Now that the MagAO team has (mostly) recovered from our epic 6 week stay at LCO, we are turning our attention to processing all of the great data we’ve been taking. We’re also happy to announce two new publications based on MagAO data which have been accepted to the Astrophysical Journal, both of which looked at stars in the constellation Chamaeleon.
Ya-Lin Wu has been studying the young star CT Cha with VisAO. You can read about his results here.
Steph Sallum used Clio2, in combination with some other instruments, and used a resolution-boosting technique called non-redundant masking to take a look at T Cha. You can find out about her results here.
We have a bunch of other papers in the works, and we’re already starting to plan for our next run, which starts May 3rd. Stay tuned!
Also, a truck on the highway had an accident, which closed the highway, so the new turno couldn’t get here so the day crew had to also be the TO’s at night. We’ve been away from home for ~3 weeks and everyone is tired, but we stayed up all night in the control room working.
So, instead, I’ve been working on reducing my data, which includes determining various necessary calibrations for Clio. One important correction needed for high-contrast photometry is calibrating the linearity of the detector. To do this calibration, I took a set of measurements of increasing integration time, and determined the counts per itime:
Raw data that are not linear.
I then fit various functional forms to the data until I found the best calibration of the linearity is a third-order polynomial that must be applied to pixels with counts above ~27,000 DN in the raw images, giving the result here:
The result of applying the linearity correction to the raw data. The linearity calibration must be applied to pixels with values above ~27,000 DN, and is not valid for pixels with values above ~45,000 DN for high-contrast photometry (there is margin up to ~52,000 DN for low-dynamic-range photometry).
Note that the data cannot be well-corrected above ~45,000–52,000 DN (depending on your tolerance for photometric error), and these values should be considered saturated in the raw images. I apply the calibration through an IDL function I wrote called “linearize_clio2.pro”. This is going onto the Clio observer’s manual.
Jared and I are working on astrometry, comparing Clio and VisAO measurements and exploiting our capabilities for boot-strapping: Clio has a wider field (up to ~30”) and can get a longer lever-arm on astrometric measurements, but VisAO has a finer pixel scale (~8mas) and a tighter PSF and can get precision astrometry on close companions. We are starting by verifying that we both get the same measurements for the locations of stars in the Trapezium cluster. To do this, I look at our Trapezium images and identify which star is which, then I compare the positions I measure to the positions measured by an earlier author. Here’s an illustration:
Measuring astrometry using Trapezium stars. (Left) Trapezium as imaged at the LBT/PISCES in the IR a year or so ago. (Right) Trapezium as imaged with MagAO/Clio here at LCO. Can you identify the stars in the picture on the right? (Ignore the black splotches which are negative star images, from the sky subtraction.)
I’ve measured the plate scale in both cameras and various filters, as well as the rotation offset to orient the images with north-up, which I’ve written in the IDL function “derot_clio.pro”. We’re working on a code repository for these data-reduction utilities that we’re calibrating on these commissioning runs.
In fact, Clio has two cameras, a wide and a narrow camera. Here is a comparison of the fields of view, including an illustration of the overlap:
The narrow field (16” x 8”) is shown within the wide field (28” x 14”).
VisAO’s field of view is similar to Clio’s narrow camera along the short direction (8” by 8”).
Finally, I’ve been having a bit of fun experimenting with the APP coronagraphs that I want to use for following up GPI planets:
Today we are going to explore the MagAO pupils and their corresponding transforms in the image plane, courtesy of Fourier optics.
So let’s have a look at the pupil. Here is a photo of the ASM, taken with a digital camera. This was from before Clio was mounted, so that we just stood on the Nasmyth platform and put the digital camera where Clio is now. The light source is the sky, and the light path is primary + secondary + tertiary.
ASM image, from before Clio was mounted. You can see bird poop on the tertiary, a splotch at about 11:00 in this image, and the lollipop-shaped "slot" is at 9:00.
The main features of the pupil are the outer diameter of the mirror, the inner diameter of the secondary obscuration, the support spiders holding up the secondary, and the slot. Here, then, is the pupil mask:
Pupil mask
Since we know what the pupil looks like, we can create simulated images of the focal plane by taking the Fourier transform modulus squared:
What the PSF will look like in the image plane (log scale)
If we really stretch the color table, you can see the diffraction off the spiders, but it is not a big effect. Also, I couldn’t find the diffraction off the slot, so it is negligible:
Stretching the color table to saturate the inner part of the PSF allows you to see the diffraction spikes off the spiders, but they are very faint
Now, Clio is an infrared camera, going out to 5 um, and so it has its own pupil mask, a cold stop. So let’s look at the pupil through Clio, by taking a pupil image (which we did after Clio was mounted). Here is an image of the pupil plane through the whole system, taken with Clio by putting in a powered lens to the focal plane to make a pupil image:
Clio pupil image, 3.4 um
It’s pretty cool because you can see the 2 spiders holding up the secondary obscuration on the cold stop, but you can also see the 4 telescope spiders and the ASM slot! Here’s just the Clio cold stop pupil mask:
Pupil mask - Clio cold stop
And here is its Fourier-transform-modulus-squared: The simulated PSF:
Simulated PSF for Clio cold stop (log scale). Diffraction off the spiders is a little bit visible here, since they are slightly wider than the telescope spiders.
And here is the zoomed-out, saturated version so that you can better see the diffraction spikes:
Clio cold stop PSF -- scaled to bring out the diffraction spikes.
Alan Uomoto has been teaching us about the power supply at LCO. Rather than calling it clean and dirty, the actual difference between the different circuitry is whether they go direct (white outlets) or through an un-interuptable power supply (UPS) (orange outlets). Alan, this one’s for you!
Before AlanAfter Alan
(And — despite how it looks from the outlets — we really are in Chile! The observatory is highly USA-compatible. I haven’t even used my plug adaptor yet!)
Update: And here is the MagAO-certified power protector I made to keep people from stepping on the plugs and cords above:
Power cords protector, standing around the plugs imaged above
The weather has taken a turn for the worse at LCO. It is currently 1.8C and blowing at 32.7 mph. And getting colder.
Speaking of cold, we installed the new liquid cooling system in the W-Unit today.
Jared and Laird installing the brass cold-plates on our CCDs. Jason getting ready to install the shutter. Jason first assembled the shutter heatsink and mounting system nearly 2 years ago.Jared checking the shutter mounting. It is a tight fit, and we don't want any metal-metal contact because the shutter vibrates. A lot.The team at work on the NAS, under appropriate supervision.The finished product.The test gauge for the CCD cooling system.
The other big accomplishment in world of the NAS today was Laird installing the Telecentric Lens. This almost flat lens lets us work off-axis, away from the guide star.
The new telecentric lens. View past the cube, through the new telecentric lens. That's L1 there.After installing new glass, we checked the system. Everything looks great - the wavefront is flat and our i' PSF is 3.2 pixels. Click for more pixels.
We also got some time in the dome, and did a little work on the Clay telescope. The vane-end trays are installed, and the leak preventing solenoid valve was plumbed and tested.
Jason and Juan working on the solenoid.Installing the vane end trays.
This hawk was hanging out over the observatory at lunch today.
A hawk over Magellan. Click for full wingspan.
Tonight’s pretty pictures are from Alan Uomoto, who spent some time messing with his camera’s settings today.
The beginning of the weather. Note the top of the fog in the valley below. Click for bigger.A panoramic view of the hotel and Las Campanas itself. Click for more awesome.
