Siek Hyung

The Origin and Evolution of the Halo PN BoBn 1: From a Viewpoint of Chemical Abundances Based on Multiwavelength Spectra

We have performed a comprehensive chemical abundance analysis of the extremely metal-poor ([Ar/H] < ?2) halo planetary nebula (PN) BoBn?1 based on International Ultraviolet Explorer archive data, Subaru/High-Dispersion Spectrograph spectra, VLT/UVES archive data, and Spitzer/IRS spectra. We have detected over 600 lines in total and calculated ionic and elemental abundances of 13 elements using detected optical recombination lines (ORLs) and collisionally excited lines (CELs). The estimations of C, N, O, and Ne abundances from the ORLs and Kr, Xe, and Ba from the CELs are done the first for this nebula, empirically and theoretically. The C, N, O, and Ne abundances from ORLs are systematically larger than those from CELs. The abundance discrepancies apart from O could be explained by a temperature fluctuation model, and that of O might be by a hydrogen-deficient cold component model. We have detected five fluorine and several slow neutron capture elements (the s-process). The amounts of [F/H], [Kr/H], and [Xe/H] suggest that BoBn?1 is the most F-rich among F-detected PNe and is a heavy s-process element rich PN. We have confirmed dust in the nebula that is composed of amorphous carbon and polycyclic aromatic hydrocarbons with a total mass of 5.8 ? 10?6 M ?. The photoionization models built with non-LTE theoretical stellar atmospheres indicate that the progenitor was a 1-1.5 M ? star that would evolve into a white dwarf with an ~0.62 M ? core mass and ~0.09 M ? ionized nebula. We have measured a heliocentric radial velocity of +191.6??1.3?km?s?1 and expansion velocity 2V exp of 40.5?? 3.3?km?s?1 from an average over 300 lines. The derived elemental abundances have been reviewed from the standpoint of theoretical nucleosynthesis models. It is likely that the elemental abundances except N could be explained either by a 1.5 M ? single star model or by a binary model composed of 0.75 M ? + 1.5 M ? stars. Careful examination implies that BoBn?1 has evolved from a 0.75 M ? + 1.5 M ? binary and experienced coalescence during the evolution to become a visible PN, similar to the other extremely metal-poor halo PN, K 648 in M 15.

DUST AND CHEMICAL ABUNDANCES OF THE SAGITTARIUS DWARF GALAXY PLANETARY NEBULA Hen2-436

We have estimated elemental abundances of the planetary nebula (PN) Hen2-436 in the Sagittarius (Sgr) spheroidal dwarf galaxy using ESO/VLT FORS2, Magellan/MMIRS, and Spitzer/IRS spectra. We have detected candidates of fluorine [F II] λ4790, krypton [Kr III] λ6826, and phosphorus [P II] λ7875 lines and successfully estimated the abundances of these elements ([F/H] = +1.23, [Kr/H] = +0.26, [P/H] = +0.26) for the first time. These elements are known to be synthesized by the neutron capture process in the He-rich intershell during the thermally pulsing asymptotic giant branch (AGB) phase. We present a relation between C, F, P, and Kr abundances among PNe and C-rich stars. The detections of these elements in Hen2-436 support the idea that F, P, Kr together with C are synthesized in the same layer and brought to the surface by the third dredge-up. We have detected N II and O II optical recombination lines (ORLs) and derived the N2+ and O2+ abundances. The discrepancy between the abundance derived from the oxygen ORL and that derived from the collisionally excited line is >1 dex. To investigate the status of the central star of the PN, nebula condition, and dust properties, we construct a theoretical spectral energy distribution (SED) model to match the observed SED with CLOUDY. By comparing the derived luminosity and temperature of the central star with theoretical evolutionary tracks, we conclude that the initial mass of the progenitor is likely to be ~1.5-2.0 M ☉ and the age is ~3000 yr after the AGB phase. The observed elemental abundances of Hen2-436 can be explained by a theoretical nucleosynthesis model with a star of initial mass 2.25 M ☉, Z = 0.008, and LMC compositions. We have estimated the dust mass to be 2.9×10–4 M ☉ (amorphous carbon only) or 4.0×10–4 M ☉ (amorphous carbon and polycyclic aromatic hydrocarbon). Based on the assumption that most of the observed dust is formed during the last two thermal pulses and the dust-to-gas mass ratio is 5.58 × 10–3, the dust mass-loss rate and the total mass-loss rate are <3.1×10–8 M ☉ yr–1and <5.5×10–6 M ☉ yr–1, respectively. Our estimated dust mass-loss rate is comparable to a Sgr dwarf galaxy AGB star with similar metallicity and luminosity.

THE DETECTION OF C60 IN THE WELL-CHARACTERIZED PLANETARY NEBULA M1-11

We performed multiwavelength observations of the young planetary nebula (PN) M1-11 and obtained its elemental abundances, dust mass, and the evolutionary status of the central star. The AKARI/IRC, VLT/VISIR, and Spitzer/IRS spectra show features due to carbon-rich dust, such as the 3.3, 8.6, and 11.3 μm features due to polycyclic aromatic hydrocarbons (PAHs), a smooth continuum attributable to amorphous carbon, and the broad 11.5 and 30 μm features often ascribed to SiC and MgS, respectively. We also report the presence of an unidentified broad feature at 16-22 μm, similar to the feature found in Magellanic Cloud PNe with either C-rich or O-rich gas-phase compositions. We identify for the first time in M1-11 spectral lines at 8.5 (blended with PAH), 17.3, and 18.9 μm that we attribute to the C60 fullerene. This identification is strengthened by the fact that other Galactic PNe in which fullerenes are detected have similar central stars, similar gas-phase abundances, and a similar dust composition to M1-11. The weak radiation field due to the relatively cool central stars in these PNe may provide favorable conditions for fullerenes to survive in the circumstellar medium. Using the photoionization code CLOUDY, combined with a modified blackbody, we have fitted the ~0.1-90 μm spectral energy distribution (SED) and determined the dust mass in the nebula to be ~3.5 × 10–4 M ☉. Our chemical abundance analysis and SED model suggest that M1-11 is perhaps a C-rich PN with C/O ratio in the gas phase of +0.19 dex, and that it evolved from a 1-1.5 M ☉ star.

Detection of Fluorine in the Halo Planetary Nebula BoBn 1: Evidence for a Binary Progenitor Star

We have found the fluorine lines [F IV] ??3996.92, 4059.90 in the extremely metal-poor ([Ar/H] = ?2.10 ? 0.21) halo planetary nebula (PN) BoBn 1 in high-dispersion spectra from the 8.2 m VLT UVES archive. Chemical abundance analysis shows that the fluorine abundance is [F/H] = +1.06 ? 0.08, making BoBn 1 the most fluorine-enhanced and metal-poor PN among fluorine-detected PNe and providing new evidence that fluorine is enhanced by nucleosynthesis in low-mass metal-poor stars. A comparison with the abundances of carbon-enhanced metal-poor (CEMP) stars suggests that BoBn 1 shares their origin and evolution with CEMP- s stars such as HE 1305+0132. BoBn 1 might have evolved from a binary consisting of ~2 M? primary and ~0.8 M? secondary stars.

High-dispersion Spectrum of the Halo Planetary Nebula DdDm 1

Using the High Dispersion Spectrograph (HDS) at the Subaru Telescope, we secured the high-resolution line spectra in the 3600-7500 A wavelength range of the Galactic halo planetary nebula DdDm 1. We also analyzed the Hubble Space Telescope Faint Object Spectrograph data in the 1200-6730 A wavelength range. The diagnostic results indicate the electron temperatures of T {sub e}psilonapprox 11,000-14,000 K and the electron number densities of N {sub e}psilonapprox 2000-10,500 cm{sup -3}. In spite of high gaseous temperatures, we have not detected high excitation lines, e.g., He II. We derived abundance based on the ionic concentration of permitted and forbidden lines and the photoionization model. A comparison of the ionic concentrations from forbidden lines to recombination lines shows the abundance discrepancy between them. We tested various possibilities, e.g., temperature fluctuation and high-density blob components, to explain the discrepancy. The high-density components or density fluctuation might be partly responsible for the discrepancy. DdDm 1 shows a low carbon abundance that corresponds to metal-poor stars, [Fe/H] <=-1. Assuming a distance of 10 kpc to DdDm 1, theoretical models suggest that the central star has T {sub eff}approx = 39,000 K and Lapprox = 2000-3000 L {sub sun}. The relatively high gas temperaturesmorexa0» appear to be caused by very low heavy elemental abundances or insufficient coolants in the shell gas. Its progenitor, born in an extremely carbon-poor environment as an initial mass of about 0.9 M {sub sun}, had probably experienced only the first dredge-up.«xa0less

Optical and IUE spectra of the planetary nebula NGC 7026

We investigated spectroscopic data of the extended planetary nebula NGC 7026 in the wavelengths 3700-10,050 A, secured with the Hamilton Echelle Spectrograph at Lick Observatory. This optical wavelength spectrum has been analyzed along with the International Ultraviolet Explorer (IUE) UV spectral data. The diagnostic diagram indicates that the planetary nebula has very complex electron densities of N ~ 3000-10,000 cm-3. The electron temperatures are relatively low: around T = 8000-9500 K, probably as a result of an enhanced heavy elemental cooling. The electron temperature variation also indicates that the low-excitation line region is slightly higher than the high-excitation line regions perhaps as a result of the hardening of escaped UV ionizing photons into the outer shell part of low-excitation lines. We construct a photoionization model, with the central star of the planetary nebula at a temperature of Teff = 80,000 K, to fit most of the relatively strong line intensities and the observed physical conditions. With this photoionization model construction and with a semiempirical ionization correction method, we derived the elemental abundances of the nebula. Compared to the average or normal planetary nebula, most elemental abundances of He, C, N, O, Ne, S, Ar, and Cl appear to be enhanced.

The electron temperature of the inner halo of the Planetary Nebula NGC 6543

We investigate the electron temperature of the inner halo and nebular core regions of NGC 6543, using archival Hubble Space Telescope ( HST ) Wide Field Planetary Camera 2 ( WFPC2 ) images taken through narrow band [Oiii] filters. Balick et al. ([CITE]) showed that the inner halo consists of a number of spherical shells. We find the temperature of this inner halo to be much higher (~15 000 K) than that of the bright core nebula (~8500 K). Photo-ionization models indicate that hardening of the UV radiation from the central star cannot be the main source of the higher temperature in the halo region. Using a radiation hydrodynamic simulation, we show that mass loss and velocity variations in the AGB wind can explain the observed shells, as well as the higher electron temperature.

Fe III emission lines in the optical spectrum of the planetary nebula IC 4997

Relative populations for the 17 fine-structure levels in the 5 D, 3 P, 3 H, 3 F, and 3 G states of the 3d 6 configuration in Fe III, calculated using electron impact excitation rates derived with the R-matrix code, are used to derive theoretical electron temperature and density sensitive emission-line ratios applicable to the spectra of astronomical objects in the 4607-5412 A wavelength range. A comparison of these with high spectral resolution observational data for the planetary nebula IC 4997 reveals generally good agreement between theory and observation. This provides experimental support for the accuracy of the theoretical ratios, and illustrates their usefulness in determining plasma parameters for the Fe III emitting region of a gaseous nebula

SIMULATIONS OF VISCOUS ACCRETION FLOW AROUND BLACK HOLES IN A TWO-DIMENSIONAL CYLINDRICAL GEOMETRY

We simulate shock-free and shocked viscous accretion flow onto a black hole in a two dimensional cylindrical geometry, where initial conditions were chosen from analytical solutions. The simulation code used the Lagrangian Total Variation Diminishing (LTVD) and remap routine, which enabled us to attain high accuracy in capturing shocks and to handle the angular momentum distribution correctly. Inviscid shock-free accretion disk solution produced a thick disk structure, while the viscous shock-free solution attained a Bondi-like structure, but in either case, no jet activity nor any QPO-like activity developed. The steady state shocked solution in the inviscid, as well as, in the viscous regime, matched theoretical predictions well. However, increasing viscosity renders the accretion shock unstable. Large amplitude shock oscillation is accompanied by intermittent, transient inner multiple shocks. Such oscillation of the inner part of disk is interpreted as the source of QPO in hard X-rays observed in micro-quasars. Strong shock oscillation induces strong episodic jet emission. The jets also showed existence of shocks, which are produced as one shell hits the preceding one. The periodicity of jets and shock oscillation were similar. The jets for higher viscosity parameter are evidently stronger and faster.

Photoionization model analysis of the planetary nebula Hu1-2

We have obtained high resolution optical spectra of the planetary nebula Hu 1-2 in the wavelength region of 3700 A-10 050 A, with the Hamilton Echelle Spectrograph (HES) at Lick Observatory. Diagnostic analysis indicates that the nebular gas can be represented by inhomogeneous shells of electron density N� � 4000-10 000 cm −3 , and a gas temperature of 12 000-18 000 K. Using the spherically symmetric photoionization model with appropriate abundances, we tried to accom- modate the observed physical conditions and high electron temperatures. The chemical composition of the nebula was derived from calculations using a photoionization model which predicts the observed IUE, HES and ISO line intensities; and the com- position was then compared to previous determinations. Model analysis confirms the semi-empirically determined abundance derivations carried out in earlier studies. He and N abundances are high, but those of C, O, Ne and S are very low.