Chapter 10
Photometry
Abstract Photometry is one of the key observation pillars of astrophysics. New
techniques have improved the precision of photometry to the point that exoplanet
transit observations are possible with small telescopes. This chapter details the methods by example to perform photometry, the reduction of images taken for photometric
purposes, and the interpretation of the results.
10.1 Introduction
Photometry, the measurement of the amount of electromagnetic radiation received
from an object, is one of the cornerstones of modern astrophysics. The ratio of two
fluxes, in astronomy a colour, is an important tool for classification and identification
of stellar objects.
Time-dependent photometry is used to understand the physics of many astronomical objects such as cataclysmic variables, accretion discs, asteroids and Cepheid
variables. Cepheid variables are an important component of the distance ladder that
leads to the measurement of the most distant objects in the observable universe.
High-precision, time-dependent photometry is one of the principal methods for
the detection of planets surrounding stars, exoplanets, used in astrophysics.
The advent of the CCD, coupled with increased computer power, has considerably
improved the accuracy, precision, and ease of photometric measurements. This coupled with modern small telescopes, such as those found in many university teaching
observatories, means that students are now able to perform milli-magnitude measurements. Such precision is needed to observe and detect exoplanet transit, and once
again, small telescopes are making a contribution to science and our understanding
of the universe.
There are two fundamental approaches to photometry: aperture and PSF. And
there are three approaches to the calibration of the results: absolute, differential, and
instrumental.
When we measure the light from a distant object, we measure the light coming
not only from the object, but also from the sky, along with stray interstellar light and
scintillation noise, in addition to the false signal caused by the remnants of the bias
© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_10
145
Photometry
Abstract Photometry is one of the key observation pillars of astrophysics. New
techniques have improved the precision of photometry to the point that exoplanet
transit observations are possible with small telescopes. This chapter details the methods by example to perform photometry, the reduction of images taken for photometric
purposes, and the interpretation of the results.
10.1 Introduction
Photometry, the measurement of the amount of electromagnetic radiation received
from an object, is one of the cornerstones of modern astrophysics. The ratio of two
fluxes, in astronomy a colour, is an important tool for classification and identification
of stellar objects.
Time-dependent photometry is used to understand the physics of many astronomical objects such as cataclysmic variables, accretion discs, asteroids and Cepheid
variables. Cepheid variables are an important component of the distance ladder that
leads to the measurement of the most distant objects in the observable universe.
High-precision, time-dependent photometry is one of the principal methods for
the detection of planets surrounding stars, exoplanets, used in astrophysics.
The advent of the CCD, coupled with increased computer power, has considerably
improved the accuracy, precision, and ease of photometric measurements. This coupled with modern small telescopes, such as those found in many university teaching
observatories, means that students are now able to perform milli-magnitude measurements. Such precision is needed to observe and detect exoplanet transit, and once
again, small telescopes are making a contribution to science and our understanding
of the universe.
There are two fundamental approaches to photometry: aperture and PSF. And
there are three approaches to the calibration of the results: absolute, differential, and
instrumental.
When we measure the light from a distant object, we measure the light coming
not only from the object, but also from the sky, along with stray interstellar light and
scintillation noise, in addition to the false signal caused by the remnants of the bias
© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_10
145