Asteroseismology and Spectropolarimetry of the Exoplanet Host Star λ Serpentis

Metcalfe, Travis S.; Buzasi, Derek; Huber, Daniel; Pinsonneault, Marc H.; van Saders, Jennifer L.; Ayres, Thomas R.; Basu, Sarbani; Drake, Jeremy J.; Egeland, Ricky; Kochukhov, Oleg; Petit, Pascal; Saar, Steven H.; See, Victor; Stassun, Keivan G.; Li, Yaguang; Bedding, Timothy R.; Breton, Sylvain N.; Finley, Adam J.; García, Rafael A.; Kjeldsen, Hans; Nielsen, Martin B.; Ong, J. M. Joel; Rørsted, Jakob L.; Stokholm, Amalie; Winther, Mark L.; Clark, Catherine A.; Godoy-Rivera, Diego; Ilyin, Ilya V.; Strassmeier, Klaus G.; Jeffers, Sandra V.; Marsden, Stephen C.; Vidotto, Aline A.; Baliunas, Sallie; Soon, Willie

doi:10.3847/1538-3881/acf1f7

Cited by 7 publications

(2 citation statements)

References 122 publications

(149 reference statements)

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“…The TESS mission observed 51 Peg at a 20 s cadence during Sector 56 (2022 September 1-30). Following the procedures described in Metcalfe et al (2023a), we extracted a custom light curve from the TESS target pixel files, substantially improving the signal-to-noise ratio (S/N) compared to the data product from the Science Processing Operations Center. Briefly, this procedure starts with a light curve from the pixel with the most signal and includes additional pixels one at a time until the S/N no longer improves.…”

Section: Asteroseismologymentioning

confidence: 99%

Weakened Magnetic Braking in the Exoplanet Host Star 51 Peg

Metcalfe,

Strassmeier,

Ilyin

et al. 2024

ApJL

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The consistently low activity level of the old solar analog 51 Peg not only facilitated the discovery of the first hot Jupiter, but also led to the suggestion that the star could be experiencing a magnetic grand minimum. However, the 50 yr time series showing minimal chromospheric variability could also be associated with the onset of weakened magnetic braking (WMB), where sufficiently slow rotation disrupts cycling activity and the production of large-scale magnetic fields by the stellar dynamo, thereby shrinking the Alfvén radius and inhibiting the efficient loss of angular momentum to magnetized stellar winds. In this Letter, we evaluate the magnetic evolutionary state of 51 Peg by estimating its wind braking torque. We use new spectropolarimetric measurements from the Large Binocular Telescope to reconstruct the large-scale magnetic morphology, we reanalyze archival X-ray measurements to estimate the mass-loss rate, and we detect solar-like oscillations in photometry from the Transiting Exoplanet Survey Satellite, yielding precise stellar properties from asteroseismology. Our estimate of the wind braking torque for 51 Peg clearly places it in the WMB regime, driven by changes in the mass-loss rate and the magnetic field strength and morphology that substantially exceed theoretical expectations. Although our revised stellar properties have minimal consequences for the characterization of the exoplanet, they have interesting implications for the current space weather environment of the system.

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Section: Asteroseismologymentioning

confidence: 99%

Weakened Magnetic Braking in the Exoplanet Host Star 51 Peg

Metcalfe,

Strassmeier,

Ilyin

et al. 2024

ApJL

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“…The Transiting Exoplanet Survey Satellite (TESS; Ricker et al 2014) observed Deneb in Sectors 41, 55, and 56 at 120 s cadence. We used the Asteroseismology-Optimized Pipeline software to align and process the photometric data (Buzasi et al 2016;Nielsen et al 2020;Metcalfe et al 2023). This essentially constructs an optimized photometric aperture one pixel at a time, minimizing the high-frequency noise in the resulting light curve, which is then iteratively detrended against centroid position and background-the result is a light curve that is consistently significantly better than the SPOC product for bright and/or saturated targets.…”

Section: Observationsmentioning

confidence: 99%

Deneb Is a Large-amplitude Polarimetric Variable

Cotton,

Bailey,

Perkins

et al. 2024

ApJL

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We write to report the discovery that Deneb is a large-amplitude polarization variable. Over a ∼400 days time span from 2022 August Deneb’s polarization was typically around 3900 parts per million (ppm) in the SDSS g ′ band. Yet, it varied by several hundred parts per million in an irregular way on a timescale of weeks. The largest polarization change, amounting to 2500 ppm, occurred shortly after the last pulsation “resumption” event identified by Abt et al. in TESS photometry. The relationship between the observed polarization—particularly corresponding to the resumption event—and its brightness and H α spectra suggests a mechanism involving density changes in its wind and/or extended atmosphere. Smaller effects due to pulsations are not ruled out, and further study is recommended.

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Multi-scale magnetic field investigation of the M-dwarf eclipsing binary CU Cancri

Hahlin,

Kochukhov,

Rains

et al. 2024

A&A

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We aim to characterise the magnetic field of the eclipsing binary CU Cancri, which consists of two M-dwarf components. The determination of the magnetic field parameters of this target enables comparisons with both observations of similar stars and theoretical predictions of the magnetic field strength in CU Cnc. The target therefore provides an excellent opportunity to test our understanding of the generation of magnetic fields in low-mass stars and its impact on stellar structure. We used spectropolarimetric observations obtained with ESPaDOnS at the CFHT to investigate the magnetic properties of CU Cnc. To improve the signal, we used least-squares deconvolution (LSD) to create average line profiles. From these LSD profiles, we extracted information about the radial velocities of the components, significantly expanding the number of radial velocity measurements available and allowing for a determination of the orbital parameters. Stokes $V$ LSD profiles were used with Zeeman Doppler imaging to obtain the large-scale magnetic field structures of the two components. We also used detailed polarised radiative transfer modelling to investigate the small-scale fields, by Zeeman-splitting magnetically sensitive Ti I lines in non-polarised spectra. We obtain both the small- and large-scale magnetic field properties of the two components. The large-scale fields are dominantly poloidal, and both components have an average strength of approximately 100\,G. This analysis of the large-scale fields likely suffers from some amount of hemisphere degeneracy due to the high inclination of the target, which would cause the large-scale field strength of the components to be underestimated. Both components also show unusual magnetic field configurations compared to stars with similar parameters: the primary is weakly axisymmetric (sim \,10\,<!PCT!>), and the secondary has a strong toroidal contribution (sim \,20\,<!PCT!>). The small-scale fields are significantly stronger, 3.1 and 3.6\,kG for the primary and secondary, respectively. This measurement is in excellent agreement with surface field strength predictions for CU Cnc from magneto-convective stellar evolution models. These results indicate that magnetic fields could play a significant role in the radius inflation due to convective inhibition.

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Asteroseismology and Spectropolarimetry of the Exoplanet Host Star λ Serpentis

Cited by 7 publications

References 122 publications

Weakened Magnetic Braking in the Exoplanet Host Star 51 Peg

Weakened Magnetic Braking in the Exoplanet Host Star 51 Peg

Deneb Is a Large-amplitude Polarimetric Variable

Multi-scale magnetic field investigation of the M-dwarf eclipsing binary CU Cancri

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