Frankfurt Quasar Monitoring

I Zw 187 = OT 546
Object data

  Cross-Identifications  OT+546, OT 546, II Zw 77, PGC 60348, 1727+502
  87GB 172704.2+501535, 2MASXi J1728186+501310
  TXS 1727+502, MG4 J172809+5013, PKS 1727+502
  RGB J1728+502, 1ES 1727+502, 1H 1730+500
  RX J172819.1+501309, 1AXG J172815+5013
  XSS J17272+5025, 1FGL J1727.9+5010
  Equat. coordinates   RA  17 28 18.6     DE  +50 13 11     (J2000)
  Constellation   Hercules
  Type   BL Lac
  Distance (2) (3)
  224 Mpc
  Total mag range (mv) (4)   14.2 - 16.8
  Catalog Magnitude (1)   15.97
  Absolute Magnitude (1)   -21.1 MB
  Light Travel-Time (2)   0.712 × 109 yrs
(1) Véron-Cetty & Véron 2006, A&A 455, 776
(2) NASA/IPAC Extragalactic Database
(3) Co-Moving Radial Distance
(4) Literature

Finding chart

Comparison stars

star V Rc Ic
B 13.14 (0.06) 12.81 (0.06)
12.49 (0.06)
H 15.29 (0.06)
14.99 (0.06)
14.66 (0.06)
L 16.10 (0.09)
15.71 (0.09)
15.35 (0.08)
comparison stars from Fiorucci et al. 1996, A&AS, 116, 403

Light curve

I Zw 187 = OT 546 = 1727+502
This 5´× 5´ section from DSS shows the host galaxy of I Zw 187 (centre)
as a bright point source, surrounded by a diffuse circular halo.
  Credit: DSS2R (ESO) / Chart by S. Karge

I Zw 187 = OT 546 is a variable BL Lac object in northern Hercules, very close to the constellation Draco. The designation I Zw 187 refers to swiss-born astronomer Fritz Zwicky (Zw), who first recognized this 16.1-mag object as a compact galaxy ("Fuzzy red variable spherical compact."). He published his find in his first catalog (1964). His initial spectral analysis showed a featureless blue continuum. In the late 1970s, the first redshift was measured. Consequently, I Zw 187 was classified as a BL Lac object, as this object shows both optical polarization and an optical variability by about 2.4 magnitudes. Around the year 1967, this object was first discovered as a strong radio source during the Ohio State University Radio Survey (OT). Later on, it has been cataloged by various other radio surveys. Radio interferometry revealed a complex jet extending towards the northwest. Furthermore, I Zw 187 was recognized as an X-ray source by ROSAT in the early 1990s. I Zw 187 can be described as an X-ray selected BL Lac object and a flat spectrum radio source. The BL Lac object resides in an elliptical galaxy with an apparent diameter of 0.28´× 0.23´, located at a distance of 237 Mpc. The central supermassive black hole has an estimated total mass of 5.4×108 solar masses.

CCD observers, as well as visual observers, shall use the comparison stars given above. Another photometric sequence was published by Craine et al. (1975). I Zw 187 was mislabeled as I Zw 186 in Craine's Handbook of QSOs.
BL Lac object I Zw 187 is located in northern Hercules, very close to the border of Draco. I Zw 187 is easy to locate as its position lies only 2° south of Beta Draconis in the Draco´s head. Visual observers need at least a 14-inch telescope or larger to glimpse this stellar object. Even with large aperture telescopes I:Zw:187 remains stellar.

Two interesting globular clusters are only about 7° away: First to mention is M92, the second brightest globular in Hercules - an easy task for 8-inch telescopes. The second globular is NGC 6229, considered to be about 100 000 light-years distant. The brightest stars of NGC 6229 are only mag 15.5, so you will need at least 12- to 14-inch of aperture to resolve some few and very faint stars of NGC 6229.

Observers who search for more
quasi-stellar objects, the constellations Draco and Hercules are rich with bright targets. No less than 6 quasars of mag 14 and mag 15 are located within a 10°-radius around
- IRAS 17500+5046 (3.7° E)  
-> CDS

- HS 1817+5342 (8.4° E)  
-> CDS
- IRAS 17596+4221 (9.8° SE)
 -> CDS
- PG 1718+481 (2.6° SW)
- PG 1700+518 (4.5° WNW)
- PG 1626+554 (10.4° NW)  
-> CDS

Angel, J.R.P., Stockman, H.S. 1980, ARA&A, 18, 321; Optical and infrared polarization of active extragalactic objects.
Akiyama, M., Ueda, Y., et al. 2003, ApJS, 148, 275; Optical Identification of the ASCA Medium Sensitivity Survey in the
     Northern Sky: Nature of Hard X-Ray-Selected Luminous Active Galactic Nuclei.
Craine, E.R.; A Handbook of Quasistellar and BL Lacertae Objects; Parchart Publishing House, Tuscon 1977.
Craine, E.R., Johnson, K., Tapia, S. 1975, PASP, 87, 123; UBVr Sequences and Observations of optically identified Radio
Fan, J.H., Lin, R.G. 1999, ApJS, 121, 131; Infrared Variation of Radio-selected BL Lacertae Objects.
Fiorucci, M., Tosti, G. 1996, A&AS, 116, 403; VRI photometry of stars in the fields of 12 BL Lacertae objects.
Healey, S.E., Romani, R.W., et al. 2007, ApJS, 171, 61; CRATES: An All-Sky Survey of Flat-Spectrum Radio Sources.
Kollgaard, R.I., Gabuzda, D.C., Feigelson, E.D. 1996, ApJ, 460, 174; Parsec-Scale Radio Structure of Four X-Ray-selected
     BL Lacertae Objects.
Oke, J.B., Sargent, W.L.W., et al. 1967, ApJ, 150, L173; A variable radio-quiet compact galaxy I Zw 1727+50.
Oke, J.B. 1978, ApJ, 219, L97; The redshift and other properties of I ZW 1727+5015.
Skrutskie, M.F., Cutri, R.M., et al. 2006, AJ, 131, 1163; The Two Micron All Sky Survey (2MASS).
Steinicke, W.; Katalog heller Quasare und BL Lacertae Objekte; Umkirch 1998.
Steinicke, W.; Beobachtungsliste für helle Quasare; Umkirch 1999.
Steinicke, W. 1999, Interstellarum 15, 42; Unbekannte Quasare für visuelle Beobachter.
Véron-Cetty, M.-P., Véron, P. 2001, A&A 374, 92; A Catalogue of Quasars and Active Nuclei: 10th edition.
Véron-Cetty, M.-P., Véron, P. 2003, A&A 412, 399; A Catalogue of Quasars and Active Nuclei: 11th edition.
Véron-Cetty, M.-P., Véron, P. 2006, A&A 455, 776; A Catalogue of Quasars and Active Nuclei: 12th edition.
Véron-Cetty, M.-P., Véron, P. 2010, A&A 518, 10; A Catalogue of Quasars and Active Nuclei: 13th edition.
Zwicky, F., Zwicky, M.A.; Catalogue of Selected Compact Galaxies and of Post-Eruptive Galaxies; Zürich 1971.


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© Stefan Karge  /  last obs. 2022-12-24