NEAR NUCLEUS STUDIES NETWORK                                                                              
                                                                                                                                  
                                                                                                                                  
I. INTRODUCTION                                                                                                                   
                                                                                                                                  
        For both comets P/Halley and P/Giacobini-Zinner, the Near Nucleus                                                         
Studies Network (NNSN) objectives were to advocate, coordinate, standardize,                                                      
and archive high resolution groundbased images. The members of the NNSN team                                                      
of discipline specialists are listed in Table I. For P/Giacobini-Zinner most                                                      
of the activities were carried out through the already established IHW NNSN,                                                      
and details of the observing circumstances were communicated to network mem-                                                      
bers in a series of newsletters. A primary justification for the international                                                    
Giacobini-Zinner campaign was to provide groundbased support for the Inter-                                                       
national Cometary Explorer (ICE) which passed through the middle of the plasma                                                    
tail 7800 km from the nucleus at 11:02 UT on September 11, 1985 (von Rosenvinge                                                   
et al. 1986). Originally designed for studies of the solar wind environment up-                                                   
stream from the Earth, the ICE spacecraft did not carry an imaging experiment,                                                    
and was thus dependent upon groundbased imaging to provide information on the                                                     
morphology of the flyby region to correlate with the in-situ fields and par-                                                      
ticles data. The groundbased imaging also permits comparison of the activity                                                      
of P/Giacobini-Zinner with that of other comets, in particular P/Halley. For                                                      
many observers, P/Giacobini-Zinner also offered an opportunity to refine their                                                    
observing techniques in preparation for P/Halley later in 1985.                                                                   
                                                                                                                                  
                                                                                                                                  
Table I.  Discipline Specialist Team of the Near Nucleus Studies Network                                                          
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Team Member           Affiliation                          Responsibility                                                         
________________________________________________________________________________                                                  
                                                                                                                                  
Stephen M. Larson     Lunar and Planetary Laboratory       Discipline Specialist                                                  
                      University of Arizona                                                                                       
                      Tucson, AZ 85721                                                                                            
                      U.S.A.                                                                                                      
                                                                                                                                  
Zdenek Sekanina       Earth & Space Sciences Division      Discipline Specialist                                                  
                      Jet Propulsion Laboratory                                                                                   
                      California Institute of Technology                                                                          
                      Pasadena, CA 91109                                                                                          
                      U.S.A.                                                                                                      
                                                                                                                                  
Juergen Rahe          Dr. Remeis Sternwarte                Discipline Specialist                                                  
                      Universitat Nurnberg-Erlangen                                                                               
                      D-8600 Bamberg                                                                                              
                      Federal Republic of Germany                                                                                 
                                                                                                                                  
David H. Levy         Lunar and Planetary Laboratory       Assistant Discipline                                                   
                      University of Arizona                  Specialist                                                           
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II. FILTERS                                                                                                                       
                                                                                                                                  
        To aid the standardization of spectrally selective imaging, the NNSN                                                      
distributed 15 sets of 35mm circular imaging quality filters manufactured by                                                      
Barr Associates, Inc., Westford, MA, whose bandpasses matched closely those                                                       
of the eight IAU standard cometary filters used by the Photometry and Polar-                                                      
imetry Network. The characteristics of the IAU standard cometary filters are                                                      
given in greater detail in the Photometry and Polarimetry Network appendix.                                                       
Some observers used other filters that were available to them, or that were                                                       
suitable for other emissions. The characteristics of the filters used in the                                                      
archived data are listed in Table II, where each filter is characterized by                                                       
its band center, its full width at half-maximum response (FWHM), the dominant                                                     
source (continuum or emission band or bands), and comments.  The tabulated                                                        
values refer to the filters only and they do not reflect the effective                                                            
bandpasses of the detectors and effects of atmospheric extinction, unless                                                         
explicitly indicated in the comments.                                                                                             
                                                                                                                                  
                                                                                                                                  
Table II.  Filter Bandpass Characteristics                                                                                        
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Filter  Band center   FWHM      Dominant        Comments                                                                          
            [A]        [A]      source(s)                                                                                         
__________________________________________________________________                                                                
                                                                                                                                  
365BC      3650         80      continuum       IAU comet standard                                                                
387CN      3871         50      CN(0-0)         IAU comet standard                                                                
406C3      4060         70      C3(3-3)         IAU comet standard                                                                
GG385      4250        110      CN,C3,C2,CO+    with Kodak IIa-O                                                                  
426CO+     4260         70      CO+(2-0)        IAU comet standard                                                                
B          4400       1070      CN,C3,C2,CO+    nominal Johnson B                                                                 
457CO+     4570         45      CO+(1-0)                                                                                          
485MC      4845         65      continuum       IAU comet standard                                                                
514C2      5139         90      C2(0-0)         IAU comet standard                                                                
V          5480       1130      C2, CO+, NH2    nominal Johnson V                                                                 
BVR        5650       3300      continuum, C2                                                                                     
598NH2     5980         40      NH2(0-9-0)                                                                                        
600NH2     5995        102      NH2(0-9-0)      KPNO No. 1047                                                                     
619H2O+    6185         40      H2O+(0-8-0)                                                                                       
625CONT    6250         30      continuum                                                                                         
630TLT     6294          5      continuum       KPNO No. 794                                                                      
630OI      6300          5      OI              KPNO No. 794                                                                      
RG610      6450        700      continuum       with Kodak 098-04                                                                 
MOULD R    6450       1540      continuum       KPNO                                                                              
R          6500       1200      continuum                                                                                         
684RC      6840         90      continuum       IAU comet standard                                                                
703H2O+    7025         23      H2O+(0-6-0)     IAU comet standard                                                                
I          8250       1920      continuum                                                                                         
852CONT    8520        511      continuum       KPNO No. 916                                                                      
860CONT    8600        120      continuum                                                                                         
918CN      9180        120      CN(1-0)                                                                                           
928CN      9280        235      CN(1-0)         KPNO No. 918                                                                      
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III. DISCUSSION OF THE RESULTS                                                                                                    
                                                                                                                                  
        The 197 NNSN images in this archive (Table III) include the recovery                                                      
observations of April 3, 1984 and the observations from 22 days in the interval                                                   
May 17 to November 4, 1985. Most observations refer to dates close to the time                                                    
of the ICE encounter and were made by a group of the NNSN members who usually                                                     
observe comets as part of their research activity. Some of the NNSN observers                                                     
were preoccupied with preparing their observing campaigns for P/Halley, while                                                     
others used P/Giacobini-Zinner to experiment with new detectors or filters, and                                                   
elected not to submit their data.                                                                                                 
                                                                                                                                  
        The primary purpose of high-resolution groundbased images was to relate                                                   
the observed spatial and temporal distribution of charged particles with the in-                                                  
situ fields and particles data from the ICE. For visible to near-infrared wave-                                                   
lengths, this usually meant observing the CO+ or H2O+ ions. The charge-coupled                                                    
device (CCD) images through the 703H2O+ filter obtained by Goldberg et al. with                                                   
the Canada-France-Hawaii Telescope (NNSN##498341-498347) some 3.6 hours after                                                     
the ICE flyby were analyzed by Slavin et al. (1986). It was found that the tail                                                   
widths measured from the ICE and CCD images were consistent if the ion emission                                                   
observed from the ground originated in a slab-shaped plasma sheet whose orien-                                                    
tation was controlled by the direction of the interplanetary magnetic field.                                                      
                                                                                                                                  
        A major scientific objective of the near nucleus studies was to obtain                                                    
images of the cometary coma with sufficient spatial and temporal resolution to                                                    
determine some fundamental properties of the unresolved nucleus. Since the coma                                                   
is a temporary atmosphere, a changing anisotropic pattern of ejected material                                                     
obviously reflects the distribution of outgassing and the motion of the nucleus.                                                  
For example, by digitally enhancing photographs of P/Halley taken in 1910, it                                                     
was demonstrated that the patterns of dust jets could be explained by emission                                                    
of dust from discrete active areas on the sunlit part of the rotating nucleus                                                     
(Sekanina and Larson 1984, 1986). As subsequent direct spacecraft observations                                                    
showed, the dust emission from P/Halley did indeed come from several vents in a                                                   
largely inert mantle. However, P/Halley may not be typical and a wide variety                                                     
of coma morphology and time variable activity could exist among periodic comets.                                                  
For P/Giacobini-Zinner, the production rate of dust was much lower than that of                                                   
P/Halley, and the absence of prominent jets gave the appearance of a relatively                                                   
stationary and featureless coma. It should be noted, however, that as of this                                                     
writing, almost no effort has been made to enhance the images to bring out very                                                   
low contrast features. Ten-micron images of P/Giacobini-Zinner by Telesco et al.                                                  
(1986) and by Hayward and Grasdalen (1987) show variable structure of the type                                                    
that might be detected in the archived images after appropriate enhancement                                                       
procedures have been applied.                                                                                                     
                                                                                                                                  
                                                                                                                                  
IV. IMAGE SELECTION CRITERIA                                                                                                      
                                                                                                                                  
        Of the 218 images submitted for possible inclusion in the archive, 197                                                    
images (90%) met our selection criteria. These included (1) our ability to read                                                   
them as standard FITS files, (2) a significant signal, and (3) adequate spatial                                                   
resolution. The factors affecting the resolution included focussing, seeing,                                                      
and guiding. In all but five cases, the images were taken with CCD cameras of                                                     
various array sizes. These flat fielded images were not usually flux calibrated                                                   
and are thus in units of relative intensity. Users requiring photometrically                                                      
calibrated images are urged to contact the observers since many have standard                                                     
star frames but did not have time to go through the decalibration process. Five                                                   
digitized photographs are in units proportional to density.                                                                       
                                                                                                                                  
                                                                                                                                  
Table III.  Distribution of the NNSN Observations of P/Giacobini-Zinner                                                           
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Date UT   Observer(s)                 Location/Aperture  Filter(s)                                                                
________________________________________________________________________________                                                  
                                                                                                                                  
1984                                                                                                                              
Apr.  3   Djorgovsky, S., Spinrad,    Kitt Peak/4.0m     Mould R                                                                  
            H., and Will, G.                                                                                                      
1985                                                                                                                              
May  17   Dacosta, G.                 Kitt Peak/.9m      Mould R                                                                  
Jun. 18   Schultz, A., Fink, U.,      Catalina/1.5m      B,V,R,I,485MC,514C2,                                                     
            and DiSanti, M.                                684RC,703H2O+                                                          
Jun. 19   Fink, U., DiSanti, M.,      Catalina/1.5m      600NH2,630TLT,630OI,                                                     
            and Schultz, A.                                852CONT,928CN                                                          
Jun. 21   DiSanti, M., Fink, U.,      Catalina/1.5m      600NH2,852CONT                                                           
            Marcialis, R., and                                                                                                    
            Schultz, A.                                                                                                           
Jul. 20   Green, J., and Barker, E.   McDonald/2.1m      387CN,406C3,485MC,514C2                                                  
Jul. 21   Marcialis, R., Fink, U.,    Catalina/1.5m      B,V,R,I                                                                  
            and Schultz, A.                                                                                                       
Jul. 26   DiSanti, M., and            Catalina/1.5m      B,V,R,I                                                                  
            Schultz, A.                                                                                                           
Aug.  5   Marcialis, R., and          Catalina/1.5m      600NH2,630OI,852CONT,                                                    
            DiSanti, M.                                    928CN                                                                  
Aug. 17   Larson, S., and Hoban, S.   Catalina/1.5m      NONE,684RC,703H2O+                                                       
Aug. 22   Fink, U., DiSanti, M.,      Catalina/1.5m      B,V,R,I                                                                  
            Fink, R., and Sill, G.                                                                                                
Aug. 31   Barker, E.                  McDonald/.76m      387CN,426CO+,485MC,                                                      
                                                           514C2,B,V,R                                                            
Sept. 1   Barker, E.                  McDonald/.76m      387CN,426CO+,485MC,                                                      
                                                           514C2                                                                  
Sept. 9   Larson, S., and Levy, D.    Catalina/1.5m      NONE,684RC,703H2O+                                                       
Sept.10   Levy, D.                    Catalina/1.5m      NONE,485MC,514C2,684RC,                                                  
                                                           703H2O+                                                                
          Goldberg, B., Halliday,     Mauna Kea/3.6m     514C2,684RC,703H2O+                                                      
            I., and Aikman, C.                                                                                                    
Sept.11   Goldberg, B., Halliday,     Mauna Kea/3.6m     684RC,703H2O+                                                            
            I., and Aikman, C.                                                                                                    
Sept.12   Levy, D.                    Catalina/1.5m      NONE,485MC,512C2,684RC,                                                  
                                                           703H2O+                                                                
          Majewski, S.                Kitt Peak/4.0m     GG385,RG610                                                              
Sept.13   Schultz, A., and Fink, U.   Catalina/1.5m      B,V,R,I                                                                  
Sept.21   Wells, K., and DiSanti, M.  Catalina/1.5m      B,R,I                                                                    
Sept.22   Fink, U., and DiSanti, M.   Catalina/1.5m      457CO+,514C2,598NH2,                                                     
                                                           600NH2,619H2O+,                                                        
                                                           625CONT,852CONT,                                                       
                                                           860CONT,918CN,928CN                                                    
Sept.23   Fink, U.                    Catalina/1.5m      514C2,619H2O+,625CONT                                                    
Oct. 18   Schultz, A., and            Catalina/1.5m      B,V,R,I                                                                  
            Wisniewski, W.                                                                                                        
Oct. 19   DiSanti, M., Fink, U.,      Catalina/1.5m      B,V,R                                                                    
            and Schultz, A.                                                                                                       
Nov.  3   Green, J., and Barker, E.   McDonald/.91m      365BC,387CN,406C3,                                                       
                                                           485MC,514C2                                                            
Nov.  4   Green, J., and Barker, E.   McDonald/.91m      485MC,684RC,703H2O+                                                      
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        The archivist cannot fully anticipate all potential uses of the images,                                                   
nor the future users' ability to correct for small guiding errors, or imperfect                                                   
focussing. Because of the somewhat limited sample of images available, we have                                                    
relaxed our selection standards in a few cases in the interest of a more com-                                                     
plete temporal coverage. The user should be aware of the possible range of res-                                                   
olution between and within the data sets when identifying intrinsic changes in                                                    
the comet.                                                                                                                        
                                                                                                                                  
                                                                                                                                  
V. ARCHIVE PREPARATION PROCEDURE                                                                                                  
                                                                                                                                  
        After receiving the digitized images on a magnetic tape, we read them                                                     
into a VAX 780 computer and displayed them to assess their eligibility for ar-                                                    
chiving. We then verified the maximum comet and minimum sky count levels, the                                                     
sense and orientation, and rated the quality for each frame. These and the other                                                  
data provided by the observers were entered into a database computer code which                                                   
checked for formal consistency and calculated other entries, including the air-                                                   
mass. The airmass at mid-exposure (AIRM-MID) was determined from the comet's                                                      
apparent equatorial coordinates (ra, dec) and from the observatory coordinates                                                    
(long, lat):                                                                                                                      
                                                                                                                                  
        AIRM-MID = sec Z + 0.0018167 (1-sec Z) - 0.002875 (1-sec Z)**2                                                            
                                                     + 0.0008083 (1-sec Z)**3,                                                    
where the apparent zenith distance Z is given by                                                                                  
                                                                                                                                  
        sec Z = 1/[sin(lat)*sin(dec) + cos(lat)*cos(dec)*cos(local hour angle)].                                                  
                                                                                                                                  
        The completed database was assembled into a report having the format                                                      
of the extended NNSN FITS headers (including comments) and then combined with                                                     
the images and written onto a tape that was sent to the Lead Center. It often                                                     
was necessary to contact the observers in order to obtain missing information                                                     
or to clarify uncertain or ambiguous data. We proofread the headers several                                                       
times before being satisfied that they were correct, but users are advised to                                                     
follow up any apparent inconsistency they may find. After the images were sent                                                    
to the Lead Center, hard copy images were produced for the printed archive as                                                     
described below.                                                                                                                  
                                                                                                                                  
        The quality rating is only a rough, qualitative guide that includes the                                                   
effects of seeing, focussing, guiding, the signal-to-noise ratio, and decalibra-                                                  
tion. The four rating categories are excellent, good, fair, and poor: excellent                                                   
refers to images with no obvious flaws and poor denotes images included only                                                      
because of the lack of better ones on that day. The user will have to gain some                                                   
experience to know what to expect from the different grades.                                                                      
                                                                                                                                  
                                                                                                                                  
VI. PRINTED ARCHIVE ENTRIES                                                                                                       
                                                                                                                                  
        For each image in the digital archive, there is a corresponding entry                                                     
in the printed archive that includes information necessary for the users to                                                       
determine whether that image will satisfy their needs. All items are derived                                                      
from the NNSN FITS header keywords. Below is a description of each entry item.                                                    
The relevant system codes are listed in Table V.                                                                                  
                                                                                                                                  
                                                                                                                                  
Table IV.  Entries in the Printed Archive                                                                                         
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Heading       Description                                                                                                         
________________________________________________________________________                                                          
                                                                                                                                  
Date(UT)      Date (day & fraction of day) of middle of observation                                                               
NNSN#         Near Nucleus Studies Network file number                                                                            
Filter        Filter used (see Table II)                                                                                          
Detector      Detector used                                                                                                       
Field         Angular field of axes (arcmin) derived from the array size                                                          
                and platescale. The field may actually be smaller due to                                                          
                field stops or vignetting.                                                                                        
PAx           Position angle (N through E) of NAXIS1 (deg)                                                                        
ExpS          Exposure duration (s)                                                                                               
Pixel         Angular scale of picture element (arcsec)                                                                           
Ap            Telescope aperture size (m)                                                                                         
Scale         Effective plate scale at the detector (arcsec per mm)                                                               
System        Observing system code (see system codes Table V)                                                                    
Observer(s)   Name(s) of observers                                                                                                
Notes         Notes from HISTORY or COMMENT keywords in the FITS header                                                           
                (see Table VI) as space permits                                                                                   
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Table V.  System Codes Used for P/Giacobini-Zinner                                                                                
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System  Array Size  Longobs    Lat-obs   Elev Observatory Aper  Detector Filter                                                   
         [pixels] [deg/min/s][deg/min/s]  [m]              [m]                                                                    
________________________________________________________________________________                                                  
                                                                                                                                  
46930101  320x512  249/16/05  +32/25/01  2510  Catalina   1.54  RCA CCD  NONE                                                     
46930106  320x512  249/16/05  +32/25/01  2510  Catalina   1.54  RCA CCD  485MC                                                    
46930107  320x512  249/16/05  +32/25/01  2510  Catalina   1.54  RCA CCD  514C2                                                    
46930108  320x512  249/16/05  +32/25/01  2510  Catalina   1.54  RCA CCD  684RC                                                    
46930109  320x512  249/16/05  +32/25/01  2510  Catalina   1.54  RCA CCD  703H2O+                                                  
46930120  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   B                                                        
46930121  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   V                                                        
46930122  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   R                                                        
46930123  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   I                                                        
46930124  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   457CO+                                                   
46930125  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   598NH2                                                   
46930126  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   600NH2                                                   
46930127  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   619H2O+                                                  
46930128  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   625CONT                                                  
46930129  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   630OI                                                    
46930130  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   630TLT                                                   
46930131  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   852CONT                                                  
46930132  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   860CONT                                                  
46930133  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   918CN                                                    
46930134  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   928CN                                                    
46930139  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   514C2                                                    
46930140  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   684RC                                                    
46930141  500x500  249/16/05  +32/25/01  2510  Catalina   1.54  TI CCD   703H2O+                                                  
46950101  800x800  248/24/02  +31/57/50  2120  Kitt Peak  4.00  TI CCD   MOULD R                                                  
46950502  312x500  248/24/00  +31/57/29  2091  Kitt Peak   .91  RCA CCD  MOULD R                                                  
46950503  320x512  248/24/00  +31/57/29  2091  Kitt Peak   .91  RCA CCD  MOULD R                                                  
46950504  316x508  248/24/00  +31/57/29  2091  Kitt Peak   .91  RCA CCD  MOULD R                                                  
46950505  800x800  248/24/00  +31/57/29  2091  Kitt Peak   .91  TI CCD   703H2O+                                                  
46950506  800x800  248/24/00  +31/57/29  2091  Kitt Peak   .91  TI CCD   MOULD B                                                  
46950107  512x512  248/24/02  +31/57/50  2120  Kitt Peak  4.00  IIA-O    GG385                                                    
46950108  512x512  248/24/02  +31/57/50  2120  Kitt Peak  4.00  098-04   RG610                                                    
47110202  192x256  255/58/42  +30/40/17  2073  McDonald   2.08  RCA CCD  387CN                                                    
47110203  192x256  255/58/42  +30/40/17  2073  McDonald   2.08  RCA CCD  406C3                                                    
47110205  192x256  255/58/42  +30/40/17  2073  McDonald   2.08  RCA CCD  485MC                                                    
47110206  192x256  255/58/42  +30/40/17  2073  McDonald   2.08  RCA CCD  514C2                                                    
47110401  192x256  255/58/42  +30/40/17  2073  McDonald    .91  RCA CCD  365BC                                                    
47110402  192x256  255/58/42  +30/40/17  2073  McDonald    .91  RCA CCD  387CN                                                    
47110403  192x256  255/58/42  +30/40/17  2073  McDonald    .91  RCA CCD  406C3                                                    
47110405  192x256  255/58/42  +30/40/17  2073  McDonald    .91  RCA CCD  485MC                                                    
47110406  192x256  255/58/42  +30/40/17  2073  McDonald    .91  RCA CCD  514C2                                                    
47110407  192x256  255/58/42  +30/40/17  2073  McDonald    .91  RCA CCD  684RC                                                    
47110408  192x256  255/58/42  +30/40/17  2073  McDonald    .91  RCA CCD  703H2O+                                                  
47110502  192x256  255/58/42  +30/40/17  2073  McDonald    .76  RCA CCD  387CN                                                    
47110504  192x256  255/58/42  +30/40/17  2073  McDonald    .76  RCA CCD  426CO+                                                   
47110505  192x256  255/58/42  +30/40/17  2073  McDonald    .76  RCA CCD  485MC                                                    
47110506  192x256  255/58/42  +30/40/17  2073  McDonald    .76  RCA CCD  514C2                                                    
47110512  352x512  255/58/42  +30/40/17  2073  McDonald    .76  RCA CCD  387CN                                                    
47110514  352x512  255/58/42  +30/40/17  2073  McDonald    .76  RCA CCD  426CO+                                                   
47110515  352x512  255/58/42  +30/40/17  2073  McDonald    .76  RCA CCD  485MC                                                    
47110516  352x512  255/58/42  +30/40/17  2073  McDonald    .76  RCA CCD  514C2                                                    
47110519  352x512  255/58/42  +30/40/17  2073  McDonald    .76  RCA CCD  BVR                                                      
45680203  325x525  204/31/40  +19/49/35  4125  Mauna Kea  3.60  RCA CCD  684RC                                                    
45680204  325x525  204/31/40  +19/49/35  4125  Mauna Kea  3.60  RCA CCD  703H2O+                                                  
45680213  325x525  204/31/40  +19/49/35  4125  Mauna Kea  3.60  RCA CCD  514C2                                                    
________________________________________________________________________________                                                  
                                                                                                                                  
                                                                                                                                  
VII. PRINTED ARCHIVE IMAGES                                                                                                       
                                                                                                                                  
        The printed archive contains one representative halftone image per                                                        
day to give the user a general idea of the appearance of the comet. The NNSN                                                      
file number is printed at the top of each frame for easy correlation with the                                                     
printed entries following. The images are reproduced with the same orientation                                                    
(north up, east to the left) and scale (100,000 km on a side at the comet). To                                                    
permit greater visibility of the near nucleus region as well as some of the                                                       
outer coma, the base 10 logarithm of the counts are displayed. The final prints                                                   
have similar densities and contrasts to maximize visibility of the comet, but                                                     
the halftone process degrades the dynamic range of the prints. For detailed                                                       
study, the user should use images from the digital archive.                                                                       
                                                                                                                                  
                                                                                                                                  
VIII. NNSN FITS HEADERS                                                                                                           
                                                                                                                                  
        The digital archive presents extended FITS headers which contain addi-                                                    
tional information, not included in the printed archive entries. Table VI lists                                                   
the header keywords and their short descriptions.                                                                                 
                                                                                                                                  
                                                                                                                                  
Table VI.  Keywords in the FITS headers                                                                                           
_______________________________________________________________________________                                                   
                                                                                                                                  
Keyword   Type  Format   Description                                                                                              
_______________________________________________________________________________                                                   
                                                                                                                                  
SIMPLE     L             Always "T" since they conform to standard FITS format                                                    
BITPIX     I             Always "16"-bit integer data                                                                             
NAXIS      I             Always "2" in our two dimensional images                                                                 
NAXIS1     I    I4       Number of pixels in X axis, samples                                                                      
NAXIS2     I    I4       Number of pixels in Y axis, rows                                                                         
OBJECT     C             Object name, 'P/GIACOBINI-ZINNER' in this archive                                                        
FILE-NUM   I    I6       Unique file number where 498XXX = NNSN P/G-Z, and                                                        
                           XXX are running numbers within data sets                                                               
DATE-OBS   C    A8       UT date of observation, dd/mm/yy                                                                         
TIME-OBS   R    F6.5     Decimal fraction of mid-UT date of observation                                                           
DATE-REL   C    A8       Date released to archive, dd/mm/yy                                                                       
DISCIPLN   C    A12      'NEAR NUCLEUS' for our network                                                                           
LONG-OBS   C    A9       Observatory longitude ddd/mm/ss (positive to east)                                                       
LAT--OBS   C    A9       Observatory latitude sdd/mm/ss (s = + or -)                                                              
SYSTEM     C    A8       Observing system code 4NNNXXYY, where 4 denotes the                                                      
                           Near Nucleus Studies Network, NNN the IAU observatory                                                  
                           code, XX the telescope, and YY the detector/filter                                                     
                           (see Table V)                                                                                          
OBSERVER   C    A        Observer(s) name(s)                                                                                      
SUBMITTR   C    A        Submitter(s) name(s)                                                                                     
SPEC-EVT   L    T or F   Special event in image if T (F for all P/G-Z images)                                                     
DAT-FORM   C    A8       "STANDARD" type of data                                                                                  
OBSVTORY   C    A        Observatory name                                                                                         
ELEV-OBS   I    I4       Elevation of observatory [m]                                                                             
TELESCOP   C    A        Telescope used                                                                                           
APERTURE   R    F4.2     Telescope aperture [m]                                                                                   
TELEFL     R    F5.3     Effective focal length [m]                                                                               
PLTSCALE   R    F5.2     Plate scale [arcsec/mm]                                                                                  
CROTA1     R    F5.1     Position angle of sample axis [deg] north through east                                                   
SENSE      L    T or F   Position angle counterclockwise (T) or clockwise (F)                                                     
DETECTOR   C    A        Detector used                                                                                            
DIGITIZE   C    A        Type of digitizer used if not detector                                                                   
APSIZE     R    F5.3     Original pixel size of detector/digitizer                                                                
FILTER     C    A7       Filter used (see Table II)                                                                               
EXPOSURE   R    F6.1     Exposure duration [s]                                                                                    
AIRM-MID   R    F5.3     Calculated airmass at mid-exposure                                                                       
QUALITY    C    A9       Quality of image (excellent, good, fair, poor)                                                           
DATE-WRT   C    A8       Date this file was written                                                                               
ORIGIN     C    A        Institution from which data were sent to NNSN center                                                     
BUNIT      C    A        Units of the digital numbers. Note that in all cases                                                     
                           that the FITS keywords BSCALE = 1 and BZERO = 0. In                                                    
                           most cases, the units are relative intensity                                                           
COMETMAX   I    I5       Maximum count in comet image. COMETMAX and SKYMIN are                                                    
                           intended to be a guide for setting display parameters                                                  
SKYMIN     I    I5       Approximate sky brightness                                                                               
COMMENT    C    A72      Comments relating to the contents of the image or addi-                                                  
                           tional observers or submitters                                                                         
HISTORY    C    A72      Comments relating to the reduction process                                                               
________________________________________________________________________________                                                  
                                                                                                                                  
                                                                                                                                  
ACKNOWLEDGEMENTS                                                                                                                  
                                                                                                                                  
        The contribution of the Near Nucleus Studies Network to the P/Giacobini-                                                  
Zinner archive is a result of the hard work and dedication of the Network mem-                                                    
bers. Participation in the NNSN has been strictly voluntary. The effort benefits                                                  
cometary and space science and has helped foster international cooperation. We                                                    
thank B.A. Smith (Lunar and Planetary Laboratory; LPL) and R. Lynds (National                                                     
Optical Astronomy Observatory; NOAO) for use of the ST VAX780 computer at NOAO.                                                   
S. Movafah (LPL), E. O'Neil (NOAO), and J. Gotobed (LPL) provided assistance                                                      
with the VAX. M. Aronsson of the Lead Center (Jet Propulsion Laboratory, Cali-                                                    
fornia Institute of Technology) offered much needed help. M. Guengerich (LPL)                                                     
did an extraordinary job helping to construct the FITS headers.                                                                   
                                                                                                                                  
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Telesco, C.M., Decher, R., Baugher, C., Campins, H., Mozurkewich, D., Thronson,                                                   
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