Star in the constellation Aquila
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! style="text-align: center; background-color: #FFFFC0;" colspan="2" | Observation dataEpoch J2000      Equinox J2000
! style="text-align:left" | Constellation
! style="text-align:left" | Right ascension
! style="text-align:left" | Declination
! style="text-align:left" | Apparent magnitude (V)
! style="background-color: #FFFFC0; text-align: center;" colspan="2"| Characteristics
! style="text-align:left" | Spectral type
! style="text-align:left" | U−B 
! style="text-align:left" | B−V 
! style="text-align:left" | Variable type
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TT Aquilae (TT Aql) is a Classical Cepheid (δ Cep) variable star in the constellation Aquila.
The visual apparent magnitude of TT Aql ranges from 6.52 to 7.65 over 13.7546 days. 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.
The announcement that the star's brightness varies was made in 1907 by Annie Jump Cannon. It had been observed on 506 photographs taken from May 22, 1888 through November 9, 1906, from which a period of 13.75 days had been derived.
TT Aql 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 the 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.
Cepheid masses can be estimated using Baade-Wesselink relations and this gives 8.6 M☉. The mass estimated by matching to evolutionary tracks is 7.7 M☉. The mass calculated by modelling the pulsations is 6.2 M☉. The discrepancies between the masses obtained by the different methods occurs for most Cepheid variables.
References.
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