EF Aql - a neglected symbiotic Mira

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EF Aql - a neglected symbiotic Mira

Postby David Boyd » Mon Nov 12, 2018 12:39 pm

The long-period variable EF Aquilae is classified as a Mira in AAVSO VSX and has been identified as a symbiotic Mira by Margon et al. in Publications of the Astronomical Society of the Pacific, 128, 960 (2016). It has a period of around 320 days and a range from 12.3 to fainter than 15.2. There is very little photometry in the AAVSO database. The star has not been extensively studied.

According to the ephemeris in VSX it is now close to its maximum brightness and therefore reasonably accessible to low resolution spectroscopy. The spectrum below is a 1.5 hour integration recorded on 2018 November 11.75 UT using a LISA spectroscope and SXVR-H694 camera. Its V magnitude was measured as 12.79 concurrently with the spectrum and used to flux calibrate the spectrum.
EF Aql 2018 Nov 11.75.png
EF Aql 2018 Nov 11.75.png (77.48 KiB) Viewed 1133 times

Comparing this to the spectrum below which is Figure 1 in the Margon paper and was recorded in 2014, the flux level is very similar but there are significant differences in the emission lines.
Margon et al. Fig 1.jpg
Margon et al. Fig 1.jpg (51.23 KiB) Viewed 1133 times

The H-delta line which was prominent in 2014 is barely visible now. Also the [O III] 5007Å line seen before is now absent. The Margon spectrum cuts off at 6800Å before the Raman OIV lines but neither the OIV 6826Å or 7088Å lines are apparent in the current spectrum.

The spectral profile of EF Aql is a good match to spectral type M7III. Margon estimated the extinction to EF Aql to be Av = 0.45 so the correction for interstellar extinction is small enough not to change this inferred spectral type.

Dimitrov et al., in the Proceedings of the XI Bulgarian-Serbian Astronomical Conference in May 2018, reported the detection of flickering in EF Aql which they argue indicates the hot component in the system is a white dwarf rather than a subdwarf as suggested in Margon et al.

David Boyd
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