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Dispersed Fixed-Delay Interferometry and its Application in SDSS-III MARVELS. Brian Lee, for the MARVELS collaboration, Aug. 31, 2011. Lots of early SDSS-III MARVELS collaborators- (list still growing!). Principal investigator: Jian Ge (UF) Survey scientist: Scott Gaudi (OSU)
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Dispersed Fixed-Delay Interferometry and its Application in SDSS-III MARVELS Brian Lee, for the MARVELS collaboration, Aug. 31, 2011
Lots of early SDSS-III MARVELS collaborators- (list still growing!) Principal investigator: Jian Ge (UF) Survey scientist: Scott Gaudi (OSU) Science Team Chair: Keivan Stassun (VU) Instrument scientist: Xiaoke Wan (UF) SWG coordinator : Eric Agol (UW) Data coordinator: Brian Lee (UF)
Basic physics of Dispersed Fixed-Delay Interferometry (DFDI)
Mirror 1 B1 B2 Input light Mirror 2 Beamsplitter Physical path difference: B2-B1 (DFDI Refs.: Erskine & Ge (2000),Ge et al. 2001, Erskine 2003, Ge 2002, Mosser et al. 2003, Mahadevan et al. 2008, van Eyken et al. 2010) MARVELS basic physics
Mirror 1 B1 B2 Input light Mirror 2 Beamsplitter Physical path difference: B2-B1 = N*lambda -> constructive interference (DFDI Refs.: Erskine & Ge (2000),Ge et al. 2001, Erskine 2003, Ge 2002, Mosser et al. 2003, Mahadevan et al. 2008, van Eyken et al. 2010) MARVELS basic physics
Mirror 1 B1 B2 Input light Mirror 2 Beamsplitter (0.5*lambda of added delay) Physical path difference: B2-B1 = N*lambda + 0.5*lambda -> destructive interference (DFDI Refs.: Erskine & Ge (2000),Ge et al. 2001, Erskine 2003, Ge 2002, Mosser et al. 2003, Mahadevan et al. 2008, van Eyken et al. 2010) MARVELS basic physics
Mirror 1 Y B1 B2 Input light Mirror 2 Beamsplitter Tilt mirror 2 over, so path length is a function of height Y Y ->Intensity is now a function of height Y = fringes MARVELS basic physics
Mirror 1 Y B1 B2 Input light Mirror 2 Now consider slightly longer wavelength of input light Beamsplitter Y New lambda Old lambda MARVELS basic physics
Mirror 1 Y B1 B2 Input light Mirror 2 Beamsplitter So multiple wavelengths look like this: Y lambda MARVELS basic physics
Zooming out in lambda, you’d see more strongly the dependence of periodicity of interference on wavelength. We call that the “interferometer fan”: MARVELS basic physics
Orders m are evenly spaced in y… m=4 m=3 m=2 m=1 MARVELS basic physics
(The MARVELS instrument can only collect a small cutout from the fan, with m~13000 and 5000A~<lambda~<5700A. We typically refer to the small cutout as, “comb.”) this way to m=13000… m=4 m=3 m=2 m=1 MARVELS basic physics
Mirror 1 Y B1 B2 Input light Mirror 2 Beamsplitter (Have to add a low-resolution spectrograph so the fringes aren't all on top of each other) Spectrograph Y MARVELS basic physics lambda
Mirror 1 Y B1 B2 Input light Mirror 2 Beamsplitter Spectrograph Gradient in tilt of fringes across lambda is present, but fairly small. Y MARVELS basic physics lambda
This was for a continuum light source... Y MARVELS basic physics lambda
Now multiply in a stellar source with absorption lines instead. Y MARVELS basic physics lambda
Now multiply in a stellar source with absorption lines instead. Note intersections. Y MARVELS basic physics lambda
Small x shift (e.g., from RV) of stellar lines gives larger y shift in intersections (amplification higher if slope is steeper)! Y shift Y X shift MARVELS basic physics lambda
Actual intensities follow a sinusoidal model, in theory. Y Line depth Continuum level Y Inten. MARVELS basic physics lambda
Y Line depth Continuum level Okay, now what messes this up? Y Inten. MARVELS basic physics lambda
…integrated onto the CCD (still assuming infinite SNR). Can you still track the intersections?
The final image: Sample full 4kx4k real data frame (ThAr lamp calib.) (60 objects give 120 spectra)
Pipeline flow- current preprocessing order (not necessarily the ideal one!) 4. Try to measure (using calib. lamp) & undo vertical distortions 2. Try to measure (using calib. lamp) & undo slant 0. Starting point (assume bias, dark, flat already done) 5. Apply a horizontal spatial freq. filter to subtract continuum fringes (since unaffected by star RV) 3. Try to measure & divide out slit illumination profile (using current image itself) 1. Try to measure (using calib. lamp) & undo trace 6. Trim the image down and fit a sinusoidal model to the intensity at each wavelength
Pipeline flow- intermediate data product “whirl” and RV extraction Phases (radians): [ 1.3, 1.4, 6.28, 2.0] Sine amplitude/DC offset: [0.02, 0.05, 0.00001, 0.034] Normalized fluxes: [0.98, 0.56, 0.9999, 0.71] 7. Record sine fit parameters (and errors) and fluxes at each wavelength into a multi-extension FITS file (“whirl”) 8. For each star or calibration source to have differential radial velocity measured, choose template epoch 8a. For each other epoch, do chi-squared minimization to find best fitting velocity (x and y axes treated as separate velocity parameters; final answer used is the y-velocity only) 9. For star exposures only, subtract off barycentric velocity 10. For star exposures only, subtract off apparent lamp velocity derived from adjacent lamp exposures from the final star velocity. 11. Write RV’s to disk as a FITS table.
Zoom of raw MARVELS data (Tungsten lamp behind Iodine cell): Above fringing spectrum, fully preprocessed:
Vital stats • Site: SDSS 2.5-m Telescope (3 deg. FOV) • Multi-object feed: 60 fibres • Spectrograph R~10000, wavelength 500-570nm • Interferometer operating order m~13000 • Throughput of telescope plus instrument: 2-3% • Magnitudes surveyed: 7.6<V<12 • Stellar types F9 through K • Up to 30% giant stars per field; similarly large % of subgiants
Data: Year 3 Data: Yrs. 1-2 20,880 RV points 348 Observations 6 Fields > 18 Epochs 2,460 Total Stars Min Epochs: 1 Max Epochs: 29 (Median: 5) • 74,040 RV points • 1234 Observations • 43 Fields > 18 Epochs • 2,580 Total Stars • Min Epochs: 18 • Max Epochs: 42 • (Median: 28) Data collection will end in year 4 with completion of a dozen spring Year 3 fields
Bonus SEGUE spectra 600 spectra per Kepler field -> R=2000, wavelength 380-920nm
Current 1 month stellar RV rms scatter (rerun v001.17)- (seems okay) -300 stars (5 plates) from Oct. 2009 -Noise floor @ 10 m/s -One-month timescales are basically okay, with rms approximately at the level of the instrument requirements -Green squares = median phot. limits of mag. bins -Magenta squares = median total rms of mag. bins
Current multi-month (<17 mo.) stellar RV rms scatter (rerun v001.17) -1680 stars (28 plates) from yrs. 1-2 -rms scatter ~2x the phot. limit at faint magnitudes -Bright-end noise floor@ 50 m/s- much larger than the one-month floor -Noise due to slowly-varying month-to-month offsets (see next slide for specific example) -Green squares = median phot. limits of mag. bins -Magenta squares = median 1-month total rms of mag. bins -Blue squares = median multi-month total rms of mag. bins 5 M_Jup det. thresh 1 M_Jup det. thresh Orange=giants Red=<1.5% visib.
Specific example of multi-month systematic noise (400 days) -Planet-bearing RV reference star HD 68988 -RV offsets and varying background slopes between months
Project 3: TYC 1240-945-1 (PUBLISHED) Lee et al. 2011: MARVELS-1b discovery msini ~ 28 Jupiter Masses, Period ~ 5.89 days.
Project 119: follow-up to Project 3 A second Coherent RV signal is present in the data
Project 119: The Plot Thickens (a bit) AO image of system (courtesy Justin Crepp). Initial photometry by Ji Wang shows that the secondary is ~3.5 mags fainter in Kp and the tertiary is ~4 mags fainter
Project 119: Summary • Intriguing inner signal on Brown Dwarf • If inner signal is a planet, this would be the first example of a combined short-period BD / Planet system • This is a very dynamically interesting system- not many stable scenarios • 3:1 period ratio (possibly a resonance?) • Further N-body simulations could be helpful • Temporary “Working group” to try and understand this system
Project 87: Defringed MARVELS spectra • MARVELS resolution → Problems for EWs. • Spectral indices → [Fe/H], log g, Teff and [α/Fe] (?). • Catalogue along with 3-D vels. from MARVELS RVs and Tycho proper motions • Galactic chemical and dynamical evolution in solar neighborhood? • Statistical studies of stars with and without companions?
