J/A+A/699/A120 LK-Ha 233 NUV polarization HST images (Marin, 2025)
High angular resolution near-ultraviolet polarization imaging of the
Herbig Ae/Be star LK-Halpha-233.
Marin F.
<Astron. Astrophys. 699, A120 (2025)>
=2025A&A...699A.120M 2025A&A...699A.120M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, emission ; Stars, pre-main sequence ; Polarization ;
Ultraviolet
Keywords: polarization - scattering - techniques: polarimetric -
circumstellar matter - stars: individual: LK-Halpha-233 -
stars: pre-main sequence
Abstract:
Herbig Ae/Be stars are young, pre-main-sequence stars that provide
critical insights into the processes of stellar formation, early
stellar evolution and protoplanetary disks.
Two of the key features of such stars are their circumstellar dusty
disk and bipolar ionized outflows, which are key components for
understanding planet formation processes and energy/matter deposition
in the interstellar medium, respectively. In this context, imaging
polarimetry is probably the sharpest tool to characterize the various
structures and dynamics around the central star, due to the
sensitivity of polarization to the morphology of the emitting,
scattering and absorbing media.
We take advantage of never published, near-ultraviolet polarimetric
data of LK-Halpha-233 taken by the Faint Object Camera aboard the
Hubble Space Telescope in 1991, 1994 and 1995, which remained dormant
in the archives despite their quality. Using the most recent and
robust reduction pipeline for this instrument, we obtained high
spatial resolution (0.0287x0.0287-arcsecond2) maps of this object at
4118Å, together with polarimetric measurements.
A dark lane, bisecting the approaching and receding polar outflows,
suggests the presence of a circumstellar disk or dust torus, obscuring
the pre-main sequence star and collimating the ejecta. Polarization
reveals that the outflows have an X-shape structure with a significant
centro-symmetric pattern in polarization angle, indicating that the
outflows are both hollow and scattering the emission from the buried
star. We constrain the half-opening angle of both the outflows and
circumstellar disk, determine the inclination of the system and
estimate the obscured star's intrinsic flux.
This study highlights the importance of high-resolution polarimetric
observations in understanding the complex environment around Herbig
Ae/Be stars and advocates for future similar instruments.
Description:
The fits files contain images of 1991, 1994 and 1995 HST/FOC
observations of the Herbig Ae/Be star LK-Halpha-233 at two different
spatial binning and smoothing (2x2 pixels or 0.1x0.1 arcsec).
Polarization information (polarization degree and angle) are
superimposed onto the total flux intensity map.
Objects:
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RA (2000) DE Designation(s)
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22 34 40.98 +40 40 04.1 LkHa 233 = V* V375 Lac
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 161 6 List of fits images
fits/* . 6 Individual fits images
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 37 A10 "date" Obs.date Observation date
39- 41 I3 Kibyte size Size of FITS file
43- 89 A47 --- FileName Name of FITS file, in subdirectory fits
91-161 A71 --- Title Title of the FITS file
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Acknowledgements:
Frederic Marin, marinf(at)unistra.fr
(End) Patricia Vannier [CDS] 22-May-2025