SEARCH

SEARCH BY CITATION

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Theory
  5. Method
  6. Phase Dependence
  7. Results
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. Editorial Handling
  12. References

Presented here are results from photometric analysis on broadband images taken of comet 21P/Giacobini-Zinner from May 24, 2011 to October 24, 2011. As the parent body of the Draconids, a meteor shower known for outbursting, 21P was studied for its dust production activity, Afρ, focusing on how it changes with heliocentric distance. An expected increase in dust production with a decrease in heliocentric distance was observed. The comet went from heliocentric distance of 3.05 –1.77 AU during the observed time that corresponded to an apparent magnitude of 19.61 to 15.72 and Afρ of 16.48 cm to 284.17 cm. These values can be extrapolated to estimate a peak Afρ value at perihelion of 3824 cm. The images were obtained using a 0.5-meter f/8.1 Ritchey-Chrétien telescope located in Mayhill, New Mexico.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Theory
  5. Method
  6. Phase Dependence
  7. Results
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. Editorial Handling
  12. References

Comet 21P/Giacobini-Zinner is a Jupiter family comet that was discovered in December of 1900 by the French astronomer Michel Giacobini and rediscovered in 1913 two orbits later by German astronomer Ernst Zinner (Pittichova et al. 2008). 21P is approximately 2 km in diameter, has a perihelion of 1.03 AU, and is the parent of the Draconids, a meteor shower known to undergo dramatic outbursts. In 1933 and 1946, up to 10,000 meteors per hour were reported for the Draconids (Jenniskens 2006); and 2011 saw a minor Draconid outburst (Vaubaillon et al. 2011). To better constrain meteor stream forecasts for the Draconids, 21P was monitored to determine the heliocentric distance variation of Afρ (A'Hearn et al. 1984), a quantity that describes the dust production rate and one that is used in cometary dust ejection models.

Afρ is a quantity independent of an observer's site and equipment, of the geometrical arrangement of the comet in the solar system, or wavelength of images taken. It has been shown that the Afρ results obtained from both CCD filter photometry and spectrophotometry agree (Schleicher and Bair 2011). Typical values of Afρ are anywhere from 5 cm to 5000 cm and are mainly affected by the size of the comet and its distance from the Sun. The quantity is calculated from the apparent magnitude and is an aperture-independent quantity for comets having a 1/ρ falloff (ρ being the distance from the nucleus to the edge of the aperture) in their brightness profile, standard for comets in a quiescent state. This study presents multi-aperture photometry of 21P for its preperihelion passage from 3.05 AU to 1.77 AU. Multi-aperture photometry gives further insights into the comet as variation seen in Afρ for various ρ's implies that the comet's activity is increasing or decreasing, often caused by changing heliocentric distance or an outburst. Observing 21P over a range of heliocentric distances also allowed a determination of the slope of how Afρ changes with distance to the Sun, also included in this report.

Comet Giacobini-Zinner has received attention in the past as it has passed close to Earth in several of its apparitions and become as bright as 7th magnitude. It was the first comet to have measurements made in situ. Comet 21P was visited by ICE (International Cometary Explorer) in 1985 to study the interaction of the cometary atmosphere with the flowing solar-wind plasma (von Rosenvinge et al. 1986). It is a carbon-depleted comet (Lara et al. 2003), and most studies show that it peaks in gas and dust production preperihelion, specifically in two well studied passages: 1985 and 1998 (McFadden et al. 1987; Lara et al. 2003). The gas emission of 21P has been studied in depth (Landaberry et al. 1991; Ellis and Neff 2000); however, there has been considerably less analysis on the dust emission. 21P's dust production during its previous two apparitions were studied by Pittichova et al. (2008) and Lara et al. (2003) and will be compared and discussed with the results found in this report.

Another comet in a similar orbit whose dust production has been analyzed was 103P/Hartley 2. 103P has an orbital period of 6.47 yr, aphelion distance of 5.88 AU, and perihelion distance of 1.06 AU. This is very similar to 21P's orbital period of 6.60 yr, aphelion distance of 6.00 AU, and perihelion distance of 1.03 AU. 103P has a measured A(θ)fρ of 45 cm at 1.2 AU from the Sun during the EPOXI campaign (A'Hearn et al. 2011; Meech et al. 2011). A study using the William Herschel Telescope at La Palma Observatory (Lara et al. 2011) also found A(θ)fρ for 103P during the same apparition, at the comet's perihelion; 102 cm on October 27, 2010 and 111 cm on October 29, 2010. These results will be compared with those found of 21P in this study.

Theory

  1. Top of page
  2. Abstract
  3. Introduction
  4. Theory
  5. Method
  6. Phase Dependence
  7. Results
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. Editorial Handling
  12. References

The quantity Afρ is based on A'Hearn et al.'s (1984) study and designed to describe how dusty or inactive comets are. Often, comet outbursts are characterized by sharp increase in Afρ, which is explicitly the albedo of the grains (A), multiplied by the filling factor of the grains (f), and the nucleocentric distance (ρ). It is calculated using the Earth-comet distance, (Δ); nucleocentric distance (the distance from the comet's nucleus to the edge of the aperture being used for photometry); the flux of the Sun at 1 AU in the same filter used to image the comet, FSOL; and the observed flux from the comet found using the apparent magnitude, FCOM. Explicitly, the filling factor (f) is N(ρ)σ/πρ2 where the numerator of that expression is the cross section of grains within the field of view, and the denominator is the area of the field of view.

  • display math(1)
  • display math(2)
  • display math(3)
  • display math(4)

Δ and ρ are in cm, but R, the heliocentric distance, is in AU. MAPP is −27.15 when finding FSOL, which corresponds to the Sun's magnitude in the R filter. In Equation (2), (5) accounts for the radius of a 10 × 10 arcsecond aperture, which is converted to radians (1 arcsecond = 1/206,265 radian), and 1.12838 is a correction factor as the true aperture is not a square, but a circle whose area is equivalent to the square used by FoCAS (Fotometria Con Astrometrica or Photometry with Astrometrica). This is a simplification; however, as shown in Hosek et al. (2013), the dust production found with this method is equal to that found with circular apertures using IRAF.

Fotometria Con Astrometrica or Photometry with Astrometrica (Roig et al. 2011), the reduction software used in this study to perform multi-aperture photometry, has set apertures of 10″ × 10″, 20″ × 20‴, 30″ × 30″, 40″ × 40″ and so on. Afρ was derived for each aperture as this gives us information about how the dust falls off with distance from the nucleus. Afρ is designed to be independent of aperture size for comets with the canonical 1/ρ falloff in surface brightness and hence dust profile (Jewitt and Meech 1987). It is, however, dependent on the solar phase angle, for which a correction was applied as discussed below. Deviations from the 1/ρ falloff can be attributed to a significant increase or decrease in dust production from seasonal changes, different active regions being stimulated, grain fading, among other effects (Schleicher et al. 1998). When new particles are lifted off the surface of the comet, they often remain in the inner coma for days or months, resulting in a higher Afρ value at lower ρ's before the particles disperse and the comet goes back to a quiescent state. This implies that smaller apertures encase younger, newer material released from the nucleus that has not yet dissipated through the comet tail (Schleicher 2009). For comet 21P, it was sufficient to use apparent magnitudes found with a 10 × 10 arcsecond aperture as 21P was not a diffuse enough comet—10 × 10 arcseconds encapsulated the dust.

Method

  1. Top of page
  2. Abstract
  3. Introduction
  4. Theory
  5. Method
  6. Phase Dependence
  7. Results
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. Editorial Handling
  12. References

Images of 21P were obtained in the Johnson R-filter from May 24, 2011 until October 24, 2011 (3.05–1.77 AU heliocentric distance). The comet was not observed below 2 airmasses. The equipment used was a 0.5-meter f/8.1 Ritchey-Chrétien telescope on a German equatorial mount with an Apogee 16M CCD camera located in the mountains of southern New Mexico (Mayhill, NM), and operated remotely from Marshall Space Flight Center. Standard bias and dark subtraction and flat-field reduction were performed on all data.

21P was imaged up to several dozen times per night, although only a few images per night were selected for analysis after examining the images for background stars, cosmic rays, image artifacts, or other problems that would affect the photometry. The chosen images had photometry analysis performed with Astrometrica (Raab 2005) and FoCAs. Astrometrica, using the Carlsberg Meridian Catalog 14 (CMC-14), produces a log file of the astrometry and photometry of all reference stars as well as the object, which must be manually chosen. The log file produced by Astrometrica is read by FoCAs, then FoCAs determines the centroid of the object to perform its multi-aperture photometry. The value of the background of the image is found as the median of the whole image, not with concentric circles around the object itself (as in other photometric software), which minimizes contamination from the tail of the comet. The results from each image analyzed per night were then averaged together to give an apparent magnitude per night.

Phase Dependence

  1. Top of page
  2. Abstract
  3. Introduction
  4. Theory
  5. Method
  6. Phase Dependence
  7. Results
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. Editorial Handling
  12. References

To see true variation in the dust production over time, a correction for solar phase angle must be applied. Phase affects a solar system body in different ways based on the composition/grains. As comets often do not have consistent outgassing, it is difficult to measure this effect and a standard correction procedure does not exist.

Figure 1 shows the curve used for phase correction applied to all data presented here. It was found using a technique that is a splice of two curves (Schleicher, personal communication), one using data from comet Halley at small phase angles (Schleicher et al. 1998), and the other based on the Henyey-Greenstein function (Marcus 2007; Schleicher and Bair 2011). All Afρ values were normalized to opposition (0°) using Equation (5), where S(θ) is the scale factor. As the phase angle of 21P went from 10.60° to 25.28°, looking at Fig. 1, one can see that all data in this report are extrapolated and the values of Afρ are higher than those originally measured. Values of Afρ before phase correction (denoted A(θ)fρ), and after phase correction are both presented in this report. As phase correction for comets is an ongoing work, the original data may be revised accordingly in the future.

  • display math(5)
image

Figure 1. Normalization curve for phase angle correction used in this report.

Download figure to PowerPoint

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Theory
  5. Method
  6. Phase Dependence
  7. Results
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. Editorial Handling
  12. References

Over the five months 21P was imaged, from May 24, 2011 to October 24, 2011, the comet went from an apparent magnitude of 19.61 to 15.72, corresponding to an absolute magnitude of 15.06 to 12.13 (Figs. 2a and 2b). This spanned a heliocentric distance of 3.05–1.77 AU. The magnitudes presented here are averages found from analyzing several images per night. The average is weighted over the night according to the signal to noise ratio of the comet in each image. Errors in the graphs correspond to the average photometric errors after performing a fit to CMC-14 catalog magnitudes. The magnitudes, and thus the Afρ graphs presented here, were determined with a 10 × 10 arcsecond aperture, which corresponds to ρ of 9100 ± 500 km (as 21P's geocentric distance, Δ, varies).

image

Figure 2. Apparent a) and absolute b) magnitude of comet 21P from May 24 to October 24, 2011, corresponding to a heliocentric distance of 3.05 AU to 1.77 AU.

Download figure to PowerPoint

The magnitudes presented in Figs. 2a and 2b correspond to Afρ of 16.48 cm to 284.17 cm. (Table 2 catalogs the results throughout the entire run of observations of 21P). The second to last column is Afρ before phase angle correction is applied, which we call A(θ)fρ because of the phase dependence on the albedo. The last column is Afρ after the phase angle correction has been applied. This is presented in graph form in Fig. 3. A(θ)fρ results (before correction for phase) are presented as the gray data, and the data after Afρ has been corrected for phase is presented in black. As discussed above, with decreasing heliocentric distance, phase correction extrapolates Afρ. Figure 4 shows a sample image of 21P used for analysis.

image

Figure 3. Dust production of comet 21P from May 24 to October 24, 2011. Gray points represent A(θ)fρ, dust production found before correcting for solar phase angle, and black points represent Afρ, dust production after the solar phase angle correction has been applied.

Download figure to PowerPoint

image

Figure 4. Sample image of comet 21P/Giacobini-Zinner (comet in center of image) used for analysis. Image taken on October 1, 2011.

Download figure to PowerPoint

Dust production of 21P followed a logarithmic slope (γ) of −4.468 with respect to heliocentric distance (Afρ ∝ Rγ). The slope permits the extrapolation of the data out to the perihelion (1.038 AU) of 21P, to an Afρ of 3824 cm. The Afρ and γ of a comet are two of the main descriptors of its dust production. There were no significant outbursts during this time. There was a slight increase in brightness around 2.8 AU for several nights, seen as a slight increase in Afρ, which could correspond to a small outburst in 21P. However, 21P was passing through a dense star-field during this time, which could have affected the photometry. As typical comet outbursts have an immediate brightening of several magnitudes, contamination by field stars appears likely.

Dust production was measured with 3 apertures (ρ). The change in the coma and tail of 21P with decreasing heliocentric distance can be clearly seen by examination of the surface brightness profile (log(Afρ) versus log(ρ)). This is reflected in Table 1. When 21P is 3.05 AU from the Sun, it is nearly a point source. However, by 1.77 AU from the Sun, 21P has grown a pronounced coma which extends into larger apertures. As the values of Afρ with smaller apertures are still greater than those at larger apertures, this indicates that there is new dust coming off the nucleus of 21P and the comet is not in a quiescent state. The new dust does not immediately dissipate throughout the coma and tail but can take days or months to do so; therefore, after new dust is released from the nucleus, the dust production tends to have higher rates with smaller apertures. The values determined using the 9,000 km aperture (10 × 10 arcseconds) yielded the peak Afρ values, and are presented in Figs. 2a, 2b, 3, and Table 2 in this paper.

Table 1. Dust production of 21P for three aperture sizes and various heliocentric distances
ρ (km)9,00018,00027,000
Afρ at 3.04 AU (cm)16.4811.077.64
Afρ at 2.29 AU (cm)82.4363.6149.72
Afρ at 1.77 AU (cm)284.17262.51211.85
Table 2. Summary of results for the entire observation run of 21P/Giacobini-Zinner
DateHeliocentric distance (AU)Geocentric distance (AU)Phase angle θ(°)ρ (*103 km)Apparent magnitudeAbsolute magnitudeA(θ)fρ (cm)Afρa (cm)
  1. a

    Phase corrected to 0° (opposition) using a composite curve by D. G. Schleicher (Schleicher and Bair 2011).

24-5-20113.04892.154510.60088.8219.60915.06310.6516.48
25-5-20113.04152.144910.7548.7819.75715.2269.2114.32
28-5-20113.019732.13711.23978.7419.5515.04410.9117.24
30-5-20113.00452.129911.61228.7219.42414.93212.1119.37
31-5-20112.99722.126611.81378.7019.65415.1699.7515.68
7-6-20112.94472.111213.31348.6419.60115.1699.7616.41
8-6-20112.93742.109913.56418.6319.31114.88112.7221.52
9-6-20112.92992.108913.79228.6319.00514.86112.9522.05
23-6-20112.82232.114517.16018.6519.00514.63915.5828.77
25-6-20112.80682.118117.62018.6719.09314.73314.2426.55
26-5-20112.79892.120117.85018.6818.69714.34020.3838.18
29-6-20112.77552.126918.53018.7018.77114.42218.7835.68
30-6-20112.76772.129218.75018.7118.85214.50517.3633.13
2-7-20112.75192.134819.18758.7418.83414.49117.5033.67
5-7-20112.72822.146919.80568.7818.93414.59415.7730.71
7-7-20112.71232.1500520.20018.8018.80014.46717.6634.63
8-7-20112.70432.1533620.39198.8118.87214.54116.4532.38
9-7-20112.69632.1567520.57998.8318.85114.52216.7032.97
18-7-20112.62392.1899622.09988.9618.85614.542316.0043.44
19-7-20112.61582.193922.24918.8918.53614.22421.3543.40
26-7-20112.55932.221523.16359.0918.56814.27020.1041.48
2-8-20112.5022.249323.91219.2018.38914.10922.9047.82
7-8-20112.462.26824.22489.2818.13813.87528.0958.97
15-8-20112.3922.29824.83829.4018.00313.76730.4764.58
23-8-20112.32412.323225.13719.5117.94013.74130.8164.60
24-8-20112.315582.3260525.16259.5217.71913.52537.4979.85
25-8-20112.306952.3288225.18529.5417.67213.48839.2683.64
26-8-20112.29832.331525.20539.5517.79313.61638.6482.42
27-8-20112.28962.334125.22299.5617.21213.03934.2673.26
29-8-20112.27232.339125.25079.5717.68613.51937.4479.85
30-8-20112.26362.341425.2619.5817.58913.42940.6486.69
31-8-20112.25492.343725.2699.5917.76213.60834.4673.52
2-9-20112.23742.347925.27839.6117.67513.53436.7978.59
6-9-20112.20242.355225.27189.6417.47513.36242.9591.63
12-9-20112.14942.363225.20699.6717.47913.41240.9087.16
13-9-20112.14052.364225.19049.6717.46113.40241.2687.91
14-9-20112.131662.365125.17259.6817.28813.23747.99102.23
17-9-20112.105692.3670225.11179.6817.21913.19449.87106.13
18-9-20112.096772.3674725.08849.6917.07713.06056.39119.96
19-9-20112.08782.367825.06389.6917.06913.06256.29119.71
20-9-20112.078892.3680725.0389.6917.07413.07555.61118.21
21-9-20112.069932.368225.0119.6917.06813.07955.43117.79
23-9-20112.05192.368224.95399.6916.96112.99260.05127.49
24-9-20112.0432.367924.92379.6916.95712.99859.73126.76
27-9-20112.01592.366724.82779.6816.83812.90964.87137.45
28-9-20112.00692.366124.7949.6816.77312.85568.21144.45
30-9-20111.98892.364524.72439.6816.74112.84468.93145.82
1-10-20111.97982.363524.68859.6716.62612.74175.87160.42
2-10-20111.97082.362524.65219.6716.43412.55989.60189.33
6-10-20111.93452.35724.50189.6416.55712.72976.94162.21
11-10-20111.88892.347824.30749.6116.33112.56589.90188.93
12-10-20111.87972.345624.26819.6016.3212.56789.84188.70
13-10-20111.870592.3432624.239.5916.18612.446100.50210.96
23-10-20111.779022.3149223.859.4715.7912.19129.10269.37
24-10-20111.769852.3115423.819.4615.71812.131136.28284.17

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Theory
  5. Method
  6. Phase Dependence
  7. Results
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. Editorial Handling
  12. References

The results presented here are in rough agreement with Pittichova et al.'s 2008 results, covering 21P's previous apparition in 2005 (Pittichova et al. 2008). They were also looking at R-band images and found 21P had an apparent magnitude of 15.91 corresponding to an A(θ)fρ (nonphase corrected) of 130.55 cm when the comet was 1.76 AU from the Sun and an apparent magnitude of 17.05 corresponding to A(θ)fρ of 82.07 cm when the comet was 2.32 AU. Also, it should be noted that these are postperihelion values as 21P has exhibited different dust emission characteristics between its pre- and postperihelion passages (Schleicher et al. 1987; Lara et al. 2003). The analysis also compares favorably to Lara et al.'s (2003) results from 21P's 1998 apparition. Their peak A(θ)fρ (nonphase corrected) value was 1010 cm in the red continuum at 1.05 AU. It was imaged at perihelion (1.03 AU) with an A(θ)fρ of 649 cm. These values are lower than the theoretical value at perihelion that this study found through extrapolation, but one needs to keep in mind that Lara et al.'s values are not corrected for phase and correcting for phase would increase their A(θ)fρ values. A third similar study by Schleicher et al. (1987) studied 21P at smaller heliocentric distances. They found a peak Afρ value of 416 cm at 1.087 AU, which is preperihelion similar to when Lara et al. (2003) found their peak value.

Pittichova et al. (2008) derived a slope of −2.04 regarding how Afρ changes with heliocentric distance. This is not as steep as the γ of −4.468 found with the data in this study, although their data were taken of 21P postperihelion. A preperihelion value, perhaps more compatible to compare with the value derived here, was found of −2.08 ± 0.15 by A'Hearn et al. (1995). The value found by A'Hearn et al. used 13 sets of observations when 21P was between 1.507 AU and 1.053 AU, a smaller heliocentric distance than observations taken for this study.

In comparing 21P's dust production with another similar comet, 103P, it is found that 21P is a much higher dust producer. 103P had an A(θ)fρ of 45 cm when it reached 1.2 AU from the Sun in A'Hearn et al.'s (2011) 2010 EPOXI study (Meech et al. 2011), and in Lara et al.'s (2011) 2010 study of the same comet they found A(θ)fρ values at perihelion (1.058 AU) of 102 and 111 cm. Looking at Table 2, it is seen that 21P is a higher dust producer. The last night of data taken with this study has 21P at 1.77 AU and finds a dust production (before phase correction) of 136.28 cm. 21P is thought to be a larger comet, which could be contributing to its higher dust production; however, the A'Hearn et al. (2011) paper comments that 103P had an atypically small increase in dust production during aphelion.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Theory
  5. Method
  6. Phase Dependence
  7. Results
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. Editorial Handling
  12. References

21P/Giacobini-Zinner behaved as expected over the five months of observations: it shows increased dust production with decreasing heliocentric distance and no outbursting. At the beginning of the observation run on May 24, 2011, when 21P was 3.05 AU from the Sun, it was found to have an apparent magnitude of 19.61 equaling an absolute magnitude of 15.06. This corresponds to an Afρ of 16.48 cm. At the end of the observation run, on October 24, 2011, 21P was 1.77 AU from the Sun and was found to have an apparent magnitude of 15.72 equaling an absolute magnitude of 12.13. This corresponds to an Afρ of 284.17 cm. The Afρ values in this report were corrected for phase as the albedo of the comet is known to have a strong dependence of the solar phase angle.

21P is an important solar system body, being the parent of the Draconids, a meteor shower known for dramatic outbursts. This meteor stream has been modeled extensively and two parameters that are helpful in modeling are the dust production at perihelion, and the slope of the dust production with heliocentric distance. This study found a slope (γ) of −4.468 and an extrapolation of the data gives an Afρ of 3824 cm at perihelion.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Theory
  5. Method
  6. Phase Dependence
  7. Results
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. Editorial Handling
  12. References

The authors thank NASA's Meteoroid Environment Office for support of this project, and D. Schleicher and M. A'Hearn for their helpful correspondence.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Theory
  5. Method
  6. Phase Dependence
  7. Results
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. Editorial Handling
  12. References
  • A'Hearn M. F., Schleicher D. G., Feldman P. D., Millis R. L., and Thompson D. T. 1984. Comet Bowell 1980b. The Astronomical Journal 89:579591.
  • A'Hearn M. F., Millis R. L., Schleicher D. G., Osip D. J., and Birch P. V. 1995. The ensemble properties of comets: Results from narrowband photometry of 85 comets, 1976-1992. Icarus 118:223270.
  • A'Hearn M. F., Belton M. J. S., Delamere W. A., Feaga L. M., Hampton D., Kissel J., Klaasen K. P., McFadden L. A., Meech K. J., Melosh H. J., Schultz P. H., Sunshine J. M., Thomas P. C., Veverka J., Wellnitz D. D., Yeomans D. K., Besse S., Bodewits D., Bowling T. J., Carcich B. T., Collins S. M., Farnham T. L., Groussin O., Hermalyn B., Kelley M. S., Li J.-Y., Lindler D. J., Lisse C. M., McLaughlin S. A., Merlin F., Protopapa S., Richardson J. E., and Williams J. L. 2011. EPOXI at comet Hartley 2. Science 332:13961400.
  • Ellis T. A. and Neff J. S. 2000. Narrowband filter photometry of five comets. Icarus 145:591600.
  • Hosek M. W., Jr., Blaauw R. C., Cooke W. J., and Suggs R. M. 2013. Outburst dust production of comet 29P/Schwassmann-Wachmann 1. The Astronomical Journal 145:122130.
  • Jenniskens P. M. M. 2006. Meteor showers and their parent comets. Cambridge, UK: Cambridge University Press. 790 p.
  • Jewitt D. C. and Meech K. J. 1987. Surface brightness profiles of 10 comets. The Astrophysical Journal 317:9921001.
  • Landaberry S. J. C., Singh P. D., and de Freitas Pacheco J. A. 1991. Ground-based observations of comets Giacobini-Zinner (1984e) and Harltey-Good (1985l). Astronomy & Astrophysics 246:597602.
  • Lara L.-M., Licandro J., Oscoz A., and Motta V. 2003. Behavior of comet 21P/Giacobini-Zinner during the 1998 perihelion. Astronomy & Astrophysics 399:763772.
  • Lara L. M., Lin Z.-Y., and Meech K. 2011. Comet 103P/Hartley 2 at perihelion: Gas and dust activity. Astronomy & Astrophysics 532:A87.
  • Marcus J. N. 2007. Forward-scattering enhancement of comet brightness. II. The light curve of C/2006 P1. International Comet Quarterly 29:119130.
  • McFadden L. A., A'Hearn M. F., Feldman P. D., Bohnhardt H., Rahe J., Festou M. C., Brandt J. C., Maran S. T., Niedner M. B., Smith A. M., and Schleicher D. G. 1987. Ultraviolet spectrophotometry of comet Giacobini-Zinner during the ICE encounter. Icarus 69:329337.
  • Meech K. J., A'Hearn M. F., Adams J. A., Bacci P., Bai J., Barrera L., Battelino M., Bauer J. M., Becklin E., Bhatt B., Biver N., Bockelée-Morvan D., Bodewits D., Böhnhardt H., Boissier J., Bonev B. P., Borghini W., Brucato J. R., Bryssinck E., Buie M. W., Canovas H., Castellano D., Charnley S. B., Chen W. P., Chiang P., Choi Y.-J., Christian D. J., Chuang Y.-L., Cochran A. L., Colom P., Combi M. R., Coulson I. M., Crovisier J., Dello Russo N., Dennerl K., DeWahl K., DiSanti M. A., Facchini M., Farnham T. L., Fernández Y., Florén H. G., Frisk U., Fujiyoshi T., Furusho R., Fuse T., Galli G., García-Hernández D. A., Gersch A., Getu Z., Gibb E. L., Gillon M., Guido E., Guillermo R. A., Hadamcik E., Hainaut O., Hammel H. B., Harker D. E., Harmon J. K., Harris W. M., Hartogh P., Hashimoto M., Häusler B., Herter T., Hjalmarson A., Holland S. T., Honda M., Hosseini S., Howell E. S., Howes N., Hsieh H. H., Hsiao H.-Y., Hutsemékers D., Immler S. M., Jackson W. M., Jeffers S. V., Jehin E., Jones T. J., de Juan Ovelar M., Kaluna H. M., Karlsson T., Kawakita H., Keane J. V., Keller L. D., Kelley M. S., Kinoshita D., Kiselev N. N., Kleyna J., Knight M. M., Kobayashi H., Kobulnicky H. A., Kolokolova L., Kreiny M., Kuan Y.-J., Küppers M., Lacruz J. M., Landsman W. B., Lara L. M., Lecacheux A., Levasseur-Regourd A. C., Li B., Licandro J., Ligustri R., Lin Z.-Y., Lippi M., Lis D. C., Lisse C. M., Lovell A. J., Lowry S. C., Lu H., Lundin S., Magee-Sauer K., Magain P., Manfroid J., Mazzotta Epifani E., McKay A., Melita M. D., Mikuz H., Milam S. N., Milani G., Min M., Moreno R., Mueller B. E. A., Mumma M. J., Nicolini M., Nolan M. C., Nordh H. L., Nowajewski P. B., Odin Team, Ootsubo T., Paganini L., Perrella C., Pittichová J., Prosperi E., Radeva Y. L., Reach W. T., Remijan A. J., Rengel M., Riesen T. E., Rodenhuis M., Rodríguez D. P., Russell R. W., Sahu D. K., Samarasinha N. H., Sánchez Caso A., Sandqvist A., Sarid G., Sato M., Schleicher D. G., Schwieterman E. W., Sen A. K., Shenoy D., Shi J.-C., Shinnaka Y., Skvarc J., Snodgrass C., Sitko M. L., Sonnett S., Sosseini S., Sostero G., Sugita S., Swinyard B. M., Szutowicz S., Takato N., Tanga P., Taylor P. A., Tozzi G.-P., Trabatti R., Trigo-Rodríguez J. M., Tubiana C., de Val-Borro M., Vacca W., Vandenbussche B., Vaubaillion J., Velichko F. P., Velichko S. F., Vervack R. J., Jr., Vidal-Nunez M. J., Villanueva G. L., Vinante C., Vincent J.-B., Wang M., Wasserman L. H., Watanabe J., Weaver H. A., Weissman P. R., Wolk S., Wooden D. H., Woodward C. E., Yamaguchi M., Yamashita T., Yanamandra-Fischer P. A., Yang B., Yao J.-S., Yeomans D. K., Zenn T., Zhao H., and Ziffer J. E. 2011. EPOXI: Comet 103P/Hartley 2 observations from a worldwide campaign. The Astrophysical Journal Letters 734:L1L9.
  • Pittichova J., Woodward C. E., Kelley M. S., and Reach W. T. 2008. Ground-based optical and spitzer infrared imaging observations of comet 21P/Giacobini-Zinner. The Astronomical Journal 136:11271136.
  • Raab H. 2005. Astrometrica software, shareware for research grade CCD photometry. http://www.astrometrica.at/. Accessed September 5, 2012.
  • Roig J. C., Nogues R. N., Lorenz E. S., and Gonzalez J. L. S. 2011. Fotometrica Con Astrometrica, a software tool. http://www.astrosurf.com/cometas-obs/. Accessed September 5, 2012.
  • Rosenvinge T. T. von, Brandt J. C., and Farquhar R. W. 1986. The international cometary explorer mission to comet Giacobinin-Zinner. Science 232:353356.
  • Schleicher D. G. 2009. The long-term decay in production rates following the extreme outburst of comet 17P/Holmes. The Astrophysical Journal 138:10621071.
  • Schleicher D. G. and Bair A. N. 2011. The composition of the interior of comet 73P/Schwassmann-Wachmann 3: Results from narrowband photometry of multiple components. The Astronomical Journal 141:177192.
  • Schleicher D. G., Millis R. K., and Birch P. V. 1987. Photometric observations of comet P/Giacobini-Zinner. Astronomy & Astrophysics 187:531538.
  • Schleicher D. G., Millis R. L., and Birch P. V. 1998. Narrowband photometry of comet P/Halley: Variation with heliocentric distance, season, and solar phase angle. Icarus 132:397417.
  • Vaubaillon J., Koten P., Gerding M., Johannink C., Langbroek M., Latteck R., Brown P., and Jenniskens P. 2011. Draconid meteors 2011. In Central bureau electronic telegrams 2862 (2). http://www.cbat.eps.harvard.edu/iau/cbet/002800/CBET002862.txt. Accessed September 5, 2012.