For optical flickering in symbiotic star MWC 560

This study is based on observations of MWC560 during the last two observational seasons (2020/2021 and 2021/2022). Other than looking for flickering we were interested in following the variability of brightness in the same period. Looking for similarities in the spectra with other types of stars is also of great interest to us because it could help clarify the stellar configuration of such objects. Our observations during the last two observational seasons of MWC560 confirm the absence of flickering. From the similarities of the gathered spectra of XX Oph and MWC560 we assume that the components in XX Oph are a red giant and a white dwarf, which are also surrounded by a common shell.


Introduction
The symbiotic star MWC 560 (V694 Mon) is an object of high interest since 1990 when it exploded and the spectra showed mass ejection with velocities around 6000 km/s [Tomov et al. 1990]. The untypical spectral behavior was accompanied by optical flickering in all colors. This flickering of MWC 560 was always present between 1984 and 2018 with a short exception during 2016. It completely disappeared in October 2018 [Goranskij et al. 2018]. V694 Mon never returned in state of rest but entered a state of continuous brightness increase modulated by different periodicities of 331 and 1860 days and possible 9570 days [Munari et al. 2016].
This study is based on observations of MWC560 during the last two observational seasons (2020/2021 and 2021/2022). Other than looking for flickering we were interested in following the variability of brightness in the same period. Looking for similarities in the spectra with other types of stars is also of great interest to us because it could help clarify the stellar configuration of such objects.

Observations
In this study we present CCD photometry and spectral observations of MWC560. The photometry was done by the 40-cm telescope at the Astronomical observatory of the Shumen University (АОShU) [Kjurkchieva et al. 2020]. The spectra were obtained with the ESPERO spectrograph [Bonev et al. 2017], mounted on the 2-m telescope at the Rozhen NAO.
The star was observed photometrically in two consecutive observational seasons during 2020-2022, a total of 7 nights were recorded. In Table 1 is presented the journal of these observations, all of which are done with two Sloan filters g' and r'. Exposition was 10 s with g', and 5 s and 10 s with r'.
The FWHM of the target images were around 3 pix in g′and 4 pix in r′. The standard procedure was used for the reduction of the photometric data (de-biasing, dark frame subtraction and flat-fielding) using the software MaxImDL 6.2. We performed differential photometry using 4 standard stars. Their magnitudes ( Table 2) were taken from the catalogue APASS DR9 [Henden et al. 2015]. We transformed the data using equations 2 and 3 from article [Kjurkchieva et al. 2020].
In this work we presented and analyzed two spectra of MWC560 from 6.    From the observations of MWC 560 during the last three decades, it is known that it consists of a mid-M non Mira giant and an white dwarf [Lucy et al. 2020]. XX Oph is one of the two stars listed as "Iron Stars" [Bopp & Howell, 1989] due to the appearance of metal emission lines in its optical spectrum.
There are no clear evidences about the components of XX Oph [Howell et al. 2009]. The spectral similarity shown in Fig. 4 is a clue that likely the components inside XX Oph are a red giant and a white dwarf. The white dwarf is probably accreting at high mass accretion rate and the components are surrounded by envelope.
This similarity can be interpreted vice versa-in this stage of the evolution of MWC560, it is mimicking behavior of an "iron star".   From the similarities of the gathered spectra of XX Oph and MWC560 we assume that the components in XX Oph are a red giant and a white dwarf, which are also surrounded by a common shell.