Frankfurt Quasar Monitoring

3C 371
Object data

  Cross-Identifications  3C 371.0, VII Zw 768, ZWG 340.35, UGC 11130
  KAZ 273, NRAO 548, MCG +12-17-000, PGC 61417
  CGCG 1807.2+6949, 7C 180717.90+694858.00
  WMAP J1806+6949, HS 1807+6948, TXS 1807+698
  IRAS 18072+6949, 2MASX J18065063+6949275
  1807+698, GB6 J1806+6949, RX J1806.8+6949
  87GB 180718.0+694904, 4C 69.24, S4 1807+69
  QSO B1807+698, H 1801+698, 1ES 1807+698
  1H 1803+696, 1RXS J180650.2+694923
  Equat. coordinates   RA  18 06 50.7     DE  +69 49 28     (J2000)
  Constellation   Draco
  Type   BL Lac
  Redshift   z=0.051 (2)  /  z=0.052 (4)
  Distance (2) (5)
  206 Mpc
  Total mag range (mv) (3)   13.5 - 15.4
  Catalog Magnitude (1)   14.22
  Absolute Magnitude (1)  -22.6 MB
  Light Travel-Time (2)   0.656 × 109 yrs
(1) Véron-Cetty & Véron 2006, A&A 455, 776
(2) NASA/IPAC Extragalactic Database
(3) Literature
(4) CDS Strasbourg Database
(5) Co-Moving Radial Distance

Finding chart

Comparison stars

star  U B V
A 14.64 14.20 13.60
B 15.93 15.08 14.21
C 15.44 15.13 14.53
D 15.52 15.26 14.67
E 16.75 15.97 15.11
F 16.71 16.06 15.42
comparison stars from McGimsey et al. 1977, AJ, 82, 7

Light curve

3C 371: High resolution image

Credit: DSS2B, ESO / Size 3´× 3´
3C 371 appears as a star-like object with a
diffuse halo (phot. diam. 15"×15"), together
with other faint galaxies [N up, E left].
Credit: K. Nilsson, NOT / Size 176" × 159"
This B-/R-band composite image shows a tidal tail
connecting the host of 3C 371 to a pair of
companion galaxies in the lower right corner.

3C 371 is a variable BL Lacertae object in Draco, about 1.8° SE of 4.2-mag Phi Draconis (43 Dra), and only 1.5° E of bright galaxy NGC 6503. This object was discovered in 1959 as a radio source by the 3. Cambridge Radio Survey (3C). In 1966, a compact galaxy of mag 14.4 (phot.) was identified as the optical counterpart. This compact galaxy was discovered only one year earlier by Fritz Zwicky (Zw), who described it as a "large blue spherical compact". The determination of the redshift of this system was only possible by spectroscopic investigations of the stellar population of the host galaxy (UGC), as the bright galaxy core (AGN) revealed only a featureless spectrum. Together with its optical variability and its high degree of polarization, 3C 371 was classified as a BL Lacertae object in 1975. Besides its nature as a strong radio source, 3C 371 has also been known as a source of both infrared and X-ray emissions. 3C 371 can be best described as a variable BL Lac object at the centre of a giant elliptical, which resides in a compact group of other galaxies. The elliptical host of 3C 371 has an impressive true size of approximately 300×260 klyrs. Direct imaging showed that the host galaxy of 3C 371 is an interacting system with a tidal tail directing towards the closest two neighbouring systems (see high resolution image above).

3C 371 is a variable object with a total range of about 2 magnitudes in the optical. At maximum, visual observers need at least an 8- to 10-inch telescope to glimpse this stellar object. In large instruments, 3C:371 becomes increasingly star-like with a very faint outer halo. CCD observers, as well as visual observers, shall use the comparison stars given above. Another sequence was published by the AAVSO.

Two deep sky showpieces in the vicinity of 3C 371 are worth visiting: First there is NGC 6503, a bright galaxy only 1.5° to the west. NGC 6503 is a large and elongated galaxy at a distance of some 16 million light-years. The second object is located some 3° to the south. There we find the showpiece planetary NGC 6543, also known as the "Cat´s Eye Nebula". NGC 6543 is rich in details and one of the brightest objects of its class.

Stargazers who like to observe more very old quasi-stellar photons may turn to quasar PGC 61965, a bright 14-mag object at a distance of about 1.5×109 light-years, only 3.8° NNE of 3C 371.
CCD observers may also take a look at S4 1749+70, a violently variable BL Lac object at a whopping distance of about 6.5×109 light-years, only 1.6° W of 3C 371, and only 4´ SW of NGC 6503.

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Kinman, T.D. 1976, ApJ, 205, 1; Photoelectric Magnitudes and Polarization Data for possible BL Lacertae Objects.
Lawrence, C.R., Zucker, C.R., et al. 1996, ApJS, 107, 541; Optical Spectra of a Complete Sample of Radio Sources.
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     3CR Radio Source Counterparts. III. Radio Galaxies with z<0.1.

McGimsey, B.Q., Miller, H.R. 1977, AJ, 82, 7; Photoelectric comparison sequences in the fields of optically active
     extragalactic objects.
Miller, J. 1975, ApJ, 200, L55; The Composite Nature of the N Galaxy 3C 371.
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     PKS 0521-365, 3C 371, and PKS 2201+044.
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Steinicke, W.; Beobachtungsliste für helle Quasare; Umkirch 1999.
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Wenzel, K. 1997, Interstellarum 10, 25; Quasare - Objekte für den beobachtenden Amateur.
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Hamburg Quasar Monitoring


© Stefan Karge  /  last obs. 2021-08-14