# How do I find the age of a star?

by ageorge95
Tags: star
 P: 19 I'm a yr 12 student doing a full year research assignment and i have decided to find the age of the star, Sirius. I have access to a pretty good telescope and equipment but I am not sure where to start. Suggestions anyone?
 Mentor P: 12,003 This is generally not possible with individual stars. See here for more. http://www.scientificamerican.com/ar...ntists-determi
P: 366
 Quote by ageorge95 I'm a yr 12 student doing a full year research assignment and i have decided to find the age of the star, Sirius. I have access to a pretty good telescope and equipment but I am not sure where to start. Suggestions anyone?
As Drakkith has advised this is generally not possible with individual stars, what you could do however is start your assignment on the pretence of finding the age of the star. Then outline the reasons this is not going to be particularly accurate as your main body of work - would still be a good assignment.

Cosmo

 P: 235 How do I find the age of a star? Couldn't you get a good approximation by its spectra? The more heavy elements, the older the star.
P: 19
 Quote by e^(i Pi)+1=0 Couldn't you get a good approximation by its spectra? The more heavy elements, the older the star.
I was hoping to do just that and use the Hertzsprung-Russell diagram which requires the luminosity and colour of a star to determine the age of the star. How would I do get this information using a telescope?
 P: 19 Thanks for the advice Cosmo Novice and Drakkith the link was very useful thank you
P: 2,195
 Quote by e^(i Pi)+1=0 Couldn't you get a good approximation by its spectra? The more heavy elements, the older the star.
This isn't correct. Stars create more heavy elements through fusion as they age, but these heavy elements remain in the core of the star and don't migrate to the surface. The spectrum only sees the surface of the star, and hence just tells you what the initial composition of the star was when it was born. So stars with more heavy elements were formed more recently, and the amount of heavy elements you see in the spectrum doesn't change as the star ages.
 Sci Advisor PF Gold P: 9,487 Using stellar evolutionary models, we have a fairly good guess as to the age of Sirius. The presence of its white dwarf companion star was an obvious plus given an accurate mass estimate is vitally important in such modelling. See http://www.astronomy.com/en/sitecore...irius%20B.aspx The original paper can be found at: http://arxiv.org/pdf/astro-ph/0507523v2.pdf Note that the authors had access to some pretty sophisticated data, and the proximity of Sirius to earth certainly didn't hurt.
Mentor
P: 12,003
 Quote by ageorge95 I was hoping to do just that and use the Hertzsprung-Russell diagram which requires the luminosity and colour of a star to determine the age of the star. How would I do get this information using a telescope?
The Hertzspurng-Russel diagram does not let you determine the age of the star. It merely shows "the relationship between the stars' absolute magnitudes or luminosities versus their spectral types or classifications and effective temperatures." -Quoted from wikipedia.

This means that if you have a star that is 10 times the Suns luminosity and and was white in color it would be a Main Sequence star. If the star had 100 times the luminosity of the Sun and was very Red in color, it's surface temperature is very cool, meaning it's grown to a large size and is on Branch III, the "Giant" branch.
P: 334
This method [a new one presently limited to certain types of stars] is based on how fast the star is spinning.

Gyrochronology

 A new method is helping scientists assess the ages of isolated stars, including all stars known to have planets....A star's rotation slows with time, research shows, giving scientists a clock to understand its age. The research is published in May 20 issue of The Astrophysical Journal Letters. http://news.discovery.com/space/star...et-110523.html
 Mentor P: 12,003 Nice! Never heard of that before, thanks Radrook.
P: 19
 Quote by Radrook This method [a new one presently limited to certain types of stars] is based on how fast the star is spinning. Gyrochronology http://www.google.com/search?sourcei...W_enUS378US378
Thanks for the suggestion Radrook. Do you think that I can measure stellar rotation with a 10" LX200 SCHMIDT CASSEGRAIN TELESCOPE. It looks like this:
P: 334
 Quote by ageorge95 Thanks for the suggestion Radrook. Do you think that I can measure stellar rotation with a 10" LX200 SCHMIDT CASSEGRAIN TELESCOPE. It looks like this:

This is what they use to make these observations possible:

 In a four year preparatory study conducted with specially designed instrument (Hectochelle) mounted on the MMT telescope on Mt. Hopkins in southern Arizona, Meibom and his colleagues sorted out information in nearly 7000 individual stars and used Kepler data to determine how fast those stars were spinning. http://www.universetoday.com/85901/a...n-stellar-age/
So we have:

1. Hectospec & Hectochelle
2. Telescope on Mt. Hopkins
3. Keppler Mission Data

 Hectospec & Hectochelle A Brief Description: http://mmto.org/node/55

 MMT Obervatory http://en.wikipedia.org/wiki/MMT_Observatory

 Keppler Data Archive The data from the Kepler Mission are processed and archived in the Multimission Archive at Space Telescope Science Institute (STScI). The public Kepler Planet Candidates are there as well. http://kepler.nasa.gov/Science/ForSc...s/dataarchive/

Links for the SCHMIDT CASSEGRAIN TELESCOPE that delineate its capabilities.

 Instruction Manual 8", 10", 12", 14", 16" LX200GPS Schmidt-Cassegrain Telescopes 7" LX200GPS Maksutov-Cassegrain Telescope with Autostar II Hand Controller http://www.cgtp.duke.edu/~plesser/ob...GPS_manual.pdf

BTW
Observation from the ground without using Keppler will significantly limit the range of stars that can be assessed

 ....the rotation periods of stars older than about half a billion years can't be measured from the ground where Earth's atmosphere interferes. Fortunately, this is not a problem for the Kepler spacecraft. http://www.sciencenewsline.com/space...512580000.html
P: 334
 Quote by Drakkith Nice! Never heard of that before, thanks Radrook.

Welcomed.
 P: 19 Since I cannot find the age of a star individually how would I find the age of a star cluster?
Emeritus
PF Gold
P: 5,196
 Quote by ageorge95 Since I cannot find the age of a star individually how would I find the age of a star cluster?
This is something you would use a Hertzsprung-Russell Diagram for. The idea is that for stars on the main sequence, the ones that are bluer, hotter, and more luminous don't "live" for as long as the stars that are redder, cooler, and dimmer. The reason for this is that the hotter and more luminous stars have a larger mass. More mass means a higher central core temperature. A higher core temperature means a higher rate of nuclear fusion. Now, the "lifetime" of a star is defined as the amount of time it spends on the main sequence. The main sequence is defined as the portion of the stellar life cycle during which stars produce energy by nuclear fusion of hydrogen into helium in their cores. If the hotter and more luminous stars have a higher fusion rate, then they will run out of their nuclear fuel (hydrogen) in their cores sooner than the dimmer stars. Therefore, the hotter and brighter stars will spend less time on the main sequence. Once they run out of core hydrogen and fusion ceases, the stellar radii and surface temperatures change. This causes those stars to move off the main sequence on the H-R diagram. They move up and to the right onto the red giant branch (corresponding to becoming brighter and having cooler surface temperatures).

The net effect of this is that if you assume that all the stars in the cluster were roughly born at the same time, then there will be certain point on the main sequence to the left of which stars simply don't exist (i.e. that portion of the main sequence is missing). The reason is because the lifetimes of stars bluer than this are shorter than the age of the cluster. So stars of those spectral types have already "veered" off the main sequence and onto the giant branch. We call this point on the H-R diagram at which the main sequence cuts off the "main sequence turn-off point." The older a cluster is, the farther to the right the main sequence turn-off point will be (because in an older cluster even the cooler, dimmer, and more longer-lived stars have "died" i.e. evolved off the main sequence).

So, you can age a cluster simply by looking at where the main sequence turn-off point occurs. The age of the cluster is equal to the main sequence lifetime of the stars at the turn-off point.
P: 19
 Quote by cepheid This is something you would use a Hertzsprung-Russell Diagram for. The idea is that for stars on the main sequence, the ones that are bluer, hotter, and more luminous don't "live" for as long as the stars that are redder, cooler, and dimmer. The reason for this is that the hotter and more luminous stars have a larger mass. More mass means a higher central core temperature. A higher core temperature means a higher rate of nuclear fusion. Now, the "lifetime" of a star is defined as the amount of time it spends on the main sequence. The main sequence is defined as the portion of the stellar life cycle during which stars produce energy by nuclear fusion of hydrogen into helium in their cores. If the hotter and more luminous stars have a higher fusion rate, then they will run out of their nuclear fuel (hydrogen) in their cores sooner than the dimmer stars. Therefore, the hotter and brighter stars will spend less time on the main sequence. Once they run out of core hydrogen and fusion ceases, the stellar radii and surface temperatures change. This causes those stars to move off the main sequence on the H-R diagram. They move up and to the right onto the red giant branch (corresponding to becoming brighter and having cooler surface temperatures). The net effect of this is that if you assume that all the stars in the cluster were roughly born at the same time, then there will be certain point on the main sequence to the left of which stars simply don't exist (i.e. that portion of the main sequence is missing). The reason is because the lifetimes of stars bluer than this are shorter than the age of the cluster. So stars of those spectral types have already "veered" off the main sequence and onto the giant branch. We call this point on the H-R diagram at which the main sequence cuts off the "main sequence turn-off point." The older a cluster is, the farther to the right the main sequence turn-off point will be (because in an older cluster even the cooler, dimmer, and more longer-lived stars have "died" i.e. evolved off the main sequence). So, you can age a cluster simply by looking at where the main sequence turn-off point occurs. The age of the cluster is equal to the main sequence lifetime of the stars at the turn-off point.
Thanks Cepheid. So you're saying all I need to do is find the luminosity and colour and apply this to the HR diagram. I only have two questions.
1. How do I measure luminosity and colour using a telescope?
2. How do I convert the point on the HR diagram to the age of the cluster?
Sorry for asking basic questions but there is little information on the internet on how to do this.
 Sci Advisor PF Gold P: 9,487 Direct measurement of color and luminosity requires expertise and equipment generally more sophisticated than accessible to most amateurs. I would suggest using published values from databases such as Vizier. Padova might be a good source for modelling cluster age, although I'm sure there are others.

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