我们讨论了附近星系M33中最亮的中红外点源（我们称之为X天体）的性质。虽然关于这个天体的多波长数据在文献中已经存在了一段时间，但它以前并没有被认为是M33中最明亮的中红外天体，因为它在光学和近红外光中都完全不起眼。在本星系群巡天中，X天体是一个在VRI和H-alpha中可见的微弱红色源，但在U或B中不可见。在2 MASS调查中很容易在JHK_s看到。它是斯皮策IRAC所有四个波段中最亮点的光源，并且在MIPS 24微米波段中也可见。它的辐射热光度为5x10^5 L_sun。它的光源在短时间尺度（数十天）上是光学可变的，在中红外线上也有轻微的变化，这表明它是一颗恒星。1949年和1991年的档案底片显示没有光源，所以这颗恒星已经被遮蔽了至少半个世纪。它的性质与银河系OH/IR星IRC+10420相似，IRC+10420具有复杂的尘埃拱星结构，这是由间歇性的低速物质抛射造成的。我们认为X是一颗M>30 M_sun演化的恒星，在至少半个世纪的时间里，它在偶发性质量损失事件中被自己的尘埃所掩盖。它可能会从目前的超短演化阶段中脱颖而出，成为一颗类似于M33 Var A的更热的后RSG恒星。这类天体的存在和稀有性可能是对一个非常短暂而又多事的恒星演化阶段的重要探测。
英文摘要：
We discuss the nature of the brightest mid-IR point source (which we dub Object X) in the nearby galaxy M33. Although multi-wavelength data on this object have existed in the literature for some time, it has not previously been recognized as the most luminous mid-IR object in M33 because it is entirely unremarkable in both optical and near-IR light. In the Local Group Galaxies Survey, Object X is a faint red source visible in VRI and H-alpha but not U or B. It was easily seen at JHK_s in the 2MASS survey. It is the brightest point source in all four Spitzer IRAC bands and is also visible in the MIPS 24-micron band. Its bolometric luminosity is 5x10^5 L_sun. The source is optically variable on short time scales (tens of days) and is also slightly variable in the mid-IR, indicating that it is a star. Archival photographic plates (from 1949 and 1991) show no optical source, so the star has been obscured for at least half a century. Its properties are similar to those of the Galactic OH/IR star IRC+10420 which has a complex dusty circumstellar structure resulting from episodic low velocity mass ejections. We propose that Object X is a M>30 M_sun evolved star obscured in its own dust ejected during episodic mass loss events over at least half a century. It may emerge from its current ultra-short evolutionary phase as a hotter post-RSG star analogous to M33 Var A. The existence and rarity of such objects can be an important probe of a very brief yet eventful stellar evolutionary phase.
The VLTI/MIDI survey of massive young stellar objects - Sounding the inner regions around intermediate- and high-mass young stars using mid-infrared interferometry
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Context. The most primitive metal-poor stars are important for studying the conditions of the early galaxy and are also relevant to big bang nucleosynthesis. Aims. Our objective is to find the brightest (V<14) most metal-poor stars. Methods. Candidates were selected using a new method, which is based on the mismatch between spectral types derived from colors and observed spectral types. They were observed first at low resolution with EFOSC2 at the NTT/ESO to obtain an initial set of stellar parameters. The most promising candidate, 2MASS J18082002-5104378 (V=11.9), was observed at high resolut…
We measured mid-infrared polarization of protoplanetary discs to gain new insight into their magnetic fields. Using CanariCam at the 10.4 m Gran Telescopio Canarias, we detected linear polarization at 8.7, 10.3, and 12.5 $μ$m from discs around eight Herbig Ae/Be stars and one T-Tauri star. We analyzed polarimetric properties of each object to find out the most likely interpretation of the data. While the observed mid-infrared polarization from most objects is consistent with polarized emission and/or absorption arising from aligned dust particles, we cannot rule out polarization due to dust sc…
We systematically investigate the mid-infrared (MIR; $λ>3 ~μ$m) time variability of uniformly selected $\sim800$ massive young stellar objects (MYSOs) from the Red MSX Source (RMS) survey. Out of the 806 sources, we obtain reliable 9-year-long MIR magnitude variability data of 331 sources at the 3.4~$μ$m (W1) and 4.6~$μ$m (W2) bands by cross-matching the MYSO positions with ALLWISE and NEOWISE catalogs. After applying the variability selections using ALLWISE data, we identify 5 MIR-variable candidates. The light curves show various classes, with the periodic, plateau-like, and dipper features.…
