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Liveblogging LathamFest Part 2

We're all caffinated now!

Stéphane Udry and The Role of Radial Velocities in the Quest for New Earths

Stability is key. Many aspects to stability! Two methods of precise RVs: absorption cell and simultaneous emission lamp. These calibrate the wavelength scale and instrumental profile.

Using a Fabry-Perot with HARPS shows that there are irregular pixel spacing on the CCD, which may be responsible for various 1-year signals.

Controlling the instrumental profile requires fiber optic cables, which scramble the input light. Octogonal fibers are much better than circulular (cross-section) fibers. Big success at SOPHIE.

HARPS-N is the latest PRV spectrometer in La Palma, Canarie Islands. David Phillips (CfA) installed a laser frequency comb on HARPS-N, tuned to work in 500-600nm bandpass (author note: previous LFCs only work in NIR). Difficult to faint stars with HARPS-N, so portion of 80-night GTO time is used for high cadence on bright stars. Shows RV time series of stable stars (author note: this is a first for the Geneva team, to my knowledge)!! rms = 1.2 m/s for two stars. "Most of this comes from stellar noise and undetected planets."

Future: ESPRESSO on VLT. Ultra-stable, R=120,000, laser-comb calibrator, dual-arm (red and blue side). 100 nights of GTO time already allocated (whoa!). Looks like a mega-HARPS.

From technical aspect to stellar stability. Stars are not really stable even if our instruments are. Asteroseismology campaigns give us expectation for amplitude and frequencies of oscillation noise. Both modes and granulation. Bin RVs over night or nights to beat down this noise. 10 cm/s can be reached for binning over several days. Simulations of effects of spots for different levels of stellar activity. 10 cm/s reached after binning over 10s of days . Longer-period planets, you can use larger bins, and simple binning can allow RV searches to reach down to 2 Mearth in ~200 day orbit. Shows cool simulation results.

Binning also works with real data and matches simulations. (author note: Very cool!)

Also need activity indicators since RV variability tracks activity cycle of the star (think butterfly diagram of the Sun). 30% of HARPS high-recision sample show activity-correlated RV signals.

Also need to watch out for aliasing (Dawson & Fabrycky 2010).

All of these lessons used for alpha Cen Bb (Dumusque et al. 2012).

Looking ahead: CHEOPs, which is a 33 cm space telescope dedicated to photometric transit followup. Launches in 2017, same time as TESS!

Enjoyed working with Dave over the years. Lots of pictures of Dave with wine. Beautiful merger of fine wine and fine science. Share one sentence to share with audience, taken from letter of reference for Stephane: "...he will always bet welcome in my office, my house and my cellar."

Suzanne Aigrian Combining Multiple Activity Diagnostics to Improve Radial Velocity Precision

Dave says he wants masses...we will get masses. Or, at least, try very hard!

Effects of spots on stars is similar to the Rossiter effect. Spots also surpress convection. Normally, hot material rises, cool material falls due to convection, averages to convective blue-shifted line profile. Spots change this averaging (Meunier et al. 2010).

Sunspots (big black smudges the size of the Earth (Earth image added for effect). Granulation from convection are smaller inhomogeneities around spots. Bright, hot rising material is yellowish, while cooler falling material is orangish. Spots surpress rising material and suppresses convective blueshift
"Note that I'm not talking about pulsations." Pulsation is short-time-scale and mitigated well by binning.

For activity-induced RV noise, use:

  • Bisector span
  • Ca H&K index
  • Sine-fitting at harmonics of the rotation period
  • Simultaneous light curves

There is a clear link between these effects and RV, but no clear, predictable correlation.

Aigrain, Pont & Zucker (2012) for FF' method. Spot-modulated RV variation looks like (and is, mathematically  the first derivative of the photometric modulation. So F = flux, F' = flux derivative. Used the example of the Sun's disk-integrated light curve, and (a form of) the sun's disk-integrated RV measurement. Simulated RVs match observations to 1 m/s. See the development of a spot region on the Sun. Currently testing using Sun RVs from sunlight reflected off of asteroid Vesta.

Working with Geoff Marcy to do the same types of tests using Kepler light curves and contemporaneous Keck/HIRES RVs. Problem is that KOIs have planets that cause RV variations! Fit expected activity RVs and planet RVs (know planet periods and phases, but not amplitudes). In case of KOI-82, the planet's dominate the RV variability. Would love to do this for more planets.

Active stars are not all bad targets. It may be easier to correct the active RVs in active stars! alpha Cen B is a good example. See also Meunier & Lagrange (2013) for planet detectability of the Sun as a star. "...we estimate that the prob larger than 50% to detect a 1 Mearth at 1. AU requires more than 1000 well-sampled observations and a Ca H&K S/N larger than 120."

What about M dwarfs? Rotation periods are very slow for M dwarfs. Really cool spots have very different spectrum than that of star. (not just convective blueshift) Actually have different, often molecular species in the center of spots! (Audience sais whoa!) Scharmer et al. (2011; Science)

Andrew Szentgyorgyi (Pronounced: Saint-Yeorge-ee) Improving Exoplanet Mass Measurements in the ELT Era

[Can't load movie] "Well, that get's me back on schedule!"

Giant Magellan Telescope (GMT) is 7x8.4m primary mirror segments for 25.4-meter effective aperture. The first primary mirror is complete, next one being cast in October.

Developing a precision RV spectrometer for the GMT called G-CLEF, which is only accepted PRV instrument for an ELT. Anna Frebel is the Science lead.

G-CLEF is very HARPS-like and mounted in a room within a room. 35% peak efficiency! Big advantage of large aperture is large S/N, which is crucial for 10 cm/s.

Going to use a laser frequency comb for wavelength calibration (astro-comb). Shows results of astro-comb test results on HARPS-N, shows plot demonstrating what Stephane said earlier about nonuniformity of CCD pixel sizes.

Shows test results from HIRES show that the spectrometer instrumental profile changes on timescales of minutes. Temperature and pressure are not changing on such a timescale. Must be guiding and/or seeing. Problem for Keck/HIRES, but GMT will have a visible-light AO system in the mirrors. Debra Fischer has been a voice in the wilderness saying that AO in the visible would stabilize the stellar PSF on the fiber/slit. This out-of-the box thinking is pretty important. You also get better fiber coupling, reducing slit losses and boosts system throughput. MagAO tests by Laird Close show that this will work really well with GMT (MagAO has a fiber port!).

You can buy a G-CLEF t-shirt. Also invited to the Oct 22-23 G-CLEF meeting at Carnegie Pasadena. Shows GMT video and warns us to watch out for lasers when you fly into Santiago!


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