We report spectroscopic and photometric follow-up of the peculiar nova V5852~Sgr (discovered as OGLE-2015-NOVA-01), which exhibits a combination of features from different nova classes. The photometry shows a flat-topped light curve with quasi-periodic oscillations, then a smooth decline followed by two fainter recoveries in brightness. Spectroscopy with the Southern African Large Telescope shows first a classical nova with an Fe II or Fe IIb spectral type. In the later spectrum, broad emissions from helium, nitrogen and oxygen are prominent and the iron has faded which could be an indication to the start of the nebular phase. The line widths suggest ejection velocities around 1000kms−1. The nova is in the direction of the Galactic bulge and is heavily reddened by an uncertain amount. The V magnitude 16 days after maximum enables a distance to be estimated and this suggests that the nova may be in the extreme trailing stream of the Sagittarius dwarf spheroidal galaxy. If so it is the first nova to be detected from that, or from any dwarf spheroidal galaxy. Given the uncertainty of the method and the unusual light curve we cannot rule out the possibility that it is in the bulge or even the Galactic disk behind the bulge.
Authors: E. Aydi, P. Mróz, P. A. Whitelock, S. Mohamed, Ł. Wyrzykowski, A. Udalski, P. Vaisanen, T. Nagayama, M. Dominik, A. Scholz, H. Onozato, R. E. Williams, S. T. Hodgkin, S. Nishiyama, M. Yamagishi, A. M. S. Smith, T. Ryu, A. Iwamatsu, I. Kawamata
An international team of astronomers made the discovery by observing a very faint binary system, J1433 which is located 730 light-years away. The system consists of a low-mass object – about 60 times the mass of Jupiter – in an extremely tight 78-minute orbit around a white dwarf (the remnant of a star like our Sun).
Due to their close proximity, the white dwarf strips mass from its low-mass companion. This process has removed about 90 per cent of the mass of the companion, turning it from a star into a brown dwarf.
Most brown dwarfs are ‘failed stars’, objects that were born with too little mass to shine brightly by fusing hydrogen in their cores. By contrast, the brown dwarf in this system was born as a full-fledged star, but has been stripped to its current mass by billions of years of stellar cannibalism.
Sorry, E.T. lovers, but the results of a new study make it far less likely that KIC 8462852, popularly known as Tabby’s star, is the home of industrious aliens who are gradually enclosing it in a vast shell called a Dyson sphere.
Public interest in the star, which sits about 1,480 light-years away in the constellation Cygnus, began last fall when Yale astronomer Tabetha (Tabby) Boyajian and colleagues posted a paper on an astronomy preprint server reporting that “planet hunters” – a citizen science group formed to search data from the Kepler space telescope for evidence of exoplanets – had found unusual fluctuations in the light coming from the otherwise ordinary F-type star (slightly larger and hotter than the sun).
Media interest went viral last October when a group of astronomers from Pennsylvania State University released a preprint that cited KIC 8462852’s “bizarre light curve” as “consistent with” a swarm of alien-constructed megastructures.
The Bubble Nebula really is a bubble. It is being blown into this shape by the bright star known as SAO20575, which sits just to the left of centre in this image. This is a giant star of 10–20 times the mass of the Sun.
The star is pumping out a fearsome torrent of ultraviolet radiation, causing the surrounding gases to glow like a fluorescent light. But it is not this ultraviolet radiation that is blowing the bubble. Instead, it is being created by SAO20575’s stellar wind.
A stellar wind is a high-speed flow of particles streaming away from the star. As they collide with the gas atoms and molecules in the surrounding cloud they push them away, creating this luminous bubble.
It's one of only about 10 stars in the entire sky classified as a recurrent nova, with two recorded outbursts to its name. Normally, the star slumbers at 10th magnitude, but on May 12, 1866, it hit the roof, reaching magnitude +2.0 and outshining every star in Corona Borealis before quickly fading back to obscurity. Eighty years later, on February 9, 1946, it sprang back to life, topping out at magnitude +3.0.
Many variable star observers include it in their nightly runs because it's easy to find 1° south-southeast of Epsilon (ε) in Corona Borealis and only requires a 3-inch telescope. Not to mention the huge payoff should you happen catch the star during one of its rare explosions.