ay45c2-page6 - Ideally Flux would be the total energy...

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Unformatted text preview: Ideally, Flux would be the total energy emitted, but in practice we measure di erent wavelength bands with di erent instruments or detectors. In such cases we label it by a letter telling which band (e.g. V = visual) and it then means \energy per area per time arriving in that band." The most common bands are U = \ultraviolet," B = \blue," V = \visual," R = \red," I, J, K = \infrared." Transparency (%) 100 80 60 40 20 0 3000 4000 5000 6000 A Wavelength Light Transmission Through UBV Filters. This graph shows the wavelength ranges over which the standardized U, B, and V lters are transparent to light. The U lter is transparent to the near-ultraviolet. The B lter is transparent from about 380 to 550 nm, and the V lter is transparent from about 500 to 650 nm. Band U B V R I J K Central Wavelength 3650 4400 5500 7000  9000 1.25 2.2 A A A A A E ective width (de ned 680 980 890 2200 2400 0.38 :48 A A A A A (by area under curve) log f (erg cm 2 s 1  1 ) -4.37 -4.18 -4.42 -4.76 -5.08 -5.48 -6.40 for m = 0 Note that 1000= 100 nm = 0.1. We write F , F , F , etc. for in-band A uxes. When we need a word for \real, total energy" we say bolometric, so: U B V L = total luminosity in all bands. bol To interpret the last line in the above table, we need to know about the magnitude scale. 15 ...
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This note was uploaded on 12/29/2011 for the course AST 350 taught by Professor Dion during the Fall '09 term at SUNY Stony Brook.

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