Delta Scuti Network observations of XX Pyx: detection of 22 pulsation modes and of short-term amplitude and frequency variations

Abstract

A B S T R A C TWe report multisite observations devoted to the main-sequence d Scuti star XX Pyx, conducted as the 17th run of the Delta Scuti Network. Over 125 nights a total of 550 h of usable time-series photometric B-and V-filter data were acquired involving both photoelectric and CCD measurements at eight observatories spread around the world, which represents the most extensive single time-series for any pulsating star other than the Sun obtained so far.We describe our observations and reduction methods, and present the frequency analysis of our new data. First, we detect six new pulsation and five new combination frequencies in the star's light curves. We also discover evidence for amplitude and/or frequency variations of some of the modes during the observations. These can occur on time-scales as short as 20 d and show quite diverse behaviour. To take them into account in the frequency analysis, a so-called non-linear frequency analysis method was developed, allowing us to quantify the temporal variability of the modes and to compensate for it. Following that we continue the frequency search and we also incorporate published multisite observations. In this way, we reveal three more pulsation and two more combination frequencies. In the end, we report a total of 30 significant frequencies ± 22 of which correspond to independent pulsation modes. This is the largest number of independent modes ever detected in the light curves of a d Scuti star.q 2000 RAS

HYBRID γ DORADUS-δ SCUTI PULSATORS: NEW INSIGHTS INTO THE PHYSICS OF THE OSCILLATIONS FROM KEPLER OBSERVATIONS

“…Although the modes considered were not in the asymptotic regime, a comparison with stellar models confirmed that this signature may stem from a quasiperiodic pattern similar to the so-called large separation in solarlike stars. Other frequency spacings have also been observed in other stars using ground-based observations (e.g., Handler et al 2000;Breger et al 2009). From numerical results, this approximate asymptotic behavior has been found to hold for p-modes of low order (e.g., Christensen-Dalsgaard 2000).…”

Revisiting bright delta Scuti stars and their period-luminosity relation with TESS and Gaia DR3

“…7) confirms that it is an ellipsoidal variable with a binary period of 1.15 d, as found by Aerts et al (2002). Handler et al (2000) detected 19 independent pulsation frequencies in the range 27-38 d −1 , and suggested a large separation of 4.63 d −1 . By generating an échelle diagram with those frequencies, Bedding et al (2020) confirmed that a value of Δ𝜈 = 4.70 d −1 gave a reasonably good alignment of the peaks.…”

“…We confirm that Δ𝜈 = 4.68 d −1 produces a ridge on the left-hand-side that we can identify as 𝑙 = 1 modes (see Bedding et al 2020 for discussion of similar stars). Three of these modes were detected by Handler et al (2000), and we see two additional weaker 𝑙 = 1 modes in this ridge. This star is clearly worthy of further study.…”

“…XX Pyx is a multi-periodic pulsator that has been the subject of three ground-based multi-site campaigns (Handler et al 2000, and references therein). The star was not observed by TESS in Cycle 1 because it fell in a gap between fields, but it was observed in Cycle 3 (Sector 35).…”

An Observer's View on the Future of Asteroseismology

“…XX Pyx was observed not only with DSN, but the WET, which happened to discover its pulsations. A different method, the Fourier Transform method was used for finding any regularity among the frequencies (Handler et al, 2000). For 4 CVn an additional instrument, the Automatic Photoelectric Telescope (APT) was also used over the years beside the DSN and WET runs (Breger & Hiesberger, 1999).…”