It is widely believed that Type Ia supernovae ( SN Ia ) originate in binary systems where a white dwarf accretes material from a companion star until its mass approaches the Chandrasekhar mass and carbon is ignited in the white dwarf ’ s core .
This scenario predicts that the donor star should survive the supernova explosion , providing an opportunity to understand the progenitors of Type Ia supernovae.In this paper we argue that rotationis a generic signature expected of most non-giant donor stars that is easily measurable . ( 36 ) examined stars in the center of the remnant of SN 1572 ( Tycho ’ s SN ) and showed evidence that a subgiant star ( Star-G by their naming convention ) near the remnant ’ s centre was the system ’ s donor star .
We present high-resolution ( R \simeq 40000 ) spectra taken with the High Dispersion Spectrograph on Subaru of this candidate donor star and measure the star ’ s radial velocity as 79 \pm 2 km s ^ { -1 } with respect to the LSR and put an upper limit on the star ’ s rotation of 7.5 km s ^ { -1 } .
In addition , by comparing images that were taken in 1970 and 2004 , we measure the proper motion of Star-G to be \mu _ { l } = -1.6 \pm 2.1 mas yr ^ { -1 } and \mu _ { b } = -2.7 \pm 1.6 mas yr ^ { -1 } .
We demonstrate that all of the measured properties of Star-G presented in this paper are consistent with those of a star in the direction of Tycho ’ s SN that is not associated with the supernova event .
However , we discuss an unlikely , but still viable scenario for Star-G to be the donor star , and suggest further observations that might be able to confirm or refute it .