              PARENAGO CATALOGUE OF ORION NEBULA STARS: Updated Positions.

Original paper, and source of numbering system/positions is -
Investigation of Stars in the Region of the Orion Nebula, Parenago, P.P.  1954.  Trudy Sternberg Astron. Inst, Vol. 25
His catalogue lists 2982 stars, with photographic and photovisual magnitudes and ancillary data, in nine square degrees, betweenRA 5h24m and 5h36m, Dec. -40 to -70 (1900). It appears to be nearly 100% complete down to 15th magnitude.

1.  Introduction.
     Since 1992 Parenagos catalogue has been available electronically from the CDS as file no. II/171.  However the positions given are of limited precision, to whole seconds of Right Ascension, and to 0.1 of  Declination, for equinox 1900.  By the beginning of the 21st century a number of deep survey catalogues, with very precise positions, are now available to permit an update of Parenagos catalogue using published material. The value of Parenagos catalogue can be summarized as follows:
*	It is a fairly complete listing of stars in the optical region, centred on M42, ie. like a durchmusterung of the Orion Nebula region.
*	It provides photoblue and photovisual magnitudes in a fairly comprehensive way. Catalogues based on POSS or southern Schmidt plates fall short in this region because of the dense nebulosity.
*	Parenagos paper is still regularly cited by the GCVS team and other researchers in studies of the Orion Nebula region. A completely updated listing of his stars would be very useful, at least for identification purposes. 

2. Updated Astrometry.
     I surmised at the outset that most of Parenagos stars would be found in the UCAC2 catalogue. This became the preferred catalogue for precise astrometry. The epoch of choice is now J2000. For stars with V >10 and not in UCAC2 I referred to Hipparcos and Tycho-2. For faint Parenago stars not in UCAC2, the USNO-A2.0 catalogue was usually preferred.  In the densest part of the Orion Nebula Cluster (ONC) variable stars abound and often hard to resolve from the bright nebulous background. Several other catalogues (2MASS, GSC2.2 etc) were consulted to track down stars not found in the primary catalogues. The catalogues by Hillenbrand (1997, 2000) were also useful in places.
     The tremendous number of variables in the ONC region and the fact that precise positions for them have appeared on the GCVS website proved to be a godsend. In the densest part of the ONC more than 50% of Parenagos stars are known variables or NSV stars, with precise positions. Truly constant stars appear to be a rarity in the region of M42!
      Parenagos original paper provides high-precision positions for about 85% of his stars, in a separate table.  Regretfully, this data is not reproduced in CDS file II/171. This high-precision data was used extensively by me in preference to the low-precision positions, which are prone to be a bit soft.  All of Parenagos positions were keyed in to spreadsheet containing formulae for applying corrections for precession, from 1900 to 2000.  Data (positions and magnitudes) for relevant UCAC2 stars were then imported and, after sorting, match-ups were easily and unequivocally made for more than 90% of his stars. The complete list of sources of precise astrometry is as follows :

Abbrev.       Author/catalogue       Citation
=====================================================================
A2            USNO-A2.0              I/252
GSC           GSC-ACT               (1999yCat.1255.....G, I/255)
GSC2.2        GSC-2.2               (2001GSC2..C......0S,  I/271)  
Hb97          Hillenbrand, L.       (1997AJ....113.1733H)
Hb00          Hillenbrand, L.       (2000ApJ...540..236H)
Hip           Hipparcos             (1997HIP...C......0E, I/239)
PAR           Parenago, P.P.        (1954TrSht..25....1P)
T2            Tycho-2               (2000A&A...357..367H, I/259)
U             UCAC2                 (2004AJ....127.3043Z, I/289)
2MASS         2MASS                 (2006AJ....131.1163S, II/246)
MM            M. Morel              [Provisional estimate of position by author]
NPM,AC,Lit..  GCVS                  [GCVS positions, from other sources.]
 
3.  Other charts of the Orion Nebula and region.
(1)  Bond, G.P.  [1867AnHar...5D...3B].  Sighted, but not used.
(2)  Brun, A.  1935.  1132 stars in band of RA. centred on 5h30.5m, -518 (1900)
(3)  Strand, K. Aa and Teska, T.M. 1958. Charts of the Orion Neb. Cluster.  No other data (mags etc).
(4)  Andrews, A.D.  1981.  16000 stars, astrometry, UBV data, identifications of variable stars.  Charts and positions based on UK Schmidt plates.  
     These charts, as well as  Parenagos charts, were regularly referred to, and compared with each other, to ensure correct identifications were made.  And, of course, DSS red images were often used to verify the hand plotted charts.

4.  Missing Parenago Stars.
    A small number (5 stars) were impossible to identify using his positions and charts. Poor positions can be blamed in most cases. Fortunately in these cases (P1675, P1777, P2159, P2204 and P2283) they appear in Bruns atlas, for which Parenago provides cross-identifications.  However, the following stars lie outside Bruns atlas and the given positions fall on empty fields, when checked with DSS images.
P119
P836
P904 (pair with P905)
P1224
P1230
P1375 (pair with P1368)
P1399 (pair with P1400)
P1804 (neb. region)
P2002 
P2834
   Nevertheless, they are included in my main table using Parenagos position, as NOT FOUND.

5. Errors and Irregularities Found.
P1144 :  Mislabelled on Parenago chart VI as 1114.
P1373 :  = V1169 Ori.  Note switch with BT Ori.
P1379 :  = BT Ori. Note switch with V1169 Ori.
P1640 :  KL Ori = V1459 Ori. Correlation apparently missed due to poor position for KL Ori. GCVS agrees. Virtually identical precise positions given for KL and V1459 Ori.
P1726 :  Parenago's chart distorted. Positions of P1726 and P1739 poorly plotted, leading 	to possible misidentifications.
P1991 :  Most charts and images examined show a star 12" due N of P1992 = V562 Ori, V1231 Ori. Parenago's charts shows P1991 (misplotted) slightly to the west. Nothing visible 	at Parenago's position in the optical region. I assume that P1991 = V1231 Ori.
      Hillenbrand's match-up for P1991 is therefore deemed to be erroneous.
P2395 :  Close pair, V1612 and V1613 Ori. Both assigned to P2395 (Hillenbrand 1997).

6.  Main Table - PARENAGO.DAT  Explanation of  columns.
Col. 1:  PAR  -  Star number assigned by Parenago.
Cols. 2,3,4:  RA2000 - Right Ascension (h,m,s) for equinox J2000.
Cols. 5,6,7:  Dec2000 - Declination (deg, min, sec) for equinox J2000.
Col. 8: Cat. - Source catalogue for astrometry.
Col. 9:  Name - Variable star name;  GCVS 4.2 complete to Name List 78.
Col. 10:  Con. - Constellation name (Orion).
Col. 11:  NSV - Number in NSV catalogue, including Supplement 1.0.
Col. 12: Mag. - Optical magnitude.
Col. 13: Sys.  -  System used for magnitude in col. 12.
                          pv = photovisual
                          v   = visual
                          V  = standard V (see note)
                          p  =  photographic (blue)
Col. 14:  Uc - Red magnitude (from UCAC2)
Col. 15:  Remarks.  Includes all HD and HDE names.
Col. 16:  Parenago number (repeated).
Col. 17:  r' magnitude (from CMC14)
Col. 18:  J magnitude  (from CMC14)
Col. 19:  H magnitude  (from CMC14)
Col. 20:  Ks magnitude (from CMC14)
Note:  Whilst Parenagos pv magnitudes are reasonably accurate, usually to within +/- 0.1 or 0.2, it was felt worthwhile to insert better V magnitudes.  These are meant to be indicative, rather than absolute values, as there could be still a number of undetected variables among these stars. No attempt has been made to reference the individual V mags., as they  are virtually all to be found in the paper of Warren and Hesser (1977).

7. Acknowledgements.
  I acknowledge the use of digitized sky survey (DSS) images, derived from the National Geographic Society - Palomar Observatory Sky Atlas (POSS-I), made by the California Institute of Technology with grants from the National Geographic Society. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under US Government grant NAG W-2166.
  I thank Dr Wayne H. Warren Jr (then at NASA Astronomical Data Centre) for furnishing a complete copy of Parenago's 1954 paper (on microfiche!), without which I would not have attempted this project.  

Bibliography.
Andrews, A.D.  1981. "A Photometric Atlas of the Orion Nebula".  Armagh Observatory.
Brun, A.  1935.  Pub. Obs. Lyon, 1, No. 12
Kholopov, P.N. et al 1982.  New Catalogue of Suspected Variable Stars, Nauka, Moscow.
Kholopov, P.N. et al 1985. General Catalogue of Variable Stars, 4th ed. Web ed. v4.2, 2006
        [http://www.sai.msu.su/groups/cluster/gcvs/]
Monet, D., Bird, A. et al 1998. USNO-A2.0  Catalog of Astrometric Standards, US Naval                   Observatory, Flagstaff, AZ.
Strand, K. Aa. and Teska, T.M. 1958. Ann. Dearborn Obs. VII,3,67
Warren, W.H. Jr and Hesser, J.E. 1977. Astrophys. J. Suppl. 34,115-206
Malkov, O. Yu. [1992BICDS..40...13M, II/171].
 

M. Morel
6 Blakewell Road
Thornton,
NSW 2322

2007 July 09.









                                                     