The Outer Rotation Curve from A -- F Supergiants
Session 58 -- The Galaxy
Display presentation, Thursday, 2, 1994, 9:20-6:30

## [58.10] The Outer Rotation Curve from A -- F Supergiants

Deane M. Peterson and Donald Slowik (SUNY Stony Brook)

We have recently shown (Slowik \& Peterson 1993, 1994 submitted) that the infrared oxygen triplet at $\lambda 7774$ provides a distance estimate for the A--F supergiants good to a half magnitude over the range $-4 \geq {\rm M_V} \geq -9.5$. Further, we have shown that the ionized calcium infrared triplet at $\lambda 8600$ provides an excellent estimate of intrinsic color and the reddening correction. These objects have excellent potential as probes of the Galaxy's rotation curve.

We have obtained a list of A--F supergiants in the Galactic plane from a SIMBAD search. At large distances from the Sun the greatest sensitivity to the rotation law is for objects at $l=\pm90^{\circ}$, so we have restricted the list to $135^{\circ} \geq {\rm l} \geq 90^{\circ}$, leaving 47 such objects, all brighter than m$_v = 10$. Spectra have been obtained with the Coude Feed at KPNO, confirming that all but two are luminous.

Preliminary reductions indicate that these objects do probe the outer Galaxy, even beyond 2R$_\odot$. We will present the results of that analysis and the shape of the rotation curve in the outer Galaxy, at least as defined by the objects from this restricted part of the second quadrant.

The spectra were obtained as part of the new KPNO ''queue'' observing program.