Negative Chlorine Ion and M-Spectral Type Stars

Two-photon detachment of the negative chlorine ion.

M–type Vega–like Stars

We carried out a search for M–type Vega–like stars by correlating the IRAS Faint Source Catalog with Hipparcos selected M–type stars. Three stars with apparent IRAS 25 μm excess emission are shown instead to be non–IR–excess stars from ground–based 11.7 and 17.9 μm photometry. Two stars previously suggested to have Vega–like mid–IR excess are also shown to be non–excess stars. These results imp...

Ages of Late Spectral Type Vega-like Stars.

We have estimated the ages of eight late-type Vega-like stars by using standard age-dating methods for single late-type stars, e.g., location on the color-magnitude diagram, Li lambda6708 absorption, Ca ii H and K emission, X-ray luminosity, and stellar kinematic population. With the exception of the very unusual pre-main-sequence star system HD 98800, all the late-type Vega-like stars are the ...

POSITIVE AND NEGATIVE ION MASS SPECTRA OF RING - SUBSTITUTED NITROBENZENES

The 70 ev positive and negative ion mass spectra of ring-substituted nitrobenzenes were studied. The influence of the substituent group on the fragmentation modes of the molecular ions is discussed. The effect of pressure in the formation of negative ions was also studied. As expected, the ratio of fragment ions to negative molecular ions decreased with increasing pressure in ion source.

Spectral analysis of O(He)-type post-AGB stars

We present an analysis of two recently discovered, very hot hydrogen-deficient post-AGB stars of spectral type O(He), namely HS 1522+6615 and HS 2209+8229, by means of state-of-the-art NLTE model atmospheres based on new optical, UV, and X-ray observations. In the spectra of HS 1522+6615 we discovered a variability of the O VI λ 5290Å line complex on a time scale of few days. We also report on ...