Cepheid variables are divided into two subclasses which exhibit markedly different masses, ages, and evolutionary histories: classical Cepheids and type II Cepheids.
What are the two types of Cepheids?
There are actually two classes of Cepheid: Type I Cepheids (δ Cepheus is a classical Cepheid) are population I stars with high metallicities, and pulsation periods generally less than 10 days. Type II Cepheids (W Virginis stars), are low-metallicity, population II stars with pulsation periods between 10 and 100 days.
What type of stars are Cepheids?
Cepheid stars are stars that have evolved off the main sequence into the Cepheid instability strip. They are regular radial-pulsating stars , with a well-defined period-luminosity relationship, which makes them ideal stars to be used as primary distance indicating standard candles.
How did Cepheids help Hubble?
Hubble obtained enough observations of V1 to plot its light curve , determining a period of 31.4 days, indicating the object was a Cepheid variable. The period yielded the star’s intrinsic brightness, which Hubble then used to calculate its distance. ... Using all the Cepheids, he obtained a distance of 900,000 light-years.
What is the difference between classical Cepheids and Type II Cepheids and why does this difference exist in the universe today?
Classical Cepheids are used to determine distances to galaxies within the Local Group and beyond , and are a means by which the Hubble Constant can be established (see below). Type II Cepheids are Population II (metal-poor) variable stars which pulsate with periods of typically between 1 and 50 days.
What are the two main types of variable stars?
There are two different categories of variable stars. Intrinsic variables are stars whose luminosity physically changes due to pulsations, eruptions or through swelling and shrinking. Extrinsic variables are stars that change in brightness because of being eclipsed by stellar rotation or by another star or planet.
How old is our universe?
Using data from the Planck space observatory, they found the universe to be approximately 13.8 billion years old .
How many galaxies are there?
The deeper we look into the cosmos, the more galaxies we see. One 2016 study estimated that the observable universe
Are Cepheids rare?
Cepheids are rare stars , and so they are typically far away and we don’t have parallaxes for many. ... Some Galactic Cepheids have parallaxes from the Hubble Space Telescope, so their luminosities are accurately known, others we can get distances for using main sequence fitting or other distance measures.
What type of stars have longer periods 2 to 60 days )?
Cepheid variables have the following properties: Period = 2 to 60 days. Average Temperature = about 6000 Kelvin.
What is a limitation of the parallax method?
Parallax angles of less than 0.01 arcsec are very difficult to measure from Earth because of the effects of the Earth’s atmosphere. This limits Earth based telescopes to measuring the distances to stars about 1/0.01 or 100 parsecs away .
Where are Cepheids found?
The classical Cepheids have periods from about 1.5 days to more than 50 days and belong to the class of relatively young stars found largely in the spiral arms of galaxies and called Population I . Population II Cepheids are much older, less luminous, and less massive than their Population I counterparts.
How do Cepheids work?
Cepheids, also called Cepheid Variables, are stars which brigthen and dim periodically . This behavior allows them to be used as cosmic yardsticks out to distances of a few tens of millions of light-years. a uniform function of their brightness.
Why do Cepheids pulsate?
Pulsating variable stars are intrinsic variables as their variation in brightness is due to a physical change within the star. In the case of pulsating variables this is due to the periodic expansion and contraction of the surface layers of the stars .
