Blue large-amplitude pulsator

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A Blue large-amplitude pulsator (BLAP) is a proposed class of pulsating variable star. They are extremely rare, with only 14 being known after examining around a billion stars from the Optical Gravitational Lensing Experiment (OGLE) survey.

Contents

Discovery

Blue large-amplitude pulsators were discovered by a team of astronomers from the University of Warsaw and announced in Nature Astronomy journal in June 2017. During a 2013 search for variable stars with periods shorter than one hour, a star with a period of 28.26 minutes was detected and tentatively classified as a δ Scuti variable although it had an unusually large amplitude and short period. [1] [2]

Examination of over one billion Milky Way stars made during the OGLE project revealed another 13 objects with similar properties: periods of 22 - 39 minutes; near-infrared amplitudes of 0.19 - 0.36 magnitudes; extremely blue, suggesting temperatures around 30,000 K; and smaller than main sequence stars of that temperature. [2]

Characteristics

Stars of this type are characterized by changes of several dozen percent of the brightness on an average of half an hour (between 20-40 minutes). [3] A detailed analysis of the observation results confirms that BLAP objects have a temperature of about 30,000 °C, and the cause for the changes in brightness is pulsation. The construction model is similar to giant star models - 96% of the mass is concentrated in a core of only 20% of the radius of the entire star. The rest of the mass is a slightly ruffled envelope that pulsates at rapid rhythm - hence the large amplitude of the glare. [4]

Currently, the theory only explains how BLAP stars are built and how their brightness changes, while there are only hypotheses about the formation of such stars. One of the hypotheses is that these stars must have lost a large portion of their mass at some point in their evolution to be as hot as they are now. Scientists assume that such a configuration can not come through the evolution of a lonely star, and one possibility is, for example, the passage of a star in the vicinity of a supermassive black hole to the center of the galaxy. Then the black hole can deprive the star of the outer layer; but as the scientists suggest, such a scenario is very unlikely. Another more likely hypothesis assumes that these objects can be formed after the merger of two small mass stars. [4]

Related Research Articles

Semiregular variable star

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Cepheid variable Type of variable star that pulsates radially

A Cepheid variable is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.

W Virginis variable

W Virginis variables are a subclass of Type II Cepheids which exhibit pulsation periods between 10–20 days, and are of spectral class F6 – K2.

Long-period variable star Description for certain cool luminous pulsating variable stars

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Red-giant branch

The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass stars. Red-giant-branch stars have an inert helium core surrounded by a shell of hydrogen fusing via the CNO cycle. They are K- and M-class stars much larger and more luminous than main-sequence stars of the same temperature.

OGLE-TR-122 Binary star in the constellation Carina

OGLE-TR-122 is a binary stellar system containing one of the smallest main-sequence stars whose radius has been measured. It was discovered when the Optical Gravitational Lensing Experiment (OGLE) survey observed the smaller star eclipsing the larger primary. The orbital period is approximately 7.3 days. The system's primary is thought to resemble the Sun.

A Delta Scuti variable is a subclass of young pulsating star. These variables as well as classical cepheids are important standard candles and have been used to establish the distance to the Large Magellanic Cloud, globular clusters, open clusters, and the Galactic Center. The variables follow a period-luminosity relation in certain passbands like other standard candles such as Cepheids. SX Phoenicis variables are generally considered to be a subclass of Delta Scuti variables that contain old stars, and can be found in globular clusters. SX Phe variables also follow a period-luminosity relation. One last sub-class are the pre-main sequence (PMS) Delta Scuti variables.

Optical Gravitational Lensing Experiment Long-term variability sky survey

The Optical Gravitational Lensing Experiment (OGLE) is a Polish astronomical project based at the University of Warsaw that runs a long-term variability sky survey (1992–present). The main goals are the detection and classification of variable stars, discovery of microlensing events, dwarf novae, and studies of the structure of the galaxy and the Magellanic Clouds. Since the project began in 1992, it has discovered a multitude of extrasolar planets, together with the first planet discovered using the transit method (OGLE-TR-56b) and gravitational microlensing. The project has been led by professor Andrzej Udalski since its inception.

W Mensae Variable star in the constellation Mensa

W Mensae is an unusual yellow supergiant star in the Large Magellanic Cloud in the southern constellation Mensa. It is an R Coronae Borealis variable and periodically decreases in brightness by several magnitudes.

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Stellar pulsation

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Type II Cepheid

Type II Cepheids are variable stars which pulsate with periods typically between 1 and 50 days. They are population II stars: old, typically metal-poor, low mass objects.

Classical Cepheid variable

Classical Cepheids are a type of Cepheid variable star. They are population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes from a few tenths of a magnitude to about 2 magnitudes.

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BL Herculis variables are a subclass of Type II Cepheids with low luminosity and mass, that have a period of less than eight days. They are pulsating stars making up a subclass of Type II Cepheids with light curves that frequently show a bump on the descending side for stars of the shortest periods and on the ascending side for longer period stars. Like other Type II Cepheids, they are very old population II stars found in the galaxy’s halo and globular clusters. Also, compared to other Type II Cepheids, BL Her variables have shorter periods and are fainter than W Virginis variables. Pulsating stars vary in spectral class as they vary in brightness and BL Herculis variables are normally class A at brightest and class F when most dim. When plotted on the Hertzsprung–Russell diagram they fall in-between W Virginis and RR Lyrae variables.

OGLE-LMC-CEP0227

OGLE-LMC-CEP0227 is an eclipsing binary star, pulsating every 3.8 days. The star, in the Large Magellanic Cloud, was the first Cepheid star system found to be orbiting exactly edge on.

OGLE-2017-BLG-1522Lb is an exoplanet thought to be orbiting a brown dwarf. It was discovered by KMTNet and the OGLE in 2018.

TU Mensae Star in the constellation Mensa

TU Mensae is a cataclysmic variable star of in the constellation Mensa. A close binary, it consists of a white dwarf and low-mass star orbiting each other in 2 hours 49 minutes. The stars are close enough that the white dwarf strips material off the other star, creating an accretion disc that periodically ignites with a resulting brightening of the system. These result in an increase in brightness lasting around a day every 37 days. Brighter outbursts, known as superhumps, last 5-20 days and take place every 194 days. The properties of TU Mensae have been difficult to calculate, as the calculated mass ratio between the two stars mean there should not be superhumps.

V630 Sagittarii Nova that appeared in 1936

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References

  1. ↑ Pietrukowicz, P.; Dziembowski, W. A.; Mróz, P.; Soszyński, I.; Udalski, A.; Poleski, R.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Wyrzykowski, Ł.; Ulaczyk, K.; Kozłowski, S.; Skowron, J. (2013). "Large Variety of New Pulsating Stars in the OGLE-III Galactic Disk Fields". Acta Astronomica. 63 (4): 379. arXiv: 1311.5894 . Bibcode:2013AcA....63..379P.
  2. 1 2 Pietrukowicz, Paweł; Dziembowski, Wojciech A.; Latour, Marilyn; Angeloni, Rodolfo; Poleski, Radosław; Di Mille, Francesco; Soszyński, Igor; Udalski, Andrzej; Szymański, Michał K.; Wyrzykowski, Łukasz; Kozłowski, Szymon; Skowron, Jan; Skowron, Dorota; Mróz, Przemek; Pawlak, Michał; Ulaczyk, Krzysztof (2017). "Blue large-amplitude pulsators as a new class of variable stars". Nature Astronomy. 1 (8): 0166. arXiv: 1706.07802 . Bibcode:2017NatAs...1E.166P. doi:10.1038/s41550-017-0166.
  3. ↑ "Blue large-amplitude pulsators as a new class of variable stars". University of Warsaw.
  4. 1 2 "BLAPs – a new class of pulsating stars". University of Warsaw. Retrieved 4 September 2017.
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