HR 7355 and HR 5907: The MOST rapidly-rotating magnetic stars

Gregg Wade (RMC)on behalf of the MiMeS Collaboration

The

MiMeS Project

Magnetism in Massive Stars

The

MiMeS Project

Magnetism in Massive Stars

Discovering the most rapidly rotating magnetic star(s)

• Before MiMeS the B2Ve He-strong star HD 37017 fastest rotating magnetic massive star• P~0.9 d

• MiMeS discovers most rapidly rotating magnetic star Sept/09 (HR 7355, Oksala et al. 2010)• P= 0.521 4404 d <- Based on HIPPARCOS/CTIO

• Feb/10 – MiMeS discovers a nearly-identical rapidly rotating magnetic star (HR 5907, B2V)• P=0.50830 d -> NEW RECORD HOLDER!!

P=0.5214404 d

HR 7355 - B2Ve

HR 5907 - B2Ve

Rotationally-supported magnetospheres

Doppler Imaging

He I

Significance of these results

– Extreme testbeds– Near twins

– Timescales and mechanisms for magnetic braking– Magnetospheric structure, density, emissivity– Role of rapid rotation and field geometry in channeling

and confining winds of massive stars– Link to Be stars: Keplerian vs. rigid discs– Role of slow rotation in generating photospheric

chemical peculiarities

– High precision lightcurves are a vital complement to spectroscopic and polarimetric monitoring:• Confirm and refine rotational periods• Test limits of RRM model in ultra-rapid rotation regime• Constrain magnetospheric geometry and density• Disentangle magnetospheric vs spot contributions• Provide baseline for direct spindown measurement

• Technical requirements:• 1 mmag errors, 1% (?) phase sampling (7 min integrations)• Acquired over multiple subsequent cycles or continuously

MOST observations ofHR 7355 and HR 5907

– HR 7355• RA 19h24• Dec -28 deg• V = 6.0• Prot = 0.5214404 d

• HR 5907• RA 15h53• Dec -24 deg• V = 5.4• Prot = 0.50283 d

Parameters ofHR 7355 and HR 5907