Astron. Astrophys. 364, 102-136 (2000)

Appendix A: Comments on other possible BHB star candidates

Philip & Adelman (1993) found 19 BHB star candidates by searching the Hauck & Mermilliod photometric catalogue (1980) for stars with the appropriate Strömgren indices (e.g. one of their criteria was that the c₁ index should exceed 1.15). Bragaglia et al. (1996) made preliminary measurements of the  of fourteen of these stars and noted that their rotations were mostly too large for them to be BHB stars. Adelman & Philip (1996b) obtained high resolution spectra of seven of these stars (HD 15042, HD 42999, HD 47706, HD 48567, HD 49224, HD 67426 & HD 79566) and also concluded that their rotational velocities were too high for them to be BHB stars. Of the remaining seven stars observed by Bragaglia et al., five (HD 53042, HD 67542, HD 128855, HD 181119 & HD 185174) have  greater than 60 km s. Two, however, (HD 83751 and  HD 140194) have   30 km s which is within the range of rotations observed for BHB stars; both stars have Population I kinematics ¹⁸ and roughly solar abundances; thus in spite of their low , they are unlikely to be BHB stars. The remaining five of the nineteen candidates listed by Philip & Adelman were not observed by us but some comments can be made on the probability that they are BHB stars. HD 100548 was classified as G8 III by Upgren (1962) from its objective prism spectrum. The photometry of this star listed in the Hauck & Mermilliod catalogue (1980) appears to be spurious because the star is not found among those in the listed reference (Drilling & Pesch 1973). Three of the remaining stars (HD 94509, HD 120401 & HD 304325) have very low galactic latitudes (b 3^o) while HD 123664 is likely to be a member of the Scorpio-Centaurus Association (Glaspey 1972; Slawson et al. 1992). It therefore seems unlikely that any of Philip & Adelman's nineteen BHB star candidates have a high probability of being BHB stars. Their work was valuable, however, because it has shown the need to use criteria in addition to Strömgren photometry in the identification of these stars.

Listed below are a number of other stars that have sometimes been suggested to be BHB stars; this list is not intended to be exhaustive. Spectra of one of them (BD +33 2171) should be obtained since its classification is doubtful from the available data. The others are almost certainly not BHB stars.

• HD 52057 Stetson (1991). Kilkenny & Hill (1975) classified the star as B6 and almost certainly subluminous.

• HD 57336 FHB 24 in Philip (1984). Huenemoerder et al. (1984) noted that the star has Population I metal-line characteristics. It is broad-lined.

• BD +33 2171 FHB 2 in Philip (1984). Its colour () = +0.276 is too red for it to be a BHB star if the reddening given by the STD maps (1998) ( = 0.021) is correct. The  of 42 km s is also somewhat high for a BHB star.

• HD 176387 Stetson (1991) is the RR Lyrae star MT Tel.

• HD 203563 Stetson (1991) is broad-lined.

• HD 214539 Stetson (1991). Feast et al. (1955) discovered its very high radial velocity (+333 km s) and Przybylski (1969) found it to be metal-poor and considered it to be an HB star. A two-sigma upper limit to its Hipparcos parallax (ESA 1997), however, means that it cannot be closer than 735 pc which would give it an of -2.1 or brighter so that it cannot be a HB star.

© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000
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