12 Lacertae
A hybrid pulsator and one of the first stars targeted by a global observing campaign.
12 Lacertae is a wide binary star system in the northern constellation Lacerta, about 1,260 light-years from the Sun. To the naked eye, it appears as a faint, blue-white point of light, with a typical apparent visual magnitude of 5.23. The system is moving toward Earth at an average heliocentric radial velocity of –12.5 km/s and is likely a member of the I Lacertae OB association (Lac OB1).
The primary star, DD Lacertae (the Flamsteed designation is 12 Lacertae), is a Beta Cephei variable with a spectral type of B1.5III—a B-type giant. Its variability has been recognized for over a century and has been studied extensively. W. S. Adams first detected its changing radial velocity in 1912, and by 1919 its brightness variations were confirmed. In 1951, P. Ledoux demonstrated the pulsational nature of these changes, leading to one of the first global observing campaigns focused on this star. Dutch mathematician F. J. M. Barning analyzed the campaign data in 1963, identifying four distinct cycles; by 1994, six periods had been confirmed.
The star’s brightness typically ranges from magnitude 5.16 to 5.28, with a dominant period of 0.1930924 days. Up to eleven different frequencies have been detected, the strongest being 5.179034 cycles per day. Three of these frequencies—5.179, 5.334, and 5.490 cycles per day—form an equally spaced triplet, though this alignment appears coincidental. DD Lacertae is a hybrid pulsator, exhibiting traits of both a Beta Cephei variable and a slowly pulsating B-type star.
The primary is a massive star, with 9.5 times the Sun’s mass and an age of just 22 million years. Its radius is about 8.4 times that of the Sun. It radiates 8,877 times the Sun’s luminosity from its photosphere, at an effective temperature of 23,809 K. The star’s equatorial rotational velocity is roughly 10% of its break-up speed, but seismic models indicate the core rotates much faster, suggesting differential rotation. The average quadratic surface magnetic field strength is not specified.
The companion is an A-type main-sequence star, classified as A3V, with a visual magnitude of 9.2. As of 2008, its angular separation from the primary was not given. A faint infrared nebulosity, likely a bow shock, lies about 0.19 parsecs from the pair.
- Apparent visual magnitude
- 5.23 (baseline), varies from 5.16 to 5.28
- Distance
- ~1,260 light years
- Spectral type (primary)
- B1.5III
- Mass (primary)
- 9.5 solar masses
- Radius (primary)
- 8.4 solar radii
- Luminosity (primary)
- 8,877 solar luminosities
- Effective temperature (primary)
- 23,809 K
Lore & Background
The variable radial velocity of the primary was discovered by W. S. Adams in 1912, and its light variations were established by 1919. The pulsational nature of the variability was shown by P. Ledoux in 1951, which led to one of the first world-wide observing campaigns with the star as its target. Dutch mathematician F. J. M. Barning analyzed the resulting data in 1963 and found four separate cycles of variation; by 1994, six periods had been confirmed. As many as eleven different frequencies have been detected, with the dominant cycle showing a frequency of 5.179034 cycles per day. Three of the frequencies form an equally-spaced triplet with cycles of 5.179, 5.334, and 5.490 per day, although this alignment appears to be a coincidence. The primary is a hybrid pulsator, showing mixed behaviors of a Beta Cephei variable and a slowly pulsating B-type star. The system is drifting closer to the Earth with a mean heliocentric radial velocity of –12.5 km/s and is a probable member of the I Lacertae OB association (Lac OB1).
Reader's Guide
12 Lacertae holds significance as a well-studied Beta Cephei variable whose pulsational nature was confirmed by P. Ledoux in 1951, prompting one of the first coordinated worldwide observing campaigns. The analysis by F. J. M. Barning in 1963 revealed four cycles of variation, later expanded to six confirmed periods by 1994, with up to eleven detected frequencies overall. Its status as a hybrid pulsator—exhibiting characteristics of both a Beta Cephei variable and a slowly pulsating B-type star—makes it a valuable object for asteroseismology. The star's differential rotation, with a core rotating much more rapidly than the surface, has been inferred from seismic models. The system also includes an A-type main-sequence companion and a faint infrared bow shock nebulosity at a separation of 0.19 pc, adding to its astrophysical interest. The primary's magnetic field and rotational properties further contribute to understanding stellar structure and evolution in massive stars.
Did You Know?
- The primary component, DD Lacertae, has been known to be variable for more than a century.
- Its variable radial velocity was discovered by W. S. Adams in 1912.
- The star was the target of one of the first world-wide observing campaigns, following P. Ledoux's 1951 demonstration of its pulsational nature.
- Seismic models suggest the core of the primary rotates much more rapidly than its surface, indicating differential rotation.
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