Thursday, June 25, 2015

PFS Preparation -- Readying an Instrument for Observing

Tonight is the first of a ten-night run of the Planet Finding Spectrograph, PFS, on Magellan II (Clay). It's my second run as a PFS observer, and I'll celebrate two anniversaries here -- my birth, and the day I officially started as a Carnegie postdoc (July 1st last year). I can't think of a more appropriate place to be! I'm excited to FIND SOME PLANETS.

From the PFS website, it's "a high resolution, optical echelle spectrograph that covers wavelengths from 388 to 668 nm with resolving powers from 38,000 to 190,000. The high efficiency optical design includes all spherical, standard optical glass and calcium fluoride lenses that function as both camera and collimator in a double-pass configuration that allows the R4 grating to be illuminated in a near-Littrow configuration. A prism is used for cross-dispersion. A molecular iodine absorption cell is used to superimpose well-defined absorption features onto the stellar spectra to aid with point spread function deconvolution and wavelength calibration. PFS has been in scientific operation since 1 January 2010."

It was designed and built by Stephen Shectman and Jeff Crane from the Carnegie Observatories, and is used for detecting planets around other stars via the "Doppler wobble" the planet causes in the star and the light we receive from the star. This is one "indirect" detection method of planets -- we never actually see the planet itself, just its effects on the stars -- versus "direct" detection methods, like what my friends are doing with MagAO.

Close up of grating vacuum valve and port.
I arrived yesterday, along with Mattias Diaz and Paul Butler, to meet up with Jeff Crane and get PFS prepped for installation on to the telescope. (We followed these instructions, if you're interested in the finer details.) Yesterday Jeff showed Mattias and I how to pump down the pressure in the grating vacuum chamber and in the CCD chamber of PFS. We then filled the CCD dewar with liquid nitrogen to start cooling it down. All of these things act to stabilize the environment inside of PFS, and keep it stable for the entirety of our observing run. Because we are trying to make very precise measurements -- tiny tiny shifts in lines of stellar spectra -- it is important that nothing change inside the instrument that could affect our observations and measurements.

Close up of CCD vacuum valve and port. Note frugality of design -- metal insert is a baking pan from Target!

Pre-slit assembly outside

Pre-slit assembly inside. Yes, that is a coffee can. It holds the iodine!
Today we got up "early" (in time for lunch) and headed up to the summit to move PFS from the Magellan auxiliary building into the dome and up onto the telescope platform. This process required multiple people, and slooow, purposeful movements. Once we had the instrument on the telescope platform, it had to be aligned with and lowered into three baseplate junctions. Apparently the "spherolinder blocks" are proprietary! They serve as hard mounts for PFS, but also allow it to move smoothly in a few directions, so there are no jerky movements or torque on the instrument. That was the trickiest part, but only took about 20 minutes. Then it was just a matter of plugging in many cables and installing the baffles around the guider camera cover place and instrument entrance aperture (where the light comes through the telescope into the instrument).

Overall the installation went smoothly with no problems, thanks in large part to the excellent Las Campanas Observatory staff. Muchas gracias! 

PFS on elevator on its way up to the telescope (nasmyth) platform

Grad student Matias Diaz helping to secure the instrument entrance aperture. It was kinda tough.

Me trying to get that darn pre-slit assembly pin to click into place.
And now...we're over halfway through our first night! We closed for about 25 minutes due to high winds, but have otherwise been cookin'. The seeing -- how much Earth's atmosphere is jittering and smearing out our observations -- isn't very good, but it isn't awful, and we are making progress. I'll write more tomorrow about how observations are going, and our food-art dinner.

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