A descriptive title
ATel #17831; Federico Manzini (Stazione Astronomica di Sozzago, Italy), David Augustin (Anglet, France), Raoul Behrend (Observatoire de Geneve, Switzerland), Costantino Sigismondi (ICRA, Italy), Virginio Oldani (Stazione Astronomica di Sozzago, Italy), Alessandra C. Mura (UniPd, INAF-OAPd, Italy), Paolo Ochner (INAF-OAPd, UniPd, Italy), Andrea Farina (UniPd, Italy), Luigi R. Bedin (INAF-OAPd, Italy), Andrea Reguitti (INAF-OAPd, Italy), Mohamed Aboushelib (National Research Institute of Astronomy and Geophysics, Egypt)
on 4 Jun 2026; 18:10 UT
Credential Certification: Andrea Reguitti (andreareguitti@gmail.com)
Comet 10P (the second comet discovered by W. Tempel in Milan in 1873), a short period comet, is
approaching perihelion on August 2, 2026, at a heliocentric distance of approximately 1.42 AU
(JPL/Horizons, https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=10p).
In recent weeks, the comet has shown a marked increase in brightness, accompanied by the development
of a diffuse coma and a dust tail at PA 260°. The nucleus has always been clearly visible,
almost point-like and well defined.
We conducted a photometric monitoring campaign on May 17, 2026, with the 0.4-m telescope at the
Stazione Astronomica di Sozzago, Italy (IAUC-MPC code, A12) and with the 0.35-m telescope at e-EyE
(Fregenal de la Sierra, Spain). A total of 15 observing sessions were collected between May 17 and June 1,
2026. During the first observing sessions, CCD images were taken without filters to collect as much signal
as possible from the area surrounding the nucleus, whose magnitude was initially around 15-16.
The comet's motion was tracked with differential tracking to maintain a point-like nucleus. Over two nights,
up to 5 hours of continuous observation were collected, taking advantage of the difference in longitude
between the two observatories.
All observation sessions were then analyzed photometrically after the standard reduction (bias, dark,
flat): the comet's color was derived statistically and the choice of comparison stars was made based on
Gaia DR3. The photometric readout circle was set to 6 pixels in diameter, centered on the comet's
optocenter to minimize the coma interference.
The light curves for each night (always very sharp) were initially phased based on the period published in
2013 (Schleicher et al., AJ, 2013), and subsequently rephased to achieve 1-sigma precision. The final light
curve is shown in the figure accompanying this ATel. The overall best observed period solution shows an
unambiguous synodic period T = 0.37345d +/- 0.00004d, corresponding to 8h57m46s +/- 4s (1 sigma).
Our observations confirm the presence of a clear variation in light in the photometry of the nucleus of
comet Tempel 2; they also confirm the presence of a period close to that last published, with a possible
slowdown of 53+/-4 seconds.
Calibration details, figures and captions are available here:
