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[vsnet-j 611] MKN421 sequence

MKN421 sequence

　追加の情報がありました。

From: bas@lowell.edu (Brian Skiff)
Date: Fri, 5 Apr 96 15:49:34 MST
Subject: [vsnet 595] Additional comparison stars in the Markarian 421 field

     The on-line version of AAVSO Alert 220 (3 April 1996) includes a
preliminary chart for the BL Lacertae-type variable galaxy Markarian 421 =
UGC 6132.  The comparison sequence on the chart derives from UBV photoelectric
photometry by McGinsey et al. 1976 (AJ 81,750).  There is photometry for
additional stars in the field by Veron & Veron 1976 (A&ASuppl 25,287; the
stars are identified on a chart by the same authors in 1976 A&A 39,281).  The
Vernon & Veron stars fill in the comparison sequence in the most important
range of the galaxy's brightness.  A concatenated list of all the stars from
both sources (plus bright field stars) is given below along with positions and
identifications.
      The galaxy has been measured for position many times by the Carlsberg
Meridian Circle as part of work linking the visible/radio reference frames;
this can probably be regarded as the best position from observations in the
visible.  The galaxy also appears in the GSC and on the "UJ 1.0" CD-ROM star
catalogue from the U.S. Naval Observatory.  All three compare favorably to the
radio-wavelength position determined using the VLA by Patnaik et al (1992,
MNRAS 254, 655).  These positions are listed below.

                RA  (J2000)  Dec
UGC 6132:  11 04 27.33  +38 12 31.8 (CMC5,6)
           11 04 27.34  +38 12 31.0 (GSC 3010-0637, n=3)
           11 04 27.36  +38 12 31.8 (UJ 1.0)
           11 04 27.31  +38 12 31.8 (VLA, Patnaik et al.)

The position derived from photographic astrometry by Clements (1983 MNRAS
204,811) appears to be off by a few arcseconds by comparison when a B1950-to-
J2000 conversion is made.  This is a bit surprising, since ordinarily these
positions are utterly reliable to high precision.  It is possible the sky 
survey and meridian circle positions have measured a different part of the
galaxy, or were affected by the faint interacting companion galaxy on the
northeast side, although the GSC has a separate entry for this object.  I
compared the position against digitized sky survey using the Goddard SkyView
facility (http://skview.gsfc.nasa.gov/cgi-bin/v2.3/skyview_advanced.html) to
confirm the Carlsberg/VLA position at the ~1 arcsecond level.
     In the table below, the star positions come from either the PPM or the 
GSC.  The sources of the photometry, abbreviated in the last column, are cited
at the bottom.  The spectral types in parentheses are _approximate_ 
"predicted" types based on the UBV photometry.  


Photometry of stars in the field of Markarian 421 = UGC 6132

Name                RA  (2000)  Dec         V     B-V  spec      source,remarks
Mark 421        11 04 27.33  +38 12 31.8                         = UGC 6132
HD 95934        11 04 31.2   +38 14 29     6.03  0.16  A3III-IV  K91
HD 96161        11 05 48.3   +38 23 39     6.94  1.33  G5III?    K91; see text
HD 95976        11 04 43.9   +38 14 48     7.50 (0.5)  F2        O83 (b-y=0.30)
HD 96016        11 04 57.3   +38 24 38     7.82  0.48  F2        O83/Walker
HD 96106        11 05 32.0   +38 16 34     8.72  0.69  (g5v)     Carney & Latham
GSC 3010-0263   11 03 18.0   +38 08 25    10.25  0.98  (k0iii)   MMW76
GSC 3010-0733   11 03 22.4   +38 23 50    11.39  0.09  (a2v)     MMW76
GSC 3010-0856   11 04 11.5   +38 00 16    11.84  0.49  (f5v)     VV76
GSC 3010-0589   11 05 13.1   +38 28 56    12.05  0.78  (k0v)     VV76
GSC 3010-0018   11 05 33.1   +38 17 54    12.68  0.79  (k0v)     VV76
GSC 3010-0506   11 05 02.7   +38 28 58    12.72  0.72  (g5v)     VV76
GSC 3010-0762   11 05 43.8   +38 09 07    12.86  0.66  (g2v)     VV76
GSC 3010-0317   11 04 07.6   +38 20 48    13.31  1.19  (k2iii)   MMW76
GSC 3010-0693   11 03 25.0   +38 10 17    13.43  0.95  (k0iii/v) MMW76; see text
GSC 3010-0252   11 04 14.7   +38 05 14    13.52  0.81  (k0v)     VV76
GSC 3010-0719   11 04 51.1   +38 17 09    14.35  0.57  (g0v)     VV76
GSC 3010-0499   11 04 16.7   +38 25 05    14.91  0.44  (f5v)     VV76
GSC 3010-2241   11 04 08.6   +38 22 26    14.99  0.57  (g0v)     VV76

sources:
K91 = Kornilov et al. 1991, Trudy Gosh. Astron. Inst. Sternberg, vol. 63.
O83 = Olsen 1983, A&ASuppl 54, 55.
Walker = Walker 1971, PASP 83, 177.
Carney & Latham = Carney & Latham 1987, AJ 92, 116; also V=8.72 in the Geneva
     seven-color photometry catalogue.
MMW76 = McGinsey et al. 1976, AJ 81, 750.
VV76 = Veron & Veron 1976, A&AS 25, 287.

     Most of the photometry for the brighter stars, by the way, was recovered
using Jean-Claude Mermilliod's Lausanne Photometric Database, at the URL:

http://obswww.unige.ch/gcpd/gcpd.html

     The spectral type for the bright star HD 96161 is clearly in error; the
UBV colors imply a type near K3III.
     GSC 3010-0693 has a faint companion ~10" south.  The MMW76 chart marks
the brighter star explicitly, but the text does not indicate the photometer
diaphragm size.  However, since they used the Kitt Peak 1.3-m telescope for
these observations, the aperture could well have been small enough to exclude
the companion.
     One puzzle remains.  The mag. 13 white dwarf PG 1101+384 = WD 1101+384
is nominally located only 50" southwest of the galaxy.  But nothing appears
here on the SkyView image, and the magnitudes cited in the PG catalogue for
the white dwarf are suspiciously similar to the galaxy itself.....  The finder
chart in the Palomar-Green catalogue (Green et al. 1986, ApJSuppl 61, 305) is
a bit ambiguous, and what seems to be indicated is possibly just a ghost image
of the bright A-type star HD 95934(!).  They claim to have taken a follow-up
spectrum, and it is difficult to see how the galaxy (z = 0.03) could have been
mistaken for a near-zero-velocity white dwarf....?

\Brian Skiff  (bas@lowell.edu)

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