[论文解读] The secrets of T Pyx: I. UV observations

R. Gilmozzi, Pierluigi Selvelli|ArXiv.org|Oct 2, 2006

Astrophysical Phenomena and Observations参考文献 33被引用 12

一句话总结

本研究分析了16年来对食双星T Pyxidis的国际紫外线探测器（IUE）观测数据，以研究其紫外光谱行为。结果发现，紫外连续谱表现出显著的稳定性，幂律指数为λ⁻².³³，且来自伴星的贡献可忽略不计；而强发射线（CIV 1550，HeII 1640）则表现出显著的变异性，表明星周壳层或吸积流中存在瞬变结构，如喷流或运动结核。

ABSTRACT

We have studied the UV spectral behavior of the recurrent nova T Pyx during 16 years of IUE observations. We examined both the IUE line-by-line images and the extracted spectra in order to understand the reality and the origin of the observed spectral variations. The UV continuum of T Pyx has remained nearly constant in slope and intensity over this time interval, without any indication of long-term trends. The reddening determined from the UV data is E(B-V}=0.25 \pm 0.02. The best single-curve fit to the dereddened UV continuum is a power-law distribution $\propto λ^{-2.33}$. The tail of this curve agrees well with the B, V, and J magnitudes of T Pyx, indicating that the contribution of the secondary star is negligible. One peculiar aspect of T Pyx is that most emission lines (the strongest ones being those of CIV 1550 and HeII 1640) show substantial changes both in intensity and detectability, in contrast to the near constancy of the continuum. Several individual spectra display emission features that are difficult to identify, suggesting a composite spectroscopic system. We tentatively ascribe the origin of these transient emission features either to loops and jets from the irradiated secondary or to moving knots of the surrounding nebula that are (temporarily) projected in front of the system. The inspection of all IUE line-by-line images has led to the detection of emission spikes outside the central strip of the spectrum, which in some cases seem associated to known emission features in the (main) spectrum. A comparison with other ex-novae reveals a surprising similarity to the spectrum of the very-slow nova HR Del, whose white dwarf primary has a mass that is allegedly about one half that of T Pyx.

研究动机与目标

• 理解在宁静期，T Pyxidis的长时序紫外光谱行为。
• 确定伴星对观测到的紫外及光学/红外辐射通量的贡献。
• 研究强可变紫外发射线的起源。
• 将T Pyx的紫外特性与其它已爆发新星（特别是HR Del）进行比较。
• 评估所观测到的紫外行为对吸积盘结构及爆发预测的启示。

提出的方法

• 分析16年观测数据中的IUE逐线图像及提取的光谱。
• 对比不同方法对扩展天体的光谱提取结果，以确保准确性。
• 推导紫外连续谱能量分布，并用幂律函数拟合：Fλ ∝ λ⁻².³³。
• 利用E(B-V) = 0.25 ± 0.02进行消光修正，以获得本征连续谱。
• 将消光后的紫外连续谱外推至光学与红外波段，与B、V和J星等进行比较。
• 在逐线图像中识别瞬变发射特征，并与已知谱线及可能的物理起源进行交叉匹配。

实验结果

研究问题

• RQ1 T Pyx在宁静期的紫外连续谱长期稳定性如何？
• RQ2 伴星对观测到的紫外和红外通量的贡献程度如何？
• RQ3 是什么导致了CIV 1550和HeII 1640等强紫外发射线的显著变异性？
• RQ4 紫外光谱中的瞬变发射特征是否源于星周壳层中的运动结核或吸积流中的动态结构？
• RQ5 T Pyx的紫外光谱行为与其他已爆发新星（如HR Del）相比有何异同？

主要发现

• T Pyx的紫外连续谱在16年中保持近乎恒定的斜率和强度，无长期趋势。
• 最佳拟合的消光后紫外连续谱为幂律，指数为λ⁻².³³，不确定性仅为±0.04。
• 消光值为E(B-V) = 0.25 ± 0.02，与低消光一致。
• 将紫外幂律外推至J波段，预测J = 13.52，与观测值J = 14.4–14.65接近，证实热源为通量主导成分。
• 伴星对J波段通量的贡献小于1%，表明其在所有波段的贡献均可忽略。
• 强发射线（CIV 1550，HeII 1640）表现出显著的强度和可探测性变化，提示系统中存在瞬变或动态结构。