Figure 8: Mapping of the chemica/ inhomogeneities in the shel/ of the recurrent nova T Pyx.C%ur coding as in Figure 7.

of oxygen in the polar blobs is due tomeridional circulation of white dwarfmaterial at the onset of the outburst(Kippenhahn and Thomas 1978) than to

differences in the ashes of nuclearburning.

The apparent abundance in-homogeneities can be mapped by com-

bining pictures taken through interfer­ence filters isolating the radiation of[0 IIIJ and [N 11] + Ha, respectively. In thecolour plots, regions with relatively high­er contributions of [0 111] are blue, thosewith relatively higher contributions of[N 11] + Ha are red (Figs. 7, 8).

Aside from their physical meaning,which must still be better substantiated,the colour plots help to determine thesymmetry axes in nova shells. This wasal ready shown for the northern nova GKPer (Duerbeck and Seitter 1987) whichuntil then was considered irregular. Theshell of RR Pic is shown in Figure 7. Thecolour method is particularly useful forshells which appear in nearly sphericalprojection, such as T Pyx (Fig. 8).

This ends our present report on novashells. With a plethora of novae andnova remnants still awaiting their obser­vational share, the field of stellar cata­c1ysms appears to be as attractive asever.

References

Duerbeck, H.W., Seitter, W.C.: 1987, in RSOphiuchi (1985) and the Recurrent NovaPhenomenon, ed. M. F. Bode, VNU Sci­ence Press, Utrecht, p. 71.

Kippenhahn, R., Thomas, H.-C.: 1978, Astr.Astrophys. 63, 265.

Marsh, T.R., Wade, R.A., Oke, J.B.: 1983,Mon. Not. R. astron. Soc. 250, 33 p.

Seitter, W.C.: 1987, in RS Ophiuchi (1985)and the Recurrent Nova Phenomenon, ed.M. F. Bode, VNU Science Press, Utrecht,p.63.

Williams, R. E., Gallagher, J. S.: 1979, Astro­phys. J. 228, 482.

Internal Dynamics of the Gum NebulaM. SRINIVASAN 1

, S. R. POTTASCH2, K. C. SAHU2 and J.-C. PECKER 1

1 Laboratoire d'Astrophysique TMorique du College de France, Institut d'Astrophysique, Paris

2 Kapteyn Laboratorium, Groningen, the Netherlands

Introduction

Among the many large and spectacu­lar objects of the southern sky, the Gumnebula with an angular diameter of 36degrees in the sky is the object with thelargest known apparent dimensions.Unlike the other large objects like theLarge Magellanic Cloud (diameter = 8°)and the Small Magellanic Cloud (diame­ter =3°) wh ich clearly stand out as high­Iy luminous regions in the night sky, theGum nebula, however, is extremely faintand is not visible to the naked eye. Theonly way to see this nebula is to look atthe photographs taken in emission lineslike Ha A 6563 Aand [Nil] A 6584 Alinessince the entire visible radiation from thenebula is confined to a few such emis-

sion lines. But the extent of the nebula isso large that it fills the conventionalSchmidt photographs and can be de­tected only from a mosaic of Schmidtphotographs. In fact, the nebula wasfirst detected this way in 1953 by Co/inS. Gum, who made a mosaic of severallong exposure Schmidt plates of thisregion, each with an 11° field, taken inthe Ha + [N 11] lines. It is befitting that thenebula now bears the name of its dis­coverer, C. S. Gum, who was unfortu­nately killed in a skiing accident in Swit­zerland in 1960, at a relatively young ageof 36.

The central region of the Gum nebulacontains Zeta Puppis (04f), the b 'ght­est O-type star in the sky, and GammaVelorum (WC 8 + 09 I). From the ESO

11 a-O and the SERC 111 a-J plates of theregion of the Gum nebula, about 29cometary globules (CGs) and 7 darkclouds have been identified (Hawardenand Brand, 1976, Sandqvist, 1976,Zealey, 1979, and Reipurth, 1983).Cometary globules are dark cloudswhich have dark, dense heads whichare completely opaque to thebackground starlight, and faint, lumin­ous tails through which backgroundstars can be seen. The heads often havebright rims on the side that points to­wards the centre of the Gum nebulacomplex while the tails, in general, pointaway from this central region. To date, atotal of about 38 CGs have been notedand catalogued of which 29 lie in theGum nebula region. Several of these

11

Figure 1: This photograph of the Gum nebula was obtained by J. P. Sivan and has beenreproduced from the ESO book "Exploring the Southern Sky", by S. Laustsen, C. Madsen andR. M. West. Superposed on the photograph are the approximate positions at which ourobservations are taken (indicated by 0) and those of Reynolds (indicated by +).

CGS show signs of star formation.Reipurth (1983), Brand et al. (1983) andPettersson (1987) have conclusivelyshown that CG 1 and CG 30 are sites ofstar formation. We have carried out astudy of CGs and dark clouds in theGum nebula using IRAS and other opti­cal data (Srinivasan et al. , 1987) wherewe find the dust to be concentrated andcompressed on the side of the head thatfaces the central region of the Gumnebula complex. Our study also showsthat there is evidence for the presenceof point sources in the heads of a fewCGs indicating that star formation iscurrent in these globules. Hence fromthe morphology of the CGs in the IR itseems that the internal dynamics of theGum nebula has played an importantpart in their formation and in triggering aseries of star forming events in theheads of the CGs.

Previous Studies

Earlier work on the internal dynamicsof the Gum nebula have clearly sug­gested the need for further work. Therehave been three attempts in this direc­tion. They are listed below with themethods and essential results.

(1) The earliest attempt to study theinternal dynamics of the Gum nebulawas made by Hippelein and Weinberger(1975) where they used a photographicFabry-Perot interferometer and de­tected no systematic expansion. Sincetheir actual interferograms are not pub­lished, it is difficult to judge the errorsand the reliability of the results. But thevelocity resolution in this study seemsrather poor and the results seem uncer­tain due to the many problems associ­ated with the difficulty in correcting forthe background using the old photo­graphic techniques, particularly whenthe object is faint.

(2) More accurate measurementswere carried out by Reynolds (1976)where he used a twin-etalon Fabry­Perot spectrometer and a photo-electricdetector to obtain line profiles in HaA6563 A, [N 11] A6584 A and [0 111]A 5007 Alines in 8 positions of the nebu­la. At a few positions, he detected ex­pansion velocities as high as 20 km/sand less in a few other positions. Thenorthern location of the telescope usedin this study (the telescope used was theMcMath telescope at KPNO) howeverforced the observations to be confinedonly to the northern parts of the nebula,leaving the southern regions of thenebula completely unexplored.

(3) Reynolds' results were con­tradicted by Wallerstein et al. (1980)where they studied optical and UV inter­stellar absorption line spectra of about70 stars in the direction of the Gum

12

nebula and concluded that the nebulaundergoes no systematic expansion.Their analysis, however, involves theassumption that the Gum nebula is thecause of the observed absorption fea­tures, although it is not clear whethersome other component of the ISM in theline of sight could also be the cause ofthese features.

Thus the need for further systematicobservations to resolve the issue wasc1ear and we have undertaken a studywhere high resolution (R = 40,000) lineprofiles could be obtained at manypoints uniformly distributed throughoutthe nebula.

Observations

The ESO 1.4-m telescope, which isequipped with a Coude Echelle Spec­trograph, a short camera and a CCOdetector, is weil suited to study suchlarge and faint nebulae. Since the nebu­la is extremely large, high spatial resolu­tion is not necessary and hence theshort camera can be used advantage-

I

ously to increase the field of view there­by increasing the light-gathering powerof the spectrometer. Use of the CCOprovides an extra advantage since it ispossible, at the data reduction stage, torebin the spectra in the direction per­pendicular to the dispersion up to about50 to 100 pixels thereby increasing theS/N by a large factor.

Observations were made in Februaryand Mal' 1987, in the Hf( A6563 A, [N 11]A6584 A and [0 111] A5007 Alines at 14positions weil distributed in the nebula,with aresolution of R = 40,000. Carewas taken to include southern regionswhich were not included in the study ofReynolds. Three of our positions coin­cide with those of Reynolds and weretaken for the sake of comparison. Fi­gure 1 shows a photograph of the Gumnebula, with the approximate positionsof Reynolds and our observation posi­tions superposed on it. Typical expo­sure time for all the three lines was1 hour. The data were reduced usingMIOAS (Munich Image Oata AnalysisSystem) at ESO, Garching.

6586

T I •020 I bJ 011 Ic j

;:er«:=

~~roer::t 009

'"§ 010

~;0

007

T

lai

6582

008

010 r

004

006

1~ I j --L --L.

6584 6586 6582 6584 6586 0582 6583 6584 6565

WAVf E~GTH AI WAVELENGTH Ai WAVElENGTHIAJ

Figure 2: (a, b, cl: The observed {N 11] A 6584 Aprofiles (histograms) obtained al positions 2, 1 and 4 respectively using the ESO l.4-m GAT +Gouda Echelle Spectrograph + GGO, along with the Gaussian best fits (smooth curves). Position 4 corresponds to position H of Reynolds.

Results

Though the detailed analysis andmodelling are in progress, some resultsean be stated here whieh are thefOliowing:

(1) To derive the true expansion velo­eity of the nebula, we have applied thegeometrie eorreetion faetors to the ob­served line of sight veloeities and ourobservations are more eonsistent withan expansion veloeity of Vexp = 10 km/sfor the Gum nebula as obtained from thesplitting of the [N 11] line profiles. Fig­ure 2 shows the [N 11] line profiles ob­tained at positions 1, 2 and 4.

(2) We failed to deteet [0 111] emissionin any of the 14 positions observed, ineontradietion with the observations ofChanot and Sivan (1983) (who madespeetrophotometrie observations of theGum nebula) and in agreement with the

observations of Reynolds. In order toeonfirm our non-deteetion, we repeatedexposures in the region near GammaVelorum (position 4) where the [0 111]emission was reported by Chanot andSivan to be high. We failed to deteet[0111] at this region in spite of integratingexposures of totally 2 hours and 20 min­utes, whieh shows that the objeet is alow-exeitation nebula.

(3) None of the Ha profiles showed anysplitting. This is however not surprisingbeeause of the large thermal width ofthe Ha line (the expeeted FWHM of theHa line is about 22 km/s at 10,000 K).The non splitting of the Ha line profilesshows the expansion veloeity to be lessthan 10 km/s whieh is eonsistent withthe results obtained from the [N 11] pro­files.

A eomparison of our observations and

results with those of the previousstudies is shown in Table 1.

A physieal model for the Gum nebulataking into aeeount the observedgeometry and the veloeity strueture isunderway. We also plan to obtain highresolution speetra at many more posi­tions in the nebula in different ionizationlines for further study of the internaldynamies and the ionization strueture ofthe nebula.

References

Brand, P.W.J.L., Hawarden, T.G., Long­more, A.J., Williams, P. M., Caldwell,J.A.R.: 1983, Monthly Notices Roy. As­tron. Soc. 203, 215.

Chanot, A., Sivan, J.-P.: 1983, Astron. Astro­phys. 121, 19.

TABLE 1.

Studies Teleseope and instrument Field of view Resolution (km/s) No. of positions Line studied Results

Hippelein and 16-em teleseope 3.5 19-28 2000 Ha no expansionWeinberger (1975) (Gamsberg, S. Afriea) + (em.)

photographieF.P.interferometer

Reynolds (1976) 60-em MeMath 57 12 8 (northern Ha Vexp = 20 km/steleseope (USA) regions) [N 11)+ twin-etalon [0111]F. P. speetrometer (em.)

Wallerstein et al. 1.5-m CTIO not relevant > 12 for (Ca 11) 70 Ca 11 no expansion(1980) (Chile) + and Nal

Coude > 25 tor (Na I) (abs.)speetrographand Copernieussatelliteresults

Present study 1.4-m ESO l' X 1':6 7.5 14 (ineluding Ha Vexp = 10 km/s(1987) (Chile) + southern [N 11)

Coude regions) [0111]Eehelle (em.)Speetrograph+ CCO

13

Hawarden, T.G., Brand, P.W.J.L.: 1976,Monthly Notices Roy. Astron. Soc. 175,19 P.

Hippelein, H. H., Weinberger, R., 1975, As­tron. Astrophys., 43, 405.

Pettersson, B.: 1987, Astron. Astrophys. 171,101.

Reipurth, B.: 1983, Astron. Astrophys. 117,183.

Reynolds, R. J.: 1976, Astrophys. J. 203, 151.Sandqvist, A.: 1976, Monthly Notices Roy.

Astron. Soc. 177, 69 P.Srinivasan, M., Pottasch, S. R., Sahu, K. C.,

Wesselius, P.R., Desai, J.N.: 1987, sub­mitted to Astron. Astrophys.

Wallerstein, G., Silk, J., Jenkins, E. B.: 1980,Astrophys. J., 240, 834.

Zealey, W.J.: 1979, New Zealand J. Sci. 22,549.

The Proceedings of the ESO Workshop on

Stellar Evolution and Dynamicsin the Outer Halo of the Galaxy

which was held at ESO-Garching from 7 to 9 April 1987, have now beenpublished. The 712-page volume was edited by M. Azzopardi and F.Matteucci and is available at a price of DM 50.- (prepayment required).

Payments have to be made to the ESO bank account 2102002 withCommerzbank München or by cheque, addressed to the attention of:

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V 605 Aquilae - a Star and a Nebula with No Hydrogenw. c. SEITTER, Astronomisches Institut der Universität Münster, F. R. Germany

Three planetary nebulae are knownwith hydrogen-poor central nebulositiesand WR-type central stars: A 30, A 78and A 58. While the former have beendiscussed extensively in the literature,the latter remained spectroscopicallyunknown until 1983. Its story, however,begins much earlier.

In 1920 Max Wolf found a 1O~ 4 staron photographic plates taken in 1919.The object had been invisible before1917; it disappeared in 1923. In 1921,Lundmark took spectra of the sus­pected nova. These had no resem­blance with spectra of any of the knownevolutionary states of novae, theylooked like those of carbon stars. De­eades later, the region around the star,now designated V 605 Aql, was in­speeted. Abell (1966) found a faint oldplanetary nebula and entered it asnumber 58 into his catalogue, Herbig(1971) noticed a very faint starlike objectnear the centre of A 58 and suggestedthat this was the remnant star of V 605Aql.

Our own story of V 605 Aql and A 58starts in 1983, when I joined H. Duer­beck in his spectral survey of faint oldnovae with the Calar Alto 2.2-m tele­scope. The central star of A 58 was notvisible on the telescope monitor. How­ever, we had just recorded another un­seen old nova, V Per, because it hadappeared somewhere along the long slitwith which the unwidened spectrumwas taken. Thus, the long slit wasplaced across the planetary nebula invarious positions. When it lay exactlyaerass the eentre, as deduced from thepattern of spectra fram neighbouringstars, a central point-like emission spec-

14

trum appeared in addition to the emis­sion lines of the extended planetarynebula. The central nebulosity showedno hydrogen, only strong [0111] andmoderately strong [N 11] lines, slightlyblueshifted with respect to the planetaryemission lines (Seitter 1985 a).

An EFOSC spectrum taken for us withthe ESO 3.6-m telescope by P.Angebault in 1986 shows the spectra ofthree objects: lines of the planetarynebula and the eentral nebula and stellaremission lines superimposed on a weakeontinuum of red magnitude 22.3 (Seit­ter 1987).

Follow-up observations were ob­tained on July 1/2, 1987, again with theEFOSC at the ESO 3.6-m telescope. Aslit width of 1" was chosen in order toelearly separate the [N 11] 658.4,654.8 nm lines at a dispersion of 23 nm/mm. The mean spectra obtained in theblue and red/near infrared regions areshown in Figures 1 to 4. In all spectra,eontributions fram the night sky and theplanetary nebula are removed. The sub­traetion of the latter rests on theassumption that the strengths of thenebular lines towards the northern partof the PN do not differ from thosesuperimposed on the central nebula.This seems to be justified from theappearance of the hydrogen Iines in thetwo-dimensional speetra, where nodifferences are noticed between the tworegions (see Figs. 2 and 3 in Seitter1985 b).

The result is striking as seen in Fig­ure 4: no trace of Ha is found betweenthe nitrogen lines. The central nebula ofA 58, which also appears to be the rem­nant nebula of the nova-like outburst of

the central star V 605 Aql in 1917, is theforemost candidate for a nebula entirelyfree of hydrogen.

The central star of the two nebulaeexhibits a strong C IV 580.6 blend, be­sides marginal lines of He II 468.6, 0 Vand 0 VI. The broad C IV feature with aFWHM of 2,300 km/s and a total widthof 4,400 km/s suggests that this star isof WR type, as are the central stars inA 30 and A 78. An additional similarity ofthe three objects is the presence of cooldust. Extended dust shells of 140 Kwere derived for both A 30 and A 78(Cohen and Barlow 1974) while the IRASdata indicate a point souree of 170 K forA 58.

The central object of A 58 is interest­ing not only because of its extremeproperties but also because the out­burst was observed photometrically andspectrascopically. This puts severe con­straints on any theory trying to explainthe observed phenomena.

Following earlier suggestions (e. g.Iben et al. 1981 for A 30 and A 78, andPottaseh 1985 for A 58) the central starsof all three PNs are candidates for posthelium shell flash evolution. The centralnebulae in A 30 and A 78 have kinema­tic ages of a few thousand years. If theeentral stars reached their observedpositions in the H-R diagram during thesame time interval, one finds fair agree­ment with evolutionary computations.V 605 Aql, on the other hand, hasreached a magnitude comparable to itspre-outburst brightness after less than70 years.

Because the temperature determina­tion is difficult for a star whieh displaysjust one well-defined line, the bolometric