SIMBAD references

2017AJ....153..275C - Astron. J., 153, 275-275 (2017/June-0)

No "maunder minimum" candidates in M67: mitigating interstellar contamination of chromospheric emission lines.


Abstract (from CDS):

The solar analogs of M67 let us glimpse the probable behavior of the Sun on timescales surpassing the duration of human civilization. M67 can serve as a solar proxy because its stars share a similar age and composition with the Sun. Previous surveys of M67 observed that 15% of its Sun-like stars exhibited chromospheric activity levels below solar minimum, which suggest that these stars might be in activity-minimum states analogous to the Maunder Minimum. The activity diagnostic used, the HK index (relative intensities of the Ca ii H & K lines integrated over 1 Å bandpasses), was measured from low-resolution spectra (R ≃ 5000), as is traditional and suitable for nearby, bright stars. However, for stars beyond the Local Bubble, the interstellar medium (ISM) imprints absorption lines in spectra at Ca ii H & K, which negatively bias activity measurements when these lines fall within the HK index bandpass. I model the ISM clouds in the M67 foreground with high-resolution spectra of blue stragglers and solar analogs. I demonstrate that ISM absorption varies across the cluster and must be accounted for on a star-by-star basis. I then apply the ISM model to a solar spectrum and broaden it to the lower spectral resolution employed by prior surveys. Comparing HK indices measured from ISM-free and ISM-contaminated spectra, I find that all stars observed below solar minimum can be explained by this ISM bias. I conclude that there is no compelling evidence for Maunder Minimum candidates in M67 at this time.

Abstract Copyright: © 2017. The American Astronomical Society. All rights reserved.

Journal keyword(s): ISM: general - open clusters and associations: individual: (M67, NGC 2682) - stars: activity - stars: chromospheres - Sun: activity - Sun: activity

Simbad objects: 32

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