T CrB on the Verge of an Outburst: H alpha Profile Evolution and Accretion Activity

ATel #17041; Gesesew R. Habtie (Debre Berhan University, Debre Berhan, Ethiopia); Ramkrishna Das (S. N. Bose National Center for Basic Sciences, Kolkata, India); Ruchi Pandey (Physical Reaserch Laboratory, Ahmedabad, India)
on 15 Feb 2025; 13:55 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Gesesew Reta Habtie (gesesew@bose.res.in)

Tweet

We analyzed three Hα profiles of symbiotic nova T CrB, observed on JD 2460691.03 (January 15, 2025), JD 2460705.03 (January 29, 2025), and JD 2460713.57 (February 7, 2025); the first two were taken from AAVSO, and the remaining profile was from ARAS (Teyssier, 2019) databases. The resolution of the instruments where these spectral profiles were taken is 13577, 13481, and 13593, respectively.

We noticed that the Hα profiles showed a significant enhancement in both intensity and width. Based on the relative flux measured on those three epochs, we calculated that the flux subtended by Hα on February 7, 2025, increased by a factor of ~2.3±0.3 and ~2.1±0.3 relative to the flux measured on January 15 and January 29, 2025, respectively. On the other hand, the flux subtended by Hα on January 29, 2025, increased only by a factor of ~1.0±0.2 relative to the flux measured on January 15, 2025. This indicates that the rate of flux increase has drastically risen in recent days, particularly in early February 2025, compared to earlier observations. This enhancement could potentially be due to an increase in the accretion rate, which in turn leads to the expansion of the accretion disk, ultimately increasing its mass around the white dwarf. A similar trend was observed in the later stages of RS Oph quiescence prior to its 2021 outburst (see Habtie & Das, 2025).

In addition to the observed significant enhancement in intensity, we also detected a slight variation in the width of the Hα line profile across the three epochs. The FWZI of Hα measured on January 15, January 29, and February 7, 2025, was 668, 678, and 755±25 km/s, respectively, determined by fitting a Gaussian profile and subtracting the continuum baseline. This suggests that the width of the emission profiles also increased slightly over time, which could be a result of accretion disk expansion due to a rising accretion rate. Similarly, RS Oph exhibited a slight increase in line width prior to its 2021 outburst (see Habtie & Das, 2025).

Overall, given the rapid and drastic increase in intensity and width of the Hα profile, we strongly anticipate that the T CrB outburst may occur soon. We acknowledge AAVSO and ARAS for generously providing publicly available data through online platforms.