Don't get confused by all the letters and numbers like I did.
Zoom in to find 5 good (different sized) stars and choose the aperture tool. Then, pick a random size for the inner circle, middle and outer circles. I started with 10, 12 and 14. Then adjust the smalled circle to fit just around the star (use the brush tool to erase your circles, but then make sure to erase your measurements too). Then, when you have it figured out, use the aperture tool on the five stars taking brightness data on each star (take one measure from the blue image, then measure the same star on the visible image). When you have all your data (I just copied and pasted into the worksheet - should have just made my own with Excel) you will need to divide the blue brightness by the visible brightness to get your ratio. Recall that the bluer the star, the hotter it is. Therefore, the star with the higher the B/V ratio will be hottest.
This is the data that I came up with (Arranged with highest ratio first(hottest))
Star 1 Filter B - 1250245.973980 Filter V - 1821863.836914 Ratio - 0.6862455
Star 2 Filter B - 1611405.915447 Filter V - 2662623.980389 Ratio - 0.605194
Star 3 Filter B - 27008.926051 Filter V - 53948.855981 Ratio - 0.500639
Star 4 Filter B - 183870.322194 Filter V - 384200.558984 Ratio - 0.478579
Star 5 Filter B - 66204.107186 Filter V - 268040.938744 Ratio - 0.24699
Using the B & C I adjusted the images in terms of brightness before I select my 5 stars. My stars are the largest and the brightest.
The only "hard part" of this module is to adjust the radius so that star will be enclosed by the circle. The main objective of this procedure is to measure the brightness of an object without including possible contributions from contaminating sources such as sky, defects or other stars and galaxies. I used my data to compute for the ratio of B/V using the source sky numbers.
Using excel, I organized all my data and derive the following results:
Star 1 - 0.604198722 Star 2 - 0.684162447 Star 3 - 0.560058459 Star 4 - 0.607114933 Star 5 - 0.585199278
Since all my stars are among the brightest (according to my eyes)... I got ratios which were closer to each other
I typed my worksheet into Excel to find the following B/V ratios:
Star 1:0.508677148 Star 2:0.439987912 Star 3: 0.372509682 Star 4:0.553154775 Star 5:1.907485876
Hotter stars are more blue, so the higher B/V ratio means you're looking at a hotter star. This means, the stars from hottest to coldest, go in this order: 5,4,1,2,3
I had some difficulty getting the plugins to work. Five computers later, I found a netbook at school that ImageJ would work on along with the astronomy plugins.
Once I got it working, I had lots of fun measuring some stars in M5.
Is there a way to convert the source-sky measurement into a magnitude?
X Y Filter Brightness B/V Rank 1221 941 B 46968 0.72 3 V 64788 1264 1049 B 10466 0.83 2 V 12600 1155 958 B 76912 0.44 5 V 174956 1071 1083 B 24807 1.59 1 V 15594 1165 1083 B 81695 0.487 4 V 167700
Okay, I used the X and Y coordinates to make suer that I was clicking on the same star in both images. All stars were within 2 pixels of each other in the X and Y values. My 5 stars and 5 B/V ratios (from hottest to coldest) were
Star 1 : 1.01 Star 2 : .810 Star 3 : .633 Star 4 : .643 Star 5 : .560
I thought for a while before posting these because it seemed squirrley that I had a B/V ratio that is greater than one but, upon thinking about it for a while, it seemed possible. That first star is just very hot, hot enough that the peak of it's emission is a lot closer to blue than any of the other stars so it *is* actually brighter in B.
Don't get confused by all the letters and numbers like I did.
ReplyDeleteZoom in to find 5 good (different sized) stars and choose the aperture tool. Then, pick a random size for the inner circle, middle and outer circles. I started with 10, 12 and 14. Then adjust the smalled circle to fit just around the star (use the brush tool to erase your circles, but then make sure to erase your measurements too). Then, when you have it figured out, use the aperture tool on the five stars taking brightness data on each star (take one measure from the blue image, then measure the same star on the visible image). When you have all your data (I just copied and pasted into the worksheet - should have just made my own with Excel) you will need to divide the blue brightness by the visible brightness to get your ratio. Recall that the bluer the star, the hotter it is. Therefore, the star with the higher the B/V ratio will be hottest.
This is the data that I came up with (Arranged with highest ratio first(hottest))
Star 1
Filter B - 1250245.973980
Filter V - 1821863.836914
Ratio - 0.6862455
Star 2
Filter B - 1611405.915447
Filter V - 2662623.980389
Ratio - 0.605194
Star 3
Filter B - 27008.926051
Filter V - 53948.855981
Ratio - 0.500639
Star 4
Filter B - 183870.322194
Filter V - 384200.558984
Ratio - 0.478579
Star 5
Filter B - 66204.107186
Filter V - 268040.938744
Ratio - 0.24699
Using the B & C I adjusted the images in terms of brightness before I select my 5 stars. My stars are the largest and the brightest.
ReplyDeleteThe only "hard part" of this module is to adjust the radius so that star will be enclosed by the circle. The main objective of this procedure is to measure the brightness of an object without including possible contributions from contaminating sources such as sky, defects or other stars and galaxies. I used my data to compute for the ratio of B/V using the source sky numbers.
Using excel, I organized all my data and derive the following results:
Star 1 - 0.604198722
Star 2 - 0.684162447
Star 3 - 0.560058459
Star 4 - 0.607114933
Star 5 - 0.585199278
Since all my stars are among the brightest (according to my eyes)... I got ratios which were closer to each other
I typed my worksheet into Excel to find the following B/V ratios:
ReplyDeleteStar 1:0.508677148
Star 2:0.439987912
Star 3: 0.372509682
Star 4:0.553154775
Star 5:1.907485876
Hotter stars are more blue, so the higher B/V ratio means you're looking at a hotter star. This means, the stars from hottest to coldest, go in this order: 5,4,1,2,3
I had some difficulty getting the plugins to work. Five computers later, I found a netbook at school that ImageJ would work on along with the astronomy plugins.
ReplyDeleteOnce I got it working, I had lots of fun measuring some stars in M5.
Is there a way to convert the source-sky measurement into a magnitude?
X Y Filter Brightness B/V Rank
1221 941 B 46968 0.72 3
V 64788
1264 1049 B 10466 0.83 2
V 12600
1155 958 B 76912 0.44 5
V 174956
1071 1083 B 24807 1.59 1
V 15594
1165 1083 B 81695 0.487 4
V 167700
Okay, I used the X and Y coordinates to make suer that I was clicking on the same star in both images. All stars were within 2 pixels of each other in the X and Y values. My 5 stars and 5 B/V ratios (from hottest to coldest) were
ReplyDeleteStar 1 : 1.01
Star 2 : .810
Star 3 : .633
Star 4 : .643
Star 5 : .560
I thought for a while before posting these because it seemed squirrley that I had a B/V ratio that is greater than one but, upon thinking about it for a while, it seemed possible. That first star is just very hot, hot enough that the peak of it's emission is a lot closer to blue than any of the other stars so it *is* actually brighter in B.
Or so I suppose!