1 / 17

Photometric System

Photometric System. ASTR 3010 Lecture 14 Textbook 10.4 & 10.5. Photometric System. Narrow meaning : wavelength response of a band ( R p )  instrumental magnitude Broader meaning: a method for standardizing measurements made with a photometric band (i.e., with specific R p and C p )

kimi
Download Presentation

Photometric System

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Photometric System ASTR 3010 Lecture 14 Textbook 10.4 & 10.5

  2. Photometric System • Narrow meaning : wavelength response of a band (Rp) instrumental magnitude • Broader meaning: a method for standardizing measurements made with a photometric band (i.e., with specific Rp and Cp) standard magnitude standardization How? Standardization: Can be done by using an object with known spectral shape. But, in practice, a set of “standard” stars are used

  3. Common photometric system • 100s of photometric systems so far • Excellent summary of photometric systems in Annual Review of Astronomy & Astrophysics by Mike Bessel (2005) • Visual and photographic systems • Visual (mvis) : naked human eye, peak λ ~ 530nm • International photographic (mpg) : photographic emulsion + atmosphere, peak λ ~ 400nm • International photovisual (mpv) : orthochromatic emulsion + yellow filter, peak λ ~ 550nm • 1922 IAU set the zero points (Cp) of both systems such that 6thmag A0V star should have the same magnitudes color index = mpg – mpv, 0 for A0V, negative for hotter, positive for cooler stars

  4. UBVRI system • Johnson-Cousins system : Most frequently used photometric system • UBV defined first by Johnson & Harris (1954) • RCA 1P21 photomultiplier + several colored glasses • V is similar to mpv • U-B and B-V zeros for A0V stars • Then, in 60s, R and I bands are added

  5. UBVRCIC system • Increased sensitivity at R-band and decreased red-edge for I-band

  6. UBVRI Bessell Filter System • Modern CCDs have difficulty replicating the original photomultiplier-based instrumental system  wide variety of CCD spectral response • published a set of combinations of cheap optical glass filters for commonly used CCDs which would reproduce reasonably well the classic Johnson-Cousins passbands

  7. UBVRI system

  8. UBVRI system color indices • U-B : Sensitive to Balmer Discontinuity  luminosity • B-V, V-R, R-I : sensitive to temperature  spectral type • B-V is more affected by metallicity than V-R and R-I • B-V becomes useless for M-type stars (why?) • V-I index is the most purely temperature sensitive index in UBVRI system (V-K) is even better! Why? A set of suggested standard stars : “Landolt Standards”  need for fainter standard stars

  9. JHKLMNQ systems (1-20 microns) • “Broadband Infrared System” : an extension of the UVBRI into IR • Common zero point: colors of an A0V star are zero by definition • Bandpass definitions can depend critically on atmospheric conditions (mainly water vapor)  different observatories with identical hardware will measure differently  same observatory will see a bandpass variation due to weather • In 2000, IAU recommended a new system (Mauna Kea Observatory) for JHK  MKO near-IR system By narrowing the passband (i.e., decreasing FWHM) • Minimize sensitivity to water vapor • Maximize S/N • A set of standard stars : “Elias Standards”, but still evolving…

  10. Strömgren System (uvbyβ) • In 1950s, Strömgren defined intermediate band system • D. Crawford used it extensively to develop observing techniques in 60s/70s • uvbyβ (six filter system) • (b-y) : temperature • c1 = (u-v)-(v-b) : luminosity • m1=(v-b)-(b-y) : metallicity • β: better luminosity index for hot * better temp index for cooler * • For some reasons, uvbyβ is not being used that much nowadays…

  11. Sloan Digital Sky Survey system • A CCD sky survey which measured hundreds of millions objects. • Filters are designed to optimize the silicon CCD sensitivity. • May take over UBVRI system…

  12. SDSS usabilities

  13. Palomar Observatory Sky Survey (POSS)

  14. Others 30 filters 48 filters

  15. Various Color-Color Diagrams Various color-color diagrams are made to “isolate” interesting Group of stars

  16. Intrinsic colors of main sequence stars

  17. In summary… Important Concepts Important Terms Photographic & photovisualmag Johnson-Cousin system Bessel system Broadband infraredbands • Photometric system • Color indices and physical parameters • Color of A0V star • Chapter/sections covered in this lecture : 10.4 & 10.5

More Related