Infrared Stars

Abstract

view Abstract Citations (73) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Stars Wing, Robert F. ; Spinrad, Hyron ; Kuhi, L. V. Abstract As the number of extremely red stars found by means of infrared sky surveys rapidly becomes larger, it becomes increasingly important to determine the spectral characteristics and the nature of the variability of at least a few such stars. We have made a detailed study of the three "infrared stars" identified by Neugebauer, Martz, and Leighton-the Taurus object, the Cygnus object, and TX Cam Our results depend primarily upon the measurements of molecular band strengths and unblanketed energy distributions made with photoelectric spectrum scanners in the wavelength range 0 8-11 j#. For the Taurus object we also have 32 A/mm coude spectrograms centered at 1 08 and a low-dispersion blue spectrogram. UB V photometry has been obtained for the Taurus object and TX Cam. That the Taurus object is a Mira-type variable is indicated by its visual and infrared light-curves, the strength of its hydrogen emission lines of the Balmer and Paschen series, its irregular Balmer decrement, and the shortward displacement of its hydrogen line P with respect to the absorption spectrum. It appears that we have not yet observed a complete cycle, and that the period is longer than 532d TX Cam was previously known to be a Mira variable, likewise with an exceptionally long period (557d) In the case of the Cygnus object, on the other hand, we have found no definite variation in magnitude, color, or molecular band strength. The radial velocity of the Taurus object is +63 l 5 km/sec; its proper motion is less than 0"02/ year. It lies far from the galactic plane (b = - 310) and probably is a disk population star like Mira itself. The great strength of its molecular hydrogen feature at Xl 1172 confirms the low temperature indicated by its energy distribution The scanner measurements have been used to define a color index, a TiO index, a VO index, and a rough index of stellar H2O; they also indicate when the molecules CN and ZrO are present. Definitions of very late spectral types, depending primarily upon the strength of the VO band complex near 1 OS are proposed. The color index is free of blanketing for all spectral types earlier than M8 and has been corrected for blanketing, in an approximate fashion, for the latest types We have observed an adequate number of giant stars and long-period variables of type M to establish that such stars normally fall upon a well-defined and nearly linear sequence (the "M sequence") in the diagram of band strength (TiO+ VO) versus color. The infrared stars in Taurus and Cygnus, like stars of type S, fall well below the M sequence These stars, which have abnormally weak TiO and VO bands for their colors, also have weak bands of 1120. In the Taurus object, the band strengths of all three molecules increase with decreasing temperature. We discuss the various mechanisms that can affect the relation between band strength and color. For the Taurus object our observational data are sufficiently complete to eliminate all but one-a low ratio of oxygen to carbon-as the cause of the observed discrepancy. This star appears to have an oxygen/ carbon ratio similar to that of the 8-type star R And, without, how ever, sharing the latter's enrichment in s-process elements Interstellar reddening may be important in the case of the Cygnus object but here the discrepancy is so great that it seems most reasonable to suppose that it is due primarily to a low oxygen/carbon ratio. It is shown that changes of only a few per cent in this ratio can produce important changes in the molecular band strengths We interpret TX Cam as a moderately reddened star of normal chemical composition. A review of the available information on the spectral types and light variations of infrared stars leads to the suggestion that the majority of such stars are Mira variables with periods longer than 1 year. Publication: The Astrophysical Journal Pub Date: January 1967 DOI: 10.1086/148985 Bibcode: 1967ApJ...147..117W full text sources ADS | data products SIMBAD (34)