Three-minute Sunspot Oscillations Driven by Magnetic Reconnection in a Light Bridge [SSA]

We report a different type of three-minute chromospheric oscillations above a sunspot in association with a small-scale impulsive event in a light bridge. During our observations, we found a transient brightening in the light bridge. The brightening was composed of elementary bursts that may be a manifestation of fast repetitive magnetic reconnections in the light bridge. Interestingly, the oscillations in the nearby sunspot umbra were impulsively excited when the intensity of the brightening reached its peak. The initial period of the oscillations was about 2.3 minutes and then gradually increased to 3.0 minutes with time. In addition, we found that the amplitude of the excited oscillations was twice the amplitude of oscillations before the brightening. Based on our results, we propose that magnetic reconnection occurring in a light bridge can excite of oscillations in the nearby sunspot umbra.

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D. Song, J. Chae, H. Kwak, et. al.
Mon, 20 Nov 17

Comments: 13 pages, 4 figures, accepted for publication in ApJL

Flare activity of the Sun and variations in its UV emission during cyrcle 24 [SSA]

The flare activity and the ultraviolet emission of the sun during its 24-th cycle are analysed. As compared to cycles 21-23, where the most powerful flares were observed during the decay phase, in cycle 24 the greatest number of powerful flares (>X2.7) occurred in the rising phase and at the maximum with the exception of the two largest flares of cycle 24 X9.3 and X8.2 in September 2017. We showed that regression fits of solar UV indices to the overall radiation level from the sun are substantially different for cycle 24 compared to cycles 21-23. It is found that for the flare of August 9, 2011 (SDO and GOES-15 observations), the flare propagates in a direction from the upper corona to the transition region and to the chromosphere. A study of the N-S asymmetry in the distribution of the flares in cycle 24 reveals a strong predominance of flares in the N-hemisphere in 2011 and in the S-hemisphere in 2014. It is also found that during cycles 23 and 24, the delays in the onset of proton events relative to the onset of the flares that cause them have a distribution with a distinct maximum corresponding to a delay of 2 hours for protons with energies >10 MeV, as well as for those with energies >100 MeV.

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E. Bruevich and G. Yakunina
Mon, 20 Nov 17

Comments: 18 pages, 9 figures,

Accuracy of inference on the physics of binary evolution from gravitational-wave observations [HEAP]

The properties of the population of merging binary black holes encode some of the uncertain physics of the evolution of massive stars in binaries. The binary black hole merger rate and chirp mass distribution are being measured by ground-based gravitational-wave detectors. We consider isolated binary evolution and explore how accurately the physical model can be constrained with such observations by applying the Fisher information matrix to the merging black hole population simulated with the rapid binary population synthesis code COMPAS. We investigate variations in four COMPAS parameters: common envelope efficiency, kick velocity dispersion, and mass loss rates during the luminous blue variable and Wolf–Rayet stellar evolutionary phases. We find that 1000 observations would constrain these model parameters to a fractional accuracy of a few percent. Given the empirically determined binary black hole merger rate, we can expect gravitational-wave observations alone to place strong constraints on the physics of stellar and binary evolution within a few years.

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J. Barrett, S. Gaebel, C. Neijssel, et. al.
Mon, 20 Nov 17

Comments: N/A

First Extended Catalogue of Galactic Bubbles InfraRed Fluxes from WISE and Herschel Surveys [GA]

In this paper, we present the first extended catalogue of far-infrared fluxes of Galactic bubbles. Fluxes were estimated for 1814 bubbles, defined here as the `golden sample’, and were selected from the Milky Way Project First Data Release (Simpson et al.) The golden sample was comprised of bubbles identified within the Wide-field Infrared Survey Explorer (WISE) dataset (using 12- and 22-$\mu$m images) and Herschel data (using 70-, 160-, 250-, 350- and 500-$\mu$m wavelength images). Flux estimation was achieved initially via classical aperture photometry and then by an alternative image analysis algorithm that used active contours. The accuracy of the two methods was tested by comparing the estimated fluxes for a sample of bubbles, made up of 126 H II regions and 43 planetary nebulae, which were identified by Anderson et al. The results of this paper demonstrate that a good agreement between the two was found. This is by far the largest and most homogeneous catalogue of infrared fluxes measured for Galactic bubbles and it is a step towards the fully automated analysis of astronomical datasets.

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F. Bufano, P. Leto, D. Carey, et. al.
Mon, 20 Nov 17

Comments: 22 pages, 16 figures, 10 tables, published on MNRAS

Statistical analysis on Dynamic Fibrils observed from NST/BBSO observations [SSA]

We present the results obtained from the analysis of dynamic fibrils in NOAA active region (AR) 12132, using high resolution H$\alpha$ observations from New Solar Telescope operating at BBSO. The dynamic fibrils are seen to be moving up and down, and most of these dynamic fibrils are periodic and have jet like appearance. We found from our observations that the fibrils follows perfect parabolic paths at the most in many cases. A statistical measure on the properties of the parabolic paths showing an analysis on deceleration, maximum velocity, duration and kinetic energy of these fibrils is presented here. We found the average maximum velocity to be around 15 km s$^{-1}$ and mean deceleration to be around 100 m s$^{-2}$. The deceleration observed appears to be a fraction of gravity of sun and is not compatible with the path of ballistic at the gravity of sun. We found positive correlation between the deceleration and the maximum velocity. This correlation is consistent with the simulations done earlier on magnetoacoustic shock waves propagating upward.

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T. Priya, S. Jiangtao, J. Chen, et. al.
Mon, 20 Nov 17

Comments: 13 pages, 8 figures, accepted for publication in RAA

The evolution of the eccentricity in the eclipsing binary system AS Camelopardalis [SSA]

In 2002, 2004, and 2017 we conducted high precision CCD photometry observations of the eclipsing binary system AS~Cam. By the analysis of the light curves from 1967 to 2017 (our data + data from the literature) we obtained photometric elements of the system and found the change of the system’s orbital eccentricity by $\Delta e=0.03 \pm 0.01$. This change can indicate that there is a third companion in the system in a highly inclined orbit with respect to the orbital plane of the central binary, and its gravitational influence may cause the discrepancy between the observed and theoretical apsidal motion rates of AS~Cam.

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V. Kozyreva, A. Kusakin and A. Bogomazov
Mon, 20 Nov 17

Comments: 12 pages, 5 figures, 3 tables; accepted by Research in Astronomy and Astrophysics

Non-equilibrium ionization by a periodic electron beam II. Synthetic Si IV and O IV transition region spectra [SSA]

Transition region (TR) spectra typically show the Si IV 1402.8 A line to be enhanced by a factor of 5 or more compared to the neighboring O IV 1401.2 A, contrary to predictions of ionization equilibrium models and the Maxwellian distribution of particle energies. Non-equilibrium effects in TR spectra are therefore expected. To investigate the combination of non-equilibrium ionization and high-energy particles, we apply the model of the periodic electron beam, represented by a kappa-distribution that recurs at periods of several seconds, to plasma at chromospheric temperatures of 10^4 K. This simple model can approximate a burst of energy release involving accelerated particles. Instantaneous time-dependent charge states of silicon and oxygen were calculated and used to synthesize the instantaneous and period-averaged spectra of Si IV and O IV. The electron beam drives the plasma out of equilibrium. At electron densities of N_e = 10^10 cm^-3, the plasma is out of ionization equilibrium at all times in all cases we considered, while for a higher density of N_e = 10^11 cm^-3, ionization equilibrium can be reached toward the end of each period, depending on the conditions. In turn, the character of the period-averaged synthetic spectra also depends on the properties of the beam. While the case of kappa = 2 results in spectra with strong or even dominant O IV, higher values of kappa can approximate a range of observed TR spectra. Spectra similar to typically observed spectra, with the Si IV 1402.8 A line about a factor 5 higher than O IV 1401.2 A, are obtained for kappa = 3. An even higher value of kappa = 5 results in spectra that are exclusively dominated by Si IV, with negligible O IV emission. This is a possible interpretation of the TR spectra of UV bursts, although an interpretation that requires a density that is 1-3 orders of magnitude lower than for equilibrium estimates.

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E. Dzifcakova and J. Dudik
Mon, 20 Nov 17

Comments: Astronomy & Astrophysics, accepted