Magnetic fields in Intermediate Mass T-Tauri Stars

Transcription

1 Magnetic fields in Intermediate Mass T-Tauri Stars Alexis Lavail Uppsala Universitet Supervisors: Oleg Kochukhov & Nikolai Piskunov Alexis Lavail SU/UU PhD #1/21

2 Stellar magnetic fields cool stars against hot stars For cool stars such as the Sun, the magnetic field is: Hot stars tend to present magnetic fields which are: > rapidly evolving > complex > weak > very strong > organized > roughly dipolar Alexis Lavail SU/UU PhD #2/21

3 Stellar magnetic fields cool stars against hot stars DYNAMO-GENERATED FIELD FOSSIL FIELD For cool stars such as the Sun, the magnetic field is: Hot stars tend to present magnetic fields which are: > rapidly evolving > complex > weak > very strong > organized > roughly dipolar Alexis Lavail SU/UU PhD #3/21

4 Stellar magnetic fields dynamo against fossil fields DYNAMO-GENERATED FIELD? FOSSIL FIELD Uncertain origin of fossil field.. > galactic magnetic field captured by the star? > leftovers from dynamo processes? Alexis Lavail SU/UU PhD #4/21

5 Intermediate Mass T-Tauri stars (IMTTS) in stellar evolution context proto-star T-Tauri star Main-Sequence star Pre-Main Sequence (PMS) Main Sequence (MS) T-Tauri stars: > roughly between 0.5 and 3.5 solar masses > accreting material from surrounding protoplanetary disc > fueled by gravitational energy from star's contraction Intermediate Mass T-Tauri Stars: > around 2 solar masses > progenitors of Herbig Ae/Be stars and ultimately A/B type stars Alexis Lavail SU/UU PhD #5/21

6 Intermediate Mass T-Tauri stars (IMTTS) in stellar evolution context HR diagram from Evelyne Alecian Alexis Lavail SU/UU PhD #6/21

7 Intermediate Mass T-Tauri stars (IMTTS) in stellar evolution context HR diagram from Evelyne Alecian Alexis Lavail SU/UU PhD #7/21

8 Intermediate Mass T-Tauri stars (IMTTS) in stellar evolution context HR diagram from Evelyne Alecian Alexis Lavail SU/UU PhD #8/21

9 Intermediate Mass T-Tauri stars (IMTTS) in stellar evolution context IMTTS HR diagram from Evelyne Alecian Alexis Lavail SU/UU PhD #9/21

10 Intermediate Mass T-Tauri stars (IMTTS) and their magnetic field IMTTS Herbig Ae/Be Ap/Bp star both large scale and complex magnetic fields ~10 % host strong large-scale magnetic fields 5-10 % host strong large-scale magnetic fields Low-Mass TTauri Stars complex magnetic fields generated by dynamo processes Alexis Lavail SU/UU PhD #10/21 Science case: Studying evolution of magnetic field with the age of IMTTS to see if: fields goes from dynamo to fossil dynamo fields gradually disappear while fossil fields stay in constant proportion

11 Observing stellar magnetic field Zeeman effect in stellar spectra Zeeman effect First observed by Zeeman in 1896 First observable > Spectral lines split into several components when a magnetic field is present Δλ = g λ² B Δλ is the component shift in nm λ is the wavelength in μ m g is the Landé factor of the component B is the m.f. strength in kg >> the component shift is proportional to the magnetic field strength, wavelength, and Landé factor Alexis Lavail SU/UU PhD #11/21

12 Observing stellar magnetic field Zeeman effect in stellar spectra Second observable > The π and σ components exhibit linear or/and circular polarization according to the magnetic field orientation w.r.t. the line of sight. Image from "Observations of Cool-Star Magnetic Fields" by Ansgar Reiners Alexis Lavail SU/UU PhD #12/21

13 Detection method spectral synthesis with no magnetic field Vienna Atomic Line Database VALD SYNMAST Atomic data Spectral synthesis code Wavelengths, Landé factors, oscillator strengths, energy levels etc No magnetic field MARCS Model atmosphere Effective temperature & surface gravity Alexis Lavail SU/UU PhD #13/21 synthetic spectrum

14 Detection method Comparison between synthetic and observed spectra Vienna Atomic Line Database VALD SYNMAST Atomic data Spectral synthesis code Wavelengths, Landé factors, oscillator strengths, energy levels etc No magnetic field synthetic spectrum MARCS Comparison Model atmosphere Effective temperature & surface gravity observed spectrum Alexis Lavail SU/UU PhD #14/21

15 Detection method spectral synthesis with magnetic field SYNMAST Spectral synthesis code synthetic spectrum strength of the magnetic field Use of weakly sensitive and non sensitive to constrain nonmagnetic broadening Comparison observed spectrum Alexis Lavail SU/UU PhD #15/21

16 Improving atomic data with the Sun as a benchmark Alexis Lavail SU/UU PhD #16/21 H-band

17 Improving atomic data with the Sun as a benchmark Alexis Lavail SU/UU PhD #17/21 H-band

18 Observations Spectra in H and K band H-band K-band Our spectra are acquired: with the CRIRES instrument sitting at the VLT for ~10 stars with effective temperature roughly between 4000 K and 6000 K in 2 infrared spectral bands: H-band (around 1.56 µm) and K-band (around 2.31 µm) Alexis Lavail SU/UU PhD #18/21

19 Real data ylw19 H-band no magnetic field 2 kg radial magnetic field Alexis Lavail SU/UU PhD #19/21

20 Future work Now what? Work on all the spectra and try to get upper limit on magnetic field strength Involvement in the upgrade of the CRIRES instrument Alexis Lavail SU/UU PhD #20/21

21 Thanks for listening Alexis Lavail SU/UU PhD #21/21