- Email: [email protected]
1995 O1 (Hale-Bopp): 1995–2001
Available online at www.sciencedirect.com
Advances in Space Research 44 (2009) 335–339 www.elsevier.com/locate/asr
Analysis of total visual and CCD V-broadband observations of Comet C/1995 O1 (Hale-Bopp): 1995–2001 A.A. de Almeida a, R. Boczko a, G.C. Sanzovo b,*, D. Trevisan Sanzovo b a
Department of Astronomy, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of Sa˜o Paulo, Main Campus, Rua do Mata˜o 1226, CEP 05508-090, Sa˜o Paulo, SP, Brazil b Laboratory of Molecular Astrophysics, Department of Physics, State University of Londrina, Perobal, CEP 86051-970, Londrina, PR, Brazil Received 17 July 2008; received in revised form 16 March 2009; accepted 24 March 2009
Abstract We developed a general method for determination of water production rates from groundbased visual observations and applied it to Comet Hale–Bopp. Our main objective is to extend the method to include total visual magnitude observations obtained with CCD detector and V filter in the analysis of total visual magnitudes. We compare the CCD V-broadband careful observations of Liller [Liller, W. Pre-perihelion CCD photometry of Comet 1995 O1 (Hale-Bopp). Planet. Space Sci. 45, 1505–1513, 1997; Liller, W. CCD photometry of Comet C/1995 O1 (Hale-Bopp): 1995–2000. Int. Comet Quart. 23(3), 93–97, 2001] with the total visual magnitude observations from experienced international observers found in the International Comet Quarterly (ICQ) archive. A data set of 400 CCD observations covering about the same 6 years time span of the 12,000 ICQ selected total visual magnitude observations were used in the analysis. A least-square method applied to the water production rates, yields power laws as a function of the heliocentric distances for the pre- and post-perihelion phases. The average dimension of the nucleus as well as its effective active area is determined and compared with values published in the literature. Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: C/1995 O1 (Hale-Bopp); CCD observations; Visual magnitudes measurements; Water production rates
1. Introduction and motivation This analysis covers the whole apparition of Comet C/1995 O1 (Hale-Bopp), which was discovered at r = 7.464 and D = 6.516 AU on 23 July 1995 and displayed a magnitude brighter than 0 mag for the continuous period of 7 weeks. Comets de Che´seaux (C/1743 X1) and Tycho 1577 were brighter than 0 mag for 6 weeks and Comet Cruls (C/1882 R1), which was a sungrazer, 5 weeks. All other bright comets since 1500 did display a magnitude greater than 0 mag for less than 2 weeks. Comet Hale-Bopp was visible with the unaided eye for 18 months. Comet Flaugergues (C/1811 F1) was visible with the naked eye for 9 months; all other comets fall drastically short of both comets. Therefore, *
Corresponding author. Tel.: +55 43 33714266; fax: +55 43 33284440. E-mail address: [email protected] (G.C. Sanzovo).
Comet Hale-Bopp could be seen with the unaided eye twice as long as Comet Flaugergues which held the record before. As a result, Comet Hale-Bopp was the one which could be seen with unaided eye for the longest period and which was brighter than 0 mag for the longest continuous time. The wealth of available information on total visual magnitudes and broadband-V CCD observations of the exceptionally bright Comet Hale-Bopp proved to be an excellent opportunity to test the semi-empirical method of visual magnitudes for very bright comets. The observational C2/CN ratios confirm the classification of Comet Hale-Bopp as ‘‘typical” comet (Rauer et al., 2003). 2. Theoretical aspects Water production rates (in molecules/s) obtained through the semi-empirical photometric method of
0273-1177/$36.00 Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2009.03.028
336
A.A. de Almeida et al. / Advances in Space Research 44 (2009) 335–339
absolute visual magnitudes are given by (Morris, 1973; Newburn, 1981; de Almeida et al., 1997; Sanzovo et al., 2001) ( )0:825 0 r2 100:4ð26:8þmV Þ pR2N /N ðaÞ ð1Þ QH 2 O ¼ ‘r R½1 þ dðr; hÞ
3. Correlation between visual magnitudes and CCD-V observations Visual magnitudes estimates by different experienced observers, using a variety of instrument types, aperture sizes and observational techniques might be very subjective and heterogeneous (Fig. 1) compared to CCD V-broadband observations (Fig. 2) carried out, in this case, by a single observer and instrument (Liller, 1997, 2001). From the graphical superimposition we note that the CCD data does not fit well to the visual magnitude estimates. For instance, we note that around 975 days after perihelion there is a clear apparent increase in the activity of the comet recorded in the CCD data, which is not followed by the visual estimates, even considering the fact that CCDs and V filter passbands record systematically more coma than does the human eye, since they have different responses to C2 (Swan bands emissions), which is the main emission feature from the coma (Mikuz and Dintinjana, 2001), and consequently should be used with larger aperture diameters (Fig. 3).
Pre-perihelion phase Post-perihelion phase
Log Q(H 2O) [molecules/s]
31.0
30.0
29.0
28.0
27.0
26.0 -600
-300
0
300
600
900
1200 1500
Days from perihelion Fig. 1. Water production rates (from visual magnitudes data) in Comet Hale-Bopp.
Pre-perihelion phase Post-perihelion phase
31.0
30.5
Log Q(H 2O) [molecules/s]
where m’V = m6.78 5log D is the total observed reduced magnitude of the coma of a comet in a standard aperture of diameter 6.78 cm when the observer is at geocentric distance D = 1 AU and the comet is at a heliocentric distance r (in AU), p (=0.04) is the visual albedo of the nucleus (Keller, 1990), RN (in cm) is the effective nuclear radius, ‘r (=6.6 104 r2 km) is the scale length for destruction of C2 radical (A’Hearn et al., 1995), and R 2 1038 (or 5.0 1039 cm2 s) for short- (or long-period) comets, respectively, is a parameter recommended by de Almeida et al. (1997). In Eq. (1), uN(a) is the nuclear phase function, where a is the phase angle (in radians) (Sanzovo et al., 1996), and d(r,h) represents the ratio between the total observed flux in continuum and the C2 total observed flux as described in details by Sanzovo et al. (2001). To extend the method in order to include the CCD-V observations, the magnitude parameter at D = 1 AU now becomes m’V = mV B(D 6.78) 5 log D, where D (cm) is the instrument aperture and B is a parameter which has values of 0.019, 0.062, 0.066 mag cm1, respectively, for a reflector, a refractor and the eye, being 0.180 mag cm1 for the CCD, obtained by v2 fitting. The total active surface area, AA (=Q(H2O)/Z(T)), on the sunlit side of the nucleus has been estimated from water production rates given by Eq. (1) combined with theoretical estimates of water sublimation rates per unit area, Z(T), through the vaporization theory of Delsemme (1982), and using the constraint AA 6 2p(RN)2 (de Almeida et al., 1997) to find the lower limit of the nuclear radius.
32.0
30.0
29.5
29.0
28.5
28.0
27.5
27.0 -900
-600
-300
0
300
600
900
1200
Days from perihelion Fig. 2. Water production rates (from CCDs data) in Comet Hale-Bopp.
A.A. de Almeida et al. / Advances in Space Research 44 (2009) 335–339 32.0
12 Pre-perihelion optical data Post-perihelion optical data CCD data
31.5
Pre-perihelion phase Post-perihelion phase
11 10
31.0
9
30.5
8
Visual magnitude
30.0 29.5
29.0 28.5 28.0
Perihelion
Log Q(H 2O) [molecules/s]
337
7 6 5 4 3
27.5 2 27.0 1999 Apr 14
1998 Dec 20
250
1998 Aug 17
0
1998 May 13
1998 Jan 11
26.0 -750 -500 -250
1997 Apr 01
26.5
1 0 3 500
750 1000 1250 1500
Days from perihelion Fig. 3. Water release rates in Comet Hale-Bopp showing data and outburst events reported by Liller (2001).
For each of the 391 (151 pre- and 240 post-perihelion) available CCD-V observations (Liller, 1997, 2001) we searched for visual estimates of magnitudes ‘‘obtained nearly simultaneously” out of the 8655 pre- and 3036 postperihelion observations. This criterion in practice obliged us to consider the visual magnitudes estimated in the range of 24 h before and 24 h after a given date for a CCD observation. The procedure resulted in only 43 pre- and 17 postperihelion matching pairs, reflecting that the dates in which the comet was observed with CCD and through visual estimates not always were close by (Fig. 4). From this figure, we note that the difference between the CCD-V and visual magnitudes increases systematically from 2 mag to 3.5 mag in the considered time spam of 6 years. 4. Results The main results obtained in this work appear in Table 1 and Figs. 1–5. In cols. 1–4 of Table 1, we show observational date (UT), heliocentric and geocentric distances, and the status of the observations, respectively, while in col. 5 we compare water release rates, estimated by Eq. (1), with those ones obtained by other authors (cols. 6 and 7). As listed in col. 5 of Table 1, our results show a discrepancy of less than a factor 2.5 for majority of the rates obtained, confirming the efficiency of the semi-empirical method here utilized. In Fig. 5, we estimate the average
4
5
6
7
8
9
10
11
12
13
CCD-V magnitude Fig. 4. Correlation between visual and CCD-V magnitudes in Comet Hale-Bopp.
effective nuclear radius of Comet Hale-Bopp at 40% of active surface area. The following general conclusions can be summarized from this work: (1) Our analysis of the visual and CCD observations covers the effective period from 23.27 July 1995 (r = 7.464 and D = 6.516 AU) pre-perihelion, to 22.54 January 2001 (r = 1.334 and D = 1.354 AU) post-perihelion. (2) The use of different models (e.g. Haser versus Vectorial) and different scale lengths/lifetimes leads to systematic model dependent differences between the obtained production rates. Our water production rates (in molecules/s) with a systematic error amounting to about ±20% are expressed by the following power-laws: a. Using visual observations: Qpre ¼ 5:150 1030 r3:526 Qpost ¼ 6:275 1030 r3:753 b. Using CCD-V observations: Qpre ¼ 1:683 1032 r3:725 Qpost ¼ 2:465 1032 r3:933 (3) On the basis of the observed water production rates, the calculated average effective radius of the nucleus
338
A.A. de Almeida et al. / Advances in Space Research 44 (2009) 335–339
Table 1 Numerical results of water production rates for Comet Hale-Bopp. Date (UT, 1997)
r D Phase Q(H2O) Instrument 1030 (AU) (AU) (mol/s)
March 22
0.93
1.32
Pre-
March 23
0.93
1.32
Pre-
0.92
1.32
Pre-
March 28
0.92
1.33
Pre-
April 01
0.91
1.35
Per.
April 01
0.91
1.35
Per.
April 06
0.92
1.40
Post-
(8.94) 9.8
April 07
0.92
1.41
Post-
April 10
0.93
1.44
Post-
April 10
0.93
1.44
Post-
(8.58) 8.81 (8.58) 9.76 (8.24) 9.99
April 12
0.93
1.47
April 16
0.95
1.53
(8.24) Post- 10.49 (8.24) Post- 9.12
April 30
1.05
1.75
Post-
(7.61) 6.76
1.11
1.87
Post-
August 9–15 2.33
2.94
Post-
(5.23) 5.91 (4.24) 0.26
Post-
(0.26) 0.24
May 07
August 27
2.48
2.99
Reference
50
*
SWAN/SOHO Web
SWAN/SOHO Web* SWAN/SOHO Web* Nancßay/RT
Colom et al. (1997)
NASA/IRTF
Dello Russo et al. (2000)
Pre-perihelion optical data Post-perihelion optical data Average value: RN= 24.0 km
45
SWAN/SOHO Web* This work SWAN/SOHO Web*
40
Nuclear radius (km)
March 25
9.49 (6.65) 8.64 (6.65) 10.03 (6.91) 9.67 (6.91) 10.19 (8.94) 11.8
55
35
30
25
20
15
SWAN/SOHO Web* SWAN/SOHO Web* NASA/IRTF
DiSanti et al. (1999)
10
5 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0
r (AU)
SWAN/SOHO Web* NASA/IRTF
DiSanti et al. (1999)
NASA/IRTF
DiSanti et al. (1999)
SWAN/SOHO Web* SWRI/SWUIS Stern et al. (1999) HST/STIS
Weaver et al. (1999)
(0.21) *
Web reference: http://www-personal.engin.umich.edu/~mcombi/ SWANhb/Tables.html
is RN = 24 km (Fig. 5), in agreement with values published in the literature (Weaver et al., 1997a; Weaver and Lamy, 1997b; Ferna´ndez, 2002). The total active area is AA = 3620 km2, considering a nuclear activity of 40% on the sunlit hemisphere (Mo¨hlmann, 1999; Weiler et al., 2003). (4) Our analysis also shows that most water was released directly from the nucleus within heliocentric distances r < 2 AU (Fig. 5) in agreement with Dello Russo et al. (2000). Acknowledgments A.A.A. is grateful to the financial support from FAPESP (Sa˜o Paulo, SP, Brazil) under Contract No. 04/
Fig. 5. Nuclear radius of Comet Hale-Bopp considering an activity of 40%.
01215-1. G.C.S. is grateful to PROPPG/UEL, and D.T.S. is grateful to CAPES/PROPPG/UEL (Londrina, PR, Brazil). References A’Hearn, M.F., Millis, R.L., Schleicher, D.G., et al. The ensemble properties of comets: results from narrowband photometry of 85 comets, 1976–1992. Icarus 118, 223–270, 1995. Colom, P., Ge´rard, E., Crovisier, J., et al. Observations of OH radical in Comet C/1995 O1 (Hale-Bopp) with the Nancßay radio telescope. Earth Moon Plan. 78, 37–43, 1997. de Almeida, A.A., Singh, P.D., Huebner, W.F. Water release rates, active areas, and minimum nuclear radius derived from visual magnitudes of comets – an application to Comet 46P/Wirtanen. Plan. Space Sci. 45, 681–692, 1997. Dello Russo, N.D., Mumma, M.J., DiSanti, M.A., et al. Water production and release in Comet C/1995 O1 Hale-Bopp. Icarus 143, 324–337, 2000. Delsemme, A.H. Chemical composition of cometary nuclei, in: Wilkening, L.L. (Ed.), Comets. University of Arizona Press, Tucson, pp. 85–130, 1982. DiSanti, M.A., Mumma, M.J., Dello Russo, N., et al. Identification of two sources of carbon monoxide in comet Hale-Bopp. Nature 399, 662– 665, 1999. Ferna´ndez, Y.R. The nucleus of comet Hale-Bopp (C/1995 O1): size and activity. Earth Moon Plan. 89, 3–25, 2002. Keller, H.U. The nucleus, in: Huebner, W.F. (Ed.), Physics and Chemistry of Comets. Springer-Verlag, Berlin, pp. 13–68, 1990. Liller, W. Pre-perihelion CCD photometry of Comet 1995 O1 (HaleBopp). Planet. Space Sci. 45, 1505–1513, 1997.
A.A. de Almeida et al. / Advances in Space Research 44 (2009) 335–339 Liller, W. CCD photometry of Comet C/1995 O1 (Hale-Bopp): 1995– 2000. Int. Comet Quart. 23 (3), 93–97, 2001. Mikuz, H., Dintinjana, B. CCD photometry of comet C/1995 O1. Int. Comet Quart. 23 (1), 6–16, 2001. Mo¨hlmann, D. Activity and nucleus properties of 46P/Wirtanen. Planet. Space Sci. 47, 971–974, 1999. Morris, C.S. On aperture corrections for comet magnitude estimates. Publ. Astron. Soc Pacific. 85, 470–473, 1973. Newburn Jr., R.L. A semi-empirical photometric theory of cometary gas and dust production: application to Comet Halley’s gas production rates, in: Comet Halley Dust and Gas Environment, ESA-SP-174, ESTEC, Noordwijk, The Netherlands, pp. 3–12, 1981. Rauer, H., Helbert, J., Arpigny, C., et al. Long-term optical spectrophotometric monitoring of Comet C/1995 O1 (Hale-Bopp). Astron. Astrophys. 397, 1109–1122, 2003. Sanzovo, G.C., de Almeida, A.A., Misra, A., et al. Mass-loss rates, dust particles sizes, nuclear active areas and minimum nuclear radii of target comets for missions STARDUST and CONTOUR. Mon. Not. R. Astron. Soc. 326, 852–868, 2001.
339
Sanzovo, G.C., Singh, P.D., Huebner, W.F. Dust colors, dust release rates, and dust-to-gas ratios in the comae of six comets. Astron. Astrophys. Suppl. Ser. 120, 301–311, 1996. Stern, S.A., Colwell, W.B., Festou, M.C., et al. Comet Hale-Bopp (C/1995 O1) near 2.3 AU postperihelion: a southwest ultraviolet imaging system measurements of the H2O and dust production. Astron. J. 118, 1120–1125, 1999. ´ Hearn, M.F., et al. The activity and size Weaver, H.A., Feldman, P.D., A of the nucleus of comet Hale-Bopp (C/1995 O1). Science 275, 1900– 1904, 1997a. Weaver, H.A., Lamy, P.L. Estimating the size of Hale-Bopp’s nucleus. Earth Moon Plan. 79, 17–33, 1997b. ´ Hearn, M.F., et al. Post-perihelion HST Weaver, H.A., Feldman, P.D., A observations of Comet Hale-Bopp (C/1995 O1). Icarus 141, 1–12, 1999. Weiler, M., Rauer, H., Knollenberg, J., et al. The dust activity of Comet C/1995 O1 (Hale-Bopp) between 3 AU and 13 AU from the Sun. Astron. Astrophys. 403, 313–322, 2003.
Advances in Space Research 44 (2009) 335–339 www.elsevier.com/locate/asr
Analysis of total visual and CCD V-broadband observations of Comet C/1995 O1 (Hale-Bopp): 1995–2001 A.A. de Almeida a, R. Boczko a, G.C. Sanzovo b,*, D. Trevisan Sanzovo b a
Department of Astronomy, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of Sa˜o Paulo, Main Campus, Rua do Mata˜o 1226, CEP 05508-090, Sa˜o Paulo, SP, Brazil b Laboratory of Molecular Astrophysics, Department of Physics, State University of Londrina, Perobal, CEP 86051-970, Londrina, PR, Brazil Received 17 July 2008; received in revised form 16 March 2009; accepted 24 March 2009
Abstract We developed a general method for determination of water production rates from groundbased visual observations and applied it to Comet Hale–Bopp. Our main objective is to extend the method to include total visual magnitude observations obtained with CCD detector and V filter in the analysis of total visual magnitudes. We compare the CCD V-broadband careful observations of Liller [Liller, W. Pre-perihelion CCD photometry of Comet 1995 O1 (Hale-Bopp). Planet. Space Sci. 45, 1505–1513, 1997; Liller, W. CCD photometry of Comet C/1995 O1 (Hale-Bopp): 1995–2000. Int. Comet Quart. 23(3), 93–97, 2001] with the total visual magnitude observations from experienced international observers found in the International Comet Quarterly (ICQ) archive. A data set of 400 CCD observations covering about the same 6 years time span of the 12,000 ICQ selected total visual magnitude observations were used in the analysis. A least-square method applied to the water production rates, yields power laws as a function of the heliocentric distances for the pre- and post-perihelion phases. The average dimension of the nucleus as well as its effective active area is determined and compared with values published in the literature. Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: C/1995 O1 (Hale-Bopp); CCD observations; Visual magnitudes measurements; Water production rates
1. Introduction and motivation This analysis covers the whole apparition of Comet C/1995 O1 (Hale-Bopp), which was discovered at r = 7.464 and D = 6.516 AU on 23 July 1995 and displayed a magnitude brighter than 0 mag for the continuous period of 7 weeks. Comets de Che´seaux (C/1743 X1) and Tycho 1577 were brighter than 0 mag for 6 weeks and Comet Cruls (C/1882 R1), which was a sungrazer, 5 weeks. All other bright comets since 1500 did display a magnitude greater than 0 mag for less than 2 weeks. Comet Hale-Bopp was visible with the unaided eye for 18 months. Comet Flaugergues (C/1811 F1) was visible with the naked eye for 9 months; all other comets fall drastically short of both comets. Therefore, *
Corresponding author. Tel.: +55 43 33714266; fax: +55 43 33284440. E-mail address: [email protected] (G.C. Sanzovo).
Comet Hale-Bopp could be seen with the unaided eye twice as long as Comet Flaugergues which held the record before. As a result, Comet Hale-Bopp was the one which could be seen with unaided eye for the longest period and which was brighter than 0 mag for the longest continuous time. The wealth of available information on total visual magnitudes and broadband-V CCD observations of the exceptionally bright Comet Hale-Bopp proved to be an excellent opportunity to test the semi-empirical method of visual magnitudes for very bright comets. The observational C2/CN ratios confirm the classification of Comet Hale-Bopp as ‘‘typical” comet (Rauer et al., 2003). 2. Theoretical aspects Water production rates (in molecules/s) obtained through the semi-empirical photometric method of
0273-1177/$36.00 Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2009.03.028
336
A.A. de Almeida et al. / Advances in Space Research 44 (2009) 335–339
absolute visual magnitudes are given by (Morris, 1973; Newburn, 1981; de Almeida et al., 1997; Sanzovo et al., 2001) ( )0:825 0 r2 100:4ð26:8þmV Þ pR2N /N ðaÞ ð1Þ QH 2 O ¼ ‘r R½1 þ dðr; hÞ
3. Correlation between visual magnitudes and CCD-V observations Visual magnitudes estimates by different experienced observers, using a variety of instrument types, aperture sizes and observational techniques might be very subjective and heterogeneous (Fig. 1) compared to CCD V-broadband observations (Fig. 2) carried out, in this case, by a single observer and instrument (Liller, 1997, 2001). From the graphical superimposition we note that the CCD data does not fit well to the visual magnitude estimates. For instance, we note that around 975 days after perihelion there is a clear apparent increase in the activity of the comet recorded in the CCD data, which is not followed by the visual estimates, even considering the fact that CCDs and V filter passbands record systematically more coma than does the human eye, since they have different responses to C2 (Swan bands emissions), which is the main emission feature from the coma (Mikuz and Dintinjana, 2001), and consequently should be used with larger aperture diameters (Fig. 3).
Pre-perihelion phase Post-perihelion phase
Log Q(H 2O) [molecules/s]
31.0
30.0
29.0
28.0
27.0
26.0 -600
-300
0
300
600
900
1200 1500
Days from perihelion Fig. 1. Water production rates (from visual magnitudes data) in Comet Hale-Bopp.
Pre-perihelion phase Post-perihelion phase
31.0
30.5
Log Q(H 2O) [molecules/s]
where m’V = m6.78 5log D is the total observed reduced magnitude of the coma of a comet in a standard aperture of diameter 6.78 cm when the observer is at geocentric distance D = 1 AU and the comet is at a heliocentric distance r (in AU), p (=0.04) is the visual albedo of the nucleus (Keller, 1990), RN (in cm) is the effective nuclear radius, ‘r (=6.6 104 r2 km) is the scale length for destruction of C2 radical (A’Hearn et al., 1995), and R 2 1038 (or 5.0 1039 cm2 s) for short- (or long-period) comets, respectively, is a parameter recommended by de Almeida et al. (1997). In Eq. (1), uN(a) is the nuclear phase function, where a is the phase angle (in radians) (Sanzovo et al., 1996), and d(r,h) represents the ratio between the total observed flux in continuum and the C2 total observed flux as described in details by Sanzovo et al. (2001). To extend the method in order to include the CCD-V observations, the magnitude parameter at D = 1 AU now becomes m’V = mV B(D 6.78) 5 log D, where D (cm) is the instrument aperture and B is a parameter which has values of 0.019, 0.062, 0.066 mag cm1, respectively, for a reflector, a refractor and the eye, being 0.180 mag cm1 for the CCD, obtained by v2 fitting. The total active surface area, AA (=Q(H2O)/Z(T)), on the sunlit side of the nucleus has been estimated from water production rates given by Eq. (1) combined with theoretical estimates of water sublimation rates per unit area, Z(T), through the vaporization theory of Delsemme (1982), and using the constraint AA 6 2p(RN)2 (de Almeida et al., 1997) to find the lower limit of the nuclear radius.
32.0
30.0
29.5
29.0
28.5
28.0
27.5
27.0 -900
-600
-300
0
300
600
900
1200
Days from perihelion Fig. 2. Water production rates (from CCDs data) in Comet Hale-Bopp.
A.A. de Almeida et al. / Advances in Space Research 44 (2009) 335–339 32.0
12 Pre-perihelion optical data Post-perihelion optical data CCD data
31.5
Pre-perihelion phase Post-perihelion phase
11 10
31.0
9
30.5
8
Visual magnitude
30.0 29.5
29.0 28.5 28.0
Perihelion
Log Q(H 2O) [molecules/s]
337
7 6 5 4 3
27.5 2 27.0 1999 Apr 14
1998 Dec 20
250
1998 Aug 17
0
1998 May 13
1998 Jan 11
26.0 -750 -500 -250
1997 Apr 01
26.5
1 0 3 500
750 1000 1250 1500
Days from perihelion Fig. 3. Water release rates in Comet Hale-Bopp showing data and outburst events reported by Liller (2001).
For each of the 391 (151 pre- and 240 post-perihelion) available CCD-V observations (Liller, 1997, 2001) we searched for visual estimates of magnitudes ‘‘obtained nearly simultaneously” out of the 8655 pre- and 3036 postperihelion observations. This criterion in practice obliged us to consider the visual magnitudes estimated in the range of 24 h before and 24 h after a given date for a CCD observation. The procedure resulted in only 43 pre- and 17 postperihelion matching pairs, reflecting that the dates in which the comet was observed with CCD and through visual estimates not always were close by (Fig. 4). From this figure, we note that the difference between the CCD-V and visual magnitudes increases systematically from 2 mag to 3.5 mag in the considered time spam of 6 years. 4. Results The main results obtained in this work appear in Table 1 and Figs. 1–5. In cols. 1–4 of Table 1, we show observational date (UT), heliocentric and geocentric distances, and the status of the observations, respectively, while in col. 5 we compare water release rates, estimated by Eq. (1), with those ones obtained by other authors (cols. 6 and 7). As listed in col. 5 of Table 1, our results show a discrepancy of less than a factor 2.5 for majority of the rates obtained, confirming the efficiency of the semi-empirical method here utilized. In Fig. 5, we estimate the average
4
5
6
7
8
9
10
11
12
13
CCD-V magnitude Fig. 4. Correlation between visual and CCD-V magnitudes in Comet Hale-Bopp.
effective nuclear radius of Comet Hale-Bopp at 40% of active surface area. The following general conclusions can be summarized from this work: (1) Our analysis of the visual and CCD observations covers the effective period from 23.27 July 1995 (r = 7.464 and D = 6.516 AU) pre-perihelion, to 22.54 January 2001 (r = 1.334 and D = 1.354 AU) post-perihelion. (2) The use of different models (e.g. Haser versus Vectorial) and different scale lengths/lifetimes leads to systematic model dependent differences between the obtained production rates. Our water production rates (in molecules/s) with a systematic error amounting to about ±20% are expressed by the following power-laws: a. Using visual observations: Qpre ¼ 5:150 1030 r3:526 Qpost ¼ 6:275 1030 r3:753 b. Using CCD-V observations: Qpre ¼ 1:683 1032 r3:725 Qpost ¼ 2:465 1032 r3:933 (3) On the basis of the observed water production rates, the calculated average effective radius of the nucleus
338
A.A. de Almeida et al. / Advances in Space Research 44 (2009) 335–339
Table 1 Numerical results of water production rates for Comet Hale-Bopp. Date (UT, 1997)
r D Phase Q(H2O) Instrument 1030 (AU) (AU) (mol/s)
March 22
0.93
1.32
Pre-
March 23
0.93
1.32
Pre-
0.92
1.32
Pre-
March 28
0.92
1.33
Pre-
April 01
0.91
1.35
Per.
April 01
0.91
1.35
Per.
April 06
0.92
1.40
Post-
(8.94) 9.8
April 07
0.92
1.41
Post-
April 10
0.93
1.44
Post-
April 10
0.93
1.44
Post-
(8.58) 8.81 (8.58) 9.76 (8.24) 9.99
April 12
0.93
1.47
April 16
0.95
1.53
(8.24) Post- 10.49 (8.24) Post- 9.12
April 30
1.05
1.75
Post-
(7.61) 6.76
1.11
1.87
Post-
August 9–15 2.33
2.94
Post-
(5.23) 5.91 (4.24) 0.26
Post-
(0.26) 0.24
May 07
August 27
2.48
2.99
Reference
50
*
SWAN/SOHO Web
SWAN/SOHO Web* SWAN/SOHO Web* Nancßay/RT
Colom et al. (1997)
NASA/IRTF
Dello Russo et al. (2000)
Pre-perihelion optical data Post-perihelion optical data Average value: RN= 24.0 km
45
SWAN/SOHO Web* This work SWAN/SOHO Web*
40
Nuclear radius (km)
March 25
9.49 (6.65) 8.64 (6.65) 10.03 (6.91) 9.67 (6.91) 10.19 (8.94) 11.8
55
35
30
25
20
15
SWAN/SOHO Web* SWAN/SOHO Web* NASA/IRTF
DiSanti et al. (1999)
10
5 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0
r (AU)
SWAN/SOHO Web* NASA/IRTF
DiSanti et al. (1999)
NASA/IRTF
DiSanti et al. (1999)
SWAN/SOHO Web* SWRI/SWUIS Stern et al. (1999) HST/STIS
Weaver et al. (1999)
(0.21) *
Web reference: http://www-personal.engin.umich.edu/~mcombi/ SWANhb/Tables.html
is RN = 24 km (Fig. 5), in agreement with values published in the literature (Weaver et al., 1997a; Weaver and Lamy, 1997b; Ferna´ndez, 2002). The total active area is AA = 3620 km2, considering a nuclear activity of 40% on the sunlit hemisphere (Mo¨hlmann, 1999; Weiler et al., 2003). (4) Our analysis also shows that most water was released directly from the nucleus within heliocentric distances r < 2 AU (Fig. 5) in agreement with Dello Russo et al. (2000). Acknowledgments A.A.A. is grateful to the financial support from FAPESP (Sa˜o Paulo, SP, Brazil) under Contract No. 04/
Fig. 5. Nuclear radius of Comet Hale-Bopp considering an activity of 40%.
01215-1. G.C.S. is grateful to PROPPG/UEL, and D.T.S. is grateful to CAPES/PROPPG/UEL (Londrina, PR, Brazil). References A’Hearn, M.F., Millis, R.L., Schleicher, D.G., et al. The ensemble properties of comets: results from narrowband photometry of 85 comets, 1976–1992. Icarus 118, 223–270, 1995. Colom, P., Ge´rard, E., Crovisier, J., et al. Observations of OH radical in Comet C/1995 O1 (Hale-Bopp) with the Nancßay radio telescope. Earth Moon Plan. 78, 37–43, 1997. de Almeida, A.A., Singh, P.D., Huebner, W.F. Water release rates, active areas, and minimum nuclear radius derived from visual magnitudes of comets – an application to Comet 46P/Wirtanen. Plan. Space Sci. 45, 681–692, 1997. Dello Russo, N.D., Mumma, M.J., DiSanti, M.A., et al. Water production and release in Comet C/1995 O1 Hale-Bopp. Icarus 143, 324–337, 2000. Delsemme, A.H. Chemical composition of cometary nuclei, in: Wilkening, L.L. (Ed.), Comets. University of Arizona Press, Tucson, pp. 85–130, 1982. DiSanti, M.A., Mumma, M.J., Dello Russo, N., et al. Identification of two sources of carbon monoxide in comet Hale-Bopp. Nature 399, 662– 665, 1999. Ferna´ndez, Y.R. The nucleus of comet Hale-Bopp (C/1995 O1): size and activity. Earth Moon Plan. 89, 3–25, 2002. Keller, H.U. The nucleus, in: Huebner, W.F. (Ed.), Physics and Chemistry of Comets. Springer-Verlag, Berlin, pp. 13–68, 1990. Liller, W. Pre-perihelion CCD photometry of Comet 1995 O1 (HaleBopp). Planet. Space Sci. 45, 1505–1513, 1997.
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Sanzovo, G.C., Singh, P.D., Huebner, W.F. Dust colors, dust release rates, and dust-to-gas ratios in the comae of six comets. Astron. Astrophys. Suppl. Ser. 120, 301–311, 1996. Stern, S.A., Colwell, W.B., Festou, M.C., et al. Comet Hale-Bopp (C/1995 O1) near 2.3 AU postperihelion: a southwest ultraviolet imaging system measurements of the H2O and dust production. Astron. J. 118, 1120–1125, 1999. ´ Hearn, M.F., et al. The activity and size Weaver, H.A., Feldman, P.D., A of the nucleus of comet Hale-Bopp (C/1995 O1). Science 275, 1900– 1904, 1997a. Weaver, H.A., Lamy, P.L. Estimating the size of Hale-Bopp’s nucleus. Earth Moon Plan. 79, 17–33, 1997b. ´ Hearn, M.F., et al. Post-perihelion HST Weaver, H.A., Feldman, P.D., A observations of Comet Hale-Bopp (C/1995 O1). Icarus 141, 1–12, 1999. Weiler, M., Rauer, H., Knollenberg, J., et al. The dust activity of Comet C/1995 O1 (Hale-Bopp) between 3 AU and 13 AU from the Sun. Astron. Astrophys. 403, 313–322, 2003.