Tucson Nighttime Scientific Staff
Areas of Interest
Galactic Structure, Galactic Halo, Horizontal Branch Stars
Recent Research Results
The oldest stars in the Galaxy are found in the Galactic Halo.
The identification of halo stars in the presence of the much more numerous
disk stars is a continuing problem. The RR Lyrae and Blue Horizontal Branch
(BHB) stars are of great value for delineating the halo because they are less
easily confused with disk stars than those of later spectral type. A recent
discussion on the problem of isolating BHB stars is given by Kinman et al.
1994 AJ 108, 1722 where it is shown that there appears to be a disk component
of the halo in addition to the familiar spherical component. A preliminary
description of the properties of the nearby BHB stars and the problem of
determining the HB morphology for these nearby stars is given in Kinman et al.
1996, "Formation of the Galactic Halo - Inside and Out", ASP Conf. Ser. vol
92, page 36 and Bragaglia et al. page 175 of the same volume.
The presence of ordered motion among the halo stars suggests that such stars
have been acquired recently by the Galaxy since it would be expected that such
motion would be randomized within a fraction of the Galactic lifetime.
Evidence for such ordered motion has been found among a sample of BHB and
RR Lyrae stars in fields near the North Galactic Pole. A short summary of
this work and a discussion of this "streaming" motion is given by Kinman et al.
(1996, AJ, 111, 1164)
Future Research Plans
It is planned to extend the current work on the kinematics of halo stars
to a larger area near the North Galactic Pole so that the area where
the "streaming" occurs may be properly delineated. This involves the
photometric evaluation of candidate halo stars as well as the
determination of their radial velocities. The photometric confirmation of
BHB star candidates is also being carried out in N. hemisphere fields in
the Anticenter and at intermediate Galactic latitudes. This data will be
used for an investigation of the halo space density within a few kpc of the
Sun. A program is also in progress (with Christine Allen of UNAM) for
investigating the orbits of nearby halo stars.
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