Robert Stobie Spectrograph FabryPerot Imaging Spectroscopy

1
Robert Stobie SpectrographFabry-Perot Imaging
Spectroscopy

T. Williams, N. Rangwala, E. Burgh, K. Nordsieck,
D. Buckley, R. Sanchez, V. Debattista, K. Gebhardt
2
Overview

• Why Imaging Spectroscopy?
• RSS Fabry-Perot Instrument
• Galactic Emission Line Spectroscopy
• Stellar Absorption Line Spectroscopy
• Galactic Stellar Absorption Lines
• RSS FP First Light

3
Imaging Spectroscopy

• Many astronomical objects are 2-dimensional
• galaxies star clusters galaxy clusters
• Want to record 3-dimensional data cube
• 2 spatial, 1 spectral
• Detectors are 2-dimensional
• normal spectrograph 1 spatial, 1 spectral
• multi-slitlet spectrograph 1 spatial, 1
  spectral
• IFU Spectrograph limited 2 spatial, 1 spectral
• imaging spectrograph 2 spatial
• third dimension through temporal multiplex

4
Fabry Perot Spectrograph

• FP etalon is a tunable narrow-band filter
• Piezo-electric actuators
• Capacitive sensing and servo control

5
Fabry Perot Schematic
Filter
Focal Plane
Detector
Image Plane
Camera
Collimator
Telescope
FP Etalon
6
RSS Fabry-Perot

• 8 arcmin Field of View
• Seeing-Limited Spatial Resolution
• Spectral Range 460 900 nm
• Spectral Resolutions 300, 800, 3000, 10000
• 3 Etalons (only 2 simultaneously)
• 40 Filters (15 simultaneously)

7
Etalons and Filters

• Dual etalon system
• R300-900 low resolution etalon filter
• R2000 low mid-resolution etalons filter
• R10000 low high-resolution etalons filter
• FP Interference Relation
• n ? 2 D cos ?
• D etalon gap n order

8
Resolution Modes

• Single Etalon TF and LR

9
Resolution Modes

• Dual Etalon MR

10
Resolution Mode

• Dual Etalon HR

11
Spiral Galaxy Dynamics

• Scan strong emission line (Ha typically)
• 12 18 exposures 2 hrs
• At each point in image, fit spectral profile
• Determine maps of velocity, line strength (also
  line width and continuum)
• Extract rotation curve, fit to determine mass
  distribution

12
NGC 1832
13
NGC 1832
14
NGC 1832 Fits
Line Strength
Velocity
15
Stellar Absorption Lines
Globular Star Cluster
Milky Way Center FP Field
16
Stellar Absorption Lines

• Globular star clusters
• Milky Way Bar
• Ha or near-IR Calcium lines
• Measure thousands of velocities and line
  strengths simultaneously
• Velocity precision 5 km/s

17
Galaxy Absorption Line Spectroscopy

• NGC 7079
• CTIO 4m
• 18 900s Images
• 8608 8631 Å
• (1 Å steps)
• FWHM 4.2 Å
• (R 2000)

18
Profile Fits

• Surface Brightness Limit µI 21 mag/sq
• (30 photons in 5x5)
• Velocities 10 km/s
• Dispersions 25 km/s

19
Kinematic Maps
Dispersion
Velocity
20
RSS Fabry-Perot

• First light 9/2006
• NGC 1365
• H a Emission Line
• 24 2-minute exposures

21
RSS Fabry-Perot
22
Summary

• RSS FP on SALT will be powerful tool for imaging
  spectroscopy
• Continuous spectral coverage 430-900 nm
• Resolutions 300, 800, 2000, 10000
• Spectropolarimetry possible
• arXiv0710.3750

23
Slit Comparison

• 1800 s ESO NTT EMMI Major-Axis Spectrum
• 4840-5490Å FWHM 1.2Å
• 1.0 x 5.5 slit
• Excellent Agreement
• Single Slit 3.3x Faster
• RFP map 6x Faster