BVR observations of Centaur 29P/Schwassmann-Wachmann before the stellar occultation on December 27, 2022
ATel #16137; Alberto Silva Betzler (UFRB-CETENS), Orahcio Felicio de Sousa
on 17 Jul 2023; 19:43 UT
Credential Certification: Alberto Betzler (betzler@ufrb.edu.br)
Subjects: Optical, Comet, Solar System Object
We observed Centaur 29P/Schwassmann-Wachmann with a Takahashi Epsilon 250 0.25 m f/3.4 hyperbolic Newtonian telescope equipped with a
CCD SBIG ST-10XME and RGB filters at Itelescope New Mexico Observatory (USA) (MPC code H06). We acquired three RGB sequences of this object during 12 minutes, starting on December 27.4392, 2022 UT, about two hours
before this object occulted the star GaiaDR3 ID 3434666624851959552.
The data reduction and photometric calibration procedures used in this work are described in Betzler & de Sousa
(2022, ATEL #15812). The coma showed bright condensation with an R-band point spread function with a mean full width at half maximum of 7.8+/-0.8 arcsec.From this condensation emanates a possible fan with its major axis at an position angle close to zero degrees and nearly orthogonal to the direction of the Sun, a structure typically observed after an outburst (see Betzler,2023, MNRAS,523,3678). The coma did not attenuate the brightness of the occulted star at an angular distance of 30+/1 arcsec from the coma's optocenter.
The weighted mean Johnson-Kron-Cousin magnitude in the V band of this star was 13.83+/0.05 (B-V=1.01+\-0.04 and V-R=0.58+\-0.02), similar to its APASS DR10 V magnitude of 14.0+/-0.1.
The weighted mean colors of this centaur were B-R=1.21+/-0.09, V-R=0.47+/-0.04; and V-magnitude= 13.80+/-0.05, measured with a photometric aperture radius of 8.3 arcsec.
Coma colors were redder than solar colors, but typical of active comets (Betzler et. 2017,AdSpR,60, 612), even considering the most recent outburst, which occurred on December 26, 2022 UT. The solar phase-corrected Af\rho parameter was Af\rho(0)=3547+/-128 cm higher than the observed value for some long-period comets at similar heliocentric distance (r=6.056 au) (Sarneczky et al.2016, AJ,152,220), but it was half the measurement during the peak of an outburst that had an amplitude of about -2 magnitudes relative to the quiescent state (see Hosek et al. 2012, CBET #3169).
