International Comet Quarterly

ICQ: Recommended (and condemned) sources for stellar magnitudes


Below is a list that observers may use to evaluate whether the source(s) that they are contemplating using for visual or V stellar magnitudes are recommended or not. Unfortunately, many errors have been found over the years in the both the individual variable-star charts of the AAVSO (ICQ code AC) and the AAVSO Variable Star Atlas (code AA); those variable-star charts were designed for the purpose of tracking the relative variation in brightness of individual variable stars, and they frequently are not adequately aligned with the proper magnitude scale. The new Hipparcos/Tycho catalogues have had new codes implemented (see below).

New additions (and changes in categories) will be made to the following list as new information reaches the ICQ.





                        MAGNITUDE-REFERENCE KEY

               Second-draft recommendation list, 1997 Dec. 1.
                         Updated 2007 April 20.



NOTE:  For visual magnitude estimation of comets, NEVER USE SOURCES for
 which the available star magnitudes are only brighter than the comet!
 For example, the SAO Star Catalog is very poor for magnitudes fainter
 than 9.0, and should NEVER be used on comets fainter than mag 9.5.  The
 Tycho catalogue should not be used for comets fainter than mag 10.5.
 (Even CCD photometrists should be wary of using bright stars for very 
 faint comets; it is always best to use comparison stars within a few
 magnitudes of the comet when doing CCD photometry.)

NOTE:  It is highly recommended that users of variable-star charts also
  specify (in descriptive notes to accompany the tabulated data) the
  specific chart(s) used for each observation; this information will be
  published in the ICQ.  Also, observers are urged to not be careless
  about the use of secondary references for comparison-star magnitudes:
  specifically, if using a secondary source (such as amateur software
  containing compilations of professional star-catalogue data, or even
  professional catalogues such as the SAOC containing magnitudes from
  other catalogues), one should note both the primary and secondary
  sources CLEARLY.


***  Recommended Sources:
                                                                                
ICQ
Key          Source  [+ location in ICQ where first introduced]
---    ----------------------------------------------------------------
AE    Planetary magnitudes from the American Ephemeris and Nautical
         Almanac (for use with bright comets) [ICQ 4, 105]; also star
         magnitudes from Astronomical Almanac
AT    Arizona-Tonantzintla Catalog (publ. in July 1965 Sky & Telescope)
         [ICQ 2, 6; 4, 8]
AU    ASAS-3 V magnitudes, available from website:
         http://archive.princeton.edu/~asas/asas3_catalog.html, and
         click on "Search: V-band" under "Photometric Catalog"
         (it is recommended that specific sequences and/or website
         URLs be mentioned in descriptive data) [ICQ 25, 160]
BR    V magnitude sequence for stars in the Coma cluster of galaxies
         including Abell 1656 (Boerngen and Richter 1978, A.N. 299, 177)
BS    Johnson V photometry by Brian Skiff at Lowell Observatory, with
         data given at the World Wide Website URL
          http://www.kusastro.kyoto-u.ac.jp/vsnet/catalogs/skiffchart.html;
         because website material may be transient, the ICQ policy for
         use of this source is to give additional information in the
         descriptive information accompanying the published tabulated
         data in the ICQ.
C     Photovisual magnitudes from "Cape Photographic Catalogue for
         1950.0", in Annals of the Cape Observatory, Vols. 17-22.  
         [ICQ 9, 142]
CA    M44 standard sequence as published in Henden and Kaitchuck's
         Astronomical Photometry (1982, New York:  Van Nostrand Reinhold),
         pp. 301-302.  [ICQ 9, 99]
CD    Open star cluster NGC 225 (R.A. = 0h43m.8, Decl. = +61 47', equinox
         2000.0) photometry; star chart with magnitudes given (9.2 < V < 16.0)
         as published in Visual Astronomy of the Deep Sky (see ref. 'CL',
         below), p. 250.
CE    Open star cluster NGC 1647 photometry (8.5 < V < 16.4), in Visual
         Astronomy of the Deep Sky, p. 252 (see ref. 'CL', below).
CF    Open star cluster NGC 2129 photometry (11.2 < V < 16.1), in Visual
         Astronomy of the Deep Sky, p. 254 (see ref. 'CL', below).
CG    Open star cluster NGC 2422 (M47) photometry (7.7 < V < 14.3), in
         Visual Astronomy of the Deep Sky, p. 256 (see ref. 'CL', below).
CH    Open star cluster NGC 6494 (M23) photometry (9.3 < V < 13.9), in
         Visual Astronomy of the Deep Sky, p. 258 (see ref. 'CL', below).
CI    Open star cluster NGC 6823 photometry (9.4 < V < 16.0), in Visual
         Astronomy of the Deep Sky, p. 260 (see ref. 'CL', below).
CJ    Open star cluster NGC 6910 photometry (9.9 < V < 14.9), in Visual
         Astronomy of the Deep Sky, p. 262 (see ref. 'CL', below).
CK    Open star cluster NGC 7031 photometry (11.2 < V < 16.5), in Visual
         Astronomy of the Deep Sky, p. 264 (see ref. 'CL', below).
CL    Photometry by Hoag et al. (1961) from one of the open-star-cluster
         charts as published in Visual Astronomy of the Deep Sky, by Roger
         N. Clark (Cambridge Univ. Press, 1990), pp. 250-266.
CM    Photovisual and photoelectric-V magnitudes from Cape Mimeograms
         (Royal Observatory, Cape of Good Hope).  [ICQ 9, 142]
CN    Open star cluster NGC 7235 photometry (8.7 < V < 16.4), in Visual
         Astronomy of the Deep Sky, p. 266 (see ref. 'CL', above).
CO    UBV photometry for 39 stars in the range 11.7 < V < 18.7, from
         "A New Stellar Standard Sequence in the Comet Cluster of Galax-
         ies" (F. Boerngen and N. Richter 1978, Astron. Nach. 299, 117)
CR    V magnitudes of 13 stars surrounding NGC 3627 (M66), as given by
          Ciatti and Rosino (1977, A.Ap. 56, 62).  The range in V is
          13.8-16.9, and the stars are fairly red.  [ICQ 11, 30]
CS    Catalogue of Stellar Identifications (1979, Strasbourg).  Large
         compilation of many catalogues.  For information, see F.
         Ochsenbein et al. (1981), A.Ap. Suppl. 43, 259, and Ochsenbein
         (1974), A.Ap. Suppl. 15, 215.  The visual magnitudes with colons
         (:) should be avoided if possible.  [ICQ 10, 35]
D     Dutch Comet Halley Handbook (E. P. Bus)  [ICQ 7, 96]
E     One of Everhart's 3 Selected Area charts (1984, Sky Telesc. 67, 28)
EA    Selected Area 51:  From Everhart (1984, Sky Telesc. 67, pp. 28-30).
EB    Selected Area 57:  From Everhart (1984, see EA, above)  [ICQ 7, 51]
EC    Selected Area 68:  From Everhart (1984, see EA, above)  [ICQ 7, 51]
FA    V photometry by Harold Ables, U.S. Naval Observatory, Flagstaff,
         "Region No. 6", unpublished (stellar V magnitude range 11.1-15.8
         photoelectric and 13.7-21.6 electronographic).  [ICQ 9, 99]
GA    Guide Star Photometric Catalog - I, in Astrophysical Journal
         Supplement Series, Volume 68, Number 1 (1988 September).
         Contains nearly 1500 stars with V magnitudes and convenient
         finder charts throughout the sky.  [ICQ 10, 124; 15, 60]
      *** NOTE:  this is VERY different from the GSC on CD, which has
             reference code 'HS' and which is a POOR source of comparison-star
             magnitudes! ***
GP    [apparently same as 'HE'; see below]
HD    Henry Draper Catalog (Harvard Coll. Obs. Annals)  [ICQ 2, 39]
HE    Harvard E Regions (declination -45 deg), Kron-Cousins V photometry
        for nine fields; stars range generally between 7 < V < 16 
        (Graham 1982, P.A.S.P. 94, 244)  [ICQ 10, 124]               
HI    Hipparcos Input Catalogue (C. Turon et al. 1992, European Space
        Agency Special Publication SP-1136; derived V magnitudes
        (118,000 stars brighter than mag 13, with the distribution
        peak around V = 9); see also HJ
HJ    magnitudes in the Hipparcos photometric system, Hp (see code
        HI, above); peak of Hp is closer to true visual than to
        Johnson V, though it has a long red wing
HK    H_p magnitudes from the Hipparcos Catalogue (ESA SP-1200).
HN    Arne Henden's photometric sequences, which can be downloaded
        from his computer at 
        ftp://ftp.nofs.navy.mil/pub/outgoing/aah/sequence
        (and especially via R. Bouma at 
        http://www.shopplaza.nl/astro/vs-charts/ and via M. Simonsen
        at http://home.earthlink.net/~joevp/index.html) -- but specific
        sequences should be specified in descriptive data [ICQ 26, 8]
HP    Harvard Photometry (Harvard College Obs. Annals)  [ICQ 4, 8]
HR    Harvard Revised Photometry (H.C.O. Annals)  [ICQ 1, 42; 4, 8]
HV    Johnson V magnitudes from Hipparcos Catalogue, ESA SP-1200.
JH    Jet Propulsion Laboratory's Horizons website (for planets):
                  http://ssd.jpl.nasa.gov/horizons.cgi
JT    Cousins VRI magnitudes of stars in M67 (M. Joner and B. Taylor
        1990, PASP 102, 1004)
L     Landolt V Photoelectric Sequences (AJ 78, 959)  [ICQ 6, 37]
LA    Landolt photoelectric sequences (1992, AJ 104, 340)
LB    Landolt (1983, AJ 88, 439 and 853) sequences as published by
        Christian Buil in ASTRONOMIE CCD (1989, Societe d'Astronomie
        Populaire), p. 261
LC    Landolt (1975, PASP 87, 379) magnitude sequence for 33 stars
               near V1057 Cyg (V magnitude range 5.5-15.5)
MC    Carlsberg Meridian Catalogue (1989).  Volume 4.  La Palma.
         More than 50,000 stars with visual magnitudes down to V = 13;
         do not use stars with magnitudes given to less than 0.01 mag.
ME    V photometry by Tedesco, Tholen, and Zellner (1982, A.J. 87, 1585);
         mag range 6-13  [ICQ 8, 77]
MK    V magnitudes for M67 in LE GUIDE PRATIQUE DE L'ASTRONOMIE CCD
         P. Martinez and A. Klotz 1994; Adagio press), p. 270
MP    McCormick Photovisual Sequence (Univ. of Virginia)  [ICQ 3, 15]
MS    From "McCormick Photovisual Sequences", by C. A. Wirtanen and
         A. N. Vyssotsky (1945, Ap.J. 101, 141-178).  [ICQ 9, 142]
MT    Visual magnitudes of stars in M67 as published by B. E. Schaefer
         (1989, SKY TEL. 77, 332); after work by Racine and Gilliland.
MV    From Publ. Leander McCormick Obs., Vol. VI, Part II, pp. 201-306
         ("Magnitudes and Coordinates of Comparison Stars in Regions of
         Long-Period Variables, by S. A. Mitchell, 1935) or Vol. IX, Part
         V, pp. 59-88 ("Sequences for Fifty Variable Stars", by Mitchell
         and C. A. Wirtanen, 1939).  [ICQ 9, 142]
NH    North Polar Sequence as published by Henden and Kaitchuck (1982,
         Astronomical Photometry, NY: Van Nostrand Reinhold), p. 305.
NN    NGC 2129/6531/1342 cluster photometry, in Publ. U.S.N.O. Vol.
         XVII, parts VII, VIII (1961), pp. 406, etc..  [ICQ 8, 130]
NO    U.S.N.O. Photoelectric Photometry Catalogue  [ICQ 2, 6; 4, 8]
NP    North Polar Sequence (publ. by the A.A.V.S.O.); 3 charts showing
         stars w/ useful range mv = 5.0 and fainter  [ICQ 1, 17; 3, 7]
NS    "Magnitudes and Colors of Stars North of +80 ", by Seares, Ross, 
          and Joyner (1941, Carnegie Inst. Publication 532)  [ICQ 4, 80]
OB    magnitudes for faint cluster stars from S. C. Odewahn, C. Bryja,
          and R. M. Humphreys (1992), PASP, 104, 553 [used by
          Spacewatch beginning 1999 Sept. 29, replacing FA; ICQ 123]
PA    M45 sequence, Johnson & Mitchell (1958, Ap.J. 128, 31)  [ICQ 8, 77]
PB    Pleiades chart in Sky and Telescope 70, 465 (1985).   [ICQ 8, 77]
PC    Pleiades sequence, Henden and Kaitchuck (1982, Astronomical Photo-
         metry; N.Y.:  Van Nostrand Reinhold), pp. 298-300  [ICQ 8, 130]
PI    IC 4665 sequence as found in Henden and Kaitchuck (1982,
         Astronomical Photometry, New York:  Van Nostrand Reinhold),
         pp. 302-304.  [ICQ 10, 35]
RB    "Photoelectric Magnitudes and Colours of Southern Stars",
      A. W. J. Cousins and R. H. Stoy (1963), in Royal Observatory
      Bulletin No. 64 (Royal Greenwich Obs.), Series E3, pp. E101-E248.
         [ICQ 9, 142]
RC    "Standard Magnitudes in the E Regions", A. W. J. Cousins and R.
      H. Stoy (1962), in Royal Observatory Bulletin No. 49 (Royal
      Greenwich Obs.), Series E2, pp. E1-E59.  [ICQ 9, 142]
SD    V magnitudes of members of the globular cluster M15 in the range
          13 < V < 22 [and also nearby field stars for 40 stars
          of mag 7.64, 10.42-11.15, and 12.9 < V < 18.8],
          by A. Sandage (1970, Ap.J. 162, 841)
SE    V magnitudes of 134 stars of the II Persei Association (stars of
          spectral types A and B, mag range 5.1-11.4;
          C. K. Seyfert et al., Ap.J. 132, 58).  [ICQ 11, 30]
SK    Brian Skiff's compilation of magnitudes as part of the LONEOS
          project (Lowell Observatory), appearing via Internet access
          at ftp://ftp.lowell.edu/pub/bas/starcats/loneos.phot
          (as of 9/25/01, containing about 33000 stars throughout
          the sky from some 600 published sources -- mostly professional
          astronomy journal articles); though magnitude range goes
          from V = 7.4 to V = 22.9, only about 40 stars in this list
          are brighter than mag 9.0 (but generally a good source of V
          magnitudes for stars fainter than mag 10 or 11)
SM    V magnitudes from "A Visual Atlas of the Small Magellanic Cloud",
         by Mati Morel (1989), Rankin Park, N.S.W., Australia
SP    Skalnate-Pleso Atlas Catalog (Atlas Coeli Cat.)  [ICQ 2, 6; 4, 10]
SS    Various regions covering declination -60 deg to +10 deg, with
         stars having general range 12 < V < 24; Stobie et al. (1985),
         Astron. Astrophys. Suppl. Ser. 60, 503
SW    Four half-degree fields with finder charts and UBV photometry,
         range 10 < V < 15 (except field IV, which has a gap between
         11.5 < V < 13.5), published by W. Saurer et al. (1992) in
         Astron. Astrophys. Suppl. Ser. 93, 553.  The four fields
         average about 40 stars each, roughly centered at the following
         R.A. and Decl. (B1950.0):  I, 1h27m, +58.2 deg; II, 3h24m,
         +45.2 deg; III, 7h15m, -10.1 deg; IV, 21h31m, +50.2 deg.
TA    Comparison-star magnitudes from "The Amateur Sky Survey"
         (TASS), which has data available at the website URL
         http://www.tass-survey.org/  [ICQ No. 133]
TG    CCD magnitudes on the Thuan-Gunn system; comparison standard
          stars in Thuan and Gunn (1976, PASP 88, 543).
TI    Tycho Input Catalogue; more than three million stars brighter
          than V = 12.1 prepared for the needs of the Tycho mission
          (Hipparcos satellite; see D. Egret et al. 1992, Astron.
          Astrophys. 258, 217); available upon request from the
          Strasbourg Data Center (France; e-mail address
          question@simbad.u-strasbg.fr)
TJ    Tycho Catalogue Johnson V magnitudes from ESA SP-1200.
TK    Tycho-2 Catalogue (Hog et al. 2000, A.Ap., in press);
                 NOTE:  *only* Tycho-2 V_T magnitudes (labeled VT)
                 from the *main* catalogue should be used.  The
                 supplements contain a mix of V-like magnitudes
                 from the original Tycho catalogue and should not
                 be taken from here.
TS    Field of 13 stars (R.A. 22h02m, Decl. -19.1 deg, equinox 1950.0),
          V magnitudes with finding chart, 9.7 < V < 19.2, by Tritton
          et al. (1984), MNRAS 206, 843-847.
TT    Tycho/Hipparcos Catalogue V_T magnitudes from ESA SP-1200.
VG    Japanese variable-star charts edited by K. Gomi and based on
         charts drawn by Y. Kawanishi, publ. in 1970 by Koseisha Co.
         as a spiral-bound book; its preface states that the magnitudes
         of comparison stars are taken from Harvard Annals (Vols. 37,
         50, 54, and 57) and from Skalnate Pleso II (Atlas Coeli).
         Akimasa Nakamura, who reported this reference to the ICQ,
         says that his comparison of Gomi charts with AAVSO charts
         show that the comparison-star magnitudes are very close to
         each other.
Y     Yale Bright Star Catalogue  [ICQ 1, 42; 4, 8]
YF    Yale Bright Star Catalogue, fourth edition (should now be used
         instead of earlier editions)
YG    Yale Bright Star Catalogue, fifth edition



***  Sources NOT recommended, but which may be used (with caution)
            if Recommended Sources are not available:
                                                                                

Key          Source  [+ location in ICQ where first introduced]
---    ----------------------------------------------------------------
AA    A.A.V.S.O. Variable Star Atlas  [ICQ 4, 6]
AC    Charts of the Amer. Assn. of Var. Star Observers  [ICQ 4, 7]
         Note, however, that the AAVSO does have numerous good charts, and
         the AAVSO charts for the North Polar Sequence are highly recommended.
AP    Atlas Photometrique des Constellations (1948), by Antoine Brun
         (has stars to mag 7.5 labeled with Harvard photometry
         magnitudes)  [ICQ 5, 24]
AS    AAVSO chart for M81 (NGC 3031) in Ursa Major, which was closely
         scrutinized and revised during April and May 1993 as a result
         of SN 1993J.  The revised sequence, which was published in the
         April 1993 issue of the ICQ, has a good sequence for the range
         10.3 < V < 15.5.  [ICQ 15, 60; 15, 102]
FD    R magnitudes of M13 stars as published in "A photoelectric BVRI
         sequence in the field of the globular cluster NGC 6205 (M13)",
         by D. Forbes and P. C. Dawson (1986), PASP 98, 102-103.
FG    from variable star charts published in *A Field Guide to the Stars
         and Planets*, by D. H. Menzel and J. M. Pasachoff (part of the
         Peterson Field Guide Series); charts by Wil Tirion for SS Cyg
         (visual mag 5.1-11.4), R CrB (7.5-12.6), Algol (2.9-5.5), beta
         Lyr, and Mira (3.5-9.2) are given on pages 158-161 of the second
         edition and pages 198-201 of the third ed. (magnitude source is
         not specified, but probably AAVSO)
LD    *Lietuvos Dangus 2007* (Vilnius, 2006), p. 171 (for planets;
         annual Lithuanian almanac)
LM    V magnitudes from "A Visual Atlas of the Large Magellanic Cloud",
         by Mati Morel (1983), Rankin Park, New South Wales  [ICQ 10, 67]
ML    V magnitudes on chart of Large Magellanic Cloud by Mati Morel
                (apparently same as LM)
MM    V magnitudes on chart of Small Magellanic Cloud by Mati Morel
                (apparently same as SM)
OH    From listing of bright stars in Observers' Handbook, R.A.S.C.
          [ICQ 7, 51]
PK    From the Soviet Program for Comet Halley; Dr. Klim Churyumov,
         Kiev University, describes the method as follows (edited):
         Comparison stars were noted on the Palomar Sky Survey prints;
         the visual magnitudes of these stars were determined by
         comparison with standards stars from the galactic cluster
         NGC 2129 (V magnitudes taken from the paper by Hoag et al.
         in Publ. U.S.N.O., Second Series, Vol. XVII, Part VII, pages
         406 and 518, 1961).  The visual magnitudes were determined
         by use of the formula mv = V + 0.16(B-V).
S     Smithsonian Astrophysical Obs. Star Catalog  [ICQ 1, 17; 4, 9]
         ONLY FOR STARS OF VISUAL MAGNITUDE 9.0 OR BRIGHTER!!
SA    M67 sequence by R. E. Schild (1983, PASP 95, 1021), Kron-Cousins
         magnitudes  [ICQ 10, 35]
SC    Sky Catalogue 2000.0 (Sky Publishing; stars of magnitude 
         V < 8.1)  [ICQ 4, 62; 4, 105]
VB    Variable star charts of the British Astr. Assn.  [ICQ 4, 64]
VF    Variable star charts of the A.F.O.E.V. (France)  [ICQ 4, 64]
VN    Variable star charts of the R.A.S. of New Zealand  [ICQ 4, 64]
W     International Halley Watch (IHW) version of an unspecified
         AAVSO chart  [ICQ 7, 96]
WA    Special IHW version of AAVSO chart for SU Tauri  [ICQ 7, 96]
WB    Special IHW version of AAVSO chart for CZ Orionis  [ICQ 7, 96]
WC    Special IHW version of AAVSO chart for Y Tauri  [ICQ 7, 96]
WD    Special IHW version of AAVSO chart for V Tauri  [ICQ 7, 96]
WE    IHW version of AAVSO chart for X Sextantis  [ICQ 8, 130]
WF    IHW version of AAVSO chart for S Sextantis  [ICQ 8, 130]
WG    IHW version of AAVSO chart for SX Leonis  [ICQ 8, 130]
WH    Unspecified IHW charts  [ICQ 8, 44]
WW    B.A.A. Charts as published in the IHW Observers' Manual [ICQ 8, 44]



***  Sources that should be used only as a last resort (preferably never):
                                                                                

Key    Source  [+ location in ICQ where first introduced]
---    ----------------------------------------------------------------

BC    Boss Catalogue
BD    Bonner Durchmusterung (Argelander et al.)  [ICQ 2, 59; 4, 63]
CC    Carte du Ciel, Paris (Astrographic Catalogue?)  [ICQ 10, 35]
GR    Groombridge  [ICQ 3, 15]
HS    V magnitudes from Hubble Space Telescope astrometric catalogue
        of stars on compact disk  [see ICQ 15, 60]
LN    Lampkin's Naked-Eye Stars  [ICQ 2, 6]
PD    "Photometrische Durchmusterung:  Generalkatalog", by G. Mueller and
         P. Kempf (1907), in Publ. Astrophysikalischen Observatoriums zu
         Postdam No. 52 (Vol. 17); B.D. stars to mag 7.5  [ICQ 10, 35]
PL    star(s) & sources quoted for photoelectric data, but difference
         (comet - comparison-star) > 4.5 mag  [ICQ 10, 35]
RA    Annual Ephemeris of the Royal Astronomical Society of Canada (not
         recommended, even for bright comets)  [ICQ 5, 64]
TB    Supernova Search Charts, by G. D. Thompson and J. T. Bryan, Jr.
         (1989, Cambridge University Press)
V     Variable star charts from recognized sources  [the specific charts
         should be stated in detail]


Sources not yet classified (use only with caution, making sure to have
  comparison-star magnitudes of the proper bandpass):
                                                                                

Key    Source  [+ location in ICQ where first introduced]
---    ----------------------------------------------------------------
AG    Astronomisches Gesellschaft Katalog  [ICQ 2, 6]
AH    G. D. Roth's Astronomy:  A Handbook, p. 534 (chart of the Pleiades)
                [ICQ 6, 64]
BS    Johnson V photometry by Brian Skiff at Lowell Observatory, with
         data given at the World Wide Website URL
         http://www.kusastro.kyoto-u.ac.jp/vsnet/catalogs/skiffchart.html;
         because website material may be transient, the ICQ policy for
         use of this source is to give additional information in the
         descriptive information accompanying the published tabulated
         data in the ICQ.
SK    Brian Skiff's compilation of magnitudes as part of the LONEOS
         project (Lowell Observatory), appearing via Internet access
         at ftp://ftp.lowell.edu/pub/bas/starcats/loneos.phot
         (as of 9/25/01, containing about 33000 stars throughout
         the sky from some 600 published sources -- mostly professional
         astronomy journal articles); though magnitude range goes
         from V = 7.4 to V = 22.9, only about 40 stars in this list
         are brighter than mag 9.0 (but generally a good source of V
         magnitudes for stars fainter than mag 10 or 11)
YZ    Yale Zone catalogue 


Sources that should never be used:
                                                                                
Old     New
Key     Key          Source  [+ location in ICQ where first introduced]
---     ---    ----------------------------------------------------------------
         A      Charts or Atlas of the AAVSO  [AC or AA should be used]
         AN     Comparison-star sequences as published by M. Beyer in articles in
                Astron. Nachrichten  [used only for Beyer's data]
         AO     USNO (S)A1.0 catalogue R magnitudes, from the first editions
                  of this catalogue; not recommended because magnitudes may
                  be off by 0.5 mag or more due to photographic calibration
                  errors, but CCD astrometric comet observers are using them
                  due to convenience; see more information on the World Wide
                  Web at http://ftp.nofs.navy.mil/projects/pmm/readpht.v10
 T       UA     Atlases Borealis, Eclipticalis, Australis  [ICQ 2, 6]
 C, CP   UC     Cape Photographic Catalogs  [ICQ 1, 42; 4, 63]
         UL     Specific comet or planet mentioned as magnitude reference, but
                     comparison object not above horizon at same time as comet
                     OR no catalog listed  [ICQ 7, 51]
 M       UM     Magnitudes of galaxies, nebulae, etc.  [ICQ 2, 6]
 R       UN     Norton's Atlas  [ICQ 2, 39; 4, 62]
         UO     USNO A2.0 catalogue R magnitudes; not recommended because
                magnitudes may be off by 0.5 to 2 full magnitudes or more
                due to photographic calibration errors, but CCD astrometric
                comet observers are using them due to convenience
 I, Q    UP     Any standard photographic atlas (e.g., Falkauer, Stellarium)
                     [ICQ 3, 15; 2, 59]
  [no code]     PPM catalogue (Roeser et al.); mostly photographic magnitudes
 J, RC   UR     Revue des Constellations  [ICQ 5, 24; 5, 64]
         UU       UCAC2 astrometric star catalogue; magnitudes with
                     uncertainty estimated as ± 0.3, intended for
                     identification only (bandpass spans V to R)
         US     Skalnate Pleso Atlas  [ICQ 7, 51]
 X       UX     Specific stars quoted, no catalogue given  [ICQ 2, 39]





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