Spectroscopic observations of Nova Cassiopeiae 2020 = TCP J00114297+6611190 = V1391 Cas
ATel #14004; K. V. Sokolovsky, E. Aydi (MSU), L. Izzo (DARK/NBI), E. J. Harvey (Liverpool JM), K. E. Atapin, A. A. Belinski, A. V. Dodin, K. A. Postnov, S. A. Potanin, N. I. Shatsky, A. M. Tatarnikov (SAI MSU), L. L. Freour, C. K. Wedderkopp, L. V. Kroer, Y. Jundiyeh, P. L. Henriksen, R. T. Rasmussen (DTU-Space), V. Quist, M. V. Madsen, K. S. Jepsen, A. E. Hartwigsen, R. N. Sorensen, N. M. B. Stovelbaek, S. L. Hansen, M. M. Otap, J. R. W. Iv, A. N. Kolborg, J. Fynbo (NBI), M. A. Keniger (IFA/Aarhus), L. Chomiuk, A. M. Kawash, J. Strader (MSU), K. Mukai (NASA/GSFC), K.-L. Li (NCKU), S. Kafka (AAVSO), S. V. Karpov (Institute of Physics, Prague), S. A. Korotkiy (Ka-Dar Obs./Astrovert)
on 11 Sep 2020; 00:52 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)
Nova Cas 2020 (V1391 Cas; TCP J00114297+6611190), was discovered on
2020-07-27.9302 UT by S. Korotkiy and classified as a Fe II type
classical nova (ATel #13903, #13919, #13939, #13941,
#13967, #13998). The pre-discovery images by FRAM-ORM wide-field
camera (Janecek et al. 2019, EPJWC 19702008) constrain the eruption
date between 2020-07-26.10104 (last non-detection) and
2020-07-27.23087 (first detection; ATel #13904). In the following
month the nova showed a series of flares (each lasting days to
a week) with the brightest flare peaking at V=10.8 on
2020-08-10.08738 (according to FRAM and AAVSO photometry).
We conducted spectroscopic observations of Nova Cas 2020 with
the 2.6m Nordic Optical Telescope (NOT; La Palma, Spain) and
the 2.5m SAI Moscow State University telescope (Kislovodsk,
Russia). Between 2020-08-11.1 and 2020-08-15.1 we obtained three
900s NOT spectra using the high-resolution FIbre-fed Echelle
Spectrograph (FIES; Telting et al. 2014, AN, 335, 41). We used
the entrance aperture of 2.5 arcsec covering a spectral range of
4000-9000 A at a resolution of R=25000. Seven spectra were obtained
between 2020-07-29.022 and 2020-09-04.979 with the Transient
Double-beam Spectrograph mounted on the 2.5m SAI telescope
(Dodin et al. 2020, AstL, 46, 429). The exposure times were 30 to
600s, the spectral resolution R=1200-2200 for the blue and red
arms of the spectrograph together covering the range 3500-7500 A
(the spectrograph is typically used with a one arcsecond slit).
The NOT spectrum on 2020-08-11.1 (near the lightcurve peak)
shows narrow P Cygni profiles of Balmer, O I, Fe II, and Na I.
The absorption troughs are at blueshifted velocities of
200-250 km/s, while the emission features of the P Cygni profiles
are relatively weak compared to the absorption. The spectrum is
characterized by a red continuum due to the interstellar reddening
E(B-V)=1.39 mag (ATel #13905). The velocities measured earlier from
the absorption troughs are -850 km/s (Balmer lines; ATel #13903)
and -385 km/s (O I 7773; ATel #13905). This dramatic apparent
deceleration of the absorption features has been observed in other
novae during the rise to a peak and it is possibly due to
the photosphere receding to inner (slower-moving) regions of
the expanding ejecta.
The spectra between 2020-08-14 and 2020-08-16 show broad
emission lines with an FWZI around 2500 km/s while the slow
velocity absorption features of around 250 km/s are superimposed on
top of the broad emission. The SAI spectrum obtained on 2020-08-20,
coinciding with one of the secondary maxima shows strong
absorption features with absorption troughs at a velocity of around
-400 km/s. In some lines, these absorptions are superimposed on top
of the broad emission (FWZI ~2800 km/s). Following spectra
(2020-08-22 to 2020-08-25) show weakening absorption.
Our latest spectrum on 2020-09-04, coinciding with yet another
flare peak, shows strong absorption with absorption troughs at
blueshifted velocities of 600-700 km/s, particularly in
Hbeta and Fe II; Halpha shows absorption at -400 km/s.
The similar behavior is observed in other novae with multiple
maxima, where the absorption lines strengthen around
the peak brightness and appear at greater velocities
(e.g. Tanaka et al. 2011 PASJ, 63, 911; Aydi et al.
arXiv:1903.09232). Such spectral evolution may be understood if
the flares are associated with multiple ejections each causing
the photosphere to move outwards (with a new bunch of
fast-moving material) during the peak and then to recede.
We thank the AAVSO observers for the dense photometric coverage of
Nova Cas 2020. The NOT data were obtained in the context of
the Danish summer Course in Observational Astrophysics 2020.
The work of the SAI team was supported by the Program
of Development of MSU.
Lightcurve and spectra of Nova Cas 2020
