Astronomers discover Cepheid with the longest pulsation period

Astronomers have discovered Cepheid with the longest known pulsation period. These giant variable stars play the role of “beacons of the Universe”, helping scientists estimate the distance to various objects.

Cepheid. Source:

Cepheid with the longest period

Astronomers from the University of Warsaw in Poland and other countries have discovered a new classical Cepheid. This variable star, which has been designated OGLE-GD-CEP-1884, has the longest pulsation period among similar variables in the Milky Way.

Variables of the type δ Cephei, or Cepheids, are bright yellow stars forming a separate horizontal sequence on the Hertzsprung—Russell diagram. They change their brightness over time due to regular pulsations. Given that the periods of their changes are closely related to their luminosity, astronomers use them to measure interstellar and intergalactic distances.

Classical Cepheids, also known as Population I Cepheids, experience pulsations with very regular periods of the order of a few days to several months. Considering that the frequency of changes in luminosity and physical parameters are closely related, these variables are also used as a test site for theories of stellar evolution.

Variable star with the longest pulsation period

In a new article, a team of astronomers led by Igor Soszyński from the University of Warsaw reports the discovery of a new variable of this type. The new star, which has a relatively long pulsation period, was discovered using the Warsaw Telescope at the Las Campanas Observatory in Chile as part of the Optical Gravitational Lensing Experiment (OGLE), a long-term sky survey involving regular photometric observations of about two billion stars in our galaxy and in the Magellanic Clouds.

According to the study, OGLE-GD-CEP-1884 has a pulsation period of approximately 78.14 days — the longest classical Cepheids known in the Galaxy. It exceeds by 10 days the duration of changes in the luminosity of the Milky Way’s second Cepheids in this parameter — S Vulpeculae.

Parameters of the discovered star

OGLE-GD-CEP-1884 has a magnitude in the V-band of 16.83, an average radial velocity of -72.3 km/s, and its age is estimated at 22 million years. Astronomers have noted that such parameters make this star probably the brightest and youngest Galactic Cepheid. The distance to this star is about 14,500 light-years. 

Astronomers noted that it was strange that OGLE-GD-CEP-1884 had not previously been identified as a long-period classical Cepheid, given its brightness, especially in long waves. Therefore, they suggest that there may be more such Cepheids in the Milky Way that remain undetected.

The discovery of such a star indicates that we do not know all the classical Cepheids in the Galaxy; they probably hide in regions that have suffered greatly from interstellar extinction. This finding highlights the need for more effective methods of detecting and classifying variable stars in current and future sky surveys.

According to

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