Time Variation Observations of Mid-Infrared Spectra of Mira Variables in NEP and LMC

Details Time Variation Observations of Mid-Infrared Spectra of Mira Variables in NEP and LMC Time Variation Observations of Mid-Infrared Spectra of Mira Variables in NEP and LMC

Sep 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sptz.prop.3583o&link_type=abstract

Spitzer Proposal ID #3583

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Scientific paper

We propose to derive the optical properties of their circumstellar dust grains and dust formation process based on variability observations of mid-infrared (MIR) spectra of oxygen-rich Mira variables with the IRS SL and LL modules. Mass-loss of stars in the asymptotic-giant branch is an important process for the evolution of matter in the Galaxy. However, there are still large uncertainties in the optical properties of silicate grains and the dust formation process in their circumstellar envelopes. Based on variability observations with the ISO of MIR spectra of a Mira variable we were able to derive the dust optical properties and the inner dust shell temperature independently, which have clearly demonstrated the effectiveness of variability observations of MIR spectra. However, they also indicate that the variability and dust properties in Mira variables have diversity and it is quite important to apply the same method to other targets and extend the investigation. We selected 3 target stars in the north ecliptic polar (NEP) region and 2 in the Large Magellanic Cloud (LMC). Both regions are located in the constant viewing zones and all the target stars can be observed for more than 11 months in a year. We propose to make observations in the intervals of 1/5 of the period over a variability cycle. Three targets in the NEP have periods less than 300 days and they can be observed over a variability cycle in Cycle-1. Two target stars in the LMC have periods longer than 500 days and we request multi-cycle observations to cover a variability cycle of the LMC targets. We allow +/-15 days for the NEP stars and +/-30 days for the LMC stars for each observation epoch and thus the timing constraint is not severe. The IRS on board the SST provides a unique opportunity to carry out this study, which enables us to investigate the diversity of properties and formation process of silicate grains in Mira variables and extend our understanding to those in the nearby galaxy LMC.

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