| BOLTWOOD OBSERVATORY
|| Paul Boltwood|
1655 Main St.
Boltwood Observatory is an amateur built and run optical observatory that was designed for, and is used for professional and recreational observing programs. It houses a computer controlled semi-automatic 40 cm. Newtonian telescope with a CCD camera that is used for Johnson-Cousins BVRI photometry, and for astrophotography. Software for the collection and automatic reduction of large numbers of images is a speciality.
Boltwood Observatory concentrates on the technical and observing aspects of astronomy, while professional partners do the science. It provides stable and well understood facilities for long term observations and reductions. The professional and recreational observing programs help support each other.
This paper explains what the Boltwood Observatory is and what it is used for. The reason for providing this paper at this symposium is to give an example of an amateur observatory that successfully helps support professional astronomical research, and to suggest the amount of effort that was required. It also shows the relationship between the recreational and scientific aspects of this observatory.
Purpose of the Observatory
This is a personal observatory - its purpose is to provide enjoyment for its owner. Before I built it, the goals I set for the observatory and the observing programs were to:
- be convenient and comfortable, and minimize boring tasks such as guiding - paramount because I am a lazy person by nature,
- allow some form of measurements useful to science,
- satisfy my desire for precision (e.g. a truly diffraction limited telescope that was nicely made mechanically),
- allow me to design and build part of the observatory because I like building things,
- be able to observe objects or phenomena that are beyond those written up over and over again in amateur astronomy books and magazines.
These goals have served me well, and have been fulfilled. An increasing desire to do photometry on deep sky objects is a driving force now.
Some of the facilities have more substantial provisions than is usual for amateur work because of the types of scientific work usually done by this observatory. Much of the work done would be quite difficult without these "conveniences".
The two room roll roof observatory was constructed with comfort and the use of electronic equipment in mind (heated equipment room, telephone and electrical service, and proper grounding). Observations are made all year round, including at -35 degrees C.
The observatory is located in my 2 acre backyard in a western suburb of Ottawa, Ontario, Canada. Being in the backyard has an important impact on the observing programs - it makes observations possible most clear nights, all night because I can work while I observe. On the bad side, the skies are suburban.
The telescope is a Newtonian with a 16 inch f/D 4.78 Ceravolo mirror, normally used with a Televue 2X Big Barlow for CCD imaging. It is mounted on a large computer controlled Byers German mount, which in turn is installed on a massive pier. It is polar aligned and collimated to 1 arc minute (but with +-3 arcmin. of flexure).
The telescope is fully baffled optically and can be used close to a full moon. It has provisions for thermal control and computerized temperature monitoring. The mirror mounting assemblies are substantial and allow accurate stable collimation. The telescope incorporates a computer controlled Hartmann screen for accurate focusing, and a rotating secondary allows the changing from visual to CCD use of the telescope without reconfiguration or re-collimation.
Much of the work mentioned later was done with an earlier instrument - a 7" Astrophysics Starfire refractor.
This home-made camera uses a Thomson-CSF TH7883 scientific-grade front-illuminated CCD chip which has 576*384 23 micron square pixels, few defects, a nearly flat response, and few hot pixels. This chip has a peak quantum efficiency of .4, but has poor response in the blue. The camera is evacuated, and the CCD is cooled with a thermoelectric cooler stack to -72 deg. C to get a low .15 electron/pixel/second dark current.
The rotary shutter can give exposures as low as .05 sec and there is a 12 position filter wheel which includes Johnson-Cousins BVRI filters. The VRI filters are close to standard but the B filter suffers from the poor blue response of the CCD chip. The CCD camera is mounted on a computer controlled focusing sled.
Both wheels' entrance to the vacuum chamber are at the bottom of the picture.
Catalogues and Charts
The observatory regularly uses Sky Catalogue 2000, Uranometria (including the catalogue), Real Sky, A2.0 catalogue, Project Pluto's Guide, and the Digital Sky Survey (via the Internet).
Control And Computation
An IBM PC clone runs the telescope and the CCD camera. The locating procedures allow the targeting of invisible objects to an accuracy of about 10 arcsec. Astrophotos and BVRI photometry are done semi-automatically without guiding. Rapidly moving objects (e.g. comets) may be tracked while being exposed.
A large amount of software (80,000 lines of C and assembler source code) has been written to control the telescope and camera in a flexible automatic way, along with simultaneous image processing. The collection of a complete set of multiband images for an object requires one command. Full calibrations have been included.
A general FITS image handling package is included, as is a data management package capable of keeping track of hundreds of thousands of images. Each image is extensively documented in its header in order to almost eliminate manual logs.
A point spread function fitting photometry program is used to reduce the images. It is capable of automatic operation on thousands of images in a run. Then statistics software is used to analyze the results.
Diffraction Limited's package MaxIm DL is used for general purpose image processing, deconvolution, and viewing.
The software used gives substantial direct benefits in signal to noise ratio over more conventional amateur software. For example, a recent improvement in my astrophoto processing gave an improvement of .4 magnitudes on top of an already better than average processing. My 16" telescope became a 23" telescope that day.
This is essential to the observatory. It initially allowed a group of European professionals to train me (for which I am very thankful), and now it provides for the transfer of images and photometric data to professional colleagues in distant places.
On an average clear night the sky is fairly bright, measured to be 18th to 19th magnitude per square arcsecond (dark skies are 22nd magnitude per square arcsecond). Many nights 5th magnitude stars are visible to the naked eye, 6th are not. Even so, R photometry is possible for objects down to 16'th magnitude. The weather, on average, allows observing on about 1/3 of the nights.
Moving from object to object is a manual operation so the most suitable observing programs involve looking at the same object for long periods of time.
The optics normally used give a plate scale of 1.03 arcsec/pixel. 2.15 down to .44 are possible. At 1.03 the sharpest images are just under 3 pixels full width half maximum.
The three types of programs undertaken (recreational, commercial, and scientific) help support each other:
The telescope is optically very good for visual work but little is done for lack of time. Many astrophotos have been taken, and a desire to work with faint objects has resulted in techniques for locating visually invisible objects to within 10 arcsec. An abhorrence of guiding has resulted in techniques that produce high quality images without guiding. Both of these techniques turned out to be important for the scientific blazar photometry programs.
A desire to do something different resulted in the development of techniques for high magnification astrophotos, and for optimizing long exposure work. The latter was used for my entry in the Sky & Telescope "Deep Field Challenge". A 25.5 hour exposure reached mag. 24.5 with an SNR of 3. The processing of this image benefited
from the photometry software I wrote for scientific use.
The FITS package developed for observatory use was licenced to others. This required many improvements to the software which benefited the research programs.
Comet Video and CDROM
When comet Hyakutake came along on short notice, I collaborated with Cyanogen Productions Inc. to do close-up movies (.70 arcsec/pixel) of the comet nucleus. This required enhancements of the control software to track the comet during exposures, and new software to process the images to bring out the streamers from the nucleus. The raw imagery is available for anyone that wishes it for scientific research.
The observatory does not attempt to do science - rather it supports science via technological skill and observation. All of the successful projects were done with professional partners, and they did the astrophysics.
Some past and present observing programs:
28 SGR - Saturn Occultation
In collaboration with Rob Dick and Jon Buchanan, this event was video-taped using a 24" telescope. The images were reduced photometrically to provide a detailed cross section of the rings.
A small amount of work on asteroids has been done with Doug George. The observatory is capable of doing this type of work but the blazar work has taken most of the available time.
Since 1992, about 100,000 images have been exposed for 2 or 4 minutes and archived. Of these, 60,000 are photometric images of blazars and Seyfert galaxies. The type of photometry done is differential Johnson-Cousins BVRI. Blazars are reduced locally and the data sent via the Internet to professional astronomers. I cannot reduce Seyfert galaxies at this time, so for those the images are sent instead. All of this work has either been done as part of the OJ-94 collaboration, or with members of the collaboration.
The OJ-94 collaboration consisted of about 40 professional astronomers that teamed up to study the expected 1994 outburst of the blazar OJ287. The study then expanded to other blazars and more years. Prior to this, OJ287 was studied for decades by the Finnish astronomers who set up this collaboration and started a series of blazar conferences.
A Sample Light Curves of OJ287. It covers a 140 days and there are no error bars.
Recent work has involved obtaining the longest possible one night light curves of several blazars and Seyfert galaxies. These light curves are then sent to Alberto Sadun for analysis as to whether their variations show chaotic behaviour or not. The hope is that when a sufficiently large data base has been gathered, the parameters that come out of the chaos analyses will show correlations with other information about these objects.
My well figured Pyrex main mirror will be replaced with an Astrositall one to remove a thermal focus shift problem. A new CCD camera has been partially designed that would have good blue sensitivity and double the quantum efficiency of the current one. Some form of dome or turret is needed to solve a serious wind problem, but the design of the existing observatory makes it difficult to do this. And of course, if someone has a spare $100K, the observatory needs to be moved to dark skies!
Thanks to God (Microsoft), a major software effort is in the offing in order to get off of DOS.
The chaos project will take a few more years. Then onto whatever project that catches my interest and I am capable of contributing to.
A text file version without photos of this article can be downloaded. (13 kb)