[vsnet-chat 1431] Bistar Survey on Sept. 12

[Seiichi Yoshida <seiichi@muraoka.info.waseda.ac.jp>]

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/ 24mm   3 images
    f/ 35mm  26 images
    f/180mm   5 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:
			    mean number
	focal len.  time      of stars   field of view
	f/ 24mm    12.5 min     2000    31.8 x 21.2 deg
	f/ 35mm     6.0 min     1800    21.9 x 14.6 deg
	f/180mm     5.1 min     3100     4.4 x  2.9 deg
	f/300mm     3.9 min     2000     2.6 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. images   ND       NC       RM        RP
	f/ 24mm     3    35(12)   55(18)   38(13)   109(36)
	f/ 35mm    26   307(12)  232( 9)  436(17)  1458(56)
	f/180mm     5    37( 5)   33( 7)  161(32)   439(88)
	f/300mm     8    60( 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.
    PR: 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:

  http://vsnet.info.waseda.ac.jp/muraoka/members/seiichi/misao/doc/reference.html

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 (LINEAR), 12.5 mag, is fainter than our
limiting magnitude and we could not find it on our images.

P.S.
The past MISAO project announce mails are available at:
  http://vsnet.info.waseda.ac.jp/muraoka/members/seiichi/misao/

--
Seiichi Yoshida
Muraoka Lab., Waseda University, Japan
seiichi@muraoka.info.waseda.ac.jp
http://vsnet.info.waseda.ac.jp/muraoka/members/seiichi/index.html

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