RADIO SCIENCE NETWORK I. INTRODUCTION Radio Astronomy is a developing new technique for the study of comets. In some areas, such as observations of the OH radical via its 18 cm transitions, the observational procedures and analysis are well developed. Studies in these areas have proved their value since they both provide new probes of important physical processes as well as a window on physical processes which are less well known and less amenable to study by other techniques. In many other areas, how- ever, the study of comets at radio wavelengths continues to be primarily an exploratory endeavor. In recognition of this fact, the IHW Radio Science Disci- pline Specialist team (see Table I) feels that it is important to attempt many different kinds of observations, since each observation tends to have some scientific merit as an exploration. Thus, we have been careful to document and include all data submitted to this archive by radio observers. Table I. Discipline Specialist Team of the Radio Science Network ___________________________________________________________________________ Team Member Affiliation Responsibility ___________________________________________________________________________ William M. Irvine Astronomy Program Discipline Specialist University of Massachusetts Amherst, MA 01003 U.S.A. F. Peter Schloerb Astronomy Program Discipline Specialist University of Massachusetts Eric Gerard Departement de Radioastronomie Discipline Specialist Observatoire de Meudon F-92190 Meudon France Ronald D. Brown Department of Chemistry Discipline Specialist Monash University 1981-85 Clayton, Victoria 3168 Australia Peter D. Godfrey Department of Chemistry Discipline Specialist Monash University 1981-85 Wayne M. Kinzel Astronomy Program Archive Manager University of Massachusetts ___________________________________________________________________________ The P/Giacobini-Zinner Archive contains data from eight observing groups, representing a range of techniques. Most of the observational data come in the well developed area of 18cm OH observations. However, other projects, including attempts to detect continuum and spectral line emission at other wavelengths and an attempt to observe the effects of absorption of galactic background emission by the comet were also undertaken. Approximately 3/4 of the groups who are known to have obtained useful data have submitted them to the archive. We are grateful to these observers for their contributions. II. THE RADIO SCIENCE FITS HEADER The IHW Radio Science archive is in FITS format. The FITS files con- sist of a header, which contains information on the observation, and data in a format specified by the FITS header. The header and the data are presented in two different files to facilitate their use by a wide range of analysis soft- ware. Users who require FITS format files have only to concatenate the header and the data files to make a standard FITS file for a particular observation. The FITS header is meant to give a description of the structure and format of the FITS data records which follow it and to provide any auxiliary information that is necessary for its interpretation. For the Radio Science FITS header, we have defined several FITS keywords which specify observational parameters which are necessary to interpret the data. A detailed description of the complete Radio Science FITS header is provided in Sec. III. In general, the Radio Science Network has tried to conform to standards which are commonly used in FITS and adopted by the IHW. The characteristics of the observation are described by assigning values to the keywords which are described in Sec. III. Special keywords have been selected to provide information vital to the data interpretation, such as specification of the observing frequency or telescope parameters. At another level, under the FITS HISTORY keywords, we describe how the data were obtained, including calibration and orbital tracking information. The organization of the parameters into these groups is admittedly somewhat arbitrary and has been made primarily to limit the number of new FITS keywords defined by our Network. In an exploratory program, like the Radio Science Network, it is to be expected that on many occasions attempts to detect the comet will fail. These nondetections are best described by an appropriate upper limit rather than through presentation of a spectrum or image. In recognition of this fact, the IHW permits FITS files to be created without any data records; the limit is then listed in the FITS HISTORY section of the Radio Science header. The FITS files of this type have the NAXIS keyword set equal to 0 and the DAT-TYPE keyword set equal to the character string 'NODATA '. Where possible, even when actual data exist, we have attempted to describe them by presenting the results of a model fit to the data. For exam- ple, in spectral line work a line is often described in terms of its peak inten- sity, the velocity of the peak, the line width, the integrated area under the line, and the mean velocity of the emission. We have provided these values in FITS HISTORY keywords by fitting a gaussian line shape model to the data. III. RADIO SCIENCE FITS HEADER DESCRIPTION Information provided in the FITS header has been organized into seven keyword blocks. A. Keyword Block I: Basic FITS Keywords This block is required of FITS tapes. The details are presented in Table II below. Table II. Keyword Block I ________________________________________________________________________________ Keyword Type Description ________________________________________________________________________________ SIMPLE L Conformity to basic FITS standards BITPIX I Bits per pixel in data record NAXIS I Number of axes in data record; if NAXIS = 0 then no data record NAXIS1 I Number of pixels in row along first axis NAXISn I Number of pixels along n-th axis in image ________________________________________________________________________________ B. Keyword Block II: International Halley Watch Keywords These keywords are agreed upon for use by the IHW and are listed in Table III. Table III. Keyword Block II ________________________________________________________________________________ Keyword Type Description ________________________________________________________________________________ OBJECT C Name of the object: 'P/GIACOBINI-ZINNER' FILE-NUM I 6NNNNV - Unique, sequential number to identify files sent to IHW Lead Center. Format description: 6 = denotes Radio Science Network NNNN = Unique 4 digit ID number assigned to each observation V = Version Number (has no effect on usage) DATE-OBS C 'DD/MM/YY' - UT date of middle of observation if observations made during several intervals, then these intervals will be specified in the HISTORY fields described below TIME-OBS R UT Time of middle of observation expressed in decimal days DATE-REL C 'DD/MM/YY' - Date when observations may be publicly released DISCIPLN C 'RADIO STUDIES' - The Network identification LONG-OBS C 'DDD/MM/SS' - East longitude of observatory (0-360 degrees) LAT--OBS C 'sDD/MM/SS' - Latitude of observatory SYSTEM C '6OOOCCTT' - System code formatted: 6 = Radio Studies Network OOO = IAU number for observatory (OOO=500 for radio observatories--no IAU numbers exist) CC = Identifies country according to LSPN Code TT = Identifies radio telescope OBSERVER C Name of Observer Format : 'LASTNAME,I' - 1 author 'LASTNAME,I/NEXTNAME,J' - 2 authors 'LASTNAME,I/ET AL.' - >2 authors For more than 2 observers, the names of all additional observers are given in special ADD. OBS. comments SUBMITTR C Name of submitter of data SPEC-EVT L Flag for special events as designated by Discipline Specialist DAT-FORM C Describes format of FITS data records 'NODATA ' - No FITS data records written 'STANDARD' - Data records conform to FITS standard 'ASCII ' - Data records are to be interpreted as logical records of 80 ASCII characters (not FITS standard) 'HARDCOPY' - Data submitted as hardcopy ________________________________________________________________________________ C. Keyword Block III: Radio Science Keywords These keywords are to be directly read by computers in the normal manner of FITS header keywords. Some attempt has been made to choose keyword names that are already in use by the astronomical community. These keywords are used to describe information that is vital to the interpretation of the data or potentially useful for searches of the data base (Table IV). Table IV. Keyword Block III ________________________________________________________________________________ Keyword Type Description ________________________________________________________________________________ DIS-CODE C 'TFESEWEABENC' Describes the parameters of the telescope/instrument T : Telescope Type S = Single Antenna I = Interferometer U = Unknown/Unclassified FE: Frequency (Center Frequency or Rest Frequency) FE=> Frequency = F X 10**(E) MHz 00= Unknown SE: Spectral Resolution SE=> Spectral Resolution = S X 10**(E) Hz 00= Unknown WE: Bandwidth WE=> Bandwidth = W X 10**(E) Hz 00= Unknown A : Beam Description C = Circular E = Ellipitical O = Other U = Unknown BE: Beam Size (Geometric Mean) BE=> Beam Size = B X 10**(E) arcsec 00= Unknown N : Noise Estimate N => RMS Noise = 10**(N) microJansky/Beam 0 = Unknown C : Information provided by observer to Discipline Specialist is complete T = TRUE F = FALSE DAT-TYPE C 'NNSTHP' Indicates the data format within Header and Data Records NN: Subnetwork OH= OH Subnetwork Spectral line observations of 18-cm OH SL= Spectral Line Subnetwork Spectral line observations (other than 18-cm OH) CN= Continuum Subnetwork Broadband continuum observations OC= Occultation Subnetwork Observation of occultation events RD= Radar Subnetwork Active experiments S : Search/Detection Status S = Search - implies nondetection (< 3 sigma) D = Detection - implies detection (> 3 sigma) M = Marginal - implies marginal detection (approx. 3 sigma) T : Type of Data in FITS Data Records N = No FITS Data Records S = Spectrum => Intensity vs Frequency C = Continuum Scan => Intensity vs Space T = Time Series => Intensity vs Time I = Image => Spatial - Spatial Image D = Dynamic Spectrum => Frequency - Time Image F = SV Image => Frequency - Spatial Image V = Visibility Function Data H : Summary of Data in Header? T = Summary of Data exists in Header History Section F = No Summary of Data in Header History Section P : Polarization Status I = Intensity Data Only P = Polarization Data Format Used OBSVTORY C Abbreviation for Observatory. TELESCOP C Telescope Identifier - usually gives aperture size in meters LOCATION C Location of Observatory as given in American Ephemeris INSTRUME C 'FRONT/BACK' - describes "frontend" and "backend" of receiver FRONT: Receiver Front End MASER = Maser Amplifier FET = Field Effect Transistor Amplifier PARA = Parametric Amplifier MIXER = Mixer SPEC = Special Front End UNK = Unknown Front End BACK : Receiver Back End FB = Filterbank SEFB = Filterbank with Spectrum Expander AC = Autocorrelator CONT = Broadband Continuum Receiver SPEC = Special Back End AOS = Acousto-Optical Spectrometer UNK = Unknown Back End CENTFREQ R Center Frequency of Observed Bandwidth (Hz) BANDWIDT R Total Bandwidth (Hz) BEAMSIZE R Geometric Mean of Major and Minor Axes of Elliptical Gaussian Beam (deg) BEAMELON R Ratio of Major Beam Axis to Minor Beam Axis BEAMROTA R Position Angle of Major Beam Axis (deg) BEAMEFF R Beam Efficiency - Fraction of power recieved that is in the Gaussian Main Beam (BEAMEFF = 0.0 if unknown or unspecified) MOLECULE C Chemical Formula for Molecule (Follows Convention of NBS Interstellar line list) TRANSITN C Quantum Numbers for Transition (Follows Convention of NBS Interstellar line list) RESTFREQ R Rest Frequency of line used by observer (Hz) RES-SPEC R Spectral Resolution (Hz) - This is intended to be the true spec- tral resolution of the spectrometer, NOT the channel spacing EQUINOX R Equinox of RA-DEC information presented in this file RAOFF R Pointing Offset in RA direction DELTA(RA)*COS(DEC) (deg) DECOFF R Pointing Offset in Dec direction DELTA(DEC) (deg) DATE-BEG C 'DD/MM/YY' - UT date on which observations began DATE-END C 'DD/MM/YY' - UT date on which observations ended ________________________________________________________________________________ D. Keyword Block IV: Special Keywords for Printed Archive This group of COMMENT lines give additional information to be used in the production of the IHW printed archive. The ADD. OBS. comment gives the names of the full observing team in the case that more than two observers carried out the observations. More than one ADD. OBS. comment may be used to specify teams with many members or long names. The format of the ADD. OBS. comment is: COMMENT ADD. OBS. NAME,I/NAME2,I/NAME3,I The NOTE comment provides information that is to be printed as a foot- note in the printed archive in the following format: COMMENT NOTE THIS IS A TEST E. Keyword Block V: Radio Science Data History Section This block of FITS HISTORY keywords is provided to give additional information about the observation, such as descriptions of calibration methods and sources, details about observing procedures, and comments by the observer and the IHW Discipline Specialist. Another important use of the HISTORY lines is to provide a summary of the data obtained, or in the case of FITS files with no data records, the actual data values reported by the observer. The general format of the HISTORY lines is: column 1 11 21 HISTORY SUBKEY__ VALUES.... where values is a list of values associated with this subkey. In most cases, the value lists are in a fixed format in order to simplify their use. E.1. DATA SUMMARY SECTION In order to transmit upper limits or a summary of the data that would be appropriate for tabular presentation in the printed archive, we utilize one of the following HISTORY keyword formats. Such summaries of the data will always be contained in the first part of the HISTORY keyword section; the presences of such a summary shall be indicated in the DAT-TYPE keyword discussed above. In the case where FITS data records accompany the header, USERS OF THE ARCHIVE ARE CAUTIONED THAT THE SUMMARY VALUES ARE ONLY MEANT TO DESCRIBE AND CHARACTERIZE THE DATA ... NOT TO REPLACE THEM. All summary lines follow the same general form: HISTORY SUBKEY ################ 'UNITS ' where the # field is a right justified floating point number. Format for Upper Limits: COMMENT *SUMMARY OF DATA - UPPER LIMIT HISTORY LIMIT 0.5 'JY/BEAM ' Upper Limits in the Radio Science Net are always given as 3 standard deviation upper limits. Format for Spectral Lines: COMMENT *SUMMARY OF DATA - SPECTRAL LINE HISTORY LINEPEAK 0.5 'JY/BEAM ' HISTORY ERR-PEAK 0.1 'JY/BEAM ' HISTORY LINE-VEL 10.0 'M/SEC ' HISTORY ERR--VEL 200.2 'M/SEC ' HISTORY LINE-WID 2532.0 'M/SEC ' HISTORY ERR--WID 130.2 'M/SEC ' HISTORY LINEAREA 1243.1 'JY/B*M/S' HISTORY ERR-AREA 143.6 'JY/B*M/S' HISTORY LINEMEAN 32.1 'M/SEC ' HISTORY ERR-MEAN 10.2 'M/SEC ' The spectral line summary values LINEPEAK, LINE-VEL, and LINE-WID are determined from gaussian fits to the line profiles. If one or more parameters were fixed in a fit to the data, the assumed values are listed with no errors. Spectral lines with hyperfine structure (e.g., HCN) are fitted on the assumption that all hyperfine components have their nominal intensity ratios. Format for Continuum Observations: COMMENT *SUMMARY OF DATA - CONTINUUM HISTORY CONTFLUX 0.5 'JY/BEAM ' HISTORY ERR-FLUX 0.1 'JY/BEAM ' E.2. OBSERVING WINDOWS SECTION Since many radio observations take place over several days, we include the precise observing windows in the HISTORY section according to the format: COMMENT *OBSERVING WINDOW SPECIFICATION HISTORY N-WINDOW # HISTORY WINDOW 'DD/MM/YY' ####### 'DD/MM/YY' ####### ... ... ... ... ... ... ... ... ... HISTORY WINDOW 'DD/MM/YY' ####### 'DD/MM/YY' ####### where N-WINDOW gives the total number of windows for observation and subsequent window lines give the date and time (in decimals as in TIME-OBS) of beginning and end of the observing window. The time fields are right justified floating point numbers. E.3. ORBITAL ELEMENTS SECTION Radio observers track the comet "blind" and it is important to know the precise position on the sky that they were tracking. We include a provision in the HISTORY section to specify the two-body elements and observatory position data used to produce the topocentric ephemeris for tracking. COMMENT *ORBITAL ELEMENT SPECIFICATION HISTORY ORBELEM T - T if orbital elements are present HISTORY LONGEAST 243.11046715 - east longitude of observatory (deg) HISTORY RHO--COS 0.8159113419 - radius*cos(lat) for observatory (units of Earth equatorial radius) HISTORY RHO--SIN 0.5765085118 - radius*sin(lat) for observatory (units of Earth equatorial radius) HISTORY ET-UT 53.18439 - Ephemeris Time - UT correction (s) HISTORY JD 2446471.16128 - Time of Perihelion passage (ET) HISTORY Q 0.5870959 - Perihelion Distance (AU) HISTORY E 0.9672671 - Eccentricity HISTORY SOMEGQ 111.85336 - Arg. of Perihelion (deg) HISTORY LOMEGA 58.15313 - Long. of Ascending Node (deg) HISTORY I 162.23779 - Inclination (deg) E.4. ANTENNA TRACKING SECTION This HISTORY keyword specifies the antenna rms pointing errors. COMMENT *RMS POINTING ERROR OF TELESCOPE HISTORY POINTERR ################ 'UNITS ' E.5. CALIBRATION SECTION This group of keywords provides information about details of the ca- libration process. COMMENT *CALIBRATION METHOD INFORMATION HISTORY CALMETH 'DESCRIPTION OF CAL METHOD' If calibration method is unknown, then no line appears. Current possible values are 'CHOPPER WHEEL', 'NOISE TUBE', 'STANDARDS' COMMENT *CALIBRATION STANDARD INFORMATION HISTORY CALSRCE 'SOURCE NAME' ########## 'UNITS ' Source (or sources) used to provide principal calibration. The # field is a right justified floating point number. For planets as the calibrators, the assumed brightness temperature is given; otherwise, the calibrator flux density is given in Jansky. There may be more than one CALSRCE HISTORY line. COMMENT *SYSTEM TEMPERATURE ETC. HISTORY TSYSTEM ############### '_SB ' HISTORY TRCVR ############### '_SB ' Total system temperature (TSYSTEM) and noise temperature of the reciver alone (TRCVR). '_SB ' allows single side band measurement ('SSB ') or double sideband measurement ('DSB ') to be indicated. The # field is a right justified floating point number. HISTORY TAUZENTH ############### Atmospheric opacity at zenith. The # field is a right justified floating point number. E.6. OBSERVER'S COMMENT SECTION This block of HISTORY lines contains any extra comments about condi- tions, data quality, etc. that are sent to the Discipline Specialist by the observer. There are generally fewer than eight such comment lines. COMMENT *OBSERVER COMMENTS HISTORY OBSCOMM ROOM TO REPORT OBSERVERS COMMENTS HISTORY OBSCOMM ... HISTORY OBSCOMM ... HISTORY OBSCOMM MORE ROOM FOR OBSERVER COMMENTS E.7. DISCIPLINE SPECIALIST'S COMMENT SECTION Comments by the Discipline Specialist team on this observation. There are generally fewer than eight such comment lines. COMMENT *DISCIPLINE SPECIALIST COMMENTS HISTORY DSCOMM ROOM TO REPORT DISCIPLINE SPECIALIST COMMENTS HISTORY DSCOMM ... HISTORY DSCOMM ... HISTORY DSCOMM MORE ROOM FOR DISCIPLINE SPECIALIST COMMENTS F. Keyword Block VI: Standard FITS Keywords These keywords are used to describe the FITS data records. They are all standard and summarized in Table V. Table V. Keyword Block VI ________________________________________________________________________________ Keyword Type Description ________________________________________________________________________________ BSCALE R Scale Factor Data = tape * BSCALE + BZERO BZERO R Zero Value BUNIT C Units of Data 'JY/BEAM ' - for line and continuum data BLANK I Value for out-of-range data CRVALn R Value of physical coordinate of nth axis at the reference pixel CRPIXn R Array location of reference pixel for nth axis CDELTn R increment in physical coordinate along nth axis CTYPEn C Type of physical coordinate 'VELO-COM' - frequency coordinate for line work in m/s defined to be velocity relative to the comet 'VELO-GEO' - velocity defined relative to center of Earth 'CIRCULAR POLARIZATION' - axis used to define different states of circular polarization: -1 = LHC; -2 = RHC 'LINEAR POLARIZATION' - axis used to define linear polarization position angle 'RAOFF ' - spatial coordinate for maps (deg) 'DECOFF ' - spatial coordinate for maps (deg) CROTAn R Rotation angle of physical coordinate axis n ________________________________________________________________________________ G. Keyword Block VII: End Statement This keyword is required by FITS to terminate the header: END IV. THE RADIO SCIENCE NETWORK INDEX TO THE CD-ROMS The IHW provides various indices to help users of the archive find the data that they want. For the Radio Science Network, there are two indices provided by the project which users will find useful: the quick look index and the printed archive (see Sec. V for description), both of which contain information on all observations in the archive. The Radio Science Network provides a third, discipline specific, index which contains much more detailed information about the radio observations than the others. In selecting the information to be included in the Radio Science Index, we have attempted to include all relevant data from the FITS headers, within limitations imposed by standards set by the Halley Watch. The detailed format of the Radio Science index is given in Table VI. Table VI. IHW Radio Science Network Index Format ________________________________________________________________________________ Field Keyword Type Format Notes ________________________________________________________________________________ 1 OBJECT C A20 2 FILE-NUM N I6 3 DATE-OBS D A8 IHW Date Format 4 TIME-OBS N F6.5 5 LONG-OBS C A9 6 LAT-OBS C A9 7 SYSTEM C A8 8 OBSERVER C A24 9 COMMENT ADD. OBS. C A60 May exclude some observers 10 SUBMITTR C A24 11 SPEC-EVT L L1 12 DAT-FORM C A8 13 DIS-CODE C A12 14 DAT-TYPE C A6 15 OBSVTORY C A10 16 TELESCOP C A10 17 LOCATION C A30 18 INSTRUME C A20 19 CENTFREQ N F11.4 in MHz 20 BANDWIDT N F11.4 in MHz 21 BEAMSIZE N F6.4 22 BEAMELON N F6.3 23 BEAMROTA N F6.1 24 BEAMEFF N F6.3 25 EQUINOX N F8.3 26 RAOFF N F7.4 27 DECOFF N F7.4 28 MOLECULE C A10 29 TRANSITN C A20 30 RESTFREQ N F11.4 in MHz 31 RES-SPEC N F11.4 in kHz 32 HISTORY LIMIT N F11.4 in Jy/Beam 33 HISTORY LINEPEAK N F11.4 in Jy/Beam 34 HISTORY ERR-PEAK N F11.4 in Jy/Beam 35 HISTORY LINE-VEL N F11.4 in m/s 36 HISTORY ERR--VEL N F11.4 in m/s 37 HISTORY LINE-WID N F11.4 in m/s 38 HISTORY ERR--WID N F11.4 in m/s 39 HISTORY LINEAREA N F11.4 in Jy/Beam * m/s 40 HISTORY ERR-AREA N F11.4 in Jy/Beam * m/s 41 HISTORY LINEMEAN N F11.4 in m/s 42 HISTORY ERR-MEAN N F11.4 in m/s 43 HISTORY CONTFLUX N F11.4 in Jy/Beam 44 HISTORY ERR-FLUX N F11.4 in Jy/Beam 45 DATE-BEG D A8 Date Format 46 DATE-END D A8 Date Format 47 HISTORY NWINDOW N I1 48 HISTORY WINDOW (1) D A8 Start Date of 1st Window (Date Fmt) 49 HISTORY WINDOW (1) N F5.3 Start Time of 1st Window 50 HISTORY WINDOW (N) D A8 End Date of Last Window (Date Fmt) 51 HISTORY WINDOW (N) N F5.3 End Time of Last Window 52 HISTORY POINTERR N F10.2 in arcsec 53 HISTORY CALMETH C A20 54 HISTORY CALSRCE (1)C A15 Name of Cal Source 1 55 HISTORY CALSRCE (1)N F10.3 Value of Cal Source 1 56 HISTORY CALSRCE (1)C A15 Units of Cal Source 1 57 HISTORY CALSRCE (2)C A15 Name of Cal Source 2 58 HISTORY CALSRCE (2)N F10.3 Value of Cal Source 2 59 HISTORY CALSRCE (2)C A15 Units of Cal Source 2 60 HISTORY TSYSTEM N F7.1 Value Only 61 HISTORY TRCVR N F7.1 Value Only 62 HISTORY TAUZENTH N F4.2 63 BITPIX N I2 64 NAXIS N I1 65 BSCALE N F15.9 66 BZERO N F10.4 67 BUNIT C A15 68 BLANK N I6 69 DATAMAX N F10.4 70 DATAMIN N F10.4 71 NAXIS1 N I4 72 CDELT1 C A15 73 CRPIX1 C A15 74 CRVAL1 C A15 75 CTYPE1 C A25 76 NAXIS2 N I4 77 CDELT2 C A15 78 CRPIX2 C A15 79 CRVAL2 C A15 80 CTYPE2 C A25 : : : : 96 NAXIS6 N I4 97 CDELT6 C A15 98 CRPIX6 C A15 99 CRVAL6 C A15 100 CTYPE6 C A25 101 Path:Volume C A8 Path to file on CD-ROM 102 Path:Year SubDirect C A5 Ditto 103 Path:Month SubDir. C A3 Ditto 104 Path:Day SubDirect C A3 Ditto 105 Path:Hour SubDirect C A3 Ditto 106 Filename C A8 Filename without extension _______________________________________________________________________________ V. THE RADIO SCIENCE NETWORK PRINTED ARCHIVE In addition to the FITS presentation of the Radio Science Network data, an additional format is available in the printed archive. This format provides most of the information that is necessary to make use of the data, as well as the "data summary" information included in the FITS headers, such as the line peak intensity and width for spectral line observations. The format of the printed archive for the Radio Science Network is shown below. A. Printed Format I: OH Subnetwork and Spectral Line Subnetwork Since the OH Subnetwork and the Spectral Line Subnetwork contain the same data type, it is most economical to print both subnetworks together in the same subsection of the Radio Science part of the archive. Detailed description of this format is in Table VII. Table VII. Printed Format I ________________________________________________________________________________ Col. FITS Field Field Notes Keywords Format Header ________________________________________________________________________________ 1 DATE-OBS,TIME-OBS DD.TTTTT Date(UT) 10 FILE-NUM I6 RSN# 17 MOLECULE A5 Mol 23 DAT-TYPE (4th Character) A1 Typ Denotes Subnetwork 25 RESTFREQ (MHz) I6 Freq 32 RES-SPEC (kHz) I4 Resol 37 HISTORY TSYSTEM (K) I5 Tsys 43 BEAMEFF (per cent) I2 BE 46 BEAMSIZE (arcsec) I4 HP 51 DIS-CODE (8th Character) A1 BS Denotes Beam Shape 53 Radial Offset of I4 Offset rho Beam from Nucleus (arcsec) 58 Position Angle of I3 Offset theta Radial Offset (degrees) For Limits: 62 A "<" symbol A1 63 HISTORY LIMIT (Jy/Beam) F6.1 Line Peak if value>10Jy/Beam or F6.3 if value<10Jy/Beam 80 A "-" symbol A1 Width 91 A "-" symbol A1 Velocity For Detections: 63 HISTORY LINEPEAK (Jy/Beam) F6.1 if value>10Jy/Beam or F6.3 if value<10Jy/Beam 69 A "plus or minus" symbol A1 Line Peak 70 HISTORY ERR-PEAK (Jy/Beam) F5.1 if value>10Jy/Beam or F5.3 if value<10Jy/Beam 76 HISTORY LINE-WID (km/sec) F4.2 80 A "plus or minus" symbol A1 Width 81 HISTORY ERR--WID (km/sec) F4.2 86 HISTORY LINE-VEL (km/sec) F5.2 91 A "plus or minus" symbol A1 Velocity 92 HISTORY ERR--VEL (km/sec) F4.2 For All: 97 SYSTEM A8 System 106 OBSERVER A21 Observer(s) 128 COMMENT NOTE A5 Notes ________________________________________________________________________________ B. Printed Format II: Continuum Subnetwork The data in the continuum subnetwork are fundamentally different from the spectral line data in the previous section. Thus they require a separate format, listed in Table VIII. Table VIII. Printed Format II ________________________________________________________________________________ Col. FITS Field Field Notes Keywords Format Header ________________________________________________________________________________ 1 DATE-OBS,TIME-OBS DD.TTTTT Date(UT) 11 FILE-NUM I6 RSN# 19 DAT-TYPE (4th Character) A1 Typ Denotes Subnetwork 22 CENTFREQ (MHz) I6 Freq 30 BANDWIDT (MHz) I6 BW 38 HISTORY TSYSTEM I5 Tsys 45 BEAMEFF (per cent) I2 BE 49 BEAMSIZE (arcsec) I4 HP 55 DIS-CODE (8th Character) A1 BS Denotes Beam Shape 58 Radial Offset of I4 Offset rho Beam from Nucleus (arcsec) 63 Position Angle of I3 Offset theta Radial Offset (degrees) For Limits: 68 A "<" Symbol A1 69 HISTORY LIMIT (Jy/Beam) F6.1 Flux Density if value>10Jy/Beam or F6.3 if value<10Jy/Beam For Detections: 69 HISTORY CONTFLUX (Jy/Beam) F6.1 if value>10Jy/Beam or F6.3 if value<10Jy/Beam 75 A "plus or minus" symbol A1 Flux Density 76 HISTORY ERR-FLUX (Jy/Beam) F5.1 if value>10Jy/Beam or F5.3 if value<10Jy/Beam For All: 83 SYSTEM A8 System 93 OBSERVER A21 Observer(s) 115 COMMENT NOTE A5 Notes ________________________________________________________________________________ C. Printed Format III: Occultation Subnetwork The data in the occultation subnetwork also require a separate format; they are listed in Table IX. Table IX. Printed Format III ________________________________________________________________________________ Col. FITS Field Field Notes Keywords Format Header ________________________________________________________________________________ 1 DATE-OBS,TIME-OBS DD.TTTTT Date(UT) 11 FILE-NUM I6 RSN# 19 SOURCE A12 Source 34 DAT-TYPE (4th Character) A1 Typ Denotes Subnetwork 37 CENTFREQ (MHz) I6 Freq 45 SYSTEM A8 System 55 OBSERVER A21 Observer(s) 77 COMMENT NOTE A5 Notes ________________________________________________________________________________ VI. UNITS IN THE RADIO SCIENCE ARCHIVE We have attempted to use a fixed set of standard units for the values given in the IHW archive. These units are given in Table X. Where these units are not used, as in the printed archive, the index tables, or in certain values in the HISTORY section of the FITS headers, the change of units is explicitly mentioned. The adoption of the flux density unit, Jansky per Beam (Jy/Beam), deserves an additional comment. This unit is well defined: the signal is described in terms of the flux density of a point source which would produce the same signal as that observed from the comet. The explicit use of "per Beam" in the unit acknowledges that the coma is possibly resolved by the beam to an unknown extent. Some observatories, such as the VLA, have naturally already adopted this choice of units since they use celestial point sources to calibrate the instrument. All continuum observations also use Janskys to express their results regardless of how the data are actually internally calibrated. Thus, in both of these cases, the Jansky is the obvious choice of unit. For spectral line work on large single antennas, however, results are typically expressed in "antenna temperature" since they are calibrated by comparing the observed signal to a calibration signal of known noise temperature. In recent years, this unit has become rather confusing as a result of efforts to convert a relatively well defined observed quantity into a more physically meaningful unit which gives an approximation to the true brightness temperature of the source. Thus, various forms of "corrected" antenna temperature are in use at different observatories, and it is often not clear which corrections have been made to the data. We therefore favor a system in which the calibration is achieved by direct comparison of the cometary signal to celestial sources of known flux density, and the natural unit for such a comparison is the unit of flux density, the Jansky. Thus, all observations in the archive have been converted to these units using data provided by the observers. Table X. Radio Science Units _____________________________ Angle Degrees Length Meters Time Seconds Frequency Hertz Velocity Meters/Second Flux Density Jansky/Beam* _____________________________ * 1 Jansky = 1.0*10(-26) Watts per square meter per Hertz VII. CALIBRATION Although we have converted the data in the archive to a common unit of flux density, we have made no attempt to recalibrate data to a common flux density scale. The calibration scale for radio astronomy is well established at centimeter wavelengths, and in general, well known standard sources were used by the network observers. For wavelengths shorter than about 1 centimeter, how- ever, the calibration becomes less precise as atmospheric attenuation becomes significant in the observations. In most cases, comparisons to celestial sources are more indirect and observers rely on absolute calibration schemes as their primary method. Ultimately, though, even these techniques use known sources, such as the planets, to calibrate the system, and we have attempted to archive information about these calibration sources with each observation. Calibration information that is supplied to us by the observer is given in the HISTORY section of the FITS header. The HISTORY CALMETH keyword provides an ASCII string with a brief description of the calibration method used. Three methods are commonly used: (1) STANDARDS indicates that the data were calibrated through direct comparison to standard sources; (2) NOISE TUBE indicates that the data were primarily calibrated by injecting power from a noise source into the receiver; (3) CHOPPER WHEEL indicates that the "chopper wheel" method was used. This latter method uses the comparison of the noise power from an ambient temperature load to that produced by the sky emission to make an estimate of the optical depth of the atmosphere, and it is commonly used at millimeter wavelengths. Even in the cases of NOISE TUBE and CHOPPER WHEEL calibration, where celestial sources are not initially used to calibrate the data, the final calibration is generally made with celestial sources. Whenever a standard source is used for this purpose, its name and assumed flux density are given in the HISTORY CALSRCE keywords. More than one of these keywords may exist in the header if more than one calibration source is used. For planetary sources, the assumed brightness temperature is given rather than the flux density since planetary flux densities vary with distance to the object. Finally, the system temperature (defined to be the total system noise temperature including receiver noise and atmospheric and ground pickup) and the receiver temperature (defined to be the noise temperature of the receiver alone) are given in the HISTORY TSYSTEM and HISTORY TRCVR keywords; the atmospheric opacity at zenith is given in the HISTORY TAUZENTH keyword where appropriate. ACKNOWLEDGEMENTS Several people who are not members of the Discipline Specialist Team (listed in Table I) have also made substantial contributions to the success of the Radio Science Network of the International Halley Watch. First of all, we wish to acknowledge the contributions from the observers who have submitted data to the archive, since if it were not for their interest and assistance, then there would be no archive. We also appreciate those who attempted to observe comet P/Giacobini-Zinner even if they did not get useful data. In many cases, these early attempts paid off in our later studies of comet Halley. The Disci- pline Specialists at the University of Massachusetts were aided in their effort by a number of collaborators during the course of our involvement with the IHW. We gratefully acknowledge the efforts of R. Bassett, M. Claussen, C. Clemens, R. Molloy, G. Moriarty-Schieven, D. Swade, and L. Tacconi-Garman, who have provided assistance to the project at various times throughout its duration.