Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Heating and Pulsations of V386 Serpentis after its 2019 Dwarf Nova Outburst
218
0
0.0
(
0
)
Authors
Paula Szkody
Ask ChatGPT about the research
No Arabic abstract
Following the pulsation spectrum of a white dwarf through the heating and cooling involved in a dwarf nova outburst cycle provides a unique view of the changes to convective driving that take place on timescales of months versus millenia for non-accreting white dwarfs. In 2019 January the dwarf nova V386 Ser (one of a small number containing an accreting, pulsating white dwarf), underwent a large amplitude outburst. Hubble Space Telescope ultraviolet spectra were obtained 7 and 13 months after outburst along with optical ground-based photometry during this interval and high-speed photometry at 5.5 and 17 months after outburst. The resulting spectral and pulsational analysis shows a cooling of the white dwarf from 21,020 K to 18,750 K (with a gravity log(g) = 8.1) between the two UV observations, along with the presence of strong pulsations evident in both UV and optical at a much shorter period after outburst than at quiescence. The pulsation periods consistently lengthened during the year following outburst, in agreement with pulsation theory. However, it remains to be seen if the behavior at longer times past outburst will mimic the unusual non-monotonic cooling and long periods evident in the similar system GW Lib.
rate research
Read More
We present a detailed study of the 2019 outburst of the cataclysmic variable V1047 Cen, which hosted a classical nova eruption in 2005. The peculiar outburst occurred 14 years after the classical nova event, lasted for more than 400 days, and reached an amplitude of around 6 magnitudes in the optical. Early spectral follow-up revealed what could be a dwarf nova (accretion disk instability) outburst in a classical nova system. However, the outburst duration, high velocity ($>$2000 km s$^{-1}$) features in the optical line profiles, luminous optical emission, and the presence of prominent long-lasting radio emission, together suggest a phenomenon more exotic and energetic than a dwarf nova outburst. There are striking similarities between this V1047 Cen outburst and those of combination novae in classical symbiotic stars. We suggest that the outburst may have started as a dwarf nova that led to the accretion of a massive disk, which in turn triggered enhanced nuclear shell burning on the white dwarf and eventually led to generation of a wind/outflow. From optical photometry we find a bf{possible} orbital period of 8.36 days, which supports the combination nova scenario and makes the system an intermediate case between typical cataclysmic variables and classical symbiotic binaries. If true, such a phenomenon would be the first of its kind to occur in a system that has undergone a classical nova eruption and is intermediate between cataclysmic variables and symbiotic binaries.
We found that the SU UMa-type dwarf nova NY Ser in the period gap [orbital period 0.097558(6) d] showed standstills twice in 2018. This is the first clear demonstration of a standstill occurring between superoutbursts of an SU UMa-type dwarf nova. There was no sign of superhumps during the standstill, and at least one superoutburst directly started from the standstill. This provides strong evidence that the 3:1 resonance was excited during standstills. This phenomenon indicates that the disk radius can grow during standstills. We also interpret that the condition close to the limit of the tidal instability caused early quenching of superoutbursts, which resulted substantial amount of matter left in the disk after the superoutburst. We interpret that the substantial matter in the disk in condition close to the limit of the tidal instability is responsible for standstills (as in the high mass-transfer system NY Ser) or multiple rebrightenings (as in the low mass-transfer system V1006 Cyg).
In this paper we present a coherent timing analysis of the 401 Hz pulsations of the accreting millisecond X-ray pulsar SAX J1808.4-3658 during its 2019 outburst. Using observations collected with the Neutron Star Interior Composition Explorer (NICER), we establish the pulsar spin frequency and orbital phase during its latest epoch. We find that the 2019 outburst shows a pronounced evolution in pulse phase over the course of the outburst. These phase shifts are found to correlate with the source flux, and are interpreted in terms of hot-spot drift on the stellar surface, driven by changes in the mass accretion rate. Additionally, we find that the long-term evolution of the pulsar spin frequency shows evidence for a modulation at the Earths orbital period, enabling pulsar timing based astrometry of this accreting millisecond pulsar.
AG Peg is known as the slowest symbiotic nova, which experienced its nova-like outburst around 1850. After 165 years, during June of 2015, it erupted again showing characteristics of the Z And-type outburst. The primary objective is to determine basic characteristics, the nature and type of the 2015 outburst of AG Peg. We achieved this aim by modelling the spectral energy distribution using low-resolution spectroscopy (330-750 nm), medium-resolution spectroscopy (420-720 nm; R=11000), and $UBVR_{rm C}I_{rm C}$ photometry covering the 2015 outburst with a high cadence. Optical observations were complemented with the archival HST and FUSE spectra from the preceding quiescence. During the outburst, the luminosity of the hot component was in the range of 2-11$times 10^{37}(d/0.8{rm kpc})^2$ erg/s. To generate the maximum luminosity the white dwarf (WD) had to accrete at $sim 3times 10^{-7}$ M$_{odot}yr^{-1}$, which exceeds the stable-burning limit and thus led to blowing optically thick wind from the WD. We determined its mass-loss rate to a few $times 10^{-6}$ M$_{odot}yr^{-1}$. At the high temperature of the ionising source, $1.5-2.3times 10^5$ K, the wind converted a fraction of the WDs photospheric radiation into the nebular emission that dominated the optical. A one order of magnitude increase of the emission measure, from a few $times 10^{59}(d/0.8 {rm kpc})^2$ cm$^{-3}$ during quiescence, to a few $times 10^{60}(d/0.8,{rm kpc})^2$ cm$^{-3}$ during the outburst, caused a 2 mag brightening in the LC, which is classified as the Z And-type of the outburst. The very high nebular emission and the presence of a disk-like HI region encompassing the WD, as indicated by a significant broadening and high flux of the Raman-scattered OVI 6825 AA line during the outburst, is consistent with the ionisation structure of hot components in symbiotic stars during active phases.
Two long AstroSat Soft X-ray Telescope observations were taken of the third recorded outburst of the Symbiotic Recurrent Nova, V3890 Sgr. The first observing run, 8.1-9.9 days after the outburst, initially showed a stable intensity level with a hard X-ray spectrum that we attribute to shocks between the nova ejecta and the pre-existing stellar companion. On day 8.57, the first, weak, signs appeared of Super Soft Source (SSS) emission powered by residual burning on the surface of the White Dwarf. The SSS emission was observed to be highly variable on time scales of hours. After day 8.9, the SSS component was more stable and brighter. In the second observing run, on days 15.9-19.6 after the outburst, the SSS component was even brighter but still highly variable. The SSS emission was observed to fade significantly during days 16.8-17.8 followed by re-brightening. Meanwhile the shock component was stable leading to increase in hardness ratio during the period of fading. AstroSat and XMM-Newton observations have been used to study the spectral properties of V3890 Sgr to draw quantitative conclusions even if their drawback is model-dependence. We used the xspec to fit spectral models of plasma emission, and the best fits are consistent with the elemental abundances being lower during the second observing run compared to the first for spectra >1 keV. The SSS emission is well fit by non-local thermal equilibrium model atmosphere used for white dwarfs. The resulting spectral parameters, however, are subject to systematic uncertainties such as completeness of atomic data.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
