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[vsnet-chat 484] BL Lac comparison stars
- Date: Thu, 31 Jul 1997 13:27:57 -0700
- To: Jean-Claude.Mermilliod@obs.unige.ch, polakis@sprintmail.com, vsnet-chat@kusastro.kyoto-u.ac.jp
- From: bas@lowell.Lowell.Edu (Brian Skiff)
- Subject: [vsnet-chat 484] BL Lac comparison stars
- Sender: owner-vsnet-chat@kusastro.kyoto-u.ac.jp
BVRI photometry for stars in the field of BL Lacertae (literature summary)
The table below shows positions and BVRI photometry for stars in the
field of the variable galaxy BL Lacertae drawn from nine sources in the
literature. My concern about there being possibly discrepant sources was
that recent visual observations showed considerable scatter even in
observations made a few minutes apart by different observers. While the
galaxy is known to exhibit large variations on timescales of weeks, the
shorter-term variations are much smaller (0.1-0.3 at most on nightly
timescales).
The AAVSO and AFOEV visual charts are clearly based on the photoelectric
observations of Bertaud et al. (1969, 1973; see references below). Gary
Poyner has just written to say the BAA chart is based on the same sequence.
Comparison of these data against newer observations (not necessarily better!)
suggest the V magnitudes for the stars are correct within perhaps +/- 0.05 mag.
The only serious discrepancy involves star 'b', which is the one immediately
east of the galaxy. DuPuy et al. (1969) show that this star is a mid-K giant;
given the scatter in the published results, it is possible that the star is
slightly variable. This star is fairly red, so probably should be avoided by
visual observers in any case.
The two sources of VRI photometry (both on the Cousins system) seem to
be discrepant until one looks at the stated errors on the measurements, which
in both cases are fairly soft, in the +/- 0.05 to 0.10 range. Thus the data
are consistent, if somewhat uncertain.
The table shows star names based on the Bertaud scheme as shown on the
charts in their two papers. N.B. that more recently the lower case lettered
stars b,c,h,k near the galaxy have tended to be referred to by capital letters.
Compare the star positions before amending your charts! The positions come
either from the GSC v1.1 (source G) or the USNO A1.0 (source A) catalogue for
the fainter stars. For a few additional bright stars in the field, I have
added information from the Hipparcos/Tycho database (source T). The position
for BL Lac itself comes from the NED database. GSC names for the brighter
stars are listed in the notes along with a few other comments. The BVRI
photometry is given as available in no particular order, with the sources
listed at the end of each line. The stars are arranged in order of decreasing
brightness.
Finally, the AAVSO on-line chart can be downloaded from:
http://vsnet.aavso.org/charts.html
Also, note that the Guide Star Photometric Catalogue sequence P236 is located
within about 20' southeast of the galaxy.
\Brian
+++++++++++++++++++++++++++++++++++++++++++++++++++++
BVRI photometry for stars in the field of BL Lacertae
Name RA (2000) Dec s V B-V V-R R-I source
BL Lac 22 02 43.3 +42 16 40 ~1.0
HD 209438 22 02 25.4 +42 25 32 T 8.41 1.03 Tycho
HIP 108776 22 02 05.7 +42 22 47 T 10.92 Tycho
G3206-1959 22 02 45.5 +42 19 11 T 11.6 0.3 Tycho
BL Lac alf 22 02 54.0 +42 13 19 G 12.02 0.45 M72
BL Lac b 22 02 45.4 +42 16 35 G 12.78 1.74 0.85 0.84 S85
12.90 0.91 0.87 F96
13.06 1.66 M72
13.04 1.64 R70
1.66 D69
12.90 1.78 B69
12.89 1.67 B73
12.89 1.66 K70
BL Lac e 22 02 16.7 +42 16 50 G 12.99 0.69 B69
BL Lac A 22 02 23.8 +42 17 17 G 13.31 0.74 B73
BL Lac f 22 02 53.6 +42 17 48 G 13.26 1.05 B69
13.36 1.04 B73
13.34 1.02 K70
BL Lac a 22 02 30.8 +42 17 10 G 13.43 0.60 B69
13.39 0.61 B73
13.39 0.57 K70
BL Lac B 22 02 39.6 +42 13 38 G 13.72 0.97 B73
13.72 0.94 K70
BL Lac g 22 02 35.1 +42 18 49 A 14.10 0.96 B69
BL Lac c 22 02 40.1 +42 17 10 A 14.19 0.90 0.50 0.46 S85
14.26 0.47 0.47 F96
14.28 0.92 B69
14.26 0.93 B73
14.23 0.88 K70
BL Lac h 22 02 32.7 +42 16 47 A 14.31 1.37 0.71 0.67 S85
14.40 0.67 0.66 F96
14.42 1.39 B69
BL Lac C 22 02 33.4 +42 14 25 A 14.50 1.06 B73
14.41 1.02 K70
BL Lac N 22 02 48.3 +42 18 46 A 14.65 0.85 B73
14.63 0.80 K70
BL Lac O 22 02 30.6 +42 19 00 A 15.29 1.02 B73
15.28 1.01 K70
BL Lac k 22 02 36.0 +42 16 54 A 15.44 0.82 0.56 0.54 S85
15.47 0.47 0.46 F96
15.48 0.88 B69
BL Lac 9 22 02 46.4 +42 16 56 A 15.79 1.08 M77
Notes:
HD 209438 spec type K0.
HIP 108776 V-I = 0.89, uncertain variable; IRAS 22000+4208.
BL Lac alf GSC 3206-1639.
BL Lac b GSC 3206-1047; spec type k3/4iii.
BL Lac e GSC 3206-0727.
BL Lac A GSC 3206-0931.
BL Lac f GSC 3206-0873.
BL Lac a GSC 3206-0907.
BL Lac B GSC 3206-0613.
Sources:
B69 Bertaud et al. 1969, A&A 3, 436.
B73 Bertaud et al. 1973, A&A 24, 357.
D69 DuPuy et al. 1969, ApJ 156, L135.
F96 Fiorucci & Tosti 1996, A&AS 116, 403.
K70 Kinman, priv. comm. cited in B73.
M72 Milone 1972, PASP 84, 723.
M77 McGimsey & Miller 1977, AJ 82, 453.
R70 Racine 1970, ApJ 159, L99.
S85 Smith et al. 1985, AJ 90, 1184.
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