UBV Observations of Nova Vulpeculae 1968 No. 1

Kato

2014

ApJ

We identified a general course of classical nova outbursts in the B − V versus U − B color-color diagram. It is reported that novae show spectra similar to those of A-F supergiants near optical light maximum. However, they do not follow the supergiant sequence in the color-color diagram, neither the blackbody nor the mainsequence sequence. Instead, we found that novae evolve along a new sequence in the pre-maximum and nearmaximum phases, which we call "the nova-giant sequence." This sequence is parallel to but ∆(U − B) ≈ −0.2 mag bluer than the supergiant sequence. This is because the mass of a nova envelope is much (∼ 10 −4 times) less than that of a normal supergiant. After optical maximum, its color quickly evolves back blueward along the same nova-giant sequence and reaches the point of free-free emission (B − V = −0.03, U − B = −0.97), which coincides with the intersection of the blackbody sequence and the nova-giant sequence, and remains there for a while. Then the color evolves leftward (blueward in B − V but almost constant in U − B), owing mainly to the development of strong emission lines. This is the general course of nova outbursts in the colorcolor diagram, which was deduced from eight well-observed novae in various speed classes. For a nova with unknown extinction, we can determine a reliable value of the color excess by matching the observed track of the target nova with this general course. This is a new and convenient method for obtaining the color excesses of classical novae. Using this method, we redetermined the color excesses of 20 well-observed novae. The obtained color excesses are in reasonable agreement with the previous results, which in turn support the idea of our general track of nova outbursts. Additionally, we estimated the absolute V magnitudes of about 30 novae using a method for time-stretching nova light curves to analyze the distance-reddening relations of the novae.

Section: T Pyx 1966supporting

confidence: 90%

“…Therefore, we expect that the early color evolution of LV Vul follows the nova-giant sequence in the color-color diagram. Figure 30(b) shows the color-color evolution, where the UBV data are taken from Abuladze (1969), Dorschner et al (1969), andFernie (1969). The color-color evolution of LV Vul resembles those of V1500 Cyg and V1668 Cyg.…”

Section: T Pyx 1966mentioning

confidence: 93%

THEUBVCOLOR EVOLUTION OF CLASSICAL NOVAE. I. NOVA-GIANT SEQUENCE IN THE COLOR-COLOR DIAGRAM

Kato

2014

ApJ

“…The reddening toward LV Vul was estimated by Fernie (1969) to be E(B − V ) = 0.6 ± 0.2 from the color excesses of 14 B stars near the line of sight. Tempesti (1972) obtained E(B − V ) = 0.55 from the color at optical maximum; i.e., E(B − V ) = (B − V ) max − (B − V ) 0,max = 0.9−0.35 = 0.55.…”

Section: Vul 1968#1mentioning

confidence: 99%

The UBV Color Evolution of Classical Novae. III. Time-stretched Color–Magnitude Diagram of Novae in Outburst

Kato²

2019

ApJS

We propose a modified color-magnitude diagram for novae in outburst, i.e., (B − V ) 0 versus (M V − 2.5 log f s ), where f s is the timescaling factor of a (target) nova against a comparison (template) nova, (B − V ) 0 is the intrinsic B − V color, and M V is the absolute V magnitude. We dub it the timestretched color-magnitude diagram. We carefully reanalyzed 20 novae based on the time-stretching method and revised their extinctionsand timescaling factors f s against the template nova LV Vul. We have found that these 20 nova outburst tracks broadly follow one of the two template tracks, LV Vul/V1668 Cyg or V1500 Cyg/V1974 Cyg group, in the time-stretched color-magnitude diagram. In addition, we estimate the white dwarf masses and (m − M ) V of the novae by directly fitting the absolute V model light curves (M V ) with observational apparent V magnitudes (m V ). A good agreement in the two estimates of (m − M ) V confirms the consistency of the time-stretched color-magnitude diagram. Our distance estimates are in good agreement with the results of Gaia Data Release 2.

“…For the reddening toward LV Vul, Fernie (1969) determined E(B − V ) = 0.6 ± 0.2 from the color excesses of 14 B stars near the line of sight. Tempesti (1972) obtained E(B − V ) = 0.55 from the color at optical maximum; i.e., E(B − V ) = (B − V ) max − (B − V ) 0,max = 0.9 − 0.35 = 0.55.…”

Section: Vulmentioning

confidence: 99%

A Light-curve Analysis of Gamma-Ray Nova V959 Mon: Distance and White Dwarf Mass

Kato

2018

ApJ

V959 Mon is one of the gamma-ray detected novae. It was optically discovered about 50 days after the gammaray detection due to proximity to the Sun. The nova speed class is unknown because of lack of the earliest half of optical light curve and short supersoft X-ray phase due to eclipse by the disk rim. Using the universal decline law and time-stretching method, we analyzed the data of V959 Mon and obtained nova parameters. We estimated the distance modulus in the V band to be (m−M ) V = 13.15±0.3 for the reddening of E(B −V ) = 0.38±0.01 by directly comparing with the similar type of novae, LV Vul, V1668 Cyg, IV Cep, and V1065 Cen. The distance to V959 Mon is 2.5±0.5 kpc. If we assume that the early phase light curve of V959 Mon is the same as that of time-stretched light curves of LV Vul, our model light curve fitting suggests that the white dwarf (WD) mass is 0.9 − 1.15 M ⊙ , being consistent with a neon nova identification. At the time of gamma-ray detection the photosphere of nova envelope extends to 5 − 8 R ⊙ (about two or three times the binary separation) and the wind mass-loss rate is (3 − 4) × 10 −5 M ⊙ yr −1 . The period of hard X-ray emission is consistent with the time of appearance of the companion star from the nova envelope. The short supersoft X-ray turnoff time is consistent with the epoch when the WD photosphere shrank to behind the elevating disk rim, that occurs 500 days before nuclear burning turned off.