Color index: Difference between revisions

Revision as of 08:37, 30 December 2023

Revision as of 06:56, 30 January 2024

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The [[passband]]s most optical [[astronomer]]s use are the [[UBVRI]] filters, where the U, B, and V filters are as mentioned above, the R filter passes red light, and the I filter passes [[infrared]] light. This [[photometric system|system of filters]] is sometimes called

the [[Johnson–Cousins filter system]], named after the originators of the system (see references). These filters were specified as particular combinations of glass filters and [[photomultiplier|photomultiplier tubes]]. [[Michael S. Bessell|M. S. Bessell]] specified a set of filter transmissions for a flat response detector, thus quantifying the calculation of the color indices.<ref name=filters/> For precision, appropriate pairs of filters are chosen depending on the object's color temperature: B−V are for mid-range objects, U−V for hotter objects, and R−I for cool ones.

== Quantitative color index terms ==

{| class="wikitable"

|+Quantitative color index terms<ref>{{Cite journal |last=Neuhäuser |first=R |last2=Torres |first2=G |last3=Mugrauer |first3=M |last4=Neuhäuser |first4=D L |last5=Chapman |first5=J |last6=Luge |first6=D |last7=Cosci |first7=M |date=2022-07-29 |title=Colour evolution of Betelgeuse and Antares over two millennia, derived from historical records, as a new constraint on mass and age |url=https://doi.org/10.1093/mnras/stac1969 |journal=Monthly Notices of the Royal Astronomical Society |volume=516 |issue=1 |pages=693–719 |doi=10.1093/mnras/stac1969 |issn=0035-8711}}</ref>

!Color

!Color index (B-V)

!Spectral class ([[main sequence]])

!Spectral class ([[Giant star|giant stars]])

!Spectral class ([[supergiant stars]])

!Examples

|-

|Red

|≥1.40

|M

|K4-M9

|K3-M9

|[[Aldebaran]], [[Betelgeuse]], [[Antares]]

|-

|Orange

|0.80-1.40

|K

|G4-K3

|G1-K2

|[[Pollux (star)]], [[Arcturus]]

|-

|Yellow

|0.60-0.80

|G

|G0-G3

|F8-G0

|[[Sun]], [[Capella]]

|-

|"Green"{{efn|Such stars would not be seen as green, but either as whitish or yellow.|name=green}}

|0.30-0.60

|F

|F

|F4-7

|[[Polaris]]

|-

|White

|0.00-0.30

|A

|A

|F0-F3

|[[Sirius]], [[Canopus]]

|-

|Blue

| -0.33-0.00

|OB

|OB

|OB

|[[Rigel]], [[Bellatrix]]

|}

==See also==

Line 43 ⟶ 96:

* [[UBV photometric system]]

* [[Zero point (photometry)|Zero point]]

== Notes ==

{{notelist}}

== References ==