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Register a new userAn Enigmatic Pointlike Feature within the HD 169142 Transitional Disk
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We report the detection of a faint pointlike feature possibly related to ongoing planet-formation in the disk of the transition disk star HD 169142. The pointlike feature has a $Delta$mag(L)$sim$6.4, at a separation of $sim$0.11 and PA$sim$0$^{circ}$. Given its lack of an H or K$_{S}$ counterpart despite its relative brightness, this candidate cannot be explained by purely photospheric emission and must be a disk feature heated by an as yet unknown source. Its extremely red colors make it highly unlikely to be a background object, but future multi-wavelength followup is necessary for confirmation and characterization of this feature.
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We investigate high resolution imaging polarimetry of HD 169142 taken in the R and I bands with the SPHERE/ZIMPOL instrument for an accurate quantitative measurement of the radiation scattered by the circumstellar disk. We observe a strong dependence of the disk polarimetry on the atmospheric turbulences, which strongly impact the AO performance. With our non-coronagraphic data we can analyze the polarimetric signal of the disk simultaneously with the strongly variable stellar PSF, correct for the convolution effects to determine the intrinsic polarization of the disk with high precision. We also extract the disk intensity signal and derive the fractional polarization. We compare the scattered flux from the inner and outer disk rings with the corresponding thermal dust emissions measured in the IR and estimate the ratio between scattered and absorbed radiation. We obtain ratios between the integrated disk polarization flux and total system flux of 0.43% for the R band and 0.55% for the I band. This indicates a reddish color for the light reflection by the dust. The inner disk ring contributes about 75% to the total disk flux. The obtained fractional polarization for the bright inner disk ring is 23.6% for the I band and similar for the R band. The ratio between scattered disk flux and star flux is about 2.3%. This is much smaller than the derived IR excess of 17.6% for the disk components observed in scattered light. This indicates that only a small fraction of the radiation illuminating the disk is scattered; most is absorbed and reemitted in the IR. We conclude that accurate, quantitative measurements of the scattered light from circumstellar disks are possible with ground based high contrast AO systems, if the PSF convolution effects are properly taken into account, and this provides important new constraints on the properties of the scattering dust.
Protoplanetary disks around young stars harbor many structures related to planetary formation. Of particular interest, spiral patterns were discovered among several of these disks and are expected to be the sign of gravitational instabilities leading to giant planets formation or gravitational perturbations caused by already existing planets. In this context, the star HD100546 presents some specific characteristics with a complex gas and dusty disk including spirals as well as a possible planet in formation. The objective of this study is to analyze high contrast and high angular resolution images of this emblematic system to shed light on critical steps of the planet formation. We retrieved archival images obtained at Gemini in the near IR (Ks band) with the instrument NICI and processed the data using advanced high contrast imaging technique taking advantage of the angular differential imaging. These new images reveal the spiral pattern previously identified with HST with an unprecedented resolution, while the large-scale structure of the disk is mostly erased by the data processing. The single pattern at the southeast in HST images is now resolved into a multi-armed spiral pattern. Using two models of a gravitational perturber orbiting in a gaseous disk we attempted to bring constraints on the characteristics of this perturber assuming each spiral being independent and we derived qualitative conclusions. The non-detection of the northeast spiral pattern observed in HST allows to put a lower limit on the intensity ratio between the two sides of the disk, which if interpreted as forward scattering yields a larger anisotropic scattering than derived in the visible. Also, we found that the spirals are likely spatially resolved with a thickness of about 5-10AU. Finally, we did not detect the candidate forming planet recently discovered in the Lp band, with a mass upper limit of 16-18 MJ.
In order to look for signs of on-going planet formation in young disks, we carried out the first J-band polarized emission imaging of the Herbig Ae/Be stars HD 150193, HD 163296, and HD 169142 using the Gemini Planet Imager (GPI), along with new H band observations of HD 144432. We confirm the complex double ring structure for the nearly face-on system HD 169142 first seen in H-band, finding the outer ring to be substantially redder than the inner one in polarized intensity. Using radiative transfer modeling, we developed a physical model that explains the full spectral energy distribution (SED) and J- and H-band surface brightness profiles, suggesting that the differential color of the two rings could come from reddened starlight traversing the inner wall and may not require differences in grain properties. In addition, we clearly detect an elongated, off-center ring in HD 163296 (MWC 275), locating the scattering surface to be 18 AU above the midplane at a radial distance of 77 AU, co-spatial with a ring seen at 1.3mm by ALMA linked to the CO snow line. Lastly, we report a weak tentative detection of scattered light for HD 150193 (MWC 863) and a non-detection for HD 144432; the stellar companion known for each of these targets has likely disrupted the material in the outer disk of the primary star. For HD 163296 and HD 169142, the prominent outer rings we detect could be evidence for giant planet formation in the outer disk or a manifestation of large-scale dust growth processes possibly related to snow-line chemistry.
The search for young planets had its first breakthrough with the detection of the accreting planet PDS70b. In this study, we aim to broaden our understanding towards the formation of multi-planet systems such as HR8799 or the Solar System. Our previous study on HD169142, one of the closest Herbig stars, points towards a shadow-casting protoplanetary candidate. Here, we present follow-up observations to test our previously proposed hypothesis. We set our new data into context with previous observations to follow structural changes in the disk over the course of 6 years. We find spatially resolved systematic changes in the position of the previously described surface brightness dip in the inner ring. We further find changes in the brightness structure in azimuthal direction along the ring. And finally, a comparison of our SPHERE data with recent ALMA observations reveals a wavelength dependent radial profile of the bright ring. The time-scale on which the changes in the rings surface brightness occur suggest that they are caused by a shadow cast by a 1-10Mj planet surrounded by dust, an orbit comparable to those of the giant planets in our own Solar System. Additionally, we find the first indications for temperature-induced instabilities in the ring. And finally, we trace a pressure maxima, for the first time spatially resolved, with a width of 4.5au. The density distribution of the ring at mm wavelengths around the pressure maxima could further indicate effects from snow lines or even the dynamics and feedback of the larger grains.
Resolved submillimeter imaging of transitional disks is increasingly revealing the complexity of disk structure. Here we present the first high-resolution submillimeter image of a recently identified transitional disk around IRAS 04125+2902 in the Taurus star-forming region. We measure an inner disk hole of ~20 AU around IRAS 04125+2902 by simultaneously modeling new 880 micron Submillimeter Array (SMA) data along with an existing spectral energy distribution supplemented by new Discovery Channel Telescope (DCT) photometry. We also constrain the outer radius of the dust disk in IRAS~04125+2902 to ~50-60 AU. Such a small dust disk could be attributed to initial formation conditions, outward truncation by an unseen companion, or dust evolution in the disk. Notably, the dust distribution of IRAS 04125+2902 resembles a narrow ring (delta R ~ 35 AU) composed of large dust grains at the location of the disk wall. Such narrow dust rings are also seen in other transitional disks and may be evidence of dust trapping in pressure bumps, possibly produced by planetary companions. More sensitive submillimeter observations of the gas are necessary to further probe the physical mechanisms at work in shaping the spatial distribution of large dust in this disk. Interestingly, the IRAS 04125+2902 disk is significantly fainter than other transitional disks that have been resolved at submillimeter wavelengths, hinting that more objects with large disk holes may exist at the faint end of the submillimeter luminosity distribution that await detection with more sensitive imaging telescopes.
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