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Session 46 - Variable Stars - Late Type.
Display session, Thursday, January 08
Exhibit Hall,

[46.09] Minimum-Light Spectral Types for Four Mira Variables

R. F. Wing, Y. Yuan (Ohio State U.), S. R. Benfer (Ohio Wesleyan U.)

Spectral types for four little-studied Mira variables have been derived from narrow-band classification photometry obtained within three weeks of minimum light. The observations were made on May 24, 1997, with the CTIO 1.5-m telescope and ASCAP photometer when targets of a primary program were not accessible. The following stars were selected for observation based on AAVSO predicted times of minimum light.

Star P \,V Sp.T.(pub) Phase \,I(104) Sp.T.(8c)


RR Aqr \,182.5 9.1--14.4 M2e--M4e 0.52 7.63 M7.5 \hspace*0.8cmRS Aqr 214.6 9.5--14.4 Me \,0.62 6.63 M7.5 \hspace*1.1cmZ Aql 129.2 8.2--14.8 M3e 0.67 7.07 M8.3 \hspace*0.8cmRU Cap 347.4 9.2--15.2 M9e 0.68 5.49 M8.8

\vspace*-0.5cm The first four columns give data from the GCVS: the star's name, mean period in days, observed range in visual magnitude, and published spectral type. The last three columns refer to our own observations: the phase on 1997 May 24 (according to the AAVSO predictions), the apparent magnitude in a narrow band centered at 10400 Åand our spectral classification on the eight-color system, which is based on measurements of TiO at 7120 Å\ and VO at 10540 ÅThe very late published spectral type of RU Cap (which appears to have been observed only at minimum) is confirmed. The three other stars, which had not previously been observed later than M4, all showed very strong TiO and significant absorption by VO, indicative of types M7.5 or later. These and earlier observations show that published spectral types of Mira variables --- even those that are brighter than V = 10 at maximum --- are often very incomplete and can be misleading. Indeed, it is difficult to find Miras that do not attain types of at least M7 at minimum.

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