scholarly journals Supersoft X-ray phases of recurrent novae as an indicator of their white dwarf masses

2020 ◽  
Vol 72 (5) ◽  
Author(s):  
Mariko Kato ◽  
Izumi Hachisu
Keyword(s):  
Light Curve ◽  
White Dwarf ◽  
Total Duration ◽  
Simple Relation ◽  
Light Curves ◽  
Curve Shape ◽  
Plateau Phase ◽  
Hydrogen Burning ◽  
X Ray ◽  
Recurrent Nova

Abstract We have examined the optical/X-ray light curves of seven well-observed recurrent novae, V745 Sco, M31N 2008-12a, LMC N 1968, U Sco, RS Oph, LMC N 2009a, T Pyx, and one recurrent nova candidate LMC N 2012a. Six novae out of the eight show a simple relation that the duration of supersoft X-ray source (SSS) phase is 0.70 times the total duration of the outburst (= X-ray turnoff time), i.e., tSSS = 0.70 toff, the total duration of which ranges from 10 to 260 d. These six recurrent novae show a broad rectangular X-ray light curve shape, the first half-period of which is highly variable in the X-ray count rate. The SSS phase also corresponds to an optical plateau phase that indicates a large accretion disk irradiated by a hydrogen-burning white dwarf (WD). The two other recurrent novae, T Pyx and V745 Sco, show a narrow triangular-shaped X-ray light curve without an optical plateau phase. Their relations between tSSS and toff are rather different from the above six recurrent novae. We also present theoretical SSS durations for recurrent novae with various WD masses and stellar metallicities (Z = 0.004, 0.01, 0.02, and 0.05) and compare them with the observed durations of these recurrent novae. We show that SSS duration is a good indicator of WD mass in recurrent novae with a broad rectangular X-ray light curve shape.

scholarly journals X-Ray Observations of Classical and Recurrent Novae in Outburst

2004 ◽  
Vol 194 ◽  
pp. 182-186 ◽  
Author(s):  
M. Orio
Keyword(s):  
Light Curve ◽  
White Dwarf ◽  
Circumstellar Matter ◽  
X Rays ◽  
Hydrogen Burning ◽  
X Ray ◽  
High Fraction ◽  
Emission Line Spectrum ◽  
Recurrent Nova ◽  
Red Giant

AbstractI review X-ray observations of classical and recurrent novae in outburst, some of them recently done with Chandra and XMM-Newton for 12 objects. Significant X-ray flux is emitted by the nova shell, with a peak luminosity up to Lx = 1035 erg s–1 in the 0.2-10 keV range. In recurrent nova systems, or in novae hosting a red giant, the source of X-rays may be previous circumstellar matter shocked by the nova wind. However, for most classical novae, X-rays originate inside the nebula ejected in the outburst. The data indicate a very high fraction of shocked material, and a non-smooth, varying wind outflow. A nebular emission line spectrum is also observed at late phases. In about half of the observed novae, the central white dwarf appears as a very luminous supersoft X-ray source for 1 to 9 years after the outburst. It is the best type of object to study the characteristics of shell hydrogen burning on white dwarfs in single degenerate systems. Still incomplete statistics indicate that the duration of the supersoft X-ray phase is peaked around ≃2 years. The correlation of the X-ray light curve with the nova properties is not quite clear. Recently, “template grating spectra” with high S/N have been obtained for V4743 Sgr. The X-ray light curve of this nova reveals a rich and complex power spectrum, with signatures of non-radial g-mode oscillations of the white dwarf. The oscillations and the spectra allow to determine the properties of the shell hydrogen burning white dwarf.

scholarly journals X-Ray Observations of Cataclysmic Variables

1987 ◽  
Vol 93 ◽  
pp. 207-223
Author(s):  
J.P. Osborne
Keyword(s):  
Light Curve ◽  
Spectral Range ◽  
Cataclysmic Variables ◽  
High Sensitivity ◽  
Light Curves ◽  
X Ray ◽  
Broad Spectral Range ◽  
Intermediate Polars ◽  
Recurrent Nova

AbstractThe X-ray observatory EXOSAT spent over 1000 hours observing cataclysmic variables. Some of the major results reviewed here are: soft X-ray light curve changes in AM Her objects, orbital effects in the X-ray light curves of intermediate polars and U Gem, regular behaviour in the inter-outburst X-ray flux of VW Hyi, and X-ray emission from the tenuous remnant of the recent recurrent nova RS Oph. The ability of EXOSAT to make long uninterupted observations at high sensitivity over a broad spectral range and to react quickly to cosmic events has yielded a dataset of a quality that will not be surpassed for many years.

scholarly journals Optical Light Curve of Nova KT Eridani

2012 ◽  
Vol 8 (S290) ◽  
pp. 191-192
Author(s):  
W. P. Chen ◽  
L. W. Hung ◽  
Fred Walter
Keyword(s):  
Light Curve ◽  
White Dwarf ◽  
Hot Spot ◽  
X Ray ◽  
Optical Emissions ◽  
Optical Light Curve ◽  
Recurrent Nova ◽  
Orbital Modulation ◽  
Type Giant

AbstractWe present the optical light curve of the very fast nova, KT Eridani, from its outburst in November 2009 to quiescence in 2012. Comparison of our data with the 24-hour monitoring by Swift on 2010 March 31 indicates a possible anticorrelation between the X-ray and optical emissions. A period of 57 d is found in the long-term optical light curve, which we interpret as the orbital modulation of the hot spot on the white dwarf disk accreting material from an early K-type giant. Our study lends support to the notation that KT Eri may be a recurrent nova.

scholarly journals Hydrodynamic Models of Solar and Stellar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 289-298
Author(s):  
Giovanni Peres
Keyword(s):  
High Resolution ◽  
Light Curve ◽  
Solar Flares ◽  
Impulsive Phase ◽  
Light Curves ◽  
Physical Parameters ◽  
The Sun ◽  
Hydrodynamic Models ◽  
X Ray ◽  
Stellar Flares

AbstractThis paper discusses the hydrodynamic modeling of flaring plasma confined in magnetic loops and its objectives within the broader scope of flare physics. In particular, the Palermo-Harvard model is discussed along with its applications to the detailed fitting of X-ray light curves of solar flares and to the simulation of high-resolution Caxix spectra in the impulsive phase. These two approaches provide complementary constraints on the relevant features of solar flares. The extension to the stellar case, with the fitting of the light curve of an X-ray flare which occurred on Proxima Centauri, demonstrates the feasibility of using this kind of model for stars too. Although the stellar observations do not provide the wealth of details available for the Sun, and, therefore, constrain the model more loosely, there are strong motivations to pursue this line of research: the wider range of physical parameters in stellar flares and the possibility of studying further the solar-stellar connection.

scholarly journals Long-term Photometric Monitoring of FUor and FUor-like Objects

2018 ◽  
pp. 240-248
Author(s):  
E. Semkov ◽  
S. Ibryamov ◽  
S. Peneva ◽  
A. Mutafov
Keyword(s):  
Light Curve ◽  
Significant Role ◽  
Stellar Evolution ◽  
Photographic Plate ◽  
Light Curves ◽  
Curve Shape ◽  
Rate Of Increase ◽  
Fu Ori ◽  
Photometric Monitoring

A phenomenon with a significant role in stellar evolution is the FU Orionis (FUor) type of outburst. The first three (classical) FUors (FU Ori, V1515 Cyg and V1057 Cyg) are well-studied and their light curves are published in the literature. But recently, over a dozen new objects of this type were discovered, whose photometric history we do not know well. Using recent data from photometric monitoring and data from the photographic plate archives we aim to study, the long-term photometric behavior of FUor and FUor-like objects. The construction of the historical light curves of FUors could be very important for determining the beginning of the outburst, the time to reach the maximum light, the rate of increase and decrease in brightness, the pre-outburst variability of the star. So far we have published our results for the light curves of V2493 Cyg, V582 Aur, Parsamian 21 and V1647 Ori. In this paper we present new data that describe more accurate the photometric behavior of these objects. In comparing our results with light curves of the well-studied FUors (FU Ori, V1515 Cyg and V1057 Cyg), we conclude that every object shows different photometric behavior. Each known FUor has a different rate of increase and decrease in brightness and a different light curve shape.

scholarly journals X-ray spectra and light curves of cooling novae and a nova like

2020 ◽  
Vol 499 (2) ◽  
pp. 3006-3018
Author(s):  
Bangzheng Sun ◽  
Marina Orio ◽  
Andrej Dobrotka ◽  
Gerardo Juan Manuel Luna ◽  
Sergey Shugarov ◽  
...  
Keyword(s):  
Light Curve ◽  
Accretion Rate ◽  
High Energy ◽  
Gravitational Energy ◽  
Light Curves ◽  
Clear Correlation ◽  
X Rays ◽  
High State ◽  
X Ray ◽  
Low X

ABSTRACT We present X-ray observations of novae V2491 Cyg and KT Eri about 9 yr post-outburst of the dwarf nova and post-nova candidate EY Cyg, and of a VY Scl variable. The first three objects were observed with XMM–Newton, KT Eri also with the Chandra ACIS-S camera, V794 Aql with the Chandra ACIS-S camera and High Energy Transmission Gratings. The two recent novae, similar in outburst amplitude and light curve, appear very different at quiescence. Assuming half of the gravitational energy is irradiated in X-rays, V2491 Cyg is accreting at $\dot{m}=1.4\times 10^{-9}{\!-\!}10^{-8}\,{\rm M}_\odot \,{\rm yr}^{-1}$, while for KT Eri, $\dot{m}\lt 2\times 10^{-10}{\rm M}_\odot \,{\rm yr}$. V2491 Cyg shows signatures of a magnetized WD, specifically of an intermediate polar. A periodicity of  39 min, detected in outburst, was still measured and is likely due to WD rotation. EY Cyg is accreting at $\dot{m}\sim 1.8\times 10^{-11}{\rm M}_\odot \,{\rm yr}^{-1}$, one magnitude lower than KT Eri, consistently with its U Gem outburst behaviour and its quiescent UV flux. The X-rays are modulated with the orbital period, despite the system’s low inclination, probably due to the X-ray flux of the secondary. A period of  81 min is also detected, suggesting that it may also be an intermediate polar. V794 Aql had low X-ray luminosity during an optically high state, about the same level as in a recent optically low state. Thus, we find no clear correlation between optical and X-ray luminosity: the accretion rate seems unstable and variable. The very hard X-ray spectrum indicates a massive WD.

scholarly journals X-ray light curves from realistic polar cap models: inclined pulsar magnetospheres and multipole fields

2019 ◽  
Vol 490 (2) ◽  
pp. 1774-1783 ◽  
Author(s):  
Will Lockhart ◽  
Samuel E Gralla ◽  
Feryal Özel ◽  
Dimitrios Psaltis
Keyword(s):  
Light Curve ◽  
Quadrupole Moment ◽  
Large Scale ◽  
Realistic Model ◽  
Light Curves ◽  
X Ray ◽  
Polar Caps ◽  
Thin Ring ◽  
Magnetic Quadrupole ◽  
South Asymmetry

ABSTRACT Thermal X-ray emission from rotation-powered pulsars is believed to originate from localized ‘hotspots’ on the stellar surface occurring where large-scale currents from the magnetosphere return to heat the atmosphere. Light-curve modelling has primarily been limited to simple models, such as circular antipodal emitting regions with constant temperature. We calculate more realistic temperature distributions within the polar caps, taking advantage of recent advances in magnetospheric theory, and we consider their effect on the predicted light curves. The emitting regions are non-circular even for a pure dipole magnetic field, and the inclusion of an aligned magnetic quadrupole moment introduces a north–south asymmetry. As the quadrupole moment is increased, one hotspot grows in size before becoming a thin ring surrounding the star. For the pure dipole case, moving to the more realistic model changes the light curves by $5\!-\!10{{\, \rm per\, cent}}$ for millisecond pulsars, helping to quantify the systematic uncertainty present in current dipolar models. Including the quadrupole gives considerable freedom in generating more complex light curves. We explore whether these simple dipole+quadrupole models can account for the qualitative features of the light curve of PSR J0437−4715.

scholarly journals Evidence for variability time-scale-dependent UV/X-ray delay in Seyfert 1 AGN NGC 7469

2020 ◽  
Vol 494 (3) ◽  
pp. 4057-4068
Author(s):  
Mayukh Pahari ◽  
I M McHardy ◽  
Federico Vincentelli ◽  
Edward Cackett ◽  
Bradley M Peterson ◽  
...  
Keyword(s):  
Light Curve ◽  
Time Lag ◽  
Accretion Disc ◽  
Light Curves ◽  
X Rays ◽  
X Ray ◽  
Cross Correlation Analysis ◽  
Optical Continuum ◽  
Delay Prediction ◽  
Ngc 7469

ABSTRACT Using a month-long X-ray light curve from RXTE/PCA and 1.5 month-long UV continuum light curves from IUE spectra in 1220–1970 Å, we performed a detailed time-lag study of the Seyfert 1 galaxy NGC 7469. Our cross-correlation analysis confirms previous results showing that the X-rays are delayed relative to the UV continuum at 1315 Å by 3.49 ± 0.22 d, which is possibly caused by either propagating fluctuation or variable Comptonization. However, if variations slower than 5 d are removed from the X-ray light curve, the UV variations then lag behind the X-ray variations by 0.37 ± 0.14 d, consistent with reprocessing of the X-rays by a surrounding accretion disc. A very similar reverberation delay is observed between Swift/XRT X-ray and Swift/UVOT UVW2, U light curves. Continuum light curves extracted from the Swift/GRISM spectra show delays with respect to X-rays consistent with reverberation. Separating the UV continuum variations faster and slower than 5 d, the slow variations at 1825 Å lag those at 1315 Å by 0.29 ± 0.06 d, while the fast variations are coincident (0.04 ± 0.12 d). The UV/optical continuum reverberation lag from IUE, Swift, and other optical telescopes at different wavelengths are consistent with the relationship: τ ∝ λ4/3, predicted for the standard accretion disc theory while the best-fitting X-ray delay from RXTE and Swift/XRT shows a negative X-ray offset of ∼0.38 d from the standard disc delay prediction.

scholarly journals Properties of CVSO 30 from TESS measurements: probably a binary T Tauri star with complex light curves and no obvious planets

2020 ◽  
Vol 494 (3) ◽  
pp. 4349-4356
Author(s):  
C Koen
Keyword(s):  
Light Curve ◽  
Small Group ◽  
T Tauri Stars ◽  
Light Curves ◽  
Tauri Star ◽  
Curve Shape ◽  
T Tauri

ABSTRACT ‘Transiting Exoplanet Survey Satellite’ (TESS) photometry of CVSO 30 spanned 21.8 d, with a single large gap of 1.1 d. This allows alias-free determination of the two periodicities in the data. It is confirmed that both of these are non-sinusoidal: the dominant P1 = 0.4990 d has two detectable harmonics and P2 = 0.4486 d has seven. The large number of harmonics in the second periodicity characterizes a very complex light curve shape. One of the features in the light curve is a sharp dip of duration ∼2 h: this is probably the source of the previously claimed planetary transit signature. The star is a member of a small group of T Tauri stars with complex light curves, which have recently been exhaustively studied using Kepler and TESS observations. The two non-commensurate periods are most simply interpreted as being from two stars, i.e. CVSO 30 is probably a binary.

scholarly journals Radio variability from corotating interaction regions threading Wolf–Rayet winds

2020 ◽  
Vol 497 (1) ◽  
pp. 1127-1134
Author(s):  
Richard Ignace ◽  
Nicole St-Louis ◽  
Raman K Prinja
Keyword(s):  
Light Curve ◽  
Phenomenological Model ◽  
Massive Stars ◽  
Light Curves ◽  
Parameter Study ◽  
Detailed Structure ◽  
Corotating Interaction Regions ◽  
X Ray ◽  
Cent Level ◽  
Interaction Regions

ABSTRACT The structured winds of single massive stars can be classified into two broad groups: stochastic structure and organized structure. While the former is typically identified with clumping, the latter is typically associated with rotational modulations, particularly the paradigm of corotating interaction regions (CIRs). While CIRs have been explored extensively in the ultraviolet band, and moderately in the X-ray and optical, here we evaluate radio variability from CIR structures assuming free–free opacity in a dense wind. Our goal is to conduct a broad parameter study to assess the observational feasibility, and to this end, we adopt a phenomenological model for a CIR that threads an otherwise spherical wind. We find that under reasonable assumptions, it is possible to obtain radio variability at the 10 per cent level. The detailed structure of the folded light curve depends not only on the curvature of the CIR, the density contrast of the CIR relative to the wind, and viewing inclination, but also on wavelength. Comparing light curves at different wavelengths, we find that the amplitude can change, that there can be phase shifts in the waveform, and the entire waveform itself can change. These characterstics could be exploited to detect the presence of CIRs in dense, hot winds.

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