starlight

the hotter the object the shorter the emitted what we “see,” then, is usually the max so, counterintuitively, hot stars appear bluer, cool stars redder our bodies’ max is in the infrared so we can’t see each other by our own light

hotter things can emit shorter, more hi-E s cooler things can only give off the longer, wimpier ’s the wavelength of maximum intensity - max - is the most abundant wavelength that something gives off

a simple relationship b/t the temp and max - Wien’s Law : max = 3,000,000/T given one, you find the other e.g. a cool red star with a surface T of 3000 K will emit most strongly at 1000 nm

stellar spectra

the formation of a spectrum 3 important properties of spectra: 1) there are three kinds 2) are determined by the energy levels 3) H gives us three obvious visible lines that can tell us the T of a star…

1) continuous spectrum, 2) absorption spectrum

3) emission spectrum

summary of the spectra

all the elements have different lines b/c they all have their unique energy states

the balmer thermometer how strong the Balmer lines are can give us an idea of how hot the surface is simply put: cool stars can’t knock off H’s e- very well, hot stars won’t let it come back both show wimpy Balmer lines K stars are perfect for knocking them off that’s why this curve…

and why this curve for calcium wimpy stars have enough E to knock it off and let it come back; hotter stars don’t let it come back doing this w/ a lot of atoms gives us something like…

this! if you can read the lines and see how strong or weak they are you can tell almost exactly how hot the surface is then you can see patterns popping up…

spectral classification in the early 1900’s a bunch of women astronomers at Harvard classified stars into classes from A to Q Annie Cannon personally classified over a quarter of a million of them!

some classes were merged, some dropped what we have now are the seven spectral classes OBAFGKM called the spectral sequence (are subclassified from 0-9, as in A0, A1, A2, etc. the Sun is a G2

see the connection!? knowing the spectral lines can help you classify stars then there’s this way of looking at them…

O B A F G K M hot cool blue-white red

the doppler effect this effect is a change in the due to moving towards or away from you ( radial velocity )

moving toward the light source the s get bunched up, and shorter (more “blue”) -called blueshift moving away gets redshifted

here is the spectrum of Arcturus, taken 6 months apart why the blueshift and then the redshift??? note: light still travels at c!!! note: the faster, the bluer or redder note: can’t detect sideways movement with this

what “-shift” does this star have? is this star moving closer to us or farther away?

chemical composition simply, we can tell what stars are made of from their lines (but the absence of lines doesn’t mean the element isn’t there) using spectroscopy we know the sun is probably like this