We performed optical simultaneous dual-band (SDSS g'- and i'- band) photometry and low-resolution spectroscopy for the WZ Sge-type dwarf nova EZ Lyn during its 2010 superoutburst. Dual-band photometry revealed that the g'-i' color reddened with a decrease in brightness, during the main superoutburst and the following rebrightening phase, whereas the color became bluer with a further decrease in brightness during the slow, final decline phase. With a fit to our photometric results by a blackbody function, we estimated the disk radius ratio (ratio of the disk radius to the binary separation) and compared this with that of V455 And, a WZ Sge-type object that did not show any rebrightening in the 2007 superoutburst.
The comparison revealed: (1) the disk radius ratio of EZ Lyn decreased more slowly than that of V455 And; and (2) the radius ratio of EZ Lyn at the end of the main superoutburst was larger than that of the V455 And. These results favor the mass reservoir model for the mechanism of rebrightening. During both the superoutburst plateau and subsequent rebrightening phase, H-alpha and H-beta lines were detected. The H-alpha line showed a double-peak profile from which we estimated the disk radius ratio. The comparison of this ratio with that derived by photometry, indicates that the H-alpha disk was larger than the photometric one, which suggests that the optically thin gas was extended to the outer region more than the optically thick gas disk and was possibly responsible for the rebrightening phenomenon. Time-series dual-band photometry during the main superoutburst revealed that color variations during the early superhump show roughly the same behavior as that of V455 And, whereas color variations during the ordinary superhump display clear anticorrelation with brightness, in contrast to that seen in the V455 And.
Context. The early-type binary MY Cam belongs to the young open cluster Alicante 1, embedded in Cam OB3. Aims. MY Cam consists of two early-O type main-sequence stars and shows a photometric modulation suggesting an orbital period slightly above one day. We intend to confirm this orbital period and derive orbital and stellar parameters. Methods. Timing analysis of a very exhaustive (4607 points) light curve indicates a period of 1.1754514 +- 0.0000015 d. High- resolution spectra and the cross-correlation technique implemented in the TODCOR program were used to derive radial velocities and obtain the corresponding radial velocity curves for MY Cam. Modelling with the stellar atmosphere code FASTWIND was used to obtain stellar parameters and create templates for cross-correlation. Stellar and orbital parameters were derived using the Wilson-Devinney code, such that a complete solution to the binary system could be described. Results. The determined masses of the primary and secondary stars in MY Cam are 37.7 +- 1.6 and 31.6 +- 1.4 Msol, respectively. The corresponding temperatures, derived from the model atmosphere fit, are 42 000 and 39 000 K, with the more massive component being hotter. Both stars are overfilling their Roche lobes, sharing a common envelope. Conclusions. MY Cam contains the most massive dwarf O-type stars found so far in an eclipsing binary. Both components are still on the main sequence, and probably not far from the zero-age main sequence. The system is a likely merger progenitor, owing to its very short period.
Authors: J. Lorenzo (Universidad Alicante), I. Negueruela (Universidad Alicante), A.K.F. Val Baker (University of Malaya), M. García (CSIC-INTA), S. Simón-Díaz (IAC), P. Pastor (Universidad Alicante), M. Méndez Majuelos (IES Arroyo Hondo)
Because a neutron star's solid crust is locked to its intense magnetic field, a disruption of one immediately affects the other. A fracture in the crust will lead to a reshuffling of the magnetic field, or a sudden reorganization of the magnetic field may instead crack the surface. Either way, the changes trigger a sudden release of stored energy via powerful bursts that vibrate the crust, a motion that becomes imprinted on the burst’s gamma-ray and X-ray signals.
It takes an incredible amount of energy to convulse a neutron star. The closest comparison on Earth is the 9.5-magnitude Chilean earthquake of 1960, which ranks as the most powerful ever recorded on the standard scale used by seismologists. On that scale, said Watts, a starquake associated with a magnetar giant flare would reach magnitude 23.
Massive black holes spewing out radio-frequency-emitting particles at near-light speed can block formation of new stars in aging galaxies, a study has found.
The research provides crucial new evidence that it is these jets of “radio-frequency feedback” streaming from mature galaxies’ central black holes that prevent hot free gas from cooling and collapsing into baby stars.
“When you look into the past history of the universe, you see these galaxies building stars,” said Tobias Marriage, assistant professor of physics and astronomy at Johns Hopkins and co-lead author of the study. “At some point, they stop forming stars and the question is: Why? Basically, these active black holes give a reason for why stars stop forming in the universe.”