What is the period of the light curve for a Cepheid variable star?

RR Lyrae variables have periods of about a day. Their brightness doubles from dimest to brightest. Typical light curve for a Cepheid variable star. Cepheid variables have longer periods, from one day up to about 50 days.

How is the variation in light of a Cepheid variable star explained?

This in turn allows one to determine the distance to the star, by comparing its known luminosity to its observed brightness. The term Cepheid originates from Delta Cephei in the constellation Cepheus, identified by John Goodricke in 1784, the first of its type to be so identified.

How are Cepheid variable stars used to measure distances?

Through observations of Cepheid variables, astronomers have determined the distances to other galaxies. They compare the Cepheid variable’s apparent brightness with its intrinsic brightness. The difference between observed and actual brightness yields the distance.

How do you find the luminosity of a Cepheid variable?

Using Cepheid Variables to Measure Distance Once the period of a distant Cepheid has been measured, its luminosity can be determined from the known behavior of Cepheid variables. Then its absolute magnitude and apparent magnitude can be related by the distance modulus equation, and its distance can be determined.

What does a light curve measure?

A light curve is a graph that shows the brightness of an object over a period of time. In the study of objects that change their brightness over time such as novae, supernovae, and variable stars, the light curve is a simple, but valuable tool to a scientist.

Why do Cepheids vary in brightness?

A Cepheid pulsates in a regular and predictable cycle. It is thought that Helium is involved in its cycle. Doubly ionized Helium is more opaque than singly ionized helium, meaning it lets little light through. At the dimmest part of the cycle, doubly ionized Helium makes up the outer layers of the star.

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

Cepheids are special in that the period at which Cepheids pulse is related to their average intrinsic luminosity. More luminous Cepheids pulse more slowly. By measuring the period of a Cepheid we can calculate its intrinsic luminosity, and thus its distance.

How are Cepheid variables measured?

Cepheid variables can be seen and measured out to a distance of about 20 million light years, compared to a maximum distance of about 65 light years for Earth-based parallax measurements and somewhat over 100 pc (326 light years) for the Hipparcos space-based instrument.

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 is light curve of stars?

Why are light curves useful?

The record of changes in brightness that a light curve provides can help astronomers understand processes at work within the object they are studying and identify specific categories (or classes) of stellar events.

Do all Cepheids have the same luminosity?

All Cepheid variables with the same period have nearly the same intrinsic brightness, but their apparent brightnesses differ because they are at different distances.

What causes Cepheids to pulsate?

Why do Cepheid variable stars pulsate?

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 so special about Cepheids?

Cepheids are extremely important to astronomers because their periodic changes in brightness can be used to figure out how far away they are. Because Cepheids are intrinsically bright stars, they can be seen far away, and astronomers can use them to determine the distance to very distant galaxies.

What is the closest Cepheid variable star to Earth?

Polaris
Polaris is not only famous as the beacon for early navigators, it is also the closest Cepheid to earth (445.5 light-years away), and a subject of intense study.

What causes the light curve?

If we make many measurements of the brightness of a variable star and graph them over time, we create a graph known as a light curve. Notice how light curves are “folded” by the period of variability of the star.

How do you plot a light curve?

To plot a light curve, determine the magnitudes of your novae on each data frame on which it can be seen. Then plot the brightness of the nova (in magnitudes) on the y-axis, versus time on the horizontal (X) axis.

How much more luminous is the Cepheid than the G2 star?

Terms in this set (75) The Cepheid star is 100 times further away than the nearby G2 star. This figure shows the Cepheid period-luminosity relation. A Cepheid star with a period of 30 days has the same apparent brightness as a nearby G2 star.

What causes the expansion and contraction of Cepheids?

Increased heat from inside the star causes the expansion – the expansion then causes cooling. The cooled layers contract only to be heated again. One of the more famous variables stars is the family of Cepheid variable stars. Discovered by Henrietta Leavitt, these stars have a pronounced Period-Luminosity relationship.

What is the shape of the light curve of a Cepheid?

A Cepheid light curve is typically asymmetric with a rapid rise to maximum light followed by a slower fall to minimum (e.g. Delta Cephei).

What is a Cepheid variable star?

A Cepheid variable is a star that pulses frequently. We see the light they produce dip and rise over a short period of time, returning to the same luminosity a few days later. Cepheids have a period-luminosity relation. The longer the period between peaks of brightness the brighter the star is.

What is the temperature and spectral type of Cepheids?

The temperature and spectral type vary as they pulsate. Their radii are a few tens to a few hundred times that of the sun. More luminous Cepheids are cooler and larger and have longer periods.

What is the relationship between luminosity and pulsation period in Cepheids?

There exists a well-defined relationship between a classical Cepheid variable’s luminosity and pulsation period, securing Cepheids as viable standard candles for establishing the galactic and extragalactic distance scales. Hubble Space Telescope (HST) observations of classical Cepheid variables have enabled firmer constraints on Hubble’s law.