Module 8 Flashcards
What are the two types of star clusters?
- Open clusters
- Globular clusters
What is a Hertzsprung-Russell diagram?
A graphical representation of stars plotted according to their luminosities and temperatures
What is the significance of the main sequence?
It represents a continuous band of stars that are in the stable phase of hydrogen burning
What are giants, supergiants, and white dwarfs?
- Giants: Large stars that are in a late stage of stellar evolution
- Supergiants: Extremely luminous and massive stars
- White dwarfs: Small, dense remnants of stars that have exhausted their nuclear fuel
Why do the properties of some stars vary?
Due to differences in mass, age, composition, and evolutionary stage
How do we measure stellar luminosities?
By distinguishing between apparent brightness and absolute luminosity
What is apparent brightness?
The amount of power reaching us per unit area from a star
What is luminosity?
The total amount of power that a star emits into space
What does the inverse square law state?
The apparent brightness of a star declines with the square of its distance
How is apparent brightness measured?
Using a detector that records energy striking its surface each second
What is the formula for calculating distance using parallax?
d = 1/p, where p is the parallax angle in arcseconds
What is a parsec?
The distance to an object with a parallax angle of 1 arcsecond
How many light-years are in one parsec?
3.26 light-years
What is the luminosity range of stars?
- Dimmest stars: 0.0001 times the luminosity of the Sun
- Brightest stars: up to 1 million times the luminosity of the Sun
What did studies of stellar luminosities reveal?
- Stars have a wide range of luminosities
- Low-luminosity stars are far more common than high-luminosity stars
What is the magnitude system?
A system that classifies stars based on their apparent brightness
What does a first magnitude star represent?
The brightest stars in the sky according to Hipparchus
True or False: A larger apparent magnitude indicates a brighter star.
False
Fill in the blank: The total luminosity is also called _______.
bolometric luminosity
What are the two main factors affecting a star’s apparent brightness?
- Distance from Earth
- Luminosity of the star
What is the relationship between luminosity and apparent brightness when distance changes?
A star’s luminosity remains constant while its apparent brightness changes with distance
What challenges are involved in measuring apparent brightness?
Calibration of detectors and atmospheric absorption of light
What is the role of interstellar dust in measuring stellar brightness?
It can absorb or scatter light, making stars appear less bright than they are
What is the relationship between stellar parallax and distance?
More distant stars have smaller parallax angles
How do astronomers use parallax measurements?
To establish distances to stars, which helps in calculating luminosities
What is the approximate angular resolution of the naked eye?
1 arcminute
What did Hipparchus designate as first magnitude?
The brightest stars in the sky
The next brightest were designated as second magnitude, and so on.
What is apparent magnitude?
A designation that describes how bright a star appears in the sky
The magnitude scale runs backward; a larger apparent magnitude means a dimmer brightness.
How does the modern magnitude system define the difference of 5 magnitudes?
It represents a factor of exactly 100 in brightness
For example, a magnitude 1 star is 100 times as bright as a magnitude 6 star.
What is absolute magnitude?
The apparent magnitude a star would have if it were at a distance of 10 parsecs from Earth
The Sun’s absolute magnitude is about 4.8.
Why do astronomers emphasize surface temperature over interior temperature?
Only surface temperature is directly measurable
Interior temperatures are inferred from mathematical models.
How can we determine a star’s surface temperature?
From either the star’s color or its spectrum.
What color indicates a cooler star?
Red
A red star is cooler than a yellow star, which is cooler than a blue star.
What causes stars to emit different colors?
Thermal radiation that depends on the surface temperature of the object.
How do astronomers measure surface temperature precisely?
By comparing a star’s apparent brightness in two different colors of light.
What is the spectral type of the hottest stars?
Spectral type O.
What is the mnemonic for the spectral types OBAFGKM?
Oh, Be A Fine Girl, Kiss Me!
What is the temperature range for spectral type M stars?
Below 3700 K.
Who was responsible for classifying stellar spectra at Harvard College Observatory?
Annie Jump Cannon.
What is a visual binary star system?
A pair of stars that can be seen distinctly as they orbit each other.
What is a spectroscopic binary?
A binary star system identified through Doppler shifts in spectral lines.
What is an eclipsing binary?
A pair of stars that orbit in the plane of our line of sight, causing periodic drops in brightness.
How do astronomers measure stellar masses?
Using Newton’s version of Kepler’s third law applied to binary star systems.
What is the absolute magnitude of the Sun?
About 4.8.
What type of stars display spectral lines of highly ionized elements?
Fairly hot stars.
What is the significance of the OBAFGKM sequence in stellar classification?
It represents the order of spectral types based on surface temperature.
What does a star’s spectrum reveal about its temperature?
The types of spectral lines present provide a direct measure of the star’s surface temperature.
Who discovered the correct explanation for the OBAFGKM spectral sequence?
Cecilia Payne-Gaposchkin.
What is the typical temperature of the hottest spectral type O stars?
Can exceed 40,000 K.
What is a light curve?
A graph of apparent brightness against time for an eclipsing binary.
How many stars did Annie Jump Cannon classify in her career?
More than 400,000.
What is an eclipsing binary?
A pair of stars that orbit in the plane of our line of sight, causing brightness variations due to eclipses.
What happens to the apparent brightness of an eclipsing binary system when one star eclipses the other?
The apparent brightness drops because some of the light is blocked from view.
What is a light curve?
A graph of apparent brightness against time that reveals the pattern of eclipses.
What is the most famous example of an eclipsing binary?
Algol, also known as the ‘demon star’ in the constellation Perseus.
How often does Algol’s brightness drop?
About every 3 days for a few hours.
What are the three ways of identifying binary stars?
- Observing visual binaries
- Analyzing spectral changes in spectroscopic binaries
- Observing eclipsing binaries
Why are eclipsing binaries particularly important for studying stellar masses?
Their Doppler shifts can tell us true orbital velocities and allow direct measurement of stellar radii.
What is the mass range of stars established through observations of binary systems?
From as little as 0.08 times the mass of the Sun to at least 150 times the mass of the Sun.
What is the significance of the Hertzsprung-Russell diagram?
It reveals key relationships among the properties of stars by plotting stellar luminosities against spectral types.
What does the horizontal axis of an H-R diagram represent?
Stellar surface temperature, which corresponds to spectral type.
What does the vertical axis of an H-R diagram represent?
Stellar luminosity, in units of the Sun’s luminosity.
What are the four major groups of stars in an H-R diagram?
- Main sequence stars
- Supergiants
- Giants
- White dwarfs
What is the definition of a luminosity class?
A classification system that describes the region of the H-R diagram where a star falls, closely related to its size.
What is the complete classification of the Sun?
G2 V, indicating it is a yellow-white main-sequence star.
What is the spectral type of Betelgeuse?
M2 I, indicating it is a red supergiant.
What does the term ‘main sequence’ refer to?
A prominent streak on the H-R diagram where most stars, including the Sun, are located.
Fill in the blank: A star’s spectral type is designated by the letters _______.
OBAFGKM
True or False: The luminosity class of a star is more closely related to its luminosity than its size.
False
What are the basic luminosity classes?
- I for supergiants
- II for intermediate stars
- III for giants
- IV for intermediate to giants
- V for main-sequence stars
How can stellar radii be inferred from the H-R diagram?
A star’s luminosity depends on both its surface temperature and its surface area or radius.
What is the formula used to measure stellar masses in binary star systems?
Newton’s version of Kepler’s third law.
What does the Doppler shift tell us about a star in a binary system?
The portion of the star’s velocity that is directed toward us or away from us.
What is the significance of the GAIA mission in studying binary systems?
It aims to increase the number of cases where astrometric and Doppler data can be combined.
What is the significance of the main sequence?
Most stars, including our Sun, are on the main sequence of the H-R diagram, where luminosity and surface temperature are related to mass.
How does mass affect a star’s properties on the main sequence?
Mass determines surface temperature, luminosity, and lifetime; more massive stars are brighter and hotter but have shorter lifetimes.
What is the relationship between stellar mass and luminosity?
More massive hydrogen-fusing stars are brighter and hotter but have shorter lifetimes.
What is the mass range for stars along the main sequence?
From 0.08 times the mass of the Sun for M stars to over 150 times the mass of the Sun for O stars.
What determines the energy balance in a star?
The mass of the star determines the balance between energy released by hydrogen fusion and energy lost from the surface.
How do surface temperature and luminosity relate to mass?
Higher mass stars have higher surface temperatures and luminosity; lower mass stars have lower surface temperatures and luminosity.
What is a main-sequence star’s lifetime?
The time a star can remain as a hydrogen-fusing main-sequence star, which varies based on its mass.
Why do more massive stars have shorter lifetimes?
They consume hydrogen fuel rapidly due to higher luminosity, despite starting with larger supplies of hydrogen.
What is the estimated lifetime of a 10 solar-mass star?
About 10 million years.
How long can a 0.3 solar-mass main-sequence star live?
About 300 billion years.
What are giants and supergiants?
Stars that have exhausted hydrogen in their cores, are cooler, but much more luminous than the Sun.
What happens to giants and supergiants at the end of their lives?
They eject their outer layers and leave behind a core, which becomes a white dwarf.
What is a white dwarf?
The remaining core of a giant star where nuclear fusion has ceased, typically small but dense.
What are variable stars?
Stars that exhibit significant brightness changes over time.
What is a Cepheid variable star?
A type of pulsating variable star with a luminosity closely related to its pulsation period.
Where are open clusters typically found?
In the disk of the galaxy and tend to be young.
What is the Pleiades cluster?
A famous open cluster in the constellation Taurus, often called the Seven Sisters.
Where are globular clusters found?
In the halo of the galaxy and contain some of the oldest stars in the universe.
How many stars can a globular cluster contain?
More than a million stars.
What is the typical size range for globular clusters?
60 to 150 light-years across.
What does the central region of a globular cluster contain?
Up to 10,000 stars packed into a few light-years.
What can a region contain in terms of stars?
A region can have 10,000 stars packed into a space just a few light-years across.
What is the age of the globular cluster M80?
More than 12 billion years old.
What type of stars are prominent in the Hubble Space Telescope photo of M80?
Red giant stars nearing the ends of their lives.
What causes the intricate dance of stars in a globular cluster?
Gravity.
What happens when two stars pass close to each other in a globular cluster?
The gravitational pull deflects their trajectories, altering speeds and directions.
How do globular clusters gradually lose stars?
Through ejections caused by close encounters of stars.
How do we measure the age of a star cluster?
By plotting its stars on an H-R diagram.
What does the absence of hot, short-lived stars in the Pleiades indicate?
The cluster is old enough for hydrogen fusion to have ended in the cores of its main-sequence O stars.
What is the main-sequence turnoff point?
The precise point on the H-R diagram where a cluster’s stars diverge from the main sequence.
What spectral type indicates the main-sequence turnoff point for the Pleiades?
Around spectral type B6.
What is the approximate age of the Pleiades cluster?
Approximately 100 million years old.
How does the main-sequence lifetime of a B6 star relate to the Pleiades?
It indicates that the Pleiades is around 100 million years old.
What will happen to the B stars in the Pleiades over the next few billion years?
They will die out, followed by the A stars and the F stars.
What can the H-R diagram tell us about star clusters?
It helps evaluate their ages based on the main-sequence turnoff points.
What is the significance of globular clusters in terms of age?
They are typically older than 10 billion years.
What do precise studies of globular cluster turnoff points suggest?
Ages of these clusters are about 13 billion years.
What is the relationship between the age of globular clusters and the universe’s history?
They imply formation within the first billion years of the universe’s roughly 14-billion-year history.
What is the main sequence of stars characterized by?
Fusing hydrogen into helium in their cores.
What do giants and supergiants represent in stellar evolution?
Stars that have exhausted their core supplies of hydrogen for fusion.
What are white dwarfs?
The exposed cores of stars that have already died.
What is the significance of the Hertzsprung-Russell diagram?
It plots stars according to their surface temperatures and luminosities.
What is the relationship between a star’s mass and its position on the main sequence?
High-mass stars are at the upper left and progressively smaller masses are toward the lower right.
What is a binary star system?
A system where the masses of stars can be measured using Newton’s version of Kepler’s third law.
What is the expected main-sequence turnoff point for a star cluster that is 10 billion years old?
Stars of spectral type K.
True or False: Open clusters are typically older than globular clusters.
False.
What happens to stars above the main-sequence turnoff point?
They have already exhausted their core supply of hydrogen.
What is the lifetime of our Sun?
About 10 billion years.
What is the primary composition of stars when they form?
Hydrogen and helium.
