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Spectroscopic observations of ASASSN-17gk

ATel #10399; Paul Luckas (International Centre for Radio Astronomy Research, University of Western Australia)
on 19 May 2017; 00:32 UT
Credential Certification: S. N. Shore (shore@df.unipi.it)

Subjects: Optical, Nova

Referred to by ATel #: 10400, 10404

Spectroscopic observations were obtained of the new Galactic nova, ASASSN-17gk (ATel #10366), on 2017 May 18.4 UT, 600 sec exposure with an Alpy600 spectrograph (0.8 A/px, 3800-7400A) using an Atik414 CCD detector. Extended absorption of the Na I D lines, blended with a maximum velocity of -2000 km/s, also shows that He I 5876 was not present (nor was He I 6678). The same absorption velocity was shown by Fe II 4923, 5169, Ca II H and K (although as always the H-epsilon line is blended with Balmer emission), and the Balmer lines, H-alpha through H-gamma, with little difference in the maximum. The Balmer absorption is, however, relatively weak compared to the emission. Fe II 5018 showed a higher maximum velocity, -2700 km/s, and a further extension toward maximum velocity than the other related Fe-curtain lines. The emission to absorption ratio for the metallic lines was > 4, while for the Balmer lines it was > 10. The forbidden lines [O I]5577, 6300,6364 were absent as were the [N II] 5755,6548,6583 lines (including the nebular lines). The nova is clearly in the very optically thick stage of the expansion, with many weak metallic line blends forming the pseudocontinuum, but with no indications yet of asphericity or filamentary structure. There was also no evidence for enhanced absorption at CN or CH, yet the Na I D line absorption was very strong and shifted. In light of the reported CO detections (ATel #10369) and the Na D lines, this may be a dust former. Observations are continuing in collaboration with the ARAS group and spectra will be available through the ARAS database.

A.R.A.S Spectral Data Base