|Frankfurt Quasar Monitoring|
|I Zw 187 = OT 546|
|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)|
Distance (2) (3)
|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|
|I Zw 187 =
OT 546 is
variable BL Lac object in northern Hercules, very close to the
constellation Draco. The designation I Zw 187 refers to swiss-born
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
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
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
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