Nova ASASSN-21eh (=V6594 Sgr) is likely forming dust
ATel #14637; U. Munari (INAF Padova), S. Dallaporta and A. Vagnozzi (ANS Collaboration)
on 18 May 2021; 06:33 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)
The transient ASASSN-21eh has been discovered on 2021 March 25.29 UT at
g=11.54 mag by the ASAS-SN survey (Shappee et al. 2014, ApJ 788, 48), and
soon classified as a FeII nova in ATel #14487 and #14488.
ANS Collaboration has been collecting optical photometry of ASASSN-21eh
at daily cadence with several telescopes operating simultaneously and
independently, with all data transformed to the Landolt system of equatorial
standards. ASASSN-21eh reached the optical maximum on March 30.15 UT, at
V=9.265, B-V=+0.740, V-R=+0.390, and V-I=+0.786. After just a hint of
decline, the nova entered a plateau phase that lasted till April 8 and that
was characterized by mean values V=9.51, B-V=+0.43, V-R=+0.45, and
V-I=+0.83. Following the plateau, the nova begun a slow and smooth decline
characterized by the average rates 0.073 mag/day in B, 0.085 in V, 0.068 in
R, and 0.069 in I, with an opposing trend of B-V (getting bluer) with
respect to the other optical colors (turning redder). The slow decline
brought ASASSN-21eh to V=12.355, B-V=+0.035, V-R=1.053, and V-I=+1.381 by May
9.070 UT, when bad weather stopped momentarily monitoring of the nova by ANS
Collaboration telescopes.
When monitoring was resumed on May 16, the nova was found much redder
and much fainter than expected from the extrapolation of the smooth decline
it was previously following, as confirmed by a new observation on May 18:
| 2021 UT | V | B-V | V-R | V-I |
|---|
| May 9.070 | 12.355 | +0.035 | +1.053 | +1.381 |
| May 16.090 | 15.232 | +0.628 | +2.118 | +2.588 |
| May 18.057 | 15.516 | +0.705 | +2.066 | +2.702 |
The behavior exhibited by ASASSN-21eh suggests it is likely forming dust
in its ejecta. We encourage the acquisition of near-IR observations to
confirm such a possibility.
