HR 7355 and HR 5907 The MOST rapidlyrotating

HR 7355 and HR 5907: The MOST rapidly-rotating magnetic stars Gregg Wade (RMC) on behalf of the Mi. Me. S Collaboration

The Mi. Me. S Project Magnetism in Massive Stars

Discovering the most rapidly rotating magnetic star(s) • Before Mi. Me. S the B 2 Ve He-strong star HD 37017 fastest rotating magnetic massive star • P~0. 9 d • Mi. Me. S 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 – Mi. Me. S discovers a nearly-identical rapidly rotating magnetic star (HR 5907, B 2 V) • P=0. 50830 d -> NEW RECORD HOLDER!!

HR 7355 - B 2 Ve P=0. 5214404 d

HR 5907 - B 2 Ve

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

MOST observations of HR 7355 and HR 5907 – 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

Parameters of HR 7355 and HR 5907 – HR 7355 • • RA 19 h 24 Dec -28 deg V = 6. 0 Prot = 0. 5214404 d • HR 5907 • RA 15 h 53 • Dec -24 deg • V = 5. 4 • Prot = 0. 50283 d