Photometric Data Collection At The Burke Gaffney Observatory

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Photometric Data Collection At The Burke Gaffney
Observatory

• By
• Jayme Derrah

2
Overview

• Photometry At The BGO
• The Photometer
• Collecting Data
• Extinction
• Polaris
• Results
• Problems Encountered

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Photometry At The BGO

• No one has done this at the BGO for years
• Collect data in hopes of finding extinction
  coefficients for Halifax skies.
• No other observations in Halifax to compare with
• Collect data on several Cepheid Variable stars,
  including Polaris

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The Photometer

• Optec SSP-3 Photometer
• Works like a 1 pixel CCD
• Measures apparent brightness of the object in
  question

5
Collecting Data

• Take readings in the blue, visual and ultraviolet
  ends of the spectrum
• Most readings on the sky are dominated by noise
  in the uncooled photometer
• Need to collect data on standard stars at
  different air masses
• For variable stars, a nearby reference star is
  needed

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Data

• Use the apparent brightness readings to determine
  the apparent magnitude of the object using the
  equation
• m1-m2 2.5log(b1/b2)

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Extinction

• Produced by haze, clouds, fog, which cause
  changes in sky transparency
• Greater extinction at larger distances from
  zenith
• The greater the air mass, the more light that is
  absorbed .
• With accurate extinction coefficients, can
  standardize data collected on stars, such as
  Polaris

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Extinction (continued)

• To determine accurate extinction coefficients,
  need readings on many different standard stars
  observed at a variety of air masses
• k'y 0.213 (0.13-0.16 at 7000 ft)
• k"y -0.025 (0.00 at 7000 ft)
• k'by 0.154 (0.10-0.13 at 7000 ft)
• k"by -0.033 (same at 7000 ft)
• k'ub 0.281 (0.21-0.25 at 7000 ft)

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Polaris

• Polaris is the closest and brightest Cepheid
  Variable star to us
• Cepheids are variable stars whose luminosities
  are proportional to their periods
• Polaris has a period of about four days
• Its period is slowly increasing, and it may soon
  stop pulsating since its amplitude is decreasing
• Not many observations done on it for years
• The air mass around Polaris stays relatively
  constant, so it is good to observe at the BGO

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Results

• Light curve from last summer

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Problems Encountered

• Transparency changes throughout the night
• Thin cirrus clouds often difficult to detect
• Tightening the clamps on the telescope
• Aligning the telescope
• Finding Polaris and the stars in its field

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Thank You

• Special thanks to Dr. David Turner