Description of the TORINO ASTEROID POLARIMETRY bundle V1.0
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Bundle Generation Date: 2020-02-28
Peer Review: 2006 Asteroid Review, 2006-05-25                                 
Discipline node: Small Bodies Node


Content description based on the data set catalog file description for the PDS3 version, EAR-A-I0066-5-TORINOPOL-V1.0
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Note: for PDS3 data sets migrated to PDS4, the following text is taken
verbatim from the data set description and confidence level note of the
PDS3 data set catalog file. In these cases, some details may not be correct
as a description of the PDS4 bundle.
                                                           
    A long term project of polarimetric observtions of asteroids is           
    being conducted at the 2.15-m telescope of the El Leoncito                
    Observatory in Argentina, using the Torino photopolarimeter.  The         
    results from 1995 through 2005 were reported in Cellino et al.            
    (2005) and are archived in this data set.                                 
                                                                              
    The Torino photopolarimeter, described in Scaltriti et al. (1989),        
    is capable of simultaneous polarimetric observations in UBVRI             
    colors, making it possible to obtain an automatic elimination of          
    the spurious polarization of the background skylight.  Since the          
    observations are simultaneous, they are not affected by  possible         
    changes of polarization due to rotation of the target.                    
                                                                              
    For all the observations included in this data set, the instrument        
    was used in the linear polarization configuration.  Data reduction        
    is based on standard routines developed for this kind of                  
    instrument, with some adaptation for the needs of asteroid                
    observation.  Specifically, the reduction routines included               
    standard procedures to derive the Stokes parameters from photon           
    countings obtained at eight different positions of a half-wave            
    plate located in front of the polarizer (a calcite block). From           
    these photon countings the Stokes parameters Q an U (also called          
    Px and Py by some authors) are derived, which fully describe the          
    state of linear polarization. Then, the Pr parameter, which is the        
    scientific result of polarization observations of asteroids, is           
    computed as P (square root of Q**2 + U**2) times cosine(2*theta),         
    theta being the angle between the plane of linear polarization of         
    the incoming beam, and the plane perpendicular to the scattering          
    plane (defined as the Earth - target - Sun plane). Theta is               
    computed from trivial geometrical considerations, being known from        
    the coordinates of the Sun and of the asteroid at the epoch of            
    observation.                                                              
                                                                              
    The observations were carried out between 1995 and 2005, with             
    typically one or two observing runs per year and 4-7 nights per           
    run.  Observing nights were usually selected around the new moon          
    to minimize the polarization contamintaion by moonlight.                  
                                                                              
    In the paper, the results are divided into Tables 1-4,                    
    representing different polarimetric investigations, plus one              
    summary table.  Here, the data in Tables 1-4 are combined into one        
    data file, torinopol.tab.  Table 5, the summary table, is included        
    here in the file table5.tab.                                              
                                                                              
    The file torinopol.tab contains object number and phase angle,            
    followed by proper polarization and theta in each of the five             
    bandpasses UBVRI, and their uncertainties.                                
                                                                              
    In addition, the file table5.tab (Table 5 in the published paper)         
    contains a summary of overall results for the IRAS-observed               
    asteroids with basic data in Table 2.                                     
                                                                              
    References:                                                               
                                                                              
    Cellino, A., R. Gil Hutton, M. DiMartino, Ph. Bendjoya, I.N.              
    Belskaya, and E.F. Tedesco, Asteroid polarimetric observations            
    using the Torino UBVRI photopolarimeter, Icarus 179, 304-324,             
    2005.                                                                     
                                                                              
    Scaltriti, F., V. Piirola, A. Cellino, E. Anderlucci, L. Corcione,        
    G. Massone, F. Racioppi, and F. Porcu, The UBVRI photopolarimeter         
    of the Torino Astronomical Observatory, Mem. Soc. Astron. It. 60,         
    243-246, 1989.


Known issues or problems with the data
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    See the published paper, Cellino et al. (2005) for detailed               
    information about the reliability of the measurements.

PDS3 Source
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Version 1.0 of this bundle was migrated from version 1.0 of the PDS3 data set EAR-A-I0066-5-TORINOPOL-V1.0.