|Frankfurt Quasar Monitoring|
|Cross-Identifications|| QSO J1719+4804, 1RXS J171937.9+480409|
RGB J1719+480, FIRST J171938.2+480412
1AXG J171940+4803, CGRaBS J1719+4804
87GB 1718+4806, MG4 J171935+4804
2MASSi J1719382+480412, 1718+481
GB6 J1719+4804, QSO B1718+481
|Equat. coordinates||RA 17 19 38.3 DE +48 04 13 (J2000)|
| Redshift (1) (3)
| Distance (2) (4)
|Total mag range (mv) (5) (6)||14.6 - 15.0|
|Catalog Magnitude (1)||14.60|
|Absolute Magnitude (1)||-29.8 MB|
|Light Travel-Time (2)||7.836 × 109 yrs|
Exposure date: 1955, March 25
POSS I, Palomar 48-inch Schmidt / Size 10´× 10´
Exposure date: 2011, November 23
Taunus Obs., 60-cm Refl., S. Karge / Size 10´× 10´
1718+481 is a flat-spectrum
radio source in northern Hercules, some 5° SW of
Draco´s head and close to the constellation Draco. The designation PG 1718+481
refers to the Palomar-Green Bright Quasar
Survey (PG), where this object was discovered between 1976 und 1980 as
blue stellar object of magnitude B=15m.33. Spectroscopic
investigations revealed broad
emission lines which led to the quasar classification. As
a blue UV-bright object,
quasar was also observed by the International Ultraviolet Explorer in
1982. The first ground based observations in the near infrared were
out in 1983 by the 5m-Hale Reflector. Despite the
large distance of nearly 8×109
light-years, a faint diffuse envelope was detected around the bright
stellar source - the first hint of
the host galaxy of PG 1718+481
was found. During
1997-2000, further observations in the infrared
undertaken by the 2 Micron All Sky Survey
a radio source, PG
1718+481 was first identified in 1987 with the 91-m Green Bank Radio
Telescope (87GB). Since 1990, quasar PG
1718+481 has also been known as
X-ray emitter, after its detection by ROSAT (RX).|
PG 1718+481 has a redshift of z=1.083, which means a light travel-time of 7.8×109 years! This is more than half the way through the observable universe! All together, quasar PG 1718+481 is an interesting object due to its very large cosmological distance, combined with exceptionally high luminosity.
PG 1718+481 is a low amplitude variable object with a total range of only about 0.4 magnitudes in the optical, confirmed by data from the literature and the Frankfurt Quasar Monitoring programme.
CCD observers, as well as visual observers, shall use the comparison stars given above.
Visual observers need at least a 10-inch telescope or larger to glimpse this quasar as a faint stellar object. Even with large instruments the quasar remains stellar. Locating quasar PG 1718+481 is quite easy: Just take the two brightest stars in the head of Draco, Gamma Draconis and Beta Draconis. Take the distance from Gamma Draconis to Beta Draconis. From Beta Draconis, just turn right to the south by the same distance (4.5°). A 6.37-mag field star, 11´NE of the quasar, leads you directly to PG 1718+481. Alternatively, you can draw a line from globular cluster M92 to Beta Draconis in the Draco´s head. Halfway between, you will come across quasar PG 1718+481.
Two interesting deep sky showpieces are worth visiting. The first is M92, a bright globular cluster about 5° to the south. M92 is some 30 000 light-years distant and can be resolved using an 8-inch telescope or larger. Another globular cluster, NGC 6229, can be found 5.5° to the east. NGC 6229 is considered to be about 100:000 light-years away. The brightest stars in NGC 6229 are of mag 15.5, so you will need at least 12- to 14-inch of aperture to resolve some few very faint stars of NGC 6229.
Observers who like to hunt down more very old quasi-stellar photons may turn to quasar PG 1700+518, a bright 14-mag object at a distance of about 3×109 light-years, only 4.7° NW.
Some 45 arcsecs to the west of the quasar position, a 15.7-mv high proper-motion star can be seen in the images above, designated 2MASS J17193377+4804178. Between 3/1955 and 11/2011 its apparent position changed significantly.
2MASS J17193377+4804178 (B 16.4, R 14.3), Proper motion -> RA 16 mas/yr, DE 160 mas/yr.
[Data from CDS Strasbourg Database (6-2013)]
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Hamburg Quasar Monitoring