Deep morphologies of type I planetary nebulae

Astronomy and Astrophysics Supplement Series, Jul 2018

Deep narrow band interference filters observations are presented for 7 type I galactic planetary nebulae (PNe). Except for the nearly circular planetary nebula A 39, the observations show overall dimensions appreciably larger than those quoted so far. The observed PN (NGC 6302 excepted) could have linear diameters larger than 1 pc. Our new observations imply ionized masses often larger than , suggesting that much of the mass ejected by the PN precursor is contained in faint outer extensions. This might contribute to the solution of the "mass deficit

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Deep morphologies of type I planetary nebulae

M Astron. Astrophys. Suppl. Ser. Deep morphologies of type I planetary nebulae? C.T. Hua 0 0 Laboratoire d'Astronomie Spatiale du CNRS , Allee Peiresc, Traverse du Siphon, 13012 Marseille , France 1 NGC 6302 was observed at Mt John University Observatory - Lake Tekapo - operated by the University of Canterbury , Christchurch, New-Zealand Deep narrow band interference lters observations are presented for 7 type I galactic planetary nebulae (PNe). Except for the nearly circular planetary nebula A 39, the observations show overall dimensions appreciably larger than those quoted so far. The observed PN (NGC 6302 excepted) could have linear diameters larger than 1 pc. Our new observations imply ionized masses often larger than 1 M , suggesting that much of the mass ejected by the PN precursor is contained in faint outer extensions. This might contribute to the solution of the mass de cit" in PNe. We have also provided calibrated fluxes for some speci c emission lines. In spite of their apparent morphological di erences, our observations suggest that these type I PNe possess the same intrinsic structure as that displayed by NGC 650-1, the Ring Nebula, and even Sh 1-89 with its elongated jet-like feature, but viewed under di erent angles. planetary nebulae 1. Introduction Since PN morphology is presumably connected with the evolution of the ensemble PN - central star, available observations obviously show a large variety of shapes, which could reflect di erent stages of this evolution. Progress in theories (Frank et al. 1993; Bryce et al. 1994) requires a large, homogeneous set of monochromatic images and isophotes (Kaler 1985) which narrow bandpass CCD imaging of PN can supply (Balick 1987) . Here we present new sensitive observations using selective lters for seven galactic type I PN (Peimbert 1978; Peimbert & Serano 1980) which are characterized by high helium and nitrogen contents and which are believed to originate from massive precursor stars (Peimbert & Peimbert 1983). Our goal in this study was to search for the so-called secondary structures, if any, around the bright central nebula, and which could be relics of primary ejections by the evolving ionizing star in the AGB phase. The overall diameter measured on the H monochromatic images should allow new estimates of the ionized mass of the planetary nebula. As a matter of fact, existing inventories of this parameter in PN reveal a shortfall as compared with theory. 2. The observational material Six northern planetary nebulae were observed with a Tektronic CCD installed at the f/6 focus of the 120-cm telescope of the Haute Provence Observatory: it o ers a total eld of view of 390 390 square arcsec (27 m pixel-size or 0.77 arcsec pixel−1). The southern object, NGC 6302, was observed with the McLellan 1-m telescope (f/7.8) at Mt John, New Zealand, using a Thomson TH7882 CDAchip (384 576 23 m square pixels, 0.61 arcsec pixel−1) covering a total eld of view of 240 360 square arcsec. The interference lters used in our study have bandwidths 10 A, with typical transmission of about 60%. In some cases, however, 44 A-wide H , [OIII]5007 A and 39 A-wide [SII]6737 A lters were used. The lters were mounted in front of the detectors in the direct imaging mode. The image quality was about 10:05 − 200 during the observations. 3. Results Table 2 displays line intensity measurements taken from Acker et al. 1993 (hereafter Acker93) and Cahn et al. 1992 (CKS92) as well as other published parameters collected from the literature for seven PN in study. Peimbert & Peimbert 1983 de ned as type I PN those having N (He)=N (H) 0:125 or N/O 0:5, and which generally display bipolar structures. Table 2 summarizes the measured parameters (PN dimensions, ionized mass in solar mass, and absolute fluxes). The line intensity values (normalized to F (H ) = 100) are from Acker 1993 's tables when available. (**) Data from Manchado & Pottasch 1989 ; indices (c) and (h) being related to the centre and the halo nebula respectively. CH are optical extinction values at H from CKS92 (their C column) and IRAS data from the IRAS catalogue. NGC 6302 was observed at the MJUO McLellan 1-m telescope. The H and [OIII]5007 A images display a nearly circular and identical shape (Figs. 1). However, this circular symmetry seems to be distorted1 by the interaction with the interstellar medium. The diameter measured on the H image ( 17500) agrees with the value of 17400 reported by Cahn & Kaler (1971) (CK71). [NII]6583 emission was not detected. At the distance of 1200 pc (CKS92), the observed diameter corresponds to a linear value of 1.0 pc. 3.2. Sh 1 − 89: PN 089:8 − 00:6 This object was not detected with the lter [OII]3727 (1800 s), and curiously HeII (600 s) as well, but we strongly suspect the e ets of the bad weather conditions during these observations. The H images are not usable for investigating internal absorption. Nevertheless, all the other images (Figs. 2) display outstanding peripheral features, the nebular dimensions being de nitely larger than 3500 quoted. The observed (H and [NII]) images show a rather complex structure. Even the bright core actually 1 We used a POLAR treatment to evidence the curvature of the borders. spreads over 6000. Bubbles and wisps extend over 6 arcminutes. Due to the faint jet-like emissions on both sides of the bright waist, we can hardly assign to Sh 1 − 89 any of the available models (bubble, butterfly, jet?) to explain such a peculiar morphology. The overall dimensions are 40000 along the major axis. Sh 1 − 89 would be one of rare planetary nebulae which have linear diameter larger than 1 pc, since its main bubble-like structure spreads over 23000 (100 = 9:41 10−3 pc). 3.3. Sh 2 − 71: PN 035:9 − 01:1 The H , [NII]6583 A, [OIII]5007 A (Figs. 3), H , and 39 A-wide [SII]6737 A images show a rather elongated and bright central nebula (13000 22000), whereas an outer faint emission spreads over a larger area 25000 30000 than previously quoted (10000, CK71). The extensions reported in this study are even much larger than that reported by Jewitt et al. 1986 who considered Sh 2 − 71 as an excellent example of PN with halo even though these authors observed only the bright elongated core. The nitrogen emission is more prominent along the radial structures outwards. The H , [NII]6583 A images display a bright elongated nebula ( 13000 22000), with faint emission Fig. 1. a) Top: H . The planetary nebula shows a nearly circular shape. At the distance of 1200 pc, A 39 has a linear diameter of 1 pc. The overall eld of view covers 386 386 arcseconds. North is towards the top and East at left for all gures. b) Bottom: The [OIII] emission is much stronger than that in H Fig. 3. c) Top: [OIII]5007. The outer halo seen in the two previous emission lines is not detected in [OIII]. d) Bottom: [SII]. A faint emission is detected southwards spreading over a more extended area 25000 30000 − 1:2 1:45 pc at the distance of 997 pc - (CKS92, 100 = 0:0048 pc), much larger than quoted so far. The [OIII]5007 image is smaller, limited to the bright (10000 15000) elliptical ring, without the outer emission detected in the H and [NII] images. 3.4. NGC 650 − 1: PN 130 − 10:1 This planetary nebula (Figs. 4) was imaged with the 320 512 RCA-CCD. The images in H , [NII]6583 A and [OIII]5007 A display an apparent morphology which shows strong similarities with Sh 1 − 89. The overall extension is certainly larger than the dimensions revealed by the CCD in use ( 30000). 3.5. NGC 6302: PN 349:5 + 01:0 (982 pc). This overall extension raises the question of the age of the nebula. The present estimated value of 3000 years probably involves solely the bright central nebula of 3000 wide. The actual dimensions of NGC 6543, along with the expansion velocity in the outer region, 10 km s−1, would infer a much larger age ( 105 years). Presumably, we see previous ejecta by the AGB progenitor. 3.7. The Ring Nebula: NGC 6720 − PN 063:1 + 13:9 The Ring Nebula is certainly one of the most extensively investigated planetary nebula since its discovery (Duncan 1937) . Moreno & Lopez 1987 showed that the Ring Nebula has dimensions de nitely larger than the optical 7600 of the bright elliptical core (Moreno & Lopez 1987; Bryce et al. 1994) . Our monochromatic observations (Figs. 7) through narrow (H , [NII]6583, [OIII]5007) and moderate (H , = 55 A, [SII] 6737, = 39 A) bandwidth lters con rm these outermost features surrounding the lamentary network. This young bipolar PN is characterized by a high interstellar absorption since the F (radio)=F (H ) ratio implies E(B − V ) = 0:96. The excitation is very high (class 10+); the helium abundance He/H is twice (0.182) the average value for known PN. Furthermore, nitrogen 4. Summary (N=H = 85 10−5) has 10 times the average abundance (CKS92). We have presented deep monochromatic images of seven Our monochromatic images (Figs. 5) in H , H , type I galactic planetary nebulae. Except for the case of A [NII]6583 A and [OIII]5007 A obviously reveal a butterfly 39 (where we have not detected outer emission) the obsershape with an \explosive" structure around a bright com- vations evidence bipolarity and multiple-shell structures. pact central core separated into two areas by an absorbing The linear diameters generally exceed 1 pc. Consequently, lane. The H and [OIII]5007 images display similar struc- the derived ionized mass is often larger than 1 M . This tures, whereas the [NII]6583 image shows a more knotty might contribute to the solution of the mass de cit in morphology. The present observations have detected even planetary nebulae. larger dimensions (> 25000) than that reported by Ashley (1990) (Proc. ASA, 8, 360). The narrowband [NII]6583 lter helps to outline conspicuous laments more extended (NW) than in H . 3.6. NGC 6543: PN 096:4 + 29:9 This is one of the most outstanding PN among the socalled multiple-shell planetary nebulae, displaying a large faint envelope ( 50 in diameter). It is obviously of interest to investigate the morphological nature of the surrounding giant halo. We have observed (Figs. 6) this PN through the H , [NII]6583 A, [OIII]5007 A, [OII]3727 A, and 39 Awide [SII] lters. All images show conspicuous ejecta far from the main nebula. The global lamentary structure appears up to 27000 from the bright core, in agreement with Middlemass et al. (1989) who considered them as low surface brightness areas and probable density enhancements, illustrating the point that ionizing photons are escaping from the system. The overall diameter in the observed images is 34000 including the faint outermost structures. This dimension corresponds to 1:6 pc at the distance given by CKS92 Acknowledgements. It is our great pleasure to thank INSU and the G0968 GDR \Milieux Circumstellaires" for travel grant, and our colleagues of the University of Canterbury (Drs. J.B. Hearnshaw, W. Tobin) for their friendly advices. Our thanks also go to Mike Clark for his assistance during the observations at the MJUO telescope. We are indebted to Prof. Michael Dopita of Mt Stromlo for fruitful discussions and corrections to improve the manuscript, to Drs. J. Lequeux, J.M. Deharveng and to the anonymous referee for pertinent comments. 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C. T. Hua. Deep morphologies of type I planetary nebulae, Astronomy and Astrophysics Supplement Series, 355-366, DOI: 10.1051/aas:1997226