Regulusastro Blog

All this rain had me wondering what was going on. I went back through the prior year’s weather summary and pulled out this for January and February of 2009:

NAME: Grainger_Observatory  CITY: Exeter   STATE: NH
ELEV:    79 ft  LAT:  42° 58′ 47″ N  LONG:  70° 56′ 31″ W

TEMPERATURE (°F), HEAT BASE 65.0, COOL BASE 65.0
DEP.  HEAT  COOL
MEAN  MEAN        FROM  DEG   DEG                        MAX  MAX  MIN  MIN
YR MO  MAX   MIN   MEAN  NORM  DAYS  DAYS  HI  DATE  LOW  DATE  >=90 <=32 <=32 <=0
————————————————————————————
09  1  29.4  10.0  20.5   0.0  1381     0  40.1  24 -14.5   16    0   17   31    5
09  2  39.0  18.2  28.9   0.0  1010     0  59.3  11  -2.5    5    0    4   27    1

Now, this is interesting: it looks like it was a lot colder then, so I pulled up this year’s summary to date. See below:

THIS YEAR Jan – Feb:
————————————————————————————
10  1  34.8  18.5  26.8   0.0  1185     0  52.6  25   1.1   10    0   10   29    0
10  2  37.1  23.6  30.2   0.0   816     0  49.5  22  11.0    5    0    5   22    0

Hmmm…. indeed it is a LOT warmer this year. Look at those means. 20.5 and 28.9F versus this year’s 26.8 and 30.2F. That is why we have no snow. It is warm.

Ok ok, I know it’s not all that scientific and that there’s a lack of statistical significance in just two years’ worth of data, but I want it to be winter in January and February.

One of the great problems in this modern day and age is data: LOTS and LOTS of data. What to do with it and how to do to it what you want: the big question. The more you have, the harder it is to do anything with it. How do we handle this? AUTOMATION!

I have been observing variable stars since I was fresh out of college and living in Hadley, Massachusetts, live ago. Back then: a clipboard, red flashlight, telescope and a pad of paper with some charts was all we needed. Then the age of cool and accurate/precise measuring equipment came out: photometers then CCD imagers. I jumped on that as soon as I could afford a CCD back in 1994.

This past couple of years, I have been working on full remote automation of two observatories, and now they are both up and running every clear night. I love that, but it generates a lot of data which all has to be dealt with. I vowed to figure out an automatic way to measure and report these variable star measurements to the AAVSO… and I have got it. Canopus is the answer. It is difficult. It takes a lot of trial and error, and learning, and persistence, and patience, and relaxed eyes, and a good strong PC with some heavy duty drive space, and, and, and… After some 300 pages of reading, waltzing through the tutorials, twice each, and then playing with my own data: it works. The flow is something like this:

1. Take flats, and any other reduction images you need/want.
2. Image two reference fields: Landolt works, and so does Henden in every filter you want to observe in. I get one up high, and one down low.
3. Image your variable stars using the filters you are interested in.
4. Sleep.
5. In Canopus, you need to set up some stuff first:
   1. Folders for each star.
   2. Imported AAVSO comp star data from their website. This is easily imported. You need to do this once per update from the AAVSO.
   3. Create an automation plan for the star/s you observe.
6. One then runs the automation plan which auto-loads each image, automatically performs an astrometric reduction on each image, then uses the imported AAVSO data in conjunction with automatically generated transforms (color indexes and also 1st, 2nd order if you want) to calculate the corrected, transformed magnitudes of the variables with error measurements. The end result is an automatically generated AAVSO formatted report form which is then given to the AAVSO WEBOBS via the web.
7. Done.
8. Sleep.

If you decide to go this route, some recommendations:

• Test and test and test again. Do not report anything until you are convinced that your automated work matches the work you would have done had you taken the long, manual route. This is how you confirm your correctness. This is also how you can sleep at night.
• Do take the time to work on getting color transforms, color index measures and such. It is worth it to transform your data onto a standard system. That’s why you bought those expensive filters, right?
• Read the manuals and do all the tutorials at least twice! Seriously. Canopus is a tough software to learn (for me anyway).
• More information at: http://www.minorplanetobserver.com/MPOSoftware/MPOCanopus.htm   It is so affordable that I recommend you go for it. You will be taking and measuring more data than ever before, and it is no longer tedious.

My favorite part of teaching science is seeing the students become more like scientists. As I say often in class, “If you don’t have a queezy feeling in your stomach, then you aren’t doing science…yet…”    The goal is to get away from the world of instant-access, wikis, search engines, and immediate gratification.

The other day, I gave them more than 400 FITs images of a particularly interesting star. Some images in R, and B, but most in V in a long three night time series. I also pointed out the RA and Dec of the star plus a link to SIMBAD… who can live without SIMBAD!?

Initial reactions to this amount of data really depended on the class: One group was decidedly more democratically broken down. Some students directed, some researched online, some took initial looks at the raw data set. The other class was much more in the “let’s-get-our-feet-wet-now!” mode. They didn’t break out into groups until the second day. The first day could best be described as organized chaos. Each group, just like each person, has their own unique way of diving into a problem.

Interestingly, when one group got to using SIMBAD, they reacted with an Ah-Ha! stating that there was at least a potential clue as to why the object is worth studying. The other group used SIMBAD and their reaction was completely different: “We have the solution! We’re done!” Well, no… they are only just beginning.

Well, the data are in and looking ok. I was surprised to see just how easy it was to overexpose the star on a D200 chip: the chip goes to 12 bits not 16, so things ramp up and then peak at pixel values of 4096! Not good really, but I got the hang of it. I opted to select low iso values and then ended up closing down the aperture as well. Tonight (if clear) I will use a shorter focal length lens (60mm portrait) to make centering the field a bit easier. I used the 300mm telephoto last night… way too shaky for a cold night at 6F. No thank you.

The data flow looks something like this:

• Take images: both lights and equal time darks. Images need to be monochrome RAW Nikon files which contain the raw, unmeshed Bayer plane data. They look black and white, but the color data is really there. Honest.
• When back inside open the light frame.
• Subtract the averaged dark frame from it.
• Check to see that the star images have ADU or pixel counts below 4096.
• Extract the Bayer plane for the color of interest: MaxIm DL allows for this in an easy menu pick. Note that the colors are not easily determined: you need to test this out on a Macbeth color chart before going out.  1 = red, 2 and 3 are the green planes which then need averaging, and 4 = blue. If you want to play, you can color combine these planes to see the full color image. It’s neat.
• Perform differential photometry on the extracted single color images. Be sure to use the correct comparison stars for the correct color.
• Report the data.
• Done.

At this time, I am averaging a slew of images together to increase S-toN.

Tonight is test night number 1.
Equipment: DLSR: Nikon D200 with a variety of lenses in manual mode.
Compression: none.
No filters.
Tripod.
Laptop running MaxIm DL.
Images in Raw monochrome mode to get raw 12 bit data.

My hope is to be able to extract the green bayer data, which is in two parts with this system, and then do the photometry. I want to find the camera’s transformation coefficients tonight as well. COLD at 9F tonight but very very clear.

I have been searching through all the CS forums to find references to methods using MaxIm DL, but have found little on the topic of the proper use of the two green Bayer frames. Are they all just averaged together? Use only one? What?! If someone knows, please write. I would love to formulate a recipe for DSLR photometry of bright stars with this system for my students. The easier, the better.

More on Citizen Sky project at:
To visit this group, browse to http://www.citizensky.org/teams/pea-observers.

Travelling this holiday season also brought upon us a unique situation: the ability to show a little more of this fine world to both of our kids (Ellen and Kate) as well as two of our family’s more beloved familiars: Frigid and Tracks. They travelled with us to Houston to visit my dad and his wife, to enjoy the holidays with the family, and to be warm and safe. Here is their photo journal.

Here we were in Manchester, NH Airport in front of the Southwest flight which will take us to Chicago. From there we transferred to another flight to Hobby in TX.

This kids were always happy to help Frigid (the Penguin) and Tracks (a Lynx) to strike an interesting pose.

Finally the two were able to strike their own pose in front of the 737. Ready to go!

While in Houston, Frigid and Tracks were able to keep in touch with their fellow animal friends. This little owl surfaced on the gutter of the neighbor’s house and hung there while the winds kicked up a mighty blow.

When in Houston, one of the big attractions is the Johnson Space Flight Center just south east of the city. It’s an easy drive, but we all discovered that modern-day GPS road navigation systems are just not modern enough to deal with the ever changing road system down there. Talking about bypasses!! Yikes! Here Frigid and Tracks took a tour of the facility. What used to be open to the public to meander around and enjoy at leisure, the campus is now closed. All visitors must enjoy the tour from a tram bus after going through a form of airport-like security.

With boarding passes in hand, Tracks and Frigid are ready to go! Where are those rockets?

No rockets just yet, but they did get to visit the might control room. Every shuttle mission ever launched has been done from this room. Frigid here thinks he might be good at CAPCOM. I have little doubt!

Ahhh, rockets! This is the bottom end of the Saturn-V launch vehicle’s 1st stage. LOOK AT THOSE NOZZLES WILL YOU!? Wow. The whole assembly is now inside a newly constructed hangar to protect the rocket from the elements. It is looking really good after its restoration.

That is one big engine. Glad it’s turned off.

Holding the two for the pose in front of the rocket.

A final family snapshot before heading back to the museum to check out the other exhibits. Here they sit under the command module and the escape launch system of the Apollo Saturn-V.

Kate and Frigid check out the Space Shuttle landing simulator. Frigid did just fine on beginner mode. Kate was successful at intermediate, and dad… well, you KNOW what dad could do

Speaking of the shuttle, here Frigid and Tracks check out the flight deck of the shuttle training simulator used by the astronauts to learn the systems. I love systems training. Can you imagine CRM at space altitudes? Must be a blast!

The two were perpetually trying to find ways to stow away on the shuttle! Here they are stuck inside a bulkhead crack. I didn’t have the heart to tell them that this shuttle would never be launched into space.

I think Tracks and Frigid were a bit jealous here: They couldn’t touch the moon rock like us mere mortals. Here they have a small triangular piece of basalt to touch. Imagine how many people have stuck their hands into these slots to touch this … rock…

Frigid tries on a helmet. It didn’t fit.

A great meeting to be sure: My intern, Allison, and I went down to Boston, well technically Newton, to meet up with the AAVSO gang and see what the association was up to. While the flu was the inevitable winner of the day (we both caught it not too long after the meeting, we both learned a lot and had a good time catching up with and meeting new friends.

http://www.aavso.org/aavso/meetings/archivefall09.shtml

http://www.aavso.org/images2/fall09/phpslideshow.php?directory=.&currentPic=26

Highlights for us were the introductions to the http://www.citizensky.org/ site and all the folks getting into the observing of a particularly bright and fascinating eclipsing variable star, Epsilon Aurigae. Go check it out: you can be an observer, too. I think this will be a really cool thing for the students to get involved with.

Great also was the talk by Arne concerning more accurate CCD photometry. I know a lot of people out there are not transforming their data. It’s not all that much more work, and it is not hard. Arne’s talk was clear, thoughtful, and easy enough to follow, that I hope the good word spreads.

It was also fun to catch up with friends: Steve Howell, Mike Simonsen and Doc Kinne to name only a few of those I saw there.

So, go now to their website and enjoy the pics from the meeting.

Introduction:

When taking CCD images, and particular, when trying to use those images for scientific purposes, it is important to reduce the amount of unwanted signal and unwanted noise from each image. Optical path “noise” (some of which is actually signal), is such a problem that many astronomers really never come to grips with it. Their data suffer, and the end result is poorer science. This treatise will spell out the simplicity of taking good flat fields to reduce optical path noise and CCD sensitivity issues and will also walk you through a couple of methods to get flats done.

Optical Path Noise:

Telescopes, CCD chips and filters all block light as well as transmit light. They also harbor dust, finger prints, and other unwanted shadow producing things in the light path. The result of such optical path obscuration is an unevenly illuminated CCD chip. This is a real nightmare for anyone doing photometry, in which a standard star of known brightness might measure a bit faint one night because it was being imaged on top of a dust speck on the filter glass! Optical path vignetting and other physical path obstructions will also cast large, non-discernable shadows onto your CCD, causing poor even illumination.

CCD Sensitivity:

In the spatial realm both on the multi-pixel and single-pixel level, a CCD chip will display uneven sensitivity to incoming light. This can depend on the thickness of the substrate and uneven cooling among many other issues. This creates issues very much like those mentioned already in the optical path noise section above.

The Solution:

Take flat field images and divide them out of your images. A flat field is an image taken of an evenly illuminated object like the dusk sky, or a special illuminated white card hanging on the wall of the observatory. These images are taken through the telescope:

· at the same temperature as your nightly work,

· through the same filter/s as your nightly work,

· at the same focal point and at the same rotational angle being used all night,

· and with integration times to allow the flat to reach an average of between 20 to 50% full well capacity of your CCD chip. Flat images should never bloom, but should also not be less than a second in integration time.

For precision work, 20 to 30 or more flats through each filter should be taken each night you are collecting science data. Each flat of a given filter should then be averaged together to create a master flat which is then divided out of your light frame on a pixel by pixel basis. These details are usually all handled automatically by your software. I will assume you are using MaxIm DL software revision 5+ for the following examples.

In Practice – Taking Sky Flats:

Taking flats is easy. Here is a step-by-step method to take sky flats which has worked well for me for years. You need no special equipment other than that you already own to take CCD images.

1. Wait until the sun is setting, but still just above the western horizon.

2. Turn on your observatory: EVERYTHING. The mount, the fans, the CCD, the PC, lights normally on, etc.

3. Cool down your CCD to the night time working temperature. Wait 10 minutes for it to settle to the working temperature.

4. If you are using filters, you should take flats in order of densest filter to most transmissive. I work in the order of Ha, B, V, R, then lastly I. Set your filter wheel to the first filter.

5. Set the focal point of the system. Minor adjustments through the night are ok in order to allow for temperature changes of your optical tube assembly. Do not make changes more than a mm or so. You’ll have to take new flats if you do make larger changes.

6. Set the CCD camera’s angle to the system. Leave it here all night.

7. Point your telescope at the blue sky towards the western side of the meridian. Avoid areas of sky where there are bright stars (which will not be visible yet, as the sun is still up).

8. Take a 1 second integration.

9. Once it downloads, use MaxIm DL’s Information Window in Area Mode to inspect the average pixel count of the image. If it is too bright, some pixels will be saturated, and you will have to wait until the sun sets some more. If you have an image that reads about 20-50% of the full well count, then proceed immediately to the take a series of flats.

a. Generally the Sun is at a point in the west where its light might just be still touching the top of the treetops on the eastern horizon. Stars are not visible to the eye, nor generally to the camera yet.

b. My full well count with an SBIG camera is 65535, so I aim to get flats with an area average of 20000.

c. You can use MaxIm DL’s image series command to take a set of flats with any given filter. Repeat all the steps above as needed until you have flats for what you need.

10. You can use these flats for as long as you wish, but for precision work, flats are taken every night and sometimes in the morning after your imaging is complete. If you are not after precision work, then taking flats once a week is enough. Some would say that’s sacrilege!

A helpful hints:

If you want to start taking flats earlier, just to give yourself some time, cut out sheets of frosted mylar (used in silkscreening) to cover the objective of the telescope. Use 5 to 10 sheets of this milky white plastic material to basically dim the incoming sky brightness to the optics.

You can take flats while aiming at evenly illuminated clouds. This is ok!

I have gotten away with as few as 6 averaged flats. For truly accurate work, I have gotten up to 40 averaged flats.

Here is a flat. Look how ugly it can be! The donuts are dust. The edge darkening in the corners is caused by vignetting.

Had a good time at the AAVSO Fall Meeting in Newton, MA: it was well attended, but not overly so. This allowed people to reacquaint themselves with friends and co-observers from around the world. Some of the neat highlights were an overview of the Epsilon Aurigae Citizen Sky project. This is an exciting opportunity for people to get involved with collecting data using all sorts of equipment, from CCDs, photometers, naked eyeballs, and DSLRs… yes, DSLRs which have been rather difficult to get to know in terms of accurate photometry. Apparently some people are having some very good luck getting these to work well.

Another highlight for me was the demonstration of a completely web-based photometric software toolset called Photometrica. All the images and software (CPU) activity resides on servers external to your web browser. Your PC just needs to browse to the site, log in and tell it what to do. Some of the exciting (read “cool”) features of this software is its ability to import and identify AAVSO program stars and their comparison stars, literally with the click of a mouse button. It may not make coffee, but, with a time saving feature like that, Photometrica will certainly give back the time that old fashioned photometric reductions used to consume. I am looking forward to working with this software more and soon!

It’s interesting being into astronomy, specifically being into observing. I like the cold weather (even though I have always been a desert kind of guy). I can make my CCD imager get down to ridiculously cold temperatures, and that gets rid of unwanted signal and various types of noise.  Life is ok… until the next morning when I try to get out of bed, and my back seizes up in a mass of iron-tight, spine-numbing, blinding pain. Cold, it seems, does not like me.

• Solution 1: Hot bath/shower.
• Solution 2: Tiger Balm, the solution to many problems.
• Solution 3: …..

Let’s just say, it can be a pain the next day. The data are great!