1 / 10

Magnetic fields in cool objects

Magnetic fields in cool objects. Sofia Randich INAF-Osservatorio di Arcetri. OUTLINE. Why magnetic fields? Some scientific cases How – Why near-IR? Previous work Technical requirements. Why magnetic fields?. Crucial role in stellar physics across the entire

leilani-snyder
Download Presentation

Magnetic fields in cool objects

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Magnetic fields in cool objects Sofia Randich INAF-Osservatorio di Arcetri

  2. OUTLINE • Why magnetic fields? • Some scientific cases • How – Why near-IR? • Previous work • Technical requirements

  3. Why magnetic fields? Crucial role in stellar physics across the entire HR diagram • Non-thermal radio emission in early-type stars • Jets in young stellar objects • Activity in the Sun, solar-type, and lower mass stars (heating of the upper atmospheres) • Mass loss and angular momentum evolution • Li depletion/preservation? (D’ Antona et al. 2000)

  4. Coronal activity vs. age M dwarfs with Mass > 0.3 MSun Median luminosities: Alpha Per: log Lx=29.00 erg/s Pleiades: log Lx=29.03 erg/s Hyades: log Lx=28.37 erg/s (Randich 1999) What about the evolution of magnetic field strength and filling factor? And the rotation – B field relation?

  5. Saturation Hyades M dwarfs Stauffer et al (1997b) Saturation of B? Saturation of f? Why two branches? Stauffer et al. (1997a)

  6. Activity in very cool objects Rotation-activity relation appears to break (and even to reverse) for very late-M and L-type dwarfs (Basri 2000, Gizis et al. 2000), though with exceptions (e.g., Berger 2002; Schmitt & Liefke 2002; Liebert et al. 2003) • Insufficient conductivity due to low ionization level in the photoshere? • Too low Rossby numbers (dynamo unable to operate)? • Large scale, relatively stable field?

  7. How can one measure B fields? Zeeman effect: 1) Circular polarization of magnetically sensitive lines 2) Zeeman broadening of magnetically sensitive lines: Split of σ components: Δλ=kλ2gB (note the dependence on λ2) F(λ)=FB(λ)*f + FQ(λ)*(1-f)

  8. Advantages of near-IR Higher accuracy, lower fields • ΔλB λ2 • Δλdopp  λ • Continuous opacity lowest in H band Lines form deeper in the atmosphere Stronger B • Line density lower Near-IR mgnetically sensitive lines: Fe I @ 1.565 μ, Ti I @ 2.2 μ, For VLMs and BDs FeH most promising candidate (but Lande factors Need to be empirically calibrated)

  9. Previous work Very little (for cool stars): • First measurement AD Leo – B=3.8±0.3 KG, f=77 (Saar & Linsky 1986) • A few dMe stars (mostly from optical spectra) with very strong B (a few KG) (Johns-Krull 2000 and ref. therein) • Ε Eri (near-IR, Johns-Krull & Valenti 1996) • A few PMS stars (Johns-Krull 2000 and ref. therein) • A K3 Pleiades member (near IR – Valenti & Johns-Krull 2003, 2004)

  10. Technical requirements **S/N** **Resolution** B=1.5 KG: 2Δλ=0.1nm For the Fe I 1.565 μ **Large spectral coverage ** Saar (1988) M dwarfs in the Hyades: H~9-11; Field dwarfs later than M9: MH=10.9-12.1 (Zapatero Osorio et al. 1997)

More Related