staff astronomers and skillful nightassistants on La Silla. 1.4 I

2 4I

6 8 10I I

I-

Figure 3: Initial-final mass relation for intermediate-mass stars according to cluster whitedwarfs identified in the course of this programme. Symbols: 0 NGC 2516, + NGC 2287,x NGC 3532, 0 NGC 2168, 0 NGC 2451, L'I NGC 6405, P Pleiades. The broken line is therelation adopted by Weidemann (1987).

-

-

-

-

I I

•

I

8I I

o

8

C> I/

/ ./ P

/

4 6M

I

I I I

+x+

I

2III

I-

I-

I-

0.6 I-

0.1 I-

0.8 I-

1.2 I-

0.2 I-

0.4 I-

1.0 I-

ReferencesGreenstein, J. L., 1974, Astron. J. 79, 964.Kennicutt, R.C., 1984, Astrophys. J. 277,

361.Koester, D., 1982, The Messenger28, 25.Koester, D., Reimers, 0.,1981, Astron. Astro­

phys. 99, L8 (I).Koester, 0., Reimers, 0., 1985, Astron. Astro­

phys. 153, 260 (111).Koester, 0., Reimers, 0., 1989, Astron. Astro­

phys. LeIters, in prep. (VI).Reimers, 0.,1975, Mem. Soc. Roy. Sci. Liege

8,369.Reimers, 0., 1987, in Circumstellar Matter,

lAU Symp. 122,307.Reimers, D., Koester, 0., 1982, Astron. Astro­

phys. 116, 341 (11).Reimers, 0., Koester, D., 1988, Astron. Astro­

phys. 202, 77 (IV).Reimers, 0., Koester, 0., 1989, Astron. Astro­

phys. M.Romanishin, W., Angel, J. R. P., 1980, Astro­

phys. J. 235, 992.Tammann, G.A., 1974, in Supernovae and

Supernova Remnants (C. B. Cosmovici,ed.) D. Reidel, p. 155.

v.d. Heuvel, E.P.J., 1975, Astrophys. J. 196,L 121.

Weidemann, V., 1987, Astron. Astrophys.188,74.

New Results About SBO Galaxies

o. BEITONI, Osservatorio Astronomico di Padova, Italy, andG. GALLEITA, Oipartimento di Astronomia, Universita di Padova, Italy

We discuss here the preliminary re­sults of a long term project on kinema­tics and photometry of SBO galaxiesbegun at ESO in 1983 and not yet fullycompleted. Beginning this study, wewere particularly interested in analysingthe mark of triaxiality that the bar in­duces in otherwise symmetrical galax­ies, by perturbing and stretching out thestellar orbits. But we did not imaginethat, progressing in this almost unex­plored land, so many new and not yetfully explained features would be dis­covered. Now, we feel it would be inter­esting to resume here before the com­pletion of the search the main results sofar obtained.

1. A Bit of History

SBO galaxies are good candidates forthis study because of the low, but notnegligible, quantity of gas and dust pre­sent in them. But despite the largenumber of theoretical models of bars,and the several works on gas kinema-

tics, stellar motions were in the pastvery little studied. A systematic attemptto analyse the kinematics of SBOs (Kor­mendy 1982, 1983) was never com­pleted and practically only one galaxy,NGC 936 (Kormendy 1983, 1984), wasstudied in detail (photometry, stellar ve­locity field and velocity dispersion field)before 1987. Similar projects at otherobservatories followed the samecourse, with observations never com­pleted or results never published. Prob­able reasons for this were the difficultyof supporting for many years a projectrequiring many observing nights againstthe idea that in the melting pot of bill ionsof stars moving within the bar it shouldbe impossible to distinguish between"families" of orbits and, last but notleast, against the occasional misunder­standing of some (too human) timecommissions. But with some vi­cissitudes and a little bit of luck, obser­vations of SB Os continued at ESO tele­scopes, demonstrating that we can lookinside the stellar and gas kinematics

with good hope of progressing towardits complete understanding. In recentyears, therefore, new data on stellarkinematics have become available foreight more SBOs (Galletta 1987, Bettoniand Galletta 1988, Bettoni et al. 1988,Jarvis et al. 1988, Bettoni 1988). Theobservational techniques used in ourobservations reflect the improvement ofESO instrumentation in these years:starting with the 3.6-m telescope withthe Boiler & Chivens spectrograph andthe 3-stage EMI image tube, the obser­vations continued at the ESO-MPI2.2-m telescope with RCA CCDs whenthese detectors became available. Par­allel to this study, the inner photometryof the selected galaxies has been per­formed using the ESO-Danish 1.52-mtelescope.

2. Observations andData Reduction

Our sampie includes 15 SB 0 galaxiesbrighter than the 12th magnitude and

51

Figura 1: The almost face-on SBO NGC 2217(bottom), and its spectrum along the bar'sminor axis (top) showing the opposite tift ofemission and absorption lines. This is thesecond case of counterrotation between gasand stars found in SB0, after NGC 4546(Gal/etta 1986).

visible for a whole night in the allottedobserving period. We selected thesegalaxies in an effort to have systemswith all possible orientations of the bar,from side-on to end-on, and with allpossible inclinations of the galaxydisk, from edge-on (i = 90°) to face-on(i = 0°). Among these, 10 systems haveal ready been observed in the previousruns at La Silla and 7 of these have beenfully reduced.

A number (from 4 to 7) of long slitspectra at different P. A. were taken foreach galaxy, with exposure times rang­ing from 60 to 120 minutes, in order tomap as much as possible the velocityfield. The spectral region observed atthe 3.6-m telescope ranged from 3500to 4500 A, including Ca 11 Hand K,G-band and the eventually present)..)., 3727-29 [Oll] doublet. The spectralregion selected at the 2.2-m rangedfrom 4800 to 5800 A, due to the differentspectral response of the RCA CCDsadopted, and includes Mg I, Fe andmany other bands. When present, H ßand )..)., 4959-5007 [0111] doublet werealso measured. In addition, the spec­trum of some giant stars of low rotation­al velocity were recorded each night, foruse in the reductions as template starsof zero velocity dispersion. All the spec­tra have been reduced by means of theESO-IHAP procedures and analysed us­ing the FQ method (Sargent et al., 1977)modified as in Bertola et al. (1984) to

plane. The second case is representedby NGC 2217, a galaxy with almostround disk isophotes where gas andstars again exhibit opposite motions,circulating around the bar major axiswith velocities lower than in the case ofNGC 4546, but not negligible (Fig. 1).

In these galaxies the presence of re­trograde motions should be interpretedas arecent acquisition from outside,lacking reasonable mechanisms whichallow such a clear decoupling betweenangular momenta of gas and stars hav­ing the same origin. They fit in the widerframe of SOs with recent interaction, likethe polar ring galaxies (Schweizer et al.1983) and confirm the idea that the gasin SO galaxies has an external origin, assuggested for the H I by Wardie andKnapp (1986).

Oifferences between gas and starkinematics could enhance particulartypes of orbits. For instance, in the caseof NGC 2217 the peculiarities observedcould be explained if the gas moved onorbits belonging to the families ofanomalous orbits (X-tube, see Van Alba­da et al. 1982), wh ich appear retrogradewhen seen from the galaxy pole. This isactually the orientation at which, in analmost face-on galaxy such as NGC2217, we observe the triaxial ellipsoidrepresented by its bar. These orbitswere originally invoked (Van Albada etal. 1982) to explain the motions ob­served in the class of elliptical galaxieswith minor axis dust lanes (Bertola andGalletta 1978) and represent a typicalcase where a single family of orbitsshould be discriminated from the heapof galactic orbits, as discussed in theintroduction.

Another family of orbits that should bedisentangled from the mass of theothers, in the very special case of NGC4546, is that of the retrograde Z-tube(Contopoulos and Papayannopoulos1980, Heisler et al. 1982, Teuben andSanders 1985). These orbits within thebar are elongated parallel to the barintermediate axis, a direction perpen­dicular to the most part of the innermost

200

150 j ~ ! j I0 bar major axisQ)

100

,H~~~~H jI~ tlVl

........E

2:. 50> •0

-50

3.1 Velocity fjelds

Two galaxies were found where gasand stars rotate with similar but oppo­site streams. This is one of the moreremarkable features found, and fully un­expected, which induces some interest­ing reflections on the nature of the gas inSO galaxies. Observing NGC 4546, anapparently normal edge-on SBO, we de­tected the presence in the same spec­trum of emission and absorption linestilted because of the rotation but inopposite way (Galletta 1986, 1987). Theamplitude of the observed motions be­tween gas and stars is of the order of400 km S-1 along the apparent majoraxis. This gas lies in a - 5 kpc wide disknot yet relaxed on the main galaxy

The main properties of the SB 0 galax­ies observed until now are resumed inTable I, where in addition to the galaxiespresent in our sampie we added NGC936 (Kormendy 1983, 1984) and the fourgalaxies studied by Jarvis et al. (1988).

We could resume the more interestingfindings:

3, Results

produce the stellar velocity and velocitydispersion curves. The emission lineseventually present have been interpo­lated by fitting gaussian profiles, obtain­ing the gas velocity curve and the equi­valent velocity dispersion agas = FWHMI2.53.

The photometric analysis has beenperformed on frames recorded in bandV, land at wavelengths around Ha onthe 1.5-m Danish telescope, with expo­sure times ranging from 10 to 30minutes. They have been reduced withthe standard ESO-IHAP procedures.The photometric zero point of V bandhas been obtained using the mag­nitudes reported by Longo and de Vau­couleurs (1983), while the isophote in­terpolation has been performed usingthe INMP programmes (Barbon et al.1975).

o 10 20 30 40 50r (arcsec)

Figura 2: The velocity curve along the bar of NGC 7079, folded about the nucleus. The typicalwavy pattern of the velocity curve, found in six more galaxies (Bettoni 1988), is clearly visible.Different symbols refer to the two opposite sides of the rotation curve.

NGC?~17

Li

Mg11

bar minor axis.

.\:

.'

\: ~.'"

..

... ..

bar~.

,[ 0 111 ]{ t

"

52

Table I: Properties of the sao galaxies studied. The main geometrie eharaeteristies of eaeh galaxy, as the estimated inelination i with repeet tothe sky or the presenee of ionized gas, are listed. In the following eolumns are also indieated: the presenee of Z-motions (perpendieular to thegalaetie plane) for almost face-on galaxies; the symmetry of the bar velocity eurve with respeet to the galaxy nueleus; the presenee in it ofsymmetrie oseillations; the trend of the bar velocity dispersion. A question mark indieates data not yet fully redueed.

GEOMETRY BAR KINEMATICS

Name Bar-Disk i lonized Presence 01 Presence 01 'Double wave' °bar Re!. Notes

P.A. gas Z-motions asymmetry effect

NGC 936 59° 49° no - yes yes IIat 1

NGC 1543 - 0° no on both axes no no - IIat 5 Double bar

NGC 1574 70° 28° no most on min. axis yes yes peaked 5NGC 2217 - 24° laint spiral arms most on min. axis ? ? ? 7 Gas retrograde

IC 456 79° 48° yes - yes yes flat 6

NGC 2983 51° 4r no - no yes peaked 4

NGC 4371 70° 66° no - ? ? ? 7

NGC 4442 10° 71° no - ? ? ? 7

NGC 4477 58° 24° no on both axes no yes flat 5

NGC 4546 45° 71° irregular disk - no no peaked 2 Gas retrograde

NGC 4643 - 0° no most on min. axis yes no peaked 7

NGC 4684 0° 75° spiral arms, - no no Ilat 7

filamentsNGC 4754 60° 59° no - yes no flat 5

NGC 6684 61° 48° no - yes yes flat 3

NGC 7079 43° 43° yes - no yes peaked 7

Rererences: 1: Kormendy (1983), 2: Galletta (1987) 3: Bettoni and Galletta (1988), 4: Bettoni et al. (1988), 5: Jarvis et al. (1988), 6: Bettoni (1988), 7: Bettoni andGalletta, in preparation.

1100 L::L:i:=i::::::I:::i::::L:::::L=-t-L----L-L.-.L-l...--L---L-..L...l---L-.l...-LL--L....J-.J-60 -40 -20 0 20 40 60

r (arcsec)

Figure 3: Velocity eurves for the face-on galaxy NGC 4643 (shown in the inset), after a gaussiansmoothing of 2". Along the bar, only an asymmetrie pattern is visible (open squares) withoseillations of - 40 km S-7. On the eontrary, the velocity inereases as the speetrograph slit istwisted away from the bar going toward the minor axis (full diamonds). At this P. A., symmetriemotions with an amplitude of 160 km S-7 are deteeted. Due to the orientation of the galaxy,these motions should be perpendieular to the galaetie plane.

Galletta 1988, Fig. 5) and NGC 2983(Bettoni et al. 1988, Fig. 4). Similarshapes were deteeted also in NGC 1574and NGC 4477 (Jarvis et al. 1988), asweil as in NGC 7079. In all these galax­ies the veloeities rise from the nueleusoutward, then reverse their direetionreaehing minimum (or negative) valuesand turn baek to inerease their am­plitude, reaehing near the end of the bar

stellar orbits, whose major axes lie onthe bar's major axis. Sinee gas motionsin NGC 4546 are retrograde with respeetto the stars, the elongation of theisoveloeity lines in the two veloeity fields(gas and stars) appears at P. A. at al­most 90° between them, eonfirming inthis fortunate (and maybe unique) easethe existenee of this theoretieally ex­peeted orbits.

Bar kinematies are sometimesasymmetrie with respeet to the wholegalaxy. As generally performed in thereduetion of rotation eurves, the veloeityeurve derived from eaeh speetrum wasfolded about the nueleus and the sys­temie veloeity. In many eases the rota­tion eurves elose to the bar differ fromthe generally symmetrie veloeity field. Inthese galaxies, bar motions are aetuallysymmetrie, but with respeet to a pointnot eoineident with the galaxy nueleus,and independent of the apparentsymmetry of the light distribution. Thiseffeet should refleet areal misalignmentof the bar within the galaxy or the pres­enee of dark and asymmetrie matter. Itis not yet clear whieh of these effeetseould be relevant.

A typieal "wave pattern" of the barrotation eurve has been revealed in allthe galaxies with intermediate inelina­tion with respeet to the sky so far ob­served. This effeet, produeing a "doublewave" appearanee of the unfolded ve­loeity eurves, was brought into evideneeduring the observations of IC 456(Bettoni 1988) by eomparing its bar ve­loeity eurve with that already publishedof the galaxies NGC 936 (Kormendy1983, Fig. 4 b, NGC 6684 (Bettoni and

1400

()

'"Vl

E1300-'<:

>

1200

the values of the general veloeity fjeld(Fig. 2). This veloeity profile might os­eillate around zero (systemie veloeity)for galaxies with bar close to the ap­parent disk minor axis (e. g. NGC 6684)or might be superimposed to the mainrotation, if the bar is eloser to the majoraxis (e. g. NGC 936). This trend must notbe eonfused with loeal minima of therotation eurve whieh appear outside the

NGC 4643° bar major axis• bar minor axis

53

Ha

Figure 4: The inner regions of NGG 4684, in a GGD frame (V band) taken at the 1.S-m Danishtelescope. The bar is seen side-on, along the galaxy major axis. In the inset, the nucleus of thegalaxy, at the same scale, observed in Ha light. The continuum near Ha has been subtracted.Dust lanes, spiral arms and filaments are visible.

NGC 4684

Vband

tribution of the angular momentum in astellar system since its protogalaxyphase.

Many bars have flat velocity disper­sion profiles. In 7 systems over 12 thebar velocity dispersion is characterizedby a constant trend, with the peak of thebulge velocity dispersion eventuallysuperimposed. An example of this effectis offered by NGC 6684 (Bettoni emdGalletta 1988) or by NGC 4477 (Jarvis etal. 1988). This could indicate that thebars are uniformly hot. A more detailedanalysis is necessary to answer thispoint.

3.2 Photometry and Ha imaging

Many systems have elongated or tri­axial components. This agrees with theresults of statistical works on rings andbulges (Kormendy 1979, Athanassoulaet al. 1982, Buta 1986). A typical collec­tion of these properties is represented

the case of NGC 1574, NGC 4477 andmay be NGC 2217, whose isophotalaxial ratio is close to 0.9 (- 27" ofinclination for disks as f1at as 0.25). Butthis hypothesis cannot explain the notnegligible velocities found in NGC 1543and NGC 4643, as weil as the amplitudeof that observed in the remaininggalaxies.

As discussed previously, the gas inNGC 2217 should stream in one of thetwo possible families of anomalous or­bits (see Schwarzschild, 1982), whilethis hypothesis is less plausible for thestellar motions, distributed in a widerrange of energies and not streamingaccording to a specific orbit. It would beinteresting to know if unbarred galaxiesalso share this property, but until nowallrequests for observing time on thisproblem have been rejected. In anycase, this feature must be clarified alsofrom the theoretical point of view, hav­ing interesting implications on the dis-

bar where the bulge fades in the lens orin another component, as is the case ofNGC 3945 (Kormendy 1982, Fig. 3) andNGC 2983 itself, where the twophenomena are present (Bettoni et al.1988, Fig. 4).

On the contrary, no wavy trendaround the systemic velocity was de­tected in NGC 4546 (Galletta 1987), inNGC 1543 and NGC 4754 (Jarvis et al.1988) or in the two remaining galaxies ofthe sampie so far reduced (see Table I).As an intrinsic feature, the observedwavy trend around the systemic velocityshould be due to the presence of retro­grade stellar streamings confined tosome radii along the bar. A similar fea­ture is expected in many models ofbarred galaxies which need someamount of retrograde motions. Amongthese the Freeman (1966 a, b)homogeneous bar model, the N-bodysimulation by Zang and Hohl (1979) andthe self-consistent model by Pfenniger(1984a, b). The last study suggests thatthree-dimensional stellar motions withina barred galaxy should periodically re­verse the sense of rotation because ofvertical instabilities. In addition, there isthe possibility that these motions areproduced by a combination of bar anddisk streamings in some sectors of thegalaxy plane, as suggested by L. Sparke(private communication) on the basis ofthe analysis of an N-body model of abarred galaxy (Sparke and Sellwood1987). A more detailed analysis of thisproperty is in progress, but a clear pic­ture will be available only when (and if)the observations of a larger galaxy sam­pie are performed. At this moment wecan only say that this effect is observedonly in galaxies with inclination between28° and 53°, lacking in almost face-onor edge-on systems.

Stellar and gas streaming perpen­dicular to the galaxy plane was de­tected. This is another unexpectedpoint, since it is generally believed thatthe main part of ordered motions takesplace parallel to the main galactic plane.On the contrary, it has been observed inall the 6 almost face-on galaxies con­sidered (see Table I). In the case of NGC4643, for instance, the velocities alongthe bar are quite low (- 40 km S-1), whilea wide rotation along the bar minor axisis present, with velocity differences of160 km S-1) (Fig. 3). A similar conditionis present in NGC 1574 (Jarvis et al.1988) and NGC 2217, while comparableamounts of rotation in both axes weredetected in NGC 1543, and NGC 4477(Jarvis et al. 1988). In some of thesecases, this effect should be due to a notfully face-on orientation of the galaxyand/or to the fact that the bar's minoraxis is close to the major axis of thedisko Looking at Table I, this could be

54

Comet Tempel 2 Turns On

by NGC 6684 (Bettoni and Galletta1988). In this galaxy, the ring is elon­gated parallel to the bar, in a directionclose to that of the line-of-sight. Thisgives the system the unusual aspect of agalaxy with a ring rounder than the diskoBut the bulge also is triaxial. Itsisophotes are not aligned at the sameP. A. of the disk and the observed stellarmotions appear to have a "kinematicalline of the nodes" not coincident withthe disk major axis, both typical signs oftriaxiality. In addition, the bar appearsdisplaced by - 2" from the nucleus ofthe galaxy along its major axis. Off-cen­tring of the bar (but along the bar'sminor axis) is actually observed in somebarred galaxies, but generally appearsin late spirals, as NGC 4027 (Christian­sen and Jefferys 1976, Pence et al.1988). But with respect to the remaininggalaxies of the sampie, the offset of theNGC 6684 bar is quite a peculiar fea­ture.

Short and smooth spiral arms, some­times forming an incomplete ring,appear in same of the studied systems,such as NGC 2983, NGC 4546 and NGC6684. This feature is brought into evi­dence by means of a decomposition ofthe images in the main galaxy compo­nents, performed by means of IHAP (seeBettoni et al. 1988). This procedure alsoindicates that in our sampie the barscontain less than 20 % of the total light.

The gas in the SB Os observed is con­centrated in disks or in complex struc­tures with spiral arms. The Ha imagingof some of the galaxies considered,which possess ionized gas (6 out of 11),indicates a spiral or a not relaxed struc­ture. NGC 2217, for instance, has faintspiral arms in a structure that should beperpendicular to the bar's major axis.This structure recalls the gas in thewarped plane which crosses the minor­axis dust-Iane galaxies (Bertola andGalletta 1978) and seems to confirm theassumption made previously concern­ing matter in anomalous orbits. Themore extended and complex structuresobserved in NGC 4546 and NGC 4684(Fig. 4) represent two more cases of gaswhose irregularity strongly suggests arecent acquisition from the outside.Again, as indicated by Wardie andKnapp (1986) for the neutral gas, thereare indications of an external origin ofmost of the gas in SO galaxies.

This work is dedicated to our daugh­ter Anna, who decided to be born duringthe drafting of this paper.

References

Athanassoula, E., Bosma, A., Greze, M.,Schwartz, M. P., 1982, Astron. Astrophys.107,101.

Barbon, R., Benacchio, L., Gapaccioli, M.,1975., Astron. Astrophys. 51, 25.

Bertola, F., Bettoni, 0., Rusconi, L., Sedmak,G., 1984, Astron. J, 89, 356.

Bertola, F., Galletta, G., 1978, Astrophys. J,226, L 115.

Bettoni, D. and Galletta, G., 1988, Astron.Astrophys., 190, 52.

Bettoni, 0., Galletta, G. and Vallenari, A.,1988, Astron. Astrophys., 197, 69.

Bettoni, 0., 1988, Astron. J, submitted..Buta, R., 1986, Astrophys. J Suppl. Ser., 61,

609.Gontopoulos, G. and Papayannopoulos, Th.,

1980, Astron. Astrophys., 92, 33.Ghristiansen, J. H. and Jefferys, W. H., 1976,

Astrophys. J, 205, 52.Freeman, K.G., 1966a, Mon. Not. R. Astr.

SOG., 133, 47.Freeman, K.G., 1966b, Mon. Not. R. Astr.

SOG., 134, 1.Galletta, G., 1986, The Messenger, 45,18.Galletta, G., 1987, Astrophys. J, 318, 531.Heisler, J., Merri!, 0., Schwarzschild, M.,

1982, Astrophys. J, 258, 490.Jarvis, B. J., Dubath, L., Martinet, R. and Ba­

con, R., 1988, Astron. Astrophys., in press.Kormendy, J., 1979, Astrophys. J, 227, 714.Kormendy, J., 1982, Astrophys. J, 257, 75.

Earlier this year, observers all over theworld began to observe Comet Tempel2, a prime object for the NASA CometRendezvous Asteroid Flyby mission(CRAF) in 1993. This short period comet(P = 5.29 years) was first observed in

Kormendy, J., 1983, Astrophys. J, 275, 529.Kormendy, J., 1984, Astrophys. J, 286,132.Longo, G., de Vaucouleurs, A., 1983, Univer-

sity of Texas Monographs, N. 3.Pence, W.D., Taylor, K., Freeman, K. G., de

Vaucouleurs, G., and Atherton, P., 1988,Astrophys. J, 134.

Pfenninger, 0., 1984a, Astron. Astrophys.,141,171.

Pfenninger, 0., 1984b, Astron. Astrophys.,134,373.

Sargent, W. L. W., Young, P. Y., Boksenberg,A., Shortridge, K., 1977, Astrophys. J,212, 326.

Schwartzschild, M., 1982, Astrophys. J, 263,599.

Schweizer, F., Whitmore, B.G., and Rubin,V.G., 1983, Astron. J, 88, 909.

Sparke, L.S. and Sellwood, J.A., 1987,Mon. Not. R. Astr. Soc., 225, 653.

Teuben, P.J., and Sanders, R. H., 1985, Mon.Not. R. Astr. SOG., 212, 257.

van Albada, T.S., Kotanyi, G.G. andSchwarzschild, M., 1982, Mon. Not. R.Astr. SOG., 198, 303.

Wardie, M. and Knapp, G. R., 1986, Astron.J, 91, 23.

Zang, T.A. and Hohl, F., 1979, Astrophys. J,226,521.

1873 and has since been seen at no lessthan 18 apparitions.

This time it was recovered already inDecember 1986, by Tom Gehreis andhis collaborators with the Spacewatchcamera. At that time the heliocentric

55