next previous
Up: A representative sample of


2 Sample selection

A Be star is defined as a B-type non-supergiant star that shows, or has shown in the past, emission lines. Jaschek & Egret (1982) provide a list of such objects, and it is from that list our sample is drawn. We note here that as the Be phenomenon is time variable we expect several of our objects not to show emission lines at present.

Our sample is termed a "representative'' sample, in that it was selected in an attempt to contain several objects that were typical of each spectral and luminosity class for which the Be phenomenon occurs. It therefore does not reflect the spectral and luminosity class space distribution of Be stars, but only the attempts to define the average properties of each subclass in temperature and luminosity. Our selection was made according to the following criteria:

1.
An equal distribution of spectral types from B0 to B9 using the spectral types listed by Jaschek & Egret (1982).
2.
An equal distribution between dwarf and giant luminosity classes listed by Jaschek & Egret (1982).

3.
No evidence of spectroscopic binarity in the literature.

The following additional constraints were imposed by the instrument sensitivity and time allocation:

1.
Right Ascensions in the range 17$^{\rm h}$ to 6$^{\rm h}$.
2.
Declinations in the range to +59$^{\circ}\gt\delta\gt -27^{\circ}$.

3.
B magnitude brighter than $\sim $11.

These criteria were designed in an attempt to create a sample containing roughly 3 objects per spectral type per luminosity class. We note here that no selection criteria was applied for $v \sin i$, as the distribution of $v \sin i$ with spectral type and luminosity class was one of the phenomena we wished to investigate. The achieved spectral and luminosity class distribution is somewhat different to the 3 per spectral type per luminosity class, with many more dwarfs than giants in the sample. This is not surprising given that Jaschek & Egret (1982) is simply a compilation of values from the literature, with most of the spectral types from low resolution photographic spectra taken in the 1950's. The achieved distribution is discussed in Sects. 4 and 5, along with a discussion of possible biases in the sample.

There are a total of 58 objects in our sample. In Table 2 we list the sample by BD number, along with other aliases for the brighter/well studied objects. Also listed in Table 2 are J2000 coordinates and B and V magnitudes for the sample from the SIMBAD database, and the historical spectral types assigned to the objects.

  
Table 2: Data on the sample from the SIMBAD database (Coordinates J2000)

Note that there is a large variation in the historical spectral types, with many objects having a spectral class uncertain by 2 sub-types and a similarly uncertain luminosity class. We assume this is due to the quality of the spectra used. Although Be stars show great time variability in their emission line spectra, we are aware of no evidence in the modern literature to indicate variability of the underlying B star absorption spectrum. Since the overall aim of this programme is to understand the relationship between the parameters of underlying stars and the circumstellar disks in these systems it is therefore necessary to reclassify all of the stars in our sample using modern CCD spectra. This need to reclassify the sample is the motivation for the observations presented here.


next previous
Up: A representative sample of

Copyright The European Southern Observatory (ESO)