arXiv subjects

Hee-Won Lee

Publications and source records attributed to Hee-Won Lee.

At least 19 recordsLinked to original sources

arXiv2026

Tracing Warm Gas through C IV Radiative Transfer

The C IV $\lambda\lambda1548,1551$ resonance doublet is a key tracer of warm gas ($T\sim10^5\,{\rm K}$) within and around galaxies. Recent observations have detected this line in both absorption and emission, revealing asymmetric profiles in galaxies and spatially extended haloes around active galactic nuclei (AGNs). Resonance scattering can strongly modify the emergent spectra and spatial distributions, complicating their interpretation. Using 3D Monte Carlo radiative transfer simulations, we study C IV resonance scattering over a broad range of column densities, intrinsic emission-line widths, and outflow velocities. We find that multiple scattering broadens the line profile and, in outflowing media, modifies the doublet ratio, $R_{\rm CIV}$, defined as the flux ratio of the K and H components at 1548 and 1551 $\mathrm{\mathring{A}}$, respectively. When the outflow velocity approaches or exceeds the doublet separation ($\simeq500\,{\rm km\,s^{-1}}$), K-line photons are redistributed around the H component, driving $R_{\rm CIV}$ below its intrinsic value and, in optically thick fast outflows, even below unity. We also combine photoionization models with resonance scattering to investigate extended C IV haloes around AGNs and compare them with He II $\lambda1640$ emission. Simple photoionization models do not produce C IV emission more extended than He II, whereas resonance scattering redistributes locally produced and central-source C IV photons to larger radii. These results demonstrate that the C IV doublet ratio and spatial distribution provide complementary diagnostics of warm gas.

astro-ph.GA↗

arXiv2026

High-Resolution Spectroscopy of Raman-scattered He II Lines in the Symbiotic Nova RR Telescopii

Raman-scattered emission features in symbiotic stars provide a powerful diagnostic of mass-loss and transfer processes, as they uniquely probe both ionized and neutral regions within interacting binaries. When resolved with high-resolution spectroscopy, these features encode detailed information on the physical properties of the neutral hydrogen medium. In this work, we present high-resolution spectroscopic observations of the symbiotic nova RR Telescopii obtained with FEROS in 2004 and GHOST in 2024, providing a $\sim$ 20 yr baseline. We report the clear detection of all three Raman-scattered He II lines at 6545 {\AA}, 4851 {\AA}, and 4332 {\AA}, and constrain the distribution and kinematics of H I through line profile analysis. The three Raman lines exhibit distinct relative velocities, indicating that they trace different depths within the H I region. The Raman conversion efficiencies of the three Raman He II lines in 2024 are significantly lower than those in 2004, indicating substantial changes in the physical properties of the neutral hydrogen region. In addition, radiative transfer modeling implies a larger covering factor (opening angle) of the neutral region in 2004 than in 2024. These results indicate that the neutral hydrogen region cannot be characterized by a single H I column density, emphasizing the need for advanced radiative transfer modeling that accounts for the complex kinematics and geometry of the H I region. Overall, these results establish Raman-scattered He II lines as a powerful tool for spectroscopic tomography, allowing for direct constraints on the structure and kinematics of neutral hydrogen in symbiotic binaries.

astro-ph.SR↗

arXiv2025

High Resolution {\it BOES} Spectroscopy of Raman-scattered He~II$λ$6545 in Young Planetary Nebulae

Young planetary nebulae (PNe) are characterized by their hot central stars and the presence of abundant neutral and molecular components, which result from significant mass loss during the asymptotic giant branch (AGB) phase of stellar evolution. Far-UV \ion{He}{2}$λ$1025 line photons produced near the central star can undergo Raman scattering by hydrogen atoms, creating a broad emission feature centered at $\sim$ 6545~Å. We conducted high-resolution spectroscopy of 12 young PNe from April 2019 to March 2020 using the Bohyunsan Observatory Echelle Spectrograph ({\it BOES}). Building on the study by Choi and Lee, who identified Raman-scattered \ion{He}{2} at 6545~Å in NGC~6881 and NGC~6886, we report new detections of this feature in NGC~6741 and NGC~6884. Profile fitting reveals that the velocity of the \ion{H}{1} component relative to the \ion{He}{2} emission region ranges from $26-33~{\rm km~s^{-1}}$ in these PNe. Using photoionization modeling, we estimate the line flux of \ion{He}{2}$λ$1025 and derive Raman conversion efficiencies of 0.39, 0.21, 0.24, and 0.07 for NGC~6881, NGC~6741, NGC~6886, and NGC~6884, respectively. These results, combined with radiative transfer modeling, suggest the presence of \ion{H}{1} components with masses around $10^{-2}~M_\odot$, moving outward from the central \ion{He}{2} emission region at speeds characteristic of the slow stellar wind from a mass-losing giant star.

astro-ph.SR↗

arXiv2023

Distribution and Kinematics of H I through Raman He II Spectroscopy of NGC 6302

The young planetary nebula NGC 6302 is known to exhibit Raman-scattered He II features at 6545 and 4851 Angstrom. These features are formed through inelastic scattering of He II$λλ$ 1025 and 972 with hydrogen atoms in the ground state, for which the cross sections are $1.2 \times 10^{-21}$ and $1.4\times 10^{-22} {\rm\ cm^2}$, respectively. We investigate the spectrum of NGC 6302 archived in the ESO Science Portal. Our Gaussian line fitting analysis shows that the Raman-scattered He II features are broader and more redshifted than the hypothetical model Raman features that would be formed in a cold static H I medium. We adopt a simple scattering geometry consisting of a compact He II emission region surrounded by a H I medium to perform Monte Carlo simulations using the radiative transfer code ${\it STaRS}$. Our simulations show that the H I region is characterized by the H I column density $N_{\rm HI}=3\times 10^{21}{\rm\ cm^{-2}}$ with the random speed component $v_{\rm ran}=10{\rm\ km\ s^{-1}}$ expanding with a speed $v_{\rm exp}= 13{\rm\ km\ s^{-1}}$ from the He II emission region. Based on our best fit parameters, we estimate the H I mass of the neutral medium $M_{\rm HI} \simeq 1.0\times 10^{-2}\ {\rm M_\odot}$, pointing out the usefulness of Raman He II spectroscopy as a tool to trace H I components.

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arXiv2022

Radiative Transfer in Lyα Nebulae: I. Modeling a Continuous or Clumpy Spherical Halo with a Central Source

To understand the mechanism behind high-$z$ Ly$α$ nebulae, we simulate the scattering of Ly$α$ in a $\rm H\,I$ halo about a central Ly$α$ source. For the first time, we consider both smooth and clumpy distributions of halo gas, as well as a range of outflow speeds, total $\rm H\,I$ column densities, $\rm H\,I$ spatial concentrations, and central source galaxies (e.g., with Ly$α$ line widths corresponding to those typical of AGN or star-forming galaxies). We compute the spatial-frequency diffusion and the polarization of the Ly$α$ photons scattered by atomic hydrogen. Our scattering-only model reproduces the typical size of Ly$α$ nebulae ($\sim 100\,$kpc) at total column densities $N_{\rm HI} \geq 10^{20} \rm cm^{-2}$ and predicts a range of positive, flat, and negative polarization radial gradients. We also find two general classes of Ly$α$ nebula morphologies: with and without bright cores. Cores are seen when $N_{\rm HI}$ is low, i.e., when the central source is directly visible, and are associated with a polarization jump, a steep increase in the polarization radial profile just outside the halo center. Of all the parameters tested in our smooth or clumpy medium model, $N_{\rm HI}$ dominates the trends. The radial behaviors of the Ly$α$ surface brightness, spectral line shape, and polarization in the clumpy model with covering factor $f_c \gtrsim 5$ approach those of the smooth model at the same $N_{\rm HI}$. A clumpy medium with high $N_{\rm HI}$ and low $f_c \lesssim 2$ generates Ly$α$ features via scattering that the smooth model cannot: a bright core, symmetric line profile, and polarization jump.

astro-ph.GA↗

arXiv2022

Formation of the Asymmetric Accretion Disk from Stellar Wind Accretion in an S-type Symbiotic Star

The accretion process in a typical S-type symbiotic star, targeting~AG Draconis, is investigated through 3D hydrodynamical simulations using the FLASH code. Regardless of the wind velocity of the giant star, an accretion disk surrounding the white dwarf is always formed. In the wind models faster than the orbital velocity of the white dwarf, the disk size and accretion rate are consistent with the predictions under the Bondi-Hoyle-Lyttleton (BHL) condition. In slower wind models, unlike the BHL predictions, the disk size does not grow and the accretion rate increases to a considerably higher level, up to $>20\%$ of the mass-loss rate of the giant star. The accretion disk in our fiducial model is characterized by a flared disk with a radius of 0.16~au and a scale height of 0.03 au. The disk mass of $\sim 5 \times 10^{-8} M_\odot$ is asymmetrically distributed with the density peak toward the giant star, being about $50\%$ higher than the density minimum in the disk. Two inflowing spiral features are clearly identified and their relevance to the azimuthal asymmetry of disk is pointed out. The flow in the accretion disk is found to be sub-Keplerian with about $90\%$ of the Keplerian speed, which indicates the caveat of overestimating the O VI emission region from spectroscopy of Raman-scattered O VI features at 6825 Å and 7082 Å.

astro-ph.SR↗

arXiv2021

Raman-scattered O VI features in the symbiotic nova RR Telescopii

RR Tel is an interacting binary system in which a hot white dwarf (WD) accretes matter from a Mira-type variable star via gravitational capture of its stellar wind. This symbiotic nova shows intense Raman-scattered O VI 1032Å and 1038Å features at 6825Å and 7082Å. We present high-resolution optical spectra of RR Tel taken in 2016 and 2017 with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph at Magellan-Clay telescope, Chile. We aim to study the stellar wind accretion in RR Tel from the profile analysis of Raman O VI features. With an asymmetric O VI disk model, we derive a representative Keplerian speed of $> 35{\rm km~s^{-1}}$, and the corresponding scale < 0.8 au. The best-fit for the Raman profiles is obtained with a mass loss rate of the Mira ${\dot M}\sim2\times10^{-6}~{\rm M_{\odot}~yr^{-1}}$ and a wind terminal velocity $v_{\infty}\sim 20~{\rm km~s^{-1}}$. We compare the MIKE data with an archival spectrum taken in 2003 with the Fibre-fed Extended Range Optical Spectrograph (FEROS) at the MPG/ESO 2.2m telescope. It allows us to highlight the profile variation of the Raman O VI features, indicative of a change in the density distribution of the O VI disk in the last two decades. We also report the detection of O VI recombination lines at 3811Å and 3834Å, which are blended with other emission lines. Our profile decomposition suggests that the recombination of O VII takes place nearer to the WD than the O VI 1032Å and 1038Å emission region.

astro-ph.SR↗

arXiv2020

3D Grid-Based Monte Carlo Code for Radiative Transfer through Raman and Rayleigh Scattering with Atomic Hydrogen -- STaRS

Emission features formed through Raman scattering with atomic hydrogen provide unique and crucial information to probe the distribution and kinematics of a thick neutral region illuminated by a strong far UV emission source. We introduce a new 3 dimensional Monte-Carlo code in order to describe the radiative transfer of line photons that are subject to Raman and Rayleigh scattering with atomic hydrogen. In this code entitled "${\bf S}$ejong Radiative ${\bf T}$r${\bf a}$nsfer through ${\bf R}$aman and Rayleigh ${\bf S}$cattering (${\it STaRS}$), each photon is traced until escape with a tag attached carrying information including the position, direction, wavelength, and polarization. The thick neutral scattering region is divided into numerous cells with each cell being characterized by its velocity and density, which ensures huge flexibility of the code in analyzing Raman-scattered features formed in a neutral region with complicated kinematics and density distribution. As a test of the code, we revisit the formation of Balmer wings through Raman scattering of far UV continuum near Ly$β$ and Ly$γ$ in a static neutral region. An additional check is made to investigate Raman scattering of O VI in an expanding neutral medium. We find fairly good agreement of our results with previous works, demonstrating the capability of dealing with radiative transfer modeling that can be applied to spectropolarimetric imaging observations of various objects including symbiotic stars, young planetary nebulae, and active galactic nuclei.

astro-ph.SR↗

arXiv2020

Discovery of Raman-scattered He II $λ$6545 in the Planetary Nebulae NGC 6886 and NGC 6881

Young planetary nebulae (PNe) retain a large amount of neutral material that was shed in the previous asymptotic giant branch stage. The thick H I region in young PNe can be effectively probed by illuminating far UV radiation that may be inelastically scattered to appear in the optical region. Raman-scattered features are unique spectroscopic tracers of neutral regions that can be used to investigate the mass-loss process in young PNe. We conduct high resolution spectroscopy of young PNe using BOES (the Bohyunsan Observatory Echelle Spectrograph) and report the discovery of a Raman-scattered He II feature at 6545 Å in NGC 6886 and NGC 6881. The Raman-scattered He II features have been found in only five PNe so far, and, in particular, it is the first direct detection of an H I component in NGC 6881. The Raman He II $λ6545$ features in the two PNe are observed to be redshifted with respect to He II $\lambda6560$, indicating that the neutral regions are expanding. We perform line profile analyses using the grid-based Monte Carlo code 'STaRS' by assuming a neutral hydrogen region in the shape of a partial spherical shell expanding radially. The profiles are well fitted with the model parameters of covering factor $CF=0.3$, H I column density $N_{\rm HI} = 5 \times 10^{20}~{\rm cm^{-2}}$, and expansion speed $v_{\rm exp} = 25~\rm\ km~s^{-1}$ for NGC 6886 and $CF=0.6$, $N_{\rm HI} = 3 \times 10^{20}~{\rm cm^{-2}}$, and $v_{\rm exp} = 30\rm\ km~s^{-1}$ for NGC 6881, respectively.

astro-ph.SR↗

arXiv2019

Line Formation of Raman-Scattered He II $λ$ 4851 in an Expanding Spherical H I Shell in Young Planetary Nebulae

We investigate line formation of Raman-scattered He II at 4851 in an expanding neutral spherical shell that surrounds a point-like He II source located at the center. A new grid-based Monte Carlo code is used to take into consideration the H I density variation along each photon path. In the case of a monochromatic He II emission source, the resultant line profiles are characterized by an asymmetric double peak structure with a tertiary peak and a significant red tail that may extend to line centers of He II$λ$4859 and H$β$. The peak separation corresponds to the expansion velocity, which we consider is in the range $20-40{\rm\ km\ s^{-1}}$ in this work. Tertiary red peaks are formed as a result of multiple Rayleigh reflections at the inner surface of a hollow spherical shell of \ion{H}{1}. Due to a sharp increase of scattering cross section near resonance, the overall Raman conversion efficiency is significantly enhanced as the expansion speed increases. In the case of a He II line source with a Gaussian line profile with a full width at half maximum of $30 - 70{\rm\ km\ s^{-1}}$, we obtain distorted redward profiles due to increasing redward cross section of H I. A simple application to the young planetary nebula IC 5117 is consistent with a neutral shell expanding with a speed $\sim 30{\rm\ km\ s^{-1}}$.

astro-ph.SR↗

arXiv2019

Stellar Wind Accretion and Raman Scattered O VI Features in the Symbiotic Star AG Draconis

We present high resolution spectroscopy of the yellow symbiotic star AG Draconis with ESPaDOnS at the {\it Canada-France-Hawaii Telescope}. Our analysis is focused on the profiles of Raman scattered \ion{O}{VI} features centered at 6825 Å and 7082 Å, which are formed through Raman scattering of \ion{O}{VI}$λλ$1032 and 1038 with atomic hydrogen. These features are found to exhibit double component profiles with conspicuously enhanced red parts. Assuming that the \ion{O}{vi} emission region constitutes a part of the accretion flow around the white dwarf, Monte Carlo simulations for \ion{O}{VI} line radiative transfer are performed to find that the overall profiles are well fit with the accretion flow azimuthally asymmetric with more matter on the entering side than on the opposite side. As the mass loss rate of the giant component is increased, we find that the flux ratio $F(6825)/F(7082)$ of Raman 6825 and 7082 features decreases and that our observational data are consistent with a mass loss rate $\dot M\sim 2 \times 10^{-7} {\rm\ M_{\odot}\ yr^{-1}}$. We also find that additional bipolar components moving away with a speed $\sim 70{\rm\ km\ s^{-1}}$ provide considerably improved fit to the red wing parts of Raman features. The possibility that the two Raman profiles differ is briefly discussed in relation to the local variation of the \ion{O}{VI} doublet flux ratio.

astro-ph.SR↗

arXiv2018

Broad Wings around H$α$ and H$β$ in the Two S-Type Symbiotic Stars Z Andromedae and AG Draconis

Symbiotic stars often exhibit broad wings around Balmer emission lines, whose origin is still controversial. We present the high resolution spectra of the S type symbiotic stars Z Andromedae and AG Draconis obtained with the ESPaDOnS and the 3.6 m Canada France Hawaii Telescope to investigate the broad wings around H$α$ and H$β$. When H$α$ and H$β$ lines are overplotted in the Doppler space, it is noted that H$α$ profiles are overall broader than H$β$ in these two objects. Adopting a Monte Carlo approach, we consider the formation of broad wings of H$α$ and H$β$ through Raman scattering of far UV radiation around Ly$β$ and Ly$γ$ and Thomson scattering by free electrons. Raman scattering wings are simulated by choosing an H I region with a neutral hydrogen column density $N_{HI}$ and a covering factor $CF$. For Thomson wings, the ionized scattering region is assumed to cover fully the Balmer emission nebula and is characterized by the electron temperature $T_e$ and the electron column density $N_e$. Thomson wings of H$α$ and H$β$ have the same width that is proportional to $T_e^{1/2}$. However, Raman wings of H$α$ are overall three times wider than H$β$ counterparts, which is attributed to different cross section for Ly$β$ and Ly$γ$. Normalized to have the same peak values and presented in the Doppler factor space. H$α$ wings of Z And and AG Dra are observed to be significantly wider than H$β$ counterpart, favoring the Raman scattering origin of broad Balmer wings.

astro-ph.SR↗

arXiv2018

Escape of Resonantly Scattered Ly$β$ and H$α$ from Hot and Optically Thick Media

We investigate the escape of Ly$β$ from emission nebulae with a significant population of excited hydrogen atoms in the level $n=2$, rendering them optically thick in H$α$. The transfer of Ly$β$ line photons in these optically thick regions is complicated by the presence of another scattering channel leading to re-emission of H$α$, alternating their identities between Ly$β$ and H$α$. In this work, we develop a Monte Carlo code to simulate the transfer of Ly$β$ line photons incorporating the scattering channel into H$α$. Both H$α$ and Ly$β$ lines are formed through diffusion in frequency space, where a line photon enters the wing regime after a fairly large number of resonance scatterings with hydrogen atoms. Various line profiles of H$α$ and Ly$β$ emergent from our model nebulae are presented. It is argued that the electron temperature is a critical parameter which controls the flux ratio of emergent Ly$β$ and H$α$. Specifically for $T=3 \times 10^4{\rm\ K}$ and H$α$ line center optical depth $τ_α=10$, the number flux ratio of emergent Ly$β$ and H$α$ is $\sim 49$ percent, which is quite significant. We propose that the leaking Ly$β$ can be an interesting source for the formation of H$α$ wings observed in many symbiotic stars and active galactic nuclei. Similar broad H$α$ wings are also expected in Ly$α$ emitting halos found in the early universe, which can be potentially probed by the {\it James Webb Telescope} in the future.

astro-ph.HE↗

arXiv2016

Polarization of Rayleigh scattered Lyα in active galactic nuclei

The unification scheme of active galactic nuclei (AGNs) invokes an optically thick molecular torus component hiding the broad emission line region. Assuming the presence of a thick neutral component in the molecular torus characterized by a \ion{H}{I} column density > $10^{22}{\rm\ cm^{-2}}$, we propose that far UV radiation around Ly$α$ can be significantly polarized through Rayleigh scattering. Adopting a Monte Carlo technique we compute polarization of Rayleigh scattered radiation near Ly$α$ in a thick neutral region in the shape of a slab and a cylindrical shell. It is found that radiation near Ly$α$ Rayleigh reflected from a very thick slab can be significantly polarized in a fairly large range of wavelength $Δλ\sim 50$ Å exhibiting a flux profile similar to the incident one. Rayleigh transmitted radiation in a slab is characterized by the central dip with a complicated polarization behavior. The optically thick part near Ly$α$ center is polarized in the direction perpendicular to the slab normal, which is in contrast to weakly polarized wing parts in the direction parallel to the slab normal. A similar polarization flip phenomenon is also found in the case of a tall cylindrical shell, in which the spatial diffusion along the vertical direction near the inner cylinder wall for core photons leads to a tendency of the electric field aligned to the direction perpendicular to the vertical axis. Observational implications are briefly discussed including spectropolarimetry of the quasar PG~1630+377 by Koratkar et al. in 1990 where Ly$α$ is strongly polarized with no other emission lines polarized.

astro-ph.GA↗

arXiv2016

A Monte Carlo Study of Flux Ratios of Raman Scattered O~VI Features at 6825 Å and 7082 Å in Symbiotic Stars

Symbiotic stars are regarded as wide binary systems consisting of a hot white dwarf and a mass losing giant. They exhibit unique spectral features at 6825 Å and 7082 Å, which are formed via Raman scattering of \ion{O}{6}$λλ$ 1032 and 1038 with atomic hydrogen. We adopt a Monte Carlo technique to generate the same number of \ion{O}{6}$λ$1032 and $λ$1038 line photons and compute the flux ratio $F(6825)/F(7082)$ of these Raman scattered \ion{O}{6} features formed in neutral regions with a simple geometric shape as a function of \ion{H}{1} column density $N_{HI}$. In cylindrical and spherical neutral regions with the \ion{O}{6} source embedded inside, the flux ratio $F(6825)/F(7082)$ shows an overall decrease from 3 to 1 as $N_{HI}$ increases in the range $10^{22-24}{\rm\ cm^{-2}}$. In the cases of a slab geometry and other geometries with the \ion{O}{6} source outside the \ion{H}{1} region, Rayleigh escape operates to lower the flux ratio considerably. For moderate values of $N_{HI}\sim 10^{23}{\rm\ cm^{-2}}$ the flux ratio behaves in a complicated way to exhibit a broad bump with a peak value of 3.5 in the case of a sphere geometry. We find that the ratio of Raman conversion efficiencies of \ion{O}{6}$λλ$1032, 1038 ranges from 0.8 to 3.5. Our high resolution spectra of 'D' type HM~Sge and 'S' type AG~Dra obtained with the {\it Canada-France-Hawaii-Telescope} show that the flux ratio $F(6825)/F(7082)$ of AG~Dra is significantly smaller than that of HM~Sge, implying that 'S' type symbiotics are characterized by higher $N_{HI}$ than 'D' type symbiotics.

astro-ph.SR↗

arXiv2016

A Profile Analysis of Raman-scattered O VI Bands at 6825 Å and 7082 Å in Sanduleak's Star

We present a detailed modeling of the two broad bands observed at 6825 Å and 7082 Å in Sanduleak's star, a controversial object in the Large Magellanic Cloud. These bands are known to originate from Raman-scattering of O VI $λλ$ 1032 and 1038 photons with atomic hydrogen and are only observed in bona fide symbiotic stars. Our high-resolution spectrum obtained with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph at the Magellan-Clay Telescope reveals, quite surprisingly, that the profiles of the two bands look very different: while the Raman 6825 Å band shows a single broad profile with a redward extended bump, the Raman 7082 Å band exhibits a distinct triple-peak profile. Our model suggests that the O VI emission nebula can be decomposed into a red, blue and central emission regions from an accretion disk, a bipolar outflow and a further compact, optically thick region. We also perform Monte Carlo simulations with the aim of fitting the observed flux ratio $F(6825)/F(7082) \sim 4.5$, which indicate that the neutral region in Sanduleak's star is characterized by the column density $N_{HI} \sim 1 \times 10^{23} {\rm\ cm^{-2}}$.

astro-ph.SR↗

arXiv2015

Formation of Raman Scattering Wings around H alpha, H beta and Pa alpha in Active Galactic Nuclei

Powered by a supermassive black hole with an accretion disk, the spectra of active galactic nuclei (AGNs) are characterized by prominent emission lines including Balmer lines. The unification schemes of AGNs require the existence of a thick molecular torus that may hide the broad emission line region from the view of observers near the equatorial direction. In this configuration, one may expect that the far UV radiation from the central engine can be Raman scattered by neutral hydrogen to reappear around Balmer and Paschen emission lines which can be identified with broad wings. We produce H$α$, H$β$ and Pa$α$ wings using a Monte Carlo technique to investigate their properties. The neutral scattering region is assumed to be a cylindrical torus specified by the inner and outer radii and the height. While the covering factor of the scattering region affects the overall strengths of the wings, the wing widths are primarily dependent on the neutral hydrogen column density $N_{\rm HI}$ being roughly proportional to $N_{\rm HI}^{1/2}$. In particular, with $N_{\rm HI}=10^{23}{\rm\ cm^{-2}}$ the H$α$ wings typically show a width $\sim 2\times 10^4{\rm\ km\ s^{-1}}$. We also find that H$α$ and Pa$α$ wing profiles are asymmetric with the red part stronger than the blue part and an opposite behavior is seen for H$β$ wings.

astro-ph.GA↗

arXiv2014

Raman Scattered Ne VII$λ$973 at 4881 Å in the Symbiotic Star V1016 Cygni

We present the high resolution spectra of the symbiotic star V1016 Cygni obtained with the Bohyunsan Optical Echelle Spectrograph in 2003 and 2005, from which we find a broad emission feature at 4881 Å. We propose that this broad feature is formed from Raman scattering of Ne VII$\lambda973$ by atomic hydrogen. Thus far, the detection of Raman scattered lines by atomic hydrogen is limited to O VI$λλ$1032, 1038 and He II$λλ$940, 972 and 1025. With the adoption of the center wavelength 973.302 Å of Ne VII$λ$973 and consideration of the air refractive index of $n_{air}=1.000279348$, the atomic line center of the Raman scattered Ne VII feature is determined to be 4880.53 Å. The total cross section at the line center of Ne VII$\lambda973$ is computed to be $2.62\times 10^{-22}{\rm\ cm^2}$ with the branching ratio of 0.17. We perform Monte Carlo simulations to fit the Raman scattered Ne VII$\lambda973$. Assuming that the Ne VII and He II emission regions share the same kinematics with respect to the neutral scattering region, we find that the Raman scattered He II$λ$972 at 4850 Å and Ne VII$λ$973 at 4881 Å are excellently fitted. We also propose that the He II and Ne VII emission regions were stationary with respect to the H I region in 2003 but that they were receding from it with a velocity $\sim 20{\rm\ km\ s^{-1}}$ in 2005.

astro-ph.SR↗