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Questions and Answers
What parameters define the shape of closed orbits?
What parameters define the shape of closed orbits?
If an ellipse has a semi-major axis of $a = 4$ and a semi-minor axis of $b = 3$, what is the area of the ellipse?
If an ellipse has a semi-major axis of $a = 4$ and a semi-minor axis of $b = 3$, what is the area of the ellipse?
An orbit is defined by how many orbital elements?
An orbit is defined by how many orbital elements?
What is the eccentricity of a circular orbit?
What is the eccentricity of a circular orbit?
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What does the variable 'e' represent when defining an orbit?
What does the variable 'e' represent when defining an orbit?
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Given the distance from the origin to a focus is $c = ae$, what does 'e' stand for?
Given the distance from the origin to a focus is $c = ae$, what does 'e' stand for?
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If the semi-major axis (a) of an ellipse is equal to the semi-minor axis (b), what shape does the ellipse become?
If the semi-major axis (a) of an ellipse is equal to the semi-minor axis (b), what shape does the ellipse become?
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What is the range of possible values for eccentricity (e) in an elliptical orbit?
What is the range of possible values for eccentricity (e) in an elliptical orbit?
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Which pair of parameters uniquely defines the shape of an ellipse?
Which pair of parameters uniquely defines the shape of an ellipse?
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Besides the semi-major axis and eccentricity, what additional information is necessary to fully describe an orbit for observational purposes?
Besides the semi-major axis and eccentricity, what additional information is necessary to fully describe an orbit for observational purposes?
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What does the orbital element 'inclination' ($i$) represent?
What does the orbital element 'inclination' ($i$) represent?
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What does the term 'longitude of ascending node' ($Ω$) define?
What does the term 'longitude of ascending node' ($Ω$) define?
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Which of the following terms refers to the point in an orbit that is closest to the Earth?
Which of the following terms refers to the point in an orbit that is closest to the Earth?
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Which of the following terms is a general term used to describe the point of closest approach in an orbit around a star?
Which of the following terms is a general term used to describe the point of closest approach in an orbit around a star?
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What is the general term for the point in an orbit that is farthest from the central body?
What is the general term for the point in an orbit that is farthest from the central body?
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What do the orbital elements omega ($ω$) and true anomaly ($ν$) define together?
What do the orbital elements omega ($ω$) and true anomaly ($ν$) define together?
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According to Kepler's Third Law, how is the orbital period ($P_b$) related to the semi-major axis ($a$) and the total mass ($M$) of a binary system?
According to Kepler's Third Law, how is the orbital period ($P_b$) related to the semi-major axis ($a$) and the total mass ($M$) of a binary system?
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What do 'post-Keplerian parameters' describe?
What do 'post-Keplerian parameters' describe?
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Why are 'post-Keplerian parameters' useful for testing theories of gravity?
Why are 'post-Keplerian parameters' useful for testing theories of gravity?
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In the context of binary systems, what does the inclination angle refer to?
In the context of binary systems, what does the inclination angle refer to?
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A binary system has a total system mass of $3 M_\odot$ and an orbital period of 5 hours. Which formula should be used to calculate the size of the orbit in metres?
A binary system has a total system mass of $3 M_\odot$ and an orbital period of 5 hours. Which formula should be used to calculate the size of the orbit in metres?
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If a binary system's orbital elements are observed to be constant over time, what can be inferred?
If a binary system's orbital elements are observed to be constant over time, what can be inferred?
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What does $dA/dt = const$ represent in Kepler's Laws?
What does $dA/dt = const$ represent in Kepler's Laws?
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What is a significant implication of Kepler's Second Law ($dA/dt = const$) for a binary system's orbit?
What is a significant implication of Kepler's Second Law ($dA/dt = const$) for a binary system's orbit?
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What does the mass-luminosity relation primarily allow us to infer about stars?
What does the mass-luminosity relation primarily allow us to infer about stars?
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What realization did the initial calculations of stellar ages based on gravitational contraction lead to?
What realization did the initial calculations of stellar ages based on gravitational contraction lead to?
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In the context of stellar ages, what does the expression age ≈ E/L
represent?
In the context of stellar ages, what does the expression age ≈ E/L
represent?
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What is the Kelvin-Helmholtz timescale ($t_{KH}$) primarily used to estimate?
What is the Kelvin-Helmholtz timescale ($t_{KH}$) primarily used to estimate?
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What is the significance of Eddington's 1924 plot in the context of stellar physics?
What is the significance of Eddington's 1924 plot in the context of stellar physics?
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What is the formula for gravitational potential energy ($U$) used to estimate the Kelvin-Helmholtz timescale?
What is the formula for gravitational potential energy ($U$) used to estimate the Kelvin-Helmholtz timescale?
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If the Kelvin-Helmholtz timescale for the Sun is approximately 20 million years, what does this suggest when compared to geological and biological data indicating a much older Earth?
If the Kelvin-Helmholtz timescale for the Sun is approximately 20 million years, what does this suggest when compared to geological and biological data indicating a much older Earth?
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According to the mass-luminosity relation, how does luminosity (L) generally scale with mass (M)?
According to the mass-luminosity relation, how does luminosity (L) generally scale with mass (M)?
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What is the main characteristic of a visual binary system?
What is the main characteristic of a visual binary system?
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How do we infer the existence of a second component in an astrometric binary system?
How do we infer the existence of a second component in an astrometric binary system?
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What effect occurs in an eclipsing binary when one star passes in front of another?
What effect occurs in an eclipsing binary when one star passes in front of another?
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In a spectroscopic binary system, how are spectral lines affected?
In a spectroscopic binary system, how are spectral lines affected?
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What allows us to determine the total system mass (M) in a binary system?
What allows us to determine the total system mass (M) in a binary system?
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Which characteristic is NOT associated with an eclipsing binary system?
Which characteristic is NOT associated with an eclipsing binary system?
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What is a common misconception about double stars being classified as binary systems?
What is a common misconception about double stars being classified as binary systems?
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In the context of binary stars, what does 'Pb' refer to?
In the context of binary stars, what does 'Pb' refer to?
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What effect does a circular orbit have on spectral variations over time?
What effect does a circular orbit have on spectral variations over time?
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If two stars in a binary system are located 1 kpc apart, what impact does their distance have on our ability to detect them?
If two stars in a binary system are located 1 kpc apart, what impact does their distance have on our ability to detect them?
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What is the relation describing the Doppler Effect in the provided formula?
What is the relation describing the Doppler Effect in the provided formula?
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What condition makes the Doppler effect potentially undetectable?
What condition makes the Doppler effect potentially undetectable?
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If a signal is transmitted at 123.456 MHz, what is a key factor that affects the observed Doppler shift?
If a signal is transmitted at 123.456 MHz, what is a key factor that affects the observed Doppler shift?
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What is the required spectral resolution to notice Doppler shifts from the Mars Rovers transmitting at 8 GHz?
What is the required spectral resolution to notice Doppler shifts from the Mars Rovers transmitting at 8 GHz?
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What information can be gathered from spectral lines of a star?
What information can be gathered from spectral lines of a star?
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How can stellar masses be determined according to the methods outlined?
How can stellar masses be determined according to the methods outlined?
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Flashcards
Binary Stars
Binary Stars
A star system consisting of two stars orbiting a common center of mass.
Kepler's Laws
Kepler's Laws
Three laws that describe the motion of planets around the sun, also applicable to binary stars.
Types of Binaries
Types of Binaries
Different classifications of binary star systems based on visibility and interaction.
Doppler Effect
Doppler Effect
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Orbital Elements
Orbital Elements
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Eccentricity
Eccentricity
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Semi-major Axis
Semi-major Axis
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Area of an Ellipse
Area of an Ellipse
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Semi-major Axis (a)
Semi-major Axis (a)
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Eccentricity (e)
Eccentricity (e)
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Inclination (i)
Inclination (i)
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Longitude of Ascending Node (Ω)
Longitude of Ascending Node (Ω)
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Argument of Periastron (ω)
Argument of Periastron (ω)
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True Anomaly (ν)
True Anomaly (ν)
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Periapsis Terms
Periapsis Terms
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Orbital Period (Pb)
Orbital Period (Pb)
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Inclination Angle
Inclination Angle
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Post-Keplerian Parameters
Post-Keplerian Parameters
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Newtonian Gravity
Newtonian Gravity
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Total System Mass (M⊙)
Total System Mass (M⊙)
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Relativistic Orbit
Relativistic Orbit
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Central Potential
Central Potential
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Relative velocity
Relative velocity
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Spectral resolution
Spectral resolution
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Eccentric orbit
Eccentric orbit
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H-R diagram
H-R diagram
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Bolometric luminosity
Bolometric luminosity
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Stellar density
Stellar density
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Stefan-Boltzmann relation
Stefan-Boltzmann relation
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Visual Binary
Visual Binary
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Astrometric Binary
Astrometric Binary
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Eclipsing Binary
Eclipsing Binary
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Spectroscopic Binary
Spectroscopic Binary
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Angular separation
Angular separation
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Parallax
Parallax
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Light Curve
Light Curve
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Main Sequence Binaries
Main Sequence Binaries
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Mass-Luminosity Relation
Mass-Luminosity Relation
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Eddington's Observation
Eddington's Observation
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Stellar Ages
Stellar Ages
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Kelvin-Helmholtz Timescale
Kelvin-Helmholtz Timescale
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Gravitational Potential Energy
Gravitational Potential Energy
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Nuclear Fusion in Stars
Nuclear Fusion in Stars
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Observational Fact
Observational Fact
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Study Notes
Lecture 3: Binary Stars
- Lecture was on binary stars, part of the "Observing the Universe" course
- The lecturer was Prof. Evan Keane
- The date of the lecture was Thursday 23rd January 2025 at 12:00
- Lecture 2 covered spectral classification of stars, spectral line origins, relevant physical processes, and the Hertzsprung-Russell diagram.
- Lecture 3 goal: Understand binarity manifestations in stars and what can be learned from quantifying binarity.
- Lecture 3 outline: Binary parameters, Kepler's laws, types of observed binaries, Doppler effect, stellar masses.
L2 Recap
- Spectral classification of stars
- Origin of spectral lines
- Physical processes relevant to spectral lines
- The Hertzsprung-Russell diagram
L3 Learning Outcomes
- Understanding the manifestations of binarity in stars
- Understanding what can be learned by quantifying binary systems
- Binary parameters and Kepler's laws
- Types of observed binaries
- Doppler effect
- Stellar masses
Aside: Ellipses
- Equation of an ellipse: x²/a² + y²/b² = 1
- Area of an ellipse: πab
- For a circle, a = b = r (center of circle is the focal point)
- Distance from origin to focus: c = ae
- For any point on ellipse: |F₁P| + |F₂P| = const = 2a
Binary Parameters
- An orbit is defined by 6 orbital elements
- Closed orbits are elliptical and defined by 2 parameters:
- a: Semi-major axis (size)
- e: Eccentricity (0 = circle, 0<e<1 = ellipse, e=1 = parabola, e>1 = hyperbola)
- b: Semi-minor axis (need either (a, b) or (a, e) to define ellipse shape)
- i: Orbital plane's inclination with respect to the observer
- Ω: Longitude of ascending node, measured in the observer's plane
- ν: True anomaly (angle defining the epoch of the orbital body during observation, cyclic in orbital period Pb)
- Argument of periapsis (ω) and longitude of ascending node (Ω) define the orbital plane orientation
- Terms like periapsis, periastron, perihelion, and perigee refer to the closest point in a system's orbit.
Jargon Buster
- Periapsis, periastron, perihelion, and perigee are all geometrically the same
- Terms differ based on the specific system in question (e.g., perihelion refers to the Earth's closest point to the Sun)
- Apapsis, apastron, aphelion, and apogee refer to the furthest point in an orbit.
Theories of Gravity
- Orbital elements are independently measurable for any observed binary system in the sky
- Theories of gravity define how interactions/motion happen
- The relationships between orbital elements, physical constants (G), and charges (like masses) can be predicted by a complete theory of gravity.
Kepler Orbits
- Kepler's laws for orbits, based on Newtonian gravity:
- K1: Orbits are ellipses
- K2: dA/dt = const
- K3: P² = 4π²a³/GM
- (where M = m₁ + m₂)
Theories of Gravity (cont.)
- Orbital elements can change with time, with additional parameters such as w(t) and Pb(t).
- These can also be used to test different gravitational theories, independently of the specific model of the system.
Doppler Effect
- The Doppler effect is a change in frequency of a wave (or other periodic event) for an observer moving relative to its source.
- Δν/ν = v/c. (where Δν is the change in frequency, ν is the emitted frequency, v is the relative velocity between source and observer and c is the speed of light)
Stellar Masses
- Using methods described, stellar masses can be determined
- Applicability is not limited to stars; also applies to exoplanets.
Stellar Properties
- Combining information from L1-L3 allows a lot to be learned about stars.
- Measure stellar flux and distance (parallax -> bolometric luminosity)
- Measure spectral features (spectral lines, shape) to determine stellar temperature and composition.
- The Stefan-Boltzmann relation is used to calculate stellar radii
- Binary systems enable mass determination
Mass-Luminosity Relation
- L ∝ M^3.5 (Luminosity is proportional to the mass raised to 3.5)
- Observationally derived
- Can be related to internal star chemistry and structure
Stellar Ages
- Calculating time-scales like timescale = (anything)/(d(anything)/dt)
- Age ~ E/L (Energy divided by Luminosity) to determine how long a process can fuel a star
- Gravitational contraction can be used to estimate the Kelvin-Helmholtz timescale (~20 million years for Sun).
- Nuclear fusion is required for long term sustained energy in the Sun.
Problems 3.1, 3.2, 3.3, 3.4
- Questions regarding binary systems, including angles of inclination, size of orbits, relativistic effects, Doppler shifts, and stellar properties.
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Description
Test your understanding of the parameters and principles that define the shape of orbits, particularly ellipses. This quiz covers topics such as semi-major and semi-minor axes, eccentricity, and orbital elements crucial for defining orbits. Perfect for students studying celestial mechanics or astrophysics.