scholarly journals Optical spectra of FO Aquarii during low and high accretion rates

2020 ◽  
Vol 495 (4) ◽  
pp. 4445-4462
Author(s):  
M R Kennedy ◽  
P M Garnavich ◽  
C Littlefield ◽  
T R Marsh ◽  
P Callanan ◽  
...  
Keyword(s):  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Cataclysmic Variables ◽  
Accretion Disc ◽  
High State ◽  
Secondary Star ◽  
Accretion Rates ◽  
Magnetic Poles ◽  
The Impact ◽  
Impact Region

ABSTRACT Between 2016 May and 2018 September, the intermediate polar (IP) FO Aquarii exhibited two distinct low states and one failed low state. We present optical spectroscopy of FO Aquarii throughout this period, making this the first detailed study of an accretion disc during a low state in any IP. Analysis of these data confirm that the low states are the result of a drop in the mass transfer rate between the secondary star and the magnetic white dwarf primary, and are characterized by a decrease in the system’s brightness coupled with a change of the system’s accretion structures from an accretion disc-fed geometry to a combination of disc-fed and ballistic stream-fed accretion, and that effects from accretion on to both magnetic poles become detectable. The failed low state only displays a decrease in brightness, with the accretion geometry remaining primarily disc-fed. We also find that the WD appears to be exclusively accretion disc-fed during the high state. There is evidence for an outflow close to the impact region between the ballistic stream and the disc which is detectable in all of the states. Finally, there is marginal evidence for narrow high-velocity features in the H α emission line during the low states which may arise due to an outflow from the WD. These features may be evidence of a collimated jet, a long predicted yet elusive feature of cataclysmic variables.

scholarly journals Long-Term Variability and Outburst Activity of FS Aurigae: Further Evidence for a Third Body in the System

2011 ◽  
Vol 7 (S282) ◽  
pp. 79-80
Author(s):  
V. Neustroev ◽  
G. Sjoberg ◽  
G. Tovmassian ◽  
S. Zharikov ◽  
T. Arranz Heras ◽  
...  
Keyword(s):  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Cataclysmic Variables ◽  
Close Binary ◽  
Third Body ◽  
Secondary Star ◽  
Long Term Monitoring ◽  
Binary Orbit ◽  
Term Monitoring

AbstractFS Aurigae is famous for a variety of uncommon and puzzling periodic photometric and spectroscopic variabilities which do not fit well into any of the established sub-classes of cataclysmic variables. Here we present preliminary results of long-term monitoring of the system, conducted during the 2010-2011 observational season. We show that the long-term variability of FS Aur and the character of its outburst activity may be caused by variations in the mass transfer rate from the secondary star as the result of eccentricity modulation of a close binary orbit induced by the presence of a third body on a circumbinary orbit.

scholarly journals VY Sculptoris stars are Magnetic Cataclysmic Variables

2004 ◽  
Vol 190 ◽  
pp. 46-52 ◽  
Author(s):  
Jean-Pierre Lasota ◽  
Jean-Marie Hameury
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Magnetic Moments ◽  
Mass Transfer Rate ◽  
Cataclysmic Variables ◽  
Accretion Disc ◽  
Intermediate States ◽  
Intermediate Polars ◽  
Magnetic Cataclysmic Variables ◽  
Evolutionary Aspects

AbstractWe show that VY Scl stars must be magnetized in order to account for the absence of outbursts during their low and intermediate states. Absence of outbursts during low states requires only rather low magnetic moments but in systems in which the drops and rises of luminosity are slower than it takes for the accretion disc to adjust viscously to the variation in mass-transfer rate preventing outbursts require magnetic moments of Intermediate Polars. We discuss some evolutionary aspects of this conclusion.

scholarly journals The disappearance and reformation of the accretion disc during a low state of FO Aquarii

2017 ◽  
Vol 606 ◽  
pp. A7 ◽  
Author(s):  
J.-M. Hameury ◽  
J.-P. Lasota
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Hot Spot ◽  
Mass Transfer Rate ◽  
Accretion Disc ◽  
Numerical Code ◽  
Light Sources ◽  
Instability Strip ◽  
Dwarf Nova ◽  
Nova Outbursts

Context. FO Aquarii, an asynchronous magnetic cataclysmic variable (intermediate polar) went into a low state in 2016, from which it slowly and steadily recovered without showing dwarf nova outbursts. This requires explanation since in a low state, the mass-transfer rate is in principle too low for the disc to be fully ionised and the disc should be subject to the standard thermal and viscous instability observed in dwarf novae. Aims. We investigate the conditions under which an accretion disc in an intermediate polar could exhibit a luminosity drop of two magnitudes in the optical band without showing outbursts. Methods. We use our numerical code for the time evolution of accretion discs, including other light sources from the system (primary, secondary, hot spot). Results. We show that although it is marginally possible for the accretion disc in the low state to stay on the hot stable branch, the required mass-transfer rate in the normal state would then have to be extremely high, of the order of 1019 g s-1 or even larger. This would make the system so intrinsically bright that its distance should be much larger than allowed by all estimates. We show that observations of FO Aqr are well accounted for by the same mechanism that we have suggested as explaining the absence of outbursts during low states of VY Scl stars: during the decay, the magnetospheric radius exceeds the circularisation radius, so that the disc disappears before it enters the instability strip for dwarf nova outbursts. Conclusions. Our results are unaffected, and even reinforced, if accretion proceeds both via the accretion disc and directly via the stream during some intermediate stages; the detailed process through which the disc disappears still requires investigation.

scholarly journals Physical Interpretation of Dwarf Nova Primary Effective Temperatures

2004 ◽  
Vol 194 ◽  
pp. 192-193
Author(s):  
Dean M. Townsley ◽  
Lars Bildsten
Keyword(s):  
Gravitational Radiation ◽  
Accretion Rate ◽  
Thermal State ◽  
Cataclysmic Variables ◽  
Theoretical Work ◽  
Dwarf Novae ◽  
Radiation Losses ◽  
Accretion Rates ◽  
The Masses ◽  
The Impact

AbstractWe have undertaken a theoretical study of the impact of the accumulating envelopes on the thermal state of the underlying white dwarf (WD). This has allowed us to find the equilibrium WD core temperatures, the classical nova ignition masses and the thermal luminosities for WDs accreting at rates of 10–11 – 10–8M⊙ yr–1. These accretion rates are most, appropriate to WDs in cataclysmic variables (CVs) of (Porb ≲ 7 hr), many of which accrete sporadically as Dwarf Novae. Over twenty Dwarf Novae have been observed in quiescence, when the accretion rate is low and the WD photosphere is detected and Teff measured. Comparing our theoretical work to these observations allows us to constrain the WD mass and the time averaged accretion rate, ⟨Ṁ⟩. If ⟨Ṁ⟩ is that given by gravitational radiation losses alone, then the WD masses are > 0.8 M⊙. An alternative conclusion is that the masses are closer to 0.6M⊙ and ⟨Ṁ⟩ is 3-4 times larger than that expected from gravitational radiation losses.

scholarly journals MHD Slip Flow of Casson Fluid along a Nonlinear Permeable Stretching Cylinder Saturated in a Porous Medium with Chemical Reaction, Viscous Dissipation, and Heat Generation/Absorption

Symmetry ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 531 ◽  
Author(s):  
Ullah ◽  
Abdullah Alkanhal ◽  
Shafie ◽  
Nisar ◽  
Khan ◽  
...  
Keyword(s):  
Porous Medium ◽  
Viscous Dissipation ◽  
Chemical Reaction ◽  
Heat Generation ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Casson Fluid ◽  
Similarity Solutions ◽  
Local Similarity ◽  
The Impact

The aim of the present analysis is to provide local similarity solutions of Casson fluid over a non-isothermal cylinder subject to suction/blowing. The cylinder is placed inside a porous medium and stretched in a nonlinear way. Further, the impact of chemical reaction, viscous dissipation, and heat generation/absorption on flow fields is also investigated. Similarity transformations are employed to convert the nonlinear governing equations to nonlinear ordinary differential equations, and then solved via the Keller box method. Findings demonstrate that the magnitude of the friction factor and mass transfer rate are suppressed with increment in Casson parameter, whereas heat transfer rate is found to be intensified. Increase in the curvature parameter enhanced the flow field distributions. The magnitude of wall shear stress is noticed to be higher with an increase in porosity and suction/blowing parameters.

scholarly journals FS Aur as a Permanent Superhump System

2004 ◽  
Vol 194 ◽  
pp. 169-171
Author(s):  
Gaghik H. Tovmassian ◽  
Sergei V. Zharikov
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Variable Mass ◽  
Accretion Disc ◽  
Light Curves ◽  
Cataclysmic Variable ◽  
Short Period ◽  
Photometric Period ◽  
Low Amplitude

AbstractWe discovered that the short period cataclysmic variable FS Aur at some epochs shows a photometric period close to the orbital. It exceeds the orbital period by ∽2%, which is a sign of the presence of a permanent superhump in the system. Superhumps tend to appear near short, low amplitude outbursts. We assume that FS Aur possesses a large thermally stable accretion disc and that the outburst may be due to the variable mass transfer rate. This, however, does not alter our previous explanation of yet another, 2.4 times longer than orbital, photometric period of FS Aur, found earlier, and persistently observed in its light curves.

scholarly journals A Beat Phenomenon in Dwarf Nova Eruptions

1977 ◽  
Vol 42 ◽  
pp. 227-233
Author(s):  
N. Vogt
Keyword(s):  
Mass Transfer ◽  
Orbital Period ◽  
Transfer Rate ◽  
Convection Zone ◽  
Mass Transfer Rate ◽  
Accretion Disc ◽  
Light Curves ◽  
Dwarf Nova ◽  
Beat Phenomenon ◽  
Photoelectric Observations

Photoelectric observations of the dwarf nova VW Hyi, obtained at the end of the December 1975 supermaximum, are presented. After decline from the outburst, the superhump period (0ḍ07622) combines with the orbital period (0ḍ07427) to a beat phenomenon: the O-C’s and the light curves of the orbital hump vary systematically with the phase of the beat period for at least one week after recovery from the supermaximum. It is suggested that the red secondary component, which rotates non-synchroneously with the superhump period, expands slightly at the beginning of a supermaximum and is heated up asymmetrically, probably due to instabilities in its convection zone. In addition, the increased mass transfer rate may trigger the long eruption in the accretion disc while short eruptions originate in the disc without participation of the secondary.

scholarly journals Minimum Orbital Period of Cataclysmic Variables

1979 ◽  
Vol 53 ◽  
pp. 504-504
Author(s):  
B. Paczynski ◽  
W. Krzeminski
Keyword(s):  
Mass Transfer ◽  
Angular Momentum ◽  
Orbital Period ◽  
Time Scale ◽  
Transfer Rate ◽  
Main Sequence ◽  
Mass Transfer Rate ◽  
Cataclysmic Variables ◽  
Transfer Rates ◽  
Angular Momentum Loss

The shortest known orbital period of a cataclysmic binary with a hydrogen dwarf secondary filling its Roche lobe is about 80 minutes. Theoretically the shortest possible orbital period for such a system is less than 60 minutes. We tried to explain why the periods shorter than 80 minutes are not observed. We estimated the time scale of angular momentum loss of a cataclysmic binary and the resulting mass transfer rate. The minimum orbital period for a given Ṁ is obtained during the transition of the secondary from the Main Sequence onto the Degenerate Dwarf Sequence. Pmin ∝ Ṁ½ Therefore, only those systems can reach low P for which Ṁ is small. This explains why among the shortest period cataclysmic variables there are no novae: presumably their mass transfer rates are too large. It also indicates that “polars” (AM Her-type stars) and SU UMa-type stars should have low Ṁ.

scholarly journals SWSex Stars, Old Novae, and the Evolution of Cataclysmic Variables

2015 ◽  
Vol 2 (1) ◽  
pp. 188-191 ◽  
Author(s):  
L. Schmidtobreick ◽  
C. Tappert
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Cataclysmic Variables ◽  
High Mass ◽  
Period Range ◽  
Transfer Rates ◽  
Low Mass ◽  
Orbital Periods ◽  
Nova Outburst

The population of cataclysmic variables with orbital periods right above the period gap are dominated by systems with extremely high mass transfer rates, the so-called SW Sextantis stars. On the other hand, some old novae in this period range which are expected to show high mass transfer rate instead show photometric and/or spectroscopic resemblance to low mass transfer systems like dwarf novae. We discuss them as candidates for so-called hibernating systems, CVs that changed their mass transfer behaviour due to a previously experienced nova outburst. This paper is designed to provide input for further research and discussion as the results as such are still very preliminary.

scholarly journals A spectroscopic analysis of the eclipsing nova-like EC 21178−5417 – discovery of spiral density structures

2020 ◽  
Vol 495 (1) ◽  
pp. 637-649 ◽  
Author(s):  
Z N Khangale ◽  
P A Woudt ◽  
S B Potter ◽  
B Warner ◽  
D Kilkenny ◽  
...  
Keyword(s):  
Mass Transfer Rate ◽  
Spectral Characteristics ◽  
Line Emission ◽  
Pure Line ◽  
Accretion Disc ◽  
Bright Spot ◽  
Balmer Series ◽  
Secondary Star ◽  
Average Spectrum ◽  
Balmer Lines

ABSTRACT We present phase-resolved optical spectroscopy of the eclipsing nova-like cataclysmic variable EC 21178−5417 obtained between 2002 and 2013. The average spectrum of EC 21178−5417 shows broad double-peaked emission lines from He ii 4686 Å (strongest feature) and the Balmer series. The high-excitation feature, C iii/N iii at 4640–4650 Å, is also present and appears broad in emission. A number of other lines, mostly He i, are clearly present in absorption and/or emission. The average spectrum of EC 21178−5417 taken at different months and years shows variability in spectral features, especially in the Balmer lines beyond Hγ, from pure line emission, mixed line absorption, and emission to pure absorption lines. Doppler maps of the He ii 4686 Å emission reveal the presence of a highly inclined asymmetric accretion disc and a two spiral arm-like structure, whereas that of the Balmer lines (Hα and Hβ) reveal a more circular accretion disc. There is no evidence of a bright-spot in the Doppler maps of EC 21178−5417 and no emission from the secondary star is seen in the tomograms of the He ii 4686 Å and Balmer lines. Generally, the emission in EC 21178−5417 is dominated by emission from the accretion disc. We conclude that EC 21178−5417 is a member of the RW Tri or UX UMa subtype of nova-like variables based on these results and because it shows different spectral characteristics at different dates. This spectral behaviour suggests that EC 21178−5417 undergoes distinct variations in mass transfer rate on the observed time-scales of months and years.

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