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From: atel@astronomerstelegram.org
Subject: ATel 17862, 17863
Message-Id: <20260702070549.1BA372880955@server.astronomerstelegram.org>
Date: Thu, 2 Jul 2026 03:05:49 -0400 (EDT)

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ATEL #17862							     ATEL #17862

Title:	Optical polarization of the central and outer coma of the short-periodical
		comet 10P/Tempel 2
Author:	Christian Woehler (Image Analysis Group, TU Dortmund University,
		Germany)
Queries:	christian.woehler@tu-dortmund.de
Posted:	1 Jul 2026; 10:35 UT
Subjects:Optical, Comet

The comet 10P/Tempel 2 has a short orbital period of only 5.36 years (JPL
Horizons, https://ssd.jpl.nasa.gov/horizons/app.html). In June 2026, we
conducted optical polarimetric measurements of the central and outer coma
of 10P/Tempel 2 at phase angles between 26.0 and 27.3 degrees. These observations
complement earlier polarimetric data of 10P/Tempel 2 at ~45 degrees phase
angle in the Johnson-Cousins V, R, and I bands, which are limited to the
central coma (Myers et al., 1985, DOI:10.1016/0019-1035(85)90005-3). To
the best of our knowledge, no further optical polarization data of this
comet have been published so far.

For the observations, a portable 150/600 mm Newton reflector in combination
with an electrically cooled QHY1253P polarization camera was used. Polarization
filters with orientation angles of 0, 45, 90, and 135 degrees are attached
to the sensor pixels of this camera, such that each 2x2 pixel subset yields
one measurement of the unpolarized intensity, DoLP, and position angle
of linear polarization (relative to the direction of the pixel rows), respectively.
To increase the SNR, two-fold binning was performed, leading to an effective
image resolution of 4.74 arcsec/pixel. Instrumental polarization effects
were compensated based on observations of the polarization standard star
HD183143 (Bailey and Hough, 1982, DOI:10.1086/131032) and the unpolarized
standard star Gamma Bootis (Turnshek et al., 1990, DOI:10.1086/115413).

The observations were conducted at Erb&eacute;viller-sur-Amezule, France,
on June 22 and 24, and near Wetter/Ruhr, Germany, on June 26. A SLOAN r
filter was used in order to block green gas emissions and focus on the
dust continuum. In each dataset, a circular region of 5,000 km radius around
the photocenter (region 1) was defined to represent the central coma. A
ring-shaped region around the photocenter with an inner and an outer radius
of 10,000 and 15,000 km (region 2) was chosen to represent the outer coma
(see also supplementary figures). For each polarizer orientation, the mean
pixel intensities were computed for each region (after subtracting the
dark current and the signal of the blank sky from each frame), and a sinusoidal
function was fitted to derive the mean DoLP of each region. Due to the
large-scale intensity averaging, the statistical measurement error of the
DoLP is below 0.01 (Arnaut et al., 2026, DOI:10.1051/0004-6361/202555905).

Date: June_22.02 June_24.02 June_26.01 
 Phase angle [degrees]: 27.3 26.7 26.0 
 Distance from Earth [AU]: 0.561 0.549 0.536 
 Distance from Sun [AU]: 1.482 1.476 1.471 
 Exposure time [hours]: 01:41:15 02:12:45 01:29:15 
 DoLP (region 1): 0.027 0.024 0.011 
 DoLP (region 2): 0.026 0.015 0.032

Phase angles and distances are from JPL Horizons. The DoLP measurements
are consistent with the polarimetric data of low-polarization comets in
the red spectral domain (Kiselev et al., 2015, DOI:10.1017/CBO9781107358249.022).
On June 22.00, the DoLP was also measured in the SLOAN g band (exposure
time 21:30 minutes). The coma brightness was significantly higher than
in the r band, hinting at a predominant C2 emission. The DoLP was 0.019
and 0.013 for region 1 and 2, respectively, which is consistent with the
value of 0.015 predicted by the standard expression of emission band polarization
(Le Borgne et al., 1987, A&A 187, 526).

The observation that the DoLP shows no clear dependence on the distance
from the photocenter suggests that the particle size distribution (and
other properties such as particle composition and morphology) is largely
constant across the coma. This is in stark contrast to the radial increase
in DoLP across the coma by a factor of ~2 observed for the dynamically
new comet C/2023 A3 that was attributed to a changing size distribution
favoring smaller particles with increasing distance from the photocenter
(Arnaut et al., 2026, DOI:10.1051/0004-6361/202555905).

Supplementary figures: https://tu-dortmund.sciebo.de/s/mtdHTD3a6QN4oNB
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Password Certification: Christian Woehler (christian.woehler@tu-dortmund.de)
https://www.astronomerstelegram.org/?read=17862
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ATEL #17863							     ATEL #17863

Title:	Correction to Atel #17856: Spectroscopic Confirmation and Physical
		Characterization of the Most Probable Host Galaxy of Repeating FRB
		20251229A
Author:	 Mohit Bhardwaj (Indian Institute of Technology Kanpur), Aida
		Kirichenko (Universidad Nacional Autonoma de Mexico), Ashwin Kharat
		(Indian Institute of Technology Kanpur), Ajay Kumar (Indian Institute
		of Technology Kanpur)
Queries:	aida@astro.unam.mx
Posted:	1 Jul 2026; 18:18 UT
Subjects:Radio, Optical, Fast Radio Burst

We wish to correct a typo in ATel #17856 in the quoted flux of the marginal
emission feature near 6680 Angstrom in the GTC/OSIRIS spectrum of the faint
irregular galaxy candidate. The flux of the tentative feature should read
~6 x 10^-18 erg s^-1 cm^-2, rather than ~6 x 10^-17 erg s^-1 cm^-2 as reported
in the original telegram. This correction does not affect any of the conclusions
presented in ATel #17856.

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