Forbidden Emission Lines Research Articles

Identification and intensity analysis on forbidden magnetic dipole emission lines of highly charged Al, Ar, Ti and Fe ions in LHD

Forbidden lines arising from magnetic dipole (M1) transitions in 2 s 2 2 p x ( x = 1 – 5 ) ground and 2s2p excited configurations of highly charged Al, Ar, Ti and Fe ions have been observed in the large helical device (LHD). Argon was puffed using a piezo-electronic valve and other metallic materials were injected using an impurity pellet injector into LHD plasma for the observation. The M1 transitions in vacuum ultraviolet (VUV) and visible regions are identified by analyzing their Doppler broadening, temporal intensity behavior and spatial intensity distribution. Wavelengths of these M1 transitions are determined with high accuracy and compared with previous experimental and calculated values. The line intensity ratios of the M1 transition to the allowed (E1) transition such as 2 s 2 2 p 5 P 3 / 2 2 – P 1 / 2 2 / 2 s 2 2 p 5 P 3 / 2 2 – 2 s 2 p 6 S 1 / 2 2 (ArX 5533 Å/165 Å, TiXIV 2118 Å/122 Å and FeXVIII 975 Å/94 Å) and 2s2p P 1 3 – P 2 3 / 2 s 2 S 0 1 – 2 s 2 p P 1 1 (ArXV 5944 Å/221 Å) are measured as a function of electron density. Results on the ArX and ArXV are compared with a simple level-population calculation. As a result, the density dependence of the ratio is well explained mainly by a competition between two decay processes of the collisional de-excitation and the radiative decay due to the forbidden line emission, although a clear discrepancy between the experimental and calculated absolute values appears for the ArX ratio. Contribution of fast proton impact excitation, which is brought by 180 keV neutral beam injection (NBI) for plasma heating, is also analyzed with the calculation for the F-like ions of ArX, TiXIV and FeXVIII.

Infrared Observations of the Helix Planetary Nebula

We have mapped the Helix (NGC 7293) planetary nebula (PN) with the IRAC instrument on the Spitzer Space Telescope. The Helix is one of the closest bright PNs and therefore provides an opportunity to resolve the small-scale structure in the nebula. The emission from this PN in the 5.8 and 8 μm IRAC bands is dominated by the pure rotational lines of molecular hydrogen, with a smaller contribution from forbidden line emission such as [Ar III] in the ionized region. The IRAC images resolve the cometary knots, which have been previously studied in this PN. The tails of the knots and the radial rays extending into the outer regions of the PN are seen in emission in the IRAC bands. IRS spectra on the main ring and the emission in the IRAC bands are consistent with shock-excited H_2 models, with a small (~10%) component from photodissociation regions. In the northeast arc, the H_2 emission is located in a shell outside the Hα emission.

The Spitzer IRS spectrum of SMP LMC 11

We present the first mid-infrared spectra of SMP LMC 11 in the Large Magellanic Cloud. While this object resembles a planetary nebula in the optical, its infrared properties are more similar to an object in transition from the asymptotic giant branch to the planetary nebula phase. A warm dust continuum dominates the infrared spectrum. The peak emission corresponds to a mean dust temperature of 330 K. The spectrum shows overlapping molecular absorption bands from 12 to 17 um corresponding to acetylene and polyacetylenic chains and benzene. This is the first detection of C4H2, C6H2, C6H6 and other molecules in an extragalactic object. The infrared spectrum of SMP LMC 11 is similar in many ways to that of the pre-planetary nebula AFGL 618. The IRS spectrum shows little evidence of nitrogen-based molecules which are commonly seen in Galactic AGB stars. Polycyclic aromatic hydrocarbons are also absent from the spectrum. The detection of the [NeII] 12.8 um line in the infrared and other forbidden emission lines in the optical indicates that an ionized region is present.

SpitzerReveals Hidden Quasar Nuclei in Some Powerful FR II Radio Galaxies

We present a Spitzer mid-infrared survey of 42 Fanaroff-Riley class II radio galaxies and quasars from the 3CRR catalog at redshift z 8 × 10 to the 43rd ergs s^-1, indicating strong thermal emission from hot dust in the active galactic nucleus. Our results demonstrate the power of Spitzer to unveil dust-obscured quasars. The ratio of narrow-line radio galaxies to quasars indicates a mean dust covering fraction of 0.56 ± 0.15, assuming relatively isotropic emission. We analyze Spitzer spectra of the 14 mid-IR luminous narrow-line radio galaxies thought to host hidden quasar nuclei. Dust temperatures of 210–660 K are estimated from single-temperature blackbody fits to the low- and high-frequency ends of the mid-IR bump. Most of the mid-IR luminous radio galaxies have a 9.7 µm silicate absorption trough with optical depth <0.2, attributed to dust in a molecular torus. Forbidden emission lines from high-ionization oxygen, neon, and sulfur indicate a source of far-UV photons in the hidden nucleus. However, we find that the other 55% ± 13% of narrow-line FR II radio galaxies are weak at 15µm, contrary to single-population unification schemes. Most of these galaxies are also weak at 30µm. Mid-IR weak radio galaxies may constitute a separate population of nonthermal, jet-dominated sources with low accretion power.

Models of forbidden line emission profiles from axisymmetric stellar winds

A number of strong infrared forbidden lines have been observed in several evolved Wolf-Rayet star winds, and these are important for deriving metal abundances and testing stellar evolution models. In addition, because these optically thin lines form at large radius in the wind, their resolved profiles carry an imprint of the asymptotic structure of the wind flow. This work presents model forbidden line profile shapes formed in axisymmetric winds. It is well-known that an optically thin emission line formed in a spherical wind expanding at constant velocity yields a flat-topped emission profile shape. Simulated forbidden lines are produced for a model stellar wind with an axisymmetric density distribution that treats the latitudinal ionization self-consistently and examines the influence of the ion stage on the profile shape. The resulting line profiles are symmetric about line centre. Within a given atomic species, profile shapes can vary between centrally peaked, doubly peaked, and approximately flat-topped in appearance depending on the ion stage (relative to the dominant ion) and viewing inclination. Although application to Wolf-Rayet star winds is emphasized, the concepts are also relevant to other classes of hot stars such as luminous blue variables and Be/B[e] stars.

Electron temperature fluctuations in H II regions

Context. The spatial electron temperature fluctuations in ionized nebulae that were initially proposed to explain the discrepancies among temperatures obtained from different sensors have been pointed to as the cause of huge inconsistencies among abundances of heavy elements calculated from recombination and forbidden emission lines. Recently, there have been some attempts of direct detection and quantification of spatial temperature fluctuations with point-to-point temperature measurements across the nebula.

Late-Time Spectroscopy of SN 2002cx: The Prototype of a New Subclass of Type Ia Supernovae

We present Keck optical spectra of SN 2002cx, the most peculiar known Type Ia supernova (SN Ia), taken 227 and 277 days past maximum light. Astonishingly, the spectra are not dominated by the forbidden emission lines of iron that are a hallmark of thermonuclear SNe in the nebular phase. Instead, we identify numerous P Cygni profiles of Fe II at very low expansion velocities of ~700 km s-1, which are without precedent in SNe Ia. We also report the tentative identification of low-velocity O I in these spectra, suggesting the presence of unburned material near the center of the exploding white dwarf. SN 2002cx is the prototype of a new subclass of SNe Ia, with spectral characteristics that may be consistent with recent pure deflagration models of Chandrasekhar-mass thermonuclear SNe. These are distinct from the majority of SNe Ia, for which an alternative explosion mechanism, such as a delayed detonation, may be required.

Subaru IR Echelle Spectroscopy of Herbig‐Haro Driving Sources. I. H2and [Feii] Emission

We present infrared echelle spectroscopy of three Herbig-Haro (HH) driving sources (SVS 13, B5-IRS 1, and HH 34 IRS) using Subaru IRCS. The large diameter of the telescope and wide spectral coverage of the spectrograph allowedustodetectseveralH2and[Feii]linesinthe HandKbands.TheseincludeH2linesarisingfromv ¼ 1 3and J ¼ 1 11, and [Fe ii] lines with upper level energies ofE/k ¼ (1:1 2:7) ; 10 4 K. For all objects the outflow is found to have two velocity components: (1) a high-velocity (� 70 to � 130 km s � 1 ) component (HVC), seen in [Fe ii ]o r H2 emission and associated with a collimated jet; and (2) a low-velocity (� 10 to � 30 km s � 1 ) component (LVC), which is seen in H2 emission only and is spatially more compact. Such a kinematic structure resembles optical forbidden emission line outflows associated with classical T Tauri stars, whereas the presence of H2 emission reflects the lowexcitation nature of the outflowing gas close to these protostars. Theobserved H2flux ratios indicate a temperature of (2 3) ;10 3 Kandagasdensityof10 5 cm � 3 ormore,supportingshocksastheheatingmechanism.B5-IRS1exhibits faint extended emission associated with the H2-LVC, in which the radial velocity slowly increases with distance from the protostar (by � 20 km s � 1 at � 500 AU). This is explained as warm molecular gas entrained by an unseen wideangled wind. The [Fe ii] flux ratios indicate electron densities to be � 10 4 cm � 3 or greater, similar to forbidden-line outflowsassociated withclassicalT Tauristars.Finally,thekinematic structureof the[Feii] emissionassociated with the base of the B5-IRS 1 and HH 34 IRS outflows is shown to support disk-wind models. Subject headingg ISM: Herbig-Haro objects — ISM: individual (B5-IRS 1, HH 34 IRS, SVS 13) — ISM: jets and outflows — ISM: kinematics and dynamics — line: formation — stars: formation

Do the Line Widths of Coronal Emission Lines Increase with Height above the Limb?

In our earlier studies we obtained off-the-limb spectroscopic observations in a number of forbidden emission lines ([Fe X-XIV]) to study the physical properties and their temporal variations in steady coronal structures. Short exposure times adopted in those observations permitted us to study the variation in line widths up to about 150'' above the limb. With a view to investigating the variations in the parameters of coronal emission lines up to about 500'', we made raster scans with exposure times that are longer than the earlier exposure times by a factor of about 10. We find that the FWHM of the [Fe XIV] 5303 Å line decreases up to 300'' ± 50'' and then remains more or less the same up to 500'', while that of the [Fe X] 6374 Å line increases up to about 250'' and subsequently remains unchanged. The FWHMs of the [Fe XI] 7892 Å and [Fe XIII] 10747 Å lines show an intermediate behavior. Furthermore, the ratio of the FWHM of 6374 to 5303 Å increases from 0.93 at the limb to 1.18 at 200'' above the limb. The nonvariability in the FWHM of emission lines after about 300'' above the limb in steady coronal structures does not support the prevailing view that the nonthermal velocity increases with height due to either the coronal waves or the high-velocity solar wind. The present results indicate the inadequacy of the earlier coronal loop models. The observed variations in FWHM of the coronal emission lines with height above the limb can be explained by assuming the recent model of coronal loops proposed by Akiyama et al.

Forbidden oxygen emission lines of Comet 116P/Wild 4 at 2.4 AU

A high dispersion spectroscopic observation of Comet 116P/Wild 4 was performed on June 10, 2003, using the High Dispersion Spectrograph (HDS) on Subaru Telescope, when the comet was at 2.4 AU from the Sun. Three forbidden oxygen emission lines in optical region, the green line at 557.7330 nm (from 1S to 1D meta-stable state) and the red doublet lines at 630.0304 and 636.3776 nm (from 1D meta-stable state to 3P state) were observed. The oxygen atoms in meta-stable state are considered to be generated by the photo-dissociation of parent molecules such as H 2O, CO, CO 2, etc. H 2O molecule is usually thought as the most dominant source of these oxygens in meta-stable state when a comet is at around 1 AU from the Sun. However, since the Comet 116P/Wild 4 was located at 2.4 AU far from the Sun at the observation, CO and/or CO 2 could be a possible main source(s) of meta-stable oxygen atoms rather than H 2O. The ratio between red doublet lines (630.0304 nm relative to 636.3776 nm) derived from our result is 2.94 ± 0.07, and the ratio of green line to the red doublet lines is 0.155 ± 0.007. The ratio of green to red doublet lines, which indicates the ratio of O( 1S) to O( 1D), give us a clue to distinguish the source of meta-stable oxygen atoms from different parent molecules. Considering the abundance of CO is comparable to or smaller than CO 2, CO 2 could be thought as the parent molecules of the meta-stable oxygen atoms as well as H 2O. The number ratio of CO 2/H 2O within our observational aperture is discussed in this paper.

The High‐Resolution X‐Ray Spectrum of MR 2251−178 Obtained with theChandraHETGS

The QSO MR 2251-178 was observed with the Chandra High Energy Transmission Grating Spectrometer (HETGS) at a 2-10 keV luminosity of 2.41 ? 1044 ergs s-1 (using H0 = 72 km s-1 Mpc-1). We observe the source in a relatively low state. The light curve shows no evidence of variability. We present the zero-order image of MR 2251-178 and compare it to previous observations. We find evidence of a highly ionized, high-velocity outflow, which we detect in a resolved Fe XXVI Ly? absorption line. The outflow appears to have a large mass and kinetic energy flux compared to the estimated nuclear accretion rate and luminosity. We examine the possibility that other absorption features in the spectrum are associated with the high-velocity outflow. We detect a narrow Fe K? line and resolved forbidden line emission from Ne IX and O VII. Modeling the emitting material enables us to constrain its properties and conclude that it is not along our line of sight.

A Starfish Preplanetary Nebula: IRAS 19024+0044

Using the Hubble Space Telescope, we have imaged the OH/IR star IRAS 19024+0044 (I19024) at 0.6, 0.8, 1.1, and 1.6 μm, as part of our surveys of candidate preplanetary nebulae. The images show a multipolar nebula of size ~3farcs7 × 2farcs3, with at least six elongated lobes emanating from the center of the nebula. Two of the lobes show limb-brightened tips having point-symmetric structure with respect to the expected location of the central star. The central region shows two dark bands southwest and northeast of a central shallow maximum that may be either two inclined dusty toroidal structures or the dense parts of a single wide, inhomogeneous, toroid. A very faint, surface brightness-limited, diffuse halo surrounds the lobes. Long-slit/echelle optical spectroscopy obtained at the Mount Palomar and Keck observatories shows a spatially compact source of Hα emission; the Hα line shows a strong, narrow, central core with very broad (±1000 km s^(-1)), weak wings, and a narrower blueshifted absorption feature signifying the presence of a ~100 km s^(-1) outflow. The spectrum is characterized by a strong, relatively featureless, continuum and lacks the strong forbidden emission lines characteristic of planetary nebulae, confirming that IRAS 19024 is a preplanetary nebula; the spectral type for the central star, although uncertain, is most likely early G. Interferometric observations of the CO J = 1-0 line emission with the Owens Valley Radio Interferometer show a marginally resolved molecular envelope (size 5farcs5 × 4farcs4) with an expansion velocity of 13 km s^(-1), resulting from the asymptotic giant granch (AGB) progenitor's dense, slow wind. We derive a kinematic distance of 3.5 kpc to I19024, based on its radial velocity. The bolometric flux is 7.3 × 10^(9-) ergs s^(-1) cm^(-2), and the luminosity 2850 L_☉. The relatively low luminosity of I19024, in comparison with stellar evolutionary models, indicates that the initial mass of its central star was ~1-1.5 M_☉. The lobes, which appear to be hollow structures with dense walls, have a total mass greater than or equal to about 0.02 M_☉. The dusty tori in the center have masses of a few times 10^(-3) M_☉. The faint halo has a power-law radial surface brightness profile with an exponent of about -3 and most likely represents the remnant spherical circumstellar envelope formed as a result of constant mass loss during the AGB phase over the past several thousand years. From the CO data we infer a molecular mass ≳ 0.025 M_☉ and an expansion age ≾ 2870 yr, giving a mass-loss rate ≳ 10^(-5) M_☉ yr^(-1). The far-infrared fluxes of I19024 indicate the presence of a large mass of dust in the nebula; from a simple model we infer the presence of cool (109 K) and warm (280 K) components of dust mass 5.7 × 10^(-4) and 1.5 × 10^(-7) M_☉. We discuss our results for I19024 in the light of past and current ideas for the dramatic transformation of the morphology and kinematics of mass-ejecta as AGB stars evolve into planetary nebulae.

Forbidden Line Emission in the Eccentric Spectroscopic Binaries DQ Tauri and UZ Tauri E Monitored over an Orbital Period

We present echelle spectroscopy of the close pre-main-sequence binary star systems DQ Tau and UZ Tau-E. Over a 16 day time interval we acquired 14 nights of spectra for DQ Tau and 12 nights of spectra for UZ Tau-E. This represents the entire phase of DQ Tau, and 63 percent of the phase of UZ Tau-E. As expected, photospheric lines such as Li I 6707 clearly split into two components as the primary and secondary orbit one another, as did the permitted line He I 5876. Unlike the photospheric features, the forbidden lines of [O I] 6300 and [O I] 5577, retain the same shape throughout the orbit. Therefore these lines must originate outside of the immediate vicinity of the two stars and any circumstellar disks that participate in the orbital motion of the stars.

Probing the Ionizing Continuum of Narrow‐Line Seyfert 1 Galaxies. I. Observational Results

We present optical spectra and emission-line ratios of 12 narrow-line Seyfert 1 (NLS1) galaxies that we observed to study the ionizing EUV continuum. A common feature in the EUV continuum of active galactic nuclei is the big blue bump (BBB), generally associated with thermal accretion disk emission. While Galactic absorption prevents direct access to the EUV range, it can be mapped by measuring the strength of a variety of forbidden optical emission lines that respond to different EUV continuum regions. We find that narrow emission line ratios involving [O II] λ3727, Hβ, [O III] λ5007, [O I] λ6300, Hα, [N II] λ6583, and [S II] λλ6716, 6731 indicate no significant difference between NLS1 galaxies and broad-line Seyfert 1 (BLS1) galaxies, which suggests that the spectral energy distributions of their ionizing EUV-soft X-ray continua are similar. The relative strength of important forbidden high-ionization lines like [Ne V] λ3426 compared to He II λ4686 and the relative strength of [Fe X] λ6374 appear to show the same range as in BLS1 galaxies. However, a trend of weaker F([O I] λ6300)/F(Hα) emission-line ratios is indicated for NLS1 galaxies compared to BLS1 galaxies. To recover the broad emission line profiles, we used Gaussian components. This approach indicates that the broad Hβ profile can be well described with a broad component (FWHM 3275 ± 800 km s-1) and an intermediate broad component (FWHM 1200 ± 300 km s-1). The width of the broad component is in the typical range of normal BLS1 galaxies. The emission-line flux that is associated with the broad component in these NLS1 galaxies amounts to at least 60% of the total flux. Thus, it dominates the total line flux, similar to BLS1 galaxies.

A Survey for Low‐Mass Stars and Brown Dwarfs in the η Chamaeleontis and ε Chamaeleontis Young Associations

I present the results of a search for new low-mass stars and brown dwarfs in the η Cha and Cha young associations. Within radii of 15 and 05 surrounding η Cha and Cha, respectively, I have constructed color-magnitude diagrams from Deep Near Infrared Survey (DENIS) and Two Micron All Sky Survey (2MASS) photometry and have obtained spectra of the candidate low-mass members therein. The five candidates in η Cha are classified as four field M dwarfs and one carbon star. No new members are found in this survey, which is complete for M/M☉ = 0.015-0.15, according to the evolutionary models of Chabrier and Baraffe. Thus, an extended population of low-mass members is not present in η Cha out to 4 times the radius of the known membership. Meanwhile, the three candidate members of Cha are classified as young stars, and thus likely members of the association, based on Li absorption and gravity-sensitive absorption lines. These new sources have spectral types of M2.25, M3.75, and M5.75, corresponding to masses of 0.45, 0.25, and 0.09 M☉ by the models of Chabrier and Baraffe. For one of these stars, intense Hα emission, forbidden line emission, and strong K-band excess emission suggest the presence of accretion, an outflow, and a disk, respectively. This young star is also much fainter than expected for an association member at its spectral type, which could indicate that it is seen in scattered light. No brown dwarfs are detected in Cha down to the completeness limit of 0.015 M☉. The absence of brown dwarfs in these associations is statistically consistent with the mass functions measured in star-forming regions, which exhibit only ~2 and ~1 brown dwarfs for stellar samples at the sizes of the η Cha and Cha associations.

On the Evolutionary Status of Class I Stars and Herbig‐Haro Energy Sources in Taurus‐Auriga

[abridged] We present high resolution optical spectra of stars in Taurus-Auriga whose circumstellar environment suggests that they are less evolved than optically revealed T Tauri stars. Many of the stars are seen only via scattered light. These spectra are used to search for differences between stars which power Herbig-Haro flows and stars which do not, and to reassess the evolutionary state of so-called protostars (Class I stars) relative to optically revealed T Tauri stars (Class II stars). The stellar mass distribution of Class I stars is similar to that of Class II stars and includes 3 Class I brown dwarfs. Class I stars in Taurus are slowly rotating; the angular momentum of a young star appears to dissipate prior to the optically revealed T Tauri phase. The mass accretion rates of Class I stars are surprisingly indistinguishable from those of Class II stars; they do not have accretion dominated luminosities. We confirm previous results that find larger forbidden-line emission associated with Class I stars than Class II stars. We suggest that this is caused by an orientation bias that allows a more direct view of the somewhat extended forbidden emission line regions than the obscured stellar photospheres, rather than because of larger mass outflow rates. Overall, the similar masses, luminosities, rotation rates, mass accretion rates, mass outflow rates, and millimeter flux densities of Class I and Class II stars are best explained by a scenario in which most Class I stars are no longer in the main accretion phase and are older than traditionally assumed. Similarly, although stars which power Herbig-Haro flows appear to have larger mass outflow rates, their stellar and circumstellar properties are generally indistinguishable from those of stars that do not power these flows.

A New Classical T Tauri Object at the Substellar Boundary in Chamaeleon II

We have obtained low- and medium-resolution optical spectra of 20 candidate young low-mass stars and brown dwarfs in the nearby Chamaeleon II dark cloud using the Magellan Baade telescope. We analyze these data in conjunction with near-infrared photometry from the Two Micron All Sky Survey. We find that one target, [VCE2001] C41, exhibits broad Hα emission as well as a variety of forbidden emission lines. These signatures are usually associated with accretion and outflow in young stars and brown dwarfs. Our spectra of C41 also reveal Li I in absorption and allow us to derive a spectral type of M5.5 for it. Therefore, we propose that C41 is a classical T Tauri object near the substellar boundary. Thirteen other targets in our sample have continuum spectra without intrinsic absorption or emission features and are difficult to characterize. They may be background giants or foreground field stars not associated with the cloud or embedded protostars and need further investigation. The six remaining candidates, with moderate reddening, are likely to be older field dwarfs, given their spectral types, lack of lithium, and Hα emission.

Subaru Spectropolarimetry of Markarian 573: The Hidden High-Ionization Nuclear Emission-Line Region inside the Dusty Torus

We report the results of our high-quality spectropolarimetric observation of the narrow-line region in a nearby Seyfert 2 galaxy, Mrk 573, with the Subaru Telescope. The polarized flux spectrum of Mrk 573 shows not only prominent scattered broad Hα emission but also various narrow forbidden emission lines. We find that the measured polarization degree of the observed forbidden emission lines is positively correlated with the ionization potential of the corresponding ions and the critical density of the corresponding transitions. We discuss some possible origins of these correlations, and then we point out that the correlations are caused by the obscuration of the stratified narrow-line region in Mrk 573 by the optically and geometrically thick dusty torus, matching findings of a previous study of NGC 4258.

Analysis of non-thermal velocities in the solar corona

Abstract. We describe new ground-based spectroscopic observations made using a 40-cm aperture coronagraph over a whole range of radial distances (up to heights of 12' above the limb) and along four different heliocentric directions N, E, S and W. The analysis is limited to the study of the brightest forbidden emission line of Fe XIV at 530.3nm, in order to reach the best possible signal-to-noise ratio. To make the results statistically more significant, the extracted parameters are averaged over the whole length of the slit, and measurements are repeated fives times at each position; the corresponding dispersions in the results obtained along the slit are given. Central line profile intensities and full line widths (FWHM) are plotted and compared to measurements published by other authors closer to the limb. We found widths and turbulent (non-thermal) velocities of significantly higher values above the polar regions, especially when a coronal hole is present along the line of sight. We do not see a definitely decreasing behaviour of widths and turbulent velocities in equatorial directions for larger radial distances, as reported in the literature, although lower values are measured compared to the values in polar regions. The variation in the high corona is rather flat and a correlation diagram indicates that it is different for different regions and different radial distances. This seems to be the first analysis of the profiles of this coronal line, up to large heights above the limb for both equatorial and polar regions.

Naked active galactic nuclei

In this paper we report the discovery of a new class of active galactic nucleus in which although the nucleus is viewed directly, no broad emission lines are present. The results are based on a survey for AGN in which a sample of about 800 quasars and emission line galaxies were monitored yearly for 25 years. Among the emission line galaxies was the expected population of Seyfert 2 galaxies with only narrow forbidden lines in emission, and no broad lines. However, from the long term monitoring programme it was clear that some 10% of these were strongly variable with strong continuum emission. It is argued that these objects can only be Seyfert 1 galaxies in which the nucleus is viewed directly, but in which broad emission lines are completely absent. We compare these observations with other cases from the literature where the broad line region is reported to be weak or variable, and investigate the possibility that the absence of the broad line component is due to reddening. We conclude that this does not account for the observations, and that in these AGN the broad line region is absent. We also tentatively identify more luminous quasars from our sample where the broad emission lines also appear to be absent. The consequences of this for AGN models are discussed, and a case is made that we are seeing AGN in a transition stage between the fuel supply from a surrounding star cluster being cut off, and the nucleus becoming dormant.