arXiv:astro-ph/9909097v1 6 Sep 1999 alycia,becklin,lowrance,murray,[email protected] rpittpstuigL using typeset Preprint ta.19) D116 a nlddbcueo t large its of because included elli was extended and 141569 emission, HD CO depth, (Schneider optical 1998). far-infrared (HST) Telescope (NIC- al. Space Spectrometer Hubble et Object the Multi t aboard with and MOS) Camera nearby of Infrared environments Near the study to project time ate 95,wihi e ie agrta h w well- two the than larger stars, times excess few infrared a known is which 1995), Kastner & iaieo neselrrdeig D116 a nabsolu an has 141569 M HD magnitude reddening, interstellar of dicative ehr hs osri t g o10 to T age its 1999). constrain al. these et gether, (Weinberger stro has stars has and companion 1995), stars, like T-Tauri Kastner A two & young Forveille, other (Zuckerman, infrared of emission an that CO has to sequence, similar main depth age optical zero the on 1998). approximately al. tha et with (Jura stars consistent A is sequence type main spectral young its other for low a depth Sh ta.19) suigisB its Assuming L134/L134N 1998). complex cloud al. dark et the (Sahu of outskirts the on lie may acsmaue itneo 99 of distance measured parcos 18)fis dnie ta ansqec trwt infrare with sequence at peaking main SED a an as and excess it identified first (1986) sB.V yJshk&Jshk(92,i ebgA/estar Ae/Be H Herbig peaked a is double (1992), with Jaschek & Jaschek by B9.5Ve as collisions. proto-stellar by remnant generated both dust of “debris” in composed secondary material, be and consiste circumstellar may Their colors disks, of and stars. form young of ci as those warm well with of as presence classes dust the Both of cumstellar stars. indicative excesses sequence infrared main have zero-age and pre- between pndpsiiiisfrsuyn acn lntr syste planetary nascent and Ae/Be studying Herbig Old for possibilities opened A CCEPTED h 1.1 The h g fH 459i o eldtrie.I slocated is It determined. well not is 141569 HD of age The D116 =IA 57-36=SO108) classified 140789), SAO = 15473-0346 IRAS (= 141569 HD h icvr fdssaon ansqec tr has stars main-sequence around disks of discovery The 3 2 1 4 nttt o srnm,Uiest fHwi,Hnll,H Honolulu, Hawaii, of University Astronomy, for Institute twr bevtr,Uiest fAioa 3 .Cer A Cherry N. 933 Arizona, of University Observatory, Steward eateto hsc n srnm,Uiest fCalifor of University Astronomy, and Physics of Department e rplinLbrtr,M 8-0,Psdn,C 91109; CA Pasadena, 183-503, MS Laboratory, Propulsion Jet τ 3 − S 3 100 eecp eel large, a reveals Telescope eetdlgtiaea 1.1 at image light reflected feto n rmr lnt a encsayt xli this explain to necessary be headings: the may Subject in planets gap, more a or or one material, of depleted effect of region A radii. smaller fsgtb 51 by sight of atr ie rgtr h ikflxdniypas15A (1. AU 185 peaks density flux disk The brighter. side, eastern µ EP eut eotdhr r ato u guaranteed our of part are here reported results m µ ooarpi mgn ihteNa nrrdCmr n Mul and Camera Infrared Near the with imaging Coronagraphic m 1999 V 16mg(a e nkre l 98.Such 1998). al. et Ancker den (van mag =1.6 L = A T O ULCTO IN PUBLICATION FOR E tl mltajv 04/03/99 v. emulateapj style X disk .J W J. A. / 1. α β L ± ∗ i nlgsaslea rniinlage transitional a at lie stars analog Pic msin ace,Jshk Egret & Jaschek, Jaschek, emission. INTRODUCTION 8 = 3 H ICMTLA IKO D116 MGDWT NICMOS WITH IMAGED 141569 HD OF DISK CIRCUMSTELLAR THE EINBERGER ◦ icmtla atr—sas msinln tr:indivi stars: — line emission stars: — matter circumstellar β h nrni cteigfnto fteds nteds ma disk the in dust the of function scattering intrinsic the ; . ∼ i n R49A iha Hip- an With 4796A. HR and Pic 4 − + × 60 8 9 A c(o1 (so pc 10 − P 6 µ ∼ L J − .9 a oo sin- is color mag 0.095 = V .Teds a noptical an has disk The m. − µ 10 0 U(4 AU 400 3 ETTERS 1 hw h ikoine tapsto nl f356 of angle position a at oriented disk the shows m .E B E. E. , Zcemn Forveille, (Zuckerman, S 7 ILVERSTONE yr. ′′ cetd3Sp19 o ulcto nAJLetters ApJ in publication for 1999 Sep 3 Accepted ≈ 0 U,testar the AU), 100 ECKLIN ′′ ais icmtla ikaon h ebgA/esa HD star Ae/Be Herbig the around disk circumstellar radius, ) 62;[email protected] 96720; I i o nee,Bx160,LsAgls A90095; CA Angeles, Los 156205, Box Angeles, Los nia e,Tco,A 52;[email protected] 85721; AZ Tucson, ve., 1 Richard.J.Terrile@jpl..gov .Z B. , 1 .S G. , ptical ms. of t ABSTRACT UCKERMAN the ng he o- nt te r- CHNEIDER d 1 nlF1Wiae nwih1AUs t ADU to 1 which applied in was images calibration F110W final photometric medianed. available were MULTIAC- best orientation three The spacecraft the each and from pixels, av- images eight weighted CUM of distance radius a a with within fiel erage corrected flat were and pixels linearization bad subtraction, known F160W bias refe the the After in in flat. replaced ence and measured F110W, to were scaled sensitivities image, pixel hole-finding the hole, the eeec a ed ihnardu f1 ies(0. pixels 12 of radius a Within field F110W flat field. on-orbit S/N coronagraphic flat high special standard reference a A modifying by created cor shading. was and detector 20 current dark on the the taken subtract rect to frames used Dark were 1998 September 1997). (MacLeod software creduce n h ooarpi oeadealn odfltfiligne flat-fielding good hole. enabling locat- the and of hole purpose coronagraphic the the for ing F160W at obtained were backgrounds µ custo rmswr bandwt h 11 ( F171M the with obtained were frames acquisition mg eswr bandwti 0minutes. 40 minimize within To obtained were other. th 8 sets variations, each image rolled (PSF) to function orientations, respect spread spacecraft point with time-dependent two axis of target the each time about at integration sec total 607.9 a for of obtained, were sequences ACCUM etme 98wt IMSCmr .TeF1Wfilter F110W The 2. Camera ( NICMOS with 1998 September ctee ih ikaon D116 a lobe observed been Th also 1.6 has at (1999). 141569 NICMOS with HD al. around et disk Silverstone light by scattered images mid-infrared in disk nua eouinwiemnmzn ctee ih.With 0. the light. in positioned scattered target minimizing while resolution angular iki etrd20A rmtesa.Tedynamical The star. the from AU 250 centered is disk λ ,FWHM=0.07 m, 1 central h UTACMdt eswr rcse ihteNi- the with processed were sets data MULTIACCUM The ro oec e fcrngahcosrain,03 targ s 0.36 observations, coronagraphic of set each to Prior ooarpi bevtoso D116 eemd n27 on made were 141569 HD of observations Coronagraphic 2 , morphology. ′′ .A S A. B. , AND 5 rmtesa n al f obt agrand larger both to off falls and star the from 85) =1.10 iOjc pcrmtro h ubeSpace Hubble the on Spectrometer Object ti .J T J. R. MITH µ ERRILE ,FWHM=0.59 m, 3 ul(D141569) (HD dual .J L J. P. , e h ieicie oadu,the us, toward inclined side the kes µ )fitr otmoaeu apflt and flats lamp Contemporaneous filter. m) µ 4 3. 2. yAgra ta.(1999a). al. et Augereau by m ± OWRANCE DATA ANALYSIS ′′ OBSERVATIONS aiscrngah he MULTI- three coronagraph, radius 3 5 ◦ n nlndt u line our to inclined and µ )wsue omxmz the maximize to used was m) 1 .D. M. , − 1 2.031 = 459 A 141569. × λ 10 central − 6 ′′ yand Jy 1 of 91) =1.72 two e ding, the he ar et r- ◦ e - 2 Imaging of HD 141569 Disk

0 mag = 1775 Jy (Rieke 1999). The corrected total flux density is 8 ± 2 mJy. The F110W mag- In the reduced and calibrated NICMOS images, scattered nitudes of 49 Cet and HD 141569 were extrapolated from their light from the star still dominates the flux levels at radii of H-band magnitudes, and the uncertainty in their flux ratio com- 1—5′′, so in order to see the disk, a PSF star must be sub- pletely dominates the uncertainty in the photometry of the disk. tracted. The same observing strategy and the F110W filter were A change of ∼2% in the subtracted PSF flux, makes a ∼20% used for 14 other stars in this GTO program, and targets which difference in the integrated disk flux density. do not show extended disk emission form a library of possible The eastern side of the disk is 1.5±0.2 times brighter than PSF stars. The detailed character of the NICMOS PSF changes the western side. This difference is not an artifact of the PSF with time primarily due to thermal variations in the HST opti- subtraction and can be explained by dust particles which prefer- cal assembly (Kulkarni et al. 1999); hence some PSF star sub- entially scatter in the forward direction. Such phase functions tractions produce much lower residuals than others. Each PSF apply even when the particles are a few times larger than the image was registered using cubic convolution interpolation to wavelength of the scattered light (van de Hulst 1957) and are both orientations of HD 141569. Only stars brighter than HD produced in recent models of fluffy grains (e.g. Wolff, Clayton, 141569 were considered, and the PSF subtraction residuals are & Gibson 1998). Small particles probably do exist in the HD dominated by systematic uncertainties. 141569 disk (see §5.2). The brighter side, therefore, is inclined Scattered light from two nearby stars outside the field of toward us, and the ratio of forward to backward scattering im- view, see §5.1, pollutes the northwest corner of the image. For plies an asymmetry parameter, g, of 0.11 in the analytic phase both roll angles, we used synthetic PSFs generated with Tiny function of Henyey & Greenstein (1941). This is consistent Tim (Krist & Hook 1997) and positioned them at the locations with the results of Augereau et al. (1999b) on HR 4796A in of the two stars to subtract this excess scatter. A small amount which the upper limit for g was 0.15. of residual flux, however, can still be seen in Figure 1. Figure 2 compares the azimuthally averaged disk flux ob- 5. DISCUSSION served after subtraction of each of the three best matched PSF stars. Two of these PSF stars, τ 1 Eri and 49 Cet, were disk can- 5.1. Disk Morphology didates in which no disk was detected, and the third, HR 4748, The surface brightness of the disk has a complicated radial was observed specifically as a PSF star. At radii greater than morphology which cannot be represented by a single power- 1.′′6 (160 AU), the morphology of the disk is consistent in all law. The density of scatterers, assuming the disk is everywhere three subtractions. Subtraction of 49 Cet yielded the smallest optically thin, is as high at radii up to about 360 AU from the amplitude residuals, and all further analysis was carried out on star as it is in the region 200 AU from the star. images using it as the PSF. Dynamical processes could play a large part in shaping the The PSF-subtracted images from each telescope roll were ro- disk. HD 141569 may be the brightest member of a multiple tated to a common orientation and averaged. Regions of the im- star system, since two bright stars (henceforth “B” and “C”) ′′ ′′ age obscured by the diffraction spikes in one roll were replaced withH=8.6and9.4maglie7. 57(∼>750AU) and 8. 93(∼>900 where possible by uncorrupted regions in the other roll. AU) away at respective position angles of 311.5◦ and 310.0◦. The high probability that these stars are physical companions 4. RESULTS and assessments of their ages are discussed in a separate paper (Weinberger et al. 1999). If the three stars are physically as- The PSF subtracted, roll-combined coronagraphic image of sociated, the two companions would likely have a significant HD 141569 is shown in Figure 1a. An elongated disk is clearly dynamical effect on the disk. If the companion stars are in the ′′ evident at radii from ∼1.6 to 4 (160 to 400 AU) from the star. plane of the disk, the physical separation of “A”–“B” is 990 AU Elliptical isophotes were fit to the disk image yielding a posi- and that of “B”–“C” is 190 AU. Then, the ratio of the semi- ◦ tion angle of 356 ± 5 and ratio of the minor to major axes of major axes of the wider to the closer pair would be only ∼5.2. 0.63 ± 0.04. If, as is likely for dust orbiting a star, the disk This is not expected to be a stable triple system (Eggleton & is intrinsically circular, the axial ratio implies an inclination of Kiseleva 1995), although such young stars may not yet have ◦ 51±3 from face-on. This geometry was used to “deproject” had time to become unbound. the disk to a face-on view (see Figure 1b). If the companions are out of the disk plane, they could be The azimuthally averaged disk surface brightness, shown in much further from the primary, and their dynamicaleffect could Figure 2 as computed from the deprojected image, peaks at 0.3 be to excite significant velocities in the disk dust perpendicular −2 mJy arcsec at a radius of 185 AU and falls off to larger and to the plane. This would puff up the disk and possibly flare smaller radii. Fitting the slope of the surface brightness with a it. Increased collision velocities could promote the breakup of −3 2 power law gives r . for 190 < r < 250 AU. At 250 AU an an- larger particles into smaller and could help account for the large nulus of lower surface brightness, or a “gap” in the disk, can be number of scatterers far out in the disk. seen, which is apparent in Figure 3 where the surface brightness The dip in surface brightness at r≈250 AU which is most 2 has been multiplied by 4πr to determine the surface density of easily seen along the major axis (Figure 1), is a striking feature scatterers (see §5.2). On either side of this gap, the surface den- of the disk. The full width at half minimum of this gap is 60 sity of scatterers does not vary appreciably. At r∼>340 AU, the AU, to which the intrinsic size of the NICMOS PSF contributes surface brightness of the disk falls off more steeply, as r−5.9. ∼5%. The depth of this dip in terms of the density of scatterers The disk flux density, in a rectangle of area 63 sq. arcsec out- (τω; Figure 3) is ∼14% of the average value between 185 and side of 0.′′6 from the star and extending to 5.′′3 from the star 340 AU. along the major axis of the disk, is 7.2±1.8 mJy. This integra- No point source is seen within the disk, and to constrain tion excluded pixels in the diffraction spikes; we make a purely the luminosities of possible companion bodies, we planted PSF geometric correction by finding the average flux density at ev- “stars,” generated with Tiny Tim (Krist & Hook 1997), at ran- ery radius and multiplying it by the number of excluded pixels. dom locations in the image at one telescope roll angle sub- Weinberger et al. 3 tracted from the image at the other roll. The limiting magni- infrared τ overestimates the optical depth in the exterior part of tude (3σ) of an object which could be detected at each radius the disk seen in reflected light and results in an underestimate is plotted in Figure 4. This limit does not apply to the region of the albedo. In the region at ∼1.′′9 (190 AU), therefore, the obscured by the diffraction spikes which, at the radius of the albedo is greater than 0.3 and probably more like 0.4. This is gap, hide ∼17% of the disk. a substantially higher albedo than the zodiacal dust in our own At the radius of the gap, the limiting magnitude of 20.3 and Solar system, 0.1 (Dumont & Levasseur-Regourd 1988), but is an assumed age ≤10 Myr correspond to a planet with similar to the albedos of mineralmixtures and ices found in ISO ≤0.003 M⊙ (3 MJUP) according to cooling curves by Burrows spectra of Herbig Ae/Be disks (Malfait et al. 1998). et al. (1997). At this age, the brown dwarf-planet transition oc- At r<150 AU, the dust temperature is ∼150 K as estimated curs at log(L/L⊙)≈ −3 which corresponds to an F110W magni- from mid-infrared colors and luminosity (Silverstone et al. tude of ∼16. Figure 4 shows that either a star or brown dwarf 1999). If the grains are icy, the decline in 1.1 µm surface bright- would be clearly detectable in our image at any radii greater ness inside 185 AU may be due to the sublimation of the ice at than ∼80 AU. temperatures ∼100 K. In this case, the grains emitting in the If the gap is cleared only by the gravity of a co-orbital planet, mid to far-infrared are the iceless counterparts of the grains at 3 the planet mass is: M/M⊙ = C(∆a/a) where ∆a and a are higher radius. the width and radius of the gap, respectively, and the constant Gaseous CO was detected by Zuckerman, Forveille, & Kast- C ≈ 0.1 (Lissauer 1993). This corresponds to a planetary mass ner (1995) with a velocity width of 7.6 km s−1, corresponding of ∼1.3 Jupiters, which given the detection limits discussed in to a radius of 86 AU given a disk inclination of 51◦ and stellar §5.1, could not have been detected. The for ma- mass of 2.3M⊙. The gas, therefore, is well inside the brightest terial 250 AU from the 2.3 M⊙ star is 2600 yr. If we assume part of the reflected light disk and the gap. In the spectrum of that it takes ∼>300 orbital periods to clear material in a gap, Sylvester et al. (1996), a large rise in the continuum shortward based on models of disks by Bryden et al. (1999), then a gap of 8 µm and a possible peak at 11.3 µm both indicate emission 5 can be opened in ∼>8×10 yr. That the gap is not completely from polycyclic aromatic hydrocarbons. The existence of gas clear may mean that processes are moving particles through the and small grains in the presence of forces which remove them disk. The Poynting-Robertson timescale for particles ∼>1µm is very quickly indicates they are constantly being resupplied. The ∼4×106 yr, similar to the age of the star. Radiation pressure disk seems to be in an active planetesimal building phase. will preferentially clear small grains on a timescale of ∼104 yr and could fill in a gap if such grains are present, or being cre- 6. CONCLUSIONS ated, in the disk. NICMOS images reveal a large circumstellar disk around the 5.2. Constituent grains Herbig Ae star HD 141569. The structure of the disk, including a region of depleted material at 250 AU can most easily be un- We can combine the information we infer from the NICMOS derstood as due to dynamical sculpting by one or more planets images with what is known about the disk from mid to far- orbiting within it. If planets exist in this system, they must have infrared measurements. For reflection from optically thin dust, formed in <107 yr and far from the central star compared with 2 S τω =4πφ F , where φ is the angular distance of the scatterers the planets in our own Solar system. from the illuminating star, S is surface brightness, F is the re- ceived flux from the star, τ is the optical depth of scatterers, and ω is the albedo (Figure 3). At the peak surface brightness, We thank David Koerner, Andrea Ghez and Mike Jura for φ=1.′′9, S=0.3 mJy arcsec−2, and τω =4 × 10−3. The optical helpful conversations. This work is based on observations with depth to visual absorption implied by the far infrared excess is the NASA/ESA , obtained at the Space 8.4×10−3; if this is also the absorption optical depth at 1.1 µm, Telescope Science Institute, which is operated by the Asso- 1 then the albedo of the scatterers is ∼0.3. However, about /3 of ciation of Universities for Research in Astronomy, Inc. un- the luminosity emitted from 3.5 – 25 µm arises from a region der NASA contract NAS-26555 and supported by NASA grant within 150 AU of the star (Silverstone et al. 1999). So, the total NAG5-3042 to the NICMOS instrument definition team.

REFERENCES

Augereau, J. C., Lagrange, A. M., & Mouillet, D. 1999a, A&A, submitted MacLeod, B., A. 1997, HST Calibration Workshop Proceedings, ed. S. Augereau, J. C., Lagrange, A. M., Mouillet, D., Papaloizou, J.C.B., & Grorod, Casertano P. A. 1999b, A&A, in press Malfait, K., Waelkens, C., Waters, L. B. F. M., Vandenbussche, B., Huygen, E., Bryden, G., Chen, X., Lin, D. N. C., Nelson, R. P., & Papaloizou, J. C. B. 1999, & de Graauw, M. S. 1998, A&A, 332, L25 ApJ, 514, 344 Rieke, M. 1999, private communication Burrows, A., Marley, M., Hubbard, W. B., Lunine, J. I., Guillot, T., Saumon, D., Sahu, M. S., Blades, J. C., He, L., Hartmann, D., Barlow, M. J., & Freedman, R., & Sharp, C. 1997, ApJ, 491, 856 Crawford, I. A. 1998, ApJ, 504, 522 Dumont, R. & Levasseur-Regourd, A. C. 1988, A&A, 191, 154 Schneider, G. 1998, NICMOS and the VLT, ed. W. Freudling & R. Hook, Eggleton, P. & Kiseleva, L. 1995, ApJ, 455, 640 (Garching:ESO), 88. Henyey, L. G. & Greenstein, J. L. 1941, ApJ, 93, 70 Silverstone, M., et al. 1999, BAAS, 30 Jaschek, C. & Jaschek, M. 1992, A&AS, 95, 535 Sylvester, R. J., Skinner, C. J., Barlow, M. J., & Mannings, V. 1996, MNRAS, Jaschek, M., Jaschek, C., & Egret, D. 1986, A&A, 158, 325 279, 915 Jura, M., Malkan, M., White, R., Telesco, C., Pina, R., & Fisher, R. S. 1998, van den Ancker, M. E., de Winter, D., & Tjin A Djie, H. R. E. 1998, A&A, ApJ, 505, 897 330, 145 Krist, J. E., & Hook, R., N. 1997, The 1997 HST Calibration Workshop with a van de Hulst, H. C. 1957, Light Scattering by Small Particles (New York: New Generation of Instruments, p. 192 Wiley) Kulkarni, V.P., Hill, J.M., Schneider, G., Weymann, R.J., Storrie-Lombardi, Weinberger, A. J., et al. 1999, in preparation L.J., Rieke, M.J., Thompson, R.I., & Januzzi, B. 1999, ApJ, submitted Wolff, M. J., Clayton, G. C., & Gibson, S. J. 1998, ApJ, 503, 815 Lissauer, J. J. 1993, ARA&A, 31, 129 Zuckerman, B., Forveille, T., & Kastner, J. H. 1995, Nature, 373, 494 4 Imaging of HD 141569 Disk

FIG. 1.— Left (a): Image of the reflected light disk around HD 141569 shown in a stretch which is linear with flux density. The eastern side of the disk is brighter because of the intrinsic scattering phase function of the dust. Right (b): Deprojected image of the disk using an inclination angle of 51◦. Artifacts from small instabilities in the PSF subtraction process include the radial “streamers” and the dark “finger” in the inner disk at the 4 o’clock position. These residuals do not significantly affect the radial profile or the integrated flux density. The diffraction spikes narrow to higher radius as the overlap between the two sets of observations at different orientations increases and allows pixels behind the spikes in one image to be replaced by pixels from the other image.

FIG. 2.— Azimuthally averaged surface brightness profile of the disk FIG. 3.— The surface density of scatterers plotted as a function of radius after subtraction of three different PSF stars. The error bars represent only π 2 the statistical uncertainty in the mean surface brightness at each radius. At computed by multiplying the surface brightness by 4 r and normalizing to radii greater than ∼160 AU the three profiles are consistent to within these the total stellar flux density. uncertainties. The subtractions with τ 1 Eri and 49 Cet suggest that the disk flux falls off substantially inside of 160 AU.

FIG. 4.— Apparent F110W limiting magnitude of an unseen companion as a function of distance from the star. The uncertainty in the detection limit is the size of the points, or ∼10%.