Temporal resolution of a pre-maximum halt in a classical nova: V5589 Sgr observed with STEREO HI-1B

Abstract

Classical novae show a rapid rise in optical brightness over a few hours. Until recently the rise phase, particularly the phenomenon of a pre-maximum halt, was observed sporadically. Solar observation satellites observing Coronal Mass Ejections enable us to observe the pre-maximum phase in unprecedented temporal resolution. We present observations of V5589 Sgr with STEREO HI-1B at a cadence of 40 min, the highest to date. We temporally resolve a pre-maximum halt for the first time, with two examples each rising over 40 min then declining within 80 min. Comparison with a grid of outburst models suggests this double peak, and the overall rise timescale, are consistent with a white dwarf mass, central temperature and accretion rate close to 1.0 M ⊙ , 5 × 10 7 K and 10 −10 M ⊙ yr −1 respectively. The modelling formally predicts mass loss onset at JD 2456038.2391±0.0139, 12 hrs before optical maximum. The model assumes a main-sequence donor. Observational evidence is for a subgiant companion; meaning the accretion rate is under-estimated. Post-maximum we see erratic variations commonly associated with much slower novae. Estimating the decline rate difficult, but we place the time to decline two magnitudes as 2.1 < t 2 (days) < 3.9 making V5589 Sgr a "very fast" nova. The brightest point defines "day 0" as JD 2456038.8224±0.0139, although at this high cadence the meaning of the observed maximum becomes difficult to define. We suggest that such erratic variability normally goes undetected in faster novae due to the low cadence of typical observations; implying erratic behaviour is not necessarily related to the rate of decline.

Discovery of a Rapid, Luminous Nova in NGC 300 by the KMTNet Supernova Program

“…Those features together with the presence of a multi- color pre-maximum halt and the smooth post-maximum evolution suggest that KSP-OT-201509a is a rapidly evolving classical nova. Indeed, the lightcurve shown in Figure 2 shows similarities with other well-sampled fast galactic novae such as V5589 Sgr (Eyres et al 2017, see §5 for a more detailed discussion). Finally, the observed peak luminosity/decline rate ratio is in good agreement with established empirical relations.…”

Pre-maximum and maximum of Novae: The spectroscopic observations of Nova ASASSN-17hx

“…The authors reported evidence of pre-maximum halts, detecting two short duration dips during the rise to maximum, as predicted by [10]. The halts are precursors of the onset of mass loss [6]. The data of V5589 Sgr have been re-analyzed by [38], who performed a different background subtraction.…”

“…The energy flux drops when convection in the expanding envelope becomes inefficient near the envelope surface and opacity decreases. Dips have been observed in RS Oph and KT Eri [11] and in V5589 Sgr (see below) [6].…”

“…The instrument has monitored 13 galactic novae [11], [12], some of them during the pre-maximum. The photometric evolution of the pre-maximum of V5589 Sgr has been investigated by [6] with a cadence of 80 min using STEREO HI-1B. The authors reported evidence of pre-maximum halts, detecting two short duration dips during the rise to maximum, as predicted by [10].…”

The Effect of Enriched Accreted Matter on the Development of Novae

“…This means that the time between eruptions, although substantially different for some of the models, cannot be used alone as an observational tool to determine the composition of the donor envelope. Another example may be the estimated modeled accretion rate for the classical nova V5589 Sgr in Eyres et al (2017), which is based on solar composition accreted material. They state that since the donor in the system is a sub-giant, the accreted material may be somewhat enriched, and thus the estimated accretion rate may be somewhat different.…”