Low-excitation Planetary Nebula Research Articles

FAST Search for Circumstellar Atomic Hydrogen. II. Is BD+30°3639 an Interacting Planetary Nebula?

The young, compact, very high surface brightness but low excitation planetary nebula (PN) BD+30°3639 is one of the very few PNe that have been reported to exhibit the 21 cm H i emission line. As part of a long-term program to search for circumstellar atomic hydrogen, we observed the 21 cm feature toward BD+30°3639 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Assuming a direct association between the PN and the detected H i emission, these new observations show that this surrounding emission is significantly more spatially extended than indicated by previous interferometric observations and can be resolved into two velocity components. The estimated H i mass is larger than 100 M ⊙, invalidating an origin from the host star itself or its ejecta for the emitting material. We discuss the possibility that the extended H i emission stems from the interstellar medium (ISM) swept out over time by the stellar wind. Moreover, we report tentative detections of H i absorption features lying near and blueward of the systemic velocity of this PN, which are probably from a stalled asterosphere at the outer boundary of the expanding ionized region. The mass of the gas producing the H i absorption is insufficient to solve the so-called “PN missing mass problem.” We demonstrate the capability of FAST to investigate the interaction process between a PN and the surrounding ISM.

K-band spectra of selected post-AGB candidates

We present medium resolution (1000) K-band spectra of 12 post-AGB candidates and related stars. For several objects in our sample, these spectra were obtained for the first time. The Br$\gamma$ line in emission is detected in seven objects indicating the onset of photo-ionization in these objects. Four objects show the presence of He i line. We detect H2 emission line in the spectra of IRAS 06556+1623, IRAS 22023+5249, IRAS 18062+2410 and IRAS 20462+3416. H2 emission line ratio 1-0 S(1)/2-1 S(1) indicate that H2 is radiatively excited due to the UV radiation of hot post-AGB central stars. When compared with the recent observations by other investigators, the Br$\gamma$ and H2 emission fluxes varied in some of the objects. The hot post-AGB stars IRAS 22495+5134, IRAS 22023+5249, IRAS 18062+2410 and IRAS 20462+3416 seem to be evolving rapidly to young low excitation planetary nebula phase. The spectra of the objects presented in this paper may be useful for future observers as some of these stars show spectral variation and since the post-AGB evolution of some of these stars is relatively rapid.

IFU spectroscopy of southern planetary nebulae – III

In this paper we describe integral field spectroscopic observations of four southern Galactic Planetary Nebulae (PNe), M3-4, M3-6, Hen2-29 and Hen2-37 covering the spectral range, 3400-7000 A. We derive the ionisation structure, the physical conditions, the chemical compositions and the kinematical characteristics of these PNe and find good agreement with previous studies that relied upon the long-slit technique in their co-spatial area. From their chemical compositions as well as their spatial and kinematic characteristics, we determined that Hen2-29 is of the Peimbert Type I (He and N rich), while the other three are of Type II. The strength of the nebular He II line reveals that M3-3, Hen2-29 and Hen2-37 are of mid to high excitation classes while M3-6 is a low excitation planetary nebula (PN). A series of emission-line maps extracted from the data cubes were constructed for each PN to describe its overall structure. These show remarkable morphological diversity. Spatially resolved spectroscopy of M3-6, shows that the recombination lines of CII, CIII, CIV and NIII are of nebular origin, rather than arising from the central star as had been previously proposed. This result increases doubts regarding the weak emission-line star (WELS) classification raised by Basurah et al. (2016). In addition, they reinforce the probability that most genuine cases of WELS are arise from irradiation effects in close binary central stars (Miszalski 2009).

Discovery of new low-excitation planetary nebulae

We report a multi-wavelength study of four new planetary nebula (PN) candidates selected from the INT/WFC Photometric Ha Survey of the Northern Galactic Plane (IPHAS) and Deep Sky Hunter (DSH) catalogues. We present mid-resolution optical spectra of these PNs. The PN status of our sample was confirmed by optical narrow-band images and mid-resolution spectra. Based on the locations of these objects in the log (Ha/[N II]) versus log (Ha/[S II]) diagnostic diagram, we conclude that these sources are evolved lowexcitation PNs. The optical and infrared appearances of these newly discovered PNs are discussed. Three of the new nebulae studied here are detected in infrared and have low infrared-to-radio flux ratios, probably suggesting that they are evolved. Furthermore, we derive the dynamical ages and distances of these nebulae and study the spectral energy distribution for one of them with extensive infrared archival data.

High-resolution spectroscopy of the high-velocity hot post-AGB star LS III +52°24 (IRAS 22023+5249)

The first high-resolution (R~50,000) optical spectrum of the B-type star, LS III +52 24, identified as the optical counterpart of the hot post-AGB candidate IRAS 22023+5249 (I22023) is presented. We report the detailed identifications of the observed absorption and emission features in the full wavelength range (4290-9015 A) as well as the atmospheric parameters and photospheric abundances (under the Local Thermodinamic Equilibrium approximation) for the first time. The nebular parameters (Te, Ne) are also derived. We estimate Teff=24,000 K, log g=3.0, xi=7 kms-1 and the derived abundances indicate a slightly metal-deficient evolved star with C/O<1. The observed P-Cygni profiles of hydrogen and helium clearly indicate on-going post-AGB mass loss. The presence of [N II] and [S II] lines and the non-detection of [O III] indicate that photoionisation has just started. The observed spectral features, large heliocentric radial velocity, atmospheric parameters, and chemical composition indicate that I22023 is an evolved post-AGB star belonging to the old disk population. The derived nebular parameters (Te=7000 K, Ne=1.2x104 cm-3) also suggest that I22023 may be evolving into a compact, young low-excitation Planetary Nebula. Our optical spectroscopic analysis together with the recent Spitzer detection of double-dust chemistry (the simultaneous presence of carbonaceous molecules and amorphous silicates) in I22023 and other B-type post-AGB candidates may point to a binary system with a dusty disk as the stellar origin common to the hot post-AGB stars with O-rich central stars.

Emission line profiles as a probe of physical conditions in planetary nebulae

We present an analysis of physical conditions in planetary nebulae (PNe) in terms of collisionally-excited line (CEL) and optical-recombination line (ORL) profiles. We aim to investigate whether line profiles could be used to study the long-standing CEL/ORL abundance-discrepancy problem in nebular astrophysics. Using 1D photoionization models and their assumed velocity fields, we simulate the line profiles of various ionic species. We attempt to use our model to account for the observed CEL and ORL profiles. As a case study we present a detailed study of line profiles of the low-excitation planetary nebula (PN) IC 418. Our results show that the profiles of classical temperature and density diagnostic lines, such as [O III] 4363,5007, [S II] 6716,6731, and [Ar IV] 4711,4740, provide a powerful tool to study nebular temperature and density variations. The method enables the CEL/ORL abundance-discrepancy problem to be studied more rigorously than before. A pure photoionization model of a chemically-homogeneous nebula seems to explain the observed disagreements in the profiles for the [O III] 4363 and the 5007 lines, but cannot account for the differences between the [O III] CELs and the O II ORLs. We also investigate the temperature and density variations in the velocity space of a sample of PNe, which are found to be insignificant.

Identification of PN G232.0+05.7 as a new halo planetary nebula and of IRAS 19336-0400 as a new type III planetary nebula

Aims.We determined the nature and Peimbert type of two low-excitation planetary nebulae, PNG 232.0+05.7 and IRAS 19336-0400.

FUSE Observations of Mass Loss in Planetary Nebulae

The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite observed several high and low excitation planetary nebulae in the wavelength range 905–1187 Å at a spectral resolution of λ/Δλ ~ 15,000.

Multipolar Bubbles and Jets in Low-Excitation Planetary Nebulae: Toward a New Understanding of the Formation and Shaping of Planetary Nebulae

First results from a Hubble Space Telescope Wide Field Planetary Camera 2 Hα imaging survey of young planetary nebulae (PNs) are reported. The PNs have been selected on the basis of their low excitation characteristics. All objects imaged so far show highly aspherical morphology, with a majority characterized by multipolar bubbles distributed roughly point-symmetrically around the central star. In some objects, bipolar ansae or collimated radial structures are seen, indicating the presence of jets, whereas in others bright structures near the minor axes indicate the presence of disks or torii. The complexity, organization, and symmetry of the above structures lead us to propose that the primary agent for shaping PNs is high-speed collimated outflows or jets that operate during the late asymptotic galactic branch (AGB) and/or early post-AGB evolutionary phase, and not a preexisting equatorial density enhancement as envisioned in the currently popular model. These outflows carve out a complex imprint within an intrinsically spherical AGB circumstellar envelope (CSE). Subsequent expansion of a hot, tenuous stellar wind from the post-AGB star inside the imprinted AGB CSE then produces the observed PN, whose shape and structure depend in detail on how the characteristics of the jets change with time.

SAO 244567 (HEN1357): A Post-Agb Star which has turned into a Planetary Nebula within the last 20 years

SAO 244567 (Henl357) (IRAS 17119-5926) is a high galactic latitude (1 = 331°, b = −12°) early type star, originally classified as a B or A type H-alpha emission line star by Henize (1976). It is an IRAS source with far infrared colours similar to planetary nebulae. The IUE ultraviolet spectra obtained during the last eight years show that the central star is rapidly evolving. It is found that the central star of this young PN has faded by a factor of 3 within the last seven eight years. The terminal velocity of the stellar wind has decreased from −3500 km/sec in 1988 to almost zero in 1994. In 1988 the C IV (1550A) line which was a P-Cygni profile with strong absorption component had almost vanished by 1994. The CIII] 1909A emission strength increased markedly within 4 years from 1988 to 1992. The optical spectra obtained since 1990 shows very clearly only the nebular spectrum which is very similar to that of low excitation planetary nebula. The optical spectrum of SAO 244567 obtained in 1971 shows that it was a post-AGB B 1 or B2 supergiant at that time. This result shows that SAO 244567 has turned into a planetary nebula within the last 20 years. Recently Bobrowsky (1994) obtained narrowband optically resolved images in both H-beta and [OIII] 5007A with the HST planetary camera which revealed a well resolved nebula of size 2 seconds of arc. In this paper we discuss the recent new results.

Hubble Space Telescope observations of planetary nebulae in the magellanic clouds. 2: SMP 85, a young planetary

We have obtained Hubble Space Telescope Planetary Camera images in the (O III) lambda 5007 A emission line, and Faint Object Spectrograph (FOS) UV spectrophotometry of the low-excitation planetary nebula SMP 85 in the Large Magellanic Cloud. By combining these results with existing optical spectrophotometry, absolute flux measurements, and dynamical and density information, we have been able to construct a fully self-consistent nebular model. This proves that SMP 85 is a dense, young, carbon-rich object which started to be ionized about 500-1000 years ago, and which contains a substantial inner reservoir of atomic or molecular gas, probably in the form of many small cloudlets. These cloudlets have been ejected at a velocity not exceeding 6 km/s, a result which, together with the morphology is an important clue to mass loss during late asymptotic giant branch (AGB) evolution. We have directly detected the central star through its UV continuum emission, and from both Zanstra techniques and nebular modeling derive a stellar temperature of 46000 +/- 2000 K, a stellar luminosity of 7300 +/- 700 solar luminosity, and a core mass of 0.63-0.67 solar mass. The nebular analysis also demonstrates that there is severe depletion of the nebular gases onto dust grains, most likely of the calcium magnesium silicate variety; a surprising result in view of the carbon-rich nature of the ionized nebula.

Core masses and abundances of low-excitation planetary nebulae in the Magellanic Clouds

We derive core masses and chemical compositions for luminous low-excitation planetary nebulae in the Magellanic Clouds. They are all on horizontal (heating) evolutionary tracks with core masses that concentrate between 0.55 and 0.6 M ⊙ , and have low He/H and N/O ratios as expected from the relation found by Kaler & Jacoby. The behavior of carbon with core mass is uncertain, but it seems consistent with the behavior of carbon stars. There is also a suggestion that C/O anticorrelates with N/O. Below 0.63 M ⊙ , O/H correlates positively with core mass.

Central star temperatures of low-excitation planetary nebulae

New Zanstra temperatures of the central stars or low-excitation PNe and Kaler's (1987) Stoy method for determining the T(e)s of such stars are correlated here with the intensity of forbidden O III 5007 A for young PNE with no or weak He II 4686 A. Recent energy balance temperatures are shown to be unsatisfactory for this class of objects. Comparisons among the temperatures in cases were He II is detected show that PNe may start becoming optically thin for central star temperatures in the 40,000-50,000 K range and that the Zanstra discrepancy for this class of objects may be resolved by invoking low optical depth. The Stoy calibration seems to give the best estimate of central star temperatures from the 5007 A line. The correlations are valuable for determining effective temperatures in cases where no nuclei can be detected and are especially useful for extragalactic objects.

Echelle spectroscopy of CD -41 deg 13967 - The young central star of a new planetary nebula

view Abstract Citations (12) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Echelle Spectroscopy of CD -41 degrees 13967: The Young Central Star of a New Planetary Nebula McCarthy, James K. ; Rich, R. Michael ; Becker, S. R. ; Butler, K. ; Husfeld, D. ; Groth, H. G. Abstract High-resolution CCD spectra obtained with the Palomar 60 inch (1.5 m) echelle spectrograph and subsequently confirmed and extended using the CTIO 4 m echelle spectrograph have revealed that the hot star CD -41° 13967 is the young central star of a previously unknown low-excitation planetary nebula. Presented in this paper is a detailed analysis of our CCD echelle spectra of CD -41° 13967, which are well fitted by non-LTE model atmosphere line profiles corresponding to Teff = 27,000 K, log (g) = 3.1, and a He abundance 3 times solar. These best-fit model parameters imply a mass of 0.63 Msun and a post-asymptotic giant branch (AGB) age of 1250 yr for the central star, based on a comparison with central star of planetary nebula (CSPN) evolutionary tracks in the distance-independent Teff-log (g) plane. Using recent UBVRI CCD photometry corrected for extinction along with the Eddington flux emerging from the best-fit non-LTE model atmosphere, we derive a spectroscopic distance estimate of 3.5 kpc to CD - 41° 13967. This together with the Galactic coordinates (lII = 359.0; bII = - 33.5) strongly suggests that CD -41° 13967 belongs to the Galactic halo population, a suggestion supported by the results of our stellar abundance analyses for silicon, [Si/H] = -0.20±0.10 and oxygen, [O/H] = -0.43±0.20 as well as by the mean of our stellar radial velocity measurements <Vr>* = -91±2 km s-1; compare also with our result, <Vr>PN = -97±2 km s-1). The surrounding planetary nebula, He 3-1863, shows an angular extent greater than 6" (FWHM) on the E/W slit of our CTIO spectrograms. The excitation class of the nebula is zero, with only Hα, Hβ, Hγ, Hδ, [N II] 5755, 6548, 6584 Å, [O I] 6300, 6364 Å, [O II] 7320, 7330 Å, and [S II] 6717, 6731 Å lines in evidence; lacking is any [O III] 4363, 4959, 5007 Å emission. This is consistent with the low Teff; determined for the central star. Subsequent narrow-band Hα CCD imaging reveals that He 3-1863 is a centrally concentrated elliptical nebula with a total E/W extent ≥17" and N/S extent ≥ 13" on the sky. Publication: The Astrophysical Journal Pub Date: April 1991 DOI: 10.1086/169898 Bibcode: 1991ApJ...371..380M Keywords: Early Stars; Echelle Gratings; Nonequilibrium Thermodynamics; Planetary Nebulae; Stellar Spectra; Charge Coupled Devices; Hot Stars; Stellar Atmospheres; nebulae: planetary; stars: abundances; stars: early-type; stars: individual (CD -41° 13967); Astrophysics full text sources ADS | data products SIMBAD (1)

Planetary nebula with a peculiar spectrum in the ultraviolet: CN 3-1

We have obtained IUE ultraviolet spectra of the low-excitation planetary nebula CN 3-1. The recordings show the well-known doublet 2800 MgII and resonance line 2852 MgI as strong absorption lines. We show that these lines cannot be of interstellar origin and that they may be formed in two envelopes surrounding the main nebula: in the transition zone (doublet 2800 MgII) and in the neutral envelope (line 2852 MgI). These envelopes possess an important property: they contain dust particles, and even a moderate amount of such particles may influence the strength of the absorption lines of MgII and MgI.

EXPANSION ANALYSES ON LOW-EXCITATION NEBULAE WITH STELLAR IMAGES

ABSTRACT The paper presents the results of analyses on the expansion characteristics of the low-excitation and unresolved planetary nebulae, M1-5, M1-9, K3-66, and K3-67. The sample nebulae are divided into two groups. The first includes the real compact planetary nebulae M1-5 and M1-9 based on their single-Gaussian profiles. The second one includes nebulae that are unresolved because of their large distances. The nebulae K3-66 and K3-67 should belong to the second group since they show the double-Gaussian components in the emission-line profiles. Relationships between expansion velocities and I(forbidden O III 5007 A)/I(H-beta) and between electron densities and expansion velocities give the basis for the above arguments and reveal that the nebulae IC 4997, Vy2-2, and M3-27 obviously are in different phases of evolution from those of other low-excitation planetary nebulae.

Two Southern Low Excitation Planetary Nebulae

Within a spectroscopic study of some southern planetary nebulae, we have observed 32 objects. Some of them are symbiotic or suspected symbiotic stars, and one (He 2-61) is evidently not an emission object.

IUE OBSERVATIONS OF THE LOW-EXCITATION PLANETARY NEBULA TC-1.

ABSTRACT Ultraviolet observations of Tc-1 confirm that the object is a low excitation planetary nebula with a central star of type O7. The nebular spectrum has few emission lines and the P Cygni character of the C IV line remains uncertain. A radial velocity of -95 km/s is found from the semiforbidden C III wavelength 1909 line, and an extinction of 0.22 m from the wavelength 2200 absorption feature.

An Optical and Ultraviolet Study of Nine Low-Excitation Planetary Nebulae

Ultraviolet and optical observations of seven very low excitation nebulae (He 2-131, He 2-138, TC 1, M 1-11, M 1-12, M 1-26, H 2-1) and of two low-excitation nebulae (IC 418 and He 2-108) are discussed.

IONIZATION STRUCTURE AND PARTIAL OBSCURATION OF THE P.N. NGC 3132 ANDNGC 3242.

ABSTRACT Monochromatic images are presented of a low-excitation planetary nebula, NGC 3132, and of a high-excitation, double-shell nebula, NGC 3242 in the light of H-alpha, H-beta, forbidden N II 6584, and forbidden S III 9232. For both nebulae, the forbidden N II radiation had a very different surface brightness distribution from that of the forbidden S III and the hydrogen. In NGC 3132, the forbidden N II emission was concentrated in a narrow outer annulus, whereas in NGC 3242, it was concentrated in the central region. The forbidden N II emission appears to originate in dense concentrations within the inner shell, and the outer shell, almost spherical in shape, seems to be density bounded. The forbidden N II/H map in both cases shows significant structural features not seen in the individual intensity maps. Reddening, determined from the H-alpha/H-beta ratio, appears to be due to dust which is external to NGC 3132, but which is found in part within NGC 3242.