1 Introduction

 

Table 3: Comparaison between our and "other'' measurements

Reference			Previous original measurements		New DSS measurements
	Accuracy		Number	Notes	Mean deviation
	RA	Dec.			RA	Dec.
Green et al. (1986)	$8\hbox{$.\!\!^{\prime\prime}$ }7$	$7\hbox{$.\!\!^{\prime\prime}$ }6$	150	POSS (KPNO Grand Mashine)	15''	15''
Sanduleak & Pesch (1987)	$3\hbox{$.\!\!^{\prime\prime}$ }0$	$6\hbox{$.\!\!^{\prime\prime}$ }0$	100	POSS (Warner & Swasey obs.)	$2\hbox{$.\!\!^{\prime\prime}$ }5$	$3\hbox{$.\!\!^{\prime\prime}$ }0$
Nelson et al. (1988)	$1\hbox{$.\!\!^{\prime\prime}$ }5$	$1\hbox{$.\!\!^{\prime\prime}$ }5$	118	PDS	$1\hbox{$.\!\!^{\prime\prime}$ }5$	$1\hbox{$.\!\!^{\prime\prime}$ }5$
Seal et al. (1990)	$1\hbox{$.\!\!^{\prime\prime}$ }5$	$1\hbox{$.\!\!^{\prime\prime}$ }5$	134	POSS	$1\hbox{$.\!\!^{\prime\prime}$ }5$	$1\hbox{$.\!\!^{\prime\prime}$ }5$
Simpson et al. (1990)	$2\hbox{$.\!\!^{\prime\prime}$ }0$	$2\hbox{$.\!\!^{\prime\prime}$ }0$	106	PDS	$3\hbox{$.\!\!^{\prime\prime}$ }0$	$3\hbox{$.\!\!^{\prime\prime}$ }0$
Stepanian (1994)	$<1\hbox{$.\!\!^{\prime\prime}$ }5$	$<1\hbox{$.\!\!^{\prime\prime}$ }5$	205	POSS (KPNO Grand Mashine)	$<1\hbox{$.\!\!^{\prime\prime}$ }5$	$<1\hbox{$.\!\!^{\prime\prime}$ }5$
Bowen et al. (1994)	$<1\hbox{$.\!\!^{\prime\prime}$ }0$	$<1\hbox{$.\!\!^{\prime\prime}$ }0$	9	DSS	$<1\hbox{$.\!\!^{\prime\prime}$ }0$	$<1\hbox{$.\!\!^{\prime\prime}$ }0$
Véron-Cetty & Véron (1996)	$0\hbox{$.\!\!^{\prime\prime}$ }6$	$0\hbox{$.\!\!^{\prime\prime}$ }6$	105	DSS	$<1\hbox{$.\!\!^{\prime\prime}$ }0$	$<1\hbox{$.\!\!^{\prime\prime}$ }0$
SBS original lists	$1\hbox{$.\mkern-4mu^\prime$ }5$	$1\hbox{$.\mkern-4mu^\prime$ }5$	741	POSS

Figure 1: A plot of the difference in RA and Declination between the newly measured positions and the previously available optical position of PG objects (Green et al. 1986)

Figure 2: Another similar plot of the differences between our position and the ones measured by Sanduleak and Pesch, indicated a standard deviation of about 2'' in both coordinates, and systematic deviation by Dec. of about +3''

Figure 3: A plot of the differences between our measured position, and the ones by Nelson et al. (1988), indicates a standard deviation of about $1\hbox{$.\!\!^{\prime\prime}$ }5$ in both RA and Dec.

Figure 4: A plot of the differences between our measured position and the ones measured by Seal et al. (1990), indicates a standard deviation of about $1\hbox{$.\!\!^{\prime\prime}$ }5$ in both and Dec.

Figure 5: A similar plot of the differences between our positions and the ones measured by Simpson (1990), indicates a standard deviation larger than 3''0 in both coordinates

Figure 6: A plot of the differences in RA and Dec. between the newly measured positions and the previously measured optical position of SBS objects by Stepanian et al. (1994)

Figure 7: A similar plot of the differences between our positions and the ones measured by Bowen et al. (1994), indicates a standard deviation smaller than 1'' in both coordinates

Figure 8: A similar plot of the differences between our positions and the ones measured by Véron-Cetty & Véron (1996), indicates a standard deviation less than 1'' in both coordinates

In 1960 Markarian initiated an objective prism survey of the northern sky (Markarian 1967). It was the first survey in which a thin objective prism was used for selecting peculiar extragalactic objects characterized by an ultraviolet emission excess. The observations were made with the 40''-52'' Schmidt camera of the Byurakan Observatory, equipped with 1.5, 3 and 4 degree objective prisms. This survey become known as the First Byurakan Survey (FBS) (see for complete references Markarian et al. 1981). The FBS covered most of the sky visible from the Byurakan Observatory in Armenia. Ten years later a similar survey in the southern sky was undertaken by Smith (1975) at the CTIO in Chile.

The FBS (the "Markarian survey") yielded a complete sample of AGNs down to limiting magnitude $m_{\rm pg}=15\hbox{$.\!\!^{\rm m}$ }5$. Subsequent optical spectroscopy revealed that over 200 Seyfert galaxies, 13 QSOs, 3 BL Lac objects and hundreds of starburst, blue compact and HII galaxies were cataloged in the FBS.

In 1974 the Second Byurakan Survey (SBS) was initiated. It was completed in 1991 (Markarian & Stepanian 1983, 1984a,b; Markarian et al. 1985, 1986; Stepanian et al. 1988, 1990; Stepanian 1994). The same Schmidt camera was used for observations. The SBS covered a smaller region of the northern sky of about 1000 sq. degrees bounded by: $07^{\rm h}40^{\rm m}<\alpha<17^{\rm h}15^{\rm m}$ and $+49\hbox{$^\circ$ }< \delta < +61\hbox{$^\circ$ }$. The advantage of the SBS is fainter limiting magnitude of $m_{\rm pg}=19\hbox{$.\!\!^{\rm m}$ }5$. The fainter detection limit of the SBS is partly due to an improved photographic sensitivity to the UV-excess continuum and to the relevant emission lines. This resulted in a larger surface density of the SBS objects (by about 15 times) in comparison to the FBS.

Selection of the SBS objects was done by visual inspection of plates based on the following criteria: (i) the presence of strong UV continuum, and (ii) the presence of emission lines and/or a peculiar energy distribution in the spectra. The main goal of the SBS was to indentify and characterize peculiar objects belonging to the following classes: (a) galaxies with UV-excess continuum radiation, (b) emission line galaxies, without appreciable UV-excess continuum, (c) QSOs and AGN candidates, (d) white dwarfs and subdwarf stars, and (e) other types of objects with strong UV continuum radiation.

Up to now $\sim1700$ galaxies and $\sim1800$ star-like objects with UV excess have been detected in the SBS survey. The SBS catalog will allow to derive a complete sample of faint AGNs down to $B\le 17\hbox{$.\!\!^{\rm m}$ }5$. It should also allow the investigation of the luminosity function of QSOs, AGNs, and UV-excess galaxies, and contribute to our understanding of the large-scale structure in the Universe at scale $\le 500$ Mpc.

For any follow-up investigation of nearly 3500 SBS objects, the knowledge of an accurate optical positions is required. In this paper we present accurate optical coordinates for 2978 objects listed in the SBS catalog.