BX MONOCEROS: THE NEW UNPREDICTED OUTBURST HAS ALREADY STARTED

ATel #15327; L. Kondratyeva (FAI, Kazakhstan) and I. Reva (FAI, Kazakhstan)
on 13 Apr 2022; 08:52 UT
Credential Certification: Ludmila Kondratyeva (lu_kondr@mail.ru)

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BX Monoceros (BX Mon), an eclipsing stellar system, consists of a M5III giant and a hot star of A7 - F0 spectral class. Optical spectrum of BX Mon originates in the ionized envelope formed by the red giant wind. It is dominated by the late M star continuum and emission lines of HI (Dumn et al., 1988, A&A 336, 637; Ivison et al., 1994, A&ASS 103, 201). The outbursts of the object took place in 1978, 1984, 2003, 2013, and its brightness reached V = 8.8 mag The next flash began in the early 2019 (Kondratyeva et al. 2019, NewA, 750130). At the Fesenkov Astrophysical Institute (FAI) observations of this object were carried out from 2019, January 5 until this day. Photometric observations in BVRc filters were carried out with the Eastern Carl-Zeiss Jena 1-meter telescope located at Tyan-Shan Observatory (TShAO). Spectroscopic observations were performed with the 70-cm reflector (Observatory) and the second Carl-Zeiss Jena reflector mounted at TShAO. The telescopes are equipped with the spectrographs and SBIG STT-3200 CCDs. Spectra were obtained within the ranges of 4200 - 5300A and 6300 -7400A with the resolution 1.1A. Results of our photometric observations in 2021 -2022 are presented in Table. Earlier data were published in (Kondratyeva et al. 2021, OEJV, 199). The object was at a high brightness until April 2021. Thus, this flash lasted about 830 d, much longer than the flash of 2003 (about 200 d). During this brightening the maximal values of HI emission line fluxes were observed in the early 2019. Then the lines began to fade, and by April 2020 all of them turned in absorption (Kondratyeva et al. 2021, OEJV, 199). After the 2021 solar conjunction, in the autumn we found BX Mon to be in minimum, which continued until March 2022. The new brightening by 3 mag and 2 mag in the B and V filters, respectively, was observed in the end of March 2022. In the following days, the brightness continued to increase. Now only absorption lines of HI and Fe II are observed in the spectrum. It can be assumed that the accretion disk of BX Mon was destroyed during the flash of 2019. Now the stellar system is surrounded by envelope formed from the accretion matter of a red giant. Unfortunately, in the coming days, the object will become unavailable for our observations, and it is desirable to continue observations at other observatories.

 
UT	B	V	R 
2021 Jan 29.738	10.034+/-0.002	09.411+/-0.012	9.011+/-0.008 
2021 Feb 02.765	10.020+/-0.002	09.391+/-0.002	8.957+/-0.008 
2021 Feb 14.726	10.027+/-0.002	09.419+/-0.016	9.005+/-0.002 
2021 Feb 27.787	10.055+/-0.006	09.454+/-0.015	9.022+/-0.005 
2021 Apr 10.631	09.993+/-0.017	09.451+/-0.014	9.027+/-0.001 
2021 Apr 11.618	10.006+/-0.028	09.446+/-0.019	8.999+/-0.018 
2021 Oct 17.894	12.378+/-0.015	11.746+/-0.009	10.720+/-0.014 
2021 Nov 06.827	13.46+/-0.004	12.081+/-0.002	10.621+/-0.002 
2021 Nov 12.829	13.488+/-0.005	12.079+/-0.004	10.625+/-0.003 
2021 Nov 20.845	13.529+/-0.005	12.095+/-0.004	10.632+/-0.002 
2012 Dec 10.775	13.527+/-0.009	12.076+/-0.009	10.622+/-0.008 
2021 Dec 28.869	13.495+/-0.011	12.018+/-0.009	10.571+/-0.002 
2021 Dec 29.777	13.502+/-0.003	12.012+/-0.011	10.589+/-0.011 
2022 Jan 21.638	13.307+/-0.003	11.768+/-0.004	10.389+/-0.002 
2022 Jan 24.669	13.255+/-0.007	11.696+/-0.007	10.347+/-0.006 
2022 Jan 31.610	13.157+/-0.004	11.618+/-0.004	10.272+/-0.002 
2022 Feb 24.676	13.304+/-0.007	11.904+/-0.007	10.499+/-0.004 
2022 Feb 27.735	13.366+/-0.011	11.979+/-0.011	10.554+/-0.002 
2022 Mar 03.596	13.400+/-0.014	12.062+/-0.014	10.622+/-0.005 
2022 Mar 31.600	10.535+/-0.015	10.096+/-0.015	09.536+/-0.001 
2022 Apr 05.602	10.255+/-0.014	09.790+/-0.014	09.292+/-0.002 
2022 Apr 06.604	10.230+/-0.014	09.570+/-0.014	09.260+/-0.001 
 

Acknowledgements The work is funded by the Aerospace Committee of the Ministry of Digital Development, Innovations and Aerospace Industry of the Republic of Kazakhstan (BR 11265408)