|Frankfurt Quasar Monitoring|
|Cross-Identifications|| 1H 1720+117, 2MASS J17250434+1152155|
1RXS J172504.4+115218, RGB J1725+118
4U 1722+11, QSO B1722+119, 1722+119
RX J1725.0+1152, CGRaBS J1725+1152
1FGL J1725.0+1151, 87GB 1722+1155
|Equat. coordinates||RA 17 25 04.3 DE +11 52 15 (J2000)|
|Type|| BL Lac
|Redshift||z=0.018 (2) (5) / z=0.159 (7) (8)|
|Distance||73.2 Mpc (2) (3) / 630 Mpc (approx.) (6)|
|Total mag range (mv) (4)||13.0 - 16.6|
|Catalog Magnitude (1) (5)||15.77|
|Absolute Magnitude||--- MB (1) / -23.7 MB (7)|
|Light Travel-Time||0.237 × 109 yrs (2) / 1.9 × 109 yrs (approx.) (6)|
is a variable
BL Lacertae object
in northern Ophiuchus, 2.5° west of
Alpha Ophiuchi (Ras Alhague). This
object was discovered by
the X-ray satellite UHURU
during 1970-1973, and was later included in the
fourth UHURU catalog
(4U). Further X-ray observations followed in
1977-1978 by the HEAO A-1 satellite
(1H), and in
1979 by its successor, the HEAO A-2 (H, Einstein). In
the late 1980s, an UV-bright 15-mag stellar
object was identified at
the position of the formerly detected X-ray
investigations of the optical counterpart during
1986 and 1988
revealed a featureless spectrum. Together with its high degree of
optical polarization, H
1722+119 was classified
as a BL
Lacertae object. As a flat-spectrum
radio source, H 1722+119
was first identified between 1985
A companion galaxy was detected only 2.6" away from H
A critical point concerning H 1722+119 is its true distance. Griffiths et al. (1989) published a redshift of z=0.018 due to an absorption feature they observed. This would make H 1722+119 a nearby object of only about 240 million light-years distance. But this absorption feature was not detected by Véron-Cetty et al. (1993). Instead, Wurtz et al. (1996) measured a redshift of z=0.159. This would move H 1722+119 to a distance of about 1.9×109 light-years, nearly 10 times more distant! The latter redshift of z=0.159 agrees well with the redshift estimation published by Brissenden et al. (1990). They point out: "Since virtually all the AGN with known redshifts <0.08 show clear evidence of their host galaxies in high-resolution images, the lack of extended emission in the optical image of H1722+119 implies a distance of z > 0.1, ..." (Brissenden et al. (1990)). So the true distance of H 1722+119 remains uncertain, although a distance of about 1.9×109 light-years seems more reasonable than a distance of only about 73 Mpc.
As for most BL Lacertae objects, also H 1722+119 is a strongly variable object with a total range of more than 3 magnitudes in the optical. CCD observers, as well as visual observers, shall use the comparison stars given above. Another sequence was published by Smith et al. (1991).
Comparison star B=13.71 mv from Smith et al. (1991) is problematic for photometry. The given magnitude of star B did not fit with the photometric measurements carried out by the Frankfurt Quasar Monitoring project. As a reference, the author used the comparison stars from Fiorucci et al. (1996) (see above) for additional photometric investigations of this star. As a result, it was found that star B is only v=15.34 (0.10), instead of v=13.71 according to Smith et al. (1991). No optical variablity of star B has been detected during FQM Project. Obviously, star B=13.71 mv from Smith et al. (1991) was labelled incorrectly.
During brighter state, visual observers need at least a 10- to 14-inch telescope or larger to glimpse H:1722+119 as a stellar object. Even in large instruments, H 1722+119 remains stellar. Observing H:1722+119 is not that easy, as the BL Lac object stands close (14") to comparison star C2=13.21. So steady air conditions and high powers are required.
Some interesting observing targets can be found nearby. First we stop at Alpha Herculis (Rasalgethi). Alpha Herculis is a close double star, consisting of a 3.5-mag primary (type M5) and a 5.4-mag companion of type G5, separated by only 4.7". The components are of orange and white-yellow color. Due to the brighter orange primary, the color impression of the secondary might be shifted to something between very pale blue and some greenish hue. In addition, the primary is an irregular variable of type Mu (µ) Cep, changing its brightness between 2.7 mag and 4.0 mag.
Another double star, Struve 2166 (=ADS 10562), can be found only 50´ SE of H 1722+119. This pair consists of a white 7.1-mag primary and a bluish 8.9-mag companion, with a comfortable separation of 27.3". Right between H 1722+119 and Struve 2166 we find NGC 6368, an elongated 13.7-mag Sb-type galaxy. Another bright face-on galaxy is located some 5° SE of H 1722+119: NGC 6384. This is a splendid 11.2-mag multi-arm spiral at a distance of about 80 million light-years.
|Brissenden, R.J.V., Remillard, R.A., et al. 1990, ApJ, 350, 578; H1722+119 - A highly polarized X-ray-selected BL |
Carangelo, N., Falomo, R., et al. 2003, A&A, 412, 651; Optical spectroscopy of BL Lac objects: new redshifts and
Falomo, R., Bersanelli, M., et al. 1993, AJ, 106, 11; The Optical to Near-Infrared Emission of BL Lac Objects:
Fiorucci, M., Tosti, G. 1996, A&AS, 116, 403; VRI photometry of stars in the fields of 12 BL Lacertae objects.
Forman, W., Jones, C., et al. 1978, ApJS, 38, 357; The fourth UHURU catalog of X-ray sources.
Griffiths, R.E., Wilson, A.S., et al. 1989, MNRAS, 240, 33; 4U1722+11: The discovery of an X-ray selected BL Lac
Karge, S.; Helle Quasare für 8- bis 10-Zoll Teleskope. Ein Beobachtungsführer zur visuellen Beobachtung von
Quasaren und BL Lacertae Objekten; Frankfurt 2005.
Smith, P.S., Jannuzi, B.T., Elston, R. 1991, ApJS, 77, 67; UBVRI photometry of stars in the fields of X-ray selected
BL Lacertae objects.
Véron-Cetty, M.-P., Véron, P. 1993, A&AS, 100, 521; Spectroscopic observations of sixteen BL Lacertae candidates.
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.
Wood, K.S., Meekins, J.F. 1984, ApJS, 56, 507; The HEAO A-1 X-ray source catalog.
Wurtz, R., Stocke, J.T., Yee, H.K.C. 1996, ApJS, 103, 109; The Canada-France-Hawaii Telescope Imaging Survey of
BL Lacertae Objects. I. Properties of the Host Galaxies.