Ring Nebula Research Articles

Far-infrared emission from ring nebulae

Ring nebulae are known to form around stars like the Wolf-Rayet and the Of stars. The dust in these nebulae is heated by the central star and, therefore, provides a positive clue to the origin of the nebulae, complementing the optical techniques. A systematic search has been carried out to study the infra-red emission from these nebulae based on the IRAS data. The influence of the local interstellar material properties on the formation of nebular dust is studied.

Imaging Spectrophotometry of the Ring Nebula

We present new results from a program of emission-line imaging spectrophotometry of planetary nebulae using the Ohio State University Imaging Fabry-Perot Spectrograph (IFPS). High-quality emission-line maps of the important diagnostic lines [NII]λλ5755,6583, [SII]λλ6717,6731, [OI]λ6300, [OIII]λ5007, Hα, and Hβ have been obtained. Maps of the ionization structure ([S II]/Hα, [N II]/Hα, [O III]/Hβ, and [O I]/[O III]), temperature in the N+ region, density in the S+ region, and Balmer decrement across the nebula are presented. These show considerable variation in ionization state, temperature and density. This detailed information will provide powerful constraints on photoionization models for the Ring Nebula.

Spatial Variations in UV-Optical Lines Across the Ring Nebula

IUE spectra of the Ring Nebula (M57=NGC 6720) were taken 16–18 May 1991 using the large aperture (10 × 20 arc sec oval) at low dispersion. SWP and LWP spectra of seven locations were acquired at 10 arc sec intervals extending along a PA = 124° line and passing through the central star of the nebula. This direction was such that the long axis of the large aperture was aligned and overlapped, thus enabling the line profiles to be “spliced” together. This provided continuous spatial variation curves at approximately 1 arc sec spatial resolution over the entire diameter (80 arc sec) of the main body of the Ring Nebula.

Spectrophotometry and Multicolour Imagery of the Planetary Nebula Around the P Cygni Star AG Carinae

Some of the high luminosity stars in our Galaxy are surrounded by planetary-like nebulae formed by material ejected from the central star. The most interesting case is that of the ring nebula PK 289-0° 1 around the P Cygni star AG Car. Long slit spectroscopy shows that nitrogen is overabundant and oxygen underabundant in the nebula. The Hα/[NII] ratio is lower in the nebula with respect to the surrounding H II region, possibly as a result of the N overabundance in the stellar wind. The emission line peak separation confirms a model of a distorted spherical shell expanding at 66 km s−1. The scattered star's spectrum is observable near the star, suggesting the presence of circumstellar dust grains. A nebular mass of at least 2.7 M⊙ is derived. While the nebula in the Hα imagery reveals the ring-like shape with many structures, in the blue it is much fainter and smoother. No nebular emission was detected in the JHK bands, suggesting a low dust temperature.

On the chemodynamics of Wolf-Rayet ring nebulae - NGC 6888

A chemodynamical study of the W-R ring nebula NGC 6888 around the WN6 star WR 136 have been made. The observations combine, for the first time, high spatial and spectral resolution covering most of the optical range in different zones of the nebula. The spectra show an emission system with three different velocity components: (1) V(LSR) = -64 km/s, (2) V(LSR) = +78 km/s, and (3) V(LSR) = +18 km/s. Components (1) and (2) correspond to the blue and red-shifted parts of the shell, and (3) is probably associated to the ambient ionized gas

The evolution of circumstellar matter around an isolated massive star during the red supergiant phase - the role of heat conduction

The evolution of circumstellar matter around a massive star during the red supergiant phase is investigated. It is shown that, if heat conduction is present, the cavity carved around the star during its main-sequence phase may deflate substantially and even disappear completely in extreme cases. It is also found that thermal conduction may cause a shrinking of the cavity already during the main-sequence phase; in this case the bubble tends to settle at a smaller radius. How the evolution of Wolf-Rayet ring nebulae and supernova remnants is affected is considered, and particular astronomical objects such as SN 1987A, the Cygnus Loop, N132D and the WR nebula around HD 197406 are discussed

An infrared study of three Wolf-Rayet ring nebulae

view Abstract Citations (40) References (49) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Infrared Study of Three Wolf-Rayet Ring Nebulae Mathis, J. S. ; Cassinelli, J. P. ; van der Hucht, K. A. ; Prusti, T. ; Wesselius, P. R. ; Williams, P. M. Abstract The IRAS colors of the Rolf-Rayet bubble RCW 58 surrounding HD 96548 are studied by analyzing the IRAS survey data with the Groningen Exportable High-Resolution Analysis system and by using the Chopped Photometric Channel high-resolution imaging at 50 microns. The IRAS fluxes of these nebulae at 25, 60, and 100 microns arise from dust emission rather than from atomic emission lines. Because of the low 12-micron fluxes from the bubbles, the emission is calculated on the basis of continuum radiation from dust, rather than emission from the 'unidentified infrared bands' and continuum associated with them. RCW 58 has an uncertain F(100 microns) flux. A simple MRN grain mixture can fit both the R25 and R60 ratios, but the required radiation energy density (100 eV/cu cm) is higher than would be expected for the mean (44 eV/cu cm). The relatively large observed 25-micron fluxes in NGC 6888 and S303 are explained in terms of emission from small grains that are transiently heated to temperatures well above 100 K. The derived mass estimates are quite sensitive to the observed fluxes. Publication: The Astrophysical Journal Pub Date: January 1992 DOI: 10.1086/170863 Bibcode: 1992ApJ...384..197M Keywords: Infrared Astronomy; Nebulae; Wolf-Rayet Stars; Cosmic Dust; Infrared Astronomy Satellite; Interstellar Extinction; Astrophysics; ISM: DUST; EXTINCTION; ISM: INDIVIDUAL ALPHANUMERIC: RCW 58; ISM: INDIVIDUAL ALPHANUMERIC: S308; ISM: INDIVIDUAL NGC NUMBER: NGC 6888; RADIATION MECHANISMS: THERMAL; STARS: WOLF-RAYET full text sources ADS | data products SIMBAD (13)

Ring nebulae around Wolf-Rayet stars in M33

We present the results of a systematic search for H II ring nebulae surrounding Wolf-Rayet (WR) stars in M33. Eleven objects are found to be good candidates, while eight others are classified as possible WR ring nebulae. The WR rings in M33 are larger on average than their galactic counterparts, but the H α luminosity of most of them is comparable to the bright Galactic wind-blown bubbles. The rings are associated with WC as well as with WN stars. No He III region has been detected.

Velocity structure of the ring nebula around supernova 1987A

THE optical fading of supernova 1987A has revealed a parsec-sized nebula glowing in narrow atomic lines. The emission is presumed to come from circumstellar material, shed during the life of the progenitor star, illuminated by the ultraviolet flash from the explosion. This material is the closest to the supernova site that has been detected (apart from some transient radio emission immediately after the explosion1) and therefore represents the youngest pre-supernova structure available for study. Here we report a series of high-resolution spectra of the nebulosity. The hollow, 1.7-arcsec-wide nebula has the velocity field of a ring expanding at 10.3 km s−1, not that of a limb-brightened spheroid. Fainter nebulosity within 3 arcsec is expanding slightly faster, as indicated by redshifted emission from behind the supernova. The geometry of the emission can be used to infer structure, provided that light travel time and recombination delays are accounted for. Our analysis sets an upper limit to the velocity of the wind from the progenitor during its red supergiant (RSG) phase, and implies an RSG lifetime of <4×l05yr and an interval of ∼2×l04yr between the end of the RSG phase and the supernova explosion.

Ring Nebulae Around Massive Stars

Ring nebulae have been found around WR stars, OB and Of stars, and luminous blue variables. Ring nebulae are formed by the interaction between the central stars and their ambient medium via different combinations of stellar winds, ejecta, and radiation. The spectral properties of the nebulae can be used to diagnose the stellar properties, such as luminosity and effective temperature. Correlations between ring nebulae and their central stars may be used to check scenarios of stellar evolution.

Far-infrared observations and the structure of Wolf-Rayet ring nebulae

view Abstract Citations (28) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-Infrared Observations and the Structure of Wolf-Rayet Ring Nebulae Marston, A. P. Abstract Detailed IRAS images of three WR ring nebulae, NGC 2359, RCW 58, and NGC 6888, are analyzed to obtain information on dust and associated gas masses within these nebulae, and these data are used together with kinematical data to derive the form and the structure of the nebulae. The IRAS maps show the presence of FIR emission that appears closely related to the optical shell structures. Calculations of forbidden line emission in the FIR associated with these nebulae suggest that only 8 to 20 percent of the observed FIR emission is due to these lines; the remaining emission is from heated dust. Dust temperatures are typically 33 K, although some high-temperature dust regions were found in the areas of greatest FIR emission. From continuum flux data, it was found that 0.25-1.3 solar mass is associated with the shells as dust, suggesting that their origins must be in the swept-up ISM near the WR stars, which has produced the ring nebulae. Publication: The Astrophysical Journal Pub Date: January 1991 DOI: 10.1086/169550 Bibcode: 1991ApJ...366..181M Keywords: Far Infrared Radiation; Nebulae; Stellar Structure; Wolf-Rayet Stars; Cosmic Dust; Emission Spectra; Infrared Astronomy Satellite; Interstellar Matter; Stellar Evolution; Stellar Winds; Astrophysics; INFRARED: SOURCES; NEBULAE: STRUCTURE; RADIATION MECHANISMS; STARS: WOLF-RAYET full text sources ADS | data products SIMBAD (3)

Ring Nebulae Around of and WO Stars

To understand the origin of WR-rings it is of interest to consider nebulae associated with the precursors of WR stars and with stars at later stages of evolution. The former are represented by numerous Of stars and the latter by only four WO stars which, according to Barlow and Hummer (1982), are the most extreme WR stars near the end of their lives.

The Chemical Composition of the Wolf-Rayet Envelopes

Model-independent information on the chemical composition of WR stars is obtained from the lines of different ions arising at transitions between highly excited energy levels.The chemical composition of WR stars strongly differs from the mean cosmic composition. Nuclear processed CNO products of H-burning are revealed in WN envelopes and He-burning products in WC envelopes. The matter enriched with He and N is also present in some ring nebulae around WN stars.

Abundances in Wolf-Rayet Stars, LBVs and OBN Stars

Current knowledge of the chemical nature of WR stars determined from UV, optical and IR spectral analyses, is reviewed. By number, the H/He ratio is low in most WN stars: 10 ≥ H/He ≥ 0.4 for WNL stars; 3.0 ≥ H/He ≥ 0.0 for WNE stars with most having near zero H-abundances. The C/N ratio in WN stars lies in the range 1–6 × 10−2, whilst N/He ∼10−4 − 4 × 10−3. These abundances for WN stars are broadly consistent with equilibrium CNO-burning products. In WC stars H/He=0 whilst C/He ∼ 0.1 − 0.7 with some evidence for increasing values from WC7 → WC4. N is highly deficient in WC stars, with C/N≥ 60, and for HD 165763 O/C ≤ 0.2 is deduced. In γ Velorum (WC8+O9), IR spectra give a value of Ne/He = 1.0×10-3 (about twice solar). Thus WC abundances are broadly consistent with He-burning products, although the Ne abundance appears lower than predicted. WO stars show C/He ∼ 0.2 − 0.7, and O/He ∼ 0.03 − 0.1, revealing both He-burning and α-capture products. Ring nebulae around several WN stars shown enhanced He and N, consistent with mass loss enrichment expectations from their chemically evolved central stars. Enhanced He (and probably N) is also seen in the atmospheres of several LBVs, OBN and Of stars - potential precursors of, at least, some WN subtypes.

AG Carinae and the WR Phenomenon in Luminous Blue Variables

AG Car is a Luminous Blue Variable which recently evolved from AIe to Ofpe/WN9 in four years at about constant bolometric luminosity, while in the visual the star faded by two magnitudes. This change is probably associated with variable opacity of an unstable massive expanding envelope of a hot star. We discuss the main spectral features of the star and of its ring nebula, and the spectral variations.

The Dynamics of the AG Car Ring Nebula

High spatial (2”) and spectral (7 km s–1) resolution observations of the ring nebula surrounding the LBV star AG Carinae are presented. The data, covering Hα and [NII], were obtained with the UCL echelle spectrograph on the AAT and cover 4 radial slit positions centred on AG Car. The nebular motions are clearly resolved and show that it is a single shell expanding at 70 km s–1 which was ejected from the central star some 7 000 years ago. The data also reveal the presence of a high velocity (~ 83 km s–1) bipolar mass outflow which has distorted the northeastern back edge of the shell.

A Two-Component Dust Model for the Wolf-Rayet Ring Nebula RCW 58

The spectacular ring nebula RCW58 around the Wolf-Rayet star WR40 (HD 96548, WN8) has been observed by the IRAS-Survey instrument and by the IRAS Chopped Photometric Channel (CPC) to study its IR flux and morphology. The survey data were examined with the Groningen Exportable Infra-red High-resolution Analysis system (GEISHA) software, and analysed in terms of line and dust contributions.

On the Chemodynamics of NGC 6888

We present preliminary results on an extensive spectroscopical study of the WR Ring nebula NGC 6888. The observations combine high spatial (1.5 arcsec/pixel) and spectral resolution (30 to 50 km s–1) covering most of the optical range - λλ 3600 to 6800 å- at 3 different slit positions along the major axis of the nebula. The spectra of the central parts give an emission system with three different velocities: a) VLSR=-64 km s–1, b) VLSR=+18 km s–1, and c) VLSR=+78 km s–1. Assuming that NGC 6888 is in fact an expanding bubble of gas, as demonstrated by Marston and Meaburn (1988), we can identify components a) and c) as those moving towards us and receeding parts of the shell, while b) could be related to the ambient interstellar ionized gas outside the bubble. We have isolated the spectrum for each component in order to analyse the ionization structure and excitation mechanism, as well as to derive their physical conditions and chemical abundances. The use of diagnostic diagrams indicates that the nebula is basically photoionized, without any significant contribution of shock excitation in the zones studied. The ambient interstellar component shows a spectrum typical of an H II region with nearly solar abundances. In the case of the bubble components, their spectra produce [N II]/Hα line ratios which are outside the H II region box, and entering the extended planetary nebulae locus, suggesting a contribution of ejected nitrogen in the bubble. This fact is evident from the abundance analysis we have performed, finding that, with respect to the values quoted for the ambient gas, the O/H is deficient by a factor 4, N/H is 2.5 times higher, and helium is enhanced by a factor 2. These quoted values clearly indicate that a substantial fraction of the gas in the bubble is processed material ejected from the central massive star.

Molecular gas in young planetary nebulae

We review our recent results concerning the molecular gas content of young planetary nebulae NGC 2346, M 2–9, and NGC 6720 (the Ring Nebula in Lyra).

High-velocity interstellar gas in the lines of sight to the Wolf-Rayet stars HD 97152 and HD 96548

The interstellar medium was studied in the direction to the WR stars HD 96548 and HD 97152, and the results are reported. New observational data on the UV spectra of several field stars near both these WR stars are presented. The high-velocity gas seen in the spectra of these stars suggests that the detected expanding interstellar gas structure consists of two OB cluster supershells. The presence of high-velocity absorption components in one of five field star spectra in the direction of the more isolated WR star HD 96548 suggests that this expanding gas does not originate from the optical ring nebula RCW 58 surrounding HD 96548, as previously believed, but instead indicates the detection of a previously unknown expanding interstellar shell in this line of sight.