h-r diagrams for star clusters. h-r diagram relation between luminosity l, temperature t and radius...
Post on 29-Jan-2016
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H-R diagrams for star clusters
H-R Diagram
Relation between luminosity L, temperature T and radius R:
L = 4R2T4
H-R diagram for closest stars
Stellar evolution on H-R diagram
Theoretical isochrones
Observational diagrams H-R
Instead of luminosity L – observed flux in V filter:
V = -2.5log10(FV/FV0) Instead of temperature – difference of fluxes in filters B and V: B-V
where B = -2.5log10(FB/FB0)
Middle-aged open cluster NGC 7789
Young open cluster M46 (NGC 2437)
Globular cluster 47 Tuc (NGC 104)
Problems
• Calibration
Standard stars with known values of Vs i Bs should be observed; values of reference fluxes FV0 i FB0 can be calculated from the formula:
Vs = -2.5log10(Fs/FV0)
Information about standard stars can be found at: http://cadcwww.hia.nrc.ca/cadcbin/wdb/astrocat/stetson/query • Interstellar extinction (reddening) Hint: observe clusters with b < –10 or b > +10• Stars in clusters may vary in brightness by a few orders of magnitude One should make observations of different length or – better – make several
observations and combine the data
Strategy
• Choose suitable clusters
Information about open clusters can be found at:
http://www.seds.org/~spider/ngc/ngc.html
http://www.univie.ac.at/webda//navigation.html
• Choose suitable field with standard stars
• Observe standard stars and the cluster
• Using SalsaJ software make photometric measurements of stars
• Export results to Excel and create H-R diagram
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