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arXiv 1401.7113astro-ph.SR
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经典新星的UBV颜色演化。I.色图中的新星-巨星序列

The UBV Color Evolution of Classical Novae. I. Nova-Giant Sequence in the Color-Color Diagram

Izumi Hachisu, Mariko Kato

摘要:

我们在B-V与U-B色图中确定了经典新星爆发的一般过程。据报道,新星在光学最大值附近显示出与A-F超巨星相似的光谱。然而,它们并不遵循色图中的超巨星序列,无论是黑体还是主序星序列。相反,我们发现新星在前极大期和近极大期沿着一个新的序列演化,我们称之为“新星-巨星序列”。“这个序列与超巨星序列平行,但Δ(U-B)\approx比超巨星序列蓝0.2等。这是因为新星包层的质量比正常的超巨星小很多(\sim 10^{-4}倍)。在光学极大值之后,它的颜色沿着相同的新星-巨星序列迅速向蓝方向发展,并达到自由-自由发射点(B-V=-0.03,U-B=-0.97),这与黑体序列和新星-巨星序列的交叉点重合,并保持一段时间。然后颜色逐渐变蓝(在B-V中是蓝的,但在U-B中几乎是恒定的),这主要是由于强发射线的发展。这是色图中新星爆发的一般过程,色图是从八颗观测良好的不同速度级别的新星中推导出来的。对于一颗灭绝未知的新星,我们可以通过将目标新星的观测轨迹与这个一般过程相匹配来确定一个可靠的颜色过剩值。这是获得经典新星色余的一种新的简便方法。使用这种方法,我们重新确定了20个观测良好的新星的颜色过剩。得到的颜色过剩是在合理的协议与以前的结果,这反过来又支持了我们的一般轨道的新星爆发的想法。

英文摘要:

We identified a general course of classical nova outbursts in the B-V versus U-B color-color diagram. It is reported that novae show spectra similar to those of A--F supergiants near optical light maximum. However, they do not follow the supergiant sequence in the color-color diagram, neither the blackbody nor the main-sequence sequence. Instead, we found that novae evolve along a new sequence in the pre-maximum and near-maximum phases, which we call "the nova-giant sequence." This sequence is parallel to but Δ(U-B) \approx -0.2 mag bluer than the supergiant sequence. This is because the mass of a nova envelope is much (\sim10^{-4} times) less than that of a normal supergiant. After optical maximum, its color quickly evolves back blueward along the same nova-giant sequence and reaches the point of free-free emission (B-V=-0.03, U-B=-0.97), which coincides with the intersection of the blackbody sequence and the nova-giant sequence, and remains there for a while. Then the color evolves leftward (blueward in B-V but almost constant in U-B), owing mainly to the development of strong emission lines. This is the general course of nova outbursts in the color-color diagram, which was deduced from eight well-observed novae in various speed classes. For a nova with unknown extinction, we can determine a reliable value of the color excess by matching the observed track of the target nova with this general course. This is a new and convenient method for obtaining the color excesses of classical novae. Using this method, we redetermined the color excesses of twenty well-observed novae. The obtained color excesses are in reasonable agreement with the previous results, which in turn supports the idea of our general track of nova outbursts.

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