The Sproul Observatory, located in Swarthmore, Pennsylvania, has been in operation since 1912. Its major research instrument is a 24-inch, f/18 refracting telescope with lenses made by Brashear. The research conducted during the 20th century concentrated on obtaining parallaxes of nearby stars and also on the exploration of visual double and multiple star systems. The Sproul plate vault contains some 90,000 plates, from which 1500 stellar parallaxes, or about 10% of the current parallax database, have been extracted. Heintz made 54,000 observations (including those made with other telescopes) of double stars over 43 years (47,500 by micrometer, 6500 by photography), resulting in the calculation of 500 orbits and 900 newly discovered double stars. Photographic observations ceased in 1994. In 1998 the refractor was fitted with an Apogee AP-6 CCD camera, which contains a Kodak KAF 1000 chip with 1024 x 1024 pixel array, and gives a 0.45 arc seconds per pixel image scale and 8 x 8 arc minute field of view at the focal plane. The camera is operated using PMIS software. A filter wheel constructed by ISI Systems and attached to the camera contains 5-mm thick B, V, and R filters. The Sproul telescope has now been given a new task: the study of variable stars. Currently under investigation are RV Tauri and semiregular variables, SX Phoenicis stars, and also stars which are suspected of being variable, taken from the New Catalogue of Stars Suspected of Variability of Light, Nauka Publishing, Moscow 1982. Thus far, the most convincing cases for variability are NSV 656 (irregular?), 1098 (large amplitude, probably Mira type), 1470 (short P, eclipsing?), and 13514 (P~105d?). This work has been supported by a Provost Grant from Swarthmore College, by a Faculty Development Grant from Widener University, and by the Howard Hughes Medical Institute-Supported Summer Research in Science Program.

• 1869 Susan J. Cunningham becomes first Professor of Mathematics & Astronomy, retires in 1906

• 1907 William Cameron Sproul expresses intention to provide funds for a large astronomical observatory on campus of Swarthmore College, construction begins 1910

• 1912 Sproul refractor begins continuous operation in January

• 1929-36 John Anthony Miller becomes first Director of Sproul Observatory, having previously served as Professor of Mathematics & Astronomy since 1906

• 1937 Peter van de Kamp appointed Professor of Astronomy and Director, serves until 1972

• 1966-7 refractor overhauled for 7 months, tracking & setting motors installed, also new electronic console

• 1971 Grant two-coordinate measuring machine installed

• 1972 Sara Lee Lippincott appointed new Director, succeeded by John Hershey in 1980 and John Gaustad in 1982

• 1994 Photographic program terminated, micrometer observations ceased in 1998

• 1998 Apogee AP-6 CCD camera attached to refractor in March

• aperture 0.61 m
• focal length 11 m
• focal ratio f/18

• lenses made by John A. Brashear Co.
• ideal for precise measurement of positions & motions of stars
• not much affected by background campus & suburban lighting

Photographic Observations
 

• used to determine distances of stars, especially nearby faint dwarfs

• Sproul plate archive contains probably largest astrometric plate collection from one telescope:

• 90,000 photographic plates obtained by faculty, staff, & students since 1912
• 1500 parallax determinations (~ 10% of current parallax database)

Micrometer Observations
 

• micrometer observations of visual binary stars, their orbits & masses

• visual observations, mainly by W.D. Heintz since 1967:

• 500 binary star orbits
• 900 newly discovered binaries
• study of low-mass binaries

 
 
Kodak KAF 1000 Chip  
 

• 1024 x 1024 pixel array, 24 m square pixels
• total surface area of chip 24.6 mm x 24.6 mm square
• front-illuminated, no antiblooming
• thermoelectrically cooled

AP-6 Camera Mounted on 24-Inch
 

• field of view 8¢ x 8¢
• pixel scale 0.45¢ ¢ per pixel at focal plane
• 16-bit images, ~ 2 Mb each
• camera operated by PMIS software, full version
• filter wheel by ISI Systems
• standard B, V, R filters from Omega Optical

Bias (Zero Exposure) Frames

• several taken during night
• measures elecronic noise

Dark Frames

• taken at same exposures as star fields, but with shutter closed
• measures thermal noise

Flat Field Frames

• taken of uniformly lit sky at sunset
• 3-5 taken through each filter B, V, and R
• used to correct for uneven sensitivity across CCD

Sample Field (Target + Comparison) for UY CMa

Long Period & Unusual Variables
 

• RV Tauri and Semiregular Variables
• Mira-type Variables
• Suspected Variables

Short Period Variables
 

• SX Phoenicis Variables
 

 


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Plots of V magnitude (or R magnitude) of the target star relative to a comparison star, usually indicated by T-C in the legend, versus Julian Date for several suspected variables. In nearly all cases, the R magnitude plot is similar. If two comparison stars were available in the field, then the difference in magnitudes between comparison stars is also plotted to show the size of the random error.
 
All processing has been done using IRAF (Image Reduction and Analysis Facility), with instrumental magnitudes obtained using the imexamine feature of the apphot package within IRAF.
 

NSV 656 (BD +36° 341)

Variation in relative V magnitude observed over 1998 October 22 through 1999 January 15, showing a definite variation in brightness of range ~1 magnitude during the interval covered. Its magnitude is listed as mpg ~ 11 to 11.5 (Sonneberg), and its spectral type is listed as M. More data over a larger baseline is needed, but it is possibly an irregular variable.

 
NSV 1098 (BD +70° 236)

Variation in relative V magnitude observed over 1998 October 23 through 1999 January 10, showing a steady decrease in brightness of about 3 magnitudes during this period. Its magnitude is listed as mpg ~ 13.5 to 15.5 (Johnson et al.), and its spectral type as M4. More data over a larger baseline are needed, but the large amplitude variability over nearly three months suggests that it may be classed tentatively as a Mira-type variable with a period in excess of 480 days.

Variation in relative V magnitude observed over 1998 July 21 through December 2, showing a periodicity of P ~ 105 d. Additionally, the two maxima display different heights. Its magnitude is listed as mpg ~ 10.5 to 11.4 (Bamberg). A second comparison star was added in October, and so the difference between the two comparison stars is plotted in the lower part of the graph beginning around JD 2451100.

Variation in relative R magnitude observed over 1998 July 21 through December 2. There is a significant gap of over 30 days in the observations in the first half of the graph, where a maximum may have occurred. If so, then the period is ~ 70 d. The random error as indicated by the relative magnitude of the comparison stars is rather large, on the order of ± 0.07 mag. The photographic magnitude of this object is listed as mpg ~ 11.6 to 12.6. Further observations taken at regular intervals of less than one week are needed.

CY Aquarii  (SX Phoenicis - Type Variable)
 
Variation in relative V magnitude observed on night of 1998 August 3. This is an 11th magnitude SX Phoenicis-type star with an amplitude of about 0.8 magnitudes and a period of 88 min.

 
The authors are grateful for support for this work by a Provost Grant from Swarthmore College, by a Faculty Development Grant from Widener University, and by the Howard Hughes Medical Institute-Supported Summer Research in Science Program at Swarthmore College. We also wish to thank Dr. Brian Martin, Dr. Larry Marschall, Dr. Dennis Dawson, and Mr. Wayne Brown for guidance in the planning and implementation of the new research program.