Large Outburst of BL Lac


(vsnet-alert 1037)

IAUC No. 6693 tells that BL Lac is undergoing a major outburst (J. C. Noble et al.) On June 23, the R-magnitude reached 12.50-12.75.

Recent observations reported to VSNET show rather faint values, possibly suggesting a large fluctuation with a short time scale.

  YYMMDD(UT)   mag  observer
  970511.103   153  (G. Poyner)
  970512.069   153  (G. Poyner)
  970514.047   153  (G. Poyner)
  970526.044   151  (G. Poyner)
  970530.053   152  (G. Poyner)
  970531.042   152  (G. Poyner)
  970602.026   153  (G. Poyner)
  970608.023   153  (G. Poyner)
  970705.016   153  (G. Poyner)
Regards,
Taichi Kato

Comparison sequence

(vsnet-chat 484)

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://www.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.

Surprisingly, this short-term variation was confirmed by CCD photometry!!

See:

Title: The 1997 Outburst of BL Lacertae and Detection of a 0.6 mag Rapid
       Variation
Authors: K. Matsumoto, T. Kato, D. Nogami, T. Kawaguchi, T. Kinnunen, G. Poyner

was published (PASJ 51, 253 (1999)).
reprint request: katsura@kusastro.kyoto-u.ac.jp


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