MISAO Project

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1998 Nov. 1

    Bistar Survey on Sept. 12    

MISAO Project Announce Mail (Nov. 1, 1998)

Hello. I am Seiichi Yoshida working on the MISAO project.

The automatic image examination system PIXY was re-designed in early October and released as Oct. 11 version (the latest version is Oct. 30 now).

The main modifications are about the inside of the system at the following two points:

  • Design of the program source is totally changed.
  • Matching and pairing process are improved.

But here I do not explain them in detail. Technical notes and class references, which explain the inner technical methods and program sources respectively, will be available via WWW in the future. So please wait for them.

The apparent change at the users' viewpoint is that the system opens four independent windows after all: the original image, the chart of detected stars, the catalog chart of the same area, and the control panel. Separating each other into independent windows makes operation much more comfortable.

Well, we operated the 4th Bistar Survey on Sept. 12. Unfortunately the weather was cloudy and we could do wide-field survey only for 1 hour and 20 minutes, from 03:10 a.m. to 04:30 a.m. In addition, the morning glow began at around 03:55 a.m. However, we could 34 survey images as:

f/ 24mm3 images
f/ 35mm26 images
f/180mm5 images

We also took 8 images of comets, etc. with 300-mm lens. Therefore we obtained 42 images totally on that night.

Here I introduce you the results of examination of these images by the PIXY system Oct. 30 version. It took 4 hours and 10 minutes to examine all images on a PentiumPro 180MHz Windows95 machine. The time is that of the PIXY system alone, not including the time of the automatic identification system. The mean time for one image by each focal length is:

focal len.timemean number
of stars
field of view
f/ 24mm12.5 min200031.8 x 21.2 deg
f/ 35mm6.0 min180021.9 x 14.6 deg
f/180mm5.1 min31004.4 x 2.9 deg
f/300mm3.9 min20002.6 x 1.8 deg

In fact, it had taken much more time by the PIXY system Oct. 11 version, especially in case of wide-field images. The time was reduced to the half by Oct. 30 version, but the characteristic is still evident that the wider the image, the longer it takes for examination. The reason is reading data from GSC takes very long time. For example, the field of view of a 35-mm image is 22x15 deg. Then the PIXY system reads data from GSC for a 44x44 deg area before matching, and for a 33x33 deg area before pairing. The index in the GSC catalog lets us access to the specific data rapidly, but it cannot work when reading data widely. Actually, The half of the total time is by reading GSC data in case of 35-mm lens. By the way, all of the GSC data are installed onto a hard disk here, so the time will be longer if reading data from CD-ROM.

An image of 35-mm lens contain several thousands or more than 10 thousands stars until 11-13 mag. But the PIXY system restricts the magnitude of stars to read from a catalog depending on the field of view size in order to defend out of memory. For example, the limiting magnitude is 9.6 mag in case of 35mm-lens. Therefore, all stars on the image fainter than 9.6 mag are ignored. Here the purpose of examination is to detect evident bright comets or novae, so I did not try to overthrow the limitation.

The number of remarkable objects detected from the images by the PIXY system are as follows:

focal len.imagesNDNCRMRP
f/ 24mm335(12)55(18)38(13)109(36)
f/ 35mm26307(12)232( 9)436(17)1458(56)
f/180mm537( 5)33( 7)161(32)439(88)
f/300mm860( 8)41( 5)175(22)385(48)

The value in parentheses are mean number per image. The code ND, NC, RM, RP means:

ND:A star not recorded in catalog is detected.
NC:A star in catalog is not found on the image.
RM:The magnitude differs between the image and catalog.
RP:The position differs between the image and catalog.

They are usually interpreted as:

ND:New object, variable star, or omission of the catalog.
NC:Variable star or catalog error.
RM:Variable star.
RP:Effect of the proper motion.

However, they can be in fact as:

ND:False detection of clouds, landscapes, ghost of a bright star, etc.
RM:Difference of magnitude is by simply difference of color band, or just an error of the PIXY system.
RP:(in case of the wide-field) Just a mistake of pairing.
(in case of the narrow-field) Just a nebula, whose position measured by the PIXY and recorded in the catalog are often both inaccurate.

Therefore, please be careful to see the remarkable objects output by the PIXY system. Of course, it is necessary for new object survey to check if it is a known variable star or not.

There is another problem in case of a wide-field image. As mentioned above, the system restricts the magnitude to read data from a catalog, for example until 9.6 mag in case of 35-mm lens. Let's think of a case that there are three close stars in a catalog (recorded magnitude are 9.7, 9.8 and 9.9 mag). They are bright enough to be detected on a 35-mm lens image. However, it can be detected as one star because they are too close. Then the system estimates the brightness as amount of the three, about 8.6 mag. A some error or difference of color band can change the value, to 8.0 mag for instance. But the three stars data in the catalog are fainter than the limitation, so they are not read by the PIXY system. As a result, it outputs this 8.0 mag star as a bright candidate of a new object. If one of the three is 9.5 mag, only one star is read by the PIXY from the catalog. As a result, it outputs that a 9.5 mag star brightens to 8.0 mag.

Now I introduce you some investigation results of remarkable objects found in Sept. 12 survey images. Many interesting facts became clear.

All images of 24-mm lens were taken after the morning glow began and the sky was rather bright. But the PIXY system could detect until 8.5 mag star from them. Because the system reads star data from GSC only until 8.7 mag, so much fainter stars may be detected by a deep examination. This is a good support of new object discovery in the glow.

Many stars became cometary on long focus images (180-mm, 300-mm, etc.) with no filter. That should be an infrared aberration blur. A CCD camera is sensitive in infrared and a normal camera lens has different focal points for visible light and infrared, so red stars often be blurred. They are stellar on images through an infrared block filter. All stars are blurred without an infrared block filter, even if stars do not look blurred. The accuracy of astrometry in case of a 300-mm lens image is about 1/20 of the pixel size (0.6 arcsec) with an infrared block filter, but about 1/10 of the pixel size (1.0 arcsec) with no filter.

A red star becomes extremely brighter on a CCD image, so it usually becomes a ND object (a candidate of new objects) or a RM object (a candidate of variable stars). In addition, a red star is often a variable star like a Mira-type, and the magnitude recorded in a catalog is often very faint. Therefore, many of ND objects output by the PIXY system are identified with known Mira-type variable stars or IRAS objects, etc.

The PIXY system outputs a candidate of variable stars as a RM object. But the color band of a CCD image differs from that of a star catalog like GSC. So the difference of magnitude between the image and a catalog does not mean the star is actually variable. I have a plan to release a software to compare two images in the near future. Then we will be able to pick up true candidates of variable stars by comparing a latest image to a past image. Furthermore, we can see evidently the motion of a comet on 300-mm images. So comparing two image at one night by the software will pick up a moving object.

There are no data in the GSC of such bright galaxies as M31, M33 and M110. So the PIXY system outputs them as candidates of a new object. Taking an image around M33, many stars recorded in the GSC could be detected. They should be just errors of the GSC catalog. Minoru Sato lists up candidates of such catalog errors and many of the invisible stars around M33 found our examination were identified data in Sato's list. The Sato's list is available at:


When there is an open cluster in the image, stars become very complicated. I was afraid that the PIXY system could not operate pairing properly in a complicated area and many false candidates of new objects or catalog errors could be listed up. But actually, the current PIXY system could make a pair of each star between the image and the catalog properly. On the other hand, the PIXY system could not work well on such images: an image whose background is very bright at one side because of the moon light, or an image containing landscapes. It sometimes output many false detections or sometimes failed examination itself.

We tried to take image of three comets, C/1997 J2 (Meunier-Dupouy), C/1998 M5 (LINEAR) and 52P/Harrington-Abell, by 300-mm lens. We aimed to a comet using a scale circle of the mount, but it was not so reliable. Unfortunately, C/1997 J2 (Meunier-Dupouy) was not in our frames.

Examining an image by the PIXY system, we must input the approximate position and approximate field of view size at first. I input the position in the ephemeris table as the approximate position to examine images of comets. In case of the image of C/1997 J2 (Meunier-Dupouy), the ephemeris said:

  R.A.=21h11m21s.12  Decl.=+02o36'20".8

so I input this position at first. However, the area of the image and that we expected to take differed about the size of the image itself, the position above was actually out of the image. Despite of the difference, the PIXY system succeeded matching and output the true area of the image. The position of the four corners and the center were output as:

  21 21 33.18  +01 07 08.5                          21 21 35.49  +03 45 19.6
                            21 18 03.14  +02 26 21.2
  21 14 31.10  +01 07 18.2                          21 14 32.77  +03 45 28.4

This fact implies that the PIXY system can find the area of an image with a rough position even if we cannot say which area is in the image. Actually, the PIXY could work well and output the true area for many images even if I changed the approximate position input at first. But in case of some images, the system strongly depended on the first position. In case of a few images, it failed matching even if I input the right center position at first.

After the examination of the PIXY system, I operated the automatic identification system, deleted stars identified with known variable stars, and listed up true candidates of new objects. Most of the ND objects (candidates of new objects) were identified with known variable stars, and most of the rest were just false detections. But some stars passed these checks.

Images by 35-mm lens were examined using the GSC 1.1. The following three stars were passed the checks and remained as candidates of new objects. The first data is the detected position and magnitude. In the GSC, there are only faint stars as below (the value at end is distance from the detected position):

R.A.=08 33 05.19  Decl.=+55 21 21.7  mag= 6.99
GSC 3800-0878  08 33 07.89  +55 21 27.6  12.56     23.8"
GSC 3800-0887  08 33 05.37  +55 21 18.3  11.01      3.8"

R.A.=08 27 38.12  Decl.=+55 11 15.6  mag= 7.46
GSC 3800-1228  08 27 38.70  +55 11 20.2  11.03      6.8"
GSC 3800-1253  08 27 35.39  +55 12 20.0  14.67     68.5"

R.A.=08 26 59.97  Decl.=+53 37 45.6  mag= 7.73
GSC 3797-1249  08 26 59.48  +53 37 46.0  11.19      4.4"
GSC 3797-1291  08 26 59.39  +53 37 07.4  14.85     38.6"

However, there is a 7.5 mag, 8 mag and 7 mag star at each position on a photo chart. So they are not new novae. They may new variable stars but I think they are just lack of data in the GSC because the three stars are in the neighborhood.

Images by 180-mm lens were examined using the GSC 1.1. The following three stars were passed the checks and remained as candidates of new objects. But there is a data for each star in the USNO-A1.0 catalog. Therefore, they are just lack of data in the GSC.

R.A.=00 36 26.54  Decl.=+56 01 04.6  mag=11.47
USNO-A1.0 1425.00875786  00 36 26.598  +56 01 04.86  11.5R  12.2B      0.6"

R.A.=00 55 22.24  Decl.=+59 28 05.5  mag=10.87
USNO-A1.0 1425.01303964  00 55 21.931  +59 28 07.00  11.8R  15.4B      2.8"

R.A.=05 42 56.95  Decl.=+12 55 36.3  mag=11.57
USNO-A1.0 0975.01921527  05 42 56.893  +12 55 39.57  12.2R  16.6B      3.4"
USNO-A1.0 0975.01921721  05 42 57.422  +12 55 32.84  13.6R  15.7B      7.7"

Images by 300-mm lens were examined using the USNO-A1.0. The following two stars were passed the checks and remained as candidates of new objects. But there is a data for each star in the GSC 1.1 catalog. Therefore, they are just lack of data in the USNO-A1.0.

R.A.=21 18 14.82  Decl.=+01 40 56.6  mag=11.93
GSC 0528-1773  21 18 14.88  +01 40 54.3  12.98      2.4"
GSC 0528-1773  21 18 14.87  +01 40 56.0  11.60      0.9"

R.A.=05 26 10.77  Decl.=+34 33 16.9  mag=11.61
GSC 2411-0572  05 26 10.70  +34 33 20.6  11.64      3.8"

Some stars are only in the GSC 1.1 catalog, and some are only in the USNO-A1.0 catalog. So please be careful when searching a new object.

For the last example above, there is a data:

USNO-A1.0 1200.03333311  05 26 10.715  +34 33 20.69  99.9R  14.8B      0.2"

in the USNO-A1.0 catalog. So this star may be reddish.

Almost all Bistar Survey images are not open in the public yet. That is why the current PIXY system and the automatic identification system is not perfect, and handy check is required to remove noises, modify mistakes on identification, etc. But most of such handy works can be done automatically, I guess, so I will work on improvement of the system at first. Then we examine all past images and put them with examination results open in the public.

The Bistar Survey is moved to a local survey in Ageo city since October. Although it is in the test step now, we will start a regular survey soon. Two bright new objects were discovered in this period, but they were our of our capacity. Nova Sco 1998, 6.9 mag, is out of our frames. Comet C/1998 U3 (Jager), 12.5 mag, is fainter than our limiting magnitude and we could not find it on our images.

The past MISAO project announce mails are available at:


Seiichi Yoshida
Muraoka Lab., Waseda University, Japan

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