Semi regular variable stars are red giant stars or supergiant stars with middle and late spectral types, which show observable periodic and photometric changes, but have various irregular or interrupted changes.At the same time, the photometric curve has some changes more or less in each cycle.The luminosity varies from hundreds to several stars (usually 1-2 stars in visible light).
Semi regular variable stars arePulsating variable starIs divided into red semi regular variable, yellow semi regular variable andTaurus RV type variableThree subtypes.Their light variation curve shape and light variation period are very irregular, and the average brightness is constant or has a long period of change.The period of semi regular variable stars ranges from dozens of days to several years.The total optical amplitude can reach 3-4 magnitudes, usually 1-2 magnitudes.Semi regular variable stars are late type giant stars or supergiant stars with spectral types ranging from F to S.The spectral types of Taurus RV type variable, yellow semi regular variable and red semi regular variable are later in turn (see stellar spectral classification), and the average luminosity is also weakened in turn.
The spectral type changes with the change of luminosity: at the moment of minimum brightness, some titanium oxide absorption bands appear; at the brightening stage, hydrogen or silicon radiation appears.Taurus RV type variable is a star class II, distributed in the silver center andSilver haloIn, inGlobular clusterThere are also some.Yellow semi regular variable and red semi regular variable mainly belong to family IGalactic spiral armMembers on.On the Herot chart, semi regular variable stars are distributed near the branches of giant stars.Taurus RV type variableClose to Cepheid II-W Virginis variable The absolute magnitude is about - 5~- 7 in the upper right of the star.The red semi regular variable star is located at the lower right of the RV type variable star in Taurus, and its absolute magnitude is roughly between - 2 and - 5.
Pulsatile variable correlation
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Pulsating variable starIt refers to the change of brightness caused by pulsationfixed star。these ones hereVariable starThe change of brightness may be caused by the periodic change that the inner body of a star (its own atmosphere) expands and contracts.The periodic expansion and contraction of stars will inevitably lead to the periodic increase and decrease of star radius, the periodic increase and decrease of star surface area, the temperature and total radiation energy change, so the luminosity also increases and decreases periodically. It seems that its brightness also periodically brightens and darkens.
In addition, its color,Spectral typeandApparent velocity, and sometimesmagnetic field, and all have changed accordingly.Among the discovered variable stars, pulsating variable stars account for more than half,GalaxyThere are about 2 million of them.The periods of pulsating variable stars can vary greatly, ranging from less than an hour to hundreds of days or even more than 10 years.The magnitude varies from more than 10 to less than a few thousandths.
According to the shape of brightness curve, pulsating variable stars can be divided into three different types: regular, semi regular and irregular.
Semi regular variable star classification
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Semi regular variable stars can be divided into several types:
SRA: A giant star of spectral type (M, C, S or Me, Ce, Se), with a certain period and a small dimming amplitude, usually when the change of visible light is less than 2.5, Tomb One (ζ Aquarius) is an example of this type.The shape of amplitude and photometric curve often changes, and the period ranges from 35 days to 1200 days.Many of these types of variable stars differ only in their luminosity.
SRB: giant stars of spectral type (M, C, S or Me, Ce, Se), but the periodic characteristics are difficult to confirm (many cycles are between 20 and 2300 days) or alternate cycles with slow and irregular changes, and some will occasionally or once completely stop changing.RR in the northern corona and AF in the Cygnus are examples of this behavior.Each star of this type usually has an average period, and two or more slightly different periods are observed at the same time.
SRC: a supergiant of spectral type (M, C, S or Me, Ce, Se), whose luminosity changes about 1 degree, and whose period ranges from 30 days to thousands of days.Cepheid IV (Cepheus) is an obvious example of this type.
SRD: Giant stars and supergiants with spectral types F, G, or K, some of which have emission spectral lines in their spectra.
The amplitude of photometric change ranges from 0.1 to 4, and the period ranges from 30 days to 1100 days.Hercules SXandUrsa Major SVIs an example of this type.Amateur observers canM 13A dozen red variable stars with luminosity ranging from 11.95 to 12.25 were observed, and the period was between 43 days (V24) and 97 days (V43).
Famous semi regular variable star
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Antares , Alpha Scorpio (the main star of Scorpio), the loneliest first-class star in the whole day, but there are many bright second-class stars near it.Also called fire in ancient ChinaOriental CanglongThe seven night lodging is used to determine the season."July Liuhuo" means that the big Mars is going west, and the weather will be cold.
Antares is the 15th bright star in the whole day. It is a visual binary star. The apparent magnitude of the main star is 1.2. The M1I type red supergiant star has a luminosity 10900 times that of the sun. The companion star is a blue dwarf star with a brightness of 5.4. The angular distance between the two stars is 3 ".The composite magnitude is 0.96, and the absolute magnitude is -5.28.The star belongs to the Scorpio Centaurus galaxy, with a distance of 430 light-years.Modern astronomy calls it "Alpha Scorpio".It is aRed supergiant。It is a semi regular variable star with obvious light change and forms a visual binary system with a blue main sequence star.Antares II is also a radio source.[1]
