Part Two

Like most astronomical observing programs, hunting supernovae requires a telescope, an observing site, and an observer with both time and patience. Yet a hunter who cannot recognize the prey has no hope of success; one also requires knowledge and practice of the specialized techniques for spotting these elusive targets. Sometimes a professional astronomer may stumble upon a supernova during an observing session when galaxies are being studied for some other purpose. Among amateurs, such a lucky find is extremely rare. The classic example in both instances is the discovery of SN 1987A in the Large Magellanic Cloud. However, relying upon such chance happenings will not prove to be the most fruitful way of doing astronomy.

Nearly all supernova discoveries made by professionals have been made photographically, although a growing number are now being made spectroscopically, by infrared or radio observations, or by the automatic search programs. The story is quite different, however, with respect to amateur discoveries.

The decade before 1988 marks the period when searching for supernovae in other galaxies clearly became an activity which amateurs could undertake on a regular basis. This project had been suggested as a domain for organized amateur effort at least forty years earlier by Dr. Fritz Zwicky. The AAVSO started a program of supernova search under the Nova Search Committee in 1973. This program had limited success, largely because of a lack of good finder charts of galaxies.

Before the 1980's, very few amateurs had any thought of the possibilities of discovering supernovae. Those who did make a serious attempt to find supernovae visually were hindered almost beyond usefulness by three factors: a lack of charts of galaxies for comparison purposes; a lack of useful published photographs of galaxies which amateurs could obtain; and there was "nowhere to go" for help with the many queries and false alarms that were bound to arise. These three problems were compounded by the fact that copies of the first Palomar Survey were either prohibitively expensive for amateurs, or they were out of reach behind the inaccessible doors of observatory libraries. For much of the southern sky no suitable survey materal existed at all.

My early, intermittent searches during the mid-1950's, and around 1970, were rendered largely useless by these factors, as well as by telescope inadequacies, and because my search was not extensive or intensive enough. The following description of what to do in supernova searching is the result of years of experience, including much frustration and defeat, and it benefits from the advice of many astronomers, both amateur and professional.

Amateur observers can employ three main methods: visual search, photographic search, and electronic search. Each of these methods has its own needs in equipment and resources, its own difficulties to overcome, and its own probabilities of success. An observer who is serious about discovering supernovae must first invest time, patience and hard work in to one of the three methods.

VISUAL SEARCH

EQUIPMENT

Telescope Aperture and Magnitude Limit

When considering what aperture telescope to procure for this work, or when trying to decide whether the telescope you now have will be useful, you will need to find out what limiting magnitude can be reached with that telescope at your observing site. The aperture and useful magnification are most important in determining the result, although other factors also at work include the degree of air turbulence, smog and light pollution that usually exist at the site, the quality of optics and eyepieces (as well as mirror alignment and the steadiness of the mounting), and the sharpness of the observer's vision.

For example, a good eight-inch mirror with high magnification can reveal magnitude 14.5 in a dark location. Under superb conditions it will reach below 15.0. Under excellent conditions, a ten-inch telescope will approach 16.0, and a twelve-inch will reach toward 16.5. However, you usually need to have a lot of experience with your telescope to be able to make the best use of your equipment, and you will naturally do better when observing overhead than when viewing closer to the horizon, because there is less air overhead to spoil the view.

You will need to study the situation at your proposed site. The above estimates represent what can be achieved by an experienced observer under very good conditions. Do not be too disappointed if you do not achieve such degrees of faintness. Judge what you can see in practice, and then proceed with the next factor.

For a number of years now, I have been living in small country towns, or in locations which are bordered by large national parks. This has meant that I had black skies (or skies that were dark enough) available from my back yard, or from a site only a few miles away. This has made an enormous difference to my ability to observe, and to make good use of very short periods of observing time which would otherwise not be used in this way. It has also meant that I could have good skies any day of the week, and this has made a serious searching program much more practical.

What Are Your Chances?

Study the list of supernova discoveries over recent years to see how many supernovae each year, on the average, rise to a brightness well within the limit of your telescope. Consider how easily you could have seen these supernovae if you had looked in the right place, and at the right time. Information about recent supernovae that were bright enough for amateurs to observe can be obtained by contacting the AAVSO Supernova Search Committee. Members of this committee can provide statistics which would be more immediately useful to someone who is just starting out in hunting for supernovae. There is an official list of supernovae kept at the California Instititute of Technology. It is available upon request from Dr. Ian N. Reid, California Institute of Technology, 105-24, Pasadena, CA 91125. The official list is generally built from information which has been published in the IAU Circulars. Normally, only a handful of supernovae brighten to within the limit of magnitude 15.0. Sometimes there are only one or two in a year, while at other times there may be half a dozen. Even fewer will become as bright as magnitude 13.0, so the number available for you to find is limited, and of course, there will be competition for these discoveries from other observers who are trying to do the same.

Remember that it is very difficult to discover a new star that is near the limit of your vision, especially when you do not already know that it is there. It is easier to find stars which are at least one magnitude brighter than the limit, depending upon the conditions at the time. You should make a realistic assessment of your chances, and think of the kind of effort and persistence you will need in order to achieve success.

Using a ten-inch f/4.3 Newtonian telescope at 120x (often at 180x), I found that I could see an average of three supernovae per year between 1980 November and 1985 October from a country location in New South Wales, Australia. By saying "I saw them" I mean that they occurred in galaxies that I was currently checking, so they fell within the scope of my search. I did not have too much competition from other observers, so I managed to discover eleven of the fifteen supernovae during that period. The other four were seen, and would have been discovered by me if they had not been found by somebody else first. It took fifty thousand galaxy observations in order to achieve this. About one thousand different galaxies were involved, many observed with great regularity. Four of my eleven supernovae were found before they reached maximum light. All were brighter than magnitude 14.5, except for one, which was just below 15.0. Also, my telescope was not working as efficiently at the beginning of the period as it was near the end, and this would have affected my results a little.

Thus an eight-inch f/6 Newtonian, or a ten-inch f/5, is probably the smallest useful telescope for a full-scale systematic visual search for supernovae from a good site. If a smaller telescope is used, the number of supernovae within reach of the instruments rapidly becomes so small that observers might feel their chances of success are too slim to make all their efforts worthwhile. A supernova has been found with only a five-inch refractor, of-course, by Jack Bennett back in 1968. But, 11th-magnitude supernovae are very rare, only one appearing every few years or so. Also, an observer with a larger telescope has a much better chance to find such a supernova early than one armed with only a five-inch telescope.

Speed of Operation

If your observing time (and your good weather) has no limits, this next point will not be so important for you. If your observing time is limited, then you will need a telescope which can be operated speedily. Then you can observe as many galaxies as possible in the time available, improving your chances of success.

Short focal length telescopes, with low and portable mountings, are excellent for quick handling. It is best if you can use the eyepiece comfortably while standing on the ground, regardless of where the telescope is pointed. If you have to move and climb ladders repeatedly, or shift domes, or fiddle with slow-motion controls or clock drives, you will lose time. If you have to use setting circles you will lose time, compared to the speed of efficient star-hopping with a "straight-through" finder-scope. After using the finder to locate the area of sky where the galaxy is lurking, a low power eyepiece must next be used in the main telescope to locate the galaxy. Then use a high power eyepiece to search the galaxy for new stars (high power means at least 12x for each inch of aperture, preferably 16x). Parfocal eyepieces are thus better than ones for which you have to refocus repeatedly.

One galaxy observed every minute or two is a good speed. Naturally, the more galaxies you can search each month the greater will be your probability of success.

RESOURCES

Apart from such essentials as star atlasses and catalogues of galaxies, the main resource that you need is to have a chart or photograph (or both) of EVERY SINGLE GALAXY that you hope to observe, along with enough information about the galaxy, and enough experience looking at it, that you will know confidently what the galaxy is supposed to look like in your telescope under varying atmospheric conditions. By repeated experience you will train yourself to know what each galaxy should be like so that you can INSTANTLY RECOGNIZE ANY NEW OBJECT. Perfection is hard to attain in this matter, but nothing less will do.

There are several ways to obtain the needed charts and photographs. Toshimasa Furuta of Japan, Juhani Salmi of Finland, and Manuel Lopez Alvarez of Argentina, have produced collections of galaxy photos which can be used as comparison material in supernova hunting. Several clubs and associations have begun the task of producing galaxy charts, for example, the observing groups in contact with Guy Hurst in England. A more substantial set of 230 charts, prepared by Gregg Thompson and James Bryan, was published in 1990. This covers nearly three hundred of the brightest galaxies. It is hoped that a supplementary atlas of about 1000 survey photographs may become available in the future.

Charts are more flexible in showing details of galaxy structure and foreground stars. Photos are often overexposed, or succeed in concealing details which a visual observer needs to be aware of. But, I believe one needs to have as much in the way of resources as one can get. Both charts and photos are important, and it is better to have two different photos than just one. The old saying is true in this area - the only thing better than having one chocolate is to have two. When a supernova appears in a galaxy, a visual discoverer will be glad to consult as many charts and photos as possible in the quest to be sure of what has been found.

If other galaxies are going to be searched which are not included in the above resources, or if the above resources cannot be procured, then some other answer has to be found.

Some observers have asked for, and gained access to, survey sets held by a nearby university or observatory. They have made their own photos, using single-lens reflex cameras and with the aid of a bellows or extending rings and a macro lens. In this way copies can be made, from the Schmidt survey fields, of all galaxies and their surrounding field stars involved in an observing program. It is a time- consuming and expensive undertaking, but, in the end, it is well worth the effort for a serious supernova hunter, and this has been my own way of coping with the problem. I now have thousands of 35mm negatives of galaxies copied from the various survey resource materials owned by the Anglo-Australian Observatory, and from other materials at the U.K. Schmidt Telescope Unit.

It is important for supernova hunters to remain on good terms with the professionals, and not to wear out their welcome by asking too often for the use of expensive materials that the professional may not want to make available to unknown enquirers. The AAVSO is willing to help the serious supernova hunter by making a path of access to survey materials, which the hunter can then use for making resource photos, as described. To do this, contact the Director of the AAVSO, Dr. Janet Mattei. The survey materials are located at the Harvard-Smithsonian Center for Astrophysics, in Cambridge, Massachusetts, and anyone wishing to use them would have to travel there. Someone visiting Australia, or living there, could contact me. Other possible sources of help may also become available as time passes.

Another option, pursued by a few, is to purchase print copies of the first Palomar survey, choosing those fields which interested them most. There are certain minimum purchase requirements of a modest kind, but fields of one's choice can be obtained from the California Institute of Technology Bookstore.

At the time of writing, a set of microfiche copies of the old Palomar Survey is to be produced by a private company in Texas at a much cheaper price than the cost of the originals. These copies are good for showing whereabouts the galaxies are in the sky, but inner details of the galaxies are of poorer quality, or are lost altogether.

The most recent resource, however, suits best those with big personal computers. A CCD atlas of galaxies has been produced by Christian Buil and Eric Thouvenot. (The Buil-Thouvenot CCD Atlas of Deep-Sky Objects, available from Sky Publishing, 49 Bay State Rd., Cambridge, MA 02138). It is avaliable on a number of floppy disks, and is quite expensive. But, it provides excellent pictures of about 1000 galaxies. For those who can afford it, this is probably the best resource, though it is not so easy to use while you are in the middle of a working session at the telescope.

It is a waste of supernova-hunting time to look at a galaxy with no way of knowing whether a star in the field is new or not. Resource-making can be time-consuming and expensive, but it is an essential part of being ready to hunt for supernovae.

TECHNIQUES AND PROCEDURES

The basic technique is to look at a galaxy, using sufficient magnification to see it to best advantage with your particular telescope, and decide whether or not the galaxy shows any unusual appearance. If it does not, then go on to the next galaxy. If you are suspicious or uncertain about any detail, then you must take steps to resolve the uncertainty. When building upon this basic technique of the supernova search, there are two principles to follow: maximize your chances of seeing, and be systematic in your search.

(1) Try to maximize your own chances of seeing a supernova, and (we hope) of discovering one. Several factors are important at this point:

(a) Galaxies must be observed regularly, so that you do not miss a supernova between observations. Once or twice per month is essential; bright and nearby galaxies should be watched more often to catch bright supernovae while they are rising.

(b) The wider the range and list of galaxies being observed, the more chance there is of success. Someone who watches two hundred galaxies per month has a much better chance of finding something than the person who watches only twenty galaxies. Similarly, watching two thousand different galaxies will be more fruitful than watching two hundred.

(c) For an observer with limited time, speed becomes an important factor. Memorizing galaxy's appearance will add greatly to the observer's speed; there is no need to check charts or photographs continually, unless something suspicious appears. If you are starting out as a hunter, I recommend that you set a goal to memorize the appearances of the galaxies as you begin to search them. As your memory of the galaxies improves you will need to consult charts less often, and this will save you much time. Thus, you will be able to cover a greater number of galaxies in the time you have available.

(d) You can also increase your speed by learning to locate a galaxy in the sky within a few seconds, using the finder-scope, and a low-powered eyepiece.

(2) Devise a method or timetable of observing which enables you to beat the competition -- at least sometimes. Many amateurs can observe only on weekends. Professional photographic searches take place during the dark of the moon. By carefully considering how and when others conduct their searches it may be possible to observe the galaxies before they do. The moon, work, the weather and how far one has to travel to get to a good observing location, will help decide what can, or cannot, be done. If the matter is pursued carefully, it may be possible to be the first to make the discovery. But be warned, a system can also backfire on you. The supernova may rise in such a fashion that the early observer misses it, while the later observer finds it. I have missed discoveries for this very reason on several occasions.

VERIFICATION PROCEDURES

This process is extremely important. It is essential that every supernova hunter has friends or team members who are willing to check on any suspected discoveries, at any time of the night, and perhaps at very short notice.

All confirmed discoveries are reported to the Central Bureau for Astronomical Telegrams, in Cambridge, Massachusetts. The Bureau has no way of confirming your report; the Central Bureau is simply an office for circulating information quickly. It is essential to verify thoroughly the supposed discovery BEFORE it is reported to the Bureau. They have the unenviable task of judging the credibility of your report before it is announced to the world. The Bureau is obligated to be very careful about what is a real discovery of a supernova among all the reports of discoveries which they receive. So, it is important for the credibility of your own work, and for the good of astronomy, to provide the Central Bureau with the best verification that is possible to obtain when a discovery is reported.

How to Handle a Suspected Discovery - First Stage

Imagine that you have come across a star-like object next to a galaxy, and you think it is a supernova.

(1) Carefully make a note of the position of your suspect in relation to the nucleus of the galaxy, and also the nearby stars.

(2) Make a quick, initial judgment as to whether the object is moving or not. Take several minutes to do this, if needed. Come back to it 30 to 60 minutes later, if possible, to check again for motion.

(3) Consult your own stock of charts and photographs, notes and comments, catalogues, and any other source of information you have about this galaxy. Keep a detailed file on each galaxy, and use it on occasions such as this. Make sure the new object is not the actual nucleus of the galaxy, or any other normal part of it. Make sure it is not a foreground star you have previously not noticed, or some other kind of galactic variable.

(4) Make sure it is not an asteroid. It is now possible for supernova hunters to have a list of close appulses between asteroids and galaxies. A list of current appulses can be obtained from one of the AAVSO Supernova Search Committee members. If you have a copy which includes this galaxy, then consult it. An alternative is to have the current issue of an asteroid ephemeris, or to know somebody who does. Another way of coping with this problem is simply to watch the object for another hour or so. If it is an asteroid it will have moved in that time, unless it is "stationary" (at the special point where it begins or ends its retrograde motion amongst the stars).

(5) If you have done the best you can about these various matters, and you still think it is a supernova, start making notes in preparation for contacting your verification team leader.

The verification team will need to know the catalogue number of the galaxy, its position in the sky, and the epoch date of that position. As carefully as you can, measure the offset of the suspect from the nucleus of the galaxy in arc seconds or minutes north or south, and then similarly east or west. Be careful that your directions are right, because it is very easy to make a mistake.

The verification team should have a leader, or co-ordinator, and this is the person who should be phoned immediately with all the details about your suspect. If, for some reason, this person cannot be contacted, then the team should have some agreement about what other steps are to be followed.

The team will also want to know how familiar you are with this particular galaxy, and when you saw it last in its normal appearance. Many times I have looked at a galaxy which I thought I knew very well indeed, and have seen some detail that made me suspicious. Generally, these are tricks played by my memory, or by changes in the seeing conditions.

The team will want to know everything you have done yourself to verify if the suspect is a supernova or not. You may also have to convince them that you are not looking at the wrong galaxy.

(6) Note the Universal Time of your discovery, and of any later observations. The time should be noted as accurately as possible -- to two decimal places if you can.

How to Handle a Suspected Discovery - Second Stage

Assume that you have made good contact with the team leader, that this has happened within two hours of your first sighting of the suspect, and that there are still some hours of darkness left.

The team leader should be a combination of the most experienced and knowledgable observer in the group, who also has the best collection of charts and photographic resources, and who has immediate access to a telescope capable of resolving difficult questions about suspected supernova discoveries. The leader also should be willing to do this work at very short notice. Based upon prior experience, the leader will decide whether this question of verification can be answered by simply consulting resources, or by observation, or both. If the leader cannot answer the question for some reason (bad weather, inadequate resources or telescope, approaching dawn) other people should be available who can be called upon for help in solving the problem. As a general principle, the leader should also involve some other observers, and should take notice of whether they think the object is a supernova or not. This adds greater support to the credibility of the final report to the Central Bureau.

It is the leader's task to give the suspected supernova such a thorough testing that other possibilities can be confidently eliminated, and the supernova can be confirmed. The leader has the final decision about when this point has been reached, and other team members (including the discoverer) should respect the leader's decision, and have confidence in their leader's reliability.

After the leader has conducted a thorough test of the suspect, and has had other observers do the same, the leader may decide that no other verification is needed, and that the Central Bureau for Astronomical Telegrams should be contacted without delay. The Central Bureau may accept the leader's report as sufficient, or may ask for more verification, involving a spectrograph, or some other equipment used by professional astronomers only. Again, remember, the Central Bureau has to judge whether to accept a report of a discovery made by a group of visual observers, without any other verification. If the Central Bureau accepts the discovery report, AAVSO Headquarters should also be alerted promptly. This enables AAVSO Headquarters to alert observers worldwide to monitor the supernova through AAVSO Alert Notices, often garnering crucial data.

Special Note

If anyone does not have a verification team available, please contact the AAVSO Supernova Verification Team member closest to where you live with a request for verification of a suspected discovery. Their addresses and phone numbers can be found at the end of this manual. Here are some guidelines to use when contacting them:

(1) Use the telephone. Ring your closest Supernova Verification Team member, or the one who is best able to view the galaxy in which the suspected supernova appears.

(2) When ringing any of the Team members, remember that they are amateurs who do not have the finances of a large institution behind them to pay for their phone calls in reply to yours. So, if you ring us with a suspected supernova, give us all the details, as mentioned above, and also your name, address and phone number. If your suspect is confirmed as a supernova, we will ring you back with the glad tidings. If your suspect proves to be a false alarm, or if we cannot confirm it quickly for some reason, you may ring us back again to enquire, or we will write to you by air mail to let you know the results.

REPORTING THE DISCOVERY

As already indicated, the place to report all verified discoveries is the Central Bureau for Astronomical Telegrams, located at the Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA. The current director is Dr. Brian Marsden.

The Central Bureau issues its own instructions, from time to time, about how reports are to be made. Team members should comply with these instructions. While some forms of sending are necessarily brief, it is important to pass on to the Bureau ALL information that you have about the supernova. This should include all details of every observation that has been made of it so far, and details about the different people who made these observations during the verification process. Everything that has been done, and all the reference sources used, to verify the supernova should be fully explained.

Central Bureau numbers are: Telephone: 617-495-7244/7440/7444 (emergency use only); e-mail: EASY LINK 62794505; marsden@cfa or green@cfa (.SPAN, .BITNET, or .HARVARD.EDU).

AFTER THE DISCOVERY

It has been my practice to try to have somebody take good quality photographs of each of my discoveries as soon as possible after it is found. I have two amateur friends who have done this for me. Also, I have always tried to get photographs taken by professional astronomers. This second course of action has not always been successful, but it has succeeded in the vast majority of cases.

These photographs serve a number of purposes. It is very important to get an exact position of the supernova. The Central Bureau wants to publish one as quickly as possible after the discovery for use by astronomers observing with large ground-based telescopes, and space satellites. Getting an exact position can be done best from a photograph. Amateur photographs can be used for this purpose. Schmidt plates have often been made for me with this purpose in mind, and then been measured by Robert A. McNaught at the Anglo-Australian Observatory.

It is also important to have good quality photographs for publication in amateur journals, or in professional research papers, or in any publication related to supernova hunting. They can also be used as slides to illustrate talks. If the photo is not taken at the time when the supernova is bright then the opportunity is lost for ever. Photos showing maximum light are of most interest. I have enjoyed keeping such pictures for my personal files.

Write a short report, telling the story of the discovery, for publication in your local club newsletter, and for sending in to the AAVSO. Include all factors which might be of scientific interest and as a historical record of your discovery. Also include human interest information such as difficulties you had, and funny or strange situations that arose. Supernova discoveries (usually including finding charts) are reported in the AAVSO Alert Notice, distributed to observers worldwide by airmail, electronic mail, and fax.

Make as many observations of your discovery as you can, and carefully note them all including the comparison stars you used for estimating the brightness. Establish a light curve of visual observations. Report all these to the Central Bureau and to the AAVSO by electronic mail and/or by phone or fax.

The Central Bureau will often be able to publish these visual magnitude estimates in the IAU Circulars. When you send your observations to the AAVSO, those observations will become part of the AAVSO International Database and will be distributed to the astronomical community with your AAVSO observing initials.

For your own interest, make sure you keep a file as complete as possible of all observations, information, scientific articles, IAU Circulars, etc., about supernovae that you have discovered. This may not be easy, because you are not likely to see all the magazines and professional journals, but do the best you can, and get your friends to help you.

YOUR OBSERVING RECORDS

It is important to keep a full list of all your observations of galaxies, and of any supernovae that you see, regardless of who discovered it.

For each night that you observe, keep a list of all galaxies that you see, and have enough information to know roughly what your limiting magnitude was, and what the seeing conditions were like. The list of galaxy observations when NO supernovae were present can be very useful in determining how frequently supernovae appear.

All galaxy observations in search of supernovae should be reported to the AAVSO on the proper reporting form (shown here). It is sufficient to send reports only twice a year to the AAVSO Supernova Search Committee Chair: in April (for observations made between September 1 and March 31), and September (for observations made between April 1 and August 31). The AAVSO Supernova Search Report may be downloaded in pdf format here Report forms may also be obtained from AAVSO Headquarters. These will then be ready for the twice yearly reports (in May and October) which the AAVSO Supernova Search Committee Chair makes about the work of the Committee. These reports will then be sent to AAVSO Headquarters for digitizing and inclusion in the data archives.

Properly made reports of all galaxy observations can be used as a basis for statistical studies about how often the different kinds of supernovae appear in the different kinds of galaxies which are within range of observation. This information is not well known, at present, and is a basic essential in several astrophysical projects.

PHOTOGRAPHIC SEARCH

EQUIPMENT

Several things must be borne in mind by amateurs who wish to search for supernovae by photographing galaxies.

(1) The telescope must have sufficient aperture to reach a faint enough limiting magnitude to give good chances of success, and must show enough area to scan efficiently your target galaxies. Photographs which do not show magnitude 17 well, or have only a tiny field of view, might not be penetrating enough to make the time, effort, and expense worthwhile, and thus the telescope concerned might not be suitable for this kind of work. Only so many photographs can be taken in a given time, so optimize your chances with a good compromise on field of vision and magnitude depth.

(2) A related problem is that the focal length of the telescope should be LONG enough to provide images with sufficient resolution to isolate the image of a star from that of the rest of the galaxy. This is not such a problem for a visual observer because one can usually gain resolution by increasing magnification. Such a course is not open to a photographer to the same degree.

(3) On the other hand, the focal length should be SHORT enough to provide a fast photographic speed. The faster the speed the more photos can be taken during the observing session, as the time taken to expose each photo will be shorter. However, this will not shorten the time required to reload films or plates into the telescope.

(4) Wide-angle cameras are clearly more useful than those having a smaller field of view, and can photograph only one or two galaxies at a time. By including many galaxies in one picture, the chances of success are greatly increased. In this regard, normal Schmidt telescopes have a decided advantage over Newtonians.

(5) Beginners in astrophotography often make the mistake of trying to photograph objects with equipment that is cheap or of poor quality. Equipment must be of sufficient quality in every detail so that good photos can be made regularly.

The general rule is that Schmidt telescopes should be of at least ten inches aperture, and of fast photographic speed. Fast Schmidts with smaller aperture will not show enough detail (as mentioned in point two). Newtonians will not give enough galaxy coverage in the available time. Certainly, it is possible to succeed with some other kind of telescope, but success will not happen often enough unless you are making a serious attempt at hunting efficiently.

TECHNIQUES

The basic technique is the same as for visual searching. Take as many pictures as you can, of as many galaxies as you can, choosing galaxies which are likely to produce supernovae which will rise well within the magnitude range of your equipment. Use an observing routine by which you do not miss supernovae between observations. There are several points which apply specially to photographic searching which should be carefully considered.

(1) Negatives should be developed and searched as soon as possible after exposure. Aim to search the photo on the SAME NIGHT you take the picture. This not only gives you the best chance of early discovery; more important, if you have caught a supernova on your negative before it has reached maximum light your observation will be that much more scientifically useful.

(2) It is essential to take TWO photographs of any suspected supernova, and confirmed by you, before the suspect can be taken seriously, to avoid being tricked by flaws and marks on your film.

There are special ways of dealing with this matter. Berne Observatory boasts twin Schmidts which take two photos simultaneously. You can take two photos of each object as a general procedure, one after the other, or you can take single photos of each field, and wait until you actually find a supernova to rephotograph that particular galaxy.

This last method is the usual practice, but it may result in several nights' delay before you get a chance to take the second photo. Somebody else may find the supernova during that time. And, if you have a pre- maximum supernova on the negative, this important early stage may be past before you get confirmation. Science is the loser under such circumstances. This loss of time is one of the great problems of photographic searching (and is a major reason for turning to an automatic search system).

Perhaps the best way to conduct the photographic search, if it is being done on a major scale, is for two people to be directly involved each night. One person takes the photos. The second person develops and examines the films as soon as they come out of the developing machine. Then it may be possible to take the second photograph on the same night a supernova suspect is found.

(3) When comparing a newly taken photo with an older reference photo, you should exercise care in making sure that both films are of the same kind and that both have the same degree of depth and density. This is to avoid a situation where an observer thinks an object is a supernova, but which is in fact simply due to differences in the photographic material.

(4) Various techniques and devices can be used to aid in the process of comparing two photos. Alternatives depend upon the physical size of the negatives - whether they are 35mm, two inches square, or larger plates. It is possible to build for yourself a suitable blinking device for comparing a new photo of a field with a file picture. A method along this line has been developed and popularized by Ben Mayer of California, and is called the PROBLICOM (Projection Blink Comparitor) method.

If you need help in making a system for yourself, then write to the AAVSO Supernova Search Committee, and we will do our best to help you.

VERIFICATION TECHNIQUES

As with visual searching and verification, it is essential to eliminate any possibility that the suspected supernova is any other kind of object. The photographer should have the resources at hand to do this quickly, and then should have access to a verification team to verify and confirm the discovery.

For an amateur photographic searcher, it may be that the quickest way to verify a supernova brighter than magnitude 15 is to use the services of a VISUAL verification team. It can be a lot quicker to make a visual verification than to go through the whole process of taking, developing and examining another photo.

AMATEUR POSSIBILITIES FOR SEARCHING WITH A CCD

Searching with a CCD by amateurs needs to be considered in two separate categories.

(1) The First procedure is to take CCD pictures of galaxies, and make a visual search of the computer picture for new objects, comparing it with a file picture.

This has commenced now as a serious amateur project, and has the great advantage that it can be carried out with good effect from a light polluted location, and even in moderate moonlight. As a result, this type of searching can be done in suburban locations where many amateurs live, and where there is not the regular access to a dark site that is required for visual searching. Highly polluted locations, however, will still be unsuitable.

Longer focussed telescopes, such as a Schmidt-Cassegrain, are good. Even the famous eight inch aperture Celestron and Meade telescopes of this sort will do an excellent job. Short focussed small telescopes should be avoided, as the scale of picture per pixel can become unsuitalbe.

Extra cost is involved in keeping all the pictures on disks for future possible reference.

(2) The second procedure is to develop and use a fully automatic system, where the computer does the actual searching. This method has not yet been used by amateurs.

The ultimate aim of an automatic search is to perform the whole search process with electronic equipment in such a way that the only part for a human observer to do is to switch on the machine, and then to read out in what galaxies the supernovae have been found. Over the years, many attempts have been made to construct a fully automatic system. See the "History" section for details of this.

The Berkeley Automatic Supernova Search project was the first to succeed at discovering supernovae by purely automatic means, but this was achieved only after enormous frustrations and enormous expense. The result is, however, that the ground has been broken for others to follow.

Fully automatic searching has the disadvantage that the computer has to be programmed to ignore faint differences between the live image and the memory image in order to overcome differences in variable seeing conditions. Otherwise, an enormous number of false alarms would occur. But this programming factor will cause faint supernovae to be lost.

It should be emphasized that a great deal of computer capacity is required for a fully automatic search. The Berkeley Group had to use five personal computers and workstations at once and in tandem in order to be successful.

The problems of verification of a discovery in any partly or fully automatic search are in many ways the same as for the other kinds of searching. Great care needs to be taken to double-check for mistakes and peculiarities arising from the special gear being used. Other observers should be brought into the checking of suspects, and completely independent verification should be obtained.

• Supernova Search Report Form
• Galaxy Report Form