Low-excitation Lines Research Articles

New aspects of line-profile variability in P Cygni's optical spectrum

High-resolution photographic spectra as well as high S/N ratio CCD spectral observations of P Cygni are analyzed in terms of line-prole variability (lpv). Four dif- ferent kinds of lpv are established: systematic variabil- ity in the absorption troughs of low and intermediate excitation lines due to propagating Discrete Absorption Components (DACs); \swaying variability consisting of continuous modulations in velocity and intensity of the absorption cores and emission peaks of lines of intermedi- ate and high excitation; red-emission-wing variability due to travelling \bumps, and long-term (LT) variability in HI and HeI lines of relatively large optical depth. DAC propagation is a slow variation of P Cygni's stellar wind. The components probably originate from large-scale, high-density (low-excitation) perturbation(s) which develop in a relatively outer part of the wind (V 0:41Vinf) but appear to be maintained, in some in- direct way, by photospheric processes. The geometry of the structures is not yet clear but they could be either spherically symmetric or curved, like kinks. The \swaying variability manifests itself by modu- lations in position and intensity of the absorption cores and emission peaks of almost all lines in the optical. Simultaneous variations in emission and absorption line- strength were also observed. The modulations are at least partially due to variations in the number density which af- fect all layers of the supersonic wind starting at its base up to layers where the H line forms (0:18 V 0:95Vinf). The phenomenon appears to be stable over many years, though on a variable time-scale. Suggestive evidence for a close relationship between the modulations and changes in the stellar brightness and temperature was found, in- dicating that the \swaying variability is more likely coupled to processes in the photosphere. Non-radial pul- sations (NRPs) either of g-mode or of s-mode oscillations are a possible cause for this variability. The LT variability makes up a very slow pattern of variation in both the velocity of the absorption cores and the intensity of the emission peaks of the stronger HI and HeI lines. This variability is found only in the outer part of the wind (V 0:82Vinf). The nature of the LT variation is not known at present. The red-emission-wing variability is localized in the high-velocity part of the emission lobes of P Cygni-type proles, +90 V +230=250 km s 1 . This variability is presumably caused by outward propagating \bumps, but its exact nature is still unknown. No indication for any clear relation between dierent kinds of lpv was found. Even when the variations operate in one and the same region of the wind (in velocity space) it is not obvious whether and how they interact. Stellar rotation does not seem to play a fundamental role in set- ting the time-scale of either the DAC-induced variability or the LT variability. The relationship between the \sway- ing variability and the rotation is still not clear but it is possible that this variability is rotationally modulated. The wind variability of P Cygni appears to be quali- tatively similar to the wind variability of the early B-type supergiant HD64760 but dierent from the variability of O-type star winds.

Fluorescence Correlation and Low Temperature Linewidth of Single Defect Centers in Diamond

Low temperature fluorescence excitation spectroscopy was carried out on single , nitrogen vacancy defect centers. At temperatures below 90, K; the fluorescence intensity of individual centers drastically diminishes because of the population of a metastable singlet state in near resonance with the . optically excited state. Low temperature fluorescence excitation spectroscopy , down to 5 K becomes possible via deshelving of this state with a second laser source. Surprisingly individual centers reveal low temperature fluorescence excitation line widths around 0.6 meV. PACS numbers: 78.20.—e, 42.30.Yc

The 1995-96 decline of R Coronae Borealis: high-resolution optical spectroscopy

A set of high-resolution optical spectra of R CrB acquired before, during and after its 1995–96 decline is discussed. All of the components reported from earlier declines are seen. This novel data set provides new information on these components including several aspects not previously seen in declines of R CrB and other R Coronae Borealis stars. In the latter category is the discovery that the onset of the decline is marked by distortions of absorption lines of high-excitation lines, and quickly followed by emission in these and in low-excitation lines. This ‘photospheric trigger’ implies that dust causing the decline is formed close to the star. These emission lines fade quickly. After 1995 November 2, low-excitation narrow (FWHM ∼12 km s−1) emission lines remain. These appear to be a permanent feature, slightly blueshifted from the systemic velocity, and unaffected by the decline except for a late and slight decrease of flux at minimum light. The location of the warm dense gas providing these lines is uncertain. Absorption lines unaffected by overlying sharp emission are greatly broadened, weakened and redshifted at the faintest magnitudes when scattered light from the star is a greater contributor than direct light transmitted through the fresh soot cloud. A few broad lines (FWHM ≃300 km s−1) are seen at and near minimum light with approximately constant flux: prominent among these are the He i triplet series, Na i D and [N ii] lines. These lines are blueshifted by about 30 km s−1 relative to the systemic velocity, with no change in velocity over the several months for which the lines were seen. It is suggested that these lines, especially the He i lines, arise from an accretion disc around an unseen compact companion which may be a low-mass white dwarf. If so, R CrB is similar to the unusual post-asymptotic giant branch star 89 Her.

Hubble Space TelescopeFaint Object Spectrograph Optical and Ultraviolet Spectroscopy of the Bow Shock HH 47A

We present new spectra obtained with the Faint Object Spectrograph aboard the Hubble Space Telescope of the HH 47A bow shock and Mach disk that cover the entire spectral range between λλ2220 and 6810. In addition to emission lines seen previously from HH objects, we uncover over a dozen weak Fe IItransitions in the ultraviolet. The flux ratios between these permitted lines can only be understood if transitions to the ground state are resonantly scattered within HH 47A. The expected column density of Fe II within HH 47A suffices to scatter these lines, although the scattering optical depths imply that the Fe II line broadening must exceed that expected from thermal motions. Excitation of ultraviolet Fe II occurs locally within HH 47A, probably from collisions within the hot postshock gas and not from UV pumping from some nearby O stars. The data show no evidence for significant depletion of Fe within HH 47A. The emission line's fluxes and ratios indicate that jet material currently enters the Mach disk with a density of ~350 cm-3 and a velocity of ~40 km s-1. The mass-loss rate of the exciting star, as measured by the mass flux through the Mach disk, is 1.6×10 M☉ yr-1. This mass-loss rate is considerably lower than that closer to the star where the jet is brighter, probably because the density along the jet is highly nonuniform. A single-shock velocity does not match the bow shock spectrum well. We propose that secondary shocks reheat the gas within the cooling zone of the HH 47A bow shock. Compression from the first shock will cause these secondary shocks to be strongly magnetized, and the secondary shocks should emit strongly in low-excitation lines such as Mg II, C II], and [S II]. The weak blue continua seen at optical wavelengths in spectra of the Mach disk and bow shock extend into the ultraviolet and have spectral energy distributions and total fluxes consistent with those expected from two-photon emission.

Long-term spectroscopy of η Carinae

Quantitative measurements of line parameters in the spectrum of η Carinae are presented for both the broad and narrow line components. A total of 655 spectral features were measured in the spectral range 3850 A to 11000 A, giving a comprehensive view of the behavior of atomic transitions ranging from a few to tens of electron volts. The spectrum on the phase of maximum intensity in the high excitation lines (1995) is compared with that on minimum intensity (June 1992), showing that at this phase the high excitation lines disappear but the broad components of low excitation lines strengthens. We reject a number of previous line identifications and propose several new ones, including FeII, [FeII], [FeIII], [NII], and the near-infrared CaII triplet. Some lines commonly used to diagnose density, temperature, chemical composition, and reddening were found to be blended, urging a revision of the results based on previous data. The existence of double-peaked lines, suggested in previous papers, is ruled out. In the case of hydrogen lines, the apparent double-peaks are shown to be real absorption components. The velocity field in the inner 2 around the central star shows additional components previously unknown. The phases of high and low excitation in η Carinae are discussed in light of a recently proposed binary system. We suggest a temperature T ~ 16000 K for the primary star, what indicates that it is close to the beginning of the core helium-burning evolutionary stage.

The evolved B[e] star HD 87643: observations and a radiation-driven disc wind model for B[e] stars

New high resolution spectroscopic and medium resolution spectropolarimetric data, complemented with optical broad and narrow band imaging, of the B[e] star HD 87643 are presented. The spectrum of HD 87643 exhibits the hybrid characteristics well known to be representative of the group of B[e] stars; a fast wind with an expansion velocity in excess of 1000 km s 1 is measured in the hydrogen and helium lines, while a slower component is traced by lower excitation lines and forbidden lines. Clues to the geometry of the rapidly expanding circumstellar shell are provided by the startling polarization changes across H�. Comparison with published schematic calculations indicates that the polarizing material is located in a slowly rotating, expanding disk structure. A hydrodynamical model is then presented whose results are consistent with the original two-wind concept for B[e] stars and exhibits kinematic properties that may well explain the observed spectral features in HD 87643. The model calculations use as input a B star undergoing mass loss, surrounded by an optically thick disk. The resulting configuration consists of a fast polar wind from the star and a slowly expanding disk wind. The model also predicts that the stellar wind at intermediate latitudes is slower and denser than in the polar region.

Evidence for a rotational velocity field about the white dwarf of V347 Puppis

We present time-resolved optical spectroscopy of the deeply eclipsing nova-like binary V347 Pup, which provides evidence for a rotational velocity field in the low-excitation lines, as expected from accretion disc emission. The low-excitation line profiles are a composite of the disc and the irradiated inner-face of the donor star. This picture is remarkably simple compared to the other members of the eclipsing nova-like family. Unsatisfactory radial velocity solutions for the accreting object provided by standard methods encourage us to apply a technique developed to measure stellar motion from tomographic reconstructions of the time-dependent line profiles. We find some evidence for a spiral pattern over the disc and for disc-overflow accretion. If the emission distribution proves to be a long-term feature, V347 Pup will provide an opportunity to study disc kinematics with greater confidence than allowed by the other eclipsing nova-like objects.

Optical long slit velocities and a combined optical and H i velocity field for the barred spiral galaxy NGC 1365

Optical emission line velocities in NGC 1365 are presented along 35 slit positions, of which 18 have not been published earlier. Diagrams of emission line velocities as function of distance along the slits are presented, and separate velocity fields are derived for the disc as given by the low excitation lines, combined with H i 21 cm VLA data, and for the nuclear outflow cone as given mainly by the high excitation lines. An algorithm for creating a velocity field and contour maps based on measurements along randomly oriented spectrograph slits is given in the Appendix. Detailed discussions and interpretations of these velocity fields are given elsewhere. The combined optical and 21 cm disc velocity field is available by an anonymous ftp.

An accretion model for the eclipsing cataclysmic variable PG 0859 + 415

The emission lines found in the majority of cataclysmic variables are generally used as tracers of accretion flows which dominate the light at optical wavelengths. It has been suggested from previous observations that the eclipsing nova-like variable PG 0859 + 415 shows individualistic orbital characteristics that are inconsistent with canonical models of stellar accretion. We present spectrophotometry of this star which suggests that the standard picture is not in conflict with observations. We provide evidence that the shallow optical eclipses are of an extended bright spot rather than of the accretion disc, and that the low-excitation lines are dominated by a transient absorption component, perhaps a result of the bright spot or the accretion stream eclipsing the disc. We argue that this object may be another nova-like variable displaying long-term or cyclic variations in mass transfer rate from the secondary star.

Excitation of the ``Arched'' Filaments near the Galactic Center

view Abstract Citations (15) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Excitation of the ``Arched'' Filaments near the Galactic Center Colgan, Sean W. J. ; Erickson, Edwin F. ; Simpson, Janet P. ; Haas, Michael R. ; Morris, Mark Abstract We present measurements of the far-infrared (FIR) fine structure lines [S III] (33 μm), [Si II] (35 μm), [O III] (52, 88 μm), [O I] (63 μm), and [C II] (158 μm) and the adjacent continua at these wavelengths in a strip crossing the E2 and W1 thermal radio filaments in the Galactic center "arc." The properties of the two filaments are similar: the line and continuum fluxes peak in the vicinity of the radio ridges, and the contrast of the ridge fluxes relative to the off-ridge fluxes is greatest for the FIR continuum and doubly ionized lines, lower for the single-dish radio measurements (Sofue et al. 1986) and smallest for the low-excitation lines. The near spatial coincidence of the line and continuum emission maxima with the radio filaments demonstrates that the same excitation source must be responsible for both the line and the continuum emission. The peak FIR luminosity of ∼2.5 x 105 Lsun per 30" beam and the association of [O III] intensity with the filaments pose difficulties for shock and MHD models. Excitation by a string of stars is also unlikely, but photoionization of molecular cloud edges by a quasi-uniform distribution of stars is the most plausible excitation source proposed. The peak ionized line intensity is shifted slightly eastward relative to the FIR continuum emission. The deduced excitation, as measured by the [O III] to [S III] line flux ratios, also peaks slightly east of the radio ridges. Together, these two measurements suggest a substantial contribution from an ionizing source to the east. The strengths of the [O I] and [C II] lines are consistent with their production in photodissociated molecular material adjacent to the photoionized gas, but the FIR luminosity and the [Si II] emission appear to originate predominantly in or very near to the ionized gas. Publication: The Astrophysical Journal Pub Date: October 1996 DOI: 10.1086/177918 Bibcode: 1996ApJ...470..882C Keywords: GALAXY: CENTER; INFRARED: ISM: LINES AND BANDS; ISM: STRUCTURE full text sources ADS | data products SIMBAD (8)

Multifrequency monitoring of the Seyfert 1 galaxy NGC 4593 - II. A small, compact nucleus?

We discuss the results of a campaign to monitor spectral variations in the low-luminosity Seyfert~1 galaxy NGC~4593, at X-rays, ultraviolet, optical and near IR frequencies. The observations and data analysis have been described in a companion paper (Santos-Lle\'o et al. 1994; Paper~1). The active nucleus in this galaxy is strongly and rapidly variable in all wavebands, implying that the continuum source is unusually compact. Its energy distribution from 1.2~$\mu$m to 1200~\AA\/ obeys a power-law whose index is significantly steeper than is usual in Seyfert's or QSO's; the ``big bump'' is either absent or shifted to wavelengths shorter than 1200~\AA\/. The variations of the soft-X~ray {\em excess\/} do not correlate with those of the UV or hard X-ray continuum. The far UV and optical fluxes are well correlated, while the correlation between the hard X-rays and 1447 \AA\ continuum is only marginally significant. Moreover, the optical flux cannot lag behind the UV by more than 6 days. These results cannot be accommodated in the framework of the standard geometrically thin accretion disk model. Rather, they suggest that the bulk of the UV and optical flux originates from thermal reprocessing of X-rays irradiating the disk. The soft X-ray excess is probably the only spectral component which originates from viscous dissipation inside the disk and the near infrared is probably emitted by hot dust heated by the UV radiation. Such a model is consistent with NGC~4593 having a relatively small black-hole mass of the order of $2\times10^{6}{\rm M_{\odot}}$ as inferred from the line variability study. The high ionization/excitation emission lines are very broad and strongly variable and their variations correlate with those of the continuum. The low excitation lines are significantly narrower and remain constant within the accuracy of our measurements. These results suggest a stratified BLR, where the degree of ionization and the velocity dispersion of the gas increase toward small radii. The \lya\ line responds to the variations of the continuum with a delay $\leq 4$ days. To a first order approximation, the BLR in NGC~4593 is well modelled with two different zones at distances of $\sim$~15 and 3 lt-ds from the ionizing source respectively.

A reanalysis of the SWP-HI IUE observations of Capella

We have reanalyzed the numerous high-resolution, far-ultraviolet observations of Capella made by the International Ultraviolet Explorer (IUE) in its 16 yr lifetime. Our purpose was to search for long-term profile variations in Capella's ultraviolet emission lines and to complement the analysis of Goddard High Resolution Spectrograph (GHRS) observations of Capella, discussed in a companion paper (Linsky et al. 1995). We implemented a state-of-the-art photometric correction and spectral extraction procedure to improve S/N and control potential sources for systematic errors. Nevertheless, we were unable to find compelling evidence for any significant long-term profile variations. Previous work has shown that the G8 primary star is only a minor contributor to the high-excitation transition region lines but is a significant contributor to the low-excitation chromospheric lines. We have found exceptions to this rule, however. We find that the G8 star is responsible for a significant portion of Capella's N V lambda lambda 1239, 1243 emission, but is not a large contributor to the S I lambda 1296, Cl I lambda 1352, and O lambda 1356 lines. We suggest possible explanations for these behaviors. We also find evidence that the He II lambda 1640 emission from the G1 star is from the transition region, while the He II lambda 1640 emission from the G8 star is chromospheric, consistent with the findings of Linsky et al. (1994). The C II lambda 1336 line shows a weak central reversal. It is blueshifted by about 9 km/s with respect to the centroid of the emission from the G1 star. While the central reversal of the C II line is blueshifted by about 9 km/s with respect to the centroid of the emission from the G1 star. While the central reversal of the C II line is blueshifted, the central reversal of the Si III lambda 1207 line discussed by Linsky et al. (1994) is not.

Observations of the acceleration regions of OH/IR stars

We have observed 4.6 micrometers fundamental band vibrational absorption lines of (12)CO and (13)CO from six optically obscured OH/IR stars. For each star, the velocities of the CO lines increase steadily with increasing excitation potential. The low-excitation lines have velocities similar to the velocity of the blueshifted component of the 18 cm maser lines of OH. The high-excitation lines have velocities near the stellar velocity as determined by the midpoint of the 18 cm OH lines. The relationship between velocity and excitation potential indicates that the CO lines are formed in the circumstellar region in which the outflow of gas from the star is accelerated from rest to nearly its asymptotic velocity. It should be possible to use models of the formation of the CO lines in OH/IR stars to discover the mechanism or mechanisms which accelerate the gas and initiate mass loss.

Analysis of the 3d[SUP]6[/SUP]4s([SUP]6[/SUP]D)4f-5g supermultiplet of Fe I in laboratory and solar infrared spectra

The combined laboratory and solar analysis of the highly-excited subconfigurations 4f and 5g of Fe I has allowed us to classify 87 lines of the 4f-5g supermultiplet in the spectral region 2545-2585 cm-1. The level structure of these JK-coupled configurations is predicted by semiempirical calculations and the quadrupolic approximation. Semiempirical gf-values have been calculated and are compared to gf values derived from the solar spectrum. The solar analysis has shown that these lines, which should be much less sensitive than lower excitation lines to departures from LTE and to temperature uncertainties, lead to a solar abundance of iron which is consistent with the meteoritic value (A_Fe = 7.51).

Near-infrared imaging of HH 1/2 in shocked molecular hydrogen and (Fe II)

view Abstract Citations (49) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-infrared imaging of HH 1/2 in shocked molecular hydrogen and [Fe II] Davis, Chris J. ; Eisloeffel, Jochen ; Ray, Thomas P. Abstract We report here on near-infrared imaging of the HH 1/2 region in the H2 nu = 1 goes to 0 S(1) (2.121 micrometer) and (Fe II) (1.645 micrometer) lines. These observations reveal in detail the morphology of low and intermediate-velocity shocks in this area. In H2 only the eastern boundary of the HH 1 bow shock is observed, presumably because of an asymmetrical distribution of ambient gas. Diffuse emission is also seen northwest (downstream) of HH 1. The VLA 1 jet is found to be more continuous, but of a similar length compared to that in the optical. A bright H2 knot is found along the jet. Close to, and within, HH 2 we see evidence for the first time of a possible counter jet: in H2 the faint optical tail to the northwest of HH 2 is seen as a series of clumps, while a string of fainter knots runs through HH 2 (and along the outflow axis) toward its southeastern corner. Many of the H2 knots in HH 2 can be identified with corresponding optical knots, though there are clear differences in morphology and relative brightness. In particular their arc-shaped geometry in H2 is indicative of 'minibow shocks' which may result from a collection of 'bullets' within HH 2. Features in the (Fe II) images are in general similar to the brightest optical emission observed in the (S II) lambda lambda 6717, 6731 low-excitation lines. Publication: The Astrophysical Journal Pub Date: May 1994 DOI: 10.1086/187348 Bibcode: 1994ApJ...426L..93D Keywords: Herbig-Haro Objects; Hydrogen Clouds; Infrared Imagery; Iron; Molecular Clouds; Shock Waves; Stellar Mass Ejection; Astronomical Photometry; Astronomical Spectroscopy; Infrared Astronomy; Astronomy full text sources ADS | data products SIMBAD (31)

Ultraviolet observations of selective wind eclipses in Gamma Velorum and evidence for colliding winds

We present a study of high-resolution ultraviolet spectra of the WC8+O9I binary system γ Velorum. The data consist of Copernicus U2 (λλ=912-1450 A) and V2 (λλ=1700-3250 A) spectra secured during two separate binary cycles in 1977 and 1980, together with 40 IUE high-resolution SWP (λλ=1150-2050 A) and 30 LWR (λλ= 1850-3250 A) spectra, secured at many binary phases during six orbital cycles in 1978 and 1979. These data reveal substantial UV spectral variations confined to resonance and low-excitation lines of Si II, Si III, Si IV, C II, C III, C IV, S IV, and Fe IV. These variations are found to be strongly dependent on binary phase and highly repeatable from one binary cycle to another

LSIV -12 deg 111 - A candidate halo proto-planetary nebula

We report on multiwavelength observations of LSIV −12°111, which may be an emerging halo planetary nebula. This object was previously classified as a young emission-line B-type star, but a model atmosphere abundance analysis of high-resolution optical spectra has revealed it to be an evolved object, probably in the postasymptotic giant branch (AGB) evolutionary phase. The presence of an infrared excess and low-excitation nebular emission lines implies that the central star may just have started to photoionize the circumstellar material ejected during the AGB phase. In this paper we discuss the nebular and dust properties of LSIV −12°111 and redetermine some metal abundances for the central star

A spectrophotometric study of the eclipsing nova-like variable V1315 Aquilae

We present photometry and spectroscopy of the nova-like variable V1315 Aquilae. The V-band light curves exhibit deep, symmetrical eclipses which recur with a period of 3.35 hr. The spectra have narrow single-peaked Balmer and HeI emission lines which, due to absorption of low-velocity emission, exhibit a double-peaked structure near the inferior conjunction of the emission line source. The lack of a primary eclipse in the Balmer and HeI lines suggests a non-disc origin for the low-excitation lines

Emission-line CCD imaging of three southern symbiotic stars

Symbiotic stars that are strong radio sources and have cool dust emitting in the infrared are expected to have extended emission nebulae around them. In order to search for such emission nebulae, we have carried out CCD imaging of three symbiotic stars (R Aqr, RR Tel and H1-36) with narrow-band filters centred at the emission lines of [O III] λ5007, Hα λ6563, [N II] λ6584, [S II] λ6717 + 6731. RR Tel and H1-36 images do not show any extended nebulosities around them. The CCD image of the R Aqr nebulosity in the high excitation [O m] line is different from its image in Hα and the low excitation lines of [N II] and [S II] indicating ionization-stratification in the nebula. In H1-36 the optical nebulosity (if it exists) is smaller than ∽2 arcsec while the radio image size is known to be large (∽5 arcsec). This behaviour is opposite to that seen in R Aqr in which the radio emission comes from the core region of a much larger optical nebulosity. Interstellar and/or circumstellar extinctions are suggested to be responsible for this difference

Comments on the observability of coronal variations

We discuss the observable variability of spectral lines in the soft X-ray and XUV region. Rapid variability of coronal emission, both in flaring and non-flaring structures has been reported and is particularly prominent when high spatial resolution is available. Examination of the ionization and recombination time-scales for the formation and removal of ions with prominent solar emission lines shows that, even though ionization equilibrium generally prevails, the observable variability time-scales are often limited by these atomic processes, independent of the physical process which is causing the change in the solar atmosphere. Rapid heating can lead to an initial freezing-in of abundances of some ions; observations of at least one low- and one high-excitation line from such an ion would permit studies of the time evolution of the emission measure and temperature. In a very limited number of cases, rapid cooling leads to freezing-in of the abundance of an ion and observations of a low-excitation line of this ion will not yield accurate information about the thermal evolution. Thus, future observations of Mgx 609 A should be augmented by simultaneous observation at another wavelength, such as 63 A. In addition, with the ability to produce images in isolated spectral lines it becomes possible to select those for which rapid variability is observable, such asOvii, rather than lines which were selected on the basis of previous hardware constraints, such asOvii.