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Register a new userHD 169142 in the eyes of ZIMPOL/SPHERE
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Added by
Gesa H.-M. Bertrang
Publication date
2017
fields
Physics
and research's language is
English
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We present new data of the protoplanetary disc surrounding the Herbig Ae/Be star HD 169142 obtained in the very broad-band (VBB) with the Zurich imaging polarimeter (ZIMPOL), a sub-system of the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE) at the Very Large Telescope (VLT). Our Polarimetric Differential Imaging (PDI) observations probe the disc as close as 0.03 (3.5au) to the star and are able to trace the disc out to ~1.08 (~126au). We find an inner hole, a bright ring bearing substructures around 0.18 (21au), and an elliptically shaped gap stretching from 0.25 to 0.47 (29-55au). Outside of 0.47, the surface brightness drops off, discontinued only by a narrow annular brightness minimum at ~0.63-0.74 (74-87au). These observations confirm features found in less-well resolved data as well as reveal yet undetected indications for planet-disc interactions, such as small-scale structures, star-disk offsets, and potentially moving shadows.
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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.
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.
We present the first optical (590--890 nm) imaging polarimetry observations of the pre-transitional protoplanetary disk around the young solar analog LkCa 15, addressing a number of open questions raised by previous studies. We detect the previously unseen far side of the disk gap, confirm the highly eccentric scattered-light gap shape that was postulated from near-infrared imaging, at odds with the symmetric gap inferred from millimeter interferometry. Furthermore, we resolve the inner disk for the first time and trace it out to 30 AU. This new source of scattered light may contribute to the near-infrared interferometric signal attributed to the protoplanet candidate LkCa 15 b, which lies embedded in the outer regions of the inner disk. Finally, we present a new model for the system architecture of LkCa 15 that ties these new findings together. These observations were taken during science verification of SPHERE ZIMPOL and demonstrate this facilitys performance for faint guide stars under adverse observing conditions.
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.
HD$,$169142 is an excellent target to investigate signs of planet-disk interaction due to the previous evidence of gap structures. We performed J-band (~1.2{mu}m) polarized intensity imaging of HD169142 with VLT/SPHERE. We observe polarized scattered light down to 0.16 (~19 au) and find an inner gap with a significantly reduced scattered light flux. We confirm the previously detected double ring structure peaking at 0.18 (~21 au) and 0.56 (~66 au), and marginally detect a faint third gap at 0.70-0.73 (~82-85 au). We explore dust evolution models in a disk perturbed by two giant planets, as well as models with a parameterized dust size distribution. The dust evolution model is able to reproduce the ring locations and gap widths in polarized intensity, but fails to reproduce their depths. It, however, gives a good match with the ALMA dust continuum image at 1.3 mm. Models with a parameterized dust size distribution better reproduce the gap depth in scattered light, suggesting that dust filtration at the outer edges of the gaps is less effective. The pile-up of millimeter grains in a dust trap and the continuous distribution of small grains throughout the gap likely require a more efficient dust fragmentation and dust diffusion in the dust trap. Alternatively, turbulence or charging effects might lead to a reservoir of small grains at the surface layer that is not affected by the dust growth and fragmentation cycle dominating the dense disk midplane. The exploration of models shows that extracting planet properties such as mass from observed gap profiles is highly degenerate.
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