Data Set Overview : This dataset presents a collection of 2334 published and 319 unpublished results in cometary polarimetry. The database contains 2653 measurements of linear and circular polarization for 65 comets since 1940. The narrow-band and broad-band measurements within the spectral region 0.3-3.5 micron are presented. The ranges of phase angles, helio- and geocentric distances of comets are 0.4-122 deg, 0.6-4.8 AU and 0.03-4.9 AU, respectively. We have compiled 64 references to the published papers and some unpublished sources. The data are presented in a tabular format (ASCII code). The database can be used as the observational basis for detailed theoretical modeling, interpretation of the phase-angle and spectral dependence of polarization, classification of comets, and for selecting future space-mission targets.  The Database of Comet Polarimetry (DBCP.TAB) was initiated in 2005 with a goal to collect an cataloque of all available data for the linear and circular polarization of comets.  A total of 65 comets are includung in this version of the DBCP. The data obtained during the years 1940 - 2005 were collected from the different published sources and partially unpublished observations of authors this database. Observations were carried out using various telescopes and various polarimetric equipment including photographic, photoelectric and imaging techniques.  DBCP is a current agglomeration cataloque and new data will be added to it periodically.  Parameters : The primary data included in each record includes polarization parameters and filter descriptions. N. Kisilev provided the following explanation of the polarization parameters recorded in the data file:  Generally polarization can be described by means of the Stokes parameters I, Q, U and V. The link between the Stokes parameters and the geometry of a polarization ellipse is given by:  I : a**2 Q : a**2 cos 2beta cos 2theta U : a**2 cos 2beta sin 2theta V : a**2 sin 2beta  where a represents the ellipse size tan beta is the ratio of the minor to major axes (beta : 0 for linear and pi/2 for circular polarization) theta is the orientation of the ellipse  In most cases observers measured four intensities J at polarizer angles 0, 45, 90 and 135 degree in a given reference system. Then for light with an arbitrary linear polarization the Stokes parameters are:  I : J(0)+J(90) : J(45)+J(135) Q : J(0)-J(90) : Ip cos2theta U : J(45)-J(135) : Ip sin2theta P : 100sqrt(Q**2+U**2)/I [percent of linear polarization] theta : 1/2arctg(U/Q) [position angle of plane of polarization]  The most commonly used related parameter is theta(r), referring to the scattering plane  theta(r) : theta-(Sca+/-90)  where Sca is the position angle of the scattering plane and the sign in the parentheses is chosen to guarantee 0theta(r)>45. Thus, sign of the polarization quoted in the data table is determined by value of theta(r) that is given in the same record.  More commonly, the negative percent of polarization for the whole coma of comets is larger than -5% and occurs at phase angles less than approximately 22 degrees. An exception to the rule is comet C/Ikeya-Seki (1965 S1), for which the percent of polarization in the tail was about -40% at phase angle 44 degrees.  Processing : The details of the data processing are reported in the individual papers (file references.tab). Users should note that the only the original papers provide any information about polarization bias correction.

Confidence Level Overview : The dataset contains the errors for linear polarization, the angle of the polarization plane, and circular polarization indicated in the corresponding columns of the main table.  Users must consult the original papers for polarization bias correction.