The Delta Scuti star 38 Eri from the ground and from space

Abstract

We present and discuss the pulsational characteristics of the Delta Scuti star 38 Eri from photometric data obtained at two widely spaced epochs, partly from the ground (1998) and partly from space (MOST, 2011). We found 18 frequencies resolving the discrepancy among the previously published frequencies. Some of the frequencies appeared with different relative amplitudes at two epochs, however, we carried out investigation for amplitude variability for only the MOST data. Amplitude variability was found for one of three frequencies that satisfy the necessary frequency criteria for linear-combination or resonant-mode coupling. Checking the criteria of beating and resonant-mode coupling we excluded them as possible reason for amplitude variability. The two recently developed methods of rotational-splitting and sequence-search were applied to find regular spacings based only on frequencies. Doublets or incomplete multiplets with l = 1, 2 and 3 were found in the rotational splitting search. In the sequence search method we identified four sequences. The averaged spacing, probably a combination of the large separation and the rotational frequency, is 1.724 ± 0.092 d −1 . Using the spacing and the scaling relationρ = [0.0394, 0.0554] gcm −3 was derived. The shift of the sequences proved to be the integer multiple of the rotational splitting spacing. Using the precise MOST frequencies and multi-colour photometry in a hybrid way, we identified four modes with l = 1, two modes with l = 2, two modes with l = 3, and two modes as l = 0 radial modes.

Pulsation and Rotation of the EL CVn-type Eclipsing Binary 1SWASP J024743.37-251549.2

“…This shows that the phase difference decreases with the increase in the value and that the = 3 mode has a high amplitude ratio, although the observation errors are not small. These tendencies are consistent with the theoretical predictions (Watson 1988;Moya et al 2004) and other observation results (for example, Breger et al 2017;Paparó et al 2018). Therefore, the theoretical pulsation modes identified in this study appear to be reliable.…”

An Observer's View on the Future of Asteroseismology

“…However, a new observable, the shift between the sequences was derived. The fact that some shifts between the sequences were integer multiples of the rotational split might suggest a possible resonance effect between eigenmodes and rotation as a selection mechanism (Paparó et al, 2018). Using 1860 CoRoT δ Scuti stars, a common regular pattern was found in agreement with island modes featured by theoretical non-perturbative treatment of fast rotation (Michel et al, 2017).…”

“…These were the Delta Scuti Network (DSN) founded by M. Breger, and STEllar PHotometry International (STEPHI) headed by E. Michel as the coordinator. However, individual organizations were also successful (Paparo et al (1996), Paparó & Sterken (2000) for θ Tuc, and Paparó et al (2018) for 38 Eri, based on a multisite campaign from 1998 and MOST observation from 2011). The ground-based campaigns collected data in at least two colours, hoping for the possibility of mode identification.…”

Challenges in 2D Stellar Modeling

“…In cases where a rotational multiplet can be identified, the rotation frequency of the star can be determined, independent of the inclination. This type of analysis has been done for stars across the HR diagram (Charpinet et al, 2018;Paparó et al, 2018). If multiple triplets are detected, they can be expected to probe different radii inside the star, and it may be possible to probe the rotation profile (Aerts et al, 2003;Suárez et al, 2010).…”