Stability in Period and Amplitude: The High-Amplitude δ Scuti Star YZ Boötis

Abstract

The variability of period and amplitude of the high-amplitude δ Scuti star YZ Boo was thoroughly investigated based on a comprehensive analysis of new time-series photometry and other available data. Fourier analysis, O-C diagram, and wavelet analysis establish a clear picture for the star's time-dependent behavior in period and amplitude. We detected no additional frequencies being intrinsic to the variable or caused by amplitude/frequency modulation confirming its mono-periodicity. We reveal the pulsation of YZ Boo is quite stable in both period and amplitude over the past 50 years. Short-term variations at cycle level including "anomalous cycles" are present clearly, while long-term variations in period and amplitude at annual base are insignificant. However, we note an increment from 2000 to 2003 in both period and amplitude. In 2000 the amplitude reached the lowest. This is indicated by the Fourier and wavelet results. In the long term, O-C fits and wavelet analysis agree with the Fourier results that the period change of YZ Boo is still inconclusive.

Pulsations of the High-AmplitudeδScuti star YZ Bootis

“…Apart from the fundamental frequency f 0 and its harmonics 2f 0 , 3f 0 , 4f 0 , as mentioned in Zhou (2006), another two harmonics 5f 0 and 6f 0 are detected. Generally, it is reasonable that a frequency whose signal-to-noise ratio is lager than 4 (i.e.…”

“…Secondly, we combined the newly determined times of maximum light with those provided by earlier studies (Eggen 1955;Broglia & Masani 1957;Spinrad 1959;Broglia 1961;Heiser & Hardie 1964;Fitch et al 1966;Gieren et al 1974;Langford 1976;Rolon 1976;Szeidl et al 1981;Joner et al 1983;Jiang 1985;Peniche et al 1985;Hamdy et al 1986;Kim 1994;Agerer et al 1999;2000;Agerer 2003;Derekas et al 2003;Jin et al 2003;Hubscher 2005Hubscher , 2006Klingenberg 2006;Zhou 2006;Ward et al 2008). Table 2. A total of 248 times of maximum light were collected.…”

“…As previous studies, we do not consider the maxima that have been derived from either photographic or visual observations. The seven photometrically determined data points omitted by Zhou (2006) and Ward et al (2008) have also been discarded in this study.…”

“…YZ Bootis (=HIP 75373, V = 10.57 mag, P 0 = 0.1041 days, A6-F1), is a high-amplitude δ Scuti star with a peak-to-peak amplitude of about 0.42 mag (Breger & Panmyatnykh 1998;Zhou 2006). Based on the uvbyβ photometry, Joner et al (1983) classified YZ Bootis as a Population I star because of the typical m 1 index of Population I star.…”

“…Subsequent observations (Szeidl et al 1981;Jiang 1985;Peniche et al 1985;Hamdy et al 1986) seems to indicate YZ Boo has different continuous period increases around a value of (1/P )dP/dt = ∼ 3 × 10 −8 yr −1 . Recently, Zhou (2006) presented an investigation on the stability in period of YZ Boo and claimed that the period change of YZ Boo is still inclusive. Ward et al (2008) gave a new value of (1/P )dP/dt = 6.3(6) × 10 −9 yr −1 , assuming this star is increasing and changing smoothly.…”