TT Aquilae
Classical Cepheid with asymmetric light curve and disputed mass.
TT Aquilae, also designated TT Aql, is a Classical Cepheid variable star—of the Delta Cephei type—located in the constellation Aquila. Its apparent visual magnitude fluctuates between 6.52 and 7.65 over a period of 13.7546 days. The star’s light curve is asymmetrical: the climb from minimum to maximum brightness takes only half as long as the subsequent decline from maximum back to minimum.
The variability of TT Aquilae was first reported in 1907 by Annie Jump Cannon. Her discovery was based on 506 photographic plates taken between May 22, 1888, and November 9, 1906, from which a period of 13.75 days was derived.
This star is a yellow-white supergiant, roughly five thousand times more luminous than the Sun. It pulsates, with its temperature varying between about 5,000 K and 6,000 K, and its spectral type shifting between F6 and G5. At maximum brightness, its radius is 91.4 times that of the Sun, and it ranges from 84 to 100 solar radii as the star expands and contracts.
Mass estimates for TT Aquilae differ depending on the method used. The Baade-Wesselink technique gives a mass of 8.6 solar masses. Matching the star to evolutionary tracks yields 7.7 solar masses. Modelling its pulsations results in 6.2 solar masses. Such discrepancies between these three methods are common among Cepheid variables.
- Constellation
- Aquila
- Variable type
- Classical Cepheid (δ Cep)
- Apparent magnitude range
- 6.52 to 7.65
- Period days
- 13.7546
- Spectral type range
- F6 to G5
- Temperature range k
- 5000 to 6000
- Radius range r☉
- 84 to 100
- Mass estimates m☉
- Baade-Wesselink: 8.6; evolutionary tracks: 7.7; pulsation modelling: 6.2
Lore & Background
The variability of TT Aquilae was announced in 1907 by Annie Jump Cannon, based on 506 photographs taken from May 22, 1888 through November 9, 1906, from which a period of 13.75 days had been derived. The star is a yellow-white supergiant around five thousand times brighter than the Sun. It pulsates and varies in temperature between about 5,000 K and 6,000 K, and its spectral type varies between F6 and G5. The radius is 91.4 R☉ at maximum brightness, varying between 84 R☉ and 100 R☉ as the star pulsates. The light curve is asymmetric, with the rise from minimum to maximum brightness only taking half the time of the fall from maximum to minimum.
Reader's Guide
TT Aquilae is significant as a Classical Cepheid, a type of variable star used as standard candles for distance measurement. Its asymmetric light curve is a characteristic feature of Cepheid pulsations. The star's mass has been estimated using three different methods: Baade-Wesselink relations give 8.6 M☉, matching to evolutionary tracks gives 7.7 M☉, and pulsation modelling gives 6.2 M☉. The article notes that discrepancies between the masses obtained by these different methods occur for most Cepheid variables, highlighting an ongoing challenge in stellar astrophysics. The star's variability was discovered from early photographic observations, and its period of 13.7546 days was refined from those data. Its legacy lies in contributing to the understanding of Cepheid pulsation and mass estimation techniques.
Did You Know?
- TT Aquilae's variability was announced in 1907 by Annie Jump Cannon.
- The star's light curve is asymmetric, with the rise to maximum taking half the time of the fall.
- Its radius varies between 84 R☉ and 100 R☉ as it pulsates.
- Mass estimates for TT Aql range from 6.2 M☉ to 8.6 M☉ depending on the method used.
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