Markarian 421 field plotted on GSC
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) 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)
Markarian 421 field plotted on GSC
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