Photometry and spectroscopy of declining Nova ASASSN-17hx, now passing at t_2
ATel #10641; U. Munari (INAF Padova), G. Traven (Univ. Ljubljana), F.-J. Hambsch, F. Castellani, A. Frigo, A. Milani, P. Valisa (ANS Collaboration), P. Ochner (Univ. Padova)
on 15 Aug 2017; 09:57 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)
ASASSN-17hx was discovered (Atel #10524) when still >4 mag below and ~41
days before maximum. Spectral classification and pre-maximum evolution have
been reported (Atel #10527, #10558, #10572, #10613), as well as the identification
in the VVVX survey of a Ks=16.7 mag star as the likely progenitor of the
nova, and recently UV observations and an upper limit to X-ray flux obtained
with Swift (Atel 10636).
We are continuing an intensive monitoring on Nova ASASSN-17hx with ANS
Collaboration photometric telescopes 210 (Atacama, Chile) and 606 (Monte
Baldo, Italy), and low-/high-resolution spectroscopy being collected with
Varese 0.6m and Asiago 1.22m and 1.82m telescopes.
The nova went through a broad maximum, that appears roughly symmetric in
shape when viewed in bolometric optical flux, but with differences in the
actual profile going from B to I bands. The peak V-band brightness was
reached on July 30.1 UT at B=9.65, V=8.44, R=7.79, and I=7.05. Our last
measurement of a few hours ago on Aug 14.8 UT gives B=11.04, V=10.26,
R=9.07, and I=8.51, indicating that the nova is quickly approaching t_2 for
the V-band. At the current decline rate, t_2 should be passed through
around Aug 17.0. The maximum reported in ATel #10572 now appears as a
temporary event during the rise toward the true peak.
The optical spectra are still dominated by FeII, with HeI growing in
intensity as the decline progresses in a normal fashion. On Aug 12.8 UT
spectra, the FeII emission included lines from multiplets 27, 28, 35, 37,
38, 40, 42, 46, 48, 49, 55, 57, 73, and 74 while most prominent HeI lines
were 4026, 4471, 5876, 6678, and 7065, the latter with pronounced P-Cyg
absorptions as for OI 7772. The profile of Balmer lines is characterized by
the presence of a sharp absorption (at heliocentric velocity -250 km/s, and
FWHM ranging from 200 km/s for Halpha to 110 km/s for Hdelta), superimposed
on the emission component that extends at its base from about -1000 to +1000
km/s.
The interstellar NaI D1,D2 doublet appears very complex on our highest
resolution Echelle spectra, with each of the two lines identically split
into at least 5 distinct components. Applying to their individual
equivalent widths the calibration by Munari and Zwitter (1997, A&A 318,
269), the interstellar extinction sums up to E(B-V)=0.62, in good agreement
with the E(B-V)=0.68 derived in ATel #10572 from the 6614 Ang diffuse
interstellar band.
