• 1910 construction of refractor begins, from donation by State Senator Sproul

• 1912 continuous operation of Sproul refractor begins in January

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

• 1998 Apogee AP-6 CCD camera attached to refractor, cables run to observing alcove at dome entrance

Specifications

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

• favorable for precise measurement of positions & motions of stars

• has advantage that instrument not much affected by background campus & suburban lighting

Seeing Limitations

• minimum seeing disk on photographic plates ~ 1.0¢ ¢ (typical ~ 1.5¢ ¢ )
• minimum visual resolution ~ 0.1¢ ¢ (typical ~ 0.3¢ ¢ )

Limiting Magnitudes

• practical limiting visual magnitude ~ 13
• practical limiting photographic magnitude ~ 14
• sky background magnitude ~ 15

• photographic observations to determine distances of stars, especially nearby faint dwarfs

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

Legacy Of Past Projects

• Sproul plate archive contains probably largest astrometric plate collection from one telescope:
• 90,000 photographic plates since early 1900s:
• used to make 1400 parallax (distance) determinations

• Visual observations, mainly by W.D. Heintz since 1967:
• 500 binary star orbits
• 900 newly discovered binaries
• study of low-mass binaries, including first "brown dwarf" candidates (Wolf 424 in 1972)

• Photographic program terminated in 1994

• Micrometer observations terminated in 1998

• very large chip yields workable field of view with f/18 refractor
• quantum efficiency ~ 50-80%

Kodak KAF 1000 Chip

• 1024 x 1024 pixel array
• surface area 24.6 x 24.6 mm square
• each pixel 24 m square
• linear well depth 170K e
• dark count ~ 1.0 e/sec at -25° C (doubles for every ~6° C warmer)

System Conversion

• download > 45K pixels/sec, total frame 24 sec

Exposures

• mechanical iris shutter
• exposure time 0.03 sec to 10,400 sec
• frame size full frame, subframe, focus mode

Cooling

• thermoelectric cooler with forced air.
• minimum 35° C below ambient at 25° C (remote boost unit adds 5-8° C cooling)
• 20 min temperature transition time for sensor safety
• Software programmable temperature

Camera Head

• 8061-T6 aluminum body, hard blue anodized
• BBAR coated silica windows
• camera head is 6x6 in x 1.3 in thick (heat sinks & fans add 1.2 in)
• 3 lbs

AP-6 Camera Mounted on 24-Inch*

• yields 8¢ x 8¢ field of view with 24-inch at f/18*
• pixel scale 0.45¢ ¢ per pixel at focal plane
• 16-bit images, each takes up ~ 2 Mb of space

Filter Wheel

• constructed by ISI Systems, Santa Barbara, CA
• contains eight, 2-inch square slots
• standard B, V, R filters, 5 mm thick, from Omega Optical
• controlled by DOS program

Software

• PMIS, full version

Computer

• PowerSpec PC
• 233 MHz Pentium II processor
• 64 Mb RAM

The New Layout & Observing Room (Alcove)*

Bias (Zero Exposure) Frames*

• "zero exposure" frames
• several taken during the night
• measures electronic 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

Focus Frames*

• usually taken of close binary star system
• focus varies with temperature

Target and Comparison Stars (Raw)*

• expose field of variable star with comparison star*
• at least one comparison star in field, preferably two
• images stored in FITS format

• use IRAF software, developed at Kitt Peak National Observatory
• correct images for bias, dark, and flat fields
• subtracts sky background
• determines peak count and FWHM of stellar profile*
• calculates instrumental magnitudes

Reasons Why Stars Vary in Brightness

• Rotation of Uneven Stellar Surface – Star Spots or Hot Spots
• Pulsation of Stellar Surface
• Chromospheric or Flare Activity
• Eclipses in Binary System
• Nova or Supernova Events

Types of Variable Stars Observed at Sproul

• Long Period & Unusual Variables

• Extragalactic Supernovae
• RV Tauri and Semiregular Variables

• Mira-type Variables
• Suspected Variables

• Short Period Variables

• SX Phoenicis Variables

• Visual Binaries

Suspected Variables Which Have Been Confirmed to Be Variable

NSV 656*

• irregular (?)

NSV 1098*

• large amplitude
• probably Mira type

NSV 1470*

• short period
• eclipsing (?)

NSV 13514*

• P ~ 105 d