Volume 550, February 2013
|Number of page(s)||14|
|Published online||18 January 2013|
The photometric calibrations discussed in Sect. 4 depend on luminosity classifications of the star sample. Here, we re-examine their luminosity and spectral classification. As reference, we adopt the classification of one anchor point of the Morgan-Keenan system (star #11) and five primary standards from N. Walborn (#6, 7, 11, 19 and 23), all listed in Gray & Corbally (2009). In a second step, spectral types and luminosity classes of the sample stars are examined via inspection of Balmer lines and silicon/helium ratios, as recommended by Walborn (1971) and Gray & Corbally (2009). Spectral type classification for the hotter stars (O9-B0.7) rely on the ratio Si ivλ4089/Si iiiλ4552 and for the cooler stars (B1-B3) on Si iiλ4128/Si iiiλ4552. In addition, luminosity classes are tested via Si ivλ4116/He iλ4121 for the hotter and Si iiiλ4552/He iλ4387 for the cooler stars.
Ratios of equivalent widths for temperature (abscissa) and gravity-sensitive (ordinate) line pairs as basis for the spectral type and luminosity classification of the star sample (Table 1). Upper panel: hotter stars O9-B0.7; lower panel: cooler stars B1–B3.
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Figure A.1 displays the relation of line ratios as spectral type and luminosity class indicators for the hotter (upper panel) and the cooler stars (lower panel). Only few cases – stars #2, 8, 10, 19 and 26 – required a correction in luminosity class. Furthermore, slight corrections to (sub-)spectral types for objects #2, 5, 8, 10, 13, 16, 28, 29, have also been implemented, as listed in Table 1. The revisions are facilitated by the higher quality of our spectra
in comparison to older photographic spectrograms used in the past, affecting in particular the weaker silicon lines. Star #15 is too cool, i.e. has a very low Si iiλ4128/Si iiiλ4552 ratio, therefore is excluded from Fig. A.1 (lower panel).
Table B.1 indicates which ionization equilibria in combination with fits to several hydrogen lines, have been matched in order to determine effective temperatures and surface gravities for the sample stars. Dots denote fits to spectral lines and boxes indicate cases where ionization equilibria were matched. A row denotes the simultaneous fits to different elements/ionization stages using the same set of atmospheric parameters.
Spectroscopic indicators for Teff and log g determination.
© ESO, 2013
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