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flattened , rotating circumstellar disks reprocess light from newly born stars in t tauri and herbig ae / be systems @xcite . disks can modify the spectral energy distribution ( sed ) of the systems , and reveal themselves in resolved images at various wavelengths @xcite . in a disk , dust grains only exist outwards the sublimation radius @xmath0 , where dust reach sublimation temperature @xmath1 , leaving a dust - free hole at the center . protoplanetary disks are usually optically thick to stellar radiation ( with exceptions such as transitional disks , @xcite ) . as a result , most part of the disk receives direct starlight only at the surface , under a small grazing angle determined by the shape of the surface @xcite . on the other hand , the entire wall of the rim at @xmath0 is in full sight of the star , heated by intense stellar radiation . as a result , the rim is vertically puffed up under the hydrostatic equilibrium condition as pressure balances gravity @xcite . as shown by @xcite and @xcite , a puffed inner rim blocks starlight from reaching to the disk behind , thereby creating a shadow in the outer disk . depending on the disk properties , the outer disk may re - emerge from the shadow at a certain distance , or remain shadowed throughout . the puffed up rim and the self - shadowing effect are more prominent in herbig ae / be stars than in t tauri stars , as dust sublimation occurs closer to the less luminous and cooler t tauri stars , and the covering angle of the rim is smaller @xcite . self - shadowing by a disk rim is a key component in explaining observations of herbig ae / be stars . in particular , the difference between group i and ii objects @xcite has been interpreted as that group i disks are flared while group ii disks are flat and ( completely ) self - shadowed by a puffed up rim @xcite . also , a puffed up rim has been involved to explain the light curves of ux orionis stars @xcite , dust emission features in disks @xcite , and cooling of the surface layer in disks @xcite . the change of rim height has been proposed to account for the variability of disk infrared excess @xcite as well as the overall surface brightness of the disk in scattered light imaging @xcite . moreover , an evolutionary sequence has been proposed by @xcite and @xcite : as the shadow cast by the rim extends further as the amount of small grains decreases due to grain growth and settling , eventually an initially flared group i object evolves into a flat self - shadowed group ii object at late stages . recently , thanks to a few high angular resolution imaging instruments that have been mounted on 8-meter class ground based mirrors in the past few years , near - infrared ( nir ) imaging of polarized scattered light from disks have found structures that may be produced by self - shadowing in disks . @xcite suggested that the two nulls seen on the ring in the @xmath2 band polarized intensity ( pi ) image of the hd 142527 system are shadows cast by an misaligned inner disk ( see also @xcite , @xcite , @xcite , @xcite , and @xcite ) . @xcite found that the two spiral arms in the mwc  758 system may have shadows in its @xmath2  band pi images ( see also @xcite ) . in addition , various rings and arcs and gaps in disks have also been suggested to be manifestations of self - shadowing ( e.g. hd  144432 , @xcite ; hd  169142 , @xcite ; hd  163296 , @xcite ; tw hydrae , @xcite ; hd  169142 , @xcite ) . in these cases , the gap region has been interpreted as being shadowed by puffed up inner disk structures , with the outer gap edge presumed to be the edge of the shadow . on the theory side , the effect of shadowing have been explored by many in the past through radiative transfer modeling , with the shadow cast by either a puffed up inner rim or hydro features produced by planets ( e.g. * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) . however , most works focused on the sed or the thermal emission of the disk . the effects of a puffed up rim in high angular resolution scattered light imaging have not been throughly examined . in particular , whether observed rings and arcs in disks can be the outer edge of shadows remain unanswered .    in this paper , the properties of the shadow cast by a puffed up inner rim in nir polarized light imaging are studied through radiative transfer simulations using the @xcite code . disk vertical structures are self - consistently calculated assuming hydro static equilibrium ( hseq ) . synthetic images of disks with either a naturally puffed up rim or a parametrized rim are produced , and their properties are measured and compared with observations . the structure of the paper is as following . the models and mcrt simulations are introduced in section  [ sec : models ] ; the results are presented in section  [ sec : results ] , followed by a summary and discussion in section  [ sec : summary ] . mcrt simulations are carried out using the ( * ? ? ? * see also @xcite ) code , which has been used to model protoplanetary disks in the past ( e.g. @xcite ) . the simulation setup is largely adopted from @xcite , and is briefly summarized here . the central star has @xmath3 , @xmath4 , and @xmath5k , typical for a herbig ae / be system . the disk is axisymmetric , and is constructed in spherical coordinates @xmath6 ( radial ) and @xmath7 ( polar , midplane is at @xmath8 and poles are at @xmath9 ) . the grid has 500 cells in @xmath6 direction with logarithmic spacing and 200 cells in @xmath7 direction with power law spacing to over sample the inner disk and the disk midplane . the inner edge of the disk is at dust sublimation radius @xmath100.5  au , where dust temperature reaches 1600  k. the outer edge of the disk is at 200 au . the surface density @xmath11 follows a power law with radius as @xmath12 where @xmath13 is the normalization at @xmath14 . the @xmath15 power law has been suggested by both detailed disk structure calculation ( e.g. * ? ? ? * ) and mm disk observations ( e.g. * ? ? ? * ; * ? ? ? the total mass of the disk is assumed to be @xmath16 . a small accretion rate of @xmath17/yr is assumed to represent a typical accretion state , and also to provide nominal heating to the shadowed region to prevent the development of a known ripple instability @xcite . all simulations are run with 1 billion photon packages . synthetic @xmath2 band ( 1.6  @xmath18 ) images for short , which has the unit [ mjy  arcsec@xmath19 , or [ ergs  s@xmath20  @xmath21  hz@xmath20  arcsec@xmath19 . this quantity is sometimes referred to as `` spectral radiance '' . ] and sed are produced for each model . all models are assumed to be at 140  pc away . full - resolution mcrt images are convolved by a circular gaussian kernel with a full width half max ( fwhm ) of @xmath22 to achieve an angular resolution comparable to observations by subaru , vlt , and gemini ( the fwhm of an airy disk is @xmath23 for a primary mirror with a diameter @xmath24  m at @xmath25 ) .    in simulations , photons from the central star are absorbed and reemitted or scattered by the dust in the surrounding disk . the temperature in each grid cell is calculated based on the radiative equilibrium algorithm described in @xcite . the anisotropic scattering phase function is approximated using the henyey - greenstein function . polarization is calculated assuming a rayleigh - like phase function for the linear polarization @xcite . the vertical density structure of the disk is solved through iterations assuming self - consistent hseq in the vertical direction @xmath26 , as gas pressure balances gravity : @xmath27 where @xmath28 is pressure and @xmath29 is density . simulations are iterated on the temperature @xmath30 calculated from the radiative equilibrium solution of the radiation transfer equation at least 10 times to achieve convergence on the vertical structures @xcite . in this study the stellar radiation is the main energy source of the disk ( heating from accretion has little effect except in the umbra region right behind the rim ) , and the gravity from the central star is the sole gravitational source . note that the vertical structure of the disk ( as well as the puffed up rim ) may be affected by other mechanisms , such as the gravitational perturbation from an orbiting companion ( particularly if on an inclined orbit ) , or turbulences in the disk . the naturally puffed up rims based on the hseq condition in this study do not account for these additional mechanisms . there are two types of dust grains in the models , the `` small '' grains and the `` big '' grains . the gas - to - dust - mass ratio ( including both the small and big grains ) is assumed to be 100:1 ( therefore the total mass of the dust grains @xmath31 is @xmath32 ) . the small grains represent primordial dust particles . their properties are assumed to be the standard interstellar medium ( ism ) grains as in @xcite . these grains contain silicate , graphite , and amorphous carbon , and their size distribution is a smooth power law in the range of 0.02 - 0.25  @xmath18 followed by a sharp cut off beyond 0.25  @xmath18 . the small grains are well mixed with gas as the two are dynamically well coupled - sized grains may still have some degree of settling , depending on the strength of the turbulences in disks that stir up dust grains vertically @xcite . due to a lack of good understanding of the nature and strength of the turbulences in protoplanetary disk , settling of these sub-@xmath18-sized small grains is not considered in this work . ] . the large grains represent an advanced stage of grain growth and coagulations . model 1 in @xcite is adopted for their properties . they are made of amorphous carbon and astronomical silicates , and have a power - law size distribution as @xmath33 , an exponential cutoff beyond @xmath34 , and a maxim size of 1 mm . the big grains tend to settle to the disk midplane , as they usually dynamically decouple from the gas and are no longer held in the vertical direction by the gas pressure @xcite . the vertical distribution of the big grains is assumed to be a gaussian profile with a small scale height @xmath35 ( i.e. their vertical structure is parametrized and not evolved in the hseq iterations ) . therefor the big grains form a thin layer at the disk midplane . the details of the properties and spatial distribution of the big grains have little effect on the scattered light images and sed presented below , as long as they are well embedded at the disk midplane . the optical properties of both grains can be found in figure  2 in @xcite . two sets of models , series a and b , are constructed and listed in table  [ tab : models ] . model base is the fiducial model , which has no big grains . series a is constructed by fixing @xmath31 while decreasing @xmath36 and increasing @xmath37 , similar to the ml series in @xcite and bl series in @xcite . this scenario ( from model base to a4 ) is to mimic an evolutionary sequence : the amount of small grains decreases with time as grain growth and coagulation gradually convert them into bigger particles that settles down at the disk mid - plane . the inner rim in base to a4 is naturally puffed up under the hseq condition ( only the small grains ) . as will be shown in the next section , while series a does gradually turn from a flared disk ( base ) into a self - shadowed disk ( a4 ) , the boundary between the shadowed inner disk and the flared outer disk is not sharp . this is because the rim does not have a sharp edge in the vertical density distribution , and the radial optical depth of the rim only gradually decreases with height . to maximize the sharpness of the rim edge and produce features with the highest contrast possible in scattered light imaging , series b is created . in b1 to b6 , an artificial opaque rim is placed at @xmath38 to @xmath39 , with a parametrized height @xmath40 expressed in the angle subtended by half of the rim to the star ( i.e. the vertical structure of the artificial rim is fixed and not evolved under the hseq condition ) . the opaque rim is constructed by filling the region with small grains of a uniform density @xmath41 , so that the radial optical depth @xmath42 of the rim is greater than @xmath43 at wavelengths of interests , therefore completely blocks the starlight in the solid angle subtended by the rim . in other words , in the polar direction @xmath44 inside the rim , then @xmath45 outside the rim . this artificial vertically constant density structure is only designed in order to create the sharpest possible shadows . it is not meant to have a physical motivation . both the naturally puffed up rim and the parametrized artificial rim are illustrated in figure  [ fig : verticalprofiles ] . this section presents the main modeling results , first the structure of the disks ( section  [ sec : structure ] ) and then observational aspects of the models ( section  [ sec : modelobservations ] ) . the density and temperature structure for models base and b2 are shown in figure  [ fig : verticalprofiles ] in spherical coordinates , with the disk surface over - plotted , defined as where the radial optical depth @xmath42 at 0.4  @xmath18 at each polar angle @xmath7 from the stellar surface ( the stellar flux peaks aroundt 0.4  @xmath18 ) reaches 1 . in spherical coordinates a shadowed region has a flat surface ( constant @xmath7 with increasing @xmath6 ) , while a flared region has a rising surface ( increasing @xmath7 with increasing @xmath6 ) . the disk surface traces out the boundary between the hot disk atmosphere and the cool interior , as most starlight intercepted by the disk is deposited near the surface .    in the model base , a puffed up inner rim is clearly visible in the density structure as a vertically extended structure close to @xmath0 . the rim casts a shadow behind from @xmath0 to @xmath46  au , where the surface comes out of the shadow and starts rising . however , as discussed in section  [ sec : models ] , the puffed up rim has a blurry edge . as a result , the edge of the shadow is not sharp , and the disk surface smoothly transits from flat to flared around 3  au .    in the model b2 , a parametrized artificial rim is placed at @xmath0 with @xmath47 . the sharp rim edge results in a sharp turning point on the @xmath48 surface at @xmath49  au , where the surface suddenly rises . inside the shadow region , the disk does not have a uniform structure , and can be separated into two regions . an umbra exists immediately behind the rim ( boundary indicated by the dashed line ) , within which the entire surface of the star is not visible . in the umbra , practically the only heating sources are radiation diffusion and accretion . this region becomes sufficiently cold to collapse to the midplane . on the other hand , the region in between the umbra and the @xmath48 surface receives additional heating from the following ways :    1 . once outside the umbra and moving towards @xmath50 , the disk receives direct radiation from a bigger and bigger polar region on the star . 2 .   inward heat diffusion from @xmath50 heats up the adjacent region , smoothing out the transition and preventing a sudden jump in @xmath51 @xcite . 3 .   indirect illumination and heating from the halo @xcite . in particular , closer to @xmath50 , secondary ( multiple ) scattering from the disk atmosphere in the flared region becomes more important . nir flux from the opposite side of the inner rim . the strength of additional heating sources 1 - 3 increases with radius , puffs up the disk moderately starting at @xmath522  au . eventually the @xmath48 surface comes out of the shadow at 13 au and disk stays flared outward . the @xmath48 surface for all models are plotted in figure  [ fig : surface ] . as shown in @xcite and @xcite , from base to a4 the disk gradually evolves from flared to flat ( completely self - shadowed by its own puffed up rim ) , as the amount of small grains decreases . the shadowed - to - flared - disk transition occurs more and more smoothly , and @xmath50 can not be clearly defined . on the other hand , the surface transition is sharp in the b series , as the surface suddenly turns upward at [ @xmath50,@xmath40 ] ( marked by dots in the right panel and labeled in table  [ tab : models ] . the entire disk in b6 is inside the shadow so @xmath50 is not defined . ) . the transition point rises and moves outward as @xmath40 increases , and the surface always converges to model base once out of the shadow , indicating that the flared part of the disk in all models are similar . the midplane temperature of the disk @xmath51 is shown in figure  [ fig : midplanet ] for the b series . there are two bumps on the curves . the first bump occurs when the disk comes out of the umbra , and the second bump occurs at the shadow edge @xmath50 . in the umbra all models have the same @xmath51 profile ( best traced out by model b6 ) . the location of the first bump moves outward as @xmath40 increases and the umbra extends . after the first bump the shadow reduces the midplane temperature , consistent with @xcite , and models converge again to another profile in cases that the two bumps are not too close to each other ( b3 to b6 ) . finally , all models converge to the base model at @xmath54 , echoing the convergence of the @xmath48 surface in figure  [ fig : surface ] , and demonstrating the similarity of the models in the flared region . the @xmath48 surface officially comes out of the shadow at @xmath50 and starts to be directly irradiated by the bulk part of the stellar surface ( @xmath55latitude@xmath56 ) . however , the transition to the `` flared profile '' occurs much earlier than @xmath50 . for example , b4 starts to deviate from its `` shadow profile '' ( traced out by b6 ) at @xmath5210 au , and gradually converges towards its `` flared profile '' ( traced out by base ) until the eventual merger at @xmath57  au . this echoes the smooth transition in temperature and density structures seen in figure  [ fig : verticalprofiles ] . vertical density structure of the disk is determined by the temperature structure under the hseq condition . therefore , at radius of a fraction of @xmath50 , the disk already starts to deviate from its thin `` shadow state '' and become modestly puffed up , until eventually smoothly joins the flared disk at @xmath50 . this is illustrated in figure  [ fig : verticalprofiles ] for b2 , in which case the thin `` shadow state '' ends at @xmath522  au , and in between 2  au and @xmath49  au the disk is modestly puffed up , and beyond 13  au the disk becomes fully flared .    in summary , the disk in series a evolves from a mostly flared disk to a self - shadowed flat disk , but the shadowed - to - flared - disk transition is smooth , due to the lack of a sharp rim edge . in the extreme cases , with parametrized sharp rims in series b , the transition on the @xmath48 surface becomes sharp , but the transition in the underlying disk density and temperature structure is still smooth and occurs over a radius range . sed for all models are shown in figure  [ fig : sed ] . series a mimics the evolutionary sequence from group i to ii , as shown in @xcite . the 1 - 100 @xmath18 infrared excess drops as the total amount of small grains decreases and the disk becomes more and more self - shadowed , meanwhile the far infrared and mm emissions beyond 100  @xmath18 rise due to more big grains . for series b , the nir excess from 1 - 10  @xmath18 comes from the artificial rim , which increases as the rim grows higher from b1 to b6 . meanwhile the 10 - 100  @xmath18 excess decreases as the shadow edge expands and a bigger disk region falls into the shadow . this is similar to the `` seesaw '' phenomenon in @xcite , which has been explained by puffed up rims with varying heights . beyond 100  @xmath18 the emissions mainly come from the outer part of the disk , which remains flared and has a similar density and temperature structure in most models thus the emission is little changed .    scattered light images trace structures at the disk surface , set by the dust distribution and intrinsically determined by the temperature structure under the hseq condition . while formally inside @xmath50 , the shadowed region may still receives and scatters nir photons from ( 1 ) the polar region of the star ( in the region immediately below the radial @xmath48 surface ) ; ( 2 ) the bulk part of the star ( high in the disk atmosphere ) ; ( 3 ) the opposite side of the rim ; and ( 4 ) secondary scattering photons from the disk halo ( in particular at radius close to @xmath50 ) . if the rim is naturally puffed up , stellar photons may also be scattered by the tenuous rim edge into the shadowed region therefore , it is expected that the shadowed region to be not completely dark , and the surface brightness should converge to the flared disk when getting closer to @xmath50 . @xmath2  band polarized intensity images for model b2 and b4 are shown in figure  [ fig : images ] . in b2 , a marginal ring / gap structure ( i.e. a region with pi@xmath58 ) at @xmath50 can be seen at face - on viewing angle , inside which the shadowed region has low surface brightness . if we define `` ring / gap contrast '' as the ratio of the azimuthally averaged surface brightness at the peak of the ring to the bottom of the gap , the contrast is 1.33 for the raw image and 1.03 for the convolved image . at a 45@xmath59 inclination angle , the ring becomes elliptical , and due to the forward / backward scattering effect the front side is brighter than the back side @xcite . in b4 , the shadow edge is not distinctive in all panels . at face - on viewing angle , the azimuthally averaged surface brightness decreases with radius throughout the disk ( see figure  [ fig : image - rp ] ) . the radial profile of face on @xmath2  band pi images for all models are shown in figure  [ fig : image - rp ] . for the a models , converting small grains into vertically settled big grains gradually turns a bright flared disk into a faint flat one . the brightness of the disk drops by 1 - 2 orders of magnitude . however this process happens in a rather smooth manner that the surface brightness of the entire disk drops all together , while the outer disk drops faster than the inner region . the dependence of pi on @xmath6 changes from pi@xmath60 in the base model to pi@xmath61 in a4 . the surface brightness distribution remains smooth and relatively featureless throughout in all cases . in particular , no ring / gap structure exists at the edge of the shadowed region , in either the original images or the @xmath62 scaled images .    for the b models , the shadowed - to - flared - disk transition is clearly visible on the radial profiles . in general , the surface brightness radial profile can be described by a 3-stage broken power law : ( 1 ) well inside the shadow different models have a similar radial profile as pi@xmath63 ( best seen in b3 to b6 as their shadows extend far enough ) ; ( 2 ) in the flared region all models converge to pi@xmath60 , the same as the base model ; and ( 3 ) a transition region with pi  @xmath64 ( constant pi ) connects the two . this is consistent with the trend seen earlier in the disk density , temperature , and surface structures , that b models have essentially the same structure both in the inner shadowed region and the outer flared region , with a wide transition region in between . and similar to the @xmath51 profile , the transition occurs over a radius range and not suddenly . for b2 to b5 in b1 is too close to the star and beyond the capability of current nir imaging facilities . ] , radial profiles smoothly deviate from the @xmath65 profile around @xmath66 , and gradually converge to the @xmath60 profile around @xmath50 . b3 has a marginal `` gap / ring '' structure similar to b2 , with very weak ring / gap contrast ratios ( listed in table  [ tab : models ] ) . pi never increases with radius throughout the disk in b4 to b6 , and a ring / gap structure is not present around the shadow edge . the difference between b2/b3 and b4/b5 is probably caused by the fact that the transition region is wider in b4/b5 due to their large shadow size , so the transition occurs even more smoothly . the effects of puffed up inner rims in protoplanetary disks in both temperature and density structure and nir scattered light imaging are studied . two types of rims are explored : natural rims that are self - consistently puffed up under the hydrostatic equilibrium condition ( series a ) , and artificial opaque rims with parametrized heights and sharp edges in the vertical direction ( series b ) . the main results from the models are :    1 . an inner rim naturally puffed up under the hseq condition creates a shadow behind , within which the disk surface is flat and beyond which it is flared ( the a models ) . decreasing the amount of small grains gradually turn the entire disk into a self - shadowed and flat disk , confirming previous results such as in @xcite ( figure  [ fig : surface ] ) . 2 .   for naturally puffed up rims , the shadowed - to - flared - disk transition occurs smoothly , and no sharp / distinct turning point on the disk surface exists . this is mainly due to the fact that hseq rims do not have a sharp vertical edge , and their `` radial optical depth '' gently decreases with height . as a result , the scattered light images have a smooth / featureless surface brightness distribution . from base to a4 , the surface brightness of the disk drops by 1 - 2 orders of magnitude , and the radial dependence changes from a shallower @xmath67 to a steeper @xmath68 ( figure  [ fig : image - rp ] ) . 3 .   the most extreme rims , which are parametrized artificial rims with a razor sharp vertical edge in the b series , do create a sharp turning point on the radial @xmath48 surface ( figure  [ fig : surface ] ) . this point formally defines the edge of the shadow @xmath50 , beyond which the surface is flared and sees the bulk part of the star . both the inner shadowed region and the flared region are similar in models with different rim heights . on the other hand , the shadowed - to - flared - disk transition does not occur abruptly in the underlying disk density and temperature structures . the midplane temperature starts to deviate from its `` shadow profile '' at a fraction of @xmath50 ( figure  [ fig : midplanet ] ) , and eventually converges to its `` flared profile '' around @xmath50 . the density structure of the disk follows the change in @xmath51 under the hseq condition , thereby exhibits a broad transition region as well ( figure  [ fig : verticalprofiles ] ) . this is mainly caused by partial illumination by the polar region of the star , multiple scattering , and radiation diffusion within the disk . 4 .   even the parametrized razor sharp rims in the b models can not produce prominent rings and arcs in scattered light images as what have been directly imaged recently . on the other hand , self - shadowing by the rim does have a clear effect on the radial profile of the scattered light . the surface brightness radial profiles of the b models can be described by a 3-stage broken power law : two steep profiles in the inner shadowed region and the flared region , connected by a shallow profile in a broad transition region ( figure  [ fig : image - rp ] ) . the enhancement around the shadow edge however is usually not strong enough to make a prominent ring / gap structure . b2 and b3 show a very marginal ring / gap structure around @xmath50 ( figure  [ fig : images ] ) , while other models remain largely smooth and featureless throughout in both the original and @xmath62 scaled images . remarks on the implications of the models and observations :    1 . a faint disk in nir direct imaging observations with a relatively steep surface brightness radial profile ( i.e. @xmath69 ) is consistent with small grains being heavily depleted and the entire disk is self - shadowed by the inner rim . the surface brightness threshold depends on the stellar luminosity . for a @xmath43  k , 2.5 @xmath70 , and 2 @xmath71 central star , the threshold is about 1/@xmath72 mjy arcsec@xmath73 . such kind of faint disks may have already been found in observations ( e.g. hd  139614 , subaru direct imaging , m. fukagawa , private communication , hashimoto et al . in prep . ) . 2 .   even with the sharpest possible rims as the parametrized rims in b models , the shadow edge fails to manifest itself as prominent rings / arcs in scattered light images . the highest ring / gap contrast ratio in full resolution images is only 1.33 , and practically no ring / gap structure is found in convolved images with an angular resolution of 0.05@xmath74 . note that the convolved images in this study have the ideal chance to review potential disk structures , as ( 1 ) they are convolved by a gaussian psf , which smears the intrinsic full resolution images less than a realistic psf that has a similar kernel but more extended wings ; ( 2 ) no observational noises and instrument effects are included , which are expected to further weaken the detectability of features in images . 3 .   realistic rims in a models can only produce structures even smoother than b models in scattered light images . radial structures with high contrast recently observed in nir direct imaging surveys , such as the arcs in the hd  163296 system @xcite , the gap in the hd  169142 system @xcite , the spiral arms in the sao  206462 system @xcite and the mwc  758 system @xcite , and various rings and arcs in transitional disks ( e.g. * ? ? ? * ; * ? ? ? * ) are unlikely to be the shadow edges of puffed up rims . it is more likely that they are created by local density or scale height structures @xcite , such as gaps ( e.g. * ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) and spiral arms ( e.g. dong et al . 2015b ) produced by planets in the density distribution . 4 .   though unable to create arcs / rings and gaps in disks , a shadow cast by a puffed up rim may still have an effect on the surface brightness radial distribution of scattered light images . with a vertically sharp rim , scattered light images show a 3-stage broken power law : 2 steep radial profiles in the inner and other disk connected by a shallow transition region around the shadow edge . such systems may have already been observed : the @xmath2  band scattered light image of tw hydrae has a shallow @xmath75 transition region located at @xmath7620 - 40  au , in between 2 steep @xmath65 and @xmath77 profiles in the inner and outer disk @xcite . the shallow region may actually be a gap , which can be either confirmed or ruled out by future observations with better image quality and s / n ratio . if the shadow region is not a gap , then comparing with the b models this may suggest that the disk is self - shadowed , and the shadow edge is around @xmath78  au ( note that tw hydrae has an @xmath79  au inner hole at the center , @xcite , therefore perhaps the shadow is created by a puffed up cavity wall at @xmath80  au instead of a rim at @xmath81  au ) . however a self - consistent structure puffed by the hseq condition is unlikely to account for the observation , as the shadowed - to - flared - disk transition is too smooth . the needed puffed up structure has to have a somewhat sharp cutoff , perhaps sculpted by other mechanisms in the system . the realization of such a structure with a physical origin can be the subject of future studies . i thank misato fukagawa , jun hashimoto , and barbara whitney for useful discussions and help on the paper , and the referee cornelis dullemond for a helpful referee report . this work is supported by nasa through hubble fellowship grant hst - hf-51320.01-a awarded by the space telescope science institute , which is operated by the association of universities for research in astronomy , inc . , for nasa , under contract nas 5 - 26555 . this research made use of the savio cluster at uc berkeley , and the lawrencium cluster at the lawrence berkeley national laboratory ( supported by the director , office of science , office of basic energy sciences , of the u.s . department of energy under contract no . de - ac02 - 05ch11231 ) .                                                                                                                                            cccccccc model & parametrized / natural rim & @xmath82 & @xmath40 ( @xmath59 ) & @xmath50 ( au ) & ring / gap contrast + base & natural & 1 & n / a & n / a & n / a + a1 & natural & @xmath83 & n / a & n / a & n / a + a2 & natural & @xmath84 & n / a & n / a & n / a + a3 & natural & @xmath85 & n / a & n / a & n / a + a4 & natural & @xmath86 & n / a & n / a & n / a + b1 & parametrized & 1 & 10 & 5 & n / a + b2 & parametrized & 1 & 12.5 & 13 & 1.33/1.03 + b3 & parametrized & 1 & 15 & 30 & 1.10/1.02 + b4 & parametrized & 1 & 17.5 & 52 & n / a + b5 & parametrized & 1 & 22.5 & 147 & n / a + b6 & parametrized & 1 & 27.5 & n / a & n / a +
we explore whether protoplanetary disks with self - shadowing from puffed up inner rims exhibit observable features in scattered light images . 
 we use both self - consistent hydrostatic equilibrium calculations and parameterized models to produce the vertically puffed up inner rims . 
 we find that , in general , the transition between the shadowed and flared regions occurs in a smooth manner over a broad radius range , and no sudden jump exists at the outer edge of the shadow in either the disk temperature or density structures . as a result , 
 a puffed up rim can not create sharp ring / arc / spiral - arm - like features in the outer disk as have been detected in recent direct nir imaging of disks . on the other hand , 
 if the puffed up rim has a sharp edge in the vertical direction , the shadowing effect can produce a distinct 3-stage broken power law in the radial intensity profile of the scattered light , with 2 steep surface brightness radial profiles in the inner and outer disk joined by a shallow transition region around the shadow edge . 
 these types of scattered light profiles may have already been observed , such as in the recent subaru direct imaging of the tw hydrae system .