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Armenian astrophysicists detect a star that becomes 15 times brighter
in less than three minutes
http://www.armradio.am/en/2013/06/15/armenian-astrophysicists-detect-a-star-that-becomes-15-times-brighter-in-less-than-three-minutes/
10:07 15.06.2013
Byurakan Observatory
Astrophysicists at the University of Santiago de Compostela (Spain)
and the Byurakan Observatory (Armenia) have detected a star of low
luminosity which within a matter of moments gave off a flare so strong
that it became almost 15 times brighter. The star in question is the
flare star WX UMa, phys.org reports
`We recorded a strong flare of the star WX UMa, which became almost 15
times brighter in a matter of 160 seconds,' explains astrophysicist
Vakhtang Tamazian, professor at the University of Santiago de
Compostela. The finding has been published in the `Astrophysics'
journal.
This star is in the Ursa Major constellation, around 15.6 light years
from the Earth, and it forms part of a binary system. Its companion
shines almost 100 times brighter, except at times such as that
observed, in which the WX UMa gives off its flares. This can happen
several times a year, but not as strongly as that which was recorded
in this instance.
Dr Tamazian and other researchers detected this exceptional brightness
from the Byurakan Observatory in Armenia. `Furthermore, during this
period of less than three minutes the star underwent an abrupt change
from spectral type M to B; in other words, it went from a temperature
of 2,800 kelvin (K) to six or seven times more than that.'
Based on their spectral absorption lines, stars are classified using
letters. Type M stars have a surface temperature of between 2,000 and
3,700 K; Type B between 10,000 and 33,000 K.
WX UMa belongs to the limited group of `flare stars', a class of
variable stars which exhibit increases in brightness of up to 100
factors or more within a matter of seconds or minutes. These increases
are sudden and irregular - practically random, in fact. They then
return to their normal state within tens of minutes.
Scientists do not know how this flaring arises, but they know how it
develops: `For some reason a small focus of instability arises within
the plasma of the star, which causes turbulence in its magnetic
field,' explains Tamazian. `A magnetic reconnection then occurs, a
conversion of energy from the magnetic field into kinetic energy, in
order to recover the stability of the flow, much like what happens in
an electric discharge.'
Next, kinetic energy in the plasma transforms into thermal energy in
the upper layers of the atmosphere and the star's corona. This
significant rise in the temperature and brightness of the star enables
astronomers to detect changes in the radiation spectrum.
`Photometric and spectroscopic monitoring of this kind of flare stars
is very relevant because it provides us with information about the
changing states and physical processes, which are in turn key to
studying the formation and evolution of stars,' Tamazian explains.
To carry out this study, in which flares in other binary systems (HU
Del, CM Dra and VW Com) have also been analysed, the SCORPIO camera of
the Byurakan Astrophysical Observatory was used. This camera enables
both the spectrum and the brightness of these objects to be detected.
Flare stars are intrinsically weak, and can therefore only be observed
at relatively short distances in astronomic terms, specifically in the
vicinity of the Sun, up to a distance of a few tens of light years,
according to phys.org.
in less than three minutes
http://www.armradio.am/en/2013/06/15/armenian-astrophysicists-detect-a-star-that-becomes-15-times-brighter-in-less-than-three-minutes/
10:07 15.06.2013
Byurakan Observatory
Astrophysicists at the University of Santiago de Compostela (Spain)
and the Byurakan Observatory (Armenia) have detected a star of low
luminosity which within a matter of moments gave off a flare so strong
that it became almost 15 times brighter. The star in question is the
flare star WX UMa, phys.org reports
`We recorded a strong flare of the star WX UMa, which became almost 15
times brighter in a matter of 160 seconds,' explains astrophysicist
Vakhtang Tamazian, professor at the University of Santiago de
Compostela. The finding has been published in the `Astrophysics'
journal.
This star is in the Ursa Major constellation, around 15.6 light years
from the Earth, and it forms part of a binary system. Its companion
shines almost 100 times brighter, except at times such as that
observed, in which the WX UMa gives off its flares. This can happen
several times a year, but not as strongly as that which was recorded
in this instance.
Dr Tamazian and other researchers detected this exceptional brightness
from the Byurakan Observatory in Armenia. `Furthermore, during this
period of less than three minutes the star underwent an abrupt change
from spectral type M to B; in other words, it went from a temperature
of 2,800 kelvin (K) to six or seven times more than that.'
Based on their spectral absorption lines, stars are classified using
letters. Type M stars have a surface temperature of between 2,000 and
3,700 K; Type B between 10,000 and 33,000 K.
WX UMa belongs to the limited group of `flare stars', a class of
variable stars which exhibit increases in brightness of up to 100
factors or more within a matter of seconds or minutes. These increases
are sudden and irregular - practically random, in fact. They then
return to their normal state within tens of minutes.
Scientists do not know how this flaring arises, but they know how it
develops: `For some reason a small focus of instability arises within
the plasma of the star, which causes turbulence in its magnetic
field,' explains Tamazian. `A magnetic reconnection then occurs, a
conversion of energy from the magnetic field into kinetic energy, in
order to recover the stability of the flow, much like what happens in
an electric discharge.'
Next, kinetic energy in the plasma transforms into thermal energy in
the upper layers of the atmosphere and the star's corona. This
significant rise in the temperature and brightness of the star enables
astronomers to detect changes in the radiation spectrum.
`Photometric and spectroscopic monitoring of this kind of flare stars
is very relevant because it provides us with information about the
changing states and physical processes, which are in turn key to
studying the formation and evolution of stars,' Tamazian explains.
To carry out this study, in which flares in other binary systems (HU
Del, CM Dra and VW Com) have also been analysed, the SCORPIO camera of
the Byurakan Astrophysical Observatory was used. This camera enables
both the spectrum and the brightness of these objects to be detected.
Flare stars are intrinsically weak, and can therefore only be observed
at relatively short distances in astronomic terms, specifically in the
vicinity of the Sun, up to a distance of a few tens of light years,
according to phys.org.