RXJ1856 .5-3754和RXJ0720 .4-3125的原点--使用新的视差测量进行更新
The origin of RXJ1856.5-3754 and RXJ0720.4-3125 -- updated using new parallax measurements
摘要：
RXJ 1856和RXJ 0720是仅有的两颗年轻的孤立射电宁静中子星，它们的三角视差被测量过。由于它们在X射线中的热发射的检测，它们是重要的研究NS冷却和探测理论冷却模型。因此，准确确定其年龄至关重要。最近，获得了RXJ 1856和RXJ 0720的新视差测量结果。考虑到NS可能起源于因不对称超新星而被破坏的二元系统，我们试图识别可能是NS祖先前伴星的失控恒星。这样的识别将有力地支持特定的出生场景与时间和地点。我们追溯每一个NS，逃逸星和可能的诞生协会的中心，以找到近距离接触。运动学年龄则由自相遇以来的时间给出。我们使用蒙特卡罗模拟来解释观测的不确定性。使用RXJ 1856最近的视差测量值8.16+/-0.80 mas，我们发现它起源于0.46+/-0.05 Mar前的U Sco协会。这略高于我们之前报告的值（0.3百万年）。我们的结果得到了它目前径向速度的有力支持，我们预测它的径向速度为6+19-20 km/s。这意味着与弓形激波一致的倾角为88+/-6度。没有发现合适的逃逸恒星是RXJ 1856的潜在前伴星。利用最近对RXJ 0720的视差测量值3.6+/-1.6 mas，我们发现该NS可能出生于Tr 10 0.85+/-0.15 Mar前。这略大于使用旧视差值（0.5百万年）获得的值。我们建议B 0逃逸超巨星HIP 43158作为前伴星的候选者。那么，RXJ 0720到太阳的距离应该是286+27-23 pc，与最近的测量结果一致。我们预计RXJ 0720的径向速度为-76+34-17 km/s。
英文摘要：
RXJ1856 and RXJ0720 are the only young isolated radio-quiet neutron stars (NSs) for which trigonometric parallaxes were measured. Due to detection of their thermal emission in X-rays they are important to study NS cooling and to probe theoretical cooling models. Hence, a precise determination of their age is essential. Recently, new parallax measurements of RXJ1856 and RXJ0720 were obtained. Considering that NSs may originate from binary systems that got disrupted due to an asymmetric supernova, we attempt to identify runaway stars which may have been former companions to the NS progenitors. Such an identification would strongly support a particular birth scenario with time and place. We trace back each NS, runaway star and the centres of possible birth associations to find close encounters. The kinematic age is then given by the time since the encounter. We use Monte Carlo simulations to account for observational uncertainties. Using the most recent parallax measurement of 8.16+/-0.80 mas for RXJ1856, we find that it originated in the U Sco association 0.46+/-0.05 Myr ago. This is slightly larger than the value we reported earlier (0.3 Myr). Our result is strongly supported by its current radial velocity that we predict to be 6+19-20 km/s. This implies an inclination angle of 88+/-6 deg consistent with the bow shock. No suitable runaway star was found to be a potential former companion of RXJ1856. Making use of a recent parallax measurement for RXJ0720 of 3.6+/-1.6 mas, we find that this NS was possibly born in Tr 10 0.85+/-0.15 Myr ago. This is somewhat larger than the one obtained using the old parallax value (0.5 Myr). We suggest the B0 runaway supergiant HIP 43158 as a candidate for a former companion. Then, the current distance of RXJ0720 to the Sun should be 286+27-23 pc, in agreement with recent measurements. We then expect the radial velocity of RXJ0720 to be -76+34-17 km/s.
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