What is the relationship between period and luminosity of a Cepheid variable star?

What is the relationship between period and luminosity of a Cepheid variable star?

Classical Cepheids exhibit a relation between period and luminosity in the sense that the longer the period of the star, the greater its intrinsic brightness; this period-luminosity relationship has been used to establish the distance of remote stellar systems.

What is the luminosity of a Cepheid variable star with a period of 30 days?

−5.3
Thus a 3-day period Cepheid has an absolute V-band magnitude of −3.1, while a 30-day period Cepheid has an absolute V-band magnitude of −5.3.

What does the period of a variable star measure?

Cepheid variable stars are intrinsic variables which pulsate in a predicatable way. In addition, a Cepheid star’s period (how often it pulsates) is directly related to its luminosity or brightness. Cepheid variables can be used to measure distances from about 1kpc to 50 Mpc.

What is the period of the variable stars magnitude variation?

Near maximum brightness, the spectrum is generally similar to that of an A or F giant star. Periods are typically 1-300+ days, and amplitudes of variation are 7-16 magnitudes.

Why is period-luminosity relationship important?

The Period-Luminosity Relation. The importance of cepheid variables lies in the fact that their periods and average luminosities turn out to be directly related. The longer the period (the longer the star takes to vary), the greater the luminosity.

How does the period-luminosity relation compare to a Cepheid variable’s peak luminosity?

As Henrietta Swan Levitt discovered, a Cepheid’s variability period relates directly to its luminosity. The longer the variability period, the more luminous the Cepheid. They compare the Cepheid variable’s apparent brightness with its intrinsic brightness.

What is the luminosity class of a star?

Luminosity class 0 or Ia+ is used for hypergiants, class I for supergiants, class II for bright giants, class III for regular giants, class IV for subgiants, class V for main-sequence stars, class sd (or VI) for subdwarfs, and class D (or VII) for white dwarfs.

What does the luminosity of a main sequence star tell us quizlet?

Luminosity classes of stars are designated by Roman numerals and tell us what region of the H-R diagram the star falls in. We use both spectral type and luminosity class to completely classify stars; the spectral type tells us the star’s temperature while the luminosity class tells us its radius.

Why is the period-luminosity relationship important?

Because the luminosity of Cepheids can be easily found from the pulsation period, they are very useful in finding distances to the star clusters or galaxies in which they reside. Edwin Hubble measured the distance to the Andromeda Galaxy in 1923 using the period-luminosity relation for Type II Cepheids.

How does the luminosity of a pulsating variable stars change with time?

Pulsating variable stars are intrinsic variables as their variation in brightness is due to a physical change within the star. This means the star actually increases and decreases in size periodically.

How does the luminosity of a pulsating variable star change with time?

In the case of pulsating variables this is due to the periodic expansion and contraction of the surface layers of the stars. This means the star actually increases and decreases in size periodically.

What is the period-luminosity relationship used for?

In astronomy, a period-luminosity relation is a relationship linking the luminosity of pulsating variable stars with their pulsation period. The best-known relation is the direct proportionality law holding for Classical Cepheid variables, sometimes called the Leavitt law.

What is the period-luminosity relation?

The Period-Luminosity relation. The absolute magnitude of a star, M v, is defined to be the apparent brightness of a star when the star is at a distance of 10 pc (32.6 light years). The difference between the apparent magnitude and absolute magnitude provides (almost) enough information to calculate the distance to the star.

How do you find the period of a variable star?

Because of this remarkable property that the period of a variable star is proportional to its luminosity, these stars make excellent tools for measuring distances. To do so: Observe the Cepheid variable star for enough nights to estimate its period (that is, the time between maximum brightness) and measure its average apparent brightness.

How are the luminosities of stars related to their size?

Luminosities are related to the star’s size, since to a good approximation stars radiate like black bodies, with L= 4πR2σT4, where R and T are the radius and effective temperature of the star, respectively. Most, if not all, stars are variable.

How do you find the luminosity of a star in Excel?

Use the plot of the period-luminosity, or a mathematical equation that represents the fit to the data in the plot, to determine the luminosity of the star. Use the standard flux / luminosity / distance equation to measure the distance to the Cepheid.