Measuring NIR Extinction with GPS 1.0 Transmission 0.8 0.6 0.4 - PowerPoint PPT Presentation

Measuring NIR Extinction with GPS 1.0 Transmission 0.8 0.6 0.4 0.2 0.0 0.5 1.0 1.5 2.0 2.5 Wavelength ( µ m) Cullen Blake & Margaret Shaw Princeton University

Water, Water Everywhere! 1.0 0.8 Transmission 0.6 0.4 0.2 0.0 0.6 0.8 1.0 1.2 1.4 Microns 1.0 0.8 Transmission 0.6 0.4 0.2 0.0 1.6 1.8 2.0 2.2 2.4 Microns Typical Transmission: Apache Point Observatory

Water Absorption: Highly Variable 1.2 1.0 0.8 0.6 Flux 0.4 ! =1.1% 0.2 Water Lines 0.0 -0.2 1.2 1.0 0.8 0.6 Flux 0.4 ! =1.8% 0.2 0.0 -0.2 0.974 0.976 0.978 0.980 0.982 0.984 Wavelength ( µ m) Two Echelle Spectra of an A Star Same Airmass, 300% Change in Optical Depth

Broadband NIR Photometry 0.0 0.06 % Change in Raw z Band Flux 0.04 2.0 0.02 4.0 z raw (%) 6.0 0.00 8.0 -0.02 10.0 -0.04 -0.06 0 2 4 6 8 10 PWV (mm) Change In Uncalibrated Flux: Repeat SDSS z Band Observations of F Stars PWV = Precipitable Water Vapor

Differential Photometry Detected Photons = ∫ Earth Atmosphere Filter Detector Source SED Telescope 1.0 d λ 0.8 Transmission X X X X 0.6 0.4 0.2 0.0 0.6 0.8 1.0 1.2 1.4 Microns ∫ Assumptions d λ X Star A 1) Contemporaneous observations of both stars ~ Constant ∫ 2) Perfectly calibrated 2D detector X d λ 3) Small angular separation between stars Star B 4) Stellar SEDs same across filter bandpass mmag Ground-based Differential Photometry Possible (Even in z Band)

Differential Photometry of Cool Stars M Star 700-900nm (i+z) M Star 700-900nm (i+z) 1.0 0.8 Transmission 0.6 x x 0.4 0.2 0.0 0.70 0.75 0.80 0.85 0.90 Microns ≠ 1.0 0.8 x x Transmission 0.6 0.4 0.2 0.0 0.70 0.75 0.80 0.85 0.90 Microns A Star Low PWV A Star High PWV Up to 1% Effect in Differential Photometry of Cool Stars Precise Telluric Models Can Help

Global Positioning System Satellites have synchronized Satellite positions precisely known atomic clocks “At the beep, the time will be exactly...” 1.2 & 1.6 GHz GPS measures light travel time: satellites to receiver If Speed of Light (Index of Refraction) is Known: Signals From Four Satellites Get You: Absolute X,Y,Z Position of Receiver Time Offset Between Receiver Clock and Satellite Clocks

GPS Timing Delays (Fixed Receiver) Ionospheric Delay: 10 m +/- 1 mm 26000 km Frequency Dependent: Precisely Measured Using Dual Frequency GPS Data e- e- e- e- e- “Dry Air”: 2 m +/- 1 mm e- e- e- e- “Hydrostatic Delay” e- Water Vapor: 0.03 to 0.3 m 50 km “Wet Delay” 12 km Many Sources of Error Eliminated By “ Double Differencing ” - Network of GPS “Pseudo Range” 10m = 3 ns Timing Delay

Measurements: GPS, Temperature, Pressure Dry Delay = (mm) Barometric Pressure Function of Position Calculated From Raw GPS Data +/- 0.3 mbar on Earth (constant) Commercial Software (e.g. Bernese) Wet Delay = Total Delay - (Ionospheric Delay+Dry Delay) PWV ∝ F(T) x Wet Delay Relative PWV +/- < 0.2 mm References: Bevis et al. 1992, 1994 Approx. Linear Function Caveat: These are Estimated Zenith Quantities of Surface Temperature Azimuthal Symmetry Assumed

GPS Monitoring Networks Suominet Network http://www.suominet.ucar.edu/ Ware et al. 2000

PWV Monitor at Apache Point Data Processed in Real Time by Suominet Project PWV Estimates Every 30 Minutes Lots of Great Work on Astronomical Applications of PWV Monitors: Talk by Kerber; Kerber 2010, Thomas-Osip 2007, Querel 2008,2011, Otarola 2011, Seifahrt 2010

Water Vapor: Highly Variable 3.5m Telescope Collecting Data All Measurements PWV at Apache Point Observatory

Water Vapor: Highly Variable 1.0 0.8 Reltaive Frequency 0.6 0.4 0.2 0.0 0 10 20 30 40 50 | � PWV| in 30 minutes (%) Histogram of Change in PWV Over 30 min Intervals Two Years of “Good” Observing Conditions at APO

A Star Observations 1.2 1.0 0.8 0.6 Flux 0.4 ! =1.1% 0.2 0.0 -0.2 Water Lines 1.2 1.0 0.8 0.6 Flux 0.4 ! =1.8% 0.2 0.0 -0.2 0.974 0.976 0.978 0.980 0.982 0.984 Wavelength ( µ m) ARCES on 3.5m at APO 100 Observations Over 1 Year, R=30,000 S/N~150

Forward Modeling of Spectra Theoretical Telluric Templates Custom Line-by-Line Radiative Transfer Code: 1.0 Transmission 0.8 0.6 + + = 0.4 0.2 0.0 0.5 1.0 1.5 2.0 2.5 Wavelength ( µ m) Fitting Telluric Templates to A Star Spectra Free Parameters: Pixel-to-Wavelength Solution Spectrograph Line Spread Function Relative Water Vapor Optical Depth ( τ )

Forward Modeling Fit RMS Typically 1% for Unsaturated Lines

GPS-based PWV vs. Observed Line Depths 1.0 Telluric Optical Depth Scale Factor τ 0.8 0.6 ! 0.4 0.2 τ +/-0.06 0.0 0.0 0.2 0.4 0.6 0.8 0.1xPWV(mm) + 0.36x(AM-1) Strong Correlation Between Best-fit Scale Factor and PWV Also Depends on Airmass Blake & Shaw, 2011,PASP, 123, 1302

Applications Precise Telluric Models: 1.0 Transmission 0.8 0.6 0.4 0.2 0.0 0.5 1.0 1.5 2.0 2.5 Wavelength ( µ m) No Free Parameters Match Observed (Unsaturated) Lines to ~1% Correcting NIR Photometry: ∫ Earth Atmosphere Filter Source SED 1.0 0.8 d λ Transmission X X 0.6 0.4 0.2 0.0 0.6 0.8 1.0 1.2 1.4 Microns

� � � � � � NIR Radial Velocity Measurements 3 � � ARCES Data 2 H2O Model Flux + Offset � � � M Star Template 1 0 0.974 0.976 0.978 0.980 Wavelength ( µ m) � � Telluric Lines as a Simultaneous Absorption Reference

SDSS Photometry of Cool Stars 0.02 0.01 0.00 ! (r-z) -0.01 -0.02 -0.03 -0.03 0.02 0 2 4 6 8 10 PWV (mm) Points: Calibrated r-z Colors of SDSS M Dwarfs Relative to Stellar Locus Dashed Line: Estimate of PWV Bias Assumes SDSS Photometric Solutions Based on an F star

SDSS Photometry of Cool Stars 0.02 G5-F5 0.01 ! z (mag) 0.00 -0.01 -0.02 0.02 M7-M4 0.01 ! z (mag) 0.00 -0.01 -0.02 0 2 4 6 8 10 PWV (mm) Calibrated Photometry of G-F and mid-M stars from Stripe 82 Important for Transiting Planet Searches Targeting M Stars

Conclusions GPS-based PWV Estimates are Useful for Astronomy! Text These Measurements Can Be Used to Generate Excellent Telluric Templates These Templates Have Many Uses: Correct Relative Photometry of Cool Stars Radial Velocities and High-resolution NIR Spectroscopy Future: A Network of Stations to Measure 3D Water Distribution in Real Time?

1.2 ! =1.5% 1.0 0.8 0.6 Flux 0.4 0.2 0.0 -0.2 1.2 ! =2.9% 1.0 0.8 0.6 Flux 0.4 0.2 0.0 -0.2 0.930 0.932 0.934 0.936 0.938 0.940 Wavelength ( µ m)

1.0 z i+z y 0.8 Relative Frequency 0.6 0.4 0.2 0.0 -0.010 -0.005 0.000 0.005 0.010 0.015 ! Differential Flux (mag)