First Results from the Hertzsprung SONG Telescope: Asteroseismology of the G5 Subgiant Star μ Herculis*

Grundahl, F.; Andersen, M. Fredslund; Christensen‐Dalsgaard, J.; Antoci, V.; Kjeldsen, H.; Handberg, R.; Houdek, G.; Bedding, Timothy R.; Pallé, P. L.; Jessen-Hansen, J.; Aguirre, V. Silva; White, T. R.; Frandsen, S.; Albrecht, S.; Andersen, M. I.; Arentoft, T.; Brogaard, K.; Chaplin, W. J.; Harpsøe, K.; Jørgensen, U. G.; Karovicova, I.; Karoff, C.; Rasmussen, P; Lund, M. N.; Lundkvist, M.; Skottfelt, J.; Sørensen, Anton Norup; Tronsgaard, R.; Weiss, Eric R.

doi:10.3847/1538-4357/836/1/142

Cited by 79 publications

(67 citation statements)

References 79 publications

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“…The Hertzsprung SONG 1-m telescope (Andersen et al 2014;Grundahl et al 2017) at Observatorio del Teide on Tenerife was used to obtain high-resolution (R = 90000) échelle spectra of HR 7322 on March 13 and September 16, 2016. Extraction of spectra, flat fielding and wavelength calibration were carried out with the SONG data reduction pipeline.…”

Section: Spectroscopymentioning

confidence: 99%

The subgiant HR 7322 as an asteroseismic benchmark star

Stokholm

Nissen

Aguirre

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present an in-depth analysis of the bright subgiant HR 7322 (KIC 10005473) using Kepler short-cadence photometry, optical interferometry from CHARA, high-resolution spectra from SONG, and stellar modelling using grids and the Bayesian grid-fitting algorithm . HR 7322 is only the second subgiant with high-quality Kepler asteroseismology for which we also have interferometric data. We find a limb-darkened angular diameter of 0.443 ± 0.007 mas, which, combined with a distance derived using the parallax from Gaia DR2 and a bolometric flux, yields a linear radius of 2.00 ± 0.03 R and an effective temperature of 6350 ± 90 K. HR 7322 exhibits solar-like oscillations, and using the asteroseismic scaling relations and revisions thereof, we find good agreement between asteroseismic and interferometric stellar radius. The level of precision reached by the careful modelling is to a great extent due to the presence of an avoided crossing in the dipole oscillation mode pattern of HR 7322. We find that the standard models predict a stellar radius systematically smaller than the observed interferometric one and that a sub-solar mixing length parameter is needed to achieve a good fit to individual oscillation frequencies, interferometric temperature, and spectroscopic metallicity.

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Section: Spectroscopymentioning

confidence: 99%

The subgiant HR 7322 as an asteroseismic benchmark star

Stokholm

Nissen

Aguirre

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…The spectra were reduced and calibrated using the SONG pipeline. Details of the Hertzsprung telescope characteristics and reduction pipeline are given in Andersen et al (2014) and Grundahl et al (2017). All observations were obtained using an iodine cell for precise wavelength calibration.…”

Section: Observations Of Hd 122563mentioning

confidence: 99%

First detection of oscillations in the Halo giant HD 122563: Validation of seismic scaling relations and new parameters

Creevey

Grundahl

Thévenin

et al. 2019

A&A

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Aims. The nearby metal-poor giant HD 122563 is an important astrophysical laboratory for which to test stellar atmospheric and interior physics. It is also a benchmark star for which to calibrate methods to apply to large scale surveys. Recently it has been remeasured using various methodologies given the new high precision instruments at our disposal. However, inconsistencies in the observations and models have been found. In order to better characterise this star using complementary techniques we have been measuring its radial velocities since 2016 using the Hertzsprung telescope (SONG network node) in order to detect oscillations. Methods.Results. In this work we report the first detections of sun-like oscillations in this star, and to our knowledge, a detection in the most metal-poor giant to date. We apply the classical seismic scaling relation to derive a new surface gravity for HD 122563 of log g ν = 1.39 ± 0.01 dex. Reasonable constraints on the mass imposed by its PopII giant classification then yields a radius of 30.8 ± 1.0 R ⊙ . By coupling this new radius with recent interferometric measurements we infer a distance to the star of 306 ± 9 pc, which places it further away than previously thought and inconsistent with the Hipparcos parallax. Independent data from the Gaia mission corroborates the distance hypothesis (d GDR2 = 290 ± 5 pc), and thus the updated fundamental parameters. Conclusions. We confirm the validity of the seismic scaling relation without corrections for surface gravity in metal-poor and evolved star regimes. The remaining discrepancy of 0.04 dex between log g GDR2 (= 1.43 ± 0.03) reduces to 0.02 dex by applying corrections to the scaling relations based on the mean molecular weight and adiabatic exponent. The new constraints on the HR diagram (L ⋆ν = 381 ± 26) significantly reduce the disagreement between the stellar parameters and evolution models, however, a discrepancy on the order of 150 K still exists. Fine-tuned stellar evolution calculations show that this can be reconciled by changing the mixing-length parameter by an amount (-0.35) that is in agreement with predictions from recent 3D simulations and empirical results. Asteroseismic measurements are continuing, and analysis of the full frequency data complemented by a distance estimate promises to bring important constraints on our understanding of this star and of the accurate calibration of the seismic scaling relations in this regime.

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“…The spectra were reduced and calibrated using the SONG pipeline and an iodine cell for precise wavelength calibration. For more details about the Hertzsprung telescope characteristics and reduction pipeline we refer to Andersen et al (2014); Grundahl et al (2017). Given that the star has an apparent magnitude of V ≃ 6.1, it was chosen to use a spectral resolution of 90 000 and an exposure time of 600 s throughout the run.…”

Section: Observationsmentioning

confidence: 99%

Acoustic oscillations and dynamo action in the G8 sub-giant EK Eridani^,

Bonanno

Corsaro

Sordo

et al. 2019

A&A

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We present further evidence of the presence of acoustic oscillations on the slowly-rotating, over-active G8 sub-giant EK Eri. This star was observed with the 1-m Hertzsprung SONG telescope, at the Observatorio del Teide for two different runs of 8 and 13 nights, respectively, and separated by about a year. We determined a significant excess of power around ν max = 253 ± 3 µHz in the first observing run and we were able to determine the large separation ∆ν = 16.43 ± 0.22 µHz. No significant excess of power was instead detected in a subsequent SONG observing season, as also supported by our analysis of the simultaneous TESS photometric observations. We propose a new amplitude-luminosity relation in order to account for the missing power in the power spectrum. Based on the evolutionary stage of this object we argue that standard α 2 Ω dynamo cannot be excluded as a possible origin for the observed magnetic field.

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First Results from the Hertzsprung SONG Telescope: Asteroseismology of the G5 Subgiant Star μ Herculis*

Cited by 79 publications

References 79 publications

The subgiant HR 7322 as an asteroseismic benchmark star

The subgiant HR 7322 as an asteroseismic benchmark star

First detection of oscillations in the Halo giant HD 122563: Validation of seismic scaling relations and new parameters

Acoustic oscillations and dynamo action in the G8 sub-giant EK Eridani^,

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First Results from the Hertzsprung SONG Telescope: Asteroseismology of the G5 Subgiant Star μ Herculis*

Cited by 79 publications

References 79 publications

The subgiant HR 7322 as an asteroseismic benchmark star

The subgiant HR 7322 as an asteroseismic benchmark star

First detection of oscillations in the Halo giant HD 122563: Validation of seismic scaling relations and new parameters

Acoustic oscillations and dynamo action in the G8 sub-giant EK Eridani,

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Acoustic oscillations and dynamo action in the G8 sub-giant EK Eridani^,