Getting stars magnitude with ASTAP
Stacking program, astrometric (plate) solver, fits file viewer
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Hi,
I'm using ASTAP for my school projet in second year of engineering (but i'm really a newby in astronomical analysis). I'm trying to recover stars magnitude from images of M35 in two different filters (g and r) to plot a HR diagram of M35. I stacked the light images with calibration files so I get very clean images of M35 in each filter and exposure time. Then I used the photometric tool on my image to plot the measured magnitudes of each stars on the image. But then, I can't find a methods to recover these magnitudes in an excel shit, and matlab don't read my stacked images correctly. The only way I could have infos of stars on excel with ASTAP was with the photometric tools for variable stars, but then I only had three of all the stars of the cluster...
So do you have any advice for me to get these magnitude, with ASTAP or something else ?
Thanks in advance,
Matthieu
Hello Matthieu,
That is an interesting project. There is an option to export the stars with magnitude from one image to the clipboard. This option is a little hidden in the viewer, tools, "inspection menu" which can be accessed with key F5.
1) You have to solve the image first.
2) Select the correct reference database, online Gaia V (green) or B.
3) Select tools, "calibrate photometry: ctrl+U
4) Hit F5 and select the check mark. Hit F4
See attached screenshots.
Today I will improve it a little, adding the used reference database and add the same option to the viewer popup menu for a selected area only. You school project could be a good field to for it. It was added only a month ago.
If you could provide two test image of M35 that would be nice to test it here.
Han
This is the output from the clipboard:
fitsX fitsY HFD RA[°] DEC[°] ADU Magnitude
1877.70 17.97 3.843 274.093663 -14.400684 229858 13.424
267.96 19.45 3.472 275.332120 -14.498080 141018 13.955
1172.71 18.24 3.040 274.635894 -14.444421 71522 14.692
2161.77 18.96 3.548 273.875327 -14.381897 167485 13.768
222.94 19.92 3.075 275.366797 -14.500390 218724 13.478
785.63 21.10 3.047 274.933882 -14.465880 169184 13.757
1392.94 22.41 3.522 274.466757 -14.427718 135043 14.002
2065.31 22.09 3.350 273.949687 -14.385719 87597 14.472
1698.29 24.89 3.774 274.232071 -14.406820 550583 12.476
1835.12 24.95 3.319 274.126855 -14.398168 89259 14.451
Hello,
Thank you for your quick response.
I tried what you said and it's working well because I can now copy the infos to the clipboard. I just have two problems : (the second is link to the first) : I think I don't have access to the Gaia's database cause it demand me to install OpenSSL to connect to AAVSO. But I look on my computer and I do have some OpenSSL files (because we installed anaconda for python use in my school). Do I have to reinstall it completely to have access to Gaia ?
Then, when I go on the clipboad, there is a "?" in the columns of magnitude of every stars. And I indeed can't plot magnitudes on the image anymore. I suppose this is due to the error in photometric calibration with Gaia.
When I use the Local star database (V50), I can plot magnitudes but I still have "?" in the clipboard after using inspection.
Here is a link to a filesender with all the light images of M35 and calibration. I must tell you that the images come from the IRiS databases (Observatoire de Haute Provence in France) and so I didn't make them myself. https://filesender.renater.fr/?s=download&token=8011b7d1-9696-42f2-ac0e-d2c386a41866. This filesender expired in 7 days.
Thanks again,
Matthieu
Ok after a new verification, I do have magnitude with local star database V50 in the clipboard (I tried again on my "r" filter and 120s exposure time stacked image). DO I neww to use Gaia or could this be good enough to plot a HR diagram ?
Hello Matthieu,
I removed the openssl.dll some time ago since I hoped it was no longer necessary. I have put it back now in this version. Can you try this one and tell me if online Gaia works for you?
http://www.hnsky.org/astap_setup.exe
The local database contains only Gaia BP magnitude which is fine for imaging without a filter. But for accurate measurement you need the calculated V and R magnitudes of Gaia. This online access is a little slow and can take up a minute.
I will look to the ? marks and if the local database can be used.
Han
I think it work with this version thank you ! The magnitude are indeed a little higher than with local database.
Just to be sure, if I look at the wavelenght range of the g and r filter used here, I suppose for filter g I must use Gaia V, and for filter r, Gaia R ?
Matthieu
Yes G is about V and R is then same as Gaia R
The link is not working:
https://filesender.renater.fr/?s=download&token=8011b7d1-9696-42f2-ac0e-d2c386a41866.
Can you check and share them again?
I'm working on a improvement that you can select with the mouse a small set of the stars only. This will be ready tonight or tomorrow.
Han
I introduced a new (development) version:
http://www.hnsky.org/astap_setup.exe
Added new popup menu "Star info to clipboard within shape". So you can select a subsection if you hold the right mouse down.
This will probably work more convenient.
Next step will be a local database for all colours. This will be more convenient then the online database.
I just try it and it's working well, thank you very much.
p.s can download your files. Can you share them again?
Ok sorry, here is the link again, tell me if it's working or not ?
https://filesender.renater.fr/?s=download&token=8011b7d1-9696-42f2-ac0e-d2c386a41866
If not, I will just send you the stacked images.
Matthieu
Yes I have the now the M35 images. They look good. Note some star are saturated. They will be ignored since it is very difficult to measure the magnitude of saturated stars.
I just noted it is not possible to select a single star with the new menu. I have just corrected that. Just install it again:
http://www.hnsky.org/astap_setup.exe
Note you can check the magnitude of a single star online at Simbad. See attached screenshot.
Wow it's really great. With this I really have every infos on the stars and a beautiful view of them in the sky, it's perfect for my projet presentation at the end of the year.
Since your images are made using SDSS filter, today I have added the online database transformation to SDSS-i, SDSS-r, SDSS-g. Use these for your magnitude measurements. I need some more checking but there is already a development version:
http://www.hnsky.org/astap_setup.exe
Han
I'm really grateful for what you did to help me thank you ! I will try it very soon.
Matthieu
Hi again.
I just have a little question. Do I have to calculate the absolute magnitude with the values I get with ASTAP or is it already calculate by the program ?
Because, in an exemple I have of a similar project made with the IRiS telescope, (in which they use SExtractor), they had to correct their values with the distance modulus and the interstellar extinction to retrieve the absolute magnitude. THe formula used are :
Mg = g − µg − Ag
Mr = r − µr − Ar
Thanks in advance,
Matthieu
ASTAP calibrates the measured flux against the known magnitude of an ensemble of Gaia stars. So it can report the measured magnitude of each star. The atmospherics extension should have no real influence. The calculate the absolute magnitude you have to use the distance of M35. The interstellar extinction is an unknown factor to me. I assume you have to apply it. So just as your formulas indicates apply the two factors
Han.
Hello.
I was doing my projet report and I realized, by looking to the png of the initial images (without calibration), that the calibrated + stacked images looked really similar to the initial images. So I wondered if you tryed to stack it yourself when you use it and if it looked really better than the initial images ?
Which PNG are you referring to?
I didn't calibrate or stacked the images as far I can remember. The images you are using are very clean. So calibration will result in a minor improvement
I added some improvement in ASTAP photometry and introduced the auto selection of the online database. This should work on your images (untested). Just uploaded.
I'm field testing it currently with DSLR images where it can extract the RGB colours from the raw images. Personally I don't have Johnson-Cousins filters but I'm considering buying Sloan filters for my setup since that seems to be the future. I'm also considering to add auto calibration of the filters. So the graph for the magnitude offset versus B-V or B-R
Maybe I make DSLR/OSC images of M35 myself to test the concept. It should be possible to do the same with extracted raw RGB colours. That field testing could help to improve ASTAP.
Latest version just released a few hours ago.
http://www.hnsky.org/astap_setup.exe
p.s Out of interest, which discipline are the students studying?
Han
(It's the png of the image show in the database of the telescope).
Ok, I was affraid to have done something wrong with the calibration because it's really similar to the initial images.
Thanks for your quick answer.
We are for now in second year of the first cycle of engineering at INSA (France). This mean that we don't have specialities this year (we specialie in third year (second cycle)).
Today as a concept test I created the Herzsprung-Russel diagram using your images. I didn't calibrate them. The darks look a little weird. I only stacked the images in mode average without darks, flats and bias. The diagram looks good.
I also fixed a bug in ASTAP. I will upload it later today or tomorrow.
It took some time to match the g and r stars in Excel but I found a way.
Attached the result. The Excel file I will add to this post the next edit.
Last edit: han.k 2023-05-28
Hello. Yeah, that's what we thought too about the darks.
Yes I also had to match the stars. first I did it manually but now we made a python program to do it for us with an arbitrary treshold on the coordinates.
Your diagram looks like ours so it's conforting. It looks like you have more stars on the bottom left of the diagrams (we have 589 with the 30s exposition). (See attached photos). But we never tried to plot the total stars magnitude r+g so I'll try.
Also something strange, we have more stars after the sorting in expo 30 than in expo 120 (you can see it on the diagram).
I also recover a ZAMS relation to plot a theorical principal sequence., it's the next thing we will do.
Looks good!
There was significant bug in ASTAP. Sometimes it would take the backup image when analysing the image. Use the latest version 2023-05-28:
http://www.hnsky.org/astap_setup.exe
I have improved the spreadsheet to v3. See previous posting (updated)
https://sourceforge.net/p/astap-program/discussion/general/thread/c7219e026d/e84d/attachment/M35_Hertzsprung-Russelldiagram3.zip
In future I have to look to the transformation. It will not effect the HR diagram much but up to now i assumed factor Tv_BV=0. See link to PPT below. I have to study that more. I'm not an expert, just an engineer
https://slideplayer.com/slide/15941281/
Han
Hello, I was trying your new version (2023-05-28), but I realised that there was no more the g and r filter in the database in the photometric menu. Is it normal ?
Matthieu
Hi,
It has moved to the popup menu. It was a doubling of the functionality. Just select all the files from where you want to extract one raw colour. (selection by shift and arrow up or down keys or just ctrl+A) Then with the right mouse popup menu you can extract R, G+G or B.
Note also that in the viewer popup menu "Star info to clipboard" I have added all transformed Gaia magnitudes to the output . This could help in calculating the transformation factors if your filters are not ideal. I expect the Sloan g', r', i' be pretty ideal so not interesting for you I expect.
Han