The ISO LWS grating spectrum of NGC 7027 (original) (raw)
Related papers
A Spectral Line Survey of NGC 7027 at Millimeter Wavelengths
The Astrophysical Journal, 2008
We report on a recent spectral line survey of the planetary nebula (PN) NGC 7027 using the Arizona Radio Observatory (ARO) 12 m telescope and the Heinrich Hertz Submillimeter Telescope (SMT) at millimeter wavelengths. The spectra covering the frequency ranges 71-111 GHz, 157-161 GHz, and 218-267 GHz were obtained with a typical sensitivity of rms < 8 mK. A total of 67 spectral lines are detected, 21 of which are identified with 8 molecular species, 32 with recombination lines from hydrogen and helium, and 14 remains unidentified. As the widths of emission lines from CO, other neutral molecules, molecular ions, as well as recombination of H + and He + are found to be different with each other, the line strengths and profiles are used to investigate the physical conditions and chemical processes of the neutral envelope of NGC 7027. The column densities and fractional abundances relative to H 2 of the observed molecular species are calculated and compared with predictions from chemical models. We found evidence for overabundance of N 2 H + and underabundance of CS and HNC in NGC 7027, suggesting that X-ray emission and shock wave may play an important role in the chemistry of the hot molecular envelope of the young PN. Subject headings: ISM: molecules -radio lines: ISM -ISM: abundanceplanetary nebulae: individual (NGC 7027) 1 The 12 m telescope and the Heinrich Hertz Submillimeter Telescope (SMT) is operated by the Arizona Radio Observatory (ARO), Steward Observatory, University of Arizona.
Near-Infrared Unidentified-Line Morphology of the Planetary Nebula NGC 7027
Publications of the Astronomical Society of Japan, 2004
Medium-resolution (R ∼ 500), K-band two-dimensional spectra are presented for the planetary nebula NGC 7027. The spatial distributions for the two bright unidentified lines near 2.199 and 2.287 µm were revealed and examined compared to those of other emission lines. It was spatially confirmed that the unidentified lines do not arise from neutral molecules, but ionized species. The ionization potentials of their parent ions are lower than that of He II, and comparable to or higher than that of Brγ. Our results support the previous studies of identification of parent species, on the condition that the carriers of the unidentified lines are partly excited by collisions.
High resolution near-infrared spectro-imaging of NGC�7027
Astronomy and Astrophysics, 2002
We present near-infrared spectro-imaging of the young planetary nebula NGC 7027 between 2.10 and 2.20 µm with high spatial (0.5 ) and high spectral (8.7 km s −1 ) resolution. The observations, made using BEAR at the CFHT, reveal the detailed morphology and kinematics of the ionized nebula (in the Brγ line and 16 other atomic lines) and the surrounding molecular envelope (in the 1-0 S(1) line of H2). The observations show that the ionized gas forms an elongated (∼6 × 12 , PA = 32 • ), limb-brightened shell with an expansion velocity of 19.5 km s −1 along the line of sight. The shell is composed of numerous small condensations and has nearly parallel sides with flattened ends that are not well matched by a uniform ellipsoidal model. Low level Brγ emission is detected at high red-and blue-shifted velocities (±55 km s −1 ) along a bipolar axis at PA = 60 • that deviates significantly from that of the main nebula. The H2 emission is distributed at the periphery of the ionized gas, in a limb-brightened, bi-conical shell (∼10 × 13 , PA = 28 • ) with enhanced emission at the equator and complex structure at the ends of the major axis. The H2 emission traces the inner edge of the extended molecular envelope seen in CO, and its distribution and intensity are well matched by model predictions of a high-density (nH ∼ 10 6 −10 5 cm −3 ) photo-dissociation region. The kinematic structure of the H2 emission reveals a remarkable series of lobes and openings in the molecular shell. These features are point symmetric about the center, and the most prominent pair aligns with the high velocity, bipolar emission seen in Brγ. These observations demonstrate recent activity by collimated outflows in NGC 7027, with a multiple, bipolar geometry. The interaction of the outflows with the surrounding envelope has significantly affected the morphology of the developing nebula and its environment, and their presence in this well-studied archetype underscores the general importance of outflows in the early shaping history of planetary nebulae.
Optical and mid-infrared observations of the planetary nebula NGC 6781
Monthly Notices of the Royal Astronomical Society, 2011
Although the planetary nebula NGC 6781 appears to possess an elliptical morphology, its kinematic and emission characteristics are in many ways unusual, and it is possible that it may represent a bipolar source oriented close to the line of sight. We shall present deep imaging of this nebula in [O III] λ5007, Hα and [N II] λ6584, and using broad-band (F555W and F814W) filters centred at λ8269 and λ5252. These were taken with the 2.56-m Nordic Optical Telescope and Hubble Space Telescope. This is combined with mid-infrared (MIR) imaging and spectroscopy acquired with the Spitzer Space Telescope (Spitzer), and nearinfrared spectroscopy deriving from the Infrared Space Observatory. These reveal details of the complex [N II] structure associated with extended shell emission, perhaps associated with highly inclined bipolar lobes. We also note the presence of narrow absorbing filaments and clumps projected against the surface of the envelope, components which may be responsible for much of the molecular emission. We point out that such clumps may be responsible for complex source structure in the MIR, and give rise to asymmetries in emission along the major axis of the source. Although most of the MIR H 2 v = 0-0 emission is clearly concentrated in the bright interior shell, we shall also find evidence for extended emission to the north and south, and determine rotational excitation temperatures of order ∼980 K.
Fluorescent H2 Emission Lines from the Reflection Nebula NGC 7023 Observed with IGRINS
The Astrophysical Journal, 2017
We have analyzed the temperature, velocity and density of H 2 gas in NGC 7023 with a high-resolution near-infrared spectrum of the northwestern filament of the reflection nebula. By observing NGC 7023 in the H and K bands at R ≃ 45,000 with the Immersion GRating INfrared Spectrograph (IGRINS), we detected 68 H 2 emission lines within the 1 ′′ × 15 ′′ slit. The diagnostic ratios of 2-1 S(1)/1-0 S(1) is 0.41−0.56. In addition, the estimated ortho-to-para ratios (OPR) is 1.63−1.82, indicating that the H 2 emission transitions in the observed region arises mostly from gas excited by UV fluorescence. Gradients in the temperature, velocity, and OPR within the observed area imply motion of the photodissociation region (PDR) relative to the molecular cloud. In addition, we derive the column density of H 2 from the observed emission lines and compare these results with PDR models in the literature covering a range of densities and incident UV field intensities. The notable difference between PDR model predictions and the observed data, in high rotational J levels of ν = 1, is that the predicted formation temperature for newly-formed H 2 should be lower than that of the model predictions. To investigate the density distribution, we combine pixels in 1 ′′ × 1 ′′ areas and derive the density distribution at the 0.002 pc scale. The derived gradient of density suggests that NGC 7023 has a clumpy structure, including a high clump density of ∼10 5 cm −3 with a size smaller than ∼5 × 10 −3 pc embedded in lower density regions of 10 3 −10 4 cm −3 .
A New Unidentified Far‐Infrared Band in NGC 7027
The Astrophysical Journal, 2004
We report on the detection of a molecular band centered at ∼98 µm (∼102 cm −1), observed with the Infrared Space Observatory 1 in the young Planetary Nebula NGC 7027. The band structure and intensity can not be reproduced by atomic fine structure lines, recombination lines or by the rotational emission of abundant molecules. We discuss the possible contribution of the low-energy bending modes of pure carbon chains to the unidentified far-IR bands observed in C-rich evolved objects. In particular, we speculate that the band emission could arise from the ν 9 and ν 7 bending modes of C 6 and C 5 , for which wavenumbers of 90±50 and 107±5 cm −1 have been estimated from photoelectron spectroscopy.
arXiv (Cornell University), 2022
The young and well-studied planetary nebula NGC 7027 harbors significant molecular gas that is irradiated by luminous, point-like UV (central star) and diffuse (shocked nebular) X-ray emission. This nebula represents an excellent subject to investigate the molecular chemistry and physical conditions within photon-and X-ray-dominated regions (PDRs and XDRs). As yet, the exact formation routes of CO + and HCO + in PN environments remain uncertain. Here, we present ∼2 resolution maps of NGC 7027 in the irradiation tracers CO + and HCO + , obtained with the IRAM NOEMA interferometer, along with SMA CO and HST 2.12 µm H 2 data for context. The CO + map constitutes the first interferometric map of this molecular ion in any PN. Comparison of CO + and HCO + maps reveal strikingly different emission morphologies, as well as a systematic spatial displacement between the two molecules; the regions of brightest HCO + , found along the central waist of the nebula, are radially offset by ∼1 (∼900 au) outside the corresponding CO + emission peaks. The CO + emission furthermore precisely traces the inner boundaries of the nebula's PDR (as delineated by near-IR H 2 emission), suggesting that central star UV emission drives CO + formation. The displacement of HCO + radially outward with respect to CO + is indicative that dust-penetrating soft X-rays are responsible for enhancing the HCO + abundance in the surrounding molecular envelope, forming an XDR. These interferometric CO + and HCO + observations of NGC 7027 thus clearly establish the spatial distinction between the PDR and XDR formed (respectively) by intense UV and X-ray irradiation of molecular gas.
High Dispersion Spectra of the Young Planetary Nebula NGC 7027
Journal of the Korean earth science society, 2015
We investigated the high dispersion spectra that had been secured at the center of the planetary nebula NGC 7027 with the Bohyunsan Optical Echelle Spectrograph (BOES) on October, 20, 2009. We analyzed the forbidden lines of [OI], [SII], [OII], [NII], [ClIII], [ArIII], [OIII], [ArIV], [NeIII], [ArV], and [CaⅤ] in the 3770-9225Å wavelength region. The expansion velocities were derived from double Gaussian line profiles of the emission lines, after eliminating the subsidiary line broadening effects. The radial variations of the expansion velocities were obtained by projecting the derived expansion velocities: 19.56-31.93 kms −1 onto the equatorial shell elements of the inner and the outer boundaries of the main shell of 2.5(2.1)'' and 3.8(3.6)'', according to the ionization potential of each ion. Analysis of equatorial shell spectra indicated that the equatorial shell generally expands in an accelerated velocity mode, but the expansion pattern deviates from a linear velocity growth with radial distance. NGC 7027, of which age is about 1000 years or less, might be still at its early stage. During the first few hundred years, plausibly in its early stage, the main shell of PN expands very slowly and, later, it gradually gain its normal expansion speed.
Discovery of far-IR pure rotational transitions of CH+ in NGC 70271
We report the discovery of the rotational spectrum of CH ϩ in the Infrared Space Observatory Long Wavelength Spectrometer (LWS) spectrum of the planetary nebula NGC 7027. The identification relies on a 1996 reanalysis of the LWS spectrum by Liu et al. and on new LWS data. The strong line at 179.62 m (coinciding with the 2 12 -1 01 transition of water vapor) and the lines at 119.90 and 90.03 m (reported as unidentified by Liu et al.), whose frequencies are in the harmonic relation 2Ϻ3:4, are shown to arise from the J ϭ 2-1, 3-2, and 4 -3 rotational transitions of CH ϩ . This identification is strengthened by the new LWS spectra of NGC 7027, which clearly show the next two rotational lines of CH ϩ at 72.140 and 60.247 m. This is the first time that the pure rotational spectrum of CH ϩ has been observed. This discovery opens the possibility of probing the densest and warmest zones of photodissociation regions. We derive a rotational temperature for the CH ϩ lines of 150 H 20 K and a CH ϩ ͞CO abundance ratio of 2-6 ϫ 10 Ϫ4 . Subject headings: planetary nebulae: individual (NGC 7027) -infrared: ISM: lines and bands FIG. 1.-CH ϩ lines observed in NGC 7027 (the continuum has been subtracted from the data). The solid lines are Gaussian line profile fits to the observed features (for blends, contributions from individual components are shown as dashed lines). The J ϭ 2-1 line at 179.62 m was previously assigned to H 2 O. For the J ϭ 4 -3 line, spectra from two different detectors-LW1 (bottom panel; the sharp rise at short wavelengths is due to the strong [O III] 88.36 m line) and SW5 (upper panel)-are shown. The J ϭ 4 -3 line is blended with the J ϭ 29 -28 line of CO at 90.16 m, which could contribute with an intensity less than 10 Ϫ19 W cm Ϫ2 -the J ϭ 27-26 and J ϭ 26 -25 lines of CO can be seen in the bottom left-hand panel of Fig. 2 with intensities of 110 Ϫ19 W cm Ϫ2 . The lines at 59.5 and 60.7 m in the top left-hand panel are unknown. L66 CERNICHARO ET AL. Vol. 483 L68 CERNICHARO ET AL.
Discovery of Far-Infrared Pure Rotational Transitions of CH[TSUP]+[/TSUP] in NGC 7027
The Astrophysical Journal, 1997
We report the discovery of the rotational spectrum of CH ϩ in the Infrared Space Observatory Long Wavelength Spectrometer (LWS) spectrum of the planetary nebula NGC 7027. The identification relies on a 1996 reanalysis of the LWS spectrum by Liu et al. and on new LWS data. The strong line at 179.62 m (coinciding with the 2 12 -1 01 transition of water vapor) and the lines at 119.90 and 90.03 m (reported as unidentified by Liu et al.), whose frequencies are in the harmonic relation 2Ϻ3:4, are shown to arise from the J ϭ 2-1, 3-2, and 4 -3 rotational transitions of CH ϩ . This identification is strengthened by the new LWS spectra of NGC 7027, which clearly show the next two rotational lines of CH ϩ at 72.140 and 60.247 m. This is the first time that the pure rotational spectrum of CH ϩ has been observed. This discovery opens the possibility of probing the densest and warmest zones of photodissociation regions. We derive a rotational temperature for the CH ϩ lines of 150 H 20 K and a CH ϩ ͞CO abundance ratio of 2-6 ϫ 10 Ϫ4 . Subject headings: planetary nebulae: individual (NGC 7027) -infrared: ISM: lines and bands FIG. 1.-CH ϩ lines observed in NGC 7027 (the continuum has been subtracted from the data). The solid lines are Gaussian line profile fits to the observed features (for blends, contributions from individual components are shown as dashed lines). The J ϭ 2-1 line at 179.62 m was previously assigned to H 2 O. For the J ϭ 4 -3 line, spectra from two different detectors-LW1 (bottom panel; the sharp rise at short wavelengths is due to the strong [O III] 88.36 m line) and SW5 (upper panel)-are shown. The J ϭ 4 -3 line is blended with the J ϭ 29 -28 line of CO at 90.16 m, which could contribute with an intensity less than 10 Ϫ19 W cm Ϫ2 -the J ϭ 27-26 and J ϭ 26 -25 lines of CO can be seen in the bottom left-hand panel of Fig. 2 with intensities of 110 Ϫ19 W cm Ϫ2 . The lines at 59.5 and 60.7 m in the top left-hand panel are unknown. L66 CERNICHARO ET AL. Vol. 483 L68 CERNICHARO ET AL.