M. Aaronson

Northern Milky Way carbon stars - New candidates, JHK photometry, and radial velocities

Data are presented for low-latitude northern Milky Way carbon stars. Coordinates and cross identifications are given for carbon stars in nine fields thought to be unusually transparent. Of these, 142 are confirmed new discoveries. Five hundred thirty-eight JHK photometric observations are reported for 480 stars. Six hundred twenty velocity measurements are presented for 424 stars. Improved coordinates are given for many previously discovered stars. Averaged JHK photometry and velocities are summarized for a sample of 400 stars. 25 refs.

Carbon stars at 2R0 and the rotation of the Milky Way

Un ensemble de 268 etoiles au carbone dont la photometrie et les vitesses sont connues est utilise pour determiner la rotation differentielle dans la Galaxie externe

On Main Sequence Distances and the Local Distance Scale

We analyze a deep CMD for the LMC cluster NGC1831, based on CTIO PFCCD frames. More than 4 magnitudes of main sequence (MS) are evident, as well as a prominent clump, and a few possible giant branch stars. We fit the MS to a series of models and Galactic clusters, and derive a distance of 18.3±0.1 and an age of 0.5±0.1 Gyr, for an abundance of about 2/3 solar ([Fe/H]~0.23), based on the VandenBerg models (Vandenberg and Poll 1989). A fit to the empirical Pleiades MS, assuming an intrisic modulus of 5.6, gives a LMC modulus of 18.25–18.35, after an adjustment for the relative abundance difference of-0.2.

Carbon star reddenings and low latitude H I column densities

Foreground H I column densities are computed toward 564 low latitude northern and southern hemisphere carbon stars, using photometric distances and an assumed rotation curve. Separate dust-to-H I ratios and dereddened (J-H, H-K) loci are obtained for the two hemispheres. A small but statistically significant difference is found between the two samples, which is attributed to a small difference in photometric systems. 16 refs.

E2 - an intermediate-age LMC cluster

A color-magnitude diagram is presented for the faint star cluster E2, located near the tip of the Magellanic Stream. The main-sequence turnoff, a few giants, and a giant clump can be discerned. Comparisons with VandenBerg models show E2 to be a 1.5 Gyr old cluster with abundance Z of about 0.01 at the distance of the LMC, and thus similar to the more populous intermediate-age LMC clusters. The existence of cluster formation at a large distance from the LMC center (E2 is at almost 8 deg radius) is discussed in the context of the star-formation history, structure, and kinematics of the outer halo of the Large Magellanic Cloud. 42 references.