Photometric System ASTR 3010 Lecture 14 Textbook Ch.10

History of Photometry Ptolemy & Tycho: by eyes, ~0.5mag Ptolemy & Tycho: by eyes, ~0.5mag 19 th century: naked eyes, ~0.3mag 19 th century: naked eyes, ~0.3mag late 19 th century: photometer, ~0.25mag late 19 th century: photometer, ~0.25mag early 20 th century: photograph, ~0.03mag early 20 th century: photograph, ~0.03mag 1940s: photomultiplier tube, ~0.005mag 1940s: photomultiplier tube, ~0.005mag late 20 th century: CCD, ~0.01mag late 20 th century: CCD, ~0.01mag present: Kepler, ~ mag  transiting planets. present: Kepler, ~ mag  transiting planets.

Response Function Bandpass: a range of wavelengths where an instrument is sensitive Bandpass: a range of wavelengths where an instrument is sensitive single-band photometry: e.g., Kepler. Time series single-band photometry: e.g., Kepler. Time series broadband multi-color photometry: shape of the spectrum, ultra low resolution spectroscopy. “broad” = Δλ/λ > 10%. “Color”=color index, brightness and color. broadband multi-color photometry: shape of the spectrum, ultra low resolution spectroscopy. “broad” = Δλ/λ > 10%. “Color”=color index, brightness and color. narrow- & intermediate band photometry: to isolate a specific line, molecular band, etc., E.g., Balmer discontinuity, TiO band, Hα, etc. narrow- & intermediate band photometry: to isolate a specific line, molecular band, etc., E.g., Balmer discontinuity, TiO band, Hα, etc.

Features relevant to narrowband photometry

Filters determined by the combined spectral response of various sources (filter, detector, atmosphere, & telescope). E.g., Johnson-U determined by the combined spectral response of various sources (filter, detector, atmosphere, & telescope). E.g., Johnson-U bandpass filter bandpass filter high-pass filter high-pass filter low-pass filter low-pass filter neutral density filter neutral density filter

Response Function bandwidth (W 0 ) bandwidth (W 0 ) λ peak λ peak λ cen λ cen

Effective Wavelength

Color correction Large survey with several passbands (e.g., all-sky survey) Large survey with several passbands (e.g., all-sky survey) Measurements with the same filter result in different λ eff Measurements with the same filter result in different λ eff Assume a certain source spectrum shape. Assume a certain source spectrum shape. λ λ cat color correction

Isophotal wavelength Bandpass measurement equivalent to a measurement of the monochromatic flux at a certain wavelength times the bandpass

Color indices Difference b/w two magnitudes ≈ slope of spectra ≈ Blackbody temperature color index = m (shorter λ) - m (longer λ) all indices should be zero for Vega  “Vega system” or “Vega magnitudes” all indices should be zero for Vega  “Vega system” or “Vega magnitudes”

Discontinuity, line strength, etc. Usually, two band magnitudes are sufficient to quantify these…

Line index line index = m narrow – m wide Good example = Hα young star survey

Curvature index (X-C) > 0 for emission (X-C) < 0 for absorption

Planet imaging filter Spectral Differencing Imaging (SDI) Spectral Differencing Imaging (SDI)

In summary… Important Concepts Color correction filter response function Kind of Important Terms effective wavelength isophotal wavelength filter bandpass Chapter/sections covered in this lecture :