Nova Cas 2020 (=V1391 Cas) is likely forming dust
ATel #14267; U. Munari (INAF Padova), D. P.K. Banerjee (PRL, India), F. Castellani, S. Dallaporta, A. Maitan, and A. Vagnozzi (ANS Collaboration)
on 15 Dec 2020; 12:46 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)
Referred to by ATel #: 14272
Nova Cas 2020 (=TCP J00114297+6611190) has been discovered on 2020 Jul
27.930 UT on images taken with an F=135mm f/2.0 telephoto lens as part of
the NMW survey (Sokolovsky et al. 2014, ASPC, 490, 395), and classified as
a FeII-type nova on spectra taken with SAI 2.5m telescope on July 29.025 UT
(ATel #13903). Various optical and infrared follow-up observations have
been later performed and reported (ATel #13967, #13998, #14004, #14006),
describing the subtle variations observed in this nova during the ~3 months
it spent fluctuating around maximum. The median values, for such a
flat maximum phase, derived from our daily photometric observations collected with various
ANS Collaboration telescopes are:
| B | V | R | I | B-V | V-R | V-I |
|---|
| 13.870 | 12.271 | 10.970 | 9.882 | +1.621 | +1.278 | +2.374 |
The brightness of the nova has dramatically dropped over the last couple
of days with a marked reddening of colors. The presence of a faint and nearby field star,
just a few arcsec away from the nova, now requires that the photometry be performed via PSF-
fitting. The night values, averaged over PSF-fitting measurements from data that
we collected with ANS Collaboration telescopes ID 0310, 0606 and 2202,
read:
| UT | B | V | R | I |
|---|
| 2020 Dec 10.083 | 16.97 | 15.26 | 13.58 | 12.40 |
| 2020 Dec 13.815 | 19.34 | 17.55 | 15.47 | 14.33 |
| 2020 Dec 14.810 | 19.55 | 18.03 | 15.91 | 14.80 |
We suggest Nova Cas 2020 is currently forming optically thick dust
in its ejecta, an event predicted to occur by Russell et al. (ATel
#13967) based on detection of emission from CO in their infrared spectra
collected with IRTF on Aug 17.
A low-resolution optical spectrum of
Nova Cas 2020 has been obtained with the Asiago 1.22m telescope on Dec
13.811 UT, when the formation of dust was already well underway. The spectrum has a
very red slope, and the only emission lines visible are those in the table below,
with no P-Cyg absorption present, all showing a narrow profile, and with an
integrated absolute flux (erg cm-2 s-1) as given in the last column:
| Ang | em. line | flux |
|---|
| 4861 | Hbeta | 3.00E-14 |
| 4923 | FeII | 1.20E-14 |
| 5018 | FeII | 1.14E-14 |
| 5169 | FeII | 9.68E-15 |
| 6300 | [OI] | 6.66E-14 |
| 6364 | [OI] | 2.21E-14 |
| 6563 | Halpha | 8.69E-13 |
| 7772 | OI | 9.46E-14 |
IR observations to confirm the condensation of dust in the ejecta
and characterize its properties are strongly encouraged.
