Data Set Information
DATA_SET_NAME LOWELL OBSERVATORY COMETARY DATABASE
DATA_SET_ID EAR-C-PHOT-3-RDR-LOWELL-COMET-DB-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : LOWELL OBSERVATORY COMETARY DATABASE [ NOTE: These files do NOT comprise the intended complete dataset. Further work is being carried out on 17 of the 85 observed comets. These 17 objects have been omitted from this initial submission. Once that work is completed, an updated version of this dataset will be submitted and ingested. ] The database presented here is comprised entirely of observations made utilizing conventional photoelectric photometers and narrowband filters isolating 5 emission species (OH, NH, CN, C3 and C2) and continua. This work was initiated by A'Hearn and Millis in 1976 and includes 2020 observations of 85 comets obtained over 429 nights through the end of 1992. The total number of observations, however, is not evenly distributed over the 85 comets. The median number of observations for a comet is 6, with only a single observation obtained for 14 comets while there were 820 observations of P/Halley. The majority of observations were obtained at either Lowell Observatory or Perth Observatory, however four other observatories were used including an extensive campaign on comet P/Halley from the Cerro Tololo Interamerican Observatory (CTIO). In this archive, results for a subset of 68 comets are presented while the results for P/Halley from this study are archived in the IHW archive. One 'observation' as defined here represents a set of measurements usually through at least 5 narrowband filters. A typical measurement sequence consisted of sets of 3 ten second integrations in each of two or three filters on the comet followed by a similar integration set on a sky position about 30 arcminutes from the comet. This would alternate from comet to sky and sky to comet until data were collected for all appropriate filters. While this description illustrates the observational method, it is important to keep in mind that deviations were common. For example, filter integration times of 90 seconds or longer were often employed for faint comets while times as short as 10 seconds were used for bright comets at high airmasses. A night of observing would normally include comet observation(s) along with standard star measurements in all filters extending over a sufficient range of airmass (most often bracketing the comet observations) to accurately determine extinction coefficients. A discussion of standard stars and the zero point for the magnitude system with respect to the International Halley Watch filter set can be found in Osborn, et al. (1990) [OSBORNETAL1990]. A full description of these data and the reduction process, along with a comparative analysis of the results of Haser model production rates can be found in A'Hearn, et al. (1995) [AHEARNETAL1995]. Several tables from that paper are included in the PDS archives as the 'LOWELL OBSERVATORY COMETARY DATABASE - PRODUCTION RATES' dataset. Parameters : All essential parameters including fluxes, aperture sizes, comet heliocentric and geocentric positions and heliocentric radial velocity are provided in this PDS submission. 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]. Filters : The program began with a set of narrowband filters isolating the emission species CN, C3,and C2 as well as three continuum regions at 392, 412, and 524 nanometers (A'Hearn, et al. 1979 [AHEARNETAL1979]). In 1979, filters isolating the emission species OH and NH were added along with an additional continuum filter at 367 nanometers (A'Hearn, et al. 1981 [AHEARNETAL1981]). By 1984, the standardized filters of the International Halley Watch (IHW) replaced the earlier filters at wavelengths greater than 365 nm. Full details of the IHW filters can be found in A'Hearn (1991) [AHEARN1991] and A'Hearn and Vanysek (1992) [AHEARN&VANYSEK1992]. Processing : The processing carried out on the Lowell Observatory Cometary Database has been described in detail elsewhere (A'Hearn & Millis 1980 [AHEARN&MILLIS1980]; A'Hearn 1991 [AHEARN1991]; A'Hearn, et al. 1995 [AHEARNETAL1995]), a brief explanation follows. The initial data product consists of Universal Times and object and sky measurements. For pulse-counting systems, count rates were measured and corrected to first order for the dead-time of the detector using: n : nobs/[1.0 - nobs*t] where n and nobs are the actual and observed counting rates and t is the detector dead-time. For direct-current systems, readings from the DC amplifier were calibrated using standard voltages. Actual counts were then converted to instrumental magnitudes. The standard stars defined for the IHW (Osborn et al. 1990 [OSBORNETAL1990]) were used for extinction and absolute calibration to reduce the instrumental magnitudes to the standard magnitude system outside the atmosphere. Extinction coefficients were evaluated for each night by least squares fitting of magnitude vs. airmass for individual standards. A global least squares solution using all standards and simultaneously solving for the extinction coefficients and the zero point correction was also often employed. For all but the OH filter, the atmospheric attenuation is linear with airmass and in these cases airmass was calculated via the standard cubic polynomial: X : secZ - 0.0018167*[secZ - 1] - 0.002875*[secZ - 1]^2 - 0.0008083*[secZ - 1]^3 where Z is the refracted zenith distance. In the case of the OH filter, the monochromatic attenuation changes appreciably across the bandpass. Therefore, a pseudo-airmass was modeled such that the attenuation would be linear in this variable. A detailed description of the modeling procedure can be found in A'Hearn (1991) [AHEARN1991] and references therein. It is straightforward to convert from the standard system magnitudes to fluxes per unit wavelength in the continuum by simply applying a scale factor depending on the specific wavelength A'Hearn (1991) [AHEARN1991]. However, a complication arises when dealing with the IHW 4845 angstrom continuum filter A'Hearn, et al. (1995) [AHEARNETAL1995]. In order to derive the fluxes in the emission bands, the underlying continuum must first be subtracted. Assuming there is no gross structure in the continuum reflectivity of the cometary grains (i.e., they vary linearly with wavelength with respect to solar colors), it is possible to use observations of the comet in a pair of continuum bandpasses along with solar analog colors to evaluate the continuum contribution to an emission band. In this study we have used two pairs of continuum filters; 3650-4845 angstroms for the IHW filter set and 3675-5240 angstroms for the earlier data. After removal of the underlying continuum, the emission band fluxes were converted to real units (ergs cm-2 s-1) by multiplying by appropriate scale factors for each filter A'Hearn, et al. (1995) [AHEARNETAL1995]. 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 & 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 & 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 0.000000 for measurements of the continuum and C3 and an error of 2 0.000000 for 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 : Three data files constitute this submission to the PDS: locdflux.tab includes the comet ID, the UT date and time, and fluxes for each of the observed species along with the percentage uncertainties in the flux measurements. locdprod.tab includes observational circumstances and Haser Model production rates for 68 of the comets included in the A'Hearn et al (1995) [AHEARNETAL1995] analysis. locdparm.tab includes comets full names, comet ID, and observational circumstances. Coverage : Following is a list of the comets included in this data set. Principal Number, Type and Name Designation ------------------------------ ----------- 49P/Arend-Rigaux 1951 C2 47P/Ashbrook-Jackson 1948 Q1 C/Austin 1982 M1 C/Austin 1984 N1 C/Austin 1989 X1 85P/Boethin 1985 T2 19P/Borrelly 1904 Y2 C/Bowell 1980 E1 C/Bradfield 1979 M1 C/Bradfield 1979 Y1 C/Bradfield 1980 Y1 C/Bradfield 1987 P1 16P/Brooks 2 1889 N1 23P/Brorsen-Metcalf 1989 N1 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 108P/Ciffreo 1985 V1 27P/Crommelin 1928 W1 6P/d'Arrest 1851 M1 C/Elias 1981 G1 2P/Encke 1818 W1 4P/Faye 1843 W1 C/Furuyama 1987 W2 78P/Gehrels 2 1981 L1 21P/Giacobini-Zinner 1900 Y1 26P/Grigg-Skjellerup 1922 K1 65P/Gunn 1970 U2 1P/Halley 1982 U1 D/Haneda-Campos 1978 R1 103P/Hartley 2 1991 N1 C/Hartley-Good 1985 R1 P/Hartley-IRAS 1983 V1 45P/Honda-Mrkos-Pajdusakova 1948 X1 88P/Howell 1981 Q1 126P/IRAS 1983 M1 C/IRAS 1983 O2 C/IRAS-Araki-Alcock 1983 H1 59P/Kearns-Kwee 1963 Q1 68P/Klemola 1965 U1 C/Kohler 1977 R1 22P/Kopff 1906 Q1 C/Levy 1990 K1 C/Levy-Rudenko 1984 V1 C/Liller 1988 A1 C/Machholz 1985 K1 C/Meier 1978 H1 C/Meier 1979 S1 C/Meier 1980 V1 97P/Metcalf-Brewington 1991 A1 28P/Neujmin 1 1913 R2 C/Nishikawa-Takamizawa-Tago 1987 B1 C/Okazaki-Levy-Rudenko 1989 Q1 C/Panther 1980 Y2 94P/Russell 4 1984 E1 31P/Schwassmann-Wachmann 2 1929 B1 102P/Shoemaker 1 1984 S2 C/Shoemaker 1983 R1 C/Shoemaker 1984 K1 C/Shoemaker 1984 U1 C/Shoemaker 1984 U2 C/Shoemaker-Levy 1991 B1 C/Shoemaker-Levy 1991 T2 C/Skorichenko-George 1989 Y1 74P/Smirnova-Chernykh 1975 E2 C/Sorrells 1986 V1 38P/Stephan-Oterma 1980 L2 C/Sugano-Saigusa-Fujikawa 1983 J1 109P/Swift-Tuttle 1992 S2 98P/Takamizawa 1984 O1 69P/Taylor 1915 W1 9P/Tempel 1 1867 G1 10P/Tempel 2 1873 N1 C/Thiele 1985 T1 C/Tsuchiya-Kiuchi 1990 N1 62P/Tsuchinshan 1 1965 A1 8P/Tuttle 1858 A1 81P/Wild 2 1978 A2 116P/Wild 4 1990 B1 C/Wilson 1986 P1 46P/Wirtanen 1948 A1 43P/Wolf-Harrington 1924 Y1 C/Kohoutek 1973 E1 C/West 1975 A1-A Ancillary Data : See the associated Production Rates dataset for tables of the Production Rate and Active Areas, Production Rate r(H) Dependencies, Assymetry of Production Rates about Perihelion, and Observational and Dynamical Parameters from A'Hearn et al. (1995) [AHEARNETAL1995]. 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.
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_NAME SUPPORT ARCHIVES
MISSION_START_DATE 2004-03-22T12:00:00.000Z
MISSION_STOP_DATE N/A (ongoing)
TARGET_NAME COMET
TARGET_TYPE COMET
INSTRUMENT_HOST_ID LOWELL
INSTRUMENT_NAME PHOTOMETER
INSTRUMENT_ID PHOT
INSTRUMENT_TYPE PHOTOELECTRIC PHOTOMETER
NODE_NAME Small Bodies
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Review : The LOCD was reviewed internally by David Osip prior to release to the planetary community. The PDS external peer review was held in September 1998.
CITATION_DESCRIPTION Unknown
ABSTRACT_TEXT The database presented here is comprised entirely of observations made utilizing conventional photoelectric photometers and narrowband filters isolating 5 emission species (OH, NH, CN, C3 and C2) and continua. This work was initiated by A'Hearn and Millis in 1976 and includes 2020 observations of 85 comets obtained over 429 nights through the end of 1992. The total number of observations, however, is not evenly distributed over the 85 comets. The median number of observations for a comet is 6, with only a single observation obtained for 14 comets while there were 820 observations of P/Halley. The majority of observations were obtained at either Lowell Observatory or Perth Observatory, however four other observatories were used including an extensive campaign on comet P/Halley from the Cerro Tololo Interamerican Observatory (CTIO). In this archive, results for a subset of 68 comets are presented while the results for P/Halley from this study are archived in the IHW archive.
PRODUCER_FULL_NAME DAVID J. OSIP
SEARCH/ACCESS DATA
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