Photometric Data Photometric Data Collection At The Burke Collection At The Burke

Gaffney ObservatoryGaffney ObservatoryBy By

Jayme DerrahJayme Derrah

Overview

• Photometry At The BGO Photometry At The BGO • The Photometer The Photometer • Collecting DataCollecting Data• ExtinctionExtinction• PolarisPolaris• ResultsResults• Problems EncounteredProblems Encountered

Photometry At The BGOPhotometry At The BGO

• No one has done this at the BGO No one has done this at the BGO for yearsfor years

• Collect data in hopes of finding Collect data in hopes of finding extinction coefficients for Halifax extinction coefficients for Halifax skies. skies.

• No other observations in Halifax No other observations in Halifax to compare withto compare with

• Collect data on several Cepheid Collect data on several Cepheid Variable stars, including PolarisVariable stars, including Polaris

The PhotometerThe Photometer

• Optec SSP-3 Optec SSP-3 PhotometerPhotometer

• Works like a 1 Works like a 1 pixel CCDpixel CCD

• Measures Measures apparent apparent brightness of brightness of the object in the object in questionquestion

Collecting DataCollecting Data

• Take readings in the blue, visual Take readings in the blue, visual and ultraviolet ends of the and ultraviolet ends of the spectrumspectrum

• Most readings on the sky are Most readings on the sky are dominated by noise in the uncooled dominated by noise in the uncooled photometerphotometer

• Need to collect data on standard Need to collect data on standard stars at different air massesstars at different air masses

• For variable stars, a nearby For variable stars, a nearby reference star is needed reference star is needed

DataData

• Use the apparent brightness Use the apparent brightness readings to determine the readings to determine the apparent magnitude of the apparent magnitude of the object using the equation:object using the equation:

m1-m2= 2.5*log(b1/b2)m1-m2= 2.5*log(b1/b2)

ExtinctionExtinction

• Produced by haze, clouds, fog, Produced by haze, clouds, fog, which cause changes in sky which cause changes in sky transparency transparency

• Greater extinction at larger Greater extinction at larger distances from zenithdistances from zenith

• The greater the air mass, the more The greater the air mass, the more light that is absorbed . light that is absorbed .

• With accurate extinction With accurate extinction coefficients, can standardize data coefficients, can standardize data collected on stars, such as Polariscollected on stars, such as Polaris

Extinction (continued)Extinction (continued)

• To determine accurate extinction To determine accurate extinction coefficients, need readings on many coefficients, need readings on many different standard stars observed at a different standard stars observed at a variety of air massesvariety of air masses

k'y = 0.213 (0.13-0.16 at 7000 ft)k'y = 0.213 (0.13-0.16 at 7000 ft)

k"y = -0.025 (0.00 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 = 0.154 (0.10-0.13 at 7000 ft)

k"by = -0.033 (same at 7000 ft)k"by = -0.033 (same at 7000 ft)

k'ub = 0.281 (0.21-0.25 at 7000 ft)k'ub = 0.281 (0.21-0.25 at 7000 ft)

PolarisPolaris

• Polaris is the closest and brightest Cepheid Polaris is the closest and brightest Cepheid Variable star to usVariable star to us

• Cepheids are variable stars whose Cepheids are variable stars whose luminosities are proportional to their luminosities are proportional to their periodsperiods

• Polaris has a period of about four daysPolaris has a period of about four days• Its period is slowly increasing, and it may Its period is slowly increasing, and it may

soon stop pulsating since its amplitude is soon stop pulsating since its amplitude is decreasingdecreasing

• Not many observations done on it for yearsNot many observations done on it for years• The air mass around Polaris stays relatively The air mass around Polaris stays relatively

constant, so it is good to observe at the constant, so it is good to observe at the BGOBGO

ResultsResults

• Light curve from last summer:Light curve from last summer:

Problems EncounteredProblems Encountered

• Transparency changes throughout Transparency changes throughout the nightthe night

• Thin cirrus clouds often difficult to Thin cirrus clouds often difficult to detectdetect

• Tightening the clamps on the Tightening the clamps on the telescopetelescope

• Aligning the telescopeAligning the telescope• Finding Polaris and the stars in its Finding Polaris and the stars in its

field field

ThankThank YouYou

• Special thanks to Dr. David Special thanks to Dr. David TurnerTurner