Model Line Profiles Research Articles

An unbiased detector of curvilinear structures

The extraction of curvilinear structures is an important low-level operation in computer vision that has many applications. Most existing operators use a simple model for the line that is to be extracted, i.e., they do not take into account the surroundings of a line. This leads to the undesired consequence that the line will be extracted in the wrong position whenever a line with different lateral contrast is extracted. In contrast, the algorithm proposed in this paper uses an explicit model for lines and their surroundings. By analyzing the scale-space behavior of a model line profile, it is shown how the bias that is induced by asymmetrical lines can be removed. Furthermore, the algorithm not only returns the precise subpixel line position, but also the width of the line for each line point, also with subpixel accuracy.

Arcsecond Imaging of CO Emission in the Nucleus of Arp 220

We report high-resolution (1'') imaging of CO (2-1) and dust continuum emission in the ultraluminous galaxy Arp 220. The CO (1-0) line was also imaged at 2'' resolution for comparison. Both data sets recover essentially all of the observed single-dish line emission. Our aperture synthesis maps reveal for the first time, multiple components in the dense gas: peaks corresponding to each of the double nuclei (separated by 095 at P.A. = 101?) seen in the near infrared and radio continuum and a more extended disklike structure at P.A. = 53?, similar to the dust lane seen in optical images. Approximately two-thirds of the total CO emission (and presumably the H2 mass) coincides with the compact double nucleus region. The ISM associated with these nuclear sources is most apparent in the 1.3 mm dust continuum emission, but the brightest CO (2-1) emission is also correlated with the near infrared nuclei and exhibits a radial velocity difference of 250-300 km s-1 between the two nuclei. The latter is in excellent agreement with published near-infrared recombination line measurements. The observed velocity difference between the two nuclei is probably much less than their orbital velocity because the nuclei do not lie along the kinematic major axis of the inner disk. The elongated disk feature exhibits a monotonic velocity gradient parallel to the major axis of the CO intensity distribution with the highest receding velocities in the southwest and the highest approach velocities in the northeast. From the major/minor axis ratio (0.66), we infer that the disk is moderately inclined to the line of sight (i = 40-50?). Detailed modeling of the CO line profiles using a Doppler image-deconvolution technique, analogous to Doppler radar imaging, yields a best-fit CO emissivity distribution and rotation curve which are mutually consistent in the sense that if the total mass distribution follows the CO emissivity, then it yields the derived rotation curve. The implied CO-to-H2 conversion ratio is 0.45 times the Galactic value if the bulk of the mass resides in the molecular gas, rather than stars. This value is also consistent with that expected based on the likely molecular density and temperature in the nuclear disk of Arp 220. The total molecular gas mass for Arp 220 is ~9 ? 109 M? with an uncertainty of ~30% based on the line profile modeling. The peak gas surface density is ~5.8 ? 104 M? pc-2 at 130 pc radius, while the two stellar nuclei are at ~235 pc radius and at position angle midway between the major and minor axes of the gaseous disk. From the profile modeling we derive an intrinsic velocity dispersion in the disk of 90 ? 20 km s-1 and thus a disk thickness (FWHM) of only 16 pc, assuming the disk is in hydrostatic equilibrium. With 5.4 ? 109 M? of molecular gas concentrated in the very thin disk associated with the twin nuclei, the mean density will be nH2${r H}2$ --> 2 ? 104 cm-3 (?30%), a value which is consistent with the strong molecular emission from high dipole moment molecules such as HCN and HCO+. From the high brightness temperatures of the observed CO emission (17-21 K), we conclude that the area filling factor of the disk is very high (0.25) and therefore the gas must fairly uniformly fill the disk, rather than being in discrete self-gravitating clouds. This thin central disk will have inward accretion at 100 M? yr-1 due to viscous and spiral arm transfer of angular momentum. The line profiles at the positions of the double nuclei are double peaked suggesting that there may also be less massive accretion disks associated with each nucleus. The fact that the bulk of the molecular gas has relaxed into a disk with large masses of gas concentrated interior to the double nuclei is consistent with scenarios in which the gas in merging systems settles into the center faster than the two stellar/starburst nuclei. We suggest that dense central accretion disks like that in Arp 220 may be a common feature in the evolution of ultraluminous starburst/AGN galaxies since similar qualitative features are seen in the molecular line data for other systems (e.g., Mrk 231 and NGC 6240).

Rotation of Algol binaries -- a line profile model applied to observations

Rotation of Algol binaries -- a line profile model applied to observations

Results of Detailed Modeling of the Narrow-Line Region of Seyfert Galaxies

We present model line profiles of [O II] lambda3727, [Ne III] lambda3869, [O I] lambda5007, [Fe VII] lambda6087, [Fe X] lambda6374, [O I] lambda6300, H(alpha) lambda6563, and [S 2] lambda6731. The profiles presented here illustrate explicitly the pronounced effects that collisional de-excitation, and that spatial variations in both the ionization parameter and cloud column density, have on Narrow-Line Region (NLR) model profiles. The above effects were included only qualitatively in a previous analytical treatment by Moore and Cohen. By making a direct correspondence between these model profiles and the analytical model profiles of Moore and Cohen, and by comparing with the observed profiles presented in a companion paper and also with those presented elsewhere in the literature, we strengthen some of the conclusions of Moore and Cohen. Most notably, we argue for constant ionization parameter, uniformly accelerated outflow of clouds that are individually stratified in ionization, and the interpretation of emission-line width correlations with ionization potential as a column density effect. For comparison with previous observational studies, such as our own in a companion paper, we also calculate profile parameters for some of the models, and we present and discuss the resulting line width correlations with critical density (n(sub cr)) and Ionization Potential (IP). Because the models we favor are those that produce extended profile wings as observed in high spectral resolution studies, the line width correlations of our favoured models are of particular interest. Line width correlations with n(sub cr) and/or IP result only if the width parameter is more sensitive to extended profile wings than is the Full Width at Half-Maximum (FWHM). Correlations between FWHM and n(sub cr) and/or IP result only after convolving the model profiles with a broad instrumental profile that simulates the lower spectral resolution used in early observational studies. The model in agreement with the greatest number of observational considerations has electron density decreasing outward from n(sub e) approx. equals 10(exp 6)/cu cm to n(sub e) approx. equals 10(exp 2)/cu cm and, due to collisional de-excitation effects in the lowest velocity clouds, it generates broad flat-topped profile peaks in the lines of lowest critical density (e.g., [O II] lambda3727 and [S II] lambda(lambda)6716, 6731). Because the observed profile peaks of both low and high critical density lines are often very similar, our favored model requires a contribution to NLR emission-line spectra from low-velocity, low-density, and low-ionization gas not included in the model NLR.

Goddard-HRS observations of variability in the RS CVn system V711 Tau (HR 1099)

Through examination of line profile asymmetries and their phase-dependent behavior at high-resolution and high S/N we can determine the spatial structure (i.e., size, location, temperature, magnetic field distribution) of atmospheric inhomogeneities on stars other than the Sun (Vogt & Penrod 1983; Walter et al. 1987; Neff et al. 1989). In an effort to simultaneously probe several lines in addition to Mg II we observed the RS CVn V711 Tau (HR 1099, Prot = 2.d8, G5 IV + K1 IV) with the GHRS in the fall of 1993. Ultraviolet observations were obtained with HST's GHRS over a one week interval beginning 1993 September 14. Full details can be found in Dempsey et al. (1996; see also Wood et al. 1995). In this paper we present results of detailed modeling of the the Mg II emission profiles. Line fluxes and profile models for the emission lines were calculated using least-squares gaussian fits as described in Neff et al. (1989).

Modeling Line Profiles of Protostellar Collapse in B335 with the Monte Carlo Method

view Abstract Citations (141) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Modeling Line Profiles of Protostellar Collapse in B335 with the Monte Carlo Method Choi, Minho ; Evans, Neal J., II ; Gregersen, Erik M. ; Wang, Yangsheng Abstract A collapsing dark cloud core, B335, is modeled as an inside-out collapse. The radiative transfer code uses the Monte Carlo method and new collision rates for CS. Line profiles for several observed transitions of CS and H2CO are computed. We confirm that a double-peaked spectrum with a stronger blue peak is a good qualitative signature of infall. Compared to the models using the large velocity gradient method by Zhou et al., our best-fit model using the Monte Carlo method has 20% smaller infall radius, 70% larger CS abundance, and 30% larger H2CO abundance. Also, infall radii found from CS and H2CO agree better than they did in the modeling by Zhou et al. Our model also produces off-center spectra close to the observations. Publication: The Astrophysical Journal Pub Date: August 1995 DOI: 10.1086/176002 Bibcode: 1995ApJ...448..742C Keywords: HYDRODYNAMICS; ISM: GLOBULES; ISM: INDIVIDUAL ALPHANUMERIC: B335; ISM: MOLECULES; METHODS: NUMERICAL; STARS: FORMATION full text sources ADS | data products SIMBAD (1)

Ion temperatures in the Io plasma torus

Observations of the radial dependence of the perpendicular ion temperatures of the four major ion species in the Io plasma torus are reported. Doppler‐resolved forbidden line emissions of S+, S2+, O+, and O2+ were observed within a period of 72 hours on March 3–5 1993, with the 3.6‐m telescope of the European Southern Observatory. The long slit spectra of S+ show a sharp (factor of 4) increase in the perpendicular ion temperature at the position of the “ribbon” where enhanced electron densities and [S II] emission were observed. The observations are broadly consistent with models of line profiles based on average ion temperatures derived from Voyager 1 plasma science data. The signal to noise for the S+ observations was sufficient to reveal two velocity components in the distribution, at 33 and 188 eV, inside Io's orbit. Modeling shows that the two components arise from the superposition of hot outer ions upon a core of cool inner torus ions as a result of line of sight effects. Outside Io's orbit, the temperature of S+ ions was observed to decrease from 120 eV at 6.0 RJ to 80 eV at 6.8 RJ.

The solar Ly-alpha line profile

Solar Ly-alpha irradiance measurements from the SOLar STellar Irradiance Comparison Experiment (SOLSTICE) on the Upper Atmosphere Research Satellite (UARS) have been made since 1991 October with a spectral resolution of 0.1 nm. The uniqueness of the small molecular oxygen cross section near Ly-alpha permits the Ly-alpha radiation to penetrate much deeper into the atmosphere than the other emissions near Ly-alpha. We have taken advantage of this phenomenon by performing solar occultation experiments near the Ly-alpha to evaluate precisely the instrument scattered light contribution. After correcting for scattered light, the broad wings of the solar Ly-alpha line can be extracted out to 5 nm from line center with a typical accuracy of +/-20%. The variability in the Ly-alpha wings near 2 nm from line center is about one-half that of the Ly-alpha core emission, defined within 0.1 nm from line center. These Ly-alpha profile measurements are found to be consistent with the Skylab radiance measurements and theoretical models of the Ly-alpha line profiles computed using partial redistribution of photons in the source function.

Bringing the cross-correlation method up to date

The cross-correlation (XC) method of Tonry & Davis (1979, AJ, 84, 1511) is generalized to arbitrary parametrized line profiles. In the new algorithm the correlation function itself, rather than the observed galaxy spectrum, is fitted by the model line profile: this removes much of the complication in the error analysis caused by template mismatch. Like the Fourier correlation quotient (FCQ) method of Bender (1990, A&A, 229, 441), the inferred line profiles are, up to a normalization constant, independent of template mismatch as long as there are no blended lines. The standard reduced chi(exp 2) is a good measure of the fit of the inferred velocity distribution, largely decoupled from the fit of the spectral template. The updated XC method performs as well as other recently developed methods, with the added virtue of conceptual simplicity.

The sensitivity of Doppler imaging to line profile models

The sensitivity of Doppler imaging to line profile models

Spatial Integration Grids in Line Profile Modelling of Nonradially Pulsating Magnetic Stars

For an optimum grid we postulate a fractional change of the emergent Stokes parameters between two adjacent surface points not to exceed some fixed value (say 20 %) at any frequency point. The contribution from a local Stokes IQUV profile to the observed integrated profile is a complicated non-linear function of rotational and pulsational Doppler shifts respectively, of Zeeman splitting, magnetic field direction relative to the line-of-sight, of the magnetic field azimuth in the observer’s frame and of limb darkening. The run of IQUV with visible disk coordinates (x, y) can be represented by curved surfaces f(x,y); these are different for each Stokes parameter and frequency point. The optimum integration grid then has to ensure that the maximum change δf(x,y) over all frequencies and Stokes parameters does not exceed the above-mentioned limit.

Near-infrared diode laser spectroscopic study of Dicke narrowing and pressure broadening in the oxygen A-band

A near-infrared diode laser spectrometer based on GaAlAs semiconductor diodes is described. Thermally tuned laser radiation is frequency modulated and detected by a silicon photodetector. The signal is obtained by a phase sensitive method. The line shapes of the rovibronic transitions of the oxygen A-band have been measured at pressures varying between 30 and 400 Torr. The line shapes exhibit collisional (Dicke) narrowing which can be reproduced by the simulation of the soft collision model line profile of Galatry (Phys. Rev., 122 (1961) 1218). At higher pressure the line shape exhibits linear pressure broadening.

Kinematic Models of BLR Gas and Line Profiles of HeIλ5876 and Hβ in AGNs

The present paper derives the modified expression of broad emission line profiles for the kinematic model of radiation pressure driving BLR gas outflow in the BLR, and discusses the intrinsic emission difference between the two lines HeIλ5876 and Hβ. It is shown that the fact that the observed line width of HeIλ5876 is broader than that of Hβ cannot be explained by W. G. Mathews modified model. For comparison, line profiles of gravitational infall model and orbital disk model are also calculated; the latter is in good agreement with the observations. Thereupon, conclusion is reached that gravitational infall is an important process in the BLR gas motion.

Line profile modeling for non-LTE partially ionized plasmas based on average atom model with l–splitting

We have developed a new opacity modeling of partially ionized high-Z plasma to solve radiation transport in fluid codes. The average atom model is used to describe the electronic state of the plasma. The electronic state of the plasma is determined by solving the collisional radiative equilibrium model. We have taken into account the electron energy level splitting owing to the difference in the azimuthal quantum number. To model the line groups made of the same electronic transitions from ions indifferent charge states, we used a statistical method and calculated the distribution of the charge states from the averaged electron population in each bound state. By using the new opacity model, we can well reproduce the X-ray spectra from the plasmas. It is found that the Δn = 0 transition can explain the peaked spectra near hv = 300 eV and l–splitted emission of the n = 5–4 transition can explain the flat spectra in the region of hv = 400–800 eV seen in the experiments.

Effect of speed-changing collisions on spectral line shape.

High-resolution inverse Raman experiments for H[sub 2] dilute in Ar [R. L. Farrow [ital et] [ital al]., Phys. Rev. Lett. 63, 746 (1989)] have revealed remarkable deviations from the usual linear mixing rule for the [ital Q]-line broadening. They have been interpreted using a line-profile model that takes into account the spectral narrowing induced by speed-changing collisions. The present approach includes the role of collisions changing both speed and phase, leading to an alternative interpretation of the above-noted experiments. This interpretation generalizes the earlier study and points out the various mechanisms of line formation.

Absolute Measurements of Starspot Area and Temperature

Photometric and spectroscopic variability of late-type stars frequently has been interpreted as evidence of magnetic activity. The standard picture of stellar activity – inherited from solar observations – includes cool, dark “spots” in the photosphere and hot, dense regions in the chromosphere and coronae. The immediate cause of each of these phenomena is a closed topology of the local magnetic field. Because stars appear as mere points of light, these localized phenomena have not been directly resolvable on stars other than the Sun. Most observed effects are produced by an asymmetric distribution of starspots. If the distribution is symmetric, it would escape detection by most current techniques of light-curve and line-profile modeling. Even more troubling, the stellar properties measured with these techniques describe only a difference between contrasting hemispheres, not an absolute measure.

Multi–line Zeeman Analysis

AbstractI present preliminary results of a multi-line Zeeman analysis of the active star ξ Boo A and the inactive star τ Cet. High S/N echelle spectra are compared with LTE model line profiles for 25 Fe I lines to deduce surface magnetic fields.

Setting null limits on pulsation in the twin F0 stars Gamma-Vir N/S

view Abstract Citations (3) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Setting Null Limits on Pulsation in the Twin F0 Stars Gamma VIR N/S Smith, Myron A. Abstract Novel observing and data-reduction methods have been explored to optimize the detection of pulsation modes in rotating stars. The first technique consisted of placing the twin components of the visual binary Gamma Vir on a spectrograph slit and analyzing the differenced radial velocities from the resulting stacked pairs of spectra on a CCD. This procedure was successful only to a point because of thermally imposed differential shifts across the detector with time. The second technique made use of the CLEAN algorithm to analyze time series of intensity fluctuations of pixels on line profiles. This application was quite successful. Provided that simple precautions are taken in data reductions, it is possible to achieve photon-limited performance with a single pixel, and very nearly so for an ensemble of pixels on lines located within the central region of the CCD. Results are calibrated against model line profiles with simulated noise and determine threshold detections for nonradial/radial pulsation modes. Publication: The Astronomical Journal Pub Date: December 1990 DOI: 10.1086/115649 Bibcode: 1990AJ....100.1943S Keywords: Binary Stars; Data Reduction; Hertzsprung-Russell Diagram; Stellar Oscillations; Stellar Rotation; Variable Stars; Charge Coupled Devices; Line Shape; Pixels; Radial Velocity; Astrophysics; STARS: INDIVIDUAL; STARS: PULSATION full text sources ADS | data products SIMBAD (2)

A double-stream model for line profiles

It is shown that gas clouds in a biconical shape may produce profiles similar to those produced in a spherical geometry. The profile shape depends on the radial velocity field, the projection angle, and most importantly, the shell luminosity distribution. If the conical region extends over a large range of radial distances, the resultant profile may be symmetrical with logarithmic wings. It is shown that the double-peaked H-beta profile in Akn 120 can be modeled with a double-stream model. 26 refs.

Observation of a speed-dependent collisional inhomogeneity in H2 vibrational line profiles.

We report observations of inhomogeneous broadening of the vibrational line profiles of a gas in the "impact" density regime. In measurements up to 27 amagat (where the spectra are dominated by collision broadening), non-Lorentzian, asymmetric features are observed in Raman $Q$-branch transitions of ${\mathrm{H}}_{2}$ dilute in a heavy perturber gas. We compare these measurements with an inhomogeneous line-profile model based on collisional shifts that strongly depend on the (thermal) speed of the ${\mathrm{H}}_{2}$ radiator. Quantitative agreement is obtained only when speed-changing collisions are considered, which result in spectral line narrowing.