2 Observations and data reduction

The near-infrared spectroscopy of our AGN subsample used the CoolSpec spectrograph (Lester et al. 2000) on the 2.7 m telescope at McDonald Observatory in Texas. We used grating #3310-FL-906 in the K-band in first order with a resolution $\lambda/\Delta\lambda=268$ and a $256\times256$ NICMOS3 CCD ( $\Delta\lambda$ at $2.2~\mu{\rm m} \equiv 2.6$ pixel). Table 1 lists all sources with the optical positions, redshifts, K magnitudes from the 2 Micron All Sky Survey (2MASS) second incremental release catalogue, observed K magnitude $K_{\rm obs}$, and observing dates and times. During the whole run the weather conditions were rather poor, therefore absolute flux calibrations are not very accurate. In order to obtain these we observed for each object a nearby bright star of spectral type A to G. The spectral types were taken from the Bright Source Catalogue, 5th revised edition (Hoffleit & Jaschek 1991). For some of our comparison stars the K magnitudes were known, for others the K magnitudes were derived from the B and V magnitudes using the relation $V-K = (2.29\pm 0.01)\times(B-V)$. This relation was obtained by fitting the colours in a sample of 196 infrared standard stars common to the list of Van der Bliek et al. (1996) and the Bright Star Catalogue, 5th Revised Ed. (Hoffleit & Jaschek 1991). These K magnitudes were converted into flux densities at 2.2 $\mu$m using the relation K = 14.0- $2.5 \log(F_{2.2\mu}$) (Van der Bliek et al. 1996) with the flux density in units of 10^-15 W m^-2 $\mu$m^-1. The flux density distribution in our observing window was then computed from the flux density at 2.2 $\mu$m assuming a Rayleigh-Jeans tail for the spectral shape.

The flux-calibrated spectrum of the AGN can then be calculated from the ratio of the observed spectra of AGN and comparison star, taking into account the different exposure times. The flux densities at 2.2 $\mu$m thus obtained for our AGN were converted into K magnitudes using the relation given above. In Table 1 we list these K magnitudes together with those given in the 2MASS catalogue. In most cases the observed magnitude is less than the one given in the 2MASS, because the poor weather conditions are more likely to reduce the flux for the long exposures of the objects than for the short exposures of the comparison stars. In this way we can scale the observed AGN spectrum, to account for variations in the extinction between source and comparison star and we are able to get more reliable absolute infrared fluxes that can be compared to our measurements in the optical range. As listed in Table 1 for six sources K magnitudes were not yet available in the 2MASS. Therefore we give line fluxes in Table 2 only for those sources for which we could do the scaling as described above.

Wavelength calibrations were obtained by fitting a linear relation to the line positions of Argon, Neon, and Xenon. Sky subtraction was done by nodding the telescope between two positions in a star-sky-sky-star sequence. For our targets such a sequence took 8 min and was repeated several times, while for the bright comparison stars a much shorter exposure time of 4 to 20 s per sequence was sufficient.

 

 

Table 1: List of the AGN; $\alpha _{2000}$ and $\delta _{2000}$are the optical positions (Grupe et al. 2001), K magnitudes are taken from the 2MASS catalogue and from the observed spectrum (before scaling), and $T_{\rm obs}$ lists the total observing time per source in minutes.

#	Name	$\alpha _{2000}$	$\delta _{2000}$	z	$K_{\rm 2MASS}$	$K_{\rm obs}$	Obs date	$T_{\rm obs}$	comp. star	spec. type
1	RX J0859.0+4846	08 59 02.9	+48 46 09	0.083	--	12.3	2001-02-18	24	HR 2692	G9V
2	Mkn 110	09 25 13.0	+52 17 12	0.035	--	12.5	2001-02-18	32	HR 4096	A2V
3	PG0953+414	09 56 52.4	+41 15 22	0.234	12.5	12.4	2001-02-19	16	HR 3811	F2V
4	RX J1005.7+4332	10 05 41.9	+43 32 41	0.178	12.7	12.9	2001-02-17	32	HR 4067	F7V
5	RX J1007.1+2203	10 07 10.2	+22 03 02	0.083	14.2	14.0	2001-02-19	32	HR 4012	F9V
6	CBS 126	10 13 03.2	+35 51 24	0.079	12.6	13.0	2001-02-18	24	HR 4096	A2V
7	RX J1034.6+3938	10 34 38.6	+39 38 28	0.044	12.7	13.8	2001-02-17	40	HR 4067	F7V
8	RX J1117.1+6522	11 17 10.1	+65 22 07	0.147	13.0	14.0	2001-02-19	32	HR 3391	G1V
9	Ton 1388	11 19 08.7	+21 19 18	0.177	11.5	12.2	2001-02-19	16	HR 4012	F9V
10	PG 1211+143	12 14 17.7	+14 03 13	0.082	--	12.0	2001-02-19	24	HR 4864	G7V
11	Mkn 766	12 18 26.6	+29 48 46	0.013	10.6	10.6	2001-02-18	16	HR 4096	A2V
12	IC 3599	12 37 41.2	+26 42 28	0.021	13.5	13.8	2001-02-18	32	HR 4096	A2V
13	IRAS 12397+3333	12 42 10.6	+33 17 03	0.044	--	12.0	2001-02-18	24	HR 4845	G0V
14	RX J1304.2+0205	13 04 17.0	+02 05 37	0.229	--	15.6	2001-02-19	16	HR 4864	G7V
15	PG 1307+085	13 09 47.0	+08 19 48	0.155	--	13.1	2001-02-19	24	HR 4864	G7V
16	RX J1355.2+5612	13 55 16.6	+56 12 45	0.122	13.3	14.1	2001-02-19	24	HR 5280	A2V
17	PG 1402+261	14 05 16.2	+25 55 34	0.164	12.2	12.8	2001-02-18	32	HR 4845	G0V
18	Mkn 478	14 42 07.5	+35 26 23	0.077	11.1	12.2	2001-02-18	32	HR 5569	A2V
19	Mkn 493	15 59 09.7	+35 01 48	0.032	11.8	12.0	2001-02-19	16	HR 5280	A2V