  In some delta Scuti stars, only one or two radial modes are excited (usually
the fundamental mode and/or first overtone mode) and the observed peak-to-peak
amplitudes exceed 0.3 mag (V). These stars are known as High Amplitude Delta
Scuti (HADS) variables. We here present a detailed photometric and
spectroscopic analysis of the HADS star TYC 3637-1152-1. We have derived a
metallicity close to solar, a spectral type of F4V and an age of log t = 9.1.
Employing archival time series data from different sources, two frequencies f0
=10.034 c/d and f1 =12.681 c/d and their harmonics and linear combinations were
identified. The period ratio of f0/f1 = 0.791 puts this star into a peculiar
position in the Petersen diagram, from which we conclude that TYC 3637-1152-1
is a unique object with peculiar pulsational properties that indicate a
transitional state between HADS stars pulsating in the fundamental and first
overtone modes and stars pulsating in higher overtones.
