V458 Vul Research Articles

Multiple flares caused by mass ejection episodes during the advanced nebular phase of Nova Scuti 2019

ABSTRACT Our photometric and spectroscopic monitoring shows that starting with 2020 June 4, day +217 from optical maximum and well into its advanced nebular stage, Nova Scuti (Nova Sct) 2019 begun displaying a series of nine large amplitude flares (up to $\Delta m \sim 1.7$ mag), characterized by a rapid rise to peak (≤10 h) and a fast exponential decline (e-folding time ∼50 h). The time interval Δt between flares follows an ordered sequence, declining from 8.43 to 4.90 d, that safely allows to exclude that any other flare occurred without being recorded by the observations. When the sequence of flares was over by 2020 July 28 (day +271), Nova Sct 2019 slowed its overall decline rate from Δm = 0.0067 to 0.0027 mag d−1. The flares were caused by material expelled at high velocity (∼1000 km s−1) from the still burning white dwarf (WD). The cooler pseudo-photosphere forming at each flare in the expelled material, resulted in a recombination wave to spread through the original nova ejecta (at ∼170 au from the WD), quenching emission from [Fe x] and [Fe vii] and boosting that from lower ionization species. After each flare, once the small amount of expelled material had turned optically thin, the original nova ejecta resumed displaying [Fe x] and [Fe vii] emission lines, a fact that clearly proves the direct photoionization action exerted on the ejecta by the burning WD. While the other known flaring novae (V458 Vul, V4745 Sgr, and V5588 Sgr) presented the flares close to maximum brightness and with increasing Δt, Nova Sct 2019 is unique in having displayed them during the advanced nebular stage and with decreasing Δt.

The short orbital period binary star at the heart of the planetary nebula M 3-1

ABSTRACT We present the discovery of a 3h5m orbital-period binary star at the heart of the planetary nebula M 3-1 – the shortest period photometrically variable central star known and second only to V458 Vul, in general. Combined modelling of light and radial velocity curves reveals both components to be close to Roche lobe filling, strongly indicating that the central star will rapidly evolve to become a cataclysmic variable, perhaps experiencing a similar evolution to V458 Vul resulting in a nova eruption before the planetary nebula has fully dissipated. While the short orbital period and near Roche lobe filling natures of both components make the central binary of M 3-1 an important test case with which to constrain the formation processes of cataclysmic variables, novae, and perhaps even supernovae type Ia.

A Spectroscopic study of the envelope of the hybrid nova V458 Vul and the surrounding planetary nebula

Spectroscopic observations of the hybrid V458 Vul obtained between days 9 and 778 after the brightness maximum are analyzed. Short-period, daily profile variations of forbidden [FeVII] iron lines were detected in the nebular phase, as well as a long-period (about 60-day) cyclic variation that was correlated with the photometric and X-ray cycles. The abundances of helium, neon, and iron in the nova's envelope have been estimated. The helium, neon, and iron abundances exceed the solar values by factors of 4.4, 4.8, and 3.7. The envelope mass is 1.4$\times$ 10$^{-5}$M$_{\odot}$. The electron temperatures and number densities have been calculated for the Northwestern and Southeastern knots of the planetary nebula. The temperature derived for the Northwestern knot is Te = 10 000 K and the electron number density, n$_{e}$ = 600 cm $^{-3}$ for the Southeastern knot, Te = 13 000 K and n$_{e}$ = 750 cm$^{-3}$.

An H I shell-like structure associated with nova V458 Vulpeculae?

Abstract We report the radio detection of a shell-like H i structure in proximity to, and probably associated with, the nova V458 Vul. High spectral resolution observation with the Giant Metrewave Radio Telescope has made it possible to study the detailed kinematics of this broken and expanding shell. Unlike the diffuse Galactic H i emission, this is a single-velocity component emission with significant clumping at ∼0.5 arcmin scales. The observed narrow-line width of ∼5 km s−1 suggests that the shell consists of mostly cold gas. Assuming a distance of 13 kpc to the system, as quoted in the literature, the estimated H i mass of the nebula is about 25 M⊙. However, there are some indications that the system is closer than 13 kpc. If there is a physical association of the H i structure and the nova system, the asymmetric morphology and the off-centred stellar system indicate past strong interaction of the mass loss in the asymptotic giant branch phase with the surrounding interstellar medium. So far, this is the second example, after GK Per, of a large H i structure associated with a classical nova.

SPECTRO-INTERFEROMETRIC OBSERVATIONS OF CLASSICAL NOVA V458 VUL 2007

We used the Palomar Testbed Interferometer (PTI) to resolve 2.2 $\mu$m emission from the classical nova V458 Vul 2007 over the course of several days following its discovery on 2007 August 8.54 UT. We also obtained K-band photometric data and spectra of the nova during the early days of the outburst. We also used photometric measurements from the AAVSO database. This is a unique data set offering a 3-technique approach: high-resolution imaging, spectroscopy and photometry. Our analysis shows that the nova ejecta can be modeled as an inclined disk at low inclination i.e. low ellipticity which is consistent with the nova being in the fireball phase at which the outflowing gas is optically thick, confirmed by the presence of strong P-Cygni Balmer lines in the spectra. The expansion velocity is $\approx$1700 $\rm km\ s^{-1}$, derived from the H$\alpha$ line. By combining the nova's angular expansion rate measured by PTI with the expansion rate measured from spectroscopy, the inferred distance to the nova is 9.9-11.4 kpc. We also used the K-band fluxes and the derived size of the emission to estimate the total mass ejected from the nova $\approx 4\times 10^{-4} M_{\odot}$. The quick transition of the nova from Fe II to He/N class makes V458 Vul 2007 a hybrid nova.

On the Rebrightenings of Classical Novae during the Early Phase

Abstract We report on the spectral evolution of 6 classical novae (V1186 Sco, V2540 Oph, V4745 Sgr, V5113 Sgr, V458 Vul, and V378 Ser), based on low-resolution spectra obtained at the Fujii-Bisei Observatory and the Bisei Astronomical Observatory, Japan. In the light curves, these 6 novae show several rebrightenings during the early phase lasting $\sim\ $10 d after the first maximum in fast novae, and $\sim\ $100 d in slow novae. The early spectra of all of these novae had emission lines with a P-Cygni profile at the maximum brightness. The absorption component of the P-Cygni profiles then disappeared after the maximum, and reappeared when the novae brightened to the next maximum. We suggest that the re-appearance of the absorption component at the rebrightening can be attributable to a re-expansion of the photosphere after it once shifts sufficiently inside. From the light curves, we found that the time intervals of the rebrightenings of these 6 novae show a similar systematic trend, which is applicable to all types of novae; fast and slow, and Fe II type and hybrid type. Moreover, we note the difference between the spectra at the rebrightenings during the early phase and at the rebrightening in V2362 Cyg, and at the oscillation during the transition phase in V1494 Aql, which means a difference in the physical mechanism of the rebrightening during the early phase and the later oscillations.

The orbital period of V458 Vulpeculae, a post-double common-envelope nova

Abstract We present time-resolved optical spectroscopy of V458 Vulpeculae (Nova Vul 2007 No. 1) spread over a period of 15 months starting 301 d after its discovery. Our data reveal radial-velocity variations in the He iiλ5412 and He iiλ4686 emission lines. A period analysis of the radial-velocity curves resulted in a period of 98.096 47 ± 0.000 25 min (0.068 122 55 ± 0.000 000 17 d) which we identify with the orbital period of the binary system. V458 Vul is therefore the planetary nebula central binary star with the shortest period known. We explore the possibility of the system being composed of a relatively massive white dwarf (M1 ≳ 1.0 M⊙) accreting matter from a post-asymptotic giant branch star which produced the planetary nebula observed. In this scenario, the central binary system therefore underwent two common-envelope episodes. A combination of previous photoionization modelling of the nebular spectra, post-asymptotic giant branch evolutionary tracks and the orbital period favour a mass of M2 ∼ 0.6 M⊙ for the donor star. Therefore, the total mass of the system may exceed the Chandrasekhar mass, which makes V458 Vul a Type Ia supernova progenitor candidate.

SWIFTX-RAY AND ULTRAVIOLET MONITORING OF THE CLASSICAL NOVA V458 VUL (NOVA VUL 2007)

We describe the highly variable X-ray and UV emission of V458 Vul (Nova Vul 2007), observed by Swift between 1 and 422 days after outburst. Initially bright only in the UV, V458 Vul became a variable hard X-ray source due to optically thin thermal emission at kT = 0.64 keV with an X-ray band unabsorbed luminosity of 2.3 × 1034 erg s–1 during days 71-140. The X-ray spectrum at this time requires a low Fe abundance (0.2+0.3 –0.1 solar), consistent with a Suzaku measurement around the same time. On day 315 we find a new X-ray spectral component which can be described by a blackbody with temperature of kT = 23+9 –5 eV, while the previous hard X-ray component has declined by a factor of 3.8. The spectrum of this soft X-ray component resembles those typically seen in the class of supersoft sources (SSS) which suggests that the nova ejecta were starting to clear and/or that the white dwarf photosphere is shrinking to the point at which its thermal emission reaches into the X-ray band. We find a high degree of variability in the soft component with a flare rising by an order of magnitude in count rate in 0.2 days. In the following observations on days 342.4-383.6, the soft component was not seen, only to emerge again on day 397. The hard component continued to evolve, and we found an anticorrelation between the hard X-ray emission and the UV emission, yielding a Spearman rank probability of 97%. After day 397, the hard component was still present, was variable, and continued to fade at an extremely slow rate but could not be analyzed owing to pile-up contamination from the bright SSS component.

A Planetary Nebula around Nova V458 Vulpeculae Undergoing Flash Ionization

Nova V458 Vul erupted on 2007 August 8 and reached a visual magnitude of 8.1 a few days later. Hα images obtained 6 weeks before the outburst as part of the IPHAS Galactic plane survey reveal an 18th magnitude progenitor surrounded by an extended nebula. Subsequent images and spectroscopy of the nebula reveal an inner nebular knot increasing rapidly in brightness due to flash ionization by the nova event. We derive a distance of 13 kpc based on light travel time considerations, which is supported by two other distance estimation methods. The nebula has an ionized mass of 0.2 M☉ and a low expansion velocity: this rules it out as ejecta from a previous nova eruption, and is consistent with it being a ~14,000 year old planetary nebula, probably the product of a prior common envelope (CE) phase of evolution of the binary system. The large derived distance means that the mass of the erupting WD component of the binary is high. We identify two possible evolutionary scenarios, in at least one of which the system is massive enough to produce a Type Ia supernova upon merging.

The early spectroscopic evolution of nova V458 Vul (Nova Vulpeculae 2007)

The early spectral evolution of the nova V458 Vul has been monitored at the Loiano Observatory, Italy. The nova exhibited a couple of oscillations during the decline from initial maximum. We have performed spectroscopic observations to study the physical properties of the ejected material. The photometric light curve has been used to derive the nova distance and its absolute magnitude at maximum. V458 Vul is a fast nova, with decline rates by two or three magnitudes of 7 and 15 days respectively. The magnitude at maximum is MV=−8.8. The nova distance is in the range 6.7–10.3 kpc. The spectra secured a few days after initial maximum showed emission lines of H I and Fe II, making V458 Vul a Fe II nova at this stage. After the oscillations V458 Vul came back to a standard decline curve, but evolved towards the He/N class. Thus V458 Vul is a hybrid nova.

SPECTROSCOPIC MONITORING OF NOVA VULPECULAE 2007 (V458 Vul)

We present results of the spectroscopic monitoring of the peculiar nova V458 Vul during eleven months. At the early decline of the brightness the nova transformed from Fe II to the He/N type. The profiles of the HI and the HeI lines showed the variability connected with the rebrightening. At the final decline of the brightness the nova displays a fast variability (within a day) of the forbidden iron line profiles. The spectral features of V458 Vul allow classifying it as a hybrid ”neon” nova. From the AAVSO light curve we obtained some photometric parameters, the mass of 458 Vul and the distance to the object. The nova showed a fast decline of the brightness (t2=7, t3=18 days). It reached Mv= -9.0 mag at the maximum of the brightness. The distance to the nova is in the range d=10.1-12.8 kpc. The reddening E(B-V)=0.59 towards the star is derived using the colour index of the nova at the maximum and the Balmer decrements. The white dwarf mass was derived about 1.1–1.2 M