Japanese version Home Page Updated on May 4, 2007
Investigate about Star
You can feel "Oh, I get a new star!?" many times when you see CCD images. You will find a star not found in your past images. You will find a star not displayed by the GUIDE. However, please be careful. If you feel you got a new star, it is often a very popular Mira type variable star.
Many people is observing faint comets with CCD cameras recently. However, please be careful. If you find some object at the predicted position, it is often a faint star at the same position and the comet is actually invisible.
You can find some interesting stars when you observe stars with a CCD camera. While observing an eclipsing variable, you can find the brightness of another star in the frame changes as well. When you measure the brightness of a comet, you can feel the data of one of the comparison stars does not correspond to the value in the catalog.
Recently, you can easily obtain various kinds of information using Internet. When you find a possible new star, when you observe a faint comet, or when you find an interesting star, please investigate about the star.
Here introduces how we investigate about a star in the course of the MISAO Project, in order to know about it in details when we find a possible new star or an interesting star.
Investigation of a star and utilization of the information can reduce mistakes in your discoveries or observations. Furthermore, you can learn various knowledge, and you can enjoy your surveys or observations much more. Sometime you may get a chance to discover an important rare object unexpectedly.
DSS (Digitized Sky Survey)
The DSS (Digitized Sky Survey) has been very popular as past images. It has three sorts of images, Bj-band (blue), R-band (red) and I-band (infrared) images.
There are some sites which provide the DSS images.
The following page is good for quick look.
There are several DSS images of different date for one area. The following page is good to look all of the images.
The following page is good to investigate very faint stars nearby the limiting magnitude in details.
2MASS (Two Micron All Sky Survey)
The 2MASS (Two Micron All Sky Survey) is infrared images. The images are available at the following page.
ASAS (All Sky Automated Survey)
The images of the ASAS (All Sky Automated Survey) are available at the following page.
The feature of the ASAS is that new images have been added day by day. You can look the very latest images within several days.
However, the area is limited south of Decl. +30 deg. The limiting magnitude is not so deep.
If you find a new star like a nova, you should investigate the ASAS images. If the star is also visible in the latest images of the ASAS, it is surely a real new object. Please report your discovery immediately.
Note on CCD Images
Because a CCD camera is strongly sensitive in infrared, please be sure that a red star like a Mira type variable becomes extremely bright in CCD images. Therefore, you should investigate the 2MASS images in order to compare with a CCD image.
If you investigate the DSS images, you have to look the I-band images. Some people may think that R-band images are OK, but it is not correct.
Here shows one example. Let's see a star MisV0001, one of the new variable stars discovered in the MISAO Project.
Please search the DSS R-band images of this star (with a size of 5x5 arcmin), and compare them with the discovery image in the page of MisV0001. A bright star is visible in the CCD image, however, no bright star is found in the DSS R-band images.
However, MisV0001 is properly visible in the 2MASS images. If you only investigate the DSS R-band images, maybe you believe it as a nova by mistake.
It is not rare that a 10-mag bright star in the CCD images becomes fainter than 15 mag in R-band images, and becomes fainter than 20 mag in Bj-band images. So please be careful.
Confirm Faint Comets
When you observe a faint comet, you have to confirm whether you really catch the comet even if you see a faint object at the predicted position. Especially, the position or brightness can be different from the prediction when the comet has not been observed for a long time,
Sometimes a faint star exists by chance exactly at the predicted position of a comet. Even if a object looks diffused, it can be blending faint stars or a faint galaxy.
The following page introduces the examples that some 2MASS objects were detected at the predicted position of comets, but actually they are not comets.
When a comet is too slow to confirm the evident motion, you should investigate the DSS images.
Large Proper Motion
When you investigate past images, please take care of stars with large proper motion. Especially some of the DSS images are very old, taken in the middle of the 20th century, so the difference of position becomes very large.
The following page introduces some examples which show how largely the position of a star with large proper motion becomes different when comparing recent amateur's CCD images with the DSS images.
When you investigate past images, please take care of the date of the images. If a star is not found at the position, please search in the neighborhood because the star may locate at the different position due to the proper motion.
If you investigate the USNO-B1.0 data, you can see the stars with large proper motion.
If you find a possible nova or supernova, sometimes an asteroid locates there by chance.
Sometimes you can take a CCD image by chance just when an asteroid locates exactly overlapping on a star, then the star looks as if the brightness changed. In that case, you can report it as a new variable star by mistake if you do not investigate asteroids.
Example of a star looking variable due to an overlapping asteroid.
(Image by Nobuo Ohkura)
You can investigate asteroids at the following page.
You can also investigate comets using the MPChecker. However, the brightness of comets are not displayed there. Please be careful because all comets within the search field will be displayed even if they are extremely faint and invisible.
You can investigate brightness of comets at the following pages.
Comet Catalog in order of Designation (since 1995)
Comet Catalog in order of Number of Periodic Comets
You can investigate light curves of stars recorded by the automated surveys.
Visual observers of comets always worry about the comparison stars, whether they are variable or not. If you investigate the light curves, you can be sure the comparison stars are not variable.
When you find a star whose brightness changes on your images, you should investigate the light curve. It may be an eclipsing variable which fades out repeatedly every several days, or it may be a Mira type variable star which repeats brightening and fading every year. It will be revealed by investigating the light curve. If the light curve looks unusual, maybe you discover an important rare object.
ASAS (All Sky Automated Survey)
The ASAS (All Sky Automated Survey) mainly covers the southern sky.
You can investigate the light curves of stars south of Decl. +30 deg and brighter than 14 mag at the following page.
The ASAS keeps taking new images still now. When a new image is taken, the new data are immediately added. So you can always investigate the very latest light curves.
NSVS (Northern Sky Variability Survey)
The NSVS (Northern Sky Variability Survey) mainly covers the northern sky.
You can investigate the light curves of stars north of Decl. -38 deg and brighter than 15.5 mag at the following page. But the light curve is limited to the period of about one year from 1999 to 2000.
TASS (The Amateur Sky Survey)
You can investigate the light curves of stars in the northern hemisphere and brighter than 14 mag at the following page.
Draw Light Curve Graph
You can draw the light curve graph of the observations searched by the ASAS or NSVS web sites using the Comet for Windows. You can change the range of the graph, select the data, draw the phase diagram with a specified period, and so on.
The following page introduces the usage of the Comet for Windows to draw the light curve graph.
Comet for Windows Tutorial
The DSS images or 2MASS images give you rough information. But if you want to know the accurate value of position or brightness, or if you want to know more information in details, you should search star catalogs and investigate the star data.
Magnitude of comparison stars for visual observations of comets, novae or variable stars, can be looked up using softwares like the GUIDE, the Comet for Windows, and so on, when the target objects are bright. However, if you observe faint objects, 12 mag or fainter, you are recommended to look up the ASAS or TASS data.
ASAS (All Sky Automated Survey)
You can look up the V magnitude of comparison stars south of Decl. +30 deg and brighter than 14 mag at the following page.
The ASAS V magnitude is recommended as comparison stars for visual observations of comets. The ICQ code is "AU".
TASS (The Amateur Sky Survey)
You can look up the V magnitude of comparison stars in the northern hemisphere and brighter than 14 mag at the following page.
The TASS V magnitude is recommended as comparison stars for visual observations of comets. The ICQ code is "TA".
USNO-A2.0 / USNO-B1.0
The USNO-A2.0 and USNO-B1.0 catalogs contain stars down to about 20 mag. When you want to investigate star data visible in the DSS images, you should search these star catalogs.
It is a feature of the USNO-B1.0 catalog that it has information of proper motion.
The star data in the USNO-A2.0 / USNO-B1.0 catalogs are available at the following page.
The infrared magnitude and color of stars in the whole sky are available at the following page. The 2MASS contains photometric data in three bands (J, H, K).
SDSS (Sloan Digital Sky Survey)
The SDSS (Sloan Digital Sky Survey) contains photometric data in five bands (u', g', r', i', z') down to about 25 mag. But the data is available only for regions where there are many galaxies.
Research Catalogs using PIXY System 2
If you have the CD-ROMs of the GSC (Guide Star Catalog) or the USNO-A2.0 catalogs, you can investigate the star data using the PIXY System 2 developed in the course of the MISAO Project.
The following page introduces the way to investigate star data using the PIXY System 2.
A star catalog contains brightness of stars in some bands. Those brightness data show the star color.
The USNO-A2.0 catalog contains two brightness data, R and B. The USNO-B1.0 catalog contains four brightness data, B1, B2, R1 and R2. The 2MASS catalog contains three brightness data, J, H and Ks.
The color of a star is expressed by the difference of brightness in two different bands. The B-V value, difference of B-band (blue) brightness and V-band (visual) brightness, is used in standard. If the B-V value is smaller than 0, it is a blue star. If larger than 1, it is a red star.
Every star catalog contains the brightness data measured in the original bands. So it is not clear how blue or red a star is based on the data. Therefore you should convert the brightness into a standard color value using a conversion formulas of magnitude systems.
The following page introduces the conversion formulas for various star catalogs in order to calculate a standard color value.
When we find a new variable star in the course of the MISAO Project, we investigate the star color in the USNO-A2.0 catalogs. If a star is not red, it can be a short periodic variable star. Then we run the concentrative observations. New eclipsing variable stars like MisV1105 have been discovered in this way, based on the star color.
You can investigate the results of various researches and observations in the past.
SDSS (Sloan Digital Sky Survey)
You can view the photometric data in five bands (u', g', r', i', z'), images, spectrums, etc., observed in the SDSS (Sloan Digital Sky Survey). But the images are available only for small part of the sky. The spectrums are available only for a few objects.
New Variable Star
When you find a new variable star, you should investigate whether it has been already discovered by someone or not. If a star has been already discovered as a variable star, the SIMBAD displays the variable star name.
Note that a variable star is not displayed if it is not issued in any papers.
While investigating the research results in the past, sometimes you can find interesting information unexpectedly, which lead to the discovery of an important rare object.
Here shows one example. Let's see a star MisV1147, one of the new variable stars discovered in the MISAO Project.
Please search about this star using the SIMBAD, and you will find it has a name HBHA 65-53. If you investigate furthermore about this name, you will find that this star has been studied in the past, in the research of stars with strong H-alpha emission line.
Based on this information, MisV1147 became to be observed by many people. Then it was revealed as a young stellar object, in addition, very special object among them.