5 Comets observed between 1982 and 1999

The rationale for cometary observations at Nançay evolved with time. In 1982, using for the first time a new receiver with a versatile backend, we tried to observe almost every "possible" object: five comets were observed, but only Austin 1982 VI yielded high quality spectra warranting meaningful scientific analyses. In the following years, we tried to optimize the scientific return of the observations by focusing our choice on bright comets, or on comets for which an observing campaign was set up. With some exceptions, the observations were scheduled only at the moments when the excitation of the OH radical was favourable.

  

Table 5: Detailed log of the observations of comet 22P/Kopff and results for integrations over selected periods of time (from Tables A.42a and A.42b). A comprehensive data set for all comets is available electronically.

The detailed log of all the observations made in 1982-1999 is given in tables available electronically. There is one entry per daily observation of a given comet. At the end of the set of observations of a given comet we also give the parameters of the spectra integrated over selected periods. Selections of the most representative spectra, for individual day observations or averages of several days as listed in the tables, are also available electronically.

As an example, we show here the log table and the figures for comet 22P/Kopff (Table 5 and Fig. 1).

The table columns are organized as follows:

• Date of the observation (date) (or range of dates for integrations);

• Geocentric distance (delta);

• Heliocentric distance (r);

• Heliocentric radial velocity (rdot);

• Theoretical inversion of the OH maser (inv) according to Despois et al. (1981);

• Theoretical inversion of the OH maser (inv) according to Schleicher & A'Hearn (1988);

• Background brightness temperature (Tbg) evaluated as explained in Sect. 3;

• The line area and its rms error (area), evaluated from -2.25 to 2.25 km s^-1;

• The line maximum intensity and its rms error (S);

• The line central velocity and its rms error (Vo);

  
  

  Figure 1: Selection of representative spectra: comet 22P/Kopff (from Fig. A.42a). The spectra are integrated over selected periods of time, as given in Table 5. A comprehensive data set for all comets is available electronically.

  
  

• The line width at half maximum and its rms error (dVo). These three last items result from a Gaussian fit to the spectrum and are only listed when the signal-to-noise ratio of the line is larger than 3;

• The OH production rate and its rms error (or its 3-$\sigma$ upper limit) (Q[OH]), using the Haser-equivalent model with quenching (Table 3, Col. 3) and the Despois et al. maser inversion. Null values are listed when the iterative algorithm to evaluate the quenching does not converge;

  
  

   

   

  Table 6: Comets observed at Nançay from 1973 to 1999: statistics of detections.

  comet	clear	marginal	not
  type	detection	detection	detected	total
  long-period comets
  dynamically new	6	0	2	8
  others	25	4	2	31
  short-period comets
  Halley-type	4	2	0	6
  Jupiter-family	5	6	4	15
  total	40	12	8	60

  
  

• The OH production rate and its rms error (or its 3-$\sigma$ upper limit) (Q[OH]), using the 1986A model (Table 3, Col. 2);

• The reference of the figure (Fig.) where the spectrum is shown.

When observations at offset positions were made, they are listed in a separate table in which the offsets (offRA and offDec) are listed instead of production rates.

Figure 2: Histograms of the number of comets with Q[OH] observed larger than a given value. Three histograms are superimposed: short-period comets (black), long-period comets (grey) and full sample (white).

Figure 3: Histogram of the number of observations per comet. The abscissa is a ranking number in order of number of observations. In Figs. 3 to 7, the black part of the histograms refer to the five most-observed comets.

Figure 4: Distribution of the observations as a function of universal time.

Figure 5: Distribution of the observations as a function of heliocentric distance (negative: pre-perihelion; positive: post-perihelion).

Unless otherwise specified, the spectra shown in the figures are sums of the left- and right-handed circular polarizations and of the 1667 and 1665 MHz components, normalized to the 1667 MHz intensity (assuming the LTE ratio 1665:1667 = 5:9).

The individual observations of each comet are discussed separately in Appendix A.