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arXiv 1208.0702astro-ph.SRastro-ph.GA
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在巨蛇座核心寻找行星质量的T矮星

Searching for planetary-mass T-dwarfs in the core of Serpens

L. Spezzi, C. Alves de Oliveira, E. Moraux, J. Bouvier, E. Winston, P. Hudelot, H. Bouy, J. -C. Cuillandre

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11 Pages, 7 Figures, Accepted for publication on A&A
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摘要：

我们在300万年前的巨蛇座核心星团中寻找孤立的行星质量T矮星。我们使用CFHT的WIRCam相机对该星团的中心部分进行了深入的成像调查。通过窄带CH4_off和CH4_on滤光片进行观测，以从1.6微米甲烷吸收带识别年轻的T矮星，并通过宽带JHK滤光片进行观测，以更好地描述所选候选者。我们用CFHT的MegaCam和斯巴鲁望远镜的Suprime-Cam的光学成像数据以及斯皮策c2 d遗产调查的中红外通量测量来补充我们的WIRCam测光。我们在巨蛇座核心方向报告了四个微弱的T矮星候选者，CH 4_on-CH 4_off大于0.2等，估计在1-9等范围内的视觉消光和光谱类型在T1-T5范围内，基于它们的去红CH 4_on-CH 4_off颜色。与T-矮星光谱模型和光学中红外色-色和色-星等图的比较表明，我们的两个候选者（ID 1和2）是背景污染物（最有可能是严重红化的低红移类星体）。其他两个候选者（ID 3和4）的属性与他们是巨蛇座核心星系团的年轻成员一致，尽管我们的分析不能被认为是结论性的。特别地，ID 3也可以是前景T矮星。它是由斯皮策c2 d调查检测到的，但只有通量上限高于5.8微米，因此，我们无法评估该对象周围可能存在的磁盘。然而，它与其他年轻的T矮星候选者有一些相似之处（在猎户座Sigma星团中的SOri 70和在IC 348方向的CFHTJ 0344 +3206）。如果ID 3和ID 4属于巨蛇座，它们的质量将只有几个木星的质量，并且是迄今为止在恒星形成区发现的最年轻、质量最低的天体之一。

英文摘要：

We searched for isolated planetary-mass T-dwarfs in the 3Myr old Serpens Core cluster. We performed a deep imaging survey of the central part of this cluster using the WIRCam camera at the CFHT. Observations were performed through the narrow-band CH4_off and CH4_on filters, to identify young T-dwarfs from their 1.6micr methane absorption bands, and the broad-band JHK filters, to better characterize the selected candidates. We complemented our WIRCam photometry with optical imaging data from MegaCam at CFHT and Suprime-Cam at the Subaru telescope and mid-IR flux measurements from the Spitzer c2d Legacy Survey. We report four faint T-dwarf candidates in the direction of the Serpens Core with CH4_on-CH4_off above 0.2 mag, estimated visual extinction in the range 1-9 mag and spectral type in the range T1-T5 based on their dereddened CH4_on-CH4_off colors. Comparisons with T-dwarf spectral models and optical to mid-IR color-color and color-magnitude diagrams, indicate that two of our candidates (ID1 and 2) are background contaminants (most likely heavily reddened low-redshift quasars). The properties of the other two candidates (ID3 and 4) are consistent with them being young members of the Serpens Core cluster, although our analysis can not be considered conclusive. In particular, ID3 may also be a foreground T-dwarf. It is detected by the Spitzer c2d survey but only flux upper limits are available above 5.8 microns and, hence, we can not assess the presence of a possible disk around this object. However, it presents some similarities with other young T-dwarf candidates (SOri70 in the Sigma Ori cluster and CFHTJ0344+3206 in the direction of IC348). If ID3 and 4 belong to Serpens, they would have a mass of a few Jupiter masses and would be amongst the youngest, lowest mass objects detected in a star-forming region so far.

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