Behavior of the Bands of Aluminum Oxide in Stellar Spectra.

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Behavior of the Bands of Aluminum Oxide in Stellar Spectra. Keenan, Philip C. Abstract 1924 (Mira itself) and 1960 (R Ser). Both times the emission is known to have persisted for several weeks when these variables were passing through maxima that were fainter than normal. Although P. W. Merrill (1956, Carnegie Inst. PubI. No. 610, p. 40) has suspected faint emission in Mira at the maxima of 1927 and 1929, both stars have had several other faint maxima at which no AlO emission was present. These bands, having their strongest head at 4842 A, belong to the blue system of AlO and are usually observed in absorption in Mira variables of about type M5e or later. They are consistently stronger in these stars than in either ordinary M-type giants or small-amplitude red variables, where they cannot usually be observed with low dispersion unless the type is as late as M7. An example of this difference had been noticed in 1940 by D. N. Davis (Publs. Astron. Soc. Pacific 52, 207) who compared a Her and Mira when both stars had types close to M6. The one remarkable exception to this rule is the supergiant p Cas, which developed AlO absorption along with TiO bands in 1946, when it was one magnitude fainter than normal. A survey of about 60 Mira variables has shown real differences from star to star, confirming Merrill's observations that the AlO absorption is unusually strong compared to the TiO bands in R Hya and RT Lib. The stars with strong AlO include SU Vir also, while RT Cyg is one of those in which the AlO bands appear weak. There are also real differences in AlO absorption from cycle to cycle of any one Mira variable. These changes are most striking in those variables which bave the strongest bands; this suggests incipient ~mission filling in the absorption heads at times. In the Mira variables which never show strong AlO absorption, however, some other explanation is neces- sary-either the concentration of AlO is lower or their atmospheres are less transparent. Publication: The Astronomical Journal Pub Date: 1960 DOI: 10.1086/108092 Bibcode: 1960AJ.....65Q.492K full text sources ADS |