AG Draconis. , AG Draconis (BD + 67 922, HIP 78512) is a variable star in the constellation Draco with apparent magnitude +9.75. It is very far away, at an indeterminate distance of about 8000 light years .
AG Draconis is a symbiotic star, a very rare class of stars of which less than 200 representatives are known. Symbiotic stars are binary stars whose components – a red giant and usually a white dwarf – are surrounded by a nebulosity that comes from the giant star.
The main star, AG Draconis A, is a giant star of the spectral type K0. Its luminosity is 1500 times greater than that of the Sun and its mass can be 50% greater than the solar mass. Little is known about AG Draconis B, except that its mass may be around 50% of the solar mass. The distance between the two stars is 1.7 AU and their orbital period is 554 days. It is a halo star with a very low metallicity, only 3% of that of the Sun.
The star erupts every 10-15 years, being a nova . However, during bursts its brightness is multiplied “only” by five, probably due to the lack of heavy elements. In autumn 2007 its brightness increased to magnitude +8.98 during an outburst.
Summary
[ hide ]
- 1 Discovery
- 2 Unusual explosive activity
- 3 Location of the constellation Drake
- 4 Sources
Discovery
AG Draconis has been listed since the beginning of the 20th century , as BD + 67 ° 922. However, its unusual character did not begin to emerge until the middle of the century. It was designated as a broadcast line object in 1943, although its nature was not understood. The emission spectrum was discovered by chance to be variable by Roman Nancy Grace when the star was observed and it was found that the spectrum had completely changed since previous observations. It was given the AG Draconis variable star designation in 1964 AG Draconis.
Unusual explosive activity
Using an array of several ground-based telescopes, European astronomers have made photometric and spectroscopic observations of a symbiotic binary known as AG Draconis. The results of this observation campaign, presented in an article published on May 10 on arXiv.org, reveal the peculiar explosive activity of the system in recent years.
Located about 16,000 light years from Earth, AG Draconis (AG Dra for short) is a strongly interacting binary system in the constellation Draco. It consists of a cold, metal-poor K3 spectral-type giant and a hot component, most likely a white dwarf. The giant star is about 35 times bigger than the sun and has a mass of around 1.5 solar masses, while the smallest component is about 0.4 times more massive than our sun and has a relatively high temperature between 10,000. and 15,000 K.
AG Dra is one of the best-studied symbiotic systems, having been observed since 1890. Observations of this binary made in the last two decades confirmed two periods in the system. The longest, lasting about 551 days, is supposed to be related to orbital motion, and the shortest, lasting about 355 days, could be due to the pulsation of the cold component.
Furthermore, AG Dra exhibits characteristic symbiotic activity with alternation of active and inactive stages. Studies show that the active stages of this system occur at intervals of nine to 15 years and consist of several bursts that are repeated at intervals of approximately one year.
Now, a team of astronomers led by Rudolf Gális of PJ Šafárik University in Košice, Slovakia , reports that a new active stage of AG Dra began in late spring 2015 when the source became brighter and showed a minor burst. This event was followed by three outbursts that took place in April 2016, May 2017, and April 2018.
However, the results of new observations show that the later bursts differ from those typically seen in the system at the beginning of the active phases. ” Photometric and spectroscopic observations suggest that all of these bursts are of the hot type. Such behavior is considerably peculiar in the nearly 130-year history of observing this object, because the main bursts at the beginning of the active stages are typically cold.” astronomers wrote in the newspaper.
Researchers distinguish hot and cold burst types based on the spectroscopic behavior of AG Dra observed in the far ultraviolet and on the behavior of emission lines in its optical spectrum. As reported in the paper, the astronomers emphasized that the last three bursts, as well as the previous minor one, were all of the hot type.
In the concluding remarks, the study authors also discuss the possible paths of the future evolution of AG Dra, taking into account the recently observed outbursts. They note that it is not yet clear whether the next outbreak in the system, which is probably expected in May 2019, will be hot or cold. In addition, there is also the possibility that AG Dra will return to inactivity, as such behavior was observed in the mid-1960s, after a period of weak activity of this binary ended.
All in all, astronomers say the peculiar burst activity at AG Dra highlights the importance of long-term monitoring of symbiotic stars in general. Such studies could reveal essential information about the nature and mechanisms of the active stages and bursts of these objects.
Drake constellation location
Latin name Draco Abbreviation Dra Genitive Draconis Symbology The Dragon Right ascension 15 h Declination + 75 ° Surface 1083 square degrees Rank 8 Number of stars (magnitude <3) 3 Brightest star γ Dra (Etamin) (magnitude ap. 2.23) Rain of meteors • Draconids
Adjacent constellations • Boötes • Hercules • Lyra • Cygnus • Cepheus • Ursa Minor • Camelopardalis • Ursa Major
Visibility At latitudes between + 90 ° and −15 ° Best visibility (9:00 p.m.)