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    • MPEC 2018-H54 : 2. A/ Objects

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    M.P.E.C. 2018-H54                                Issued 2018 Apr. 20, 16:47 UT

     The Minor Planet Electronic Circulars contain information on unusual
         minor planets and routine data on comets.  They are published
    on behalf of Division F of the International Astronomical Union by the
          Minor Planet Center, Smithsonian Astrophysical Observatory,
                          Cambridge, MA 02138, U.S.A.

             Prepared using the Tamkin Foundation Computer Network

                              MPC@CFA.HARVARD.EDU
            URL https://www.minorplanetcenter.net/    ISSN 1523-6714

                       COMET MAGNITUDES AND A/ OBJECTS


1. Comet Magnitudes

     Comet observations were first published routinely by the Minor Planet
Center (MPC) after the move from Cincinnati to Cambridge in 1978.  The
Editorial Notice on Minor Planet Circular 4391 [1978 Mar. 1] remarks (noting
that the original all-capitals text has been changed to mixed-case):

    "We intend to continue to issue the M[inor]P[lanet]C[ircular]s in
essentially the same form as before.  The principal change being that some of
the less urgent cometary data, hitherto published on the IAU Circulars,
will be transferred here."

and, in referring to the lists of observations published in these
Circulars:

    "In the case of comets, the notations T and N stand for the total (m_1)
and nuclear (m_2) magnitudes, respectively."

     Since 1978 the MPC has made the use of T and N mandatory for magnitude
estimates of comets.

     In the new ADES format, the notations T and N are not supported.  Rather,
a comet's magnitude is there expressed as a value in a given photometric-
aperture in a given band.

     The MPC intends to end its enforcement of the use of T and N on comet
magnitudes effective Apr. 24.

     Starting on the above date, observers should report comet magnitudes in
the same form that they report minor-planet magnitudes.  See MPEC 2018-H21
for examples.

     Observers who wish to continue using T and N may do so, for as long as
they report their observations in the 80-column format.


2. A/ Objects

     The MPC is clarifying the circumstances under which an A/ designation
is assigned.  The original implementation of the current cometary designation
system (see Editorial Notice on MPC 23803-23804 [1994 Aug. 28]) describes A/
designations as:

    "If necessary, the prefix A/ would precede a comet designation that
actually refers to a minor planet (or asteroid)"

It is not a requirement that an object has been designated previously as a
comet for an A/ designation to be assigned.

     An A/ designation will be used for an object with an osculating
hyperbolic orbit that has not been reported as cometary.

Gareth V. Williams           (C) Copyright 2018 MPC           M.P.E.C. 2018-H54

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