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The super-soft X-ray and CH/Ba-enhanced symbiotic star StHa 32 is in outburst

ATel #11304; U. Munari (INAF Padova), S. Dallaporta, M. Graziani, G. L. Righetti, S. Tomaselli, S. Moretti, A. Maitan, F. Castellani, P. Valisa, L. Baldinelli (ANS Collaboration)
on 15 Feb 2018; 11:12 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

Subjects: Optical, Ultra-Violet, X-ray, Cataclysmic Variable

The supersoft X-ray source, Barium-enhanced, metal-deficient and Halo symbiotic star StHa 32 in going into outburst, the first ever recorded to the best of our knowledge.

We are intensively following StHa 32 both photometrically and spectroscopically since 2005. Its photometric behavior in B band begun to deviate from the P=626 days orbital modulation at the beginning of November 2017. The initial rise has been very slow, gaining pace with passing time. The following are some of our most recent measurements:

Feb 13.83913.6712.4511.7311.16
Feb 11.86013.7612.5111.7811.22
Feb 10.86413.8512.5511.8211.23

The brightness gain in B band is already 0.85 mag compare to quiescence value at the same orbital phase, with all colors turning bluer.

A low resolution spectrum (3300-8000 Ang, 2.31 Ang/pix) has been obtained on UT Feb 14.8 with the Asiago 1.22m. Comparing with similar archive spectra obtained in quiescence at exactly the same orbital phase, the major differences are: (1) a brighter and bluer continuum at shorter wavelengths, with enhanced veiling of the absorption features of the cool giant (in particular the C2 bands at 4740, 5165 Ang, and the CH band at 4303); (2) a large increase in the integrated absolute flux of all emission lines; (3) a large increase in the ionization degree: HeII 4686/Hbeta changing from 1.45 to 2.15, HeII 4686/HeI 5016 from 15 to 28, OVI 6825/HeI 6678 from 1.35 to 2.32. No obvious nebular line is present (in particular [FeVII] and [NeV]). This is consistent with a high density, density-bounded nebula increasingly ionized by a now hotter and more luminous WD. Still, enough neutral hydrogen survives in the system to be able to efficiently Raman scatter OVI 1032, 1036 to observed 6825 and 7088 Ang (the latter 0.38 times the intensity of HeI 7065).