TCP J1822 is a symbiotic star, according to observations

Using the Himalayan Chandra Telescope (HCT), Indian astronomers carried out spectroscopic observations of a star discovered in 2021, known as TCP J1822. The results of the observation campaign indicate that TCP J1822 is a symbiotic star. The discovery was published in the December issue of Monthly Notices of the Royal Astronomical Society.

Symbiotic stars, among the largest interacting binaries, exhibit dramatic, episodic changes in their light spectra because one pair is a small, very hot star while the other is a cool giant. . These systems can provide essential information to researchers studying certain aspects of stellar evolution.

Located some 26,000 light years away, TCP J18224935-2408280, or TCP J1822 for short, was discovered on May 19, 2021 during an explosion. The outburst is estimated to have begun between May 13 and 16, reaching the first maximum in about five days, followed by a slight decrease in brightness of 0.5 mag for 10 days.

Follow-up observations of TCP J1822 revealed that it exhibits long-term variability and exhibits strong neutral lines of hydrogen, helium, and a doubly ionized oxygen line. Overall, the results suggest that the symbiotic nature of TCP J1822 and its infrared colors are consistent with a symbiotic S-type star.

To confirm this hypothesis, LS Sonith and US Kamath of the Indian Institute of Astrophysics in Bengaluru decided to use the HCT’s Himalayan Faint Object Spectrograph Camera (HFOSC) to study the low-resolution optical spectra of TCP J1822.

“The optical spectrum of TCP J1822 shows the Balmer series lines, OI, He I and high excitation lines such as He II, O(III), Raman-scattered O VI and TiO bandheads of the cold component, which unambiguously confirms the symbiotic nature of the system,” explained the researchers.

Furthermore, observations revealed that after returning to rest, TCP J1822 exhibits a temperature above 100,000 K and a brightness at the level of 1,000 solar luminosities. These values ​​are typical of the hot component (most likely a white dwarf) of quietly burning symbiotic stars.

As for the coldest component of the TCP J1822 system, the data collected indicates that it is a star of spectral type M1-2 III with a temperature of approximately 3,600 K. The star is approximately 69 times larger than the sun and has a luminosity of approximately 700 solar luminosities.

According to the study, TCP J1822 exhibits a combined nova-type explosion. This is because the explosion started with an instability of the accretion disk and ended with burning of the shell and an expansion of the photospheric radius of the white dwarf.

The observations also revealed that the light curve before and after the explosion of TCP J1822 displays a periodicity of approximately 631.25 days, which the paper’s authors believe is an orbital period of the system.

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