PREDNASAJUCI / LECTURER :

Jan Budaj

NAZOV / TITLE :

PM 1-322: a variable planetary nebula or something else?

ABSTRAKT / ABSTRACT :

Context. Spectra of planetary nebulae (PNe) are characterised
by strong forbidden emission lines and often also by IR excess.
A few PNe show dust obscuration events and/or harbour long-period
binaries. Some post-AGB stars, symbiotic stars, or B[e] stars may
feature similar characteristics. Recently, dust clouds eclipsing
white dwarfs were also detected.
Aims. We report the discovery of an object with a very peculiar
variability pattern that bears signatures compatible with the above
mentioned classes of objects. The object is ZTFJ201451.59+120353.4
and identifies with PM 1-322.
Methods. The object was discovered in ZTF archival data and investigated
with historical and newly obtained photometric and spectroscopic observations.
Results. The ZTF r and g data show a one magnitude deep, eclipse-like event
with a duration of about half a year that occurred in 2022.
The variability pattern of the star is further characterised by several dimming
events in the optical region that are accompanied by simultaneous brightenings
in the red and infrared regions. Apart from that, two fast eruption-like events
were recorded in ZTF r data.
Archival data from WISE indicate long-term variability with a possible period
of 6 or 12 yr. Our follow-up time series photometry reveals a stochastic short-term
variability with an amplitude of about 0.1 mag on a time scale of about one hour.
The spectral energy distribution is dominated by infrared radiation. Our high-resolution
spectroscopy shows strong forbidden emission lines from highly ionised species and symmetric
double-peaked emission in Hα, which is very different from what is seen in earlier spectra
obtained in 2007.
Conclusions. Several explanatory scenarios are presented. Our most likely
interpretation is that our target object involves a hot central star surrounded
by gaseous and dusty disks, an extended nebula, and a possible companion star.
Further observations are required to shed more light on the true nature of this enigmatic object.