Data Set Information
DATA_SET_TERSE_DESCRIPTION Derived production rates and error bars from the Lowell Observatory Cometary Database
Data Set Overview
      This dataset presents several data tables from A'Hearn et al. (1995)
      [AHEARNETAL1995], which contain a comparative analysis of Haser
      model production for the observations included in the Lowell
      Observatory Cometary Database (LOCD). In addition, similar data
      for two more comets, West (1975 A1-A) and Kohoutek (1973 E1), are
      The LOCD observational dataset is also available from the PDS.
      For more information about the collection and reduction of the
      data in the LOCD, see the PDS documentation for that dataset in
      addition to the source paper for the present data.
      Each table lists object identifications in several systems in
      addition to the other parameters.  The user is strongly urged to
      consult A'Hearn et al. (1995) for detailed explanations of the
      parameters and values in the tables and for cautionary notes
      regarding interpretation of the various values.
      ''  lists difference values for log Q of OH and CN
                      as well as log (A*f*rho)
      ''  lists the number of pre- and post-perihelion
                      observations and the minimum and maximum heliocentric
                      distances observed on both sides of perihelion
      ''  lists production rate dependencies pre- and post-
                      perihelion as the slope of the production rates,
                      with error bars
      ''  lists the mean ratio of production rates of various
                      species to those of OH and CN, with error bars and
                      additional information, including dynamical class.
      ''  lists the results for a restrited set of observations,
                      chosen to minimize error bars.
      The fluorescence efficiencies used for the column density calculations
      as well as all additional Haser Model parameters can also be found in
      A'Hearn et al. (1995) [AHEARNETAL1995].
      See the Lowell Observatory Cometary Database observational dataset
      for a brief description of the techniques employed in gathering the
      data and performing the initial reduction. A summary of the technique
      employed by A'Hearn et al. (1995) follows.
      Fluxes-Column Abundances of Emission Species
      The emission band fluxes were converted to molecular abundances in
      the observed column by means of the fluorescence efficiency (L/N),
      commonly referred to as the g-factor.  The g-factor values used for
      this analysis can be found in A'Hearn, et al. (1995) [AHEARNETAL1995].
      The fluorescence efficiencies for OH (Schleicher and A'Hearn 1988
      [SCHLEICHER&AHEA1988]) and NH (Kim, et al. 1989 [KIMETAL1989]) were
      interpolated from tables as a function of heliocentric radial
      velocity at 1 AU in order to account for the Swings effect.  They
      were then scaled by the standard heliocentric distance (rH)
      dependence of rH^-2.  For CN, a double interpolation in heliocentric
      radial velocity and heliocentric distance was used to account for
      the Swings effect as well as known deviations from the standard
      rH^-2 dependence (Schleicher 1983 [SCHLEICHER1983]).  Again the
      interpolated values were then scaled by rH^-2.  Fluorescence
      efficiencies for C2 and C3 are taken as single values scaled by
      rH^-2.  The Swings effect is not prevalent in these bands due to
      the much larger number of lines involved as even a significant
      effect for an individual line will have basically no effect on
      the band intensities.
      Column Abundances - Molecular Production Rates
      The column abundances for each species were converted to production
      rates by means of the classic Haser model.  Haser modeling consists
      of two steps.  For a detailed description of the original model the
      reader is referred to Haser (1957) [HASER1957]; the following is a
      brief explanation.
      First, two scale-lengths are required to infer the spatial distribution
      in the coma and allow extrapolation from the molecular abundance in a
      given field of view to the entire coma abundance.  Second, the lifetime
      of the observed species is needed in order to calculate a production
      rate.  If the parent species is known (not the case for most of our
      species) and a branching ratio for production of the daughter from the
      parent is also known, the production rate of the parent can likewise be
      determined.  This study is limited to the production rates of the
      observed species, so the branching ratio is set to one.
      The scale-lengths used for this reduction are all recently determined
      independently from wide-field CCD images and long-slit spectra
      (Randall, et al. 1992 [RANDALLETAL1992]; Cochran and Schleicher 1993
      Continuum Fluxes - Dust Production
      As a factor to compare intrinsic dust production from comet to comet,
      we have adopted the parameter A(q)frho, as described by A'Hearn, et al.
      (1984) [AHEARNETAL1984].  The formula is A(q)frho = q*rH^2*D*Fl/a
      where A(q) is the Bond albedo at the observed scattering angle, q; f
      is the filling factor of grains in the field of view; rho is the radius
      of the circular field of view; rH and D are heliocentric and
      geocentric distances (measured in AU); Fl is the mean continuum flux
      averaged over the filter bandpass (in erg cm-2 s-1 A-1); a is the
      angular diameter of the field of view (in arcsec); and q is a filter-
      dependent numerical coefficient that incorporates the solar flux
      within the filter bandpass.
      Provided the dust flows away from the nucleus without changing its
      velocity or breaking up and without brightening or darkening, A*f*rho
      will be proportional to the dust production rate.
      While the A*f*rho measure of the dust production is rather ad hoc, it
      serves as an adequate means, essentially independent of the aperture
      size, of comparing dust production between comets or for the same
      comet at different times.
      Error Propagation
      Photometric uncertainties in the raw data were initially determined
      assuming the most common filter integration time of 30 seconds and
      using the rms scatter of the individual 1 second integrations.  All
      uncertainties were expressed as percent errors.
      The percentage uncertainties estimated for each filter were then
      propagated through the reduction procedure described in the previous
      sections.  Additional errors in the extinction coefficients, the zero
      point of the photometric system, and the flux transformation
      coefficients were added in quadratically.  An additional source of
      uncertainty, the dominant source for the bright comets, was centering
      error due to the comet's motion and diffuse nature.  In this study,
      we have quadratically added a centering error of 3 0.000000or
      measurements of the continuum and C3 and an error of 2 0.000000or all
      other species.  These values are higher for the continua and C3 since
      these species have the most sharply peaked spatial distributions.
      The percentage errors for the emission band fluxes were then calculated
      via the following equation:
      SigEM = SQRT[P_EM^2.0+((((W_cont2-W_em)/(W_cont2-W_cont1))^2*P_cont1^2 +
      where P_EM, P_cont1, and P_cont2 are the percentage uncertainties in the
      emission band filter and the two respective continuum bands; W_em,
      W_cont1, and W_cont2 are the wavelengths of the emission band and the
      continuum bands and Cp_em is the precentage of underlying continuum in
      the emission band.
      The final photometric flux errors provide an adequate representation
      of statistical uncertainties in the data.  These percentage errors in
      the fluxes are representive of the uncertainties in most other derived
      parameters (e.g., column densities and production rates).  In the case
      of gassy comets, these final errors underestimate the uncertainty in
      the C3 and NH filters since they fail to include the additional error
      from contamination of the underlying continuum as previously
      discussed.  There may be additional uncertainties introduced from the
      choice of model parameters (e.g., scale-lengths, lifetimes) that are
      not well understood at this time.  However, since they affect the
      results for all comets the same way (i.e., they will not affect a
      comparative analysis), they are not incorporated.
      Five data files constitute this submission to the PDS:      Production rate assymetry about perihelion      Observational parameters      Production rate dependencies expressed as slopes      Production rate ratios      Results for the restricted data set
      Following is a list of the comets included in this data set. All are
      listed in the '' and '' files. Comets listed
      in the '', '', and '' files are
      indicated by an 'x' in the corresponding column.
      Number, Type and Name         Designation  asymmtry  prdepend restrict
      ------------------------------ ----------  --------  -------- --------
       49P/Arend-Rigaux               1951 C2        x         x       x
       47P/Ashbrook-Jackson           1948 Q1        x
         C/Austin                     1982 M1                  x
         C/Austin                     1984 N1                  x       x
         C/Austin                     1989 X1        x         x       x
       85P/Boethin                    1985 T2                          x
       19P/Borrelly                   1904 Y2        x         x       x
         C/Bowell                     1980 E1        x
         C/Bradfield                  1979 M1
         C/Bradfield                  1979 Y1                  x       x
         C/Bradfield                  1980 Y1
         C/Bradfield                  1987 P1        x         x       x
       16P/Brooks 2                   1889 N1                          x
       23P/Brorsen-Metcalf            1989 N1                  x       x
       87P/Bus                        1981 E1
         C/Bus                        1981 H1
         C/Cernis                     1983 O1
         C/Cernis-Petrauskas          1980 O1
      101P/Chernykh                   1977 Q1
       67P/Churyumov-Gerasimenko      1969 R1        x         x       x
      108P/Ciffreo                    1985 V1
       27P/Crommelin                  1928 W1        x         x       x
        6P/d'Arrest                   1851 M1        x                 x
         C/Elias                      1981 G1
        2P/Encke                      1818 W1        x         x       x
        4P/Faye                       1843 W1        x                 x
         C/Furuyama                   1987 W2
       78P/Gehrels 2                  1981 L1
       21P/Giacobini-Zinner           1900 Y1        x         x       x
       26P/Grigg-Skjellerup           1922 K1                          x
       65P/Gunn                       1970 U2
        1P/Halley                     1982 U1        x         x       x
         D/Haneda-Campos              1978 R1
      103P/Hartley 2                  1991 N1                          x
         C/Hartley-Good               1985 R1        x         x       x
         P/Hartley-IRAS               1983 V1
       45P/Honda-Mrkos-Pajdusakova    1948 X1
       88P/Howell                     1981 Q1
      126P/IRAS                       1983 M1                  x       x
         C/IRAS                       1983 O2
         C/IRAS-Araki-Alcock          1983 H1        x                 x
       59P/Kearns-Kwee                1963 Q1        x
       68P/Klemola                    1965 U1                  x       x
         C/Kohler                     1977 R1
       22P/Kopff                      1906 Q1        x         x       x
         C/Levy                       1990 K1        x         x       x
         C/Levy-Rudenko               1984 V1                          x
         C/Liller                     1988 A1
         C/Machholz                   1985 K1
         C/Meier                      1978 H1
         C/Meier                      1979 S1
         C/Meier                      1980 V1        x         x       x
       97P/Metcalf-Brewington         1991 A1                          x
       28P/Neujmin 1                  1913 R2
         C/Nishikawa-Takamizawa-Tago  1987 B1
         C/Okazaki-Levy-Rudenko       1989 Q1        x         x       x
         C/Panther                    1980 Y2        x                 x
       94P/Russell 4                  1984 E1
       31P/Schwassmann-Wachmann 2     1929 B1        x
      102P/Shoemaker 1                1984 S2
         C/Shoemaker                  1983 R1        x
         C/Shoemaker                  1984 K1                  x
         C/Shoemaker                  1984 U1        x
         C/Shoemaker                  1984 U2                          x
         C/Shoemaker-Levy             1991 B1
         C/Shoemaker-Levy             1991 T2                  x       x
         C/Skorichenko-George         1989 Y1
       74P/Smirnova-Chernykh          1975 E2        x
         C/Sorrells                   1986 V1        x                 x
       38P/Stephan-Oterma             1980 L2        x         x       x
         C/Sugano-Saigusa-Fujikawa    1983 J1                  x       x
      109P/Swift-Tuttle               1992 S2                          x
       98P/Takamizawa                 1984 O1                          x
       69P/Taylor                     1915 W1
        9P/Tempel 1                   1867 G1                  x       x
       10P/Tempel 2                   1873 N1        x         x
         C/Thiele                     1985 T1                  x       x
         C/Tsuchiya-Kiuchi            1990 N1        x         x       x
       62P/Tsuchinshan 1              1965 A1
        8P/Tuttle                     1858 A1                  x
       81P/Wild 2                     1978 A2                  x       x
      116P/Wild 4                     1990 B1
         C/Wilson                     1986 P1
       46P/Wirtanen                   1948 A1
       43P/Wolf-Harrington            1924 Y1        x                 x
         C/Kohoutek                   1973 E1        x         x
         C/West                       1975 A1-A                x
      This dataset is released in the form of ASCII files which may be
      stored on disk or other magnetic medium and which may be
      distributed by ftp, email, real-time access by remote login, or by
      whatever means is most convenient.
DATA_SET_RELEASE_DATE 1998-02-01T00:00:00.000Z
START_TIME 1976-08-12T06:24:28.800Z
STOP_TIME 1991-10-11T11:15:12.600Z
MISSION_START_DATE 2004-03-22T12:00:00.000Z
NODE_NAME Small Bodies
      The LOCDPR was included in the PDS external peer review of comet data
      held September 1998.  Significant revisions were recommended, so the
      data are being presented for a second review in December 2002.
ABSTRACT_TEXT 20 Oct 2008, A.C.Raugh AddedThis dataset presents several data tables from A'Hearn et al. (1995) [AHEARNETAL1995], which contain a comparative analysis of Haser model production for the observations included in the Lowell Observatory Cometary Database (LOCD). In addition, similar data for two more comets, West (1975 A1-A) and Kohoutek (1973 E1), are included.
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