J/A+A/618/A151 HD 172555 polarimetric images (Engler+, 2018)
Detection of scattered light from the hot dust in HD 172555.
Engler N., Schmid H.M., Quanz S.P., Avenhaus H., Bazzon A.
<Astron. Astrophys. 618, A151 (2018)>
=2018A&A...618A.151E 2018A&A...618A.151E (SIMBAD/NED BibCode)
ADC_Keywords: Stars, nearby ; Polarization
Keywords: planetary systems - scattering - stars: individual object: HD 172555 -
techniques: high angular resolution - techniques: polarimetric
Abstract:
Debris disks or belts are important signposts for the presence of
colliding planetesimals and, therefore, for ongoing planet formation
and evolution processes in young planetary systems. Imaging of debris
material at small separations from the star is very challenging but
provides valuable insights into the spatial distribution of the
so-called hot dust produced by solid bodies located in or near the
habitable zone. We report the first detection of scattered light from
the hot dust around the nearby (d=28.33pc) A star HD 172555.
We want to constrain the geometric structure of the detected debris
disk using polarimetric differential imaging (PDI) with a spatial
resolution of 25mas and an inner working angle of about 0.1".
We measured the polarized light of HD 172555, with SPHERE/ZIMPOL, in
the very broadband (VBB) or RI filter (λc=735nm,
Δλ290nm) for the projected separations between 0.08"
(2.3au) and 0.77" (22au). We constrained the disk parameters by
fitting models for scattering of an optically thin dust disk taking
the limited spatial resolution and coronagraphic attenuation of our
data into account.
The geometric structure of the disk in polarized light shows roughly
the same orientation and outer extent as obtained from thermal
emission at 18µm. Our image indicates the presence of a strongly
inclined (i~=103.5°), roughly axisymmetric dust belt with an outer
radius in the range between 0.3" (8.5au) and 0.4" (11.3au). An inner
disk edge is not detected in the data. We derive a lower limit for the
polarized flux contrast ratio for the disk of
(Fpol)disk/F*>(6.2±0.6)x10-5 in the VBB filter. This ratio is
small, only ∼9%, when compared to the fractional infrared flux excess
(~=7.2x10-4). The model simulations show that more polarized light
could be produced by the dust located inside ~=2au, which cannot be
detected with the instrument configuration used.
Our data confirm previous infrared imaging and provide a higher
resolution map of the system, which could be further improved with
future observations.
Description:
The fits files contain the reduced SPHERE-ZIMPOL polarimetric
observations of HD 172555 in the Very Broad Band filter (lambda = 735
nm) on June 26th (observation 177) and Sep. 9th (observation 249,
selected frames), 2015. These are the total intensity Iq and Iu
(Stokes I) and Stokes Q and U images shown in the second row
(observation 177) and fourth row (observation 249) of Fig. B.1 of the
paper. Images are not derotated (field offset) and the True North
offset is not corrected. To get North up and East to the left, images
of observation 177 should be derotated by 120 deg counterclockwise. To
correct for the True North offset, images of both observations (177
and 249) should be rotated by 2° clockwise. Each image has
1024x1024 pixels with one pixel corresponding to 3.6x3.6 mas on sky.
Objects:
--------------------------------------------------
RA (2000) DE Designation(s)
--------------------------------------------------
18 45 26.90 -64 52 16.5 HD 172555 = HR 7012
--------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 111 8 List of fits images
fits/* . 8 Individual fits images
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 33 I4 Kibyte size Size of FITS file
35- 43 A9 --- FileName Name of FITS file, in subdirectory fits
45-111 A67 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Natalia Engler, englern(at)phys.ethz.ch
(End) N. Engler [ETH Zurich, Switzerland], P. Vannier [CDS] 31-Jul-2018