|Frankfurt Quasar Monitoring|
|W Com (ON 231)|
231, ON+231, 10.1916 Comae, VRO 28.12.02
SDSS J122131.69+281358.4, 1219+285, W Comae
1ES 1218+285, RX J1221.5+2813, 2EG J1222+2821
7C 1219+2830, 87GB 1219+2830, RGB J1221+282
QSO B1219+285, AAVSO 1216+28, S3 1219+28
B2 1219+28, TXS 1219+285, GeV J1222+2837
|Equat. coordinates||RA 12 21 31.7 DE +28 13 58 (J2000)|
|Total mag range (mv) (4)||11.4 - 17.3|
|Catalog Magnitude (1)||16.11|
|Absolute Magnitude (1)||-22.2 MB|
|Light Travel-Time (2)||1.285 × 109 yrs|
Credit: SDSS / Size 3´× 3´/ N up, E leftThe host galaxy of W Com and the distorted companion galaxy
Credit: Nilsson et al. (2003) / Size 35.4" × 35.4"R-band image by the Nordic Optical Telescope (image inverted)
Com (W Comae=ON 231=1219+285) is a violently variable BL Lac object in
Coma Berenices, located in
the north-western part of Coma Cluster Mel 111. W Com is also often
termed ON 231. W
Com was discovered by Max Wolf at Heidelberg, Germany. While
analyzing photographs, taken during the years 1892-1903 with the
Bruce-Astrograph, he found an optical variability ranging between mag
und mag 14.
Wolf classified this new object as an
ordinary variable with the
preliminary designation 10.1916 Comae. He published his discovery in
the Astronomische Nachrichten Nr. 202 in
1916. Only until 1969, this object was cataloged as the irregular
Comae in the GCVS. In
the 1960s, W Com was recognized as a radio source by the Ohio Radio
Browne and Biraud independently identified this radio source with a
stellar object (W Com) in 1971, and realized its extragalactic nature.
Just one year later, W Com was classified as a BL Lac object by
analysis. An accurate redshift was determined in 1982.
The strong AGN activity of W Com is obviously triggered by the gravitational interaction between the Blazar host and a small companion galaxy (SDSS J122131.37+281349.2, 18.85g), only some 8 arcsec to the SW. The companion appears elongated and distorted due to tidal forces (see the high resolution images above).
Both visual and CCD observers will detect W Com as a stellar object on an average brightness level ranging between 14 mag and 16 mag. W Com is an interesting target for visual observers with telescopes of 8- to 10-inch of aperture and larger during active state. It is very easy to locate, as the two 6-mag stars, 9 Com and 10 Com, show the way. From the two stars, just turn your telescope about 30 arcmin to the west - and there you are.
CCD observers, as well as visual observers, shall use the comparison stars given above. Other photometric sequences were published by Véron et al. (1975) and Doroshenko et al. (2005). Try to avoid using comparison star D when observing with clear filter. Its reddish colour (see chart above) leads to "strange" photometric results.
Starting our visual trip into the surrounding area we first take a look at the large open cluster Mel 111, also dubbed the "Coma Cluster", only about 280 light-years away. Mel 111 is an easy catch for the naked eye and binoculars, located in the close neighbourhood to W Com.
W Com is surrounded by a large number of bright galaxies. Deep sky showpieces like NGC 4559, NGC 4494 and NGC 4565, dubbed "The Needle", are all close by. Right next to W Com, we find two faint galaxies, easily detectable by CCD observers: NGC 4295 (14.9m, 0.6´× 0.5´, type S0) is located only 6 arcmin to the SW (see charts above). IC 3212 is an even fainter spiral, 7 arcmin to the SE (15.7m, 0.5´× 0.5´, Sc), see finding chart above. GZ Com, only 2 arcmin NE (see finding chart above), is a faint RR Lyrae-type variable, ranging between B=16.5 and B=17.5.
Another violently variable quasar, 4C 29.45, is located only 5° W of W Com - at a whopping distance of more than 6×109 light-years.
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Hamburg Quasar Monitoring
Gary Poyner (light curve)
Sloan Digital Sky Survey