Photometric Data Collection At The Burke Gaffney Observatory By Jayme Derrah

Overview Photometry At The BGOPhotometry At The BGO The PhotometerThe Photometer Collecting DataCollecting Data ExtinctionExtinction PolarisPolaris ResultsResults Problems EncounteredProblems Encountered

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

The Photometer Optec SSP-3 PhotometerOptec SSP-3 Photometer Works like a 1 pixel CCDWorks like a 1 pixel CCD Measures apparent brightness of the object in questionMeasures apparent brightness of the object in question

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

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

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

Extinction (continued) To determine accurate extinction coefficients, need readings on many different standard stars observed at a variety of air massesTo determine accurate extinction coefficients, need readings on many different standard stars observed at a variety of air masses k'y = ( at 7000 ft) k"y = (0.00 at 7000 ft) k'by = ( at 7000 ft) k"by = (same at 7000 ft) k'ub = ( at 7000 ft)

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

Results Light curve from last summer:Light curve from last summer:

Problems Encountered Transparency changes throughout the nightTransparency changes throughout the night Thin cirrus clouds often difficult to detectThin cirrus clouds often difficult to detect Tightening the clamps on the telescopeTightening the clamps on the telescope Aligning the telescopeAligning the telescope Finding Polaris and the stars in its fieldFinding Polaris and the stars in its field

ThankYou Thank You Special thanks to Dr. David TurnerSpecial thanks to Dr. David Turner