We report on new simultaneous phase-resolved spectroscopic and polarimetric observations of the polar (AM Herculis star) V834 Cen during a high state of accretion. Strong emission lines and high ...levels of variable circular and linear polarization are observed over the orbital period. The polarization data are modelled using the Stokes imaging technique of Potter et al. The spectroscopic emission lines are investigated using the Doppler tomography technique of Marsh and Horne and the Roche tomography technique of Dhillon and Watson. Up to now, all three techniques have been used separately to investigate the geometry and accretion dynamics in cataclysmic variables. For the first time, we apply all three techniques to simultaneous data for a single system. This allows us to compare and test each of the techniques against each other and hence to derive a better understanding of the geometry, dynamics and system parameters of V834 Cen. All three techniques are consistent with an interpretation in which a ballistic stream extends to a minimum of ∼40 degrees in azimuth around the white dwarf before becoming threaded by the magnetic field lines. Interestingly, the observed ballistic Doppler velocities do not show a reduced vy component, as found in Doppler imaging of other AM Her systems. Furthermore, the secondary star in V834 Cen shows more He ii (4686 Å) emission on its leading inner face, as opposed to the trailing face like in other AM Her systems. We propose that the accretion shock preferentially illuminates the leading face of the secondary star. In addition, the ballistic stream does not obscure the leading face of the secondary from the accretion shock, and, in fact, our Doppler maps show that the ballistic stream is a strong He ii (4686 Å) emission source in itself and thus adds to the illumination of the leading face of the secondary.
We have investigated 136 Chandra extragalactic sources, including 93 galaxies with narrow emission lines (NELGs)and 43 with only absorption lines (ALGs). Based on fx/fo, L sub(X), X-ray spectral ...hardness, and optical emission-line diagnostics, we have conservatively classified 36 normal galaxies and 71 AGNs. Their redshift ranges from 0.01 to 1.2, with normal galaxies in the range z = 0.01-0.3. Our normal galaxies appear to share characteristics with local galaxies, as expected from the X-ray binary populations and the hot interstellar matter (ISM). In conjunction with normal galaxies found in other surveys, we found no statistically significant evolution in L sub(X)/L sub(B), within the limited z range ( 0.1). The best-fit slope of our log(N)-log(S) relationship is -1.5 for both S (0.5-2 keV) and B (0.5-8 keV) energy bands, which is considerably steeper than that of the AGN-dominated cosmic background sources, but slightly flatter than the previous estimate, indicating that normal galaxies will not exceed the AGN population until f sub(X)(0.5-2.0 keV) 62 x 10 super(-18) ergs s super(-1) cm super(-2) (a factor of 65 lower than the previous estimate). A group of NELGs appear to be heavily obscured in X-rays. After correcting for intrinsic absorption, their X-ray luminosities could be L sub(X) > 10 super(44) ergs s super(-1), making them type 2 quasar candidates. While most X-ray-luminous ALGs do not appear to be significantly absorbed, we found two heavily obscured objects that could be as luminous as an unobscured broad-line quasar. Among 43 ALGs, we found two E+A galaxy candidates. The X-ray spectra of both galaxies are soft, and one of them has a nearby close companion galaxy, supporting the merger/interaction scenario rather than the dusty starburst hypothesis.
We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one active galactic nucleus (AGN) (NGC 3227) from a 2014 campaign. ...Our main goals are (1) to determine the black hole masses from continuum-Hβ reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure Hβ time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity-dependent Hβ lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.
Context. NGC 1566 is a local face-on Seyfert galaxy and is known for exhibiting recurrent outbursts that are accompanied by changes in spectral type. The most recent transient event occurred from ...2017 to 2019 and was reported to be accompanied by a change in Seyfert classification from Seyfert 1.8 to Seyfert 1.2. Aims. We aim to study the transient event in detail by analyzing the variations in the optical broad-line profiles. In particular, we intend to determine the structure and kinematics of the broad-line region. Methods. We analyzed data from an optical spectroscopic variability campaign of NGC 1566 taken with the 9.2 m Southern African Large Telescope (SALT) between July 2018 and October 2019 triggered by the detection of hard X-ray emission in June 2018. We supplemented this data set with optical to near-infrared (NIR) spectroscopic archival data taken by VLT/MUSE in September 2015 and October 2017, and investigated the emission from different line species during the event. Results. NGC 1566 exhibits pronounced spectral changes during the transient event. We observe the emergence and fading of a strong power-law-like blue continuum as well as strong variations in the Balmer, He I , and He II lines and the coronal lines Fe VII , Fe X , and Fe XI . Moreover, we detect broad double-peaked emission line profiles of O I λ 8446 and the Ca II λ λ 8498, 8542, 8662 triplet. This is the first time that genuine double-peaked O I λ 8446 and Ca II λ λ 8498, 8542, 8662 emission in AGN is reported in the literature. All broad lines show a clear redward asymmetry with respect to their central wavelength and we find indications for a significant blueward drift of the total line profiles during the transient event. The profiles and the FWHM of the Balmer lines remain largely constant during all observations. We show that the double-peaked emission line profiles are well approximated by emission from a low-inclination, relativistic eccentric accretion disk, and that single-peaked profiles can be obtained by broadening due to scale-height-dependent turbulence. Small-scale features in the O I and Ca II lines suggest the presence of inhomogeneities in the broad-line region. Conclusions. We conclude that the broad-line region in NGC 1566 is dominated by the kinematics of a relativistic eccentric accretion disk. The broad-line region can be modeled to be vertically stratified with respect to scale-height turbulence with O I and Ca II being emitted close to the disk in a region with high (column) density, while the Balmer and helium lines are emitted at greater scale height above the disk. The observed blueward drift might be attributed to a low-optical-depth wind launched during the transient event. Except for this wind, the observed kinematics of the broad-line region remain largely unchanged during the transient event.
We undertook a multisite spectroscopic campaign for the β Cephei star ν Eridani. A total of 2294 high-resolution spectra were obtained from telescopes at 11 different observatories around the world. ...The time base of dedicated multisite observations is 88 d. To this data set we have added 148 older, previously unpublished spectra, such that the overall time-span of the 2442 spectra is 430 d. The analysis of the radial velocity variations derived from the Si iii triplet centred on 4560 Å leads to 19 significant frequencies, of which seven correspond to independent pulsation frequencies. Five of these are members of multiplets with an average spacing of 0.018 ± 0.002 cd−1. Our spectroscopic results agree well with those derived from a simultaneous multisite photometric campaign of the star, albeit that we do not recover their low frequency at 0.43218 cd−1. We find three different candidate frequencies below 1 cd−1 instead. We also find that the radial velocity amplitude of the main mode has increased by some 30 per cent over the last 15 years, which is consistent with the photometry data. We derive a relative equivalent width variation of 6.5 per cent, which is completely dominated by the main radial mode. The phase difference between the radial velocity and light variations for the main frequency is , which is clearly deviant from the adiabatic value and confirms the radial nature of the dominant mode. The spectral line broadening leads to an upper limit of 20 km s−1 for v sin i, which is consistent with the long rotation period derived from the frequency splittings.
We present the first results from an optical reverberation mapping campaign executed in 2014 targeting the active galactic nuclei (AGNs) MCG+08-11-011, NGC 2617, NGC 4051, 3C 382, and Mrk 374. Our ...targets have diverse and interesting observational properties, including a "changing look" AGN and a broad-line radio galaxy. Based on continuum-Hβ lags, we measure black hole masses for all five targets. We also obtain Hγ and He ii λ4686 lags for all objects except 3C 382. The He ii λ4686 lags indicate radial stratification of the BLR, and the masses derived from different emission lines are in general agreement. The relative responsivities of these lines are also in qualitative agreement with photoionization models. These spectra have extremely high signal-to-noise ratios (100-300 per pixel) and there are excellent prospects for obtaining velocity-resolved reverberation signatures.
We present optical continuum lags for two Seyfert 1 galaxies, MCG+08-11-011 and NGC 2617, using monitoring data from a reverberation mapping campaign carried out in 2014. Our light curves span the ...ugriz filters over four months, with median cadences of 1.0 and 0.6 days for MCG+08-11-011 and NGC 2617, respectively, combined with roughly daily X-ray and near-UV data from Swift for NGC 2617. We find lags consistent with geometrically thin accretion-disk models that predict a lag-wavelength relation of τ ∝ λ4/3. However, the observed lags are larger than predictions based on standard thin-disk theory by factors of 3.3 for MCG+08-11-011 and 2.3 for NGC 2617. These differences can be explained if the mass accretion rates are larger than inferred from the optical luminosity by a factor of 4.3 in MCG+08-11-011 and a factor of 1.3 in NGC 2617, although uncertainty in the SMBH masses determines the significance of this result. While the X-ray variability in NGC 2617 precedes the UV/optical variability, the long (2.6 day) lag is problematic for coronal reprocessing models.
We present the analysis of 1 week of single-site high-speed CCD photometric observations of the cool ZZ Ceti star HS 0507+0434B. 10 independent frequencies are detected in the light variations of the ...star: one singlet and three nearly equally spaced triplets. We argue that these triplets are caused by rotationally split modes of spherical degree ℓ= 1. This is the first detection of consistent multiplet structure in the amplitude spectrum of a cool ZZ Ceti star and it allows us to determine the rotation period of the star: 1.70 ± 0.11 d. We report exactly equal frequency, not period, spacings between the detected mode groups. In addition, certain pairs of modes from the four principal groups have frequency ratios that are very close to 3 : 4 or 4 : 5; while these ratios are nearly exact (within one part in 104), they still lie outside the computed error bars. We speculate that these relationships between different frequencies could be caused by resonances. One of the three triplets may not be constant in amplitude and/or frequency. We compare our frequency solution for the combination frequencies (of which we detected 38) to Wu's model thereof. We obtain consistent results when trying to infer the convective thermal time and the inclination angle of the rotational axis of the star. Theoretical combination-frequency amplitude spectra also resemble those of the observations well, and direct theoretical predictions of the observed second-order light-curve distortions were also reasonably successful assuming the three triplets are caused by ℓ= 1 modes. Attempts to reproduce the observed combination frequencies adopting all possible ℓ= 2 identifications for the triplets did not provide similarly consistent results, supporting their identification with ℓ= 1.
Line ratio diagnostics provide valuable clues as to the source of ionizing radiation in galaxies with intense black hole accretion and starbursting events, such as local Seyfert galaxies or galaxies ...at the peak of their star formation history. We aim to provide a reference joint optical and mid-IR line ratio analysis for studying active galactic nucleus (AGN) identification via line-ratio diagnostics and testing predictions from photoionization models. We first obtained homogenous optical spectra with the Southern Africa Large Telescope for 42 Seyfert galaxies with available
Spitzer
/IRS spectroscopy, along with X-ray to mid-IR multiband data. After confirming the power of the main optical (O
III
λ
5007) and mid-IR (Ne
V
14.3 μm, O
IV
25.9 μm, Ne
III
15.7 μm) emission lines in tracing AGN activity, we explored diagrams based on ratios of optical and mid-IR lines by exploiting photoionization models of different ionizing sources (AGN, star formation, and shocks). We find that pure AGN photoionization models are good at reproducing observations of Seyfert galaxies with an AGN fractional contribution to the mid-IR (5 − 40 μm) continuum emission larger than 50 per cent. For targets with a lower AGN contribution, even assuming a hard ionizing field from the central accretion disk (
F
ν
∝
ν
α
, with
α
≈ −0.9), these same models do not fully reproduce the observed mid-IR line ratios. Mid-IR line ratios such as Ne
V
14.3 μm/Ne
II
12.8 μm, O
IV
25.9 μm/Ne
II
12.8 μm, and Ne
III
15.7 μm/Ne
II
12.8 μm show a dependence on the AGN fractional contribution to the mid-IR, unlike optical line ratios. An additional source of ionization, either from star formation or radiative shocks, can help explain the observations in the mid-IR. While mid-IR line ratios are good tracers of the AGN activity versus star formation, among the combinations of optical and mid-IR diagnostics in line-ratio diagrams, only those involving the O
I
/H
α
ratio are promising diagnostics for simultaneously unraveling the relative roles of AGN, star formation, and shocks. A proper identification of the dominant source of ionizing photons would require the exploitation of analysis tools based on advanced statistical techniques as well as spatially resolved data.
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