Comparison stars

Colour chart

Credit: DSS2  /  Size 14´× 14´ /  Chart by S. Karge

---

Light curve

---

Notes

PDS 456 is a bright radio-quiet quasar in the south-western part of the constellation Serpens Cauda, close to the constellation Ophiuchus. This object was discovered during the IRAS-Survey in the 1980s. Follow-up spectroscopic investigations of this luminous infrared source were carried out by the Pico dos Dias Survey (PDS) in 1996. They revealed broad emission lines in the spectrum, which soon led to the classification as a quasar at a distance of a little more than 2 giga light-years. Due to the small cosmological distance and the high luminosity, Torres et al. (1997) concluded that PDS 456 is 1.3 times more luminous than 3C 273 - and is the most luminous quasar in the nearby (z ≤ 0.3) universe. In the optical band pass, PDS 456 appears less luminous than 3C 273 as its position lies close to the galactic plane (+11°). As a result, the galactic foreground extinction is considered as 1.5 magnitudes in the optical. In the 1990s, X-ray emissions were detected by ROSAT. PDS 456 later turns out to be an extreme X-ray variable object. It shows strong short-term variations in both the X-ray and optical regions. The central supermassive black hole has an estimatet mass of 1x109 solar masses. High resolution images could not resolve the host galaxy of PDS 456 due to the high luminosity of the central quasar, outshining the stellar population of the host. Instead, three compact sources were found lying about 3" (~10 kpc) to the southwest of the QSO. They are considered as small companion galaxies that are very likely physically associated with PDS 456. The host galaxy may have undergone a tidal interaction or a merger recently, possibly triggering the strong AGN activity of PDS 456 we see today. What makes PDS 456 so very special is its nature being an object undergoing a transition from an ultraluminous infrared galaxy (ULIRG) to a classical QSO phase. PDS 456 is a low amplitude variable object with a total range of only about 0.5 magnitudes in the optical. CCD observers, as well as visual observers, shall use the comparison stars given above. Unfortunately, Véron-Cetty et al. (1998-2001) published a wrong position of PDS 456 in their quasar catalogs, so the author´s visual observations between 1999 and 2003 focused on the wrong object. Visual observers need at least an 8- to 10-inch telescope or larger to glimpse PDS 456 as a stellar object. Even in large instruments PDS 456 remains stellar. Observing PDS 456 is a little tricky as this 14-mag quasar is located in a dense starfield of the western outskirts of the Milky Way. Search for the two stars Xi [55] Ser (3.5 mag) and Nu [53] Ser (4.3 mag). Right between them you will find PDS 456. In before, you shall prepare a detailed finding chart with a planetarium software like "Guide" or "TheSky", etc.. ____________ Some interesting observing targets can be found nearby. First we stop for NGC 6309, dubbed the "Box Nebula", an 11-mag planetary, some 3.7° WNW of PDS 456. 4.8° to the SSW we meet M9, a bright 7.7-mag globular, some 25 000 light-years distant. Only 25`W of M 9, you may like to visit the remarkable dark cloud B64, with an apparent diameter of about 0.6°. Stargazers who like to observe some more interesting quasi-stellar objects may turn to quasar PKS 1749+096 (OT 081), a violently variable object at a distance of about 3.5×109 light-years, some 24° NNE of PDS 456. Another variable BL Lac object, H 1722+119, is located 26° north of PDS 456, at a distance of approximately 1.9×109 light-years.

---

Literature

Gaskell, C.M., et al. 2006, ASP Conference Series, Vol. 390 (astro-ph/0701005v1); Optical Variability of the three      brightest nearby Quasars. Nardini, E., Reeves, J.N., et al., 2015, Science, 347, 860; Black hole feedback in the luminous quasar PDS 456. Reeves, J.N., Braito, V., et al. 2014, ApJ 780, 45; Variability of the High-velocity Outflow in the Quasar PDS 456. Torres, C.A.O., et al. 1997, ApJ, 488, L19; Discovery of a luminous Quasar in the Nearby Universe. Véron-Cetty, M.-P., Véron, P., 1998, ESO Scientific Report 18; A Catalogue of Quasars and Active Nuclei (8th Edition). Véron-Cetty, M.-P., Véron, P., 2000, ESO Scientific Report 19; A Catalogue of Quasars and Active Nuclei (9th Edition). 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. Yun, M.S., et al. 2004, ApJ, 601, 723; Multiwavelength Observations of the Gas-rich Host Galaxy of PDS 456: A New      Challenge for the ULIRG-to-QSO Transition Scenario.

---

Link: APASS

---

© Stefan Karge (FQM)  /  last obs. 2024-09-17

home