SUBARU & HST High Resolution Near-Infrared
Multi-Color Images of Class II Young Stellar Object, RNO91
Satoshi Mayama (National Astronomical Observatory of Japan) email:mayamast@subaru.naoj.org

Motohide Tamura(NAOJ), Masahiko Hayashi(NAOJ), Yoichi Itoh(Kobe U.), Miki Ishii(NAOJ),
Misato Fukagawa(Osaka U.), Saeko S. Hayashi(NAOJ), Yumiko Oasa(Kobe U.), and Tomoyuki Kudo(NAOJ)
ABSTRACT
Understanding a variety of planetary systems is one of the most important subjects of current astronomical research. It is important to investigate whether thevariety comes from different initial conditions of primordial disks. Also, the evolution of protoplanetary disks should be observed directly as the change incircumstellar structures along the evolution of central stars, thus allowing us to trace the early evolutionary phases of planet formation as a consequence ofdisk structure evolution.
In order to better understand the variety and evolution of planet formation in early stages, we made a systematic imaging survey of circumstellar disks andcompanions stars. We have conducted high-resolution imaging observations in the near-infrared with the infrared camera CIAO mounted on the Subaru 8.2m
Telescope since 2002. We present one example of our obtained images in which circumstellar structures around young stellar objects are detected in thescattered light at the sub-arcsecond resolutions, and discuss mainly morphology of such structures.

1. INTRODUCTION
What is RNO91?
① located in the L43 dark cloud in Ophiuchus at a distance of 160 pc(Herbst & Warner 1981)②class II embedded source in the transient phase between protostar
and visible PMS star (Parker 1991).
③a source of complex molecular outflow. The redshifted outflow lobe
extends to the north; the blueshifted outflow lobe extends to the south(Levreault 1988; Myers et al. 1988; Mathieu et al. 1988).
④associated with an ammonia envelope (Mathieu et al. 1988), HCO+envelope (Lee et al. 2005), a reflection nebula (Hodapp 1994), andshock-excited H2 emission (Kumar et al. 1999).
⑤mass: 0.5 solar mass (Levreault 1988)⑥magnitude: J=11.0, H=9.6, K=8.5 (2MASS: 1998 April)

2. OBSERVATION

Fig. 6. Azimuthally averaged radial profile ofthe surface brightness of RNO91.

Fig. 5. Pseudo-true color composites ofSubaru-CIAO(K), Subaru-CIAO(J), andHST-WFPC2(optical) broadband
observations of RNO91. Major features
are identified.

Telescope+instrument : SUBARU+CIAO
Venue: Mauna Kea (Hawaii)
Wavelength: 1.25, 1.65, 2.2μm(J, H, K band)
Pixel scale: 0”.0213 pixel-1
Field of View: 22”.0×22”.0
Observation Date: 2001 May 15, 2005 June 27
Diameter of Occulting Mask: no mask
Exposure time: 400s(J), 180s(H), 180s(K) Fig.1. JHK color-composite imageof RNO91. The field of view is
FWHM: 0”.55(J), 0”.52(H), 0”.46(K)4’.8×4’.6. This image was

3. RESULTS

Fig. 7. Illustration of front view of RNO91 and its
surrounding. The position of the central source ismarked by the star. The hatched regions represent
compact component of molecular outflow resolved byArce & Sargent (2006). The sizes of disk, outflow, andmolecular core are not drawn with the same scale. The
field of view of our SUBARU images covers immediate
circumstellar environment around the central sourcesuch as disk and roots of bipolar cavity.

obtained with IRSF1.4m+SIRIUS.
(Nagoya Univ. & NAOJ.2004)

3-1. Nearby Emission around RNO91
The J, H and K band images of RNO91 obtained in 2001 are presented inFigure 2 together with an HST optical image (HST archive). We categorized thefaint nebulosity structures associated with RNO91 to categories based on awavelength which detects the each structures as follows. Names of eachstructures can be identified in Figure 3.
KKJ
Q1
Q2
Q1
Q2(R)---seen at J and optical, unseen at H
Central region
N3PPN2and K, arc-like shaped.
N1(S)---seen at KTTL
M1
Dark lane
GG(V)---seen at all wavelength
M2VVR
S(P)---seen at all wavelength, westernarm
Fig. 3. J and K band image of RNO91 as(T)---seen at all wavelength, eastern arm same as Fig.2. Major features are(G)---seen at all wavelength, southidentified
western arm(M1, M2)---seen at J, H and optical,
unseen at K
(N1, N2, N3)---seen at J and optical(Q1, Q2)---seen at all wavelength

3-2. Color of RNO91

Fig. 2. SUBARU J, H and K band images of RNO91
with an HST optical image (HST archive). Field of View(FOV) is 17’’. North is up and east to the left.

4. DISCUSSIONSWe discuss the each structures based upon the results described above. We suggest the morphology of RNO91 as seenin Fig. 5 and 7.

4-1. DiskDisk-like structure
The NIR images show significant halo emission detected within 2‘’ around the peak position (see Fig. 3) while less haloemission is seen in the optical image. The nebula appears to become more circular and more diffuse with increasingwavelengths. An azimuthally averaged radial surface brightness profile showed a cut-off at 2“ from the central peak,suggesting the morphological difference beyond this point. The power-law dependence of this profile is shallower thanthat of normal stars, indicating that RNO91 is still optically thick objects. It is thus natural to suggest that this haloemission within 2” around the peak position is the near-infrared light scattered by an optically thick disk surrounding theRNO91 and outer region beyond 2‘’ is the near-infrared light scattered by an envelope structure (See Fig. 5). Based on
the assumption that this halo emission is attributed to a disk, calculated inclination and P.A. of the disk would be 45～
90°and 145°, respectively.
At J and optical, several bluer clumps (M1, M2, N1, N2 and N3 in Fig. 3) are detected around the central peak position
and they are aligned nearly perpendicular to the outflow axis. Schild et al. (1989) conducted spectroscopic observation
toward RNO91, and did not detect any emission lines in their spectra of the nebular features except for the bright Hα also
seen in RNO91. They concluded that the nebular emission is mostly , and likely entirely, reflection light from RNO91, andnot from other emission sources. They also showed optical images and reveal that RNO91 comprises a group of clumps
which are aligned nearly perpendicular to the outflow axis and suggested these clumps may be attributed to a disk.
Positions of these bluer clumps are measured in our images and compared with those in images obtained by Schild et al.
(1989). These positions are almost consistent, but our images showed higher resolved clumps. Thus as suggested by
Schild et al. (1989), these bluer clumps seen in our shorter wavelength images, are not other emission sources, but part ofreflection nebula. Furthermore, in conjunction with the conclusions of Schild et al. (1989), these optically thin clumps
would be interpreted as fragments or part of erosion occurred in a disk and envelope structures which are disrupted bymolecular outflows.

Fig. 4 shows H-K, J-K color image of RNO91. Inthese figures, brighter parts indicate redder
regions, while darker parts indicate bluer regions.
Fig. 5 shows pseudo-true color composites ofCIAO(K), CIAO(J), and HST-WFPC2(optical)
broadband observations of RNO91. Detailed
descriptions for each color image are as follows:(i)H-K color:① Central redder region is extending to north-west
4-2. Outflow
Æoptically thick structures.
In J band and HST optical images, the nebula appears to become more extended (2‘’.3 long) to the southwest (P.A.～②a bridge-like structure extending to west from225°)(G in Fig. 3). Previous radio observations revealed that the redshifted outflow lobe extends to the north; thecentral peak position.
blueshifted outflow lobe extends to the south (Levreault 1988; Myers et al. 1988; Mathieu et al. 1988). Lee et al. (2000)(ii)J-K color
indicated that the blue lobe is not symmetric about the driving source: the centroid of the outflow emission seems to curve①looks very similar to H-K color.
eastward with increasing distance from the source. This could indicate that there is an interaction with ambient material②Very red color of central region Æoptically thick Fig. 4. H-K(top) and J-K(bottom) that guides the orientation of the outflow. Alternatively, it could be that the intrinsic outflow axis is changing with time as acolor images of RNO91.
structures
result of precession in the exciting source (Lee et al.2000). An orientation of extended nebula in our J band and HST
optical image is almost consistent with that of blueshifted outflow axis derived from previous radio observations, whichsuggest that this extended emission might trace a bottom of outflow cavity opening to the southwest direction.
3-3. Radial Surface Brightness ProfileFig. 6 shows an azimuthally averaged radial brightness profile of RNO91.
The surface brightness decreases as r-1.3±0.1, r-1.5±0.1, r-2.0±0.1 with the radius r 4-3. cavity
from 48 to 192 AU, for J, H, and K band, respectively. The surface brightness Our color composite image of RNO91 shows that the color of arc-shaped emission extending to the north (Q1 and Q2 indecreases as r-1.6±0.1, r-1.8±0.1, r-1.8±0.1 with the radius r from 256 to 688 AU, for Fig.3) and to the east (T in Fig. 3) through RNO91 is redder than the inner region of this arc. And an orientation of thisJ, H, and K band, respectively. The power-law dependence revealed thearc-shaped structure is almost parallel to that of extended emission discussed above. Thus, this arc-shaped structure isfollowing point.
interpreted as a part of the cavity wall seen relatively edge-on. Redshifted molecular outflow might construct this cavity
At all wavelength, power-law index is shallower than that of r-2 for the normal opening to north-east. The northern ridge is 11" long and eastern ridge is 7" long.
stars, and indicating that RNO91 is still optically thick objects. The profile
showed a cut-off at 256AU from the central peak especially at H, suggesting[1]Herbst W., Warner J., 1981, AJ, 86, 885 [2]Heyer M. H., Ladd E. F., Myers P. C., Campbell B., 1990, AJ, 99, 1585 [3]Hodapp, K.-W. 1994, ApJS, 94, 615 [4] Kumar, M.
the morphological difference beyond this point.

references

S. N., Anandarao, B. G., ¥& Davis, C. J. 1999, A¥&A, 344, L9 [5]Lee, C.-F., Mundy, L. G., Reipurth, B., Ostriker, E. C., & Stone, J. M., 2000, ApJ, 542, 925 [6]Lee, C.-F.,
Ho, Paul T. P., 2005, ApJ, 624, 841 [7]Levreault, R. M. 1988, ApJ, 330, 897 [8]Mathieu R. D., Benson P. J., Fuller G. A., Myers P. C., Schild R. E., 1988, ApJ, 330, 385[9]Myers, P. C., Heyer, M., Snell, R. L., & Goldsmith, P. F. 1988, ApJ, 324, 907 [10]Parker N. D., 1991, MNRAS, 251, 522 [11]Schild, R., Weir, N., & Mathier, R. D. 1989,AJ, 97, 1110 [12] Weintraub, D. A., Tegler, S. C., Kastner, J. H., ¥& Rettig, T. 1994, ApJ, 423, 674