Archive for the ‘ Jon Jenkins ’ Category

HAT-p-7b and the Grail quest – With Jon Jenkins

jenkins_jon_3_enh11I went to bed the evening of May 13th exhausted from the long, intense campaign of commissioning the Kepler spacecraft. The long march started about a week after launch when we began to receive data from the photometer and needed to process it to verify that it was behaving as we expected and to prepare all the data products needed for nominal science operations. These included taking very special data sets to characterize the 2D bias frame of the CCDs (the image you get with no light falling on the detectors), the noise characteristics, the sky to pixel mapping, the science data compression tables, and the detailed shape of the stellar images (the Point Spread Functions) across the focal plane. We had been calculating the PSFs and getting our first science target tables together while the Combined Differential Photometric Precision (CDPP) data set was being collected during the last ten days of Commissioning. This was the first science-like data to be collected. So we had a target table in place with 52,496 targets and were compressing the 30-minute samples for each pixel of interest and storing these on board the Solid State Recorder. (During nominal science operations we collect pixel data for ~145,000 stars.) On Monday May 11 we turned the spacecraft to point the High Gain Antenna to Earth and downlinked the CDPP data set, all ten days of it, to the Deep Space Network, who transferred it through our Ground System* to the Science Operations Center at NASA Ames Research Center where we process the pixels, extract the photometric light curves and search for transiting planets. Nominal science operations commenced on May 12 and we could turn our attention to processing the CDPP data.

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Kepler Mission – Mr. Ian Bradley you have an answer

A question made by Ian Bradley arrived my e-mail via Stuart Atkinson, since there might be other Kepler fans with the same doubt I decided to bring it here:

Regarding the Kepler 1st light image…
 
The imaged area is well away from the ecliptic to allow 24/7 viewing of the image area without Sun being a problem. On a quick glance at the high res 23Mb image from the Kepler website, there are several diagonal tracks [not the vertical or horizontal blooming from bright stars]. One is particularly bright (see below for position). Are these earth orbit satellites (given that Kepler is in an Earth trailing heliocentric orbit, this seems unlikely) or are they other solar system bodies e.g. minor planets, asteroids, Keuper Belt objects etc, etc. I guess it could be crap from the spacecraft itself…
 
Clearly they cannot be in the ecliptic! Few surveys have been done at large angles away from the ecliptic, so have we got a way to discover other members of the Solar System? 
 
Bright diagonal object position – treat ccd array as 5 rows x 5 columns, each row, column element consists of 2 ccds of either horizontal or vertical alignment! Object is in 2nd row, 2nd column in the top ccd of the pair towards the bottom left of image.

Jon Jenkins, Kepler Co-Investigator, was, once more, kind enough to provide us an answer:

Ian is most likely seeing cosmic ray tracks which are the result of energetic particles whizzing through the CCD and depositing energy along the way. (I couldn’t tell from Ian’s email which direction he was counting CCD modules, although I found a bright cosmic ray track 2nd row, 2nd col from the top left, near the middle and low on the upper CCD in this pair.) We estimated a hit rate of 5 per square cm per second pre launch from counts reported by analysis of the LASCO CCDs aboard SOHO, which agrees well with the rates we’ve estimated from the dark frames we took prior to Dust Cover Ejection. The physics of our CCDs indicates that most cosmic rays deposit about 2500 electrons but some can deposit a whopping amount of charge. We identify and remove the “brightest” cosmic ray events from the data in ground-based processing. Most cosmic rays deposit too little energy for us  to detect them in or near the cores of our relatively bright target stars. The Field Of View (FOV) is tipped up 60 degrees above the ecliptic plane, so the chances of seeing solar system bodies is rather small, and Kuiper belt objects, for example, would not be bright enough to be seen as a bright streak in our images, and travel fast enough that to see them eclipsing stars in the FOV would require much shorter exposures than Kepler is capable of. The first light image pair consisted of one 6-sec integration (not including the 0.51 sec readout time) and one 65 sec integration (10 co-adds of individual 6-sec integrations with 0.51 sec readout times). During nominal science operations the CCD images are co-added for 30 minutes (a sum of 270 individual 6 sec exposures).

Cheers,
Jon

Kepler mission – It’s full of stars!

Image credit: NASA/Ames/JPL-Caltech

Here’s what you have been waiting for, NASA Kepler’s full field of view – an expansive star-rich patch of sky in the constellations Cygnus and Lyra stretching across 100 square degrees, or the equivalent of two side-by-side dips of the Big Dipper.

And now let us stay with Jon Jenkins, Kepler’s Co-Investigator:

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Kepler’s Prima Lux – Reactions

Let the games begin! Starlight is falling on our detectors, so now hopefully it is only a matter of time before the remaining hurdles are jumped and the Kepler mission reports the first Earth-sized planets. This could prove an historic juncture for our sense of our place in the Universe. There will need to be some patience; the first planets we find will again be “hot jupiters” (because they are so easy). I’m predicting that the first terrestrial planets announced in a habitable zone will be around the small cool stars that are the most common in our Galaxy. That is again because those are the easiest sort for Kepler to detect. It may be a year before such an announcement. Kudos to all the team members who produced a working spacecraft, and got it into the right place and condition!

 

Gibor Basri, Co-Investigator

University of California-Berkeley, Dept. of Astronomy

   

jenkins_jon_3_enh11We popped the cork on the champagne about 15 minutes past 7 pm PDT after watching the breathtaking signature of the dust cover release in the Doppler residuals at DSS 26 (Goldstone) and in the spacecraft telemetry. There was quite a “twang” when it happened and we saw the reaction wheels spin up to counter the nudge the departing cover imparted to the photometer and we saw that the Fine Guidance Sensors are responding to starlight entering the barrel of the photometer. Now our real work begins in earnest!

 

Jon Jenkins, Co-Investigator

SETI Institute

 

Kepler Mission – Pre Prima Lux update – With Jon Jenkins

Time zones always provide us with curious situations…I’ve e-mailed Jon Jenkins yesterday, just before going off to my own safe mode over the pillows and under the sheets, so I have just read the answer after seing our own star shining above the hills…

Jon’s first words left me thinking that we would have to wait a little longer until Kepler open its own eyes and stare to myriads of stars, but read a little further ahead…I did it and a smile made an appearance in my face…

We get some some precious details about how things will work after First Light and…if all goes well…it looks like today it will be a day to remember…

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Kepler Mission – First Light update for 280309 – With Jon Jenkins

jenkins_jon_3_enh11The stray light inside the telescope was sunlight scattered through baffles at two gaps around the dust cover where the pins holding the dust cover to the sunshade are located. The stray light illuminated an “arc” around the edge of the dust cover opposite the entry points. (Interestingly enough, there are some dust particles on the field flattening lenses that functioned as inverse pin hole cameras, so we actually saw reverse images of the illumination pattern inside the sunshade.) The images we first obtained were very dark at the top of the focal plane array, and became gradually lighter towards the bottom of the focal plane. We aren’t talking about much light: at most, about 12,000 photoelectrons per read were falling on the brightest edge of the focal plane. When we tilted the photometer away from the sun, we almost completely eliminated the stray sun light getting through the simple baffles in these gaps (more complex baffles could prevent the dust cover from releasing cleanly). The maximum amount of light we measured on these final images was less than about 10 photoelectrons per readout, so the light was reduced by over a factor of 1000.

Keep in mind that these dark or bias frames were pictures only a parent could love: we were very happy to see the same intricate patterns in the dark frames matched those that we saw in preflight characterization tests. It was just like seeing the wizened face of a dear old friend or relative and noting that every wrinkle and freckle was in place and that no additional ones had appeared after launch.

We’re having a hard time waiting for the dust cover to be released so that we can finally see what the stars look like through Kepler’s eyes. I’m confident that we won’t have to wait too much longer.

Kepler Mission – First Light Update – With Jon Jenkins

We’ve all been here walking from one side of the room to the other, eagerly waiting for that special moment, the moment when Kepler peels of its sleep mask and awakes up, beholding the stars ahead, capturing its first light.

Well…it looks like Kepler is already slightly opening its dreamy eyes to the Milky Way!

It is like when you are sleeping and the blinds allow the first rays of the morning Sun to pass, touching your eyelids, calling you for a whole new day ahead…

 

Let us read what BtC collaborator, Jon Jenkins, Kepler Co-Investigator, had to tell us:

 

jenkins_jon_3_enh11We had our “first light” already with some sunlight making it in around the dust cover, but found a different attitude at which almost no light entered the telescope so that we could get a good dark frame for comparison with preflight test, and that can be used to formulate some of our calibration products. In retrospect, it’s nice to see that all 42 science CCDs and 4 Fine Guidance Sensor CCDs are responding to light as well as behaving as expected in dark frames.

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