DETECTION OF ℓ = 4 AND ℓ = 5 MODES IN 12 YEARS OF SOLAR VIRGO-SPM DATA—TESTS ONKEPLEROBSERVATIONS OF 16 Cyg A AND B

Abstract

We present the detection of = 4 and = 5 modes in power spectra of the Sun, constructed from 12 yr full-disk VIRGO-SPM data sets. A method for enhancing the detectability of these modes in asteroseismic targets is presented and applied to Kepler data of the two solar analogues 16 Cyg A and B. For these targets we see indications of a signal from = 4 modes, while nothing is yet seen for = 5 modes. We further simulate the power spectra of these stars and from this we estimate that it should indeed be possible to see such indications of = 4 modes at the present length of the data sets. In the simulation process we briefly look into the apparent misfit between observed and calculated mode visibilities. We predict that firm detections of at least = 4 should be possible in any case at the end of the Kepler mission. For = 5 we do not predict any firm detections from Kepler data.

Standing on the Shoulders of Dwarfs: the Kepler Asteroseismic LEGACY Sample. I. Oscillation Mode Parameters

“…The value found for the solar ν max of 3078 ± 13 µHz is in agreement with the value of ν max, = 3090 ± 30 µHz by Huber et al (2011). We obtained ∆ν and from a fit to the extracted mode frequencies with an extended version of the asymptotic relation, as in Lund et al (2014a) (see also Mosser et al 2011Mosser et al , 2013. This fit was made in a Bayesian manner using emcee, with a likelihood function assuming Gaussian frequency errors, and with final parameter values and uncertainties given by the posterior medians and HPDs.…”

“…The comparisons do, however, qualitatively match those obtained by Mosser et al (2012) for giants observed by Kepler ; the l = 3 modes disagree most with theory in their results too. Similar discrepancies with theory have also been observed for individual CoRoT and Kepler targets analyzed by Deheuvels et al (2010), Mathur et al (2013), andLund et al (2014a), and the Sun by Salabert et al (2011). Given these discrepancies we discourage the adoption of fixed mode visibilities in peak-bagging exercises.…”

“…This, and the fact that discrepancies between measured and modeled visibilities are found for the Sun (Salabert et al 2011), where the LD is well known as a function of wavelength (Neckel & Labs 1994), indicates that the simplified assumptions concerning the mode physics likely are the main contributor to the discrepancies. We note, however, that modes of l = 3 would be relatively more affected by details of the LD, because of the considerably stronger cancellation for l = 3 modes (total in the absence of LD), compared to modes of l = 1, 2 (Lund et al 2014a). It could also be questioned if the assumption of equipartition of energy between modes of different angular degree holds true.…”

“…In any case Sing (2010) showed from fits to planetary transit curves that model com- putations of LDC generally disagree with those derived empirically. The treatment of the LD is, however, likely a secondary effect -as shown in Lund et al (2014a) the specific LD law adopted (neglecting the linear one) only has minor effects on the visibilities, and the shape has to be changed by a large amount away from the limb in order to take effect. This, and the fact that discrepancies between measured and modeled visibilities are found for the Sun (Salabert et al 2011), where the LD is well known as a function of wavelength (Neckel & Labs 1994), indicates that the simplified assumptions concerning the mode physics likely are the main contributor to the discrepancies.…”

Observational techniques to measure solar and stellar oscillations

“…This is because the fitting models do not usually account for the presence of "leakage" from = 4 and 5 into the fitting window (as we also omitted to do it here), although they can be measured in, for example, Sun-as-a-star observations using 12 years of VIRGO/SPM data (e.g. Lund et al 2014). …”