Observed the open star cluster M103, reduced the data, a created an H-R diagram. An H-R diagram relates the brightness and the color of stars and is a useful tool in astronomy.

1. 1
Final​ ​Report
Madeline​ ​Boyce
December​ ​12,​ ​2017
Abstract:​​ ​​ ​The​ ​purpose​ ​of​ ​this​ ​project​ ​was​ ​to​ ​observe​ ​and​ ​create​ ​an​ ​Hertzsprung-Russell
diagram​ ​of​ ​the​ ​M103​ ​star​ ​cluster.​ ​​ ​Isochrones​ ​were​ ​fitted​ ​to​ ​the​ ​H-R​ ​diagrams​ ​to
determine​ ​the​ ​age​ ​of​ ​the​ ​cluster,​ ​which​ ​was​ ​found​ ​to​ ​be​ ​25​ ​million​ ​years​ ​old.​ ​​ ​Most​ ​of​ ​the
stars​ ​in​ ​M103​ ​are​ ​massive,​ ​hot​ ​burning​ ​blue​ ​stars,​ ​with​ ​very​ ​few​ ​cooler​ ​red​ ​stars.
Motivation:​​ ​A​ ​Hertzsprung-Russell​ ​(H-R)​ ​diagram​ ​is​ ​a​ ​very​ ​important​ ​part​ ​of​ ​astronomy.​ ​​ ​The
magnitudes​ ​and​ ​color​ ​of​ ​the​ ​stars​ ​can​ ​be​ ​read​ ​directly​ ​from​ ​the​ ​diagram,​ ​while​ ​the​ ​luminosity,
temperature,​ ​and​ ​mass​ ​can​ ​be​ ​determined​ ​relative​ ​to​ ​the​ ​other​ ​stars​ ​(stars​ ​near​ ​the​ ​top​ ​of​ ​the
diagram​ ​are​ ​more​ ​luminous​ ​and​ ​massive​ ​than​ ​stars​ ​near​ ​the​ ​bottom​ ​and​ ​stars​ ​near​ ​the​ ​right​ ​of​ ​the
diagram​ ​are​ ​cooler​ ​than​ ​those​ ​on​ ​the​ ​left).​ ​​ ​The​ ​age​ ​of​ ​the​ ​cluster​ ​of​ ​stars​ ​can​ ​also​ ​be​ ​determined
by​ ​fitting​ ​isochrones​ ​to​ ​the​ ​H-R​ ​diagram.​ ​​ ​To​ ​make​ ​the​ ​H-R​ ​diagram,​ ​the​ ​M103​ ​cluster​ ​was
observed.​ ​​ ​Fluxes​ ​in​ ​three​ ​different​ ​filters​ ​(V,​ ​R,​ ​and​ ​I)​ ​were​ ​measured​ ​and​ ​turned​ ​into
magnitudes,​ ​from​ ​which​ ​color​ ​could​ ​also​ ​be​ ​calculated.​ ​​ ​A​ ​standard​ ​star​ ​was​ ​used​ ​to​ ​calibrate
these​ ​magnitudes.​ ​​ ​The​ ​V​ ​magnitude​ ​was​ ​then​ ​plotted​ ​against​ ​color​ ​to​ ​make​ ​the​ ​H-R​ ​diagram​ ​and
isochrones​ ​were​ ​fitted​ ​to​ ​determine​ ​the​ ​age.
Observing​ ​Run​ ​Details:
Date Location Conditions Equipment Field​ ​of
View
Pixel
Scale
Seeing
FWHM
Oct.
17,
2017
Smith
College,
Northampton,
MA
Clear,​ ​45℉ Telescope:
Meade​ ​LX200
ACF​ ​16-inch​ ​f/10
Camera:
SBIG​ ​STXL6303
CCD
24.4’​ ​by
15.5’
0.46”​ ​by
0.46”
Mean​ ​of​ ​8.28
pixels

2. 2
Image Number​ ​of​ ​Exposures Exposure​ ​Times Filters
SA​ ​113342 3/3/3 60/60/60 V/R/I
M103 10/10/10 60/60/60 V/R/I
Bias 10 ------- -------
Dark 10 60 -------
Flat 5/5/5 10/1/1 V/R/I
Data​ ​Reduction:​​ ​The​ ​table​ ​above​ ​lists​ ​three​ ​kinds​ ​of​ ​calibration​ ​images:​ ​bias,​ ​dark,​ ​and​ ​flat.
The​ ​bias​ ​is​ ​an​ ​image​ ​taken​ ​with​ ​the​ ​shutter​ ​closed​ ​and​ ​with​ ​zero​ ​exposure​ ​time​ ​that​ ​measures​ ​a
background​ ​voltage​ ​in​ ​each​ ​pixel.​ ​​ ​The​ ​bias​ ​is​ ​present​ ​in​ ​every​ ​image​ ​taken​ ​with​ ​the​ ​CCD.​ ​​ ​A
master​ ​bias​ ​was​ ​found​ ​by​ ​finding​ ​the​ ​median​ ​value​ ​of​ ​each​ ​pixel​ ​in​ ​the​ ​10​ ​exposures.​ ​​ ​This
master​ ​bias​ ​was​ ​then​ ​subtracted​ ​from​ ​every​ ​image​ ​of​ ​M103​ ​and​ ​SA​ ​113342.​ ​​ ​The​ ​dark​ ​is​ ​an
image​ ​that​ ​measures​ ​a​ ​background​ ​current​ ​flowing​ ​through​ ​each​ ​pixel​ ​due​ ​to​ ​the​ ​temperature​ ​of
the​ ​environment​ ​and​ ​detector​ ​itself.​ ​​ ​The​ ​dark​ ​also​ ​depends​ ​on​ ​the​ ​exposure​ ​time.​ ​​ ​The​ ​dark
should​ ​be​ ​taken​ ​with​ ​the​ ​same​ ​exposure​ ​time​ ​as​ ​the​ ​images​ ​of​ ​the​ ​target,​ ​as​ ​well​ ​as​ ​in​ ​the​ ​same
environmental​ ​conditions.​ ​A​ ​master​ ​dark​ ​was​ ​found​ ​by​ ​finding​ ​the​ ​median​ ​value​ ​of​ ​each​ ​pixel​ ​in
the​ ​10​ ​exposures,​ ​the​ ​same​ ​was​ ​as​ ​with​ ​the​ ​master​ ​dark.​ ​​ ​The​ ​master​ ​bias​ ​was​ ​then​ ​subtracted
from​ ​the​ ​master​ ​dark.​ ​​ ​The​ ​flat​ ​image​ ​is​ ​an​ ​image​ ​taken​ ​of​ ​a​ ​blank​ ​white​ ​surface​ ​in​ ​each​ ​of​ ​the
filters​ ​used​ ​in​ ​the​ ​images​ ​of​ ​the​ ​target​ ​and​ ​measures​ ​the​ ​sensitivity​ ​of​ ​each​ ​pixel​ ​in​ ​the​ ​detector.
Five​ ​exposures​ ​were​ ​taken​ ​in​ ​each​ ​of​ ​the​ ​three​ ​filters.​ ​​ ​All​ ​other​ ​images​ ​were​ ​taken​ ​with​ ​the​ ​same
exposure​ ​time​ ​for​ ​each​ ​filter.​ ​​ ​The​ ​flat​ ​however,​ ​did​ ​not​ ​have​ ​the​ ​same​ ​exposure​ ​time​ ​for​ ​each
filter.​ ​​ ​This​ ​is​ ​because​ ​the​ ​R​ ​and​ ​I​ ​filters​ ​are​ ​more​ ​sensitive​ ​than​ ​the​ ​V​ ​filter,​ ​and​ ​therefore
saturated​ ​the​ ​detector​ ​at​ ​longer​ ​exposure​ ​times.​ ​​ ​It​ ​was​ ​necessary​ ​to​ ​have​ ​unsaturated​ ​pixels,​ ​but
not​ ​necessary​ ​to​ ​have​ ​the​ ​same​ ​exposure​ ​time​ ​for​ ​each​ ​filter.​ ​​ ​A​ ​master​ ​flat​ ​was​ ​found​ ​for​ ​each
filter​ ​in​ ​the​ ​same​ ​was​ ​as​ ​the​ ​master​ ​bias​ ​and​ ​dark.​ ​​ ​The​ ​master​ ​bias​ ​and​ ​master​ ​dark​ ​were​ ​then
subtracted​ ​from​ ​the​ ​three​ ​master​ ​flats.​ ​​ ​Each​ ​V​ ​filter​ ​image​ ​of​ ​the​ ​target​ ​was​ ​then​ ​divided​ ​by​ ​the
V​ ​filter​ ​master​ ​flat​ ​to​ ​normalize​ ​it.​ ​​ ​This​ ​was​ ​done​ ​for​ ​the​ ​R​ ​and​ ​I​ ​filters​ ​as​ ​well.​ ​​ ​The​ ​now
reduced​ ​images​ ​of​ ​the​ ​target​ ​were​ ​aligned​ ​and​ ​stacked​ ​into​ ​one​ ​image​ ​for​ ​each​ ​filter.
Photometry:​​ ​The​ ​blanks​ ​in​ ​the​ ​photometry​ ​code​ ​were​ ​filled​ ​in​ ​and​ ​the​ ​code​ ​was​ ​run​ ​to​ ​test​ ​that
it​ ​worked.​ ​​ ​When​ ​a​ ​reasonable​ ​number​ ​of​ ​stars​ ​were​ ​found,​ ​I​ ​decided​ ​not​ ​to​ ​change​ ​any​ ​of​ ​the
parameters​ ​that​ ​had​ ​been​ ​set​ ​in​ ​the​ ​code.​ ​​ ​​This​ ​meant​ ​leaving​ ​the​ ​aperture​ ​size​ ​at​ ​10​ ​pixels,​ ​the
star​ ​finding​ ​threshold​ ​at​ ​10​ ​sigma,​ ​and​ ​the​ ​sky​ ​annulus​ ​size​ ​at​ ​5​ ​pixels,​ ​with​ ​a​ ​buffer​ ​of​ ​10​ ​pixels
in​ ​between​ ​the​ ​aperture​ ​radius​ ​and​ ​beginning​ ​of​ ​the​ ​annulus.​ ​​ ​In​ ​a​ ​previous​ ​class,​ ​it​ ​was​ ​found
that​ ​an​ ​aperture​ ​with​ ​a​ ​radius​ ​of​ ​10​ ​pixels​ ​was​ ​adequate​ ​to​ ​measure​ ​the​ ​flux​ ​of​ ​the​ ​stars.​ ​​ ​This

3. 3
was​ ​found​ ​by​ ​looking​ ​at​ ​a​ ​radial​ ​profile​ ​of​ ​several​ ​of​ ​the​ ​(non​ ​saturated)​ ​stars​ ​and​ ​seeing​ ​that​ ​the
radial​ ​profile​ ​seemed​ ​to​ ​level​ ​off​ ​to​ ​the​ ​background​ ​value​ ​at​ ​a​ ​radius​ ​of​ ​10​ ​pixels.​ ​​ ​The​ ​annulus
and​ ​buffer​ ​needed​ ​to​ ​be​ ​enough​ ​to​ ​measure​ ​a​ ​ring​ ​of​ ​background​ ​around​ ​each​ ​star​ ​without​ ​for​ ​the
most​ ​part​ ​​ ​measuring​ ​the​ ​star​ ​itself​ ​or​ ​neighboring​ ​stars.​ ​​ ​5​ ​pixels​ ​and​ ​10​ ​pixels​ ​respectively
seemed​ ​to​ ​provide​ ​a​ ​reasonable​ ​number​ ​of​ ​stars.​ ​​ ​758​ ​stars​ ​were​ ​found.​ ​​ ​The​ ​magnitude​ ​of​ ​each
of​ ​these​ ​stars​ ​in​ ​each​ ​filter​ ​was​ ​found​ ​from​ ​the​ ​equation
− .5log(f)m = 2
These​ ​magnitudes​ ​were​ ​the​ ​measured​ ​magnitudes,​ ​but​ ​not​ ​the​ ​actual​ ​magnitudes.​ ​​ ​These
measured​ ​magnitudes​ ​were​ ​calibrated​ ​with​ ​standard​ ​star​ ​SA​ ​113342.​ ​​ ​The​ ​Landolt​ ​catalog​ ​lists
V,​ ​V-R,​ ​and​ ​V-I​ ​magnitudes​ ​to​ ​SA​ ​113342.​ ​​ ​The​ ​R​ ​and​ ​I​ ​magnitudes​ ​respectively​ ​were​ ​found
from​ ​subtracting​ ​the​ ​V-R​ ​and​ ​V-I​ ​magnitudes​ ​from​ ​the​ ​V​ ​magnitude.​ ​​ ​These​ ​magnitudes​ ​should
theoretically​ ​be​ ​the​ ​same​ ​as​ ​those​ ​calculated​ ​by​ ​using​ ​the​ ​measured​ ​fluxes​ ​of​ ​the​ ​standard​ ​star,
however​ ​this​ ​is​ ​not​ ​true.​ ​​ ​They​ ​are​ ​off​ ​by​ ​some​ ​amount​ ​called​ ​the​ ​zero​ ​point.​ ​​ ​The​ ​zero​ ​point​ ​was
found​ ​by​ ​using​ ​the​ ​magnitude​ ​equation
− .5log(f) ero pointm = 2 + z
ero point .5log(f)z = m + 2
This​ ​zero​ ​point​ ​was​ ​added​ ​to​ ​the​ ​calculated​ ​magnitudes​ ​in​ ​each​ ​respective​ ​filter​ ​to​ ​find​ ​the​ ​actual
magnitude​ ​of​ ​the​ ​stars​ ​in​ ​the​ ​cluster.
Table​ ​of​ ​Results:
Filter Zero​ ​Point Sensitivity​ ​reached​ ​with
S/N=10​ ​(magnitude​ ​of
faintest​ ​star​ ​found)
V 20.3359414536 21.9316218692
R 20.3606562998 17.65279583
I 19.2775257582 17.6938546354
A​ ​signal​ ​to​ ​noise​ ​ratio​ ​of​ ​10​ ​sigma​ ​was​ ​used​ ​instead​ ​of​ ​a​ ​ration​ ​of​ ​5​ ​sigma​ ​because​ ​5​ ​sigma
allows​ ​too​ ​many​ ​very​ ​faint​ ​stars​ ​and​ ​adds​ ​more​ ​noise.

4. 4
Figures:
Top​ ​left-​ ​figure​ ​1 Top​ ​right-​ ​figure​ ​2
Bottom​ ​left-​ ​figure​ ​3 Bottom​ ​right-​ ​figure​ ​4

5. 5
Analysis​ ​of​ ​H-R​ ​Diagram:​​ ​There​ ​are​ ​three​ ​distinct​ ​main​ ​sequences​ ​in​ ​the​ ​H-R​ ​diagrams​ ​of
M103,​ ​most​ ​prominent​ ​in​ ​the​ ​V-R​ ​color.​ ​​ ​It​ ​is​ ​also​ ​very​ ​prominent​ ​in​ ​the​ ​V-I​ ​color​ ​diagram
found​ ​on​ ​Webda.​ ​​ ​The​ ​most​ ​massive​ ​stars​ ​are​ ​in​ ​the​ ​top​ ​left​ ​corner​ ​of​ ​the​ ​H-R​ ​diagram,​ ​while​ ​the
largest​ ​stars​ ​are​ ​in​ ​the​ ​top​ ​right.​ ​​ ​Mass​ ​increases​ ​as​ ​a​ ​diagonal​ ​line​ ​from​ ​the​ ​bottom​ ​right​ ​to​ ​the
top​ ​left​ ​and​ ​size​ ​increases​ ​as​ ​a​ ​diagonal​ ​line​ ​from​ ​the​ ​bottom​ ​left​ ​to​ ​the​ ​top​ ​right.​ ​​ ​Most​ ​of​ ​these
stars​ ​are​ ​smaller​ ​in​ ​size​ ​but​ ​more​ ​massive.​ ​​ ​Redness​ ​increases​ ​along​ ​the​ ​x​ ​axis,​ ​so​ ​the​ ​fact​ ​that
most​ ​stars​ ​are​ ​on​ ​the​ ​left​ ​side​ ​show​ ​that​ ​their​ ​colors​ ​are​ ​more​ ​blue​ ​than​ ​red.​ ​​ ​Blue​ ​stars​ ​burn
hotter​ ​than​ ​red​ ​stars,​ ​so​ ​this​ ​is​ ​also​ ​an​ ​estimate​ ​of​ ​their​ ​temperature.​ ​​ ​In​ ​the​ ​colored​ ​picture
attached​ ​at​ ​the​ ​end,​ ​it​ ​can​ ​be​ ​seen​ ​that​ ​most​ ​of​ ​the​ ​stars​ ​have​ ​a​ ​blue​ ​color​ ​to​ ​them,​ ​while​ ​a​ ​few
stars​ ​are​ ​bright​ ​red.​ ​​ ​These​ ​stars​ ​probably​ ​represent​ ​the​ ​few​ ​stars​ ​that​ ​are​ ​on​ ​the​ ​very​ ​right​ ​of​ ​the
H-R​ ​diagram.​ ​​ ​However,​ ​some​ ​of​ ​the​ ​stars​ ​on​ ​the​ ​H-R​ ​diagram​ ​do​ ​not​ ​seem​ ​to​ ​follow​ ​the​ ​main
sequence​ ​(bottom​ ​right​ ​stars​ ​seen​ ​in​ ​figures​ ​1​ ​and​ ​2).​ ​​ ​These​ ​stars​ ​are​ ​likely​ ​to​ ​not​ ​be​ ​part​ ​of​ ​the
cluster,​ ​but​ ​foreground​ ​or​ ​background​ ​stars​ ​that​ ​were​ ​captured​ ​in​ ​the​ ​image​ ​along​ ​with​ ​the​ ​target
cluster​ ​stars.
Isochrone​ ​Fitting:​​ ​The​ ​cluster​ ​was​ ​found​ ​to​ ​be​ ​25​ ​million​ ​years​ ​old.​ ​​ ​This​ ​makes​ ​sense,​ ​since​ ​it
is​ ​an​ ​open​ ​cluster​ ​in​ ​the​ ​plane​ ​of​ ​the​ ​galaxy,​ ​which​ ​tend​ ​to​ ​be​ ​fairly​ ​young​ ​in​ ​the​ ​scale​ ​of​ ​the
universe.​ ​​ ​The​ ​metallicity​ ​did​ ​not​ ​seem​ ​to​ ​have​ ​a​ ​great​ ​effect​ ​on​ ​the​ ​different​ ​isochrones​ ​that
were​ ​fit​ ​to​ ​the​ ​H-R​ ​diagram.​ ​​ ​At​ ​first​ ​a​ ​25​ ​million​ ​year​ ​old​ ​isochrone​ ​had​ ​the​ ​same​ ​general​ ​shape
of​ ​the​ ​H-R​ ​diagrams,​ ​but​ ​were​ ​not​ ​lining​ ​up​ ​quite​ ​right.​ ​​ ​The​ ​difference​ ​in​ ​distance​ ​had​ ​to​ ​be
accounted​ ​for​ ​by​ ​adding​ ​a​ ​distance​ ​modulus​ ​to​ ​the​ ​magnitudes​ ​of​ ​the​ ​isochrone.​ ​​ ​This​ ​distance
modulus​ ​was​ ​found​ ​from​ ​Webda​ ​to​ ​be​ ​12.9​ ​magnitudes.​ ​​ ​The​ ​isochrones​ ​then​ ​matched​ ​the​ ​data
points​ ​in​ ​the​ ​y​ ​direction,​ ​but​ ​were​ ​still​ ​off​ ​in​ ​the​ ​x​ ​direction.​ ​​ ​This​ ​was​ ​due​ ​to​ ​dust​ ​extinction.​ ​​ ​An
excess​ ​color​ ​factor​ ​had​ ​to​ ​be​ ​added​ ​to​ ​the​ ​colors​ ​for​ ​each​ ​plot.​ ​​ ​The​ ​values​ ​of​ ​these​ ​were​ ​found
by​ ​eye​ ​to​ ​be:
Color V-R V-I R-I
Excess​ ​Color​ ​Factor 0.4​ ​magnitudes -0.4​ ​magnitudes -0.8​ ​magnitudes
A​ ​plot​ ​of​ ​a​ ​V​ ​vs​ ​V-I​ ​H-R​ ​diagram​ ​with​ ​a​ ​25​ ​million​ ​year​ ​old
isochrone​ ​fit​ ​found​ ​from​ ​Webda

6. 6
Sources​ ​of​ ​Error:​​ ​The​ ​main​ ​source​ ​of​ ​error​ ​came​ ​from​ ​the​ ​background​ ​of​ ​the​ ​images.​ ​​ ​The
background​ ​consisted​ ​of​ ​both​ ​the​ ​sky​ ​brightness​ ​and​ ​the​ ​read​ ​noise​ ​from​ ​the​ ​detector.​ ​​ ​This​ ​noise
is​ ​impossible​ ​to​ ​completely​ ​remove,​ ​however​ ​it​ ​is​ ​possible​ ​to​ ​increase​ ​the​ ​signal​ ​to​ ​noise​ ​ratio​ ​to
decrease​ ​the​ ​error.​ ​​ ​Poisson​ ​noise​ ​is​ ​also​ ​present​ ​in​ ​the​ ​data,​ ​however​ ​the​ ​poisson​ ​noise
dominates​ ​for​ ​only​ ​the​ ​brightest​ ​10%​ ​of​ ​stars.​ ​​ ​The​ ​other​ ​90%​ ​are​ ​dominated​ ​by​ ​the​ ​background
error.​ ​​ ​It​ ​was​ ​therefore​ ​reasonable​ ​to​ ​use​ ​the​ ​background​ ​error​ ​for​ ​the​ ​error​ ​bars​ ​in​ ​each​ ​H-R
diagram.​ ​​ ​There​ ​is,​ ​however,​ ​cell​ ​blocks​ ​in​ ​the​ ​calibration​ ​code​ ​that​ ​find​ ​both​ ​the​ ​background
error​ ​and​ ​the​ ​poisson​ ​error.​ ​​ ​The​ ​signal​ ​to​ ​noise​ ​ratio​ ​can​ ​be​ ​improved​ ​by​ ​taking​ ​images​ ​with
longer​ ​exposure​ ​times.​ ​​ ​It​ ​can​ ​also​ ​be​ ​improved​ ​by​ ​combining​ ​images​ ​by​ ​either​ ​averaging​ ​them
or​ ​by​ ​finding​ ​their​ ​median.​ ​​ ​In​ ​this​ ​case​ ​the​ ​noise​ ​is​ ​reduced​ ​by​ ​the​ ​square​ ​root​ ​of​ ​the​ ​number​ ​of
images​ ​combined.​ ​​ ​For​ ​example​ ​combining​ ​five​ ​images​ ​reduces​ ​the​ ​noise​ ​by​ ​ .​ ​​ ​Taking​ ​more√5
images​ ​with​ ​longer​ ​exposure​ ​times​ ​could​ ​improve​ ​the​ ​measurements​ ​taken​ ​in​ ​this​ ​project.
Comparison​ ​to​ ​Published​ ​Diagram:​​ ​A​ ​published​ ​H-R​ ​diagram​ ​mapping​ ​the​ ​V​ ​magnitude
against​ ​the​ ​V-I​ ​color​ ​was​ ​found​ ​on​ ​Webda​ ​(left).​ ​​ ​It​ ​does​ ​not​ ​exactly​ ​match​ ​the​ ​H-R​ ​diagram
created​ ​during​ ​this​ ​project​ ​(right),​ ​but​ ​they​ ​have​ ​similar​ ​features.​ ​​ ​Both​ ​have​ ​three​ ​distinct​ ​main
sequences​ ​and​ ​both​ ​have​ ​most​ ​of​ ​their​ ​stars​ ​grouped​ ​nearer​ ​the​ ​bottom​ ​of​ ​the​ ​sequences.​ ​​ ​Both
also​ ​have​ ​some​ ​outlying​ ​stars​ ​in​ ​similar​ ​positions​ ​on​ ​the​ ​diagram.
Conclusions:​​ ​M103​ ​is​ ​a​ ​fairly​ ​young​ ​open​ ​cluster​ ​in​ ​the​ ​plane​ ​of​ ​the​ ​Milky​ ​Way,​ ​with​ ​an​ ​age​ ​of
only​ ​25​ ​million​ ​years.​ ​​ ​This​ ​was​ ​found​ ​by​ ​fitting​ ​25​ ​million​ ​year​ ​old​ ​isochrones​ ​with​ ​a​ ​distance
modulus​ ​of​ ​12.9​ ​magnitudes​ ​and​ ​color​ ​excess​ ​corrections​ ​of​ ​0.4​ ​for​ ​V-R,​ ​-0.4​ ​for​ ​V-I,​ ​and​ ​-0.8
for​ ​R-I.​ ​​ ​M103​ ​has​ ​three​ ​distinct​ ​main​ ​sequences,​ ​most​ ​visible​ ​in​ ​the​ ​V-I​ ​color.​ ​​ ​A​ ​two​ ​color
diagram​ ​plotting​ ​R-I​ ​against​ ​V-R​ ​shows​ ​that​ ​most​ ​stars​ ​have​ ​the​ ​same​ ​metallicity,​ ​which
suggests​ ​that​ ​the​ ​three​ ​sequences​ ​were​ ​born​ ​from​ ​the​ ​same​ ​materials​ ​but​ ​at​ ​different​ ​times.​ ​​ ​The

7. 7
outliers​ ​in​ ​this​ ​two​ ​color​ ​diagram​ ​show​ ​stars​ ​formed​ ​with​ ​a​ ​different​ ​metallicity,​ ​which​ ​suggests
that​ ​these​ ​stars​ ​are​ ​not​ ​part​ ​of​ ​the​ ​cluster.​ ​​ ​Most​ ​of​ ​the​ ​stars​ ​in​ ​M103​ ​are​ ​more​ ​blue​ ​than​ ​red,
which​ ​suggests​ ​that​ ​they​ ​burn​ ​at​ ​a​ ​higher​ ​temperature.​ ​​ ​The​ ​stars​ ​in​ ​the​ ​top​ ​left​ ​of​ ​the​ ​sequence
are​ ​the​ ​most​ ​massive​ ​in​ ​the​ ​cluster.​ ​​ ​There​ ​are​ ​not​ ​many​ ​stars​ ​in​ ​the​ ​top​ ​right​ ​corner​ ​of​ ​the​ ​HRD,
which​ ​means​ ​there​ ​are​ ​not​ ​many​ ​stars​ ​that​ ​are​ ​very​ ​large​ ​in​ ​size.​ ​​ ​This​ ​makes​ ​sense,​ ​since​ ​most​ ​of
the​ ​very​ ​large​ ​stars​ ​are​ ​very​ ​old​ ​stars​ ​that​ ​have​ ​left​ ​the​ ​main​ ​sequence​ ​to​ ​become​ ​giants,​ ​and
M103​ ​is​ ​too​ ​young​ ​of​ ​a​ ​cluster​ ​for​ ​this​ ​to​ ​have​ ​happened​ ​yet.
Color​ ​Images:
Color​ ​Image​ ​of​ ​M103​ ​(NGC​ ​581)​ ​taken​ ​in​ ​V,
R,​ ​and​ ​I​ ​filters​ ​on​ ​October​ ​17,​ ​2017​ ​at​ ​Smith
College,​ ​Northampton​ ​Ma
Color​ ​Image​ ​of​ ​Standard​ ​Star​ ​SA​ ​113342​ ​taken
in​ ​V,​ ​R,​ ​and​ ​I​ ​filters​ ​on​ ​October​ ​17,​ ​2017​ ​at
Smith​ ​College,​ ​Northampton​ ​MA
References:
http://www.cfht.hawaii.edu/ObsInfo/Standards/Landolt/
Mike​ ​Peterson,​ ​class​ ​TA
Webda
http://stev.oapd.inaf.it/cgi-bin/cmd_3.0
http://astro.unl.edu/classaction/outlines/stellarprops2/hr_diagram2.html