期刊
ASTROPHYSICAL JOURNAL
卷 718, 期 1, 页码 522-526出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/718/1/522
关键词
infrared: stars; stars: individual (Population II); stars: mass-loss; techniques: photometric
资金
- JPL/Caltech
- Agenzia Spaziale Italiana [ASI-INAF I/016/07/0]
- Ministero dell'Istruzione
- dell'Universita e della Ricerca
We present additional evidence that dust is really forming along the red giant branch (RGB) of 47 Tuc at luminosities ranging from above the horizontal branch to the RGB tip. The presence of dust had been inferred from an infrared excess in the (K - 8) color, with K measured from high spatial resolution ground-based near-IR photometry and 8 referring to Spitzer-Infrared Array Camera (IRAC) 8 mu m photometry. We show how (K - 8) is a far more sensitive diagnostic for detecting tiny circumstellar envelopes around warm giants than colors using only the Spitzer-IRAC bands, for example, the (3.6 - 8) color used by Boyer et al. In addition, we also show high-resolution Hubble Space Telescope Advanced Camera for Surveys I-band images of the giant stars that have (K - 8) color excess. These images clearly demonstrate that the Boyer et al. statement that our detections of color excess associated with stars below the RGB tip arise from blends and artifacts is simply not valid.
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