We present photometric study of NY Ser, an in-the-gap SU UMa-type nova, in 2002 and 2013. We determined the duration of the superoutburst and the mean superhump period to be 18 d and 0.10458 d, respectively. We detected in 2013 that NY Ser showed two distinct states separated by the superoutburst. A state of rather infrequent normal outbursts lasted at least 44 d before the superoutburst and a state of frequent outbursts started immediately after the superoutburst and lasted at least for 34 d. Unlike a typical SU UMa star with bimodal distribution of the outbursts duration, NY Ser displayed a diversity of normal outbursts. In the state of infrequent outbursts, we detected a wide ~12 d outburst accompanied by 0.098 d orbital modulation but without superhumps ever established in NY Ser. We classified this as the "wide normal outburst". The orbital period dominated both in quiescence and during normal outbursts in this state. In the state of the most frequent normal outbursts, the 0.10465 d positive superhumps dominated and co-existed with the orbital modulation. In 2002 we detected the normal outburst of "intermediate" 5-6 d duration that was also accompanied by orbital modulations.
Authors: Elena P. Pavlenko, Taichi Kato, Oksana I. Antonyuk, Tomohito Ohshima, Franz-Josef Hambsch, Kirill A. Antonyuk, Aleksei A. Sosnovskij, Alex V. Baklanov, Sergey Yu. Shugarov, Nikolaj V. Pit, Chikako Nakata, Gianluca Masi, Kazuhiro Nakajima,Hiroyuki Maehara, Pavol A. Dubovsky, Igor Kudzej, Maksim V. Andreev, Yuliana G. Kuznyetsova, Kirill A. Vasiliskov
Type Ia supernovae happen when a white dwarf, the “corpse” of a star similar to the Sun, absorbs material from a twin star until it reaches a critical mass--1.4 times that of the Sun—and explodes. Because of their origin, all these explosions share a very similar luminosity. This uniformity made type Ia supernovae ideal objects to measure distances in the universe, but the study of supernova 2014J suggests a scenario that would invalidate them as “standard candles".
A new model postulating the fusion of two white dwarfs is now challenging the predominant one, consisting of a white dwarf and a normal star. The new scenario does not imply the existence of a maximum mass limit and will not, therefore, necessarily produce explosions of similar luminosity.
Radio observation makes it possible to reveal what stellar systems lie behind type Ia supernovae. If the explosion proceeds from a white dwarf being nourished by a twin star, for example, a great amount of gas should be present in the environment; after the explosion, the material ejected by the supernova will collide with this gas and produce an intense emission of X rays and radio waves. By contrast, a couple of white dwarfs will not generate this gaseous envelope and, therefore, there will be no emission of either X rays or radio waves.
Stellar flares, winds and coronal mass ejections form the space weather. They are signatures of the magnetic activity of cool stars and, since activity varies with age, mass and rotation, the space weather that extra-solar planets experience can be very different from the one encountered by the solar system planets. How do stellar activity and magnetism influence the space weather of exoplanets orbiting main-sequence stars? How do the environments surrounding exoplanets differ from those around the planets in our own solar system? How can the detailed knowledge acquired by the solar system community be applied in exoplanetary systems? How does space weather affect habitability? These were questions that were addressed in the splinter session "Cool stars and Space Weather", that took place on 9 Jun 2014, during the Cool Stars 18 meeting. In this paper, we present a summary of the contributions made to this session.
Read the summary paper from the Proceedings of the 18th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun.
NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) has captured an extreme and rare event in the regions immediately surrounding a supermassive black hole. A compact source of X-rays that sits near the black hole, called the corona, has moved closer to the black hole over a period of just days.
"We still don't understan exactly how the corona is produced or why it changes its shape, but we see it lighting up material around the black hole, enabling us to study the regions so close in that effects described by Einstein's theory of general relativity become prominent," said NuSTAR Principal Investigator Fiona Harrison of the California Institute of Technology (Caltech).