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Register a new userThe recurrent nova RS Oph - simultaneous B and V band observations of the flickering variability
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Added by
Radoslav K. Zamanov
Publication date
2018
fields
Physics
and research's language is
English
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We performed 48.6 hours (in 28 nights) of simultaneous B and V band observations of the flickering variability of the recurrent nova RS Oph in quiescence. During the time of our observations the brightness of the system varied between 13.2 > B > 11.1 and the colour in the range 0.86 < B-V < 1.33 . We find that RS~Oph becomes more blue, as it becomes brighter, however the hot component becomes more red as it becomes brighter (assuming that the red giant is non-variable). During all the runs RS Oph exhibits flickering with amplitude 0.16 - 0.59 mag in B band. For the flickering source we find that it has colour -0.14 < B-V < 0.40, temperature in the range 7200 < T_fl < 18900, and average radius 1.1 < R_fl < 6.7 R_sun. We do not find a correlation between the temperature of the flickering and the brightness. However, we do find a strong correlation (correlation coefficient 0.81, significance 1.1x10^{-7} ) between B band magnitude and the average radius of the flickering source - as the brightness of the system increases the size of the flickering source also increases. The estimated temperature is similar to that of the bright spot of cataclysmic variables. The persistent presence of flickering indicates that the white dwarf is actively accreting material for the next outburst.
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We report observations of the flickering variability of the symbiotic recurrent nova RS~Oph at quiescence in five bands ($UBVRI$). We find evidence of a correlation between the peak-to-peak flickering amplitude ($Delta F$) and the average flux of the hot component ($F_{rm av}$). The correlation is highly significant, with a correlation coefficient of 0.85 and a $p$-value of~$sim 10^{-20}$. Combining the data from all wavebands, we find a dependence of the type $Delta F propto F^k_{rm av}$, with power-law index $k = 1.02 pm 0.04$ for the $UBVRI$ flickering of RS~Oph. Thus, the relationship between the amplitude of variability and the average flux of the hot component is consistent with linearity. The rms amplitude of flickering is on average 8 per cent ($pm2$ per cent) of $F_{rm av}$. The detected correlation is similar to that found in accreting black holes/neutron stars and cataclysmic variables. The possible reasons are briefly discussed. The data are available upon request from the authors.
We report on interferometric AMBER/VLTI observations of the recurrent nova RS Oph five days after its outburst on 2006 Feb 12. Using three baselines from 44 to 86m, and a spectral resolution of 1500, we measured the extension of the emission in the K band continuum and in the BrG and HeI2.06 micron lines. The continuum visibilities were interpreted by fitting simple geometric models consisting of uniform and Gaussian ellipses, ring and binary models. The visibilities and differential phases in the BrG line were interpreted using skewed ring models aiming to perform a limited parametric reconstruction of the extension and kinematics of the line forming region. The limited uv coverage does not allow discrimination between filled models and rings. Binary models are discarded because the measured closure phase in the continuum is close to zero. The visibilities in the lines are at a low level compared to their nearby continuum, consistent with a more extended line forming region for HeI2.06 than BrG. The ellipse models for the continuum and for the lines are highly flattened and share the same position angle. Two radial velocity fields are apparent in the BrG line: a slow expanding ring-like structure (v~1800km/s), and a fast structure extended in the E-W direction (v~2500-3000km/s). These results confirm the basic fireball model, contrary to the conclusions of other interferometric observations conducted by Monnier et al. (2006).
The recurrent nova RS Oph experienced an outburst in 2006, 21 years after its previous explosion in 1985, as expected. It was observed at almost all wavelengths, and important information about its properties is still being extracted. We present theoretical models of the explosion of this fascinating object, which indicate that the mass of the accreting white dwarf should be very close to the Chandrasekhar mass, to allow for such a short recurrence period. In addition, since models suggest that this nova ejects less mass than it accretes, it is an excellent candidate for a thermonuclear supernova explosion, in about $10^5-10^7$ years from now. We also analyze the emission of soft gamma-rays by RS Oph detected with the BAT instrument onboard Swift, and with the PCA onboard RXTE. We rule out that this emission has its origin in radioactive decays in the expanding nova envelope.
We report observations of the flickering variability of the recurrent nova RS Oph at quiescence on the basis of simultaneous observations in 5 bands (UBVRI). RS Oph has flickering source with (U-B)_0=-0.62 pm 0.07, (B-V)_0=0.15 pm 0.10, (V-R)_0=0.25 pm 0.05. We find for the flickering source a temperature T_fl = 9500 pm 500 K, and luminosity L_fl = 50 - 150 L_sun (using a distance of d=1.6kpc). We also find that on a (U-B) vs (B-V) diagram the flickering of the symbiotic stars differs from that of the cataclysmic variables. The possible source of the flickering is discussed. The data are available upon request from the authors and on the web www.astro.bas.bg/~rz/RSOph.UBVRI.2010.MNRAS.tar.gz.
We report observations of the flickering variability of the dwarf nova RX And in five bands (UBVRI) on two nights. On 25 October 2019 the brightness of the star was $Bapprox 13.9$ mag, the amplitude of the flickering was 0.47 mag, and we estimate for the flickering source temperature $T_{fl} = 10700 pm 400$ K, and radius $R_{fl} =0.046 pm 0.004$ $R_odot$. On 2 January 2020, the star was about 3 magnitudes brighter ($B approx 10.7$), the amplitude of the flickering was significantly lower (0.07 mag) and we derive for the flickering source $T_{fl} = 9600 pm 700$ K, and radius $R_{fl} = 0.098 pm 0.009$ $R_odot$. The results indicate that 3 magnitudes brightening of the star doubled the radius of the flickering source. The data are available upon request from the authors.
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