| DATA_SET_DESCRIPTION |
Data Set Overview
=================
LOWELL OBSERVATORY COMETARY DATABASE - PRODUCTION RATES
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
included.
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.
Parameters
==========
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.
'asymmtry.tab' lists difference values for log Q of OH and CN
as well as log (A*f*rho)
'obsparam.tab' lists the number of pre- and post-perihelion
observations and the minimum and maximum heliocentric
distances observed on both sides of perihelion
'prdepend.tab' lists production rate dependencies pre- and post-
perihelion as the slope of the production rates,
with error bars
'prodrate.tab' 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.
'restrict.tab' 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].
Processing
==========
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
[COCHRAN&SCHLEIC1993]).
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 +
((W_em-W_cont1)/(W_cont2-W_cont1))^2*P_cont2^2)*Cp_em^2)/(100-Cp_em)^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.
Data
====
Five data files constitute this submission to the PDS:
asymmtry.tab Production rate assymetry about perihelion
obsparam.tab Observational parameters
prdepend.tab Production rate dependencies expressed as slopes
prodrate.tab Production rate ratios
restrict.tab Results for the restricted data set
Coverage
========
Following is a list of the comets included in this data set. All are
listed in the 'prodrate.tab' and 'obsparam.tab' files. Comets listed
in the 'asymmtry.tab', 'prdepend.tab', and 'retrict.tab' files are
indicated by an 'x' in the corresponding column.
Principal
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
Media/Format
============
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.
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