Nova Scorpii 1941 (V697 Sco): A Probable Intermediate Polar

V697 Sco, the remnant of Nova Scorpii 1941 and currently at V ~ 20.0, is found from photometric observations to have the characteristics of an intermediate polar (IP) with an orbital period (Porb) of 4.49 h and a rotation period (Prot) of 3.31 h. It therefore appears to be a member of the rare class of IPs where Prot ~ Porb, which are probably discless systems. The prominence of the modulation at 0.5 Prot, and its orbital sidebands, indicates two-pole accretion.Comment: To appear in the November 2002 issue of PAS

Magnetic structures of NaLMnWO_6 perovskites (L=La,Nd,Tb)

The magnetic structures of the perovskites NaLaMnWO_6, NaNdMnWO_6, and NaTbMnWO_6, with rocksalt ordering of the Mn/W ions and layered ordering of Na and the rare-earth ions, have been determined by neutron powder diffraction. The manganese moments in NaLaMnWO_6 order below 10 K with a propagation vector of k_14=(1/2,0,1/2) and a moment of 3.99μB per Mn^2+ ion. The Mn^2+ and Nd^3+ ions order simultaneously in NaNdMnWO_6 at 11 K. The resulting magnetic structure is incommensurate with the underlying crystal structure and has the propagation vector of k_5=(0,0.48,1/2). NaTbMnWO_6 undergoes two magnetic phase transitions at 15 and 9 K. The structure determined at 11 K is based on two propagation vectors of k_14=(1/2,0,1/2) and k_5=(0,0.427,1/2). Upon cooling at 6 K the incommensurate vector is no longer present and the moments order only according to k_14. The moments of the Nd and Tb ions are found to remain within the planes of the A-site cations, and in NaTbMnWO_6 the Mn moments also lie within the xy plane. This study not only reveals magnetic structures with previously unexplored topologies but it also sheds light on the intricate coupling between the two magnetic sublattices