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Hundreds of Mira Candidates Discovered from LAMOST Survey

Nov 28, 2017     Email"> PrintText Size

Recently, YAO Yuhan of Peking University, LIU Chao of National Astronomical Observatories (NAOC) of the Chinese Academy of Sciences and other researchers discovered 191 new Mira candidates from the LAMOST DR4 data. 

Mira stars are a class of long period variables with periods in excess of 80 days that coincide with the final stellar evolutionary phase of low-to intermediate-mass (18 M) stars before the envelope ejection phase. 

Because they are visible beyond the Local Group, and their distances can be roughly determined by their period-luminosity relationship, Mira stars have long been used as tracers of many astrophysical problems.  

For example, the picture of their chemical composition and spatial distribution can help to probe the structure and evolution of the Milky Way Galaxy (MWG). Therefore, the more Mira stars we know, the better we understand the MWG. 

Traditionally, the search of Mira stars involves long-term IR photometry followed by carefully planned spectroscopic observations. Thanks to LAMOST, we now have a chance to search for Mira stars based on their spectral characteristics.  

Different from normal giant stars, the spectra of Mira stars have high-excitation emission lines of hydrogen and some metal elements. By measuring the intensity of emission lines, absorption bands, and using the archival near-infrared photometric data (2MASS), researchers have found 191 new Mira candidates from millions of spectra in the LAMOST DR4 catalogue. Photometric follow-ups are needed to confirm that these candidates are bona fide Mira stars. 

In addition, researchers compiled a sample of 281 spectra of known Mira stars, including 12 early-type Mira stars that previously had not been carefully studied because of their rareness.  

After comparison and quantification, the relationship between relative Balmer emission-line strength and spectral temperature of O-rich Mira stars was found. The relative flux of higher orders in the Balmer series (Hdelta) increases as stars cool down from M0 to M10, which is likely driven by increasing TiO absorption above the deepest shock- emitting regions.

The findings have already been published in The Astrophysical Journal. 


Left: LAMOST spectra of Mira stars, with decreasing temperature from M0 to M10. Right: Spectra of normal M giants. (Image by NAOC) 


(Editor: LI Yuan)


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