Continued monitoring of activity in T CrB: Rapid intensification of He II and spectroscopic gyrations
ATel #16912; Firstname1 F. Teyssier, F. Sims, J. Guarro, E. Bertand (ARAS Group), S. N. Shore (Univ. of Pisa; INAF-OATS) (Affil1), Firstname2 Lastname2 (Affil2)...
on 18 Nov 2024; 14:45 UT
Distributed as an Instant Email Notice Novae
Credential Certification: S. N. Shore (shore@df.unipi.it)
Subjects: Nova, Transient
We report recent results from the ARAS group small telescope monitoring of T CrB in anticipation of its expected eruption with low (500 - 1000) resolution grism and grating spectra and medium (10000-22000) resolution grating and echelle spectra optical (~3750 - 9300A). To date a total of more than 1500 spectra have been archived since 2012 Apr. The current monitoring, with nearly daily observations, has been ongoing for more than one full observing season. The spectra reported here were obtained in the last few weeks between 2024 Oct. 16.07 through Nov. 15.04. The full data set is publicly available in the ARAS Spectral Database. Flux calibration was performed using AAVSO photometry (Vega magnitudes). The orbital phase was 0.51 - 0.55, with the WD seen through the M star wind. The line flux measurements and diagnostic ratios are listed in the table. The He II 4686 line has undergone a strong increase relative to the end of 2024 Oct. with fluctuations in the intensity. Halpha increased in flux by nearly 1.5x and the profile has changed from a central absorption at vrad ~ -31 km/s on Oct. 13.8 UT to a weak emission peak on Nov. 11.8 UT. The two profiles resemble those reported in ATel #16214, the emission only from 2021 Apr. 1, the ones including absorption from 2023 Aug. 27. The measured velocity for the peak is consistent with the systemic radial velocity (-27 km/s) . Hbeta showed a similar variation although the absorption at -50 km/s had, originally, been less visible. Several new emission lines are now visible, including [O I] 5577, 6300A, [O III] 4959, 5007 (but not [O II] 4363A; and several He I lines, especially 5876, 6678 A (4922, 5015 were weak but present).. The highest ionization stage seen so far is N III 4640. The most recent very active state definitively ended in 2023 Jun Atel # 16109. The activity now resembles that reported historical variations in 2015 and is similar to a number of other shortlived active intervals since the 1990s. The line fluxes are provided in Table 1; all were obtained with a LISA spectrograph (R ~ 1000, 3750-7250A).
Integrated line fluxes (units: erg/s/cm^2)
\begin{table}[!ht]
\centering
\begin{tabular}{lllllll}
Date & JD & He II & He I 5876 & H beta & He II / H beta & He II / He I \\
2024-11-16.039 & 630.5 & 6.70E-13 & 1.05E-12 & 2.92E-12 & 0.23 & 0.64 \\
2024-11-15.041 & 629.5 & 7.63E-13 & 1.15E-12 & 3.05E-12 & 0.25 & 0.66 \\
2024-11-14.044 & 628.5 & 5.8E-13 & 1.06E-12 & 3.26E-12 & 0.18 & 0.55 \\
2024-11-13.041 & 627.5 & 1.46E-12 & 1.08E-12 & 3.84E-12 & 0.38 & 1.35 \\
2024-11-12.041 & 626.5 & 9.412E-13 & 1.06E-12 & 3.523E-12 & 0.27 & 0.89 \\
2024-11-11.043 & 625.5 & 9.101E-13 & 1.118E-12 & 3.625E-12 & 0.25 & 0.81 \\
2024-11-10.043 & 624.5 & 1.53E-12 & 1.142E-12 & 4.353E-12 & 0.35 & 1.34 \\
2024-11-08.045 & 622.5 & 5.568E-13 & 5.72E-13 & 2.779E-12 & 0.20 & 0.97 \\
2024-11-05.048 & 619.5 & 2.622E-13 & 5.43E-13 & 2.041E-12 & 0.13 & 0.48 \\
\end{tabular}
\end{table}
During the interval from Oct. 16 through Oct. 26, the Hbeta line decreased from a flux of 13.23E-13 to 7.08E-13. In the monitored interval, the Hbeta and He II fluxes were linearly correlated. Wind fluctuations, probed by the line of sight, may be responsible for some of the modulation of the fluxes and line profiles. Absorption from the intervening wind and fluctuations from the accretion environment may be responsible for the observed flux variations. The increase in the nebular lines and N III, along with the increase in He II, all indicate a hard incident spectrum that may signal a change in the accretion environment and rate. Monitoring is continuing and the data are available by the cited website.
ARAS Spectral Database Eruptive Stars
