Chasing Shadows: Rotation of the Azimuthal Asymmetry in the TW Hya Disk*

Debes, John H.; Poteet, C. A.; Jang‐Condell, Hannah; Gáspár, András; Hines, Dean C.; Kastner, Joel H.; Pueyo, Laurent; Rapson, Valerie; Roberge, Aki; Schneider, Glenn; Weinberger, Alycia J.

doi:10.3847/1538-4357/835/2/205

Cited by 134 publications

(155 citation statements)

References 37 publications

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“…This hinted toward significantly misaligned inner disc components and/or the need for other dipper mechanisms. Evidence of misaligned inner discs has also been recently inferred for several systems using high-contrast optical/infrared images, which have revealed shadows in the outer disc cast by unseen inclined inner disc components (e.g., Marino et al 2015;Stolker et al 2016;Debes et al 2017; Benisty et al 2018;Casassus et al 2018). A notable example is the dipper J1604, which hosts a face-on transition disc resolved by ALMA (Ansdell et al 2016a) and variable shadows seen by VLT/SPHERE (Pinilla et al 2018a), suggesting a highly misaligned (∼70-90 • ) and dynamic inner disc component.…”

Section: Introductionmentioning

confidence: 83%

Are inner disc misalignments common? ALMA reveals an isotropic outer disc inclination distribution for young dipper stars

Ansdell

Gaidos

Hedges

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Dippers are a common class of young variable star exhibiting day-long dimmings with depths of up to several tens of percent. A standard explanation is that dippers host nearly edge-on (i d ≈ 70 • ) protoplanetary discs that allow close-in (<1 au) dust lifted slightly out of the midplane to partially occult the star. The identification of a face-on dipper disc and growing evidence of inner disc misalignments brings this scenario into question. Thus we uniformly (re)derive the inclinations of 24 dipper discs resolved with (sub-)mm interferometry from ALMA. We find that dipper disc inclinations are consistent with an isotropic distribution over i d ≈ 0 − 75 • , above which the occurrence rate declines (likely an observational selection effect due to optically thick disc midplanes blocking their host stars). These findings indicate that the dipper phenomenon is unrelated to the outer (>10 au) disc resolved by ALMA and that inner disc misalignments may be common during the protoplanetary phase. More than one mechanism may contribute to the dipper phenomenon, including accretion-driven warps and "broken" discs caused by inclined (sub-)stellar or planetary companions.

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Section: Introductionmentioning

confidence: 83%

Are inner disc misalignments common? ALMA reveals an isotropic outer disc inclination distribution for young dipper stars

Ansdell

Gaidos

Hedges

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…• 5 separations among adjacent images, thus obtaining a total field rotation of 120. • During data reduction, we reduce the impact from STIS' diffraction spikes and the BAR5 occulter using a mask created by Debes et al (2017). For a specific application to a groundbased dataset, see Section 4.2.…”

Section: Data Reductionmentioning

confidence: 99%

Using Data Imputation for Signal Separation in High-contrast Imaging

Ren

Pueyo

Chen

et al. 2020

ApJ

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To characterize circumstellar systems in high contrast imaging, the fundamental step is to construct a best point spread function (PSF) template for the non-circumstellar signals (i.e., star light and speckles) and separate it from the observation. With existing PSF construction methods, the circumstellar signals (e.g., planets, circumstellar disks) are unavoidably altered by over-fitting and/or self-subtraction, making forward modeling a necessity to recover these signals. We present a forward modeling-free solution to these problems with data imputation using sequential non-negative matrix factorization (DI-sNMF). DI-sNMF first converts this signal separation problem to a "missing data" problem in statistics by flagging the regions which host circumstellar signals as missing data, then attributes PSF signals to these regions. We mathematically prove it to have negligible alteration to circumstellar signals when the imputation region is relatively small, which thus enables precise measurement for these circumstellar objects. We apply it to simulated point source and circumstellar disk observations to demonstrate its proper recovery of them. We apply it to Gemini Planet Imager (GPI) K1-band observations of the debris disk surrounding HR 4796A, finding a tentative trend that the dust is more forward scattering as the wavelength increases. We expect DI-sNMF to be applicable to other general scenarios where the separation of signals is needed.

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“…Several works have also suggested that the inner few AU of the TW Hya disk may either be warped or feature deviations from Keplerian rotation (e.g. Roberge et al 2005;Rosenfeld et al 2012;Debes et al 2017). These effects alone cannot create the axisymmetric substructures observed in the main CO isotopologues, but they would be worth considering in a more detailed analysis of the disk vertical structure.…”

Section: Comparison To Other Sourcesmentioning

confidence: 99%

CO and Dust Properties in the TW Hya Disk from High-resolution ALMA Observations

Huang

Andrews

Cleeves

et al. 2018

ApJ

183

202

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We analyze high angular resolution ALMA observations of the TW Hya disk to place constraints on the CO and dust properties. We present new, sensitive observations of the 12 CO J = 3 − 2 line at a spatial resolution of 8 AU (0. 14). The CO emission exhibits a bright inner core, a shoulder at r ≈ 70 AU, and a prominent break in slope at r ≈ 90 AU. Radiative transfer modeling is used to demonstrate that the emission morphology can be reasonably reproduced with a 12 CO column density profile featuring a steep decrease at r ≈ 15 AU and a secondary bump peaking at r ≈ 70 AU. Similar features have been identified in observations of rarer CO isotopologues, which trace heights closer to the midplane. Substructure in the underlying gas distribution or radially varying CO depletion that affects much of the disk's vertical extent may explain the shared emission features of the main CO isotopologues. We also combine archival 1.3 mm and 870 µm continuum observations to produce a spectral index map at a spatial resolution of 2 AU. The spectral index rises sharply at the continuum emission gaps at radii of 25, 41, and 47 AU. This behavior suggests that the grains within the gaps are no larger than a few millimeters. Outside the continuum gaps, the low spectral index values of α ≈ 2 indicate either that grains up to centimeter size are present, or that the bright continuum rings are marginally optically thick at millimeter wavelengths.

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Chasing Shadows: Rotation of the Azimuthal Asymmetry in the TW Hya Disk*

Cited by 134 publications

References 37 publications

Are inner disc misalignments common? ALMA reveals an isotropic outer disc inclination distribution for young dipper stars

Are inner disc misalignments common? ALMA reveals an isotropic outer disc inclination distribution for young dipper stars

Using Data Imputation for Signal Separation in High-contrast Imaging

CO and Dust Properties in the TW Hya Disk from High-resolution ALMA Observations

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