5. Bolometric magnitudes
Bolometric luminosities were calculated by applying a bolometric correction to , the extinction-corrected L. The reddenings derived above were used to compute . In order to estimate , we selected from the literature various LPVs and IRAS sources towards the Galactic bulge for which infrared photometry existed and for which bolometric magnitudes had been derived by integrating under the observed flux distribution. For K-L 1, the data of Wood & Bessell (1983) were used. For stars with redder intrinsic colours (i.e. substantial circumstellar shells), the IRAS sources with periods 500 days listed in Table 3 of Whitelock et al. (1991) were used. Note that the interstellar extinction to all these objects is relatively small compared to the extinction to the Galactic Center OH/IR stars, while their intrinsic colour range matches that of the OH/IR stars.
The data of Wood & Bessell and of Whitelock et al. used L and defined at 3.8 and 3.45 µm, respectively. The conversion of K-[3.8] to K-[3.45] for very red stars was obtained by using the data in Table 2a of Blommaert et al. (1993): a good fit to the data is K-[3.8] = 1.12(K-[3.45]). For our L filter defined at 3.59 µm, we interpolate to derive K-[3.59] = 1.05(K-[3.45]). Similarly, we made an appropriate modification to the bolometric corrections. For example, by definition, = [3.45]+ = [3.59]+ so that =+(K-[3.59])-(K-[3.45]) = +0.05(K-[3.45]). In Fig. 9, we plot against K-L (where L is defined at 3.59 µm). Also shown on the figure is the of Blommaert et al. (1997) (converted to our L filter) and a fitting function that we have used to derive from K-L. There is clearly a large scatter in the individual values. Our fitting function agrees with that of Blommaert et al. (1997) to within 0.2 magnitudes for K-L 3.6, which is where the majority of our objects lie. An examination of modelling of the spectral energy distributions of oxygen-rich stars with thick envelopes by Le Sidaner and Le Bertre (1993, 1996), combined with the measurements by Le Bertre (1993), confirms the results of Fig. 9. For stars with very thick envelopes (K-L 5) these model spectra predict a larger than we use here, as do the results of Blommaert et al. (1997). However, only two of our objects are this red.
Given the reddening, the observed K and L magnitudes, and , the apparent bolometric magnitude can be derived for each source. The reddening E(H-K), dereddened K magnitude , intrinsic colour (K-L), and the period are given in Tables 4, 5 and 6 for the LWHN sources, the Sjouwerman(1997) sources, and the new variables, respectively.
Table 4. Reddening and intrinsic properties of LWHN sources
Table 5. Reddening and intrinsic properties of Sjouwerman sources
Table 6. Reddening and intrinsic properties of new variables
© European Southern Observatory (ESO) 1998
Online publication: July 27, 1998