Late-type giant variables in NGC 6522, LMC and SMC. How do they differ?
Late-type giant variables in NGC 6522, LMC and SMC. How do they differ?
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DOI：
10.1051/0004-6361:20041454
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发表时间：
2004-08
影响因子：
6.5
通讯作者：
M. Schultheis;I. Glass;M. Cioni
中科院分区：
文献类型：
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作者：
M. Schultheis;I. Glass;M. Cioni
完整的样品2 MASS恒星在三个领域的不同金属丰度（可能不同的年龄分布）已被提取和交叉相关的CAMO和ISO数据，以确定其可变性和质量损失的属性。在每个MK直方图中，在RGB的顶端上方可以看到数字的下降。尖端的光度随着金属丰度的增加而增加，在给定的MK 0下，平均（J-K）0也是如此。这些量已经与Ferraro等人（2000）获得的银河球状星团的数据进行了比较。在J − H、H − K色图中，高H − K值的恒星比例的增加在较低金属丰度处是明显的。众所周知，这是由于碳星的比例越来越大。所有三个字段都包含类似类型的变量，主要是短周期（通常为数十天），Mira like（长周期，大幅度）和双周期（具有长周期和短周期）。在较低的金属丰度下，变化的恒星比例减少，并且与给定振幅相关的最小周期变长。在各场的K、logP图中可以看到各种趋势。麦哲伦星云的场彼此很相似，但膨胀场却明显不同。在球状星云中遵循“A”K，logP关系的恒星几乎没有延伸到M Tip K，0之外，其他恒星群相对于它们的麦哲伦星云对应物也在MK中被截断。在星云中，有许多恒星的周期在200-300 d左右，遵循“C”或Mira关系，但振幅相对较小。在麦哲伦云小型巡天（MCMS）期间，ISOCAM探测到的中红外样本似乎是可靠的，并且对于MK亮度超过-7等的源来说是完整的，即，对于那些接近AGB高层的人来说。不同的颜色-颜色和颜色-星等图反映了碳星在低金属丰度时的优势。Mira星等与log P的关系至少在7 µm处存在。质量损失从较长的周期和双周期SRVs发生在每个领域的相似的速度，尽管金属丰度的差异。
Complete samples of 2MASS stars in three fields of differing metallicities (and possibly differing age distributions) have been extracted and cross-correlated with MACHO and ISO data to determine their variability and mass-loss properties. In each MK histogram a fall-off in numbers is seen above the tip of the RGB. The luminosity of the tip increases with metallicity as does the average (J − K)0 at a given MK0 . These quantities have been compared with the data for galactic globular clusters obtained by Ferraro et al. (2000). In the J − H, H − K colour-colour diagrams, the increasing proportion of stars with high H − K values is conspicuous at lower metallicities. This is well-known to result from the increasing proportion of carbon stars. All three fields contain similar types of variables, mainly short-period (usually tens of days), Mira like (long-period, large ampli- tude) and double-period (having both long and short periods). The proportion of stars that vary decreases at lower metallicities and the minimum period associated with a given amplitude gets longer. Various trends are seen in the K ,l ogP diagrams of each field. The Magellanic Cloud fields largely resemble each other but the Bulge field is noticeably different. The stars that follow the "A" K ,l ogP relation in the Bulge hardly extend beyond M Tip K,0 and the other groups also appear truncated in MK relative to their Magellanic Cloud counterparts. In the Clouds there are many stars with periods around 200-300 d that follow the "C" or Mira relation but have relatively small amplitudes. The mid-IR sample detected by ISOCAM during the Magellanic Cloud Mini-Survey (MCMS) appears to be reliable and com- plete for sources with MK more luminous than −7 mag, i.e., for those close to the top of the AGB. The various colour-colour and colour-magnitude diagrams reflect the increasing dominance of carbon stars at low metallicity. Mira magnitude vs. log P rela- tions exist at least up to 7 µm. Mass-loss from longer-period and double-period SRVs occurs at similar rates in each field, in spite of the metallicity differences.