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Precise, high-cadence, long-term records of stellar spectral variability at different temporal scales lead to better understanding of a wide variety of phenomena including stellar atmospheres and dynamos, convective motions, and rotational periods.
Comparison of high- and low-resolution IUE spectra of HD 269665 (Sanduleak -68 deg 110) show that the star is a subdwarf with a temperature in the range 30,000-50,000 K. The visual spectrum shows Balmer lines and weak He II 4686 A lines. Balmer-line width and a fit of the UV-visual flux distribution using the Blackwell-Shallis (1977) algorithm yields an effective temperature between 30,000 and 38,000 K and log g = 5-6. A table is presented of photospheric UV spectral lines in HD 269665. The radial velocity of the star is found to be 5.8 + or - 0.5 km/s.
Multichannel spectrophotometry data acquired from 1969 to 1980 are used to study the absolute energy distribution and emission line variability of the N galaxies 3C 382 and 3C 390.3. It is shown that: (1) the continuum spectra can be decomposed into a nuclear nonthermal component of constant spectral shape and a constant elliptical galaxy component; (2) apparent visual magnitudes within a 10 arcsec aperture are derived for underlying galaxies, 3C 382 being 15.27 and 3C 390.3, 16.04; (3) forbidden lines and narrow Balmer lines do not change with the central continuum, but (4) the intensity variations of the broad Balmer lines are correlated nonlinearly with changes in the luminosity of the central continuum source. This correlation can be explained by a time-lag effect if there are two components of broad-line emission, one varying on a time scale of a few months and the other over a few years.
Calculations of the anisotropy of line emission from photoionized clouds, and the resulting asymmetry in the line profiles are discussed. The permitted emission-line profiles of Seyfert galaxies and QSO's often contain more light in the red than in the violet wing, and this asymmetry can arise from self-absorption of the line radiation in an expanding system of optically thick clouds. It is shown that the Balmer line optical depths are large enough to give strongly asymmetric line profiles for pure expansion, but the observed lack of strong asymmetry in the Balmer lines of most Seyfert galaxies suggests that the broad-line widths may result from random motions, or that clouds radiate isotropically. It is concluded that the frequently observed absorption of the violet wing of Lyman-alpha must occur in a surrounding region undergoing systematic outflow, or that the weakness of the Balmer line asymmetries is explained by the Balmer line emission resulting from collisional excitation from n=2.
Careful studies of various chromospheric spectral signatures are very important in order to explore their possible sensitivity to the modifications of the thermodynamic quantities produced by the flare occurrence. Pioneer work of Canfield and co-workers have shown how the H alpha behavior is able to indicate different changes in the atmospheric parameters structure associated to the flare event. It was decided to study the behavior of the highest Balmer lines and of the Balmer continuum in different solar flare model atmospheres. These spectral features, originating in the deep photosphere in a quiet area, may have a sensitivity different from H alpha to the modification of a flare atmosphere. The details of the method used to compute the Stark profile of the higher Balmer line (n is greater than or equal to 6) and their merging were extensively given elsewhere (Donati-Falchi et al., 1985; Falchi et al., 1989). The models used were developed by Ricchiazzi in his thesis (1982) evaluating the chromospheric response to both the nonthermal electron flux, for energy greater than 20 kev, (F sub 20) and to the thermal conduction, (F sub c). The effect of the coronal pressure values (P sub O) at the apex of the flare loop is also included.
The Balmer 9 and 11 lines of He II at 959 A and 942 A in solar spectra are identified. These lines are produced mainly by recombination following photoionization of He II by coronal XUV radiation. From analysis of the line intensities, the theoretical model of Avrett et al. (1976), is confirmed where it was found that an appreciable amount of He (2+) is present at temperatures of 1 - 2 x 10 to the 4th K and that the anomalously strong He II 304 line is produced primarily by collisional excitation. The suggestion of Kohl (1977) that the photoionization-recombination process is more important in active regions than in the quiet sun is confirmed, and we find that the 304-A line is produced largely by recombination in solar flares.
The N-galaxy 3C 390.3 has been monitored spectroscopically since 1974 (Osterbrock, Koski and Phillips 1975; Oke 1988). From various archives and literature, it is found that the Balmer lines change their intensities and profiles in a dramatic manner. The H alpha profile is very broad and peculiar, and the relative intensities of its two humps changes consistently with time, possibly periodically. Before 1980, the blue hump was significantly stronger than the one in the red. From 1980 to 1983 the blue hump became stronger (see Oke 1988). After 1983 the H alpha profile has returned to its early shape and seems to have completed a full circle. Unlike the rapid (on the order of a month or even less) and aperiodic variation in the continuum and integrated line intensities, the change in broad profile seems slow and consistent. Taking the analogy of cataclysmic variables, the double-horn profiles have been observed in cases of interacting stars. For example, the emission lines, both in He II and hydrogen Balmer lines in GD 552 (Stover 1985) show double-horn profiles and periodical changes in their line profiles, including the change in ratios of two humps. It is understood that the D-wave components (Smak 1976) are the signature of an emitting disk and the S-wave component is from the emission at a hot spot which rotates and results in a moving component in the velocity space. The mass flow from the nearby interacting star provides the stream toward the core of a neutron star or white dwarf. Therefore, it is proposed that the variation of broad line profiles observed in 3C 390.3 may be the result of a pair of interacting massive cores. The rotational velocity dominates and produces a variable double-horn profile. However, the line widths observed in broad line radio galaxies are one order larger than that in interacting stars. The Balmer decrements imply a much smaller density (10(exp 10-12) cm(exp-3)) than that in the cataclysmic variables. The much larger velocity and much thinner density make it unlikely that the broad line emission is simply formed in an accretion disk. The authors postulate that a significant rotational motion is involved. If the observed squared profiles are indeed due to the rotational velocity field, one can naturally explain their rare occurrence.
Seven QSOs of low to intermediate redshift are characterized on the basis of: 320-850-nm spectra obtained with the UVITS spectrograph and image-dissector scanner at the f/9 Cassegrain focus of the 2.7-m reflecting telescope at McDonald Observatory; improved model calculations for the Fe II, Mg II, and Balmer lines and the Balmer continuum; and the theoretical results of Netzer and Wills (1983). The data are presented in tables, spectra, and difference spectra and described in detail. Fe II is found to be the largest contributor to the emission line spectrum, with strong UV Fe II lines in all QSOs (regardless of the strength of the optical Fe II lines) and an abundance ratio suggesting a factor-of-three overabundance of Fe relative to Mg and probably H. A discrepancy between the observed Fe II strength and the predictions of dustless standard photoionization models is noted, and the addition of a high-density component to the models is suggested.
The UV spectra of three Be stars (gamma Cas, sigma Tau, eta Cen) were studied. Of the six Be stars observed in the first four lines of the Balmer series, three stars showed at least one of the Balmer lines to be variable in the equivalent width amounting to a few percent with time scales of 3 to 30 minutes. Photoelectric spectrum scans of five southern Wolf-Rayet stars showed night-to-night variations. A simple model is proposed to account for the behavior of these emission lines. Scans of gamma square Vel showed rapid variations of emission strengths of He II 4686 and C III - IV 4650. These variations have time scales of 1 minute and longer. Night-to-night variations were also found. Scans of four Be stars in H alpha showed a definite variation of 3 to 4 percent, with time scales of 1 minute and longer in sigma Tau. In 48 Per and kappa Dra the variations are not as well established. No variation of any significance was found for nu Gem.
A number of faint filaments in the Puppis A supernova remnant have been found to have spectra with strong oxygen lines, extremely weak Balmer lines, and radial velocities greater than 1500 km/s. These are very different from the bright filaments, which are nitrogen-rich and have velocities less than 300 km/s. The newly discovered filaments are spectroscopically similar to those found in young, oxygen-rich remnants, as typified by the fast-moving knots in Cas A. These Puppis A filaments are interpreted as knots of oxygen-rich supernova ejecta which remain relatively uncontaminated by interstellar material, despite the probable age of Puppis A of several thousand years. Spectra of the newly discovered filaments show, in addition to strong forbidden lines of O I, O II, and O III, permitted lines of O I: 7774, 8446 A. The permitted lines are attributed to recombination of O(+), and their strength relative to H is used to estimate that the O:H mass ratio is about 30.
We present spectroscopic observations of some 115 stars of the cluster Blanco 1, extending from the Ca II(H,K) region to the Ca II(I-R) triplet, supporting an age similar to that of the young cluster alpha Persei. The H-alpha absorption equivalent with vs (B - V) diagram forms a well-defined locus, with decreasing absorption equivalent width for decreasing effective temperature, akin to solar neighborhood dwarfs. A large spread in the Ca II surface flux, as a function of (B - V), also indicates the presence of a high degree of surface inhomogeneity, synonymous with high magnetic activity in young stars. A drop-off in the Ca II flux at (B - V) = 1.0 is also similar to the solar neighborhood stars, and shows that the primary chromospheric cooling changes from the Ca II and Mg II lines to the Balmer lines. The mean chromospheric temperature for stars at 4800 K lies between 8000 K and 10,000 K, based on theoretical models, which is somewhat higher than the older solar neighborhood dwarfs. The high mean Ca II surface flux of the sample is also consistent with that of other young clusters. We were able to measure the equivalent width of the Li(6708) line, whose strength as a function of (B - V) indicates an age similar to the young cluster alpha Persei. The lithium abundance decreases with decreasing effective temperature, consistent with the premise of lithium depletion in stars with larger convection zones. Using published photometry and a recent Zero Age Main Sequence (ZAMS) fitting method, we also re-define the distance to the cluster to be 246 pc.
The nova outburst of V407 Cyg in 2010 Mar. 10 was the first observed for this star but its close resemblance to the well known symbiotic-like recurrent nova RS Oph suggests that it is also a member of this rare type of Galactic novae. The nova was the first detected at gamma-ray energies and is the first known nova explosion for this system. The extensive multiwavelength coverage of this outburst makes it an ideal comparison with the few other outbursts known for similar systems. We extend our previous analysis of the Mira and the expanding shock from the explosion to detail the time development of the photoionized Mira wind, circumstellar medium, and shocked circumstellar environment to derive their physical parameters and how they relate to large scale structure of the environment, extending the previous coverage to more than 500 days after outburst. We use optical spectra obtained at high resolution with the Nordic Optical Telescope (NOT) (R approx. =.45000 to 65000) and medium resolution Ondrejov Observatory (R approx. = 12000) data and compare the line variations with publicly available archival measurements at 30 GHz OVNR and at X-rays with Swift during the first four months of the outburst, through the end of the epoch of strong XR emission. We use nebular diagnostics and high resolution profile variations to derive the densities and locations of the extended emission. We find that the higher the ionization and/or the higher the excitation energy, the more closely the profiles resemble the He II/Ca V-type high velocity shock profile discussed in Paper I. This also accounts for the comparative development of the [N II] and [O III] isoelectronic transitions: the [O III] 4363A profile does not show the low velocity peaks while the excited [N II] 5754A does. If nitrogen is mainly N(+3) or higher in the shock, the upper state of the [N II] nebular lines will contribute but if the oxygen is O(+2) then this line is formed by recombination, masking the nebular contributor, and the lower states are collisionally quenched but emit from the low density surroundings. Absorption lines of Fe-peak ions formed in the Mira wind were visible as P Cyg profiles at low velocity before Day 69, around the time of the X-ray peak and we identified many absorption transitions without accompanying emission for metal lines. The H Balmer lines showed strong P Cyg absorption troughs that weakened during the 2010 observing period, through Day 128. The Fe-peak line profiles and flux variations were different for permitted and forbidden transitions: the E1 transitions were not visible after Day 128 but had shown a narrow peak superimposed on an extended (200 km/s) blue wing, while the M1 and E2 transitions persisted to Day 529, the last observation, and showed extended redshifted wings up of the same velocity. We distinguish the components from the shock, the photoionized environment, and the chromosphere and inner Mira wind using spectra taken more than one year after outburst. The multiple shells and radiative excitation phenomenology are similar to those recently cited for GRBs and SNIa .
A new optical spectrum of the nearby broad-line radio galaxy (BLRG) Pictor A reveals a prominent double-peaked component of the Balmer lines which does not appear in any historical spectra of this object. Carried out with the hope of obtaining exactly such a result, this observation is a key to the interpretation of double-peaked emitters. If bolsters our previous conclusion that there is a set of additional properties which are associated with the rare class of double-peaked emitters, namely F-R II radio morphology, strong low-ionization forbidden lines, weak UV continuum, and flat far-infrared spectrum. Furthermore, the low-velocity, 'ordinary' broad Balmer lines in Pictor A remained relatively unchanged as the new twin peaks appeared, which justifies the practice of applying models that fit only the double peaks and not the low-velocity components that are often present in spectra of this type. We discuss the relative merits of accretion-disk models and other models for double-peaked emission lines in the light of this new observation.
An attempt is made to account for the observational fact that the intensity ratios of the lower Balmer lines seen in emission from QSOs, type 1 Seyfert galaxies, and other related active galaxies are not what would be expected from the conventional picture of lines generated in a recombining hydrogen plasma. Previous observations of emission-line intensities in QSOs and Seyfert galaxies are reviewed. The various processes included in the rate coefficients of the calculations are then described, viz., free-free, bound-free, and bound-bound transitions, radiative transfer, and angular-momentum mixing. The strengths of the various emission lines are calculated by using more accurate values for the transition rates, including excitation and deexcitation simultaneously, and providing for finite rates in optically forbidden transitions. Numerical results are presented for the cases of ground-state collisional excitation, reabsorption of the upper Balmer lines, and collisional deexcitation. The results are applied to construct a model for the emission-line gas in a QSO and to discuss limits on models of Seyfert galaxies.
Spectroscopic observations of 13 Seyfert 1 galaxies made from 1979 to 1984 at Palomar and Steward Observatories were analyzed for Balmer-line and optical continuum variability. The majority of the galaxies showed significant variations, particularly in the continuum. Typical peak-to-peak changes for H-beta and H-gamma integrated line fluxes were 100-200 percent, while the continua varied by 200-350 percent. In several cases, Balmer-line and continuum variations were found to be strongly correlated, as expected for photoionization by a central continuum source. However, these correlations were found to be highly nonlinear. Significant correlations were found between variability amplitude and global AGN properties such as luminosity. Moreover, a significant number of variations occurring on short time scales constrains the size of the broad-line region in Seyfert galaxies to about 90 lt-days across or less.
Recent observational results based on a joint infrared/optical survey of the hydrogen line spectra of a significant number of low and high redshift quasars are summarized. The spectra show that the Paschen-alpha and Balmer line ratios do not agree with the result of nominal case B recombination theory and vary widely within the quasars sampled. The range of P-alpha to H-beta ratios is a factor of roughly 6, while the range in Ly-alpha to H-alpha ratios is a factor of roughly 5. For the P-alpha:Balmer series, the deviations from case B recombination are not consistent with reddening, but appear, within large dispersions, to be consistent with optical depth effects in the Balmer lines affecting the lines ratios.
Inside a line-emitting cloud the density of trapped photons could be so high that they ionize hydrogen atoms from excited levels far more efficiently than electronic collisions. Such ionizations can reduce the population of high-level hydrogen and consequently reduce the Balmer line emissivity by a factor of 3 or more. As a result, the Balmer line emission is not enhanced as significantly in the partially ionized zone as predicted by current models unless an exceptionally large column density is assumed.
Strong flare heating that penetrates deeply into the solar chromosphere is examined, and a simple model that is supported by a numerical radiative transfer simulation is applied to study how elevated free electron densities produce markedly increased Stark emission in the wings of hydrogen Lyman and Balmer lines. The proportionality that exists between the observed Stark wing intensity and the total energy deposition in the partially ionized layer is calculated for various Lyman and Balmer lines. It is concluded that when the effects of background opacity sources on the wing enhancements are not important, the magnitude of the nonthermal heating that penetrates the chromosphere may be inferred from the observed line wings. It is predicted that Ly-alpha extended wings will exhibit enhancement of Stark shape, even when inherent damping wing opacity exceeds Stark wing opacity over the entire absorption profile.