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Impact of angular differential imaging on circumstellar disk images

Milli, J. and Mouillet, D. and Lagrange, A.-M. and Boccaletti, A. and Mawet, D. and Chauvin, G. and Bonnefoy, M. (2012) Impact of angular differential imaging on circumstellar disk images. Astronomy and Astrophysics, 545 . Art. No. A111. ISSN 0004-6361. doi:10.1051/0004-6361/201219687.

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Context. Direct imaging of circumstellar disks requires high-contrast and high-resolution techniques. The angular differential imaging (ADI) technique is one of them, initially developed for point-like sources but now increasingly applied to extended objects such as disks. This new field of application raises many questions because the disk images reduced with ADI depend strongly on the amplitude of field rotation and the ADI data reduction strategy. Both of them directly affect the disk observable properties. Aims. Our aim is to characterize the applicability and biases of some ADI data reduction strategies for different disk morphologies. A particular emphasis is placed on parameters mostly used for disks such as their surface brightness distribution, their width if the disk is a ring, and local features such as gaps or asymmetries. We first present a general method for predicting and quantifying those biases. In a second step we illustrate them for some widely used ADI algorithms applied to typical debris disk morphologies: inclined rings with various inner/outer slopes and width. Last, our aim is also to propose improvements of classical ADI to limit the biases on extended objects. Methods. Simulated fake disks seen under various observing conditions were used to reduce ADI data and quantify the resulting biases. These conclusions are complemented by previous results from NaCo L’ real-disk images of HR 4796A. Results. As expected, ADI induces flux losses on disks. This makes this technique appropriate only for low- to medium-inclination disks. A theoretical criterion is derived to predict the amount of flux loss for a given disk morphology, and quantitative estimates of the biases are given in some specific configurations. These biases alter the disk observable properties, such as the slopes of the disk surface brightness or the radial/azimuthal extent of the disk. Additionally, this work demonstrates that ADI can very easily create artificial features without involving astrophysical processes. For example, a particularly striking feature appears for a ring when the amplitude of field rotation is too small. The two ring ansae are surrounded by two flux-depleted regions, which makes them appear as bright blobs. This observation does not require any astrophysical process such as dust blown by radiation pressure, as previously proposed in H-band images of HR 4796A. Conclusions. The ADI techniques behave as spatial filtering algorithms and can bias disk observables. Therefore, the filtering process needs to be properly calibrated when deriving disk parameters from processed images.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle paper
Milli, J.0000-0001-9325-2511
Boccaletti, A.0000-0001-9353-2724
Mawet, D.0000-0002-8895-4735
Bonnefoy, M.0000-0001-5579-5339
Additional Information:© 2012 ESO. Article published by EDP Sciences. Received 25 May 2012; Accepted 20 July 2012. We would like to thank J-C Augereau for letting us use the GRaTer code to simulate fake disk images.
Subject Keywords:methods: data analysis – techniques: high angular resolution – circumstellar matter
Record Number:CaltechAUTHORS:20150520-125725911
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Official Citation:J. Milli, D. Mouillet, A.-M. Lagrange, A. Boccaletti, D. Mawet, G. Chauvin and M. Bonnefoy A&A 545 A111 (2012) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57713
Deposited By: Tony Diaz
Deposited On:20 May 2015 21:16
Last Modified:10 Nov 2021 21:54

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