ASTR633 Astrophysical Techniques Course slides Chapter 5: - - PowerPoint PPT Presentation

ASTR633 Astrophysical Techniques Course slides

Chapter 5: Photometry

(note: we’re not covering polarimetry — see book if you’re interested)

Spectral Energy Distributions and Spectra

Andrews et al. 2012, ApJ

Aperture photometry

https://astrobites.org/2016/04/15/astroimagej-a-simple-and-powerful-tool-for-astronomical-image-analysis-and-precise-photometry/

What is the “right” aperture size?

King 1971, PASP

The need for PSF photometry

https://www.eso.org/public/usa/images/eso9953a/

Figure 1 Schematic passbands of broad-band systems.

Photometric systems (optical)

Bessell 2005 Ann. Reviews

Photometric systems (infrared)

Bessell 2005 Ann. Reviews

TABLE 2 Isophotal, Effective, Mean, and Pivot Wavelengths for the MKO-NIR Filters Filter liso (mm) leff (mm)

• leff

(mm) l0 (mm) lpivot (mm) J ....... 1.250 1.241 1.243 1.248 1.247 H ....... 1.644 1.615 1.619 1.630 1.628 ......

• K

2.121 2.106 2.111 2.123 2.121 Ks ...... 2.149 2.138 2.141 2.151 2.150 K ....... 2.198 2.186 2.190 2.202 2.200 .......

• L

3.754 3.717 3.727 3.757 3.752 ......

• M

4.702 4.680 4.681 4.684 4.684

Tokunaga & Vacca 2005 PASP

Converting between different systems

Blue object Red object The observed flux density (magnitude) will differ from one telescope/camera to another due to the system response and also on the color of the object

Table 6 Pan-STARRS1 Bandpass Transformations x y A0 A1 A2 ± B0 B1 ± (g − r)SDSS (gP 1 − gSDSS) −0.011 −0.125 −0.015 0.006 −0.012 −0.139 0.007 (g − r)SDSS (rP 1 − rSDSS) 0.001 −0.006 −0.002 0.002 0.000 −0.007 0.002 (g − r)SDSS (iP 1 − iSDSS) 0.004 −0.014 0.001 0.003 0.004 −0.014 0.003 (g − r)SDSS (zP 1 − zSDSS) −0.013 0.040 −0.001 0.009 −0.013 0.039 0.009 (g − r)SDSS (yP 1 − zSDSS) 0.031 −0.106 0.011 0.023 0.031 −0.095 0.024 (g − r)SDSS (wP 1 − rSDSS) 0.018 0.118 −0.091 0.012 0.012 0.039 0.025 (B − V ) (gP 1 − B) −0.108 −0.485 −0.032 0.011 −0.104 −0.523 0.013 (B − V ) (rP 1 − V ) 0.082 −0.462 0.041 0.025 0.077 −0.415 0.025 (B − V ) (rP 1 − RC) 0.117 0.128 −0.019 0.008 0.119 0.107 0.009 (B − V ) (iP 1 − IC) 0.341 0.154 −0.025 0.012 0.343 0.126 0.013 (J2MASS − H2MASS) (zP 1 − J2MASS) 0.418 1.594 −0.603 0.068 0.428 1.260 0.073 (J2MASS − H2MASS) (yP 1 − J2MASS) 0.528 0.962 −0.069 0.061 0.531 0.916 0.061 (g − r)P 1 (gSDSS − gP 1) 0.013 0.145 0.019 0.008 0.014 0.162 0.009 (g − r)P 1 (rSDSS − rP 1) −0.001 0.004 0.007 0.004 −0.001 0.011 0.004 (g − r)P 1 (iSDSS − iP 1) −0.005 0.011 0.010 0.004 −0.004 0.020 0.005 (g − r)P 1 (zSDSS − zP 1) 0.013 −0.039 −0.012 0.010 0.013 −0.050 0.010 (g − r)P 1 (zSDSS − yP 1) −0.031 0.111 0.004 0.024 −0.031 0.115 0.024 (g − r)P 1 (rSDSS − wP 1) −0.024 −0.149 0.155 0.018 −0.016 −0.029 0.031 (g − r)P 1 (B − gP 1) 0.212 0.556 0.034 0.032 0.213 0.587 0.034 (g − r)P 1 (V − rP 1) 0.005 0.462 0.013 0.012 0.006 0.474 0.012 (g − r)P 1 (RC − rP 1) −0.137 −0.108 −0.029 0.015 −0.138 −0.131 0.015 (g − r)P 1 (IC − iP 1) −0.366 −0.136 −0.018 0.017 −0.367 −0.149 0.016 (g − r)P 1 (V − wP 1) −0.021 0.299 0.187 0.025 −0.011 0.439 0.035 (g − r)P 1 (V − gP 1) 0.005 −0.536 0.011 0.012 0.006 −0.525 0.012

• Note. The table provides the coefficients for Equation (6).

and SDSS, Johnson/Cousins (Vega), and 2MASS (Vega). Both linear and quadratic versions are provided, with coefficients y = A0 + A1x + A2x2 = B0 + B1x. (6) 3.2. Stellar Color Transformations We used the synthetic magnitudes from the SEDs to fit for conversions between the Pan-STARRS1 photometric system

Pan-STARRS Photometric System

Tonry et al. 2012, ApJ

• C. Buton et al.: Mauna Kea atmospheric extinction properties
• Fig. 17. Mean SN atmospheric extinction (solid line) and its physical components (dashed lines). For comparison we overplot the previous

Mauna Kea extinction measures derived by Boulade (1987) (diamonds), Bèland et al. (1988) (triangles) and Krisciunas et al. (1987) (stars).

Atmospheric extinction

Buton et al (2013, A&A, 549, A8)

http://www.cfht.hawaii.edu/en/gallery/cloudcams

CFHT Cloudcams

http://www.cfht.hawaii.edu/Instruments/Elixir/skyprobe/tonight.html

Calibration practices

• 10-20% accuracy: use standard values for extinction
• ~1-5% accuracy:
• observe standard stars close in airmass and time to your science target
• observe standards close in color to your target
• note that if you have SDSS, PS1, or 2MASS standards in your images, you can

calibrate directly from your science data without taking separate calibration images

• <1% accuracy: measure a variety of different color standards at a variety of

airmasses throughout the night. Very large overhead so needs to be science- driven.

Magnier et al. 2013, ApJ

Scatter of bright stars in uber-calibrated data (griz filters)

Magnier et al. 2013, ApJ

(magnitudes)

g r i z

Aumann et al. 1984

Vega is not a blackbody…

The first time I remember a newspaper article on a scientific discovery

Vega is not a blackbody…