R. Mark Crockett, Justyn R. Maund, Stephen J. Smartt, Seppo Mattila, Andrea Pastorello, Jonathan Smoker, Andrew W. Stephens, Johan Fynbo, John J. Eldridge, I. J… 展开作者
R. Mark Crockett, Justyn R. Maund, Stephen J. Smartt, Seppo Mattila, Andrea Pastorello, Jonathan Smoker, Andrew W. Stephens, Johan Fynbo, John J. Eldridge, I. John Danziger, Christopher R. Benn
备注：
12 pages, 3 figures, resolution of fig 1. has been reduced, some revision based on referee's comments, Accepted ApJL 27 Nov 2007
We report our attempts to locate the progenitor of the peculiar type Ic SN 2007gr in HST pre-explosion images of the host galaxy, NGC 1058. Aligning adaptive optics Altair/NIRI imaging of SN 2007gr from the Gemini (North) Telescope with the pre-explosion HST WFPC2 images, we identify the SN position on the HST frames with an accuracy of 20 mas. Although nothing is detected at the SN position we show that it lies on the edge of a bright source, 134+/-23 mas (6.9 pc) from its nominal centre. Based on its luminosity we suggest that this object is possibly an unresolved, compact and coeval cluster and that the SN progenitor was a cluster member, although we note that model profile fitting favours a single bright star. We find two solutions for the age of this assumed cluster; 7-/+0.5 Myrs and 20-30 Myrs, with turn-off masses of 28+/-4 Msun and 12-9 Msun respectively. Pre-explosion ground-based K-band images marginally favour the younger cluster age/higher turn-off mass. Assuming the SN progenitor was a cluster member, the turn-off mass provides the best estimate for its initial mass. More detailed observations, after the SN has faded, should determine if the progenitor was indeed part of a cluster, and if so allow an age estimate to within ~2 Myrs thereby favouring either a high mass single star or lower mass interacting binary progenitor.
The Radio Lifetime of Supernova Remnants and the Distribution of Pulsar Velocities at Birth
我们对三颗年轻超新星周围的磁场进行了VLA成像，发现了两颗新的超新星遗迹，并确认了第三颗。我们认为，在至少两种情况下，也许是第三种情况下，超新星与这些超新星遗迹的物理联系。对所有已知的年轻超新星的回顾表明，大多数都与超新星遗迹有关。我们表明，典型的密度的星际介质的超新星遗迹正在演变的密度为0.2厘米$^{-3}$，而不是低的值0.01厘米$^{-3}$已从其他研究计算，并在一个相当长的射电寿命的超新星遗迹的结果。超新星遗迹的形态和超新星的位置都意味着这些年轻的超新星大多数都具有很大的横向速度（$\sim$ 500 km s $^{-1}$）。脉冲星速度分布中的这种高速度平均值似乎是脉冲星出生时的一般属性，由于选择效应，在自行研究中看不到。我们探讨了这一结果的影响，因为它涉及到这些速度的起源和银河系分布的星系。高速超新星可以在很短的时间内逃离超新星遗迹，与遗迹的寿命相当，甚至可能在延长遗迹的可观测无线电寿命方面发挥作用。很大一部分将能够逃离银河系的磁盘，产生一个扩展的光环人口。
Open Cluster Birth Analysis and Multiple Spiral Arm Sets in the Milky Way
The Milky Way spiral arm dynamics is studied using the birth place of open clusters . We separately study the nearby spiral arms, and find evidence for multiple spiral sets. In particular, the Sagittarius-Carina arm appears to be a superposition of two sets. The first has a pattern speed of Omega_P,Carina,1=16.5^{+1.2}_{-1.4sys}+/-1.1_{stat} (km/s)/kpc, while the second has Omega_P,Carina,2=29.8^{+0.6}_{-1.3sys}+/-1.3_{stat} (km/s)/kpc. The Perseus arm located at larger galactic radii exhibits only one clear set with Omega_P,Perseus=20.0^{+1.7}_{-1.2sys}+/-1.6_{stat} (km/s)/kpc. The Perseus an…
