High spatial resolution observations (~1 ) of the jet feature associated with the symbiotic variable R Aquarii were obtained with the Very Large Array (VLA). The peak radio intensity of the jet lies at a 29~3 P.A. with respect to the radio emission from R Aquarii itself. If the line defined by the jet and star is extended ~196 , it intercepts a previously reported and heretofore unresolved radio source. In our high spatial resolution 6 cm map, this feature is resolved into a compact double radio source, whose peak intensity lies on an axis defined by the jet and star. The possible association of this feature with R Aquarii or with the extended filamentary nebula that surrounds the system cannot be determined from these radio morphology studies alone. If this feature is associated with R Aquarii, it may represent ejecta from the system which occurred previously. Moreover, a new unresolved radio feature has been detected - 2\u27\u27:7 from the central star at - 45° P.A. It may represent material recently ejected from the system, perhaps as the object precesses. Weak evidence for a counter-jet is suggested from radio contours centered on R Aquarii

Hollis, J. M.

Kafatos, Menas

Michalitsianos, A. G.

English

Chapman University Digital Commons

Chapman UniversityChapman University Digital CommonsMathematics, Physics, and Computer ScienceFaculty Articles and ResearchScience and Technology Faculty Articles andResearch1983High Spatial Resolution VLA Observations of theR Aquarii JetMenas KafatosChapman University, kafatos@chapman.eduJ. M. HollisBlue Bay Res IncA. G. MichalitsianosNASA, Goddard Space Flight CenterFollow this and additional works at: http://digitalcommons.chapman.edu/scs_articlesPart of the Stars, Interstellar Medium and the Galaxy CommonsThis Article is brought to you for free and open access by the Science and Technology Faculty Articles and Research at Chapman University DigitalCommons. It has been accepted for inclusion in Mathematics, Physics, and Computer Science Faculty Articles and Research by an authorizedadministrator of Chapman University Digital Commons. For more information, please contact laughtin@chapman.edu.Recommended CitationKafatos, M., Hollis, J.M., Michalitsianos, A.G. (1983) High Spatial Resolution VLA Observations of the R Aquarii Jet, TheAstrophysical Journal, 267: L103-L107. doi: 10.1086/184012High Spatial Resolution VLA Observations of the R Aquarii JetCommentsThis article was originally published in Astrophysical Journal, volume 267, in 1983. DOI: 10.1086/184012CopyrightIOP PublishingThis article is available at Chapman University Digital Commons: http://digitalcommons.chapman.edu/scs_articles/1241983ApJ...267L.103KTHE ASTROPHYSICAL JOURNAL, 267:L103-LJ07, 1983 April 15 1983. The American Astronomical Society. All rights reserved. Printed in U.S.A. HIGH SPATIAL RESOLUTION VLA OBSERVATIONS OF THE R AQUARII JET M. KAFATOS Department of Physics, George Mason University AND J. M. HOLLIS AND A. G. MICHALITSIANOS Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center Received 1982 November 16; accepted 1982 December 17 ABSTRACT High spatial resolution observations (- I") of the jet feature associated with the symbiotic variable R Aquarii were obtained with the Very Large Array (VLA). The peak radio intensity of the jet lies at a 29~3 P.A. with respect to the radio emission from R Aquarii itself. If the line defined by the jet and star is extended - 196", it intercepts a previously reported and heretofore unresolved radio source. In our high spatial resolution 6 em map, this feature is resolved into a compact double radio source, whose peak intensity lies on an axis defined by the jet and star. The possible association of this feature with R Aquarii or with the extended filamentary nebula that surrounds the system cannot be determined from these radio morphology studies alone. If this feature is associated with R Aquarii, it may represent ejecta from the system which occurred previously. Moreover, a new unresolved radio feature has been detected - 2':7 from the central star at - 45° P.A. It may represent material recently ejected from the system, perhaps as the object precesses. Weak evidence for a counter-jet is suggested from radio contours centered on R Aquarii. Subject headings: stars: accretion- stars: circumstellar shells- stars: long period variables-stars: mass loss- stars: radio radiation I. INTRODUCTION R Aquarii (M7e + pee) is a symbiotic star suspected of being a binary stellar system which consists of a 387 day period Mira variable with a hot subdwarf. This stellar region is characterized by an extended diffuse filamentary nebula that encircles an inner compact ionized region. A jetlike feature of the inner compact nebula appeared between 1970 and 1977. The jet has been observed in the optical (Wallerstein and Greenstein 1980; Herbig 1980), in the radio at 6 and 2 em with the VLA (Sopka et a/. 1982), and in the far-ultraviolet with the International Ultraviolet Explorer (IUE) (Michalitsianos and Kafatos 1982). A theoretical interpretation (Kafatos and Michalitsianos 1982) for the formation of the jet proposes that it involves supercriti-cal accretion onto the hot companion star and occurs during periastron in a highly elliptical 27-44 year orbit. Optical spectra obtained by G. Herbig (see Sopka et a/. 1982) suggest radial velocity differences between the jet and adjacent nebular emission knots are substan-tial; the mean heliocentric radial velocity of the jet is - - 70 km s- 1, while the mean radial velocity centered on the star is - 44 ± 2 km s- 1• Enhanced micro-densitometer images of Lick 3 m direct plates obtained by Herbig (1980) suggest the jet feature is detached from Ll03 the star. Previously obtained radio continuum integrated flux measurements at 6 em by Sopka et a/. indicated the jet is weaker by a factor of - 4 compared with the star. These initial VLA observations, obtained with the C antenna configuration, lacked sufficient spatial resolu-tion (- 5") to discern structure in the jet; however, they did show the radio emission was coincident with the optical jet feature photographed by Herbig (see Sopka et a/.). These radio observations also reported an unre-solved radio spot approximately 3' from the R Aquarii radio source toward the NE along the 29~3 P.A. line. It is not clear whether this radio source is associated with R Aquarii or is a background extragalactic radio source. Michalitsianos and Kafatos (1982) obtained UV-spec-tra of the jet and the inner compact ionized region. The jet's far-UV continuum flux between 1200 and 2000 A rises steadily with decreasing wavelength and is signifi-cantly different in appearance than the continuum flux distribution exhibited by the stellar ionized region. The compact inner region exhibits UV continuum emission which is flat or independent with wavelength over this spectral range. Moreover, prominent emission lines of Si II Xl815 and Si III] Xl892 seen in the central region are absent in the jet. These observations suggest the material in the jet is comparatively cooler and less dense than the central region. This has been confirmed by © American Astronomical Society • Provided by the NASA Astrophysics Data System 1983ApJ...267L.103K-15°30145" 0 50" ~ - ~ 0 0 0 LO 0) -"0 55" '" 1,/<;1 ¢ 00" 20~6 20~2 a (1950.0) PEAK FLUX= 6.57m Jy/BEAM CONTOUR LEVELS IN %OF PEAK FLUX: -1, 2, 3, 4, 5, 6, 7,8,9, 10, 20,30,40,50, 60, 70,80, 90,100 -q 0 LO 0) 40" "0 45" 50" 0 0 PEAK FLUX= 1.407m Jy/BEAM CONTOUR LEVELS IN %OF PEAK FLUX: -1 0, 1 0, 20, 30,40, 50, 60,70,80,100 196" (1 /\ ' t ,,.., I I I I '\ /i 0 \ ,_, \ ... ) 0 I' 1 I I I I I -~ " o' •,1 /1 I I ,, "• \} ,,-\ I I I / ,_ ,, 0 I " I' II' ' I I II ~~ ._, () I \ rl I / 1} ! , , ,_ i'""\ .__, 0 (':' ., 0 0 0 •"o I I ,_, v 1\ () (J I, I " I I I 'I ._, I ',) 't> () 14~4 14~0 a (1950.0) 1\ ... ,., I I 0 0 \,,_/ /) .. I 0 ,,_, ., I I \..) { .. , 0 I I 0 ,_1 FIG. !.-(lower) This 6 em map shows structure extending from R Aquarii along a position angle of - 29?3; contour levels and the peak flux for this map are shown to the left. Note the unresolved nature of the nearby point source (A) to the NE of R Aquarii and R Aquarii itself. The jetlike feature (B) farther to the NE shows some structure. (upper) This 6 em map shows the CDRS with contour levels and its peak flux to the right. The double nature of this source is clearly resolved, but each component remains pointlike, reflecting the approximate shape of the synthesized beam (see text). The peak flux of the jetlike feature falls along the superposed position angle line, whose length is not to scale of the maps, from the peak flux of R Aquarii to the peak flux of the stronger CDRS component. The integrated flux of the CDRS and the jetlike feature are approximately the same (see Table 1). Caution is advised in drawing conclusions from any apparent complementary map morphology shown here between the CDRS and the R Aquarii environment until confirming observations of a different nature (e.g., spectrographic) are available. © American Astronomical Society • Provided by the NASA Astrophysics Data System 1983ApJ...267L.103KR AQUARII JET TABLE I Ll05 OBSERVATIONAL SUMMARY OF POSITIONS AND FLUXES Source a(l950) (I) (2) Fig. I, R Aquarii Map: 23h4I.,;i4~270(1) RAquarii ................... Nearby point (feature A) ... 23 41 14.398(7) Jet (feature B) .............. 23 41 14.493(7) Fig. I, CDRS Map: Stronger feature ............ 23 41 20.444(1) Weaker feature ............. 23 41 20.548(3) Calibration Sources: 3C 48 ....................... 01 34 49.832 3C 138 ...................... 05 18 16.532 2345-167 .... ··············· 23 45 27.687 8(1950) (3) -15°33'42'.'76(1) -15 33 40. 85(10) -15 33 37. 23(10) -15 30 51. 66(2) - 15 30 51. 29(4) +32 5420.52 + 16 35 26.92 -16 47 52. 59 Integrated Flux a (mJy) (4) 11.793b 7.746c 0.6J4C 3.433d 4.034b.e 1.926c 1.282c 5360fj5360f 3095(20)/3018(13) 4198(33)/4055(29) Date (1982 Sep) (5) 26 26 26 26 27 27 27 26-27 26-27 26-27 a The I a error on the background field of all maps was - 0.05 mJy per beam. bTotal map flux. cFiux under a fitted elliptical Gaussian. dFiux resulting from subtraction of the contribution of R Aquarii and the nearby point feature from the total flux of the R Aquarii map. •Note that the total flux of the CDRS map is more than the sum of the fluxes under the two fitted Gaussians which approximate this source (see text). rAssumed known (Baars eta/. 1977); flux density errors in this column reflect the uncertainty in determining flux calibration ratios from observations relative to 3C 48 (see text). recent optical spectra of the forbidden 0 II and 0 III emission lines (R. Fesen, private communication) ob-tained of the jet feature. II. OBSERVATIONS The observations, centered on R Aquarii and the compact double radio source (CDRS), were made on 1982 September 26 and 27, respectively, with the NRAO 1 VLA. The B antenna configuration with all27 antennas was employed at 4885 MHz (A6 em). The intermediate frequency bandwidth was 50 MHz. The spacing between antenna pairs varied between 0.2 and 11.1 km which yielded a synthesized CLEAN beam of 1':42 X 1':04 with a position angle of -1 ?64. The observations of R Aquarii were interleaved with observations of 2345-167 which was used as the calibration source; time dedicated to each object was 12.5 and 2.5 minutes, respectively, inclusive of array move time. This observa-tional procedure for R Aquarii was followed for a period of 8 hours centered on Oh LST. The flux density scale was established by assuming 3C 48 to have a flux density of 5.36 Jy (Baars et a/. 1977). A single 3C 48 observation of at least 4 minutes was made to establish proper flux density ratios with 2345-167 and R Aquarii. Identical observing and calibration procedures were fol-lowed for the CDRS, using 2345-167 as the calibrator source. The data were edited and 2345-167 observations were used to calibrate the correlated amplitude and 1 The N a tiona) Radio Astronomy Observatory is operated by Associated Universities, Inc., under contract with the National Science Foundation. phase data of R Aquarii and the CDRS. The standard programs at the VLA site were used. The calibrated amplitudes and phases were transformed to produce the CLEANed 6 em maps with no taper applied as shown in Figure 1. The presentation of the maps demonstrates the relative orientation of the CDRS with respect to the R Aquarii environment. R Aquarii itself is largely unre-solved but does display some structure on the side opposite the jetlike feature (B in Fig. I) which is - 6'.' 4 toward the NE along the 29~3 P.A. line. Moreover, an unresolved feature (A in Fig. I) - 2~'7 away from R Aquarii toward the NE is readily apparent. The CDRS is resolved into two pointlike features, and it is curious that all five distinct features in Figure 1 lie along the position angle determined by the peak flux in the CDRS and R Aquarii. Table I is a compilation of the positions and integrated fluxes of the radio features mentioned above. The total integrated flux of the CDRS map is comparable to the integrated flux we attribute to the jetlike feature near R Aquarii. Source count statistics predict the brightest background source at a 2.3 mJy level within a 9' beam at 6 em (Hjellming and Basart 1982). Thus, with just the observed morphology and attendant flux levels, we are unable to determine unam-biguously if the CDRS is associated with R Aquarii. Future spectrographic observations in either the optical or ultraviolet may be able to resolve this important issue. III. DISCUSSION AND CONCLUSIONS R Aquarii is known to undergo erratic outbursts in which the hot source dominates the visible light of the © American Astronomical Society • Provided by the NASA Astrophysics Data System 1983ApJ...267L.103KLl06 KAFATOS, HOLLIS, AND MICHALITSIANOS Vol. 267 cool Mira primary. The binary period of the system is believed to be 44 years (Willson, Garnavich, and Mattei 1981 ), although a shorter period is not ruled out by the observations (Kafatos and Michalitsianos 1982). Merrill (1950) suspected the orbital eccentricity, e, of the system to be large. If outbursts observed in the system are the result of tidal interaction between the Mira and hot subdwarf companion, an e ~ 0.85 is necessary in order for the cool primary to fill its Roche lobe, which can occur only at or near periastron (Kafatos and Michalitsianos 1982). We point out that the Mira would fail to fill its Roche lobe by at least a factor - 5 for a 44 year orbit if the orbit were perfectly circular. The high eccentricity ensures that mass transfer can occur in the system at or near periastron: such mass transfer would proceed at supercritical rates and form an accretion disk. According to this model, the jet formed during the previous periastron encounter, which accounts for its appearance in the mid-1970s, roughly one binary period after the 1928-1935 outburst. Present VLA observations of the R Aquarii environ-ment suggest that the integrated radio flux emission at 6 em has not changed over approximately 1 year ( cf. Sopka eta/. 1982). However, owing to the lower spatial resolution of the earlier 6 em maps of the jet feature, we cannot determine if any morphologic changes have oc-curred in radio features (Fig. I). The nearby point feature A is - 2'!7 away from the star and could repre-sent material more recently ejected from the system. If this is the case, taking a distance of 300 pc to R Aquarii (cf. Michalitsianos, Kafatos, and Hobbs 1980; and Whitelock et a/. 1982), 1" corresponds to a linear sep-aration of - 4.5 X 1015 em. Feature A is, therefore, about 1.2 X 1016 em from R Aquarii. Its dimensions are less than the beam size of our VLA map at 6 em. On the other hand, the jet (feature B) is elongated and spatially resolved. Its peak radio emission is located - 6'.' 4 or - 2.9 x 1016 em from R Aquarii at 29?3 P.A. The expansion rate is likely supersonic, where the sound speed, c s - 10 km s- 1, corresponds to the pre-vailing electron temperatures in the jet (Te - 104 K). Our VLA observations enable us to obtain a lower limit for the velocity of feature B: its distance from R Aquarii is - 4 times its size, i.e., it has moved 4 times farther than it has expanded. It follows that feature A is moving with an ejection velocity, vej, of at least 40 km s- 1• The ejection velocity may be as high as 7 60-1800 km s- 1, if ejection took place between 1970 and 1977. Assuming that feature A was expelled with the same velocity as feature B, we find that it was ejected 3-7 years follow-ing the emergence of feature B. If this interpretation is correct, these observations suggest material may be ejected successively every few years from the system. As the two stars are presently receding from one another, we expect that tidal interaction will subside and, therefore, less and less material will be ejected from the system. The kinetic energy of feature B could be quite high. Taking an electron density ne- 3 X 106 em- 3 as appropriate for the jet (Wallerstein and Greenstein 1980; Michalitsianos and Kafatos 1982), we find that the kinetic energy of feature B is EB - 2.5 X 1046 (nB/3 X 106 cm- 3)(ve/700 km s- 1) 2 (RB/8 X 1015 cm) 3 ergs, where nB and RB are the density and spatial extent of the feature respectively. The corre-sponding upper limits to the kinetic energy of unre-solved feature A would be - 1/30 that of feature B for similar densities. The energetics involved in mass exp-ulsion would be sufficient to maintain the extended filamentary nebula that surrounds the R Aquarii system at moderate excitation temperatures, say T. ~ 104 K (Kafatos and Michalitsianos 1982). Future observations in both the optical and radio will be undertaken in order to determine the kinematics of various features of the nebula. At present we cannot unambiguously associate the CDRS with R Aquarii or with the nebulosity that sur-rounds the system. However, it is curious that the peak intensities of the CDRS, the jet B, and R Aquarii itself are collinear. If the jet and the nearby point source (feature A) are ejecta, their difference in position angles could be in-terpreted as precession of the system while it expells material. The morphology of the outer - 2' nebula perhaps could be accounted for in this manner, thus explaining the characteristic lens-shaped filamentary structure. Repeated high spatial resolution observations could confirm this suggestion. The proximity of R Aquarii makes this the closest known object exhibit-ing jet activity. Continued monitoring of this symbiotic system over a wide variety of wavelengths is important in the next several years in order to determine if epi-sodic mass transfer in the suspected binary system accounts for its observed optical and radio properties. We wish to thank Messrs. K. Clark, P. Hicks, and F. Puelo for operating the array and for sundry help with the computer systems. We appreciate the advice and help concerning our observations provided by Dr. and Mrs. R. Perley and Drs. P. Palmer and R. L. Brown. We are especially grateful to Mr. H. G. D. Van Hom for facilitating our observing session. REFERENCES Baars, J. W. M., Genzel, R., Pauliny-Toth, I. I. K., and Witzel, A 1977, Astr. Ap., 61, 99. Herbig, G. 1980, TAU Circular, No. 3535. Hjellming, R. M., and Basart, J.P. 1982, in An Introduction to the NRAO Very Large Array, ed. R. M. Hjellming, (Green Bank, West Virginia: NRAO), p. 5-9. © American Astronomical Society • Provided by the NASA Astrophysics Data System 1983ApJ...267L.103KNo.2, 1983 RAQUARIIJET Ll07 Kafatos, M., and Michalitsianos, A. G. 1982, Nature, 298, 540. Merrill, P. W. 1950, Ap. J., 111, 514. Michalitsianos, A. G., and Kafatos, M. 1982, Ap. J. (Letters), 262, L47. Michalitsianos, A. G., Kafatos, M., and Hobbs, R. W. 1980, Ap. J., 237, 506. Sopka, R. J., Herbig, G., Kafatos, M., and Michalitsianos, A. G. 1982, Ap. J. (Letters), 258, L35. Wallerstein, G., and Greenstein, J. L. 1980, Pub. A.S.P., 92, 275. Whitelock, P. A., Feast, M. W., Catchpole, R. M., Carter, B. S., and Roberts, G. 1982, Smithsonian Ap. Obs., preprint. Willson, L. A., Garnavich, P., and Mattei, J. A. 1981, lnf. Bull. Variable Stars, Nos. 1961-1963. J. M. HOLLIS and A. G. MICHALITSIANOS: Code 685, Laboratory for Astronomy and Solar Physics, NASA-Goddard Space Flight Center, Greenbelt, MD 20771 M. KAFATOS: Department of Physics, George Mason University, Fairfax, VA 22030 © American Astronomical Society • Provided by the NASA Astrophysics Data System 

High Spatial Resolution VLA Observations of the R Aquarii Jet

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High Spatial Resolution VLA Observations of the R Aquarii Jet

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