Spectral Resolution in Interferometry

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1 Spectral Resolution in Interferometry Christopher Tycner Michelson Postdoctoral U. S. Naval Observatory Flagstaff Station

2 Outline Spectral Resolution in Interferometry Implementation Benefits Examples Technical Scientific Examples

3 Implementation Extra Geometrical Distance Incident Wave fronts Baseline Telescope For spectrally resolved interferometry the light beams need to be separated into smaller bandpasses either before or after the interference fringes are formed Beam Combination Fringe Detection Delay Line

4 Example: NPOI The Navy Prototype Optical Interferometer beam combiner Sample Flux Distribution

5 Example: GI2T The Grand Interféromètre à 2 Télescopes beam combiner Detector Gratings From South Telescope From North Telescope Mourard et al. 1994

6 Example: PTI The Palomar Testbed Interferometer beam combiner Prism Primary Star Secondary Star Colovita et al. 1999

7 Example: MIRC The Michigan Infra-Red Combiner for the CHARA array Fibers Without Prism Courtesy of John Monnier

8 Example: AMBER 2-D detector Single mode fibers Petrov et al. (2003) Photometric beam Prism or Grism R = 30, 1500, 10000

9 Example: MIDI MID-infrared Interferometer for the VLTI From Telescope 1 Beam Compressors From Telescope 2 Filter Grism / Prism Delay Line

10 Spectral Resolution in Interferometry Implementation Benefits Examples Technical Scientific Examples

11 Spectral Resolution in Interferometry Smaller Bandwidth Fringe envelope λ Figs. 2.3 and Course Notes from the 1999 Michelson Summer School

12 Group-delay Fringe Tracking Delay between beams zero positive NPOI Raw fringe frame negative Buscher 1988 (p. 74)

13 Spectral Resolution in Interferometry Improved (u,v)-plane Coverage 1 channel / baseline 16 channels / baseline Sample (u,v)-plane coverage for Vega on 8 baselines of the NPOI

14 Differential Calibration Wavelength Hα-emitting Source Atmospheric and Instrumental degradation Uniform- Disk 0.39 mas Tycner et al. (2003)

15 Vega i = 4.54 o PA = 8.6 o Differential Phases Model NPOI Observations Phase (degrees) Phase (degrees) Schmitt et al. (2006) Wavelength (nm) Wavelength (nm)

16 Spectral Resolution in Interferometry Implementation Benefits Examples Technical Scientific Examples

17 Recent Observations of γ Cas NPOI observations in the Hα channel Central star (0.56 mas) Ring + Models without the central star UD + Gaussian + Tycner et al. (2006)

18 Mira variables with PTI Cal Mira Mira Cal Thompson et al. (2002)

19 Mira variables with PTI Thompson et al. (2002)

20 Line formation in Keplerian Disk Horne & Marsh 1986

21 Line Emission

22 GI2T and line emission Hα observations of γ Cas Stee 1995

23 Density Waves in ζ Tau Asymmetric Disk

24 One-armed Oscillation: GI2T Observations Vakili et al. 1998

25 One-armed Oscillation: GI2T Results Vakili et al. 1998

26 MWC297 with AMBER Malbet et al. (2006)

27 MWC297 with AMBER Malbet et al. (2006)

28 Post-AGB star HD VLTI/MIDI N-band interferometry Deroo et al The increase towards longer wavelengths is consistent with a dust-distribution where T decreases with distance from the star

29 Summary It is common for long-baseline interferometers to incorporate spectral resolution Main technical advantages are: Smaller bandwidth and wider fringe envelope Allows for group-delay fringe tracking Differential measurements are possible resulting in high accuracy measurements Main scientific advantages Probing disks via spectrally resolved emission lines Measuring the opacity effects in absorption lines/bands Spatially resolving the emitting regions at different wavelengths simultaneously