Results from the first spectropolarimetric survey of magnetism in gamma Dor pulsators
Abstract
Magnetism can fundamentally alter interior processes, such as chemical mixing and angular momentum transport. However, stellar structure and evolutionary models require observational calibrations in order to describe stellar interiors and the role of magnetism. To address this, we have conducted a spectropolarimetric survey of about 50 gDor stars with ESPaDOnS at CFHT to determine the surface magnetic field properties of the gDor population for the first time. Our investigation of the magnetic properties of this sample will be described, including detections and non-detections, plus the space photometry from the TESS and Kepler missions which drove our target selection process and encodes the pulsational signals that enable asteroseismic analysis. The observed small magnetic detection occurrence in gDor stars highlights the need for theoretical and modeling work to understand interactions between magnetic fields and the sub-surface convection zones that drive gDor pulsation.
Full text
Results from the first magnetic survey of pulsating gamma Dor stars Jonathan Labadie-Bartz, DTU Space Coralie Neiner, Rhita Ouazzani, Vichi Antoci
Searching for strongly magnetic gamma Dor pulsators ●Spectropolarimetry : aiming to directly measure surface fields ●Detection threshold of 100 Gauss ●‘Normal’ ‘fossil’ fields are > 300 Gauss ●Observed 50 gamma Dor pulsators with high-SNR high-res spectropolarimetry
Searching for strongly magnetic gamma Dor pulsators ●Spectropolarimetry : aiming to directly measure surface fields ●Detection threshold of 100 Gauss ●‘Normal’ ‘fossil’ fields are > 300 Gauss ●Observed 50 gamma Dor pulsators with high-SNR high-res spectropolarimetry Non-detection Detection Avg. line profile
Searching for strongly magnetic gamma Dor pulsators ●Spectropolarimetry : aiming to directly measure surface fields ●Detection threshold of 100 Gauss ●‘Normal’ ‘fossil’ fields are > 300 Gauss ●Observed 50 gamma Dor pulsators with high-SNR high-res spectropolarimetry Why bother? ●Knowing how magnetism impacts structure and internal processes is best done for pulsators ●Intermediate mass stars excellent testbeds for stellar physics ●Surface magnetic properties are useful boundary conditions
Are there strongly magnetic gamma Dor pulsators?
Are there strongly magnetic gamma Dor pulsators? Nope, seems like not. Or they are very rare. (this is the most important slide)
Pulsators all over the HRD From Aerts 2021 (provided by P´eter P´apics)
There are plenty of strongly magnetic pulsators What about Be stars, gamma Dor stars? Beta Cephei 7 - 15 M☉P modes ~300+ G Henrichs et al. 2013 SPB 3 - 7 M☉G modes ~300+ G Lecoanet et al. 2022, Briquet et al. 2013 Delta Scutis 1.5 - 3 M☉p/g modes ~100+ G Keegan’s talk (paper soon) Solar-like ⪅1 M☉P modes ~20 - 2k G Kochukhov et al. 2020 Red Giants 1.5 - 2 M☉P modes ⪅100 G (but stronger internal fields) Aurière et al. 2015 White dwarfs ~0.3 - 1 M☉G modes MG Dufour et al. 2008 Cepheids ~4 - 20 M☉G modes weak e.g. Polaris, Barron et al. 2022 (talk to me at yesterday’s poster session, #61) (mostly) radiative envelopes + Main Sequence
What about intermediate mass main-sequence stars? Credit: ESO ●Goals: use pulsating and/or spotted A and F stars to study the incidence rates and effects of magnetism The Quest for MAGNetIc Fields in A and F TYpe Stars (PI: Dr. Victoria Antoci; DTU Space) Coralie Neiner, Rhita Ouazzani, (Paris Observatory) in the context magneto-asteroseismology
But we actually got 4 magnetic detections… A quick look at these
MagStar 1: TIC 387515681 = BD+07 442 (A7IV) Obs. CFHT 2019. Photometry hinted at gDor pulsation and rotational modulation Clear + strong magnetic field in Stokes V Hooray! Signal = magnetism Avg. line profile
MagStar 1: TIC 387515681 = BD+07 442 (A7IV) Obs. CFHT 2019. (selected pre-TESS) Photometry hinted at gDor pulsation and rotational modulation Clear + strong magnetic field in Stokes V Hooray! Clear rotation in TESS …but no gamma Dor pulsations after all
MagStar 2: TIC 144276313 = iot Phe (HD 221760, ApSrCrEu) First found to be magnetic in Sikora et al. 2019 (4 mag measurements), but Prot could not be determined and pulsational nature not yet known (again, pre-TESS) Bz = 52 +/- 10 G FAP = 6e-6 Bz = 43 +/- 11 G FAP = 6e-9 From TESS, Prot = 2.638 d
MagStar 2: TIC 144276313 = iot Phe (ApSrCrEu) Bz = 52 +/- 10 G FAP = 6e-6 Bz = 43 +/- 11 G FAP = 6e-9 Rotation dSct pulsation dSct G modes? Not diff freqs
MagStar 3: TIC 172414656 = TYC 2430-1205-1 Cleaned mask Bz = 146 +/- 28 G FAP = 4e-15 - dSct p modes in magnetic Ap primary - g modes in which star? Spectroscopic binary (RV motion of Ap star lines in APOGEE spectra, Porb~10d?)
MagStar 3: TIC 172414656 = TYC 2430-1205-1 - dSct p modes in magnetic Ap primary - g modes in which star? Spectroscopic binary (RV motion of Ap star lines in APOGEE spectra, Porb~10d?)
MagStar 3: TIC 172414656 = TYC 2430-1205-1 Analysis of g mode frequencies hints at frot = 1.1 c/d (~3.5x faster than the magnetic star surface). Presumed l = 1, m=-1 (prograde)
MagStar 4: TIC 229534764 = 78 UMa SB2, narrow lined component is magnetic gDor pulsation is not from a very slow rotator Possible rotation of the broad-lined star? Probably rotation of narrow-lined magnetic star
MagStar 4: TIC 229534764 = 78 UMa Amplitude/frequency vary. Probably unresolved pulsation or dynamo field -> variable spots. Not indicating fossil field.