, 1994. Jenniskens, P., Betlem, H., de Lignie, M., Langbroek, M. The detection of a dust trail in the orbit of an Earth-threatening long-period comet. Astrophys. J. 479, 441–447, 1997. Jenniskens, P., Betlem, H. Massive remnant of evolved cometary dust trail detected in the orbit of Halley-type comet 55P/Tempel-Tuttle. Astrophys. J. 531, 1161–1167, 2000. Hasegawa, I. Orbits of ancient and medieval comets. PASJ 31, 257–270, 1979. Kronk, G.W. Cometography, A Catlog of Comets. Vol. 1: Ancient – 1799. Cambridge University Press, London, 1999, pp. 157–159. Lyytinen, E., Jenniskens, P. Meteor outbursts from long-period comet dust trails. Icarus 162, 443–452, 2003. Neslusan, L., Svoren, J., Porubcan, V. A computer program for calculation of a theoretical meteor-stream radiant. Astron. Astrophys. 331, 411–413, 1998. Vsekhsvyatskij, S.K. Physical Characteristics of Comets. Jerusalem: Israel Program for Scientific Translations, 49, 1964. Vaubaillon, J., Colas, F., Jorda, L. A new method to predict meteor showers. I. Description of the model. Astron. Astrophys. 439, 751–760, 2005. Whipple, F. A comet model. I. The acceleration of Comet Encke. Astrophys. J. 111, 375–394, 1950. Winnecke, A., Page, C.F. Bahnbestimmung des Cometen 1854 III, von Herren Winnecke und Pape. Astron. Nachrichten 42, 113, 1856. Wood, J. The epsilon Eridanid meteor stream. W.A.M.S. Bull., 167, 1981.
Dust trail evolution applied to long-period comet C/1854 L1 (Klinkerfues) and the e-Eridanids Jeremie Vaubaillon a
a,*
, Peter Jenniskens
b
Institut de Me´canique Ce´leste et de Calcul des E´phe´me´rides, 75014 Paris, France b The SETI Institute, 515 N. Whisman Rd., Mountain View, CA 94043, USA
Received 24 June 2005; received in revised form 1 November 2005; accepted 14 November 2005
Abstract In recent years, meteor outbursts and storms have greatly increased the likelihood of detection for meteor spectrographs with a small field of view. The successful prediction of the Leonid storms has made the deployment of new spectrographic techniques possible. Here, we apply a prediction model developed for the Leonid storms to the evolution of dust ejected from comet C/1854 L1 (Klinkerfues) in an effort to determine whether the 1981 outburst of e-Eridanids may have been caused by this comet, and if so to predict future returns. We also investigated the possible link to comet C/962 B2. We find that the 1981 outburst may be explained as a Filament component (10–100 year old dust trails) from comet C/1854 L1, if that comet has an orbital period P 127 years. 2007 Published by Elsevier Ltd on behalf of COSPAR. Keywords: Meteor; Comet; Klinkerfues; Celestial mechanics
1. Introduction In 1981, observer Murray Gayski of the Western Australian Meteor Society reported high activity from the constellation of Eridanus in the night of September 10/11 (Fig. 1). Wood (1981) writes about GayskiÕs observation: Into his third hour which began at 14:00 UT, he started noticing fast bright trained yellow-orange meteors streaking out of Eridanus, which at this time was low on the eastern horizon. There was a near-full Moon. The meteors had an average magnitude of +1.2 (r = 2.0) were mostly yellow or orange in color, and 44% left a brief train. Three 1-h counts were reported starting at 14:00 UT (September 10): 3, 11 and 34 meteors, with no meteors seen in the 3 h prior when the radiant was below the horizon. * Corresponding author. Present address: Department of Physics and Astronomy, University of Western Ontario, London, Ont., Canada N6A 3K7. E-mail address: [email protected] (J. Vaubaillon).
0273-1177/$30 2007 Published by Elsevier Ltd on behalf of COSPAR. doi:10.1016/j.asr.2005.11.001
Wood (1981) associated the event with long-period or Halley-type comet C/1854 L1 (Klinkerfues), comet 1854 III, not to be confused with comet C/1853 L1 (1853 III) Klinkerfues. The theoretical radiant is at RA = 54, Dec. = 16 on September 10, for a relative velocity of 39.2 km/s. During the return in 1854, it just barely reached naked eye brightness. The comet was intrinsically bright, with H10 = +6.0 (D 4.8 km), making this a good candidate for a meteor shower parent. However, the miss distance is a large +0.011 AU. Moreover, the outburst occurred a day before passing the comet node, more than the usual discrepancy for the 1-revolution dust trails of long-period comets (Lyytinen and Jenniskens, 2003). The outburst was also not as sharp as that expected for a 1-revolution old long-period comet dust trail, lasting for several hours at least. Finally, there is an annual shower active from a radiant near the star e-Eridanus, referred to as the p-Eridanids to discriminate from the e-Eridanid outburst. Rates are about ZHR = 1.5/h at ko = 167 (Jenniskens, 1994). It is possible that some p-Eridanids are sporadic apex shower meteors, but if not, then there is a dense stream just outside Earth orbit.
J. Vaubaillon, P. Jenniskens / Advances in Space Research 39 (2007) 612–615
Fig. 1. The e-Eridanid outburst as reported by Murray Gayski. The stream profile may have been as broad as suggested by the dashed line, or as narrow as indicated by the gray area.
All these observations suggest to us that the parent comet is of Halley-type, rather than a long-period comet. Comet C/1854 L1 Klinkerfues (1854 III) is one of those long-period comets not well enough observed to reveal whether they are of Halley-type or long-period. Observations in 1854 only span a period of two months in June and July, when the comet was near perihelion. An orbit was calculated by Winnecke and Page (1856) who found no significant deviation from a parabolic orbit over the period that the comet was observed: Die Bahn la¨sst nicht die geringste Abweichung von der Parabel mit Sicherheit erkennen, wodurch die Anfangs vermuthete Identita¨t dieses Cometen mit dem von 960 umgestossen wird, ein Resultat, zu dem shon fru¨her Oudemans durch Betrachtungen anderer Art ebenfalls gelangt ist. Winnecke and Pape therefore dismissed the possible identity of comet C/962 B1 as the same object, following an opinion expressed by Jean Abraham Chretien Oudemans at Leiden Observatory (without providing a reference). Here, we studied the dust generated by comet Klinkerfues and its subsequent planetary perturbations to reveal if the 1981 e-Eridanid outburst could have had its source at this comet, whether this comet is of Halley-type or a long-period comet, and how the event may be related to comet C/962 B2. 2. Methodology The model used here is the one developed by Vaubaillon et al. (2005). It is based on the dirty snowball model of a comet (Whipple, 1950). Meteoroid streams are created by the ejection of the particles by water vapor drag from the sunlit hemisphere of the cometary nucleus. The ejection velocity is computed from the model developed by Crifo and Rodionov (1997), as soon as the nucleus reaches a heliocentric distance rh less than 3 AU (q < rh < 3 AU). It depends on the size of the meteoroids, the angle of ejection
613
from the sub-solar point and the physical parameters of the cometary nucleus. These parameters were arbitrary set, since there is obviously no available observation to exploit. The radius of the body is chosen as 1 km, for a Bond Albedo of 0.04, and a fraction of active area of 0.3 (typical values for an average comet of this kind). Once released, the meteoroids endure the gravitation of the Sun and the nine planets, as well as the Moon. In addition, non-gravitational forces are taken into account (radiation pressure and Poynting-Robertson effect). This model is applied in a massive numerical simulation, involving 5 size bins of meteoroids. The radii considered here are in the size bins: [0.1;0.5], [0.5;1], [1;5], [5;10] and [10;100] mm, for a density of 1000 kg/m3. Ten thousand (104) particles were simulated per size bin, for a total of 5 · 104 particles per perihelion passage. Trying several solutions of the orbital elements of the comet, the total number of simulated particle is 7.5 · 105 particles. The program was run on 5–50 parallel processors of an IBM SP3 located at CINES (France). In order to know the timing of a possible meteor shower, the nodes of the particles were saved, but only if they are close enough to the Earth. Even with such an amount of particles, it is very unlikely that any simulated meteoroid would hit the Earth itself. Therefore, we have to set a space criterion to select the particles in a region much larger than the path of the planet. This criterion is usually a function of the relative velocity of the comet and the Earth (see Vaubaillon et al., 2005 for further details). As this quantity is unknown, we choose a space criterion (diameter of the spatial region in the ecliptic plane) of 0.46 AU, corresponding to a hypothetical relative velocity of 40 km/s, and a time criterion (length of the spatial region along the dust trail) of 20 days. These are considered particles passing in the vicinity of the Earth. A further analysis of the node of these individual meteoroids examines how close they really are, and whether to consider them as impacting the planet or not. This also allows us to have a look at the influence of the selection criterion. Results show that these criteria are not critical, because of the stability and inclination of the orbit. The position and velocity of the meteoroids were regularly saved in order to understand the behavior of the stream. 3. Results First, we confirmed that the observations in 1854 permit an elliptic orbit for this comet. The comet was observed near perihelion only, and over too short an arc to make a significant distinction between parabolic and elliptic orbits of Halley-type with period P 100–250 years. Next, we considered the possibility that C/962 B1 could be the same object. From the two descriptions in the Chinese chronicles, comet C/962 B1 was estimated to be similarly intrinsically bright, with an uncertain H10 +2.5 (Vsekhsvyatskij, 1964). Matching a different number of orbits between 962 and 1854, solutions with N = 4–9 would make this a Halley-type comet with few recent returns. We discovered that N = 7 (or P 127
614
J. Vaubaillon, P. Jenniskens / Advances in Space Research 39 (2007) 612–615
years) would have had the comet come back in 1981, when Gayski observed the outburst. Halley-type comets such as 55P/Tempel-Tuttle and 109P/Swift-Tuttle are known to have most intense shower activity in the years when the comet is near perihelion, because the dust does not disperse as rapidly along the comet orbit as with long-period comets (from large range in orbital periods) or Jupiter-family comets (from large perturbations by Jupiter). We then integrated back the orbit of Klinkerfues until 961 AD, by permitting a range of initial velocities at perihelion, to find the orbit with close to matching perihelion time (Fig. 1). The resulting orbit is: C/1854 L1 C/962 B2
T
a (AU)
q
i(, J2000)
x
Node
961 Dec. 27.0 (UT) 961 Dec. 28.0 (UT)
23.258 Inf.
0.6659 0.63
108.569 119
75.631 85
349.394 362
The inclination is the most significant discrepancy between the calculated orbit of C/1854 L1 in 962 AD and the orbit derived from observations (Hasegawa, 1979; Kronk, 1999). It is significant that the inclination does not change much from planetary perturbations over time. When plotting the calculated positions of the comet in 961 AD, it appears higher in the sky (by 10 to 20) than was reported by the three accounts from China. No close encounters with planets occurred that could account for the difference. Oudemans may have been right, and the association of Klinkerfues and C/962 B2 remains uncertain. Starting with the position of comet Klinkerfues in 1854, we integrated a series of comet orbit solutions, for a range of semi-major axis close to a = 25 AU, backward in time. The planetary perturbations on these orbits, results in surprisingly modulated dispersion of solutions and would mimick the shape of a dust trail for large grains with no significant radiation pressure. The distribution of orbital elements remains in a narrow range of elements (Fig. 2) and the spatial distribution remains much confined (Fig. 3). The large-scale loops are due to the perturbations of Jupiter, while the small excursions are due to encounters with the Earth. Only after 7 orbits does the distribution become more dispersed to form a filament, much as observed for the dust ejected from 55P/Tempel-Tuttle with shorter semi-major axis a 10 AU. Based on a study of the Monocerotids, our earlier assumption that many of the large grains would have been
Fig. 3. One-revolution dust trail of a long-period comet back at aphelion (no radiation pressure). Case of an a = 50 AU comet in the orbit of C/ 1854 L1 (Klinkerfues).
Fig. 4. The spatial distribution of dust after 1.5 revolutions for an initial a = 68 AU comet orbit solution, for a range of radiation pressures.
ejected in hyperbolic orbits because of radiation pressure (Jenniskens et al., 1997) does not pan out by the models. Instead, most larger meteoroids responsible for visible meteors are ejected in bound orbits. Fig. 4 shows the a = 68 AU trail 1.5 orbits after ejection in 1030 AD.
Fig. 2. The distribution of orbital elements semi-major axis (a, in AU) and eccentricity (e) for different solutions of the orbit of comet C/1854 L1 integrated backward in time, centered the orbit of C/1854 L1 during the 1854 return for different values of the semi-major axis.
J. Vaubaillon, P. Jenniskens / Advances in Space Research 39 (2007) 612–615
615
with the program created by Neslusan et al. (1998) and for a semi-major axis a 25 AU, is at RA = 64.2, Dec. = 6.6, but considerably less certain given the orbit and therefore perhaps consistent with the observed value. However, in that case the comet has not been seen since 962 AD, which means that it is either in a long-period orbit or intrinsically faint. Both conditions argue against an association with the broad 1981 e-Eridanid outburst. The next outburst of this shower is expected only around the time of the next return of comet C/1854 L1 to perihelion, which is about 127 years after AD 1981, in about AD 2108. Acknowledgements Fig. 5. Particles are close to the orbit of the Earth but do not cross it. The same situation is found in the late 70Õs until the late 90Õs.
This means that the peculiar magnitude distribution (with a high-mass cut-off) measured for the a-monocerotids dust trail by Jenniskens et al. (1997) is not due to large grains being lost during ejection, but must come on account of the larger grains not being able to disperse far enough along the comet dust trail all the way out to where Earth encounters the meteoroids. If so, this implies that the meteoroid distribution can determine where the parent comet is in its orbit. Until now, the parent of the a-monocerotid shower has not been discovered. We subsequently investigated the possibility that dust ejected by comet 1854 L1 in a prior return could have caused the 1981 outburst. We find that the meteoroid orbits evolved from ejection during the 1854 return have nodes in the next return in 1981 that are systematically outside of Earth orbit with a closest encounter 1.4 days after the observed peak, at September 12.1 UT instead of September 10.68 UT (Fig. 5). We conclude that the 1981 outburst was not caused by a recent dust trail crossing. This, in fact, is consistent with the relatively long duration of the shower. Due to the high inclination, Earth would have crossed a recent dust trail in less than an hour. That leaves open the possibility that the 1981 outburst was similar to the Leonid fireball shower of 1998, the Filament component of 10–100 orbits old ejecta (Asher et al., 1999; Jenniskens and Betlem, 2000). In the case of 55P/Tempel-Tuttle, the 1998 Fireball shower peaked 0.75 days before the younger dust trails were encountered. This situation is similar. The type of dispersion found in the Filament component is generated only after more than 10 revolutions in the case of C/1854 L1. Even after 7 revolutions, only some parts of the dust trail start to catch up on each other (Fig. 3). It is not so likely that the 1981 meteors derived from comet C/962 B2, if in a manner unrelated to comet C/ 1854 L1. The theoretical radiant of C/962 B2 computed
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