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 ________________________________________________________________________________ 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 ________________________________________________________________________________ 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 __________________________________________________________________ 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 _________________________________________________________________ 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 ________________________________________________________________________________ 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+ ________________________________________________________________________________ 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 ________________________________________________________________________ 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 ________________________________________________________________________ Table V. System Codes Used for P/Giacobini-Zinner ________________________________________________________________________________ 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. REFERENCES Hayward, T.L., and Grasdalen, G.L. (1987). Astron. J. 94, 1339. Sekanina, Z., and Larson, S.M. (1984). Astron. J. 89, 1408. Sekanina, Z., and Larson, S.M. (1986). Astron. J. 92, 462. Slavin, J.A., Goldberg, B.A., Smith, E.J., McComas, D.J., Bame, S.J., Strauss, M.A., and Spinrad, H. (1986). Geophys. Res. Lett. 13, 1085. Telesco, C.M., Decher, R., Baugher, C., Campins, H., Mozurkewich, D., Thronson, H.A., Criukshank, D.P., Hammel, H.B., Larson, S., and Sekanina, Z. (1986). Astrophys. J. 310, L61. von Rosenvinge, T.T., Brandt, J.C., and Farquhar, R.W. (1986). Science 232, 353.