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Table 2: Summary of papers published in refereed journals describing observations of comets at Nançay (see text for other publications).

Comet	reference
Kohoutek 1973 XII	Biraud et al. (1974)
Kobayashi-Berger-Milon 1975 IX	Despois et al. (1981)
West 1976 VI	Despois et al. (1981)
P/Encke 1977 XI	Despois et al. (1981)
Kohler 1977 XIV	Despois et al. (1981)
Bradfield 1978 VII	Despois et al. (1981)
Meier 1978 XXI	Bockelée-Morvan et al. (1981)
Bradfield 1979 XX	Bockelée-Morvan et al. (1981)
P/Encke 1980 XI	Bockelée-Morvan et al. (1981)
Meier 1980 XII	Bockelée-Morvan et al. (1981)
Bradfield 1980 XV	Bockelée-Morvan et al. (1981)
Austin 1982 VI	Bockelée-Morvan & Gérard (1984), Gérard (1985), Bockelée-Morvan et al. (1990a)
27P/Crommelin	Bockelée-Morvan et al. (1985)
Austin 1984 XIII	Bockelée-Morvan et al. (1990a)
21P/Giacobini-Zinner 1985 XIII	Gérard et al. (1988), Bockelée-Morvan et al. (1990a)
Hartley-Good 1985 XVII	Bockelée-Morvan et al. (1990a)
Thiele 1985 XIX	Bockelée-Morvan et al. (1990a)
1P/Halley	Gérard et al. (1987), Colom & Gérard (1988), Gérard et al. (1989), Gérard (1990),
	Bockelée-Morvan et al. (1990a)
Sorrells 1987 II	Bockelée-Morvan et al. (1990a)
Wilson 1987 VII	Bockelée-Morvan et al. (1990a)
Bradfield 1987 XXIX	Bockelée-Morvan et al. (1990a)
Okazaki-Levy-Rudenko 1989 XIX	Crovisier et al. (1992)
Zanotta-Brewington 1992 III	Bockelée-Morvan et al. (1994)
Bradfield 1992 VII	Bockelée-Morvan et al. (1994)
Mueller 1992 VIII	Bockelée-Morvan et al. (1994)
Shoemaker -Levy 1992 XIX	Bockelée-Morvan et al. (1994)
109P/Swift-Tuttle 1992 XXVIII	Bockelée-Morvan et al. (1994)
24P/Schaumasse 1993 III	Bockelée-Morvan et al. (1994)
73P/Schwassmann-Wachmann 3	Crovisier et al. (1996a)
C/1996 B2 (Hyakutake)	Gérard et al. (1998)
C/1995 O1 (Hale-Bopp)	Biver et al. (1996, 1997), Colom et al. (1999)
C/1999 H1 (Lee)	Biver et al. (2000)

Appendix A: Comments on individual comets

Comments on individual comets are given below. Comets are listed following their perihelion dates as in Table 1. Individual passages (for 2P/Encke and 21P/Giacobini-Zinner) are listed separately.

A.1 Bowell 1982 I (1980b)

Table A.1 and Figs. A.1a to A.1d.

This comet reached perihelion on 12 March 1982, at q = 3.36 AU from the Sun. Despite its large heliocentric distance, it was very active and presented occasional outbursts (A'Hearn et al. 1984). The UV bands of OH were detected as far as r = 5.3 AU from the Sun, which is unusual, and which was attributed to an important icy grain halo whose very large surface compensated the weak water sublimation at that heliocentric distance (A'Hearn et al. 1984). These observations and speculations motivated the observations at Nançay. They suffered from internal interferences in the receiving system. As a consequence, the 1665 MHz data are spoiled. The comet was not detected when observed again late after perihelion: this could be due to the disappearance of the icy grains after perihelion, as suggested by the decrease of the OH signal observed in the UV.

Figure A.1:

A.2 26P/Grigg-Skjellerup 1982 IV (1982a)

Table A.2 and Figs. A.2a to A.2d.

This short-period comet (period P = 5.09 years; perihelion on 14 April 1982 at q = 0.99 AU) was not detected at Nançay, despite the favourable distance to the Earth ( $\Delta = 0.40$ AU). The integrated spectra reveal a marginal signal which is too broad to be of cometary origin. This comet was the target of the Giotto Extended Mission (GEM) in July 1992. The Nançay upper limit Q[OH] $< 1.5 \times 10^{28}$ s^-1 is consistent with the production rates derived from optical observations at that time.

Figure A.2:

A.3 Austin 1982 VI (1982g)

Table A.3 and Figs. A.3a to A.3g.

The Nançay observations of this comet (perihelion on 24 August 1982 at q = 0.65 AU) extended from the end of June to the beginning of September 1982. In August, the comet approached the Earth to only $\Delta = 0.33$ AU. The June observations were made according to the elements of IAU Circ. 3706. In July, the elements of IAU Circ. 3708 were used, resulting in a position error increasing with time and amounting to about 1.5 beams in right ascension at the end of the month. Despite this offset, the comet was detected at the end of July. The ephemeris was updated in August with the elements of IAU Circ. 3716 and a strong signal was detected at the correct position. At the end of August and in September, the position error, according to the IAU Circ. 3721 elements, was only a small fraction of the beam.

Figure A.3:

In early August, the peak line intensity exceeded 0.25 K at 1667 MHz, which was then the strongest cometary signal ever recorded at Nançay (the signal was strengthened in part due to enhanced background radiation when the comet crossed the galactic plane on August 5). The high signal-to-noise ratios and the high spectral resolution of these data permitted an analysis of the line profiles to derive the kinematic properties of the coma (Bockelée-Morvan & Gérard 1984; Bockelée-Morvan et al. 1990a), and a study of the Zeeman effect in order to estimate the magnetic field within the coma (Gérard 1985). The satellite lines were also observed and marginally detected.

Schenewerk et al. (1986) reported unsuccessful observations of this comet at the VLA (Very Large Array).

A.4 6P/d'Arrest 1982 VII (1982e)

Table A.4 and Figs. A.4a to A.4g.

This short-period comet (P = 6.38 years; perihelion on 14 September 1982 at q = 1.29 AU) was observed at Nançay during most of July and August 1982 when it was at $\Delta \approx 0.7$ AU. The integration of all spectra shows a marginal detection of the comet at the 3-$\sigma$ level. This comet is known to have a very asymmetric light curve, being brighter post-perihelion, where the water production rate could be as high as $3 \times 10^{28}$ s^-1 according to IUE observations (Festou et al. 1992). The Nançay observations were made only pre-perihelion, the maser inversion being unfavourable post-perihelion.

The OH radio lines were observed in 6P/d'Arrest at its preceding return in July 1976, when it was at $\Delta = 0.2$ AU, by Webber & Snyder (1977); these authors claimed detection of the 1665 MHz line in emission and of the 1667 MHz line in absorption, but the signal-to-noise ratio was poor.

Figure A.4:

A.5 67P/Churyumov-Gerasimenko 1982 VIII (1982f)

Table A.5 and Figs. A.5a to A.5d.

This short-period comet (P = 6.61 years; perihelion on 12 November 1982 at q = 1.31 AU) was observed on October 1982 taking advantage of a favourable geocentric distance ( $\Delta \approx 0.50$ AU). Like for comet Bowell 1982 I, internal interferences in the receiving system ruined most of the observations and only part of the 1667 MHz spectra could be analysed. The integration of all spectra shows a marginal detection of the comet at the 3.5-$\sigma$ level.

Figure A.5:

A.6 27P/Crommelin 1984 IV (1983n)

Table A.6 and Figs. A.6a to A.6g.

This weak comet (P = 27.4 years; perihelion on 10 February 1984 at q = 0.73A) was proposed as a "trial run comet" in order to prepare the international campaign of 1P/Halley's observations. This comet was hardly detectable.

The significant average spectra from the Nançay observations were published, together with observations made with the Effelsberg 100-m and Green Bank 43-m telescopes, by Bockelée-Morvan et al. (1985). They are also included in the International Halley Watch (IHW) archive (IHW Archive 1992). The comet was also observed unsuccessfully at Arecibo (Deich et al. 1985) and at the VLA (Schenewerk et al. 1986).

Figure A.6:

A.7 Austin 1984 XIII (1984i)

Table A.7 and Figs. A.7a to A.7d.

The comet (perihelion on 12 August 1984 at only q = 0.29 AU) was clearly detected at Nançay as soon as the observations were possible (Gérard & Drouhin 1984). At that moment, an outburst was obviously present, since the signal disappeared afterwards more rapidly than expected. See also Bockelée-Morvan et al. (1990a).

Figure A.7:

A.8 21P/Giacobini-Zinner 1985 XIII (1984e)

Tables A.8a and A.8b and Figs. A.8a to A.8v.

This comet was designated as a target for an international campaign of observation in order to provide a ground support for its fly-by by the International Comet Explorer (ICE) spacecraft on September 11, 1985. It reached perihelion on 5 September 1985 at q = 1.03 AU (coinciding with the closest approach at $\Delta = 0.47$ AU). The Nançay observations were published by Gérard et al. (1988). They are included in the IHW archive (IHW Archive 1992) as well as OH radio observations by several other groups which are not given in detail here. See also Bockelée-Morvan et al. (1990a).

Figure A.8a:

Figure A.8b:

A.9 Hartley-Good 1985 XVII (1985l)

Tables A.9a and A.9b and Figs. A.9a to A.9r.

This comet (perihelion on 9 December 1985 at q = 0.69 AU) was observed daily from the end of September 1985 to mid-January 1986. It was detectable until the end of November. See Gérard et al. (1986) and Bockelée-Morvan et al. (1990a).

This comet was also observed at the Green Bank 43-m telescope (Tacconi-Garman et al. 1990).

Figure A.9a:

Figure A.9b:

A.10 Thiele 1985 XIX (1985m)

Tables A.10a and A.10b and Figs. A.10a to A.10g.

This comet (perihelion on 19 December 1985 at q = 1.32 AU) was observed daily at Nançay from the end of October to mid-December. It was clearly detected on integrated spectra. See Gérard et al. (1986) and Bockelée-Morvan et al. (1990a).

This comet was also observed at the Green Bank 43-m telescope (Tacconi-Garman et al. 1990).

Figure A.10:

A.11 1P/Halley 1986 III (1982i)

Tables A.11a to A.11c and Figs. A.11a to A.11bz (including offset position spectra).

This comet (perihelion on 9 February 1986 at q = 0.59 AU) was the object of a well documented international observing campaign (International Halley Watch IHW) as a support to its space exploration. The Nançay observations of this comet were published by Gérard et al. (1989) and are included in the IHW archive (IHW Archive 1992). They are not discussed in detail here. See also Gérard et al. (1987), Colom & Gérard (1988), Gérard (1990) and Bockelée-Morvan et al. (1990a).

Many other radio observations of this comet were performed, like the OH excited lines, the microwave transitions of other molecules and the continuum (see Crovisier & Schloerb 1991 and IHW Archive 1992).

Figure A.11a:

Figure A.11b:

Figure A.11c:

Figure A.11d:

A.12 Sorrells 1987 II (1986n)

Table A.12 and Figs. A.12a to A.12c.

This comet (perihelion on 9 March 1987 at q = 1.72 AU) was detected in January-February 1987. See also Bockelée-Morvan et al. (1990a).

Figure A.12:

A.13 Nishikawa-Takamizawa-Tago 1987 III (1987c)

Table A.13 and Figs. A.13a to A.13c.

This comet (perihelion on 17 March 1987 at q = 0.87 AU) was observed and detected in early March. Like for the preceding one, the signal-to-noise ratio was not large enough to justify continuous and detailed observations.

Figure A.13:

A.14 Wilson 1987 VII (1986l)

Tables A.14a and A.14b and Figs. A.14a to A.14w.

This comet was discovered in August 1986, well ahead of perihelion (20 April 1987, at q = 1.20 AU). It was observed at Nançay from the end of August 1986 until the end of June 1987. The comet was, as a rule, monitored every second day, except from 5 April to 15 May when it was under the declination range accessible to the telescope (which, unfortunately, was the period of closest approach to the Sun and to the Earth). At other times, the comet was observed daily: at the beginning of the observing period and around the moment of molecular millimetre observations with the IRAM (Institut de radioastronomie millimétrique) 30-m telescope (Crovisier et al. 1987; Crovisier et al. 1990).

The comet was detected right at the beginning of the observations, at the end of August 1986 when it was at r = 2.8 AU, as a weak and narrow line (Gérard 1987). The comet, which was detectable all along the observing period, is one of the comets best studied at large heliocentric distances, allowing us to study the kinematics of H₂O and OH at large heliocentric distances. The production rate increased significantly from October to November 1986 (Gérard et al. 1986) and high signal-to-noise spectra were secured. These observations represent, besides 1P/Halley's and C/1995 O1 (Hale-Bopp) observing campaigns, the most continuous and rewarding cometary project undertaken at Nançay. See also Bockelée-Morvan et al. (1990a).

This comet was also observed and detected at the Green Bank 43-m telescope (Tacconi-Garman et al. 1990) and at the VLA (Palmer et al. 1989).

Figure A.14a:

Figure A.14b:

Figure A.14c:

A.15 Bradfield 1987 XXIX (1987s)

Tables A.15a and A.15b and Figs. A.15a to A.15g.

This relatively bright comet (perihelion on 7 November 1987 at q = 0.87 AU) was observed daily during October and the second half of November 1987. It was detected during the whole period. See also Bockelée-Morvan et al. (1990a).

Figure A.15:

A.16 Ichimura 1988 I (1987d₁)

Table A.16 and Figs. A.16a to A.16c.

This comet was included in Nançay observing program because of its small perihelion distance (q = 0.20 AU on 10 January 1988) in order to test the quenching models versus heliocentric distance. It was tracked from orbital elements given in IAU Circ. 4505. It was found afterwards (MPC 12710) that the tracked position was offset by 0.4 to $1.0\hbox{$^\prime$ }$ in right ascension relative to the comet nucleus, which has negligible influence on the observations. In the integration of the 4-6 January spectra, the comet was detected at the 4.5-$\sigma$ level as a relatively broad line. This increased line width is likely due to the small heliocentric distance: with an average value of r = 0.26 AU, the heliocentric distance of the observation is the smallest at which the OH radio lines were detected.

Figure A.16:

A.17 Liller 1988 V (1988a)

Table A.17 and Figs. A.17a and A.17b.

This comet (perihelion on 31 March 1988 at q = 0.85 AU) was observed at Nançay to complement the OH observations scheduled at the VLA (de Pater et al. 1991). The comet was tracked from parabolic orbital elements given in MPC 12587. Subsequent improved elliptic elements (MPC 13459) revealed that on March 22, the tracking was offset by $1.3\hbox{$^\prime$ }$ in right ascension, $-5.5\hbox{$^\prime$ }$in declination and 0.27 km s^-1 in velocity. The resulting line area is underestimated by a factor of 1.35. The comet was nevertheless clearly detected in the integration of the 6 spectra.

Figure A.17:

A.18 Machholz 1988 XV (1988j)

Table A.18 and Figs. A.18a to A.18d.

This comet was discovered at the beginning of August 1988; a simple extrapolation of its light curve predicted that this object could be very interesting in mid September, because of its small perihelion distance (only 0.15 AU on 17 September 1988; IAU Circ. 4637, 4644). Millimetre observations of HCN could be scheduled on short notice at IRAM 30-m telescope (Crovisier et al. 1990). Unfortunately, the Nançay radio telescope was closed for maintenance in September; it was nevertheless possible to squeeze observations on September 12-13. We used orbital elements from Green (1988, personal communication) almost identical to those given in MPC 13591.

Comet Machholz did not behave as expected. Its brightness ceased to increase at the beginning of September. It was then lost optically because of its small solar elongation. Deep searches between 25 and 35 days after perihelion were negative (IAU Circ. 4669). It is thus one of those comets which disappears near perihelion. The moment at which the comet actually ceased outgassing is unknown. The Nançay observation gives an upper limit to its activity around perihelion.

This comet was observed at 18 cm at the VLA (de Pater et al. 1991), also unsuccessfully.

Figure A.18:

A.19 23P/Brorsen-Metcalf 1989 X (1989o)

Table A.19a and A.19b and Figs. A.19a to A.19m.

This comet is of the Halley type with a period of 70.6 years. It was already observed at its two last passages and had a favourable return in 1989 (perihelion on 11 September 1989 at q = 0.48 AU; closest approach to Earth: $\Delta = 0.62$ AU at the beginning of August). It appeared to be the best opportunity among short-period comets until the end of the century, besides 1P/Halley and 109P/Swift-Tuttle (whose return was still speculative at that time). Therefore, several observations on large instruments could be scheduled and an observing campaign could be coordinated. The Nançay radio telescope participated in this campaign by observing this comet almost daily from the beginning of August until the end of October. Until September 30, the observations were made with orbital elements of IAU Circ. 4805. Later, osculating elements for October 1 provided by Yeomans (personal communication, August 11, 1989) were used.

The comet was detected at the beginning of the observations; at that moment, the signal was weak due to the low inversion of the OH $\Lambda$-doublet. Spectra with high signal-to-noise ratios were obtained at the end of August-beginning of September. In October, the comet could only be detected after long integration times, showing that the gas production rate was smaller post-perihelion than pre-perihelion (Bockelée-Morvan et al. 1990b).

Like the following comets, this comet was observed at a time of high solar activity. As a consequence, the water life time is expected to be shorter (by a factor which may be as high as two), and the quenching by collisions with ions may be higher (due to the higher ionization rate by solar UV), compared to periods of quiet Sun.

This comet was also observed (but not detected) at the Green Bank 43-m telescope (Schloerb 1989, personal communication, as quoted by Crovisier 1992).

Figure A.19a:

Figure A.19b:

A.20 Okazaki-Levy-Rudenko 1989 XIX (1989r)

Tables A.20a and A.20b and Figs. A.20a to A.20k.

This comet (perihelion on 11 November 1989 at q = 0.64 AU; closest approach to Earth at $\Delta = 0.52$ AU at the beginning of December) was detected after the first few days of observation in October. It was observed until December 2, when it was below the southern declination limit at Nançay. Observations of 3-7 October were made with the orbital elements of MPC 15053; the error in right ascension was $-0.7\hbox{$^\prime$ }$. All subsequent observations were made with orbital elements of MPC 15215; the maximum error was $0.4\hbox{$^\prime$ }$in right ascension and $1.5\hbox{$^\prime$ }$ in declination at the end of November (with respect to final elements of MPC 15520).

On October 13.54 we observed serendipitously the occultation of a background point radio source by this comet (Bockelée-Morvan et al. 1989; Crovisier et al. 1992): the line has increased in intensity and decreased in width, compared to the average line observed before and after the occultation of the source B2 1426+295, as expected from the hypothesis of the OH maser amplification of the background. From mid-October until the end of November, the OH production rate derived from the radio observations is nearly constant, despite the varying distance to the Sun (Bockelée-Morvan et al. 1990b).

This comet was also observed at the VLA (de Pater et al. 1989, personal communication) and with the Green Bank 43-m telescope (Schloerb 1989, personal communication, as quoted by Crovisier 1992).

Figure A.20a:

Figure A.20b:

A.21 Aarseth-Brewington 1989 XXII (1989a₁)

Table A.21 and Figs. A.21a to A.21e.

This comet (perihelion on 27 December 1989 at q = 0.30 AU) was observed from December 8 until December 30 when it went below the declination range accessible to the Nançay telescope. Observations were made with orbital elements of MPC 15520; the position errors (RA, $\delta$), which were negligible at the beginning of the observations, were ( $0.4\hbox{$^\prime$ }$, $0.7\hbox{$^\prime$ }$) on Dec. 25, ( $1.0\hbox{$^\prime$ }$, $0.6\hbox{$^\prime$ }$) on Dec. 30 with respect to confirmed elements of MPC 15672.

The comet was easily detected until Dec. 17. Afterwards, the signal was harder to extract, due to the rapidly changing OH inversion near perihelion, and presumably of the large collisional quenching at this small solar distance (Bockelée-Morvan et al. 1990b).

Figure A.21:

A.22 Austin 1990 V (1989c₁)

Tables A.22a and A.22b and Figs. A.22a to A.22t.

This comet passed perihelion on 9 April 1990 at q = 0.35 AU and made a close approach to Earth at $\Delta = 0.24$ AU on 25 May 1990. The observations are described by Bockelée-Morvan et al. (1990b). Successful millimetre observations of this comet were also conducted at IRAM.

Figure A.22a:

Figure A.22b:

Figure A.22c:

A.23 Levy 1990 XX (1990c)

Tables A.23a to A.23c and Figs. A.23a to A.23v (including offset position spectra).

This comet passed perihelion on 24 October 1990 at q = 0.94 AU. The observations are described by Bockelée-Morvan et al. (1992) and Gérard et al. (1993). The strong OH lines allowed to detect the satellite lines and the Zeeman effect. It was the first comet in which a reversal of the projected magnetic field was observed. The evolution of the magnetic field seems to be correlated with $\sin \theta \sin \phi$, $\theta$ being the Sun-comet-Earth angle and $\phi$ the heliomagnetic latitude of the comet (Gérard et al. 1993).

Successful millimetre observations of this comet were also conducted at IRAM. An analysis of the OH radio line shapes was made by Xie (1994).

Figure A.23a:

Figure A.23b:

A.24 Zanotta-Brewington 1992 III (1991g₁)

Table A.24 and Figs. A.24a to A.24d.

This comet passed perihelion on 31 January 1992 at q = 0.64 AU. It was detected in mid-January. Post-perihelion observations were not possible because of the low declination of the comet. See also Bockelée-Morvan et al. (1994).

Figure A.24:

A.25 Bradfield 1992 VII (1992b)

Table A.25 and Figs. A.25a to A.25c.

This comet passed perihelion on 19 March 1992 at q = 0.50 AU. OH could not be detected pre-perihelion. It was not recovered post-perihelion from visible observations (IAU Circ. 5469). See also Bockelée-Morvan et al. (1994).

Figure A.25:

A.26 Mueller 1992 VIII (1991h₁)

Table A.26 and Figs. A.26a to A.26c.

This comet passed perihelion on 21 March 1992 at only q = 0.20 AU. Like the preceding one, it could not be detected pre-perihelion at Nançay (the feature on the integrated spectrum is due to interferences) and was not recovered post-perihelion from visible and infrared observations (IAU Circ. 5482 and 5496). See also Bockelée-Morvan et al. (1994).

Figure A.26:

A.27 Shoemaker-Levy 1992 XIX (1991a₁)

Tables A.27a and A.27b and Figs. A.27a to A.27h.

This comet passed perihelion on 23 August at q = 0.83 AU. The observations are described by Bockelée-Morvan et al. (1994).

Figure A.27:

A.28 109P/Swift-Tuttle 1992 XXVIII (1992t)

Tables A.28a to A.28c and Figs. A.28a to A.28m (including offset position spectra).

The observations of this Halley-type comet (P = 135 years, perihelion on 12 December 1992 at q = 0.96 AU) are described by Colom et al. (1992) and Bockelée-Morvan et al. (1994). Strong asymmetries were observed in the OH lines as well as in the molecular millimetre and submillimetre lines observed at IRAM and with the JCMT (James Clerk Maxwell Telescope) (Bockelée-Morvan et al. 1994; Despois et al. 1996), which could be the counterpart of the strong dust jets observed in the visible.

Figure A.28a:

Figure A.28b:

A.29 24P/Schaumasse 1993 III (1992x)

Tables A.29a and A.29b and Figs. A.29a to A.29f.

This comet, which passed perihelion on 3 March 1993 at q = 1.20 AU, was formerly a possible target for the ROSETTA mission. It was detected at Nançay in January-February 1993. These observations are described by Bockelée-Morvan et al. (1994).

Figure A.29:

A.30 2P/Encke 1994 V

Tables A.30a and A.30b and Figs. A.30a to A.30g.

Despite a long integration time and a rather favourable return ( $\Delta \approx 0.63$ AU), the comet was - at most - only marginally detected. Thus our observations of the same comet in 1980 (Bockelée-Morvan et al. 1981), favoured by the crossing of the galactic plane, could not be improved.

Figure A.30:

A.31 Mueller 1994 IX (1993p)

Tables A.31a and A.31b and Figs. A.31a to A.31h.

This comet reached perihelion on 26 March 1994 at q = 0.97 AU. It was observed and detected at Nançay during two runs in February and March. The tracking was based upon the elements of MPC 22663 and 23106, the position error being at most $0.2\hbox{$^\prime$ }$ in RA in February.

Figure A.31:

A.32 McNaught-Russell 1994 XI (1993v)

Tables A.32a and A.32b and Figs. A.32a to A.32f.

This comet reached perihelion on 31 March 1994 at q = 0.87 AU from the Sun and was then relatively close to the Earth ( $\Delta \approx 0.6$ AU). The observations were made using elements of MPC 23107 and 23224, which did not significantly differed, for the positions at the moment of the observations, from the confirmed elements of MPC 23322. The comet was detected during three observing runs in March and April at Nançay.

Figure A.32:

A.33 8P/Tuttle 1994 XV (1992r)

Table A.33 and Figs. A.33a to A.33c.

8P/Tuttle was observed at Nançay just before its perihelion on 25 June 1994 (MPC 20775) at q = 1.00 AU. Despite its large geocentric distance, but benefiting from an enhanced background continuum, this comet was marginally detected with a production rate ($\approx$ $3 \times 10^{28}$ s^-1) in agreement with that determined optically at its preceding passage in 1980 (A'Hearn et al. 1995).

Figure A.33:

A.34 141P/Machholz 2 1994 XXVI (1994o)

Table A.34 and Figs. A.34a to A.34c.

141P/Machholz 2 passed perihelion on September 18, 1994, at q = 0.75 AU. Soon after its discovery, this comet was found to have multiple nuclear components (IAU Circ. Nos. 6066, 6070 and 6071). The Nançay observations, made on September 1994 just before perihelion, were aimed at the main component. We used elements of MPC 23858, which at the time of the observations differed by less than $0.3\hbox{$^\prime$ }$ in RA from the confirmed elements of MPC 23956. We only obtained a marginal detection with an intensity lower than that expected from its visual magnitude. We infer that the brightness of the comet in the visible was enhanced by the release of dust following the disruption of its nucleus.

Figure A.34:

A.35 19P/Borrelly 1994 XXX (1994l)

Tables A.35a and A.35b and Figs. A.35a to A.35j.

19P/Borrelly, which was the flyby target of the Deep Space 1 mission on 22 September 2001, made a favourable return in 1994, staying at $\Delta \approx 0.65$ AU in November-December. It passed perihelion on November 1, 1994, at q = 1.37 AU. This comet was observed as part of a campaign which included radio observations at IRAM and at the JCMT, space observations with IUE and the HST, and several ground-based observations in the visible.

19P/Borrelly was detected at Nançay during the 5 September-11 October pre-perihelion period (Bockelée-Morvan et al. 1995), with a production rate of $\approx$ $2.5 \times10^{28}$ s^-1, whereas the production rate expected at perihelion from previous observations is $\approx$ $5 \times 10^{28}$ s^-1. It could not be detected in a post-perihelion run in January 1995 (upper limit < $2\times 10^{28}$ s^-1), presumably because of unfavourable observing conditions (high declination and weaker maser inversion).

Figure A.35:

A.36 15P/Finlay (1995 passage)

Table A.36 and Figs. A.36a to A.36d.

15P/Finlay was one of the backup targets for the ROSETTA international mission. Its 1995 return (perihelion on 15 May 1995 at q = 1.04 AU) was not favourable, the comet being on the other side of the Sun, always at a small solar elongation and at $\Delta > 1.9$ AU from the Earth. Thus it could not be recovered before the Nançay observations, which were based on elements extrapolated from last passage astrometric positions (MPC 20122). Observed in April 1995, the comet was not detected, the upper limit on the gas production rate (< $2.5 \times10^{28}$ s^-1) being in agreement with the expected production rate from the visible magnitudes ($\approx$ $2\times 10^{28}$ s^-1) according to Jorda et al. (1996).

Figure A.36:

A.37 C/1995 Q1 (Bradfield)

Table A.37 and Figs. A.37a to A.37d.

This comet was discovered late, just before its perihelion passage (on August 31, 1995, at q = 0.44 AU). It was then as bright as $m_{\rm v} = 5.5$. The first observations were made (until September 5) using orbital elements communicated by Marsden (personal communication), close to those published in IAU Circ. 6208. Then, elements of MPC 25623 were used. The RA offset was $0.8\hbox{$^\prime$ }$on 4 September. The OH lines were detected at the 5-$\sigma$ level around perihelion (August 24-September 5).

Figure A.37:

A.38 73P/Schwassmann-Wachmann 3 (1995 passage)

Tables A.38a and A.38b and Figs. A.38a to A.38h.

73P/Schwassmann-Wachmann 3 was formerly the nominal target of the ROSETTA international mission and was present in the list of backup targets. From the visual magnitudes observed at its preceding passages, the OH production rate of this comet was expected to be only of the order of $2\times 10^{28}$ s^-1. The comet was observed at Nançay from the beginning of September 1995, before its perihelion on 22 September at q = 0.93 AU. No signal was detected during the first days of observation. Unexpectedly, a signal appeared on September 8 and persisted on the following days, as long as the inversion was significant (Crovisier et al. 1995). The corresponding production rate is about $2\times 10^{29}$ s^-1, ten times larger than expected. This strongly suggests that the comet had an outburst. Following the announcement of this unexpected high production rate, visible observations revealed that the comet was indeed in a state of outburst with $m_{\rm v} \approx 8.3$, i.e., a brightening of $\sim$5 mag. (IAU Circ. 6234). Images taken at a later time showed that the comet nucleus had split (IAU Circ. 6274).

We benefited from the passage of the comet in front of the galactic centre region at the end of October 1995 to observe an enhanced signal due to the stronger background continuum. A full account of these observations is given by Crovisier et al. (1996a).

Figure A.38a:

Figure A.38b:

A.39 122P/de Vico (1995 passage)

Table A.39 and Figs. A.39a to A.39c.

This Halley-type comet (P = 74.4 years), which was considered as lost after its 1846 apparition, was recovered only three weeks before its perihelion (6 October 1995 at q = 0.66 AU). Observations could be organized at Nançay around perihelion, revealing a production rate exceeding $2\times 10^{29}$ s^-1.

Figure A.39:

A.40 45P/Honda-Mrkos-Pajdusáková (1996 passage)

Tables A.40a and A.40b and Figs. A.40a to A.40g.

This comet passed at only $\Delta = 0.17$ AU from the Earth on 6 February 1996 after its perihelion on 25 December 1995 at q = 0.53 AU. Millimetre and submillimetre observations were attempted at the JCMT at the moment of the closest approach. Only marginal detections could be obtained at Nançay.

Figure A.40:

A.41 C/1996 B2 (Hyakutake)

Tables A.41a and A.41b and Figs. A.41a to A.41i.

C/1996 B2 (Hyakutake) made a very close approach to Earth at only $\Delta = 0.11$ AU on 25 March 1996 before its perihelion on 1 May 1996 at q = 0.23 AU, which made it an exceptionally bright comet at the end of March.

This comet was observed at Nançay since the first of March 1996. Rough mapping revealed stronger signal at offset positions, indicating the effect of quenching. The OH satellite lines could be detected, but only a marginal Zeeman effect could be observed. These observations were reported by Gérard et al. (1998). The spectra obtained at offset positions are not presently included in the data base.

The OH 18-cm lines were searched for, but not detected, at the VLA around perihelion time (de Pater, personal communication). It was the object of extensive millimetre and submillimetre observations.

Figure A.41:

A.42 22P/Kopff (1996 passage)

Tables A.42a and A.42b and Figs. A.42a to A.42h.

This Jupiter-family comet (perihelion on 2 July 1996 at q = 1.58 AU) was designated as a target for the ISO Central Program. It was observed pre-perihelion at Nançay using orbital elements provided by the Bureau des longitudes during most of April and May 1996. Despite its small OH production rate ($\approx$ $2.5 \times10^{28}$ s^-1), it was easily detected since the beginning of the observations, benefiting from enhanced galactic continuum when it crossed the galactic plane (at $l = 14.5\hbox{$^\circ$ }$ on 24 May). Galactic contamination was noted at that moment; it was especially strong on May 26 when the comet passed across the radio source M 17.

The log of the observations of 22P/Kopff is given in Table 5 and representative spectra are shown in Fig. 1, as an example of the data which are only available electronically.

This comet was also observed at IRAM.

Figure A.42:

A.43 C/1996 Q1 (Tabur)

Table A.43 and Figs. A.43a to A.43d.

C/1996 Q1 (Tabur) passed perihelion on 3 November 1996 at q = 0.84 AU. Its orbit similar to that of comet Liller 1988 V strongly suggests that both objects are fragments from the same parent body. It made a close approach to Earth in early October 1996 (0.42 AU) and was then very easily observable at Nançay with a production rate $\approx$ $5 \times 10^{28}$ s^-1. It could not be detected on 20-27 October, with a production rate upper limit 5 times smaller that observed at the beginning of October. Its visual brightness dropped similarly at the same moment. This comet may have had a fate similar to that of comet C/1999 S4 (LINEAR), whose nucleus was completely disrupted close to perihelion. This comet was also observed at IRAM.

Figure A.43:

A.44 C/1995 O1 (Hale-Bopp)

Tables A.44a to A.44c and Figs. A.44a to A.44dn (including offset position spectra).

This comet was intrinsically very bright ( $m_{\rm v} \approx 10.5$) when it was detected in July 1995, at more than 7 AU from the Sun. This comet was about 100 times brighter than P/Halley at the same heliocentric distance. It passed perihelion on 1 April 1997, at q = 0.91 AU. An international campaign was organized for this comet, also designated as an exceptional target-of-opportunity comet for ISO observations.

A first try to detect OH at Nançay in this comet, on 4-9 August 1995 when it was at r = 7 AU, was negative (Biver et al. 1996). The upper limit is $2\times 10^{29}$ s^-1 with the standard model. However, CO production rates of several 10²⁸ s^-1 were measured soon after at the JCMT (IAU Circ. 6234) and at IRAM (IAU Circ. 6236 and Biver et al. 1996). Periodic observations of this comet were made at the rate of about 8 days every month in order to detect the onset of water sublimation from its icy grains. The first OH detection at 18-cm was made in mid-April 1996 (Crovisier et al. 1996b), just after its detection in the UV by the HST (IAU Circ. 6376). The comet was then at 4.7 AU from the Sun: this is the farthest heliocentric distance at which 18-cm OH has been detected. More regular observations could be done afterwards, allowing a detailed monitoring of its OH production rate, to be compared with the monitoring of production rates of other molecules at other wavelengths, and especially those made at IRAM, JCMT and CSO (Caltech Submillimeter Observatory). This monitoring is reported in Biver et al. (1997, 1999a) and Colom et al. (1999).

The comet was observed until September 1997, when it escaped the declination range accessible to Nançay. For a large part of the time, it was close to the galactic plane (it even passed in front of the W 49 galactic source). As long as the signal was strong (from 10 October 1996 to 3 August 1997), offset observations were made in addition to centre observations in order to better determine the quenching conditions (see Colom et al. 1999).

Other radio OH observations of this comet are summarized by Despois (1999).

An attempt to observe the 9-cm lines of the CH radical at Nançay was made from 30 April to 20 May 1997. Neither the 3263 nor the 3335 MHz line of CH was detected down to a 3-$\sigma$ level of 0.035 K km s^-1. The CH lines of a background source (L1534 of the Taurus molecular cloud complex), however, were detected at a velocity different from that of the comet, providing a check of the instrumentation. Detection of the 9-cm radio lines of CH in comet Kohoutek (1973 XII) was claimed by Black et al. (1974), but could not be confirmed (Rydbeck et al. 1974). These lines are $\Lambda$-doubling transitions within the $X^2\Pi$ rotational ground state of CH, similar to the 18-cm lines of OH. Their excitation should also be similar and governed by fluorescence of the A-X system in the violet: one would expect weakly masering lines, with inversion of the $\Lambda$-doublet depending upon the heliocentric velocity. The model has never been made, but even in case of maximum inversion, one would expect lines much weaker than the OH 18-cm lines because of the smaller column density of CH (the lifetime of CH is much shorter than that of OH).

Figure A.44a:

Figure A.44b:

Figure A.44c:

Figure A.44d:

Figure A.44e:

Figure A.44f:

Figure A.44g:

A.45 46P/Wirtanen (1997 passage)

Tables A.45a and A.45b and Figs. A.45a to A.45h.

46P/Wirtanen is the target of the ROSETTA mission. It passed perihelion on 14 March 1997 at q = 1.06 AU. The observing conditions of the present return were highly unfavourable, the comet being at small solar elongation and at $\Delta > 1.5$ AU. The comet was observed at Nançay during two periods, pre- and post-perihelion, when the inversion of the OH maser is predicted to be high. The OH lines could not be detected. Since during these two periods, the observing conditions (distances to Sun and Earth, OH maser inversion) were practically constant, the spectra were averaged over each period of observation. We thus derived Q[OH] $< 1.5 \times 10^{28}$ s^-1 between beginning of February and beginning of March, Q[OH] $< 2.4 \times 10^{28}$ s^-1 between end of April and beginning of May (Crovisier et al. 2001).

From the light curves of previous returns, Jorda & Rickman (1995) and Rickman & Jorda (1998) evaluated the water production rate of 46P/Wirtanen to be 1.5-6 $\times 10^{28}$ s^-1 at perihelion. A'Hearn et al. (1995) measured Q[OH] $\sim 1.1 \times 10^{28}$ s^-1 close to the perihelion of the 1991 return; as discussed by Rickman & Jorda (1998), this evaluation might be an underestimate because of the use of inappropriate parameters in the Haser model describing the OH distribution.

During the 1997 return, optical observations could only be performed pre-perihelion due to unfavourable viewing conditions. Using the FOS instrument of the Hubble Space Telescope on 15 January (at r = 1.3 AU from the Sun) to measure the OH band in the UV, Stern et al. (1998) reported a water production rate $\sim$ $0.6 \times 10^{28}$ s^-1. From measurements of the Ly $\alpha$ line with the SWAN instrument aboard the SOHO spacecraft, Bertaux et al. (1999) estimated Q[H₂O] $= 1.6 \pm 0.4 \times 10^{28}$ s^-1 near perihelion. Farnham & Schleicher (1998) measured $Q{\rm [OH]} = 0.8 \times 10^{28}$ s^-1 from narrow-band photometry at Lowell Observatory on 5 March (r = 1.07 AU).

The intercomparison of these results and of the Nançay limits is not direct because the production rates were not always derived with the same Haser model parameters for OH. However, the non-detections at Nançay appear to be consistent with the low production rates derived from the UV observations.

Figure A.45:

A.46 81P/Wild 2 (1997 passage)

Tables A.46a and A.46b and Figs. A.46a to A.46h.

81P/Wild 2 (the target of the Stardust mission) passed perihelion on 6 May 1997 at q = 1.58 AU. It was observed at Nançay almost daily from the end of January to the end of March. This corresponds to the period of best observing conditions. The observations of this comet were more sensitive than those of comet 46P/Wirtanen due to the closest distance of the comet to the Earth. The comet is detected from the average of all the observations (Crovisier et al. 2001). The line is relatively narrow, with a width comparable to those observed for comets with small gas production rates (Bockelée-Morvan et al. 1990a). The production rate is Q[OH] $= 0.8 \pm 0.2 \times 10^{28}$ s^-1 at an average distance $r_{\rm h} = 1.74$ AU. With SOHO/SWAN, Mäkinen et al. (2001b) observed Q[H₂O] $= 1.3 \times 10^{28}$ s^-1 around perihelion, which compares well with our determination. Fink et al. (1999) also measured pre-perihelion production rates from the [OI] line which agree with ours.

Figure A.46:

A.47 2P/Encke (1997 passage)

Table A.47 and Figs. A.47a to A.47c.

2P/Encke was observed at its 1997 passage despite unfavourable conditions, as a programme proposed by M. C. Festou. It was not detected.

Figure A.47:

A.48 C/1998 J1 (SOHO)

Table A.48 and Figs. A.48a to A.48c.

As a consequence of the work for the upgrading of the radio telescope, comets could only be observed for less than 40 min in 1998 and 1999 instead of one hour.

C/1998 J1 (SOHO) was one of the many comets discovered by the space coronagraph LASCO aboard SOHO. It passed perihelion on 8 May 1998 at q = 0.15 AU. Unlike most of the other SOHO comets, this comet was not a member of the Kreutz family and was sufficiently bright post-perihelion to justify radio observations. Unfortunately, the astrometric positions provided by SOHO suffered from systematic errors and the first observations at Nançay were a failure. Only later observations made at the beginning of June on the basis of confirmed orbital elements from ground based observations (IAUC 6913) could be successful (Crovisier et al. 1998). They were made at the moment of an outburst noted by visual observers (IAUC 6926) and the production rate was as large as $\approx$ $3 \times 10^{29}$ s^-1. They had to be interrupted soon after when the comet passed below the declination limit of the radio telescope.

Figure A.48:

A.49 C/1998 P1 (Williams)

Table A.49 and Figs. A.49a to A.49c.

C/1998 P1 (Williams) (perihelion on 17 October 1998 at q = 1.15 AU) was barely detected during a short pre-perihelion run. This comet was also observed at the JCMT.

Figure A.49:

A.50 21P/Giacobini-Zinner (1998 passage)

Tables A.50a and A.50b and Figs. A.50a to A.50e.

The 1998 return of 21P/Giacobini-Zinner was less favourable than the 1985 return (see Sect. 5.8). However, the comet crossed the galactic plane at the end of October, resulting in a significantly enhanced signal. Observations at Nançay were scheduled in coordination with other radio and infrared observations at JCMT, CSO, IRAM and IRTF. The OH production rate was found to be close to that of the preceding return.

Figure A.50:

A.51 C/1998 U5 (LINEAR)

Table A.51 and Figs. A.51a to A.51d.

C/1998 U5 (LINEAR) (perihelion on 21 December 1998 at q = 1.24 AU) passed at $\Delta = 0.44$ AU on 16 November. Its brightness increased abruptly by $\approx$1.5 mag in mid-November. Observations began at Nançay on 24 November using orbital elements of MPC 32866, then the updated elements of MPEC 1998-W45. Only a marginal detection was obtained. This comet was also observed at the CSO.

Figure A.51:

A.52 C/1999 H1 (Lee)

Tables A.52a and A.52b and Figs. A.52a to A.52m.

C/1999 H1(Lee) passed perihelion on 11 July 1999 at q = 0.708 AU. It was easily detected pre-perihelion with a production rate that culminated at $1.5 \times 10^{29}$ s^-1, but could not be detected post-perihelion (Biver et al. 1999b). The observations are published together with the campaign of radio observations at other wavelengths (Biver et al. 2000).

Figure A.52a:

Figure A.52b:

A.53 C/1999 N2 (Lynn)

Table A.53 and Figs. A.53a and A.53b.

C/1999 N2 (Lynn) was discovered shortly before it passed perihelion (on 23 July 1999 at q = 0.761 AU). It was observed during four days pre-perihelion on short notice, and was just detected (production rate $\approx$ $6 \times 10^{28}$ s^-1).

Figure A.53: