* Astronomy

Title: The shadow knows: using shadows to investigate the structure of the pretransitional disk of HD 100453
Author: Zachary C. Long, Rachel B. Fernandes, Michael Sitko, Kevin Wagner, Takayuki Muto, Jun Hashimoto, Katherine Follette, Carol A. Grady, Misato Fukagawa, Yasuhiro Hasegawa, Jacques Kluska, Stefan Kraus, Satoshi Mayama, Michael W. McElwain, Daehyon Oh, Motohide Tamura, Taichi Uyama, John P. Wisniewski, Yi Yang

We present GPI polarized intensity imagery of HD 100453 in Y-, J-, and K1 bands which reveals an inner gap (9-18 au), an outer disk (18-39 au) with two prominent spiral arms, and two azimuthally-localized dark features also present in SPHERE total intensity images (Wagner 2015). SED fitting further suggests the radial gap extends to 1 au. The narrow, wedge-like shape of the dark features appears similar to predictions of shadows cast by a inner disk which is misaligned with respect to the outer disk. Using the Monte Carlo radiative transfer code HOCHUNCK3D (Whitney 2013), we construct a model of the disk which allows us to determine its physical properties in more detail. From the angular separation of the features we measure the difference in inclination between the disks 45°, and their major axes, PA = 140° east of north for the outer disk and 100°for the inner disk. We find an outer disk inclination of 25±10° from face-on in broad agreement with the Wagner 2015 measurement of 34°. SPHERE data in J- and H-bands indicate a reddish disk which points to HD 100453 evolving into a young debris disk.

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