Study of UV Line and Continuum Variabilities in the Broadline Seyfert 1 Galaxy ESO 141– G55

We present an investigation into the nature of the jet‐gas interactions in a sample of 10 radio galaxies at 2.3 < z < 2.9 using deep spectroscopy of the ultraviolet (UV) line and continuum emission obtained at Keck II and the Very Large Telescope. Kinematically perturbed gas, which we have shown to be within the radio structure in previous publications, is always blueshifted with respect to the kinematically quiescent gas, is usually spatially extended, and is usually detected on both sides of the nucleus. In the three objects from this sample for which we are able to measure line ratios for both the perturbed and quiescent gases, we suggest that the former has a lower ionization state than the latter. We propose that the perturbed gas is part of a jet-induced outflow, with dust obscuring the outflowing gas that lies on the far side of the object. The spatial extent of the blueshifted perturbed gas, typically ∼35 kpc, implies that the dust is spatially extended at least on similar spatial scales. We also find interesting interrelationships between UV line, UV continuum and radio continuum properties of this sample.

Non-Maxwellian $κ$ electron energy distributions (EEDs) have been proposed in recent years to resolve the so-called ``electron temperature and abundance discrepancy problem'' in the study of planetary nebulae (PNe). Thus the need to develop diagnostic tools to determine from observations the EED of PNe is raised. Arising from high energy levels, the ultraviolet (UV) emission lines from PNe present intensities that depend sensitively on the high-energy tail of the EED. In this work, we investigate the feasibility of using the \ion{C}{2}]$λ$2326/\ion{C}{2}$λ$1335 intensity ratios as a diagnostic of the deviation of the EED from the Maxwellian distribution (as represented by the $κ$ index). We use a Maxwellian decomposition approach to derive the theoretical $κ$-EED-based collisionally excited coefficients of \ion{C}{2}, and then compute the \ion{C}{2} UV intensity ratio as a function of the $κ$ index. We analyze the archival spectra acquired by the {\it International Ultraviolet Explorer} and measure the intensities of \ion{C}{2} UV lines from 12 PNe. By comparing the observed line ratios and the theoretical predictions, we can infer their $κ$ values. With the Maxwellian-EED hypothesis, the observed \ion{C}{2}]$λ$2326/\ion{C}{2}$λ$1335 ratios are found to be generally lower than those predicted from the observed optical spectra. This discrepancy can be explained in terms of the $κ$ EED. Our results show that the $κ$ values inferred range from 15 to infinity, suggesting a mild or modest deviation from the Maxwellian distribution. However, the $κ$-distributed electrons are unlikely to exist throughout the whole nebulae. A toy model shows that if just about 1--5 percent of the free electrons in a PN had a $κ$-EED as small as $κ=3$, it would be sufficient to account for the observations.

We present a spectroscopic study of two intermediate polar systems, AO Psc and V1223 Sgr observed with the Hubble Space Telescope Space Telescope Imaging Spectrograph (HST STIS) and International Ultraviolet Explorer (IUE) during the period 1980–2000. The reddening of two systems is determined from the 2200 A feature. The ultraviolet emission lines are originating in the accretion disk as a result of existing an extra component of emission in the EUV/soft X-ray range with luminosity comparable to the accretion luminosity which reprocessed to produce the observed ultraviolet line strengths. Different spectra for both systems showing the variations in line fluxes at different orbital phases are presented. We concentrated on calculating the line fluxes of C IV 1550 A & He II 1640 A emission lines. From HST and IUE data, we derived an accretion luminosities and an accretion rates for two systems. Our results show that there are variations in line fluxes, accretion luminosities and accretion rates with time for two systems. These variations are attributed to the variations of both density and temperature as a result of a changing rate of mass transfer from the secondary star to the white dwarf. These results from the IUE and HST observations are consistent with the models of Ko et al. (Astrophys. J., 457:363K, 1996).

ABSTRACTWe present results from ultraviolet and X‐ray observations of the low‐mass X‐ray binary Cygnus X‐2. The simultaneous Hubble Space Telescope/GHRS and ASCA observations took place during the low state of an 82 day cycle. We compare our observations as well as archival IUE and RXTE data with models that predict ultraviolet and optical continuum emission from an X‐ray–heated disk and a Roche lobe–filling star. The model predictions are consistent with observed optical, ultraviolet, and X‐ray variations over both orbital and long‐term periods. The X‐ray spectral state, the luminosities implied by fits to the X‐ray data, the ultraviolet continuum and line fluxes, and the mass accretion rates obtained from fits to the ultraviolet continuum are consistent with location of our observations on the normal and horizontal branches of the Z‐shaped X‐ray color‐color diagram. A combination of changes to mass accretion rate and obstruction by a warped disk can be invoked as a possible explanation for the motion of the “Z” in the color‐color plane. The GHRS/G160M measurements concentrated on N v (λ1238.8; λ1242.8) and He ii (λ1640.5). The low‐resolution (GHRS/G140L) observations captured Si iv (λ1393.8; λ1402.8), N iv (λ1486.5), and C iv (λ 1548); absorption lines detected in the spectra are interstellar. Although the relative line fluxes are consistent with emission from an X‐ray–heated accretion disk corona, predictions from models of line emission from simple disks do not fit the observed emission‐line profiles. The lack of double peaks suggests that most of the line emission is from the surface of the companion and the radial velocities (80–130 km s−1) are consistent with emission from the optical star at the orbital phase (0.70–0.74) of our observations.

The physical and chemical properties of planetary atmospheres are affected by temporal evolution of ultraviolet (UV) radiation inputs from their host stars at all time scales. While studies of X-ray/UV flare properties and long-term stellar evolution of exoplanet host stars have provided new constraints regarding stellar inputs to exoplanetary systems, the UV temporal variability of cool stars on the timescale of stellar cycles remains largely unexplored. To address this gap in our understanding of the UV temporal variability of cool stars, we analyze far-ultraviolet (FUV) emission lines of ions that trace the chromosphere and transition region of nearby stars (C ii, Si iii, Si iv, and N v; formation temperatures ∼ 20–150 kK) using data from the Hubble Space Telescope (HST) and International Ultraviolet Explorer (IUE) archives spanning temporal baselines of months to years. We select 33 unique stars of spectral types F-M with observing campaigns spanning over a year, and create ionic light curves to evaluate the characteristic variability of cool stars on such timescales. Screening for large flare events, we observe that the relative variability of FUV light curves decreases with increasing stellar effective temperature, from 30% to 70% variability for M-type stars to <30% variability for F and G-type stars. We also observe a weak trend in the temporal variability with the Ca ii RHK′ stellar activity indicator, suggesting that stars with lower Ca ii activity exhibit a smaller range of FUV flux variability. Screening for data sets with optimal temporal spread, and a sufficient number of individual observations, we select 5 data sets for further periodicity analysis (HST α Centauri A, HST α Centauri B, IUE α Centauri B, IUE ϵ Eri, IUE ξ Boo). Various periodic structures within the FUV flux were detected, with most significant being a 79 days frequency present within the IUE observations of ξ Boo, with a significance of 6σ, and a periodic signal in the FUV observations of α Centauri B, for both HST and IUE measurements, at ≈210 days frequency with significance of 3σ and 3.7σ, respectively. Our results suggest that extreme ultraviolet flux from cool stars varies by less than a factor of two on decade timescales, significantly smaller than variations on flare or stellar evolutionary timescales.

Spectral interferences on arsenic and mercury prominent emission lines in vacuum inductively coupled plasma-atomic emission spectrometry and use of methanol vapor as optical filter for spectral order sorting

We examine the diagnostic power of rest-frame ultraviolet (UV) nebular emission lines, and compare them to more commonly used rest-frame optical emission lines, using the test case of a single star-forming knot of the bright lensed galaxy RCSGA 032727–132609 at redshift $z$ ∼ 1.7. This galaxy has complete coverage of all the major rest-frame UV and optical emission lines from Magellan/MagE and Keck/NIRSPEC. Using the full suite of diagnostic lines, we infer the physical properties: nebular electron temperature (Te), electron density (ne), oxygen abundance (log (O/H), ionization parameter [log (q), and interstellar medium (ISM) pressure (log (P/k)]. We examine the effectiveness of the different UV, optical, and joint UV–optical spectra in constraining the physical conditions. Using UV lines alone we can reliably estimate log (q), but the same is difficult for log (O/H). UV lines yield a higher (∼1.5 dex) log (P/k) than the optical lines, as the former probes a further inner nebular region than the latter. For this comparison, we extend the existing Bayesian inference code izi, adding to it the capability to infer ISM pressure simultaneously with metallicity and ionization parameter. This work anticipates future rest-frame UV spectral data sets from the James Webb Space Telescope (JWST) at high redshift and from the Extremely Large Telescope (ELT) at moderate redshift.

A previous narrow-slit (0.1 arcsec) Hubble Space Telescope observation unveiled a broad relativistic Hα profile in NGC 3147, a low-luminosity (Lbol ∼ 1042 erg s−1), low-Eddington ratio (Lbol/LEdd ∼ 10−4) active galactic nucleus (AGN), formerly believed to be a candidate true type 2 AGN intrinsically lacking the broad-line region. The new observations presented here confirm the double-peaked profile of the Hα line, which further shows variability both in flux and in the inner radius of the emitting disc with respect to the previous epoch. Similar disc line profiles are also found in prominent ultraviolet (UV) lines, in particular Lyα and C iv. The new data also allow us to build a simultaneous subarcsec optical-to-X-ray spectral energy distribution of NGC 3147, which is characterized by the absence of a thermal UV bump, and an emission peak in the X-rays. The resulting very flat αox = −0.82 is typical of low-luminosity AGNs, and is in good agreement with the extrapolation to low luminosities of the well-known trend with luminosity observed in a standard AGN. Indeed, we are possibly observing the accretion disc emission in NGC 3147 in the optical, close to the expected peak. On the other hand, the steep −2 UV power law may be Comptonization of that cold disc by a warm corona, what is instead generally observed as a ‘soft excess’ in a more luminous AGN.

view Abstract Citations (226) References (67) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiwavelength Tests of the Dusty Torus Model for Seyfert Galaxies Mulchaey, John S. ; Koratkar, Anuradha ; Ward, Martin J. ; Wilson, Andrew S. ; Whittle, Mark ; Antonucci, Robert R. J. ; Kinney, Anne L. ; Hurt, Todd Abstract We present a compilation of emission properties for a sample of 116 Seyfert galaxies based on both previously unpublished data and measurements available in the literature. These measurements include fluxes in the emission lines [O III] λ5007 and Hβ, as well as the infrared (25-60 microns), ultraviolet (1450 A), soft (0.2-4 keV), and hard (2-10 keV) X-ray continua. These data are used to try to distinguish between isotropic and anisotropic emission properties of Seyfert galaxies. The distribution functions of [O III] λ5007, infrared, and hard X-ray continuum are similar for Seyfert 1's and Seyfert 2's, consistent with these properties being isotropic. The ultraviolet and soft X-ray continua of Seyfert 2's are underluminous relative to the type 1's suggesting photons at these energies escape from the central source anisotropically. There is a correlation between the ultraviolet continuum and emission-line fluxes in Seyfert 1's consistent with the idea that the central engine is responsible for powering the line emission. No such correlation is found for the Seyfert 2's. Instead, the scatter in the plot of ultraviolet continuum versus line emission suggests the true nuclear continuum luminosity is not seen at Earth in these objects. These properties are consistent with those expected in the dusty torus model. Publication: The Astrophysical Journal Pub Date: December 1994 DOI: 10.1086/174933 Bibcode: 1994ApJ...436..586M Keywords: Active Galactic Nuclei; Astronomical Models; Emission Spectra; Infrared Spectra; Line Spectra; Seyfert Galaxies; Ultraviolet Spectra; Astronomical Spectroscopy; Infrared Astronomy; Mathematical Models; Ultraviolet Astronomy; Astrophysics; GALAXIES: ACTIVE; GALAXIES: NUCLEI; GALAXIES: SEYFERT; INFRARED: GALAXIES; ULTRAVIOLET: GALAXIES; X-RAYS: GALAXIES full text sources ADS | data products SIMBAD (117) NED (117) MAST (1)

We have obtained deep optical spectra of medium resolution for a sample of 12 Galactic planetary nebulae (PNe). Optical recombination lines (ORLs) from carbon, nitrogen and oxygen have been detected in 11 of them and neon ORLs in nine of them. All spectra were obtained by scanning a long slit across the nebular surface, yielding relative line intensities for the entire nebula that are suitable for comparison with integrated line fluxes measured in other wavelength regions using space-borne facilities, such as the Infrared Space Observatory (ISO) and the International Ultraviolet Explorer (IUE). For 11 PNe, ISO infrared spectra between 2.4 and 197 μm are available, most of them taken by ourselves, plus a Kuiper Airborne Observatory (KAO) infrared spectrum of NGC 6210. IUE ultraviolet (UV) spectra are available for all nebulae except one in our sample. The UV, optical and infrared spectra have been combined to study nebular thermal and density structures and to determine elemental abundances. We have determined UV to optical extinction curves towards these PNe by examining observed fluxes of H i and He ii recombination lines, radio free–free continuum flux density, and UV to optical nebular continua. For 11 PNe in our sample, the derived optical reddening curves are found to be consistent with the standard Galactic extinction law for a total-to-selective extinction ratio, R≡A(V)/EB–V= 3.1. However, the optical extinction curve towards Hu 1–2 yields R= 2.0. The UV extinction towards Hu 1–2 and NGC 6572 is also found to be much steeper than the standard Galactic reddening law. In contrast, the UV extinction curve along the sight lines towards NGC 6210 is found to be much shallower, although in the latter case the uncertainties involved are quite large. Electron temperatures and densities have been derived using a variety of diagnostic ratios of collisionally excited lines (CELs) in the UV, optical and infrared. The results show clear stratifications, both in temperature and density. Lines emitted by ions formed in regions of higher ionization degree yield higher temperatures than lines arising from regions of lower ionization degree, while densities deduced from ratios of infrared diagnostic CELs of low critical densities, such as the [O iii] 88-μm/52-μm ratio, are systematically lower than those derived from UV and optical diagnostic lines, which in general have much higher critical densities than the infrared fine-structure lines. Electron temperatures have also been derived from the ratio of the nebular continuum Balmer discontinuity to H 11 for 11 PNe. For four of these, the Balmer jump temperatures are more than 1000 K lower than values derived from the [O iii] optical collisionally excited diagnostic line ratio. With a difference of 3580 K, NGC 40 has the lowest Balmer jump temperature relative to the [O iii] optical forbidden-line temperature. High-order Balmer line decrements have been used to determine electron densities. The results are consistent with values derived from forbidden-line density-diagnostics.

Rest-frame ultraviolet (UV) emission lines probe electron densities, gas-phase abundances, metallicities, and ionization parameters of the emitting star-forming galaxies and their environments. The strongest main UV emission line, Lyα, has been instrumental in advancing the general knowledge of galaxy formation in the early universe. However, observing Lyαemission becomes increasingly challenging atz ≳ 6 when the neutral hydrogen fraction of the circumgalactic and intergalactic media increases. Secondary weaker UV emission lines provide important alternative methods for studying galaxy properties at high redshift. We present a large sample of rest-frame UV emission line sources at intermediate redshift for calibrating and exploring the connection between secondary UV lines and the emitting galaxies’ physical properties and their Lyαemission. The sample of 2052 emission line sources with 1.5 &lt; z &lt; 6.4 was collected from integral field data from the MUSE-Wide and MUSE-Deep surveys taken as part of Guaranteed Time Observations. The objects were selected through untargeted source detection (i.e., no preselection of sources as in dedicated spectroscopic campaigns) in the three-dimensional MUSE data cubes. We searched optimally extracted one-dimensional spectra of the full sample for UV emission features via emission line template matching, resulting in a sample of more than 100 rest-frame UV emission line detections. We show that the detection efficiency of (non-Lyα) UV emission lines increases with survey depth, and that the emission line strength of He IIλ1640 Å, [O III]λ1661 + O III]λ1666, and [Si III]λ1883 + Si III]λ1892 correlate with the strength of [C III]λ1907 + C III]λ1909. The rest-frame equivalent width (EW0) of [C III]λ1907 + C III]λ1909 is found to be roughly 0.22 ± 0.18 of EW0(Lyα). We measured the velocity offsets of resonant emission lines with respect to systemic tracers. For C IVλ1548 + C IVλ1551 we find that ΔvC IV≲ 250 km s−1, whereas ΔvLyαfalls in the range of 250−500 km s−1which is in agreement with previous results from the literature. The electron densitynemeasured from [Si III]λ1883 + Si III]λ1892 and [C III]λ1907 + C III]λ1909 line flux ratios is generally &lt; 105cm−3and the gas-phase abundance is below solar at 12 + log10(O/H)≈8. Lastly, we used “PhotoIonization Model Probability Density Functions” to infer physical parameters of the full sample and individual systems based on photoionization model parameter grids and observational constraints from our UV emission line searches. This reveals that the UV line emitters generally have ionization parameter log10(U) ≈ −2.5 and metal mass fractions that scatter aroundZ ≈ 10−2, that isZ ≈ 0.66 Z⊙. Value-added catalogs of the full sample of MUSE objects studied in this work and a collection of UV line emitters from the literature are provided with this paper.

Context. Radiation-driven mass loss is key to our understanding of massive-star evolution. However, for low-luminosity O-type stars there are big discrepancies between theoretically predicted and empirically derived mass-loss rates (called the weak-wind problem). Aims. We compute radiation-line-driven wind models of a typical weak-wind star to determine its temperature structure and the corresponding impact on ultra-violet (UV) line formation. Methods. We carried out hydrodynamic simulations of the line-deshadowing instability (LDI) for a weak-wind star in the Galaxy. Subsequently, we used this LDI model as input in a short-characteristics radiative transfer code to compute synthetic UV line profiles. Results. We find that the line-driven weak wind is significantly shock heated to high temperatures and is unable to cool down efficiently. This results in a complex temperature structure where more than half of the wind volume has temperatures significantly higher than the stellar effective temperature. Therefore, a substantial portion of the weak wind will be more ionised, resulting in a reduction of the UV line opacity and therefore in weaker line profiles for a given mass-loss rate. Quantifying this, we find that weak-wind mass-loss rates derived from unsaturated UV lines could be underestimated by a factor of between 10 and 100 if the high-temperature gas is not properly taken into account in the spectroscopic analysis. This offers a tentative basic explanation for the weak-wind problem: line-driven weak winds are not really weaker than theoretically expected, but rather a large portion of their wind volume is much hotter than the stellar effective temperature.

Non-Maxwellian κ electron energy distributions (EEDs) have been proposed in recent years to resolve the so-called “electron temperature and abundance discrepancy problem” in the study of planetary nebulae (PNs). Thus the need to develop diagnostic tools to determine from observations the EED of PNs is raised. Arising from high-energy levels, the ultraviolet (UV) emission lines from PNs present intensities that depend sensitively on the high-energy tail of the EED. In this work, we investigate the feasibility of using the C ii]λ2326/C ii λ1335 intensity ratios as a diagnostic of the deviation of the EED from the Maxwellian distribution (as represented by the κ index). We use a Maxwellian decomposition approach to derive the theoretical κ-EED-based collisionally excited coefficients of C ii, and then compute the C ii UV intensity ratio as a function of the κ index. We analyze the archival spectra acquired by the International Ultraviolet Explorer and measure the intensities of C ii UV lines from 12 PNs. By comparing the observed line ratios and the theoretical predictions, we can infer their κ values. With the Maxwellian-EED hypothesis, the observed C ii]λ2326/C ii λ1335 ratios are found to be generally lower than those predicted from the observed optical spectra. This discrepancy can be explained in terms of the κ EED. Our results show that the κ values inferred range from 15 to infinity, suggesting a mild or modest deviation from the Maxwellian distribution. However, the κ-distributed electrons are unlikely to exist throughout the whole nebulae. A toy model shows that if just about 1%–5% of the free electrons in a PN had a κ EED as small as κ = 3, it would be sufficient to account for the observations.

By virtue of its spectrometers having simultaneous multichannel integration capability and relatively large input apertures, the International Ultraviolet Explorer satellite has been the first instrument capable of effective study of the ultraviolet spectra of the gas from extended H ii regions. This review will concentrate on discussing the results of the studies made of the ultraviolet emission line and continuum spectra of the gas and dust of extended H ii regions in the Galaxy and the Magellanic Clouds. However, it should be noted also that ultraviolet spectral studies with the IUE have contributed new information about the extinction and dust associated with H ii regions, the nature of the highly ionized gas surrounding their exciting stars via ultraviolet absorption lines, and the integrated stellar + nebular spectra of more distant extragalactic H ii regions. Since the latter three subjects are parts of other reviews in this book, herein we will limit our discussion to results related to the continuous and emission line ultraviolet spectra from the gas and dust within the H ii regions themselves.

We studied the evolution of the normalized flux of selected ultraviolet (UV) emission lines of two classical novae (PW Vul and V1668 Cyg) using International Ultraviolet Explorer (IUE) short wavelength observations. Different phases of the outburst are studied. Emission lines covering a wide range of ionization states are investigated. We use the calculated fluxes to estimate the mass accretion rates during quiescence of both novae. We found average values of the UV luminosity for PW Vul to be of 1.0 ± 0.1 × 1035 erg s−1, and the corresponding value for V1668 Cyg is 4.0 ± 0.2 × 1035 erg s−1. In quiescence, we obtained average values for the mass accretion rates of 8.7 ± 0.4 × 10−10 M⊙ year−1 and 1.8 ± 0.1 × 10−10 M⊙ year−1, respectively. We attribute the spectral behavior of the two systems to the variation of the optical thickness and temperature of the envelope during the different phases of the outburst. Our results demonstrate the effect of the white dwarf mass on the evolution of the nova. The results of IUE observations are consistent with the theoretical CO models of classical nova of.