Optical spectroscopy of AT 2019qwf, a FeII-class nova
ATel #13283; Ulisse Munari (INAF Padova)
on 9 Nov 2019; 15:59 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)
AT 2019qwf was discovered as PGIR19brv by Palomar Gattini-IR survey on UT
2019-09-17.25 at J=11.3 mag, and as ZTF 19abyukuy by the Zwicky Transient
Facility on 2019-09-15. Spectroscopic classification was
reported in ATel #13130 (SED Machine on the Palomar 60-inch telescope) and
ATel #13149 (Kast spectrograph on Lick 3m telescope), both noticing Halpha,
Hbeta and OI 7772 lines with a broad emission profile superimposed onto a
red continuum, and both concluded that AT 2019qwf is a highly reddened
Galactic nova, of an unspecified class. Further spectral observations were
obtained several weeks later on 2019-11-01.71 UT with MFOSC-P spectrograph/imager
on Mt. Abu 1.2m telescope and described in ATel #13258, where attention was
focused on the nova still lingering around maximum brightness
since its discovery, and on the possible narrowing of emission lines as
it could be expected in the case of a nova erupting in a symbiotic binary,
where the ejecta are decelerated while trying to expand within the
pre-existing wind of a cool giant companion. This type of novae are usually of
the He/N type.
We have obtained a 30min spectrum of AT 2019qwf on 2019-11-05.94 UT with the
B&C spectrograph on the Asiago 1.22m telescope, extending from 3300 to 8000
Ang at a dispersion of 2.31 Ang/pix and a resolving power 1500 (as derived
from the width of night-sky lines). Integrating the band transmission
profiles over the fluxed spectrum returns B=17.72, V=15.72, and R=14.08 mag
for the nova at the time of observation.
Our spectrum is characterized by a steep red slope and marked by strong
signatures of the interstellar reddening, in particular several Diffuse
Interstellar Bands (DIBs), the strongest being those at 5780 and 6280 Ang
(E.W. 2.8 and 3.7 Ang, respectively). In addition to the strong Halpha,
Hbeta and OI 7772 emission lines already reported before, our spectrum reveals
several FeII multiplets in emission, in particular N. 38, 42, 48, 49, and
74. NII multiplet 3, and NIII multiplet 3 could be present too, while no
HeI line is seen. This allows to classify AT 2019qwf as a nova belonging to
the FeII spectral class. The integrated flux of some representative
emission lines is given in Table (in units of 10(-15) erg / cm2 sec
Ang):
| OI 7772 | 160 |
| Halpha | 450 |
| FeII 6456 (#74) | 10 |
| FeII 5276 (#49) | 5 |
| FeII 5169 (#42) | 7 |
| Hbeta | 17 |
The huge Halpha/Hbeta ratio confirms the high reddening affecting the nova.
All the emission lines appear sharp and symmetric. The FWHM (corrected for
instrumental PSF) of OI 7772 is 380 km/s, and those of Halpha and FeII are
430 and 360, respectively, wider than the ~300 km/s reported in ATel 13258
for Halpha in spectra obtained four days earlier. Other differences are (a) on our
spectrum Halpha presents wings only in weak excess of a Gaussian profile,
similar to those caused by a high electronic pressure (and the profile for
OI 7772 is a pure Gaussian without excess wings), and (b) a P-Cyg absorption
component is clearly present only in OI 7772, at -265 km/sec from the
emission line, compared with -540 km/s derived in ATel 13258.
The nova, even if photometrically stable around maximum brightness for 50
days already, is nonetheless spectroscopically active, and further
observations will be relevant, especially if performed at the time when the
nova will finally exit the present plateau and begin the decline from it.
Should it duplicate HR Del, the evolution at that time could be spectacular and going all the way through the diffuse-enhanced spectroscopic stage in a matter of just a few days.
