Engineering topics

Stetson, P. B.

Publications and source records attributed to Stetson, P. B..

21 records · Page 2

NASA NTRS1980

The dwarf spheroidal galaxy in Draco. III - Proper motion membership probabilities

PDS astrometry from photographic plates of the Draco dwarf galaxy is used to derive proper motion membership probabilities for stars measured in earlier photometric studies. It is found that removing probable foreground stars from the color-magnitude diagram of Draco tends to strengthen earlier conclusions about the structure of the giant and subgiant branches. The possible existence of an upper horizontal branch containing core helium-burning stars of more than one solar mass is still questionable. A reduced proper motion diagram for probable foreground stars is presented and discussed briefly.

Stetson, P. B.↗

NASA NTRS1979

The dwarf spheroidal galaxy in Draco. I - New BV photometry. II - Galactic foreground reddening

BV photoelectric photometry for 39 stars and BV photographic photometry for 514 stars in the field of the Draco dwarf spheroidal galaxy are presented. The color-magnitude diagram for 512 of these field stars is found to display a well-defined red horizontal branch as well as a red giant branch whose observed width is comparable to the accidental photometric error. The results also indicate that a more diffuse sequence of stars lies about 0.1 mag to the blue of the giant branch and that an upper horizontal branch of more massive core helium-burning stars may also be present. The foreground reddening toward Draco is then determined by narrow-band uvby-beta photometry of galactic B-A-F stars.

Stetson, P. B.↗

NASA NTRS1979

Photographic stellar photometry with the PDS microdensitometer

A technique for photographic stellar photometry with the PDS microdensitometer is described. It employs a least-squares fit to a model density profile to derive an instrumental magnitude index, an image-abnormality index, and the local value of the background density for each image. The instrumental magnitude index is calibrated in terms of true magnitude by the same methods as for iris photometry. A preliminary test of the method using plates of the open cluster NGC 188 indicates that a precision comparable to or slightly better than that of conventional iris photometry or other methods of PDS reduction may easily be attained. Possibilities for the future elaboration of the technique are mentioned.

Stetson, P. B.↗