Extended envelopes around Galactic Cepheids IV. T Monocerotis and X Sagittarii from mid-infrared interferometry with VLTI/MIDI
Extended envelopes around Galactic Cepheids IV. T Monocerotis and X Sagittarii from mid-infrared interferometry with VLTI/MIDI
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银河造父变星 IV 周围的扩展包络线。
DOI：
10.1051/0004-6361/201322257
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
W. Gieren
中科院分区：
文献类型：
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作者：
A. Gallenne;A. Mérand;P. Kervella;O. Chesneau;J. Breitfelder;W. Gieren
目标。利用VLTI/MIDI双光束干涉重组仪，对造父变星附近的近距离环境进行了高空间分辨率的中红外观测。方法。我们获得了经典造父变星X Sgr和T Mon的光谱和可见性。我们将MIDI测量值与B、V、J、H、K文献光度法进行拟合，并使用数值传递代码DUSTY来确定尘埃壳参数。我们在星周环境中使用了典型的尘埃成分。结果。我们在两颗恒星的光谱和可见性中发现了一个扩展的尘埃环境，尽管“天王星”可能受到热背景污染。我们把这归因于造父变星周围存在一个星周包层（CSE）。对于X Sgr （tau（0.55微米）= 0.008）来说，这是光学薄的，而对于T Mon （tau（0.55微米）= 0.15）来说，它似乎更厚。它们位于大约15-20个恒星半径处。根据我们之前的工作，我们推导出VISIR PAH1过滤器中可能的周期过量关系，f（8.6微米）[%]= 0.81(+/-0.04)P[天]。我们认为，CSEs对中红外周期-光度（P-L）关系的影响不可忽略，因为它们可以使造父变星的亮度偏差高达30%左右。对于k波段的P-L关系，CSE的贡献似乎更低（< 5%），但需要扩大样本，才能坚定地得出在该波段中CSE的影响可以忽略不计的结论。
Aims. We study the close environment of nearby Cepheids using high spatial resolution observations in the mid-infrared with the VLTI/MIDI instrument, a two-beam interferometric recombiner. Methods. We obtained spectra and visibilities for the classical Cepheids X Sgr and T Mon. We fitted the MIDI measurements, supplemented by B, V, J, H, K literature photometry, with the numerical transfer code DUSTY to determine the dust shell parameters. We used a typical dust composition for circumstellar environments. Results. We detect an extended dusty environment in the spectra and visibilities for both stars, although T Mon might suffer from thermal background contamination. We attribute this to the presence of a circumstellar envelope (CSE) surrounding the Cepheids. This is optically thin for X Sgr (tau(0.55microns) = 0.008), while it appears to be thicker for T Mon (tau(0.55micron) = 0.15). They are located at about 15-20 stellar radii. Following our previous work, we derived a likely period-excess relation in the VISIR PAH1 filter, f(8.6micron)[%]= 0.81(+/-0.04)P[day]. We argue that the impact of CSEs on the mid-IR period-luminosity (P-L) relation cannot be negligible because they can bias the Cepheid brightness by up to about 30 %. For the K-band P-L relation, the CSE contribution seems to be lower (< 5 %), but the sample needs to be enlarged to firmly conclude that the impact of the CSEs is negligible in this band.