Sat, 11/20/2021 - 16:59
Dear friends,
Well, this is pretty easy to go behind the 20th / 21th magnitude, with a small scope, and a few dozen minutes of imaging, but what about going deeper ? Here is the limite of the GAIA catalog.
So, I was wondering if one could find, somewhere in the AAVSO archives, or elsewhere on the web, maybe some papers I don't know, some photometrically calibrated star fields / Maps that could be used to go very very deep, in order to calibrate the scopes, in the 21-24th mag range, or deeper, maybe. So as to document the limits of a particular setup.
Maybe some of you could helps me in finding the necessary maps ? It would be much appreciated.
Thanks in advance.
Christophe
Well, this is pretty easy to go behind the 20th / 21th magnitude, with a small scope, and a few dozen minutes of imaging, but what about going deeper ?
Christophe,
Quite surprised with your remarks and questions based upon previous experience.
Going that faint (20/21 V or even CV) is anything but easy with a small scope… therefore could you supply scope size, specific image details (imager, filter, length of image, # images, etc) and the target? Also have you reported any such observations that you have made to the AAVSO data base?
Hi Tomothy,
Sorry for the misunderstood. I didn't said that I could perform usefull and scientific photometric measurements and star following at mag 20 in a small scope.
My english is somewhat imperfect.
Indeed, one can easily go that deep with modern and small gear :
i.e. : DSLR canon650 unfiltered + FS102 refractor fd6 : about 20 min exposure time : limiting mag 19.5 on very faint background galaxies.
Same setup, 90 to 120 min exposure time, depending on the sky conditions : mag 20.5.
Measurements made with Patrick Chevalley's SkyChart, Gaia DR 2, and Leda/Hyperleda cat, or Aladin/Simbad.
Probably could someone go deeper in a very dark country, or mountains ; I live a few km away from a 50 000 inhabitants town, and the sky quality is not really that good (5-6/10)
Well, I have sold some old telescopes I had for many years (T150 and T200 mm), and bought a used C11, and I now needed to see how deep I could go with this new OTA.
I suspect, I can go as deep as mag 21-22, probably more, on very long exposure times, but need to prove it in the right way and test it to the sky.
Maps with stars, and star fields calibrated in the 20-21 range can be found quite easily (Gaia, photometric surveys near M31, M81 ...), but going deeper seems not as easy.
A friend send me some links to some interesting papers, and I located and downloaded data from the Lockman Hole survey, but to date, I'm not able to put this on a map for easy handling.
Any help would be much appreciated.
Cheers,
Christophe
Hi Christophe,
I recommend an article I wrote a few years ago:
2017SASS...36...75H
where I calibrated a region of M67 down to about 24th magnitude. If you can't access that article, I can send you a copy. It is in the 2017 proceedings volume for SAS:
http://socastrosci.org/Publications.html
I have data for a couple of other fields that go down to the same depth.
With a 1m telescope, I could detect 20th magnitude in V in about 2 minutes. That would correspond to about a half hour with your C11. Unfiltered, you can go to 20th in about 6 minutes. Those are rough numbers; I strongly suggest looking at the M67 region and testing for yourself. Those exposures seem long, until you realize that the 48-inch Oschin Schmidt telescope at Palomar typically used hour-long exposures for the Palomar Observatory Sky Survey to reach 20-21mag on photographic plates!
Arne
Would it be appropriate to have these data included in VSD and available via VSP?
George
I think that is a great idea.
Phil
While that sounds good on the surface, the problem is that the DSS (and USNO-A) option does not go faint enough. They basically end around 19-20 mag, while some of the stars in the sequence are 24th magnitude. I think a better approach is to have 3-4 such fields, either on a web page, or a new journal article. Automating the process through VSD, or through VPHOT, probably won't work - manual inspection is the more likely method to analyze the data.
Arne
I've created a VPhot sequence from the stars of Arne's deep field. It is a common sequence, so available to all. It's name DeepDiveSeq.
What you do is bring up your image of M67 in V and select this sequence. VPhot will put a circle around the positions of the stars, from A, the brightest, through U, the dimmest. You can look through each comp to see the SNR. How far down the alphabet can you go?
The field is high in the M67 region; my images just catch the bottom of the deep field. Worth while taking another shot.
George
Here is some exploration of Arne's deep calibrated field in M67.
One is an image from the SAS paper showing the calibrated stars.
The second is a screen shot from VPhot using the deepDiveSequence derived from the SAS paper.
Well, the images would be here if only. If you are interested, send a note to SGEO@gasilvis.net with subject DeepField.
This is an image from my 12" scope, 20x 30s images stacked. I can see that I was able to get a SNR of 24 for a 17.8 mag star in V.
Fun!
The DeepDiveSequence is available to anyone to select. Center your imaging on 08:51:05 +11:51:20. VPhot will draw a circle for any star it sees. In my case it could not see J and beyond. The sequence goes all the way to U-245.
George
I can see a bit over mag 17.7 and rarely mag 18 , typically with 20 x 2 minute exposures stacked.
But that's OK, because there are more stars than I can possibly study anyway.
Ray
Hello Arne,
I've downloaded the paper you wrote and will read it very carefully. I think this is exactly what I was needed.
Where are located the two other star fields ? Is it possible to find the papers somewhere on the web ?
Indeed, I remember quite well the magnitude challenge that was published in S&T more than 20 years ago. I'm a S&T reader for decades. Paul Boltwood was the winner, when going to 24+ in about 20 hours in his 16" Newton. I re-read the paper a couple of weeks ago.
I think I will try to dig the sky with an hyperstar (as soon as I could put my hands on such an item - the global astronomical shortage would not help me for a long time, it seems), so as to use the C11 à f1.9. It could be able to break the 20mag in about 2-3 minutes. Possibly - I hope so.
Thank you so much.
Christophe
Here is a link to the proceedings, select 2017, and save your copy. Arne's article starts on p.75
http://www.socastrosci.org/Publications.html
Jim DeYoung (DEY)