As part of a high resolution (0.55Å) spectroscopic survey of southern Seyfert galaxies, we observed a number of objects in the Hα region. The main goal of this survey is to study the profiles of the narrow lines in Seyfert 1 and Seyfert 2 galaxies. As a by-product, one can search for and analyse weak broad components in Ha that sometimes show up when Seyfert 2 galaxies are observed with high resolution and high signal to noise. Such objects are usually classified as Seyfert 1.8 or 1.9. The search and detailed study of these objects is of great importance for characterizing the weak end of the luminosity function of active galactic nuclei (AGN). The observations were made with a two channel intensified Reticon at the Coude spectrograph of the 1.6m telescope at the Laboratorio Nacional de Astrofisica (CNPq/LNA).

Gaskell and Sparke (1986) showed that one can determine the sizes of BLRs more accurately that the mean sampling interval by cross-correlating the continuum flux time series with a line flux time series. The position of the peak in the cross-correlation function (CCF) and its shape give an indication of the BLR size. The technique is explained in detail in Gaskell and Peterson (1987). The widely propagated misunderstanding is that the method involves simply interpolating both time series and cross-correlating them (in which case the CCF is dominated by the cross-correlations of “made-up” data). Actually the method involves cross correlating the observed points in one time series (continuum, say) with the linear interpolations of the other series (line flux). The line flux time series must always be smoother than the continuum time series it is derived from. We have usually employed the method with the interpolation done both ways round and averaged them (to reduce errors due to the interpolation) and we can intercompare the two results (to investigate errors).

A method of measuring correlation functions without interpolating in the temporal domain, the Discrete Correlation Function, is introduced. It provides an assumption-free representation of the correlation measured in the data, and allows meaningful error estimates. This method does not produce spurious correlations at zero lag due to correlated errors. It is shown that physical interpretation of the cross-correlation function of two series believed to be related by a convolution requires knowledge of the input function's fluctuation power spectrum. In the case of AGN line-continuum cross-correlation functions, the interpretation also involves model-dependence in the form of symmetry assumptions, and must take into account intrinsic scale bias. Application to published data for Akn 120 and NGC 4151 illustrates this method's capabilities. No correlation was found for the optical data for Akn 120, but the ultraviolet NGC 4151 data show a strong correlation, indicating that the broad C IV feature emanates from a region whose size is greater than 1.2 and less than 20 light days. These bounds on the size of the line-emitting region in NGC 4151 are in good agreement with the predictions of photoionization models.

Variability of the emission-line spectra of broad-line AGNs is now a well-established phenomenon (see Peterson 1988 for a review). The rapid variability of the emission lines and the strong correlation between continuum and line fluxes suggests broad-line region (BLR) dimensions too small to be consistent with theoretical estimates based on photoionization equilibrium considerations.

It has been apparent for some time that comparison of continuum and emission-line light curves of AGN may enable determination of the dimensions and structure of the Broad Line Region (BLR)(see Peterson 1988, and references therein). Observations to this end (Antonucci and Cohen 1983, Peterson et al. 1985, Clavel et al. 1987) and their analysis using cross-correlation to find the time lag between line and continuum variations (Gaskell and Sparke 1986), indicate BLR sizes an order of magnitude smaller than allowed by standard photoionization models for several AGN. Gaskell and Peterson (1987) analyzed errors in the cross-correlation method as applied to AGN time series in general and specifically to the Seyfert galaxy Akn120. In order to generalize and extend their analysis we investigated the significance of BLR sizes derived by cross-correlation under different model assumptions and observational circumstances (Maoz and Netzer 1988).

Twelve AGN classified as Seyfert 1.8s or 1.9s were observed with a CCD spectropolarimeter on the 3-m Shane telescope on Mount Hamilton. The instrument and data reduction procedures are described in Miller, Robinson, and Goodrich (1988). Three of the objects (NGC 2622, NGC 7603, and Mrk 1018) have undergone extreme variability, at times being classified as Seyfert 1.8s or 1.9s and at other times having spectra classifiable as Seyfert 1s. A set of IDS data on these three objects was generously provided by D. E. Osterbrock and collaborators, and allows comparison of the spectra in the “low state” (i.e. Seyfert 1.8 or 1.9) and the “high state” (Seyfert 1 spectrum).

The Einstein IPC observed the bright (5 mCrab) X-ray emitting BL Lac Object PKS 2155-304 on 1979 November 4th and 5th through 7th and on 1980 May 16th through 18th. A total of 17.4 hours were spent monitoring the source. Changes in intensity of between 10–50% are evident in the data for time scales of days and months. The source was constant to within 10% of the mean intensity on hourly time scales for all intervals of data except one. Repeated factor of 2 variations in intensity, occuring on 10–30 second time scales, were observed during the first 50 minutes of the 1979 Nov. 5th observation. These variations, however, were anticorrelated with variations seen in an adjacent background region. Concurrent MPC observations also failed to confirm the rapid changes, although they should have been readily detected. Thus, we conclude that the observed rapid variations are not intrinsic to the source, but originated in the IPC. These results can have implications for other IPC reports of short time scale variability for active galaxies and for source models based on such observations.

In order to compare X-ray-selected BL Lac objects with radio-selected BL Lac objects, we have carried out optical monitoring of some of these objects for about three years at Yunnan Observatory in China. All observations have been made with a CCD-image system at the f/13.3 Cassegrain focus of the 102-cm RCC telescope. The CCD-image system was developed by Ye et al. in Kitt Peak National Observatory of USA (Ye et al., 1985). The filters used were as follows: B-GG385(2mm)+BG12(1mm)+BG18(1mm), V-GG495(2mm)+BG18(2mm). After observing many times, more complete light curves have obtained for the X-ray-selected BL Lac object IE 0317+186 and the radio-selected BL Lac object ON 231, respectively(Fig 1 and Fig 2). Fig 1 shows that IE 0317+186 has a characteristic timescale of about 4.5hours with an amplitudes of ΔV≃0.65 mag. Fig 2 indicates that a timescale of short-term variability in ON 231 is about 70 min with an amplitudes of ΔB≃0.8 mag.

The quasar 3C273 varied by up to 100% on timescales as short as one day in the optical and IR domains during February and March 1988. In February the source changed from a behavior characterised by a stable IR flux and slow optical variations to one of recurrent optical and IR flares. Five optical flares, of amplitude up to 30–40% were observed, along with two IR flares, both of which were simultaneous with optical events. The second IR flare on March 9th rose from 46mJy to 66mJy (twice the normal (quiescent) value) in one day. The data and some of their implications are described in Courvoisier et al. (1988).

The quasar 3C273 has been repeatedly observed at radio, mm, IR, optical, UV and X-ray frequencies since December 1983. A complex pattern of continuum variations has been discovered, which can be used to provide model independent physical parameters, and to constrain different models. The main features revealed by our set of observations are:

1. (i) A flux decrease by 40% in the 2–10 kev flux in 20 days in early 1984 (Courvoisier et al. 1987).

2. (ii) Differences between the X-ray light curves at 0.5 keV and 2–10 keV.

3. (iii) A drop in the mm to mid-IR emission by factors 2–4 in early 1986, while the near infrared flux remained stable (Robson et al. 1986).

4. (iv) A decrease in the ultraviolet intensity of ∼40% in about 6 months in 1987 (Ulrich, Courvoisier and Wamsteker 1988).

5. (v) Rapid variability in the infrared and optical emission on timescales as short as one day in 1988 (Courvoisier et al. 1988 and Robson, Courvoisier and Bouchet this conference).

Since broad line variations can, in principle, constrain the structure and kinematics of the broad line region in active galaxies we have conducted a monitoring program of 20 Seyfert galaxies over a 5 year period in order to study broad line flux and profile changes. Included in our sample is the Seyfert 1.5 galaxy NGC 5548. Fifteen observations were taken from 1979 to 1984 mainly with the 60″ Palomar telescope and a SIT vidicon spectrograph. Measurements show (Fig. 1) that both the Hβ and Hγ line flux varied by 200% and the continuum varied by 300%. Furthermore, these changes were positively correlated as one would expect from photoionization by a central continuum source.

The BL Lacertae objects, OJ 287, has long been known to exhibit large amplitude variations on time scales as short as a few days. The time rate of change in brightness for these variations has been observed to be in excess of 1.0 mag. per day on several occasions. However, the nature of the optical variations on time scales significantly shorter than a day has not been well established, and in many cases the results have been controversial (Carrasco et al, 1985, Lawrence et al 1987, McHardy and Czerny, 1987). In order to address this problem, we have obtained observations of OJ 287 on four different nights during the past two years using the KPNO 0.9 meter telescope equipped with the direct CCD camera. Variations were detected for OJ 287 on each night with ranges of 0.05 mag. to 0.10 mag. The variations detected on 1986 November 9 are typical of those observed on each of the nights and is shown in Figure 1. A power spectrum analysis of the data was performed and no convincing evidence for the presence of any periodicity was found. Based on this analysis, the short term optical variations observed for OJ 287 have a very different character than the rapid x-ray flickering observed for Seyfert galaxies which have been characterized by 1/f - noise. Therefore, these observations would imply sizes for the source region 3 × 10−5 pc. If one assures that the underlying engine is a supermassive blackhole, then the time scales of the variability suggests masses for the blackhole of 107M⊙ – 108M⊙.

The variability of soft X-rays (0.2 – 2 keV) in some low-luminosity type 1 Seyferts may partly be due to an extrinsic mechanism: dense clouds of gas in the broad-line region, opaque to soft X-rays, move across our line of sight to the X-ray emitting portions of the accretion disk (Reichert, Mushotzky, and Holt 1986; Lawrence and Elvis 1982; Halpern 1984). As the clouds move, the covering fraction changes stochastically. Evidence for partial covering of the X-ray source in low-luminosity AGNs has been seen in soft X-ray spectra by Holt et al. (1980) and Reichert et al. (1985).

NGC 4151 passes rather frequently through states of deep minima characterized by a weak UV continuum and a nearly complete fading of the broad components of CIV and other permitted lines. The phenomenon described in this short article is best observed during these minima [7]. Other properties of the UV and X-ray continuum and of the emission and absorption lines of NGC 4151 have been presented and discussed elsewhere [1–6].

Redshift differences between QSO emission lines reflect the kinematical differences between the regions where the lines are produced. Gaskell (1982) discovered a systematic redshift difference between the broad lines of high ionization and the narrow forbidden lines that amounted to a blueshifting of C IV λ1549 by 600 km s−1. Gaskell obtained this result basically by comparing C IV emission and Mg II λ2798 emission in one sample of QSOs and by comparing Mg II emission and the narrow forbidden lines in a different sample. So the distribution of C IV emission redshifts relative to the narrow forbidden lines was not sampled directly by Gaskell. By observing QSOs with redshifts near 1.3, it is possible to directly sample the redshift difference between C IV and the narrow forbidden lines. This redshift difference and its distribution should provide kinematical information on the clouds of gas that give rise to the broad lines of high ionization. The narrow forbidden lines are the preferred velocity reference because they may reflect the systemic velocity of the QSO.

The strongest lines have been measured in 73 quasar spectra from the archives of the International Ultraviolet Explorer Satellite. The optically bright quasars observed with IUE were typically discovered by powerful radio emission or ultraviolet excess. They therefore should not be biased directly by observational selection with respect to ultraviolet line strength.

Because of the metastability of the 23S level of He I, a variety of effects can change the line strengths from pure recombination values in Seyfert galaxies (see Feldman and MacAlpine 1978). This occurs because the population which builds up in the 23S level can be collisionally excited to the 23P level, enhancing λ10830. The expected ratios of λ10830/λ5876 can be altered by internal or external reddening and vary with temperature, density and optical depth.

The presence of Call emission in the red spectra of AGN is now commonly observed. A sample of forty AGN has been surveyed by Persson (1988): fourteen of his objects show a clear emission of the Call triplet at 8498, 8542, 8662A (CaIIT) with a strength correlated with that of the optical Fell emission. The study of the Call triplet puts new constraints to the physical conditions in the low ionisation region of the BLR.

We present fits of models for the C IV λ 1549, N V λ1240 and Lα lines to observed profile data. Since these lines depend sensitively on the cloud ionization parameter (defined as the ratio of the illuminating flux to the cloud pressure; c.f. Krolik, McKee, and Tarter, 1981) and pressure, their relative strengths constrain the distribution of clouds in quasar broad line regions. We make the following assumptions: That the distribution of clouds around the continuum source is spherical and that the cloud motion relative to the continuum source is radial; that the clouds are in pressure equilibrium with hot intercloud medium (ICM) whose mass flux is conserved; and that the line fluxes emitted by the clouds as a consequence of the continuum illumination is given by “standard” (e.g. Kwan and Krolik, 1981) photoionization models. The cloud mass flux is not assumed to be constant, but is allowed to vary with velocity in order to fit the data. For the purposes of illustration, we have chosen a specific dynamical model: isothermal freefall with TICM = 108K. The cloud column density is assumed to be fixed at 1023cm−2.

Seven low redshift QSOs have been observed spectroscopically at infrared and optical wavelengths at McDonald Observatory. The two instruments used were the infrared grating spectrometer (IRGS; see Lester, Harvey, and Carr 1988 for a description) on the 2.7m reflector, and the es-2 cassegrain spectrometer on the 2.1m. Table 1 shows the objects and spectra taken.