Simultaneous Photometric and Spectroscopic Observations of the unusual Variable F-type stars HD 224638 and HD 224945.

Abstract

The stars HD 224638 and HD 224945 belong to the new class of F0 V spectral type stars which show an unusual kind of variability for that region of the HR diagram (Mantegazza et al. 1993).The variability of these two stars has been discovered and studied by Mantegazza, Poretti & Zerbi (1994). They show small amplitude light variations with characteristic time scales of the order of one day. The light curves are not periodic and it is difficult to satisfactorily fit them even with several periodic terms.In order to explain our 1991 B colour observations we tentatively suggested that in both stars two close periodic terms were present with a characteristic frequency of about 0.8 c/d, and that these terms had a double wave shape for HD 224638 and a triple wave one for HD 224945.

Models and mode identifications of the δ Scuti star FG Vir

“…We choose the effective temperature of the first model so that the observed 281 μΗζ frequency corresponds to log Teff the fifth radial overtone, as suggested by Breger et al In this model, the dominant frequency at 147 μΗζ corresponds to an £ = 1 p-mode, in agreement with the suggestion based on photometric phase shifts of Dawson et al (1995). We choose the effective temperature of the second model so that the dominant 147 μΗζ frequency corresponds to the radial first overtone, as suggested by Mantegazza et al (1994). Table 1 summarizes the properties of our models.…”

“…Breger (1995, private communication) also reports that at least 9 additional modes were detected in the 1995 DSN campaign. Breger et al (1995) identify 10 frequencies as low-order nonradial ρ-and g-modes using evidence from several sources, including: (1) matches to the frequencies by stellar models of W. Dziembowski presented in Breger et al (1995), (2) amplitude ratios and phase differences between photometric measurements in different colors and (3) the spectroscopic moment method (analysis of line profile asymmetries, see Mantegazza, Poretti & Bossi 1994). Here, we evolve stellar models of FG Vir, similar to those of Dziembowski, and compare our frequency predictions and mode identifications to those of Breger et al In particular, we would like to determine how much differences in the evolution and pulsation codes by themselves affect mode identifications and inferences about the internal structure of the star.…”

The multiperiodicity of the γ Doradus stars HD 224945 and HD 224638 as detected from a multisite campaign

“…On that occasion the observer was M. Bossi; the results obtained on BH Psc are reported by Mantegazza et al (1996). The measurements were distributed over 13 nights, with a total useful observing time of 64 hours and a baseline of 14.9 d.…”

Line profile variations in the δ Scuti star FG Virginis: A high number of axisymmetric modes

“…Such a night was simultaneous with the 7 nights of photometry performed by Mantegazza et al (1994) in 1992. However, owing to the short baseline and the complex pulsation spectrum of the star, only preliminary results were proposed about the mode identification on the basis of these observations.…”