Need TG Beta tester with access to NGC 1252 and NGC 3532 images

Gordon et al:

A large FOV would be nice but even a smaller FOV (e.g., 30 minutes) would be useful to test TG with a smaller number of standard comps in these new standard clusters?? I'll take some on one of the iTelescope small refractors. I'm sure they would like new transform coeffs for their scopes, especially the small ones. Help from others appreciated as you said. And, our southern observers get some reliable new transform coeffs!!

Ken

Gordon, Ken,

I am the 'activist' pushing for southern standard clusters to be loaded into VSP so must take some responsibility to image them for you!

My plan is to try and image the open cluster remnant NGC 1252 in the next 2 months (if this awful weather we are having ever abates). I typically confine my measurements to BVI but do have an R filter so can do those 4 bands. Unfortunately NGC 3532 may have to wait until the new year.

I already have many V and I images of NGC 3532 but they have a FoV of less than 1 degree and are mostly short exposures as I was interested in the brighter stars. May be able to find some B images as well. I've just finished CCD Photometry Part II course (Ed Wiley was the instructor). Tried using VPHOT a few months back and couldn't get it working for me. I plan to do the VPHOT course next time it's offered but in the interim I can:

• Make my images available via my Google drive (by giving you access to this).
• Measure images using my current software (AutostarIP or IRIS) and plot instrumental versus standards colors.

Attached are JPEG versions of V and I band images taken on 11 June 2015 to give you an idea of the images I've taken. The FoV of these images is only 42 x 33 arcmins. This year I have been imaging with a larger format ZWO 174MM camera which yields a FoV of 77 x 48 arcmins. I will try and dig out as many images of NGC 3532 taken with this camera as I can.

Tex

Tex,

Can you upload your images to VPHOT and share with my id - mgw ?

If not, send me the link to your google drive.  My email is gordonmyers@hotmail.com

Then I'll generate transfoms and send to you for comparison.

Gordon

Gordon,

I believe I have given you access to the southern clusters folder on my Google Drive? Let us know if it hasn't worked.

My plan is to start becoming familiar with VPHOT and move to using that. I have been retired only 10 months so still in process of learning and harmonizing my methods with those of AAVSO. I have uploaded my many years of PEP data (20,000+ measurements, I think), updated photometric equipment and software, and undertaken CCD Photometry course hence reason for not spending time on learning VPHOT! Apologies for the inconvenience.

Tex

Gordon

Have you been able to obtain the images of NGC 1252 you were wanting for beta testing?

I have recently captured a few images with iTelescope instrument t12. It's a 4-inch Takahashi with a FOV of about 2.5 x 4 degrees. That's rather larger than you wanted but I had to choose that particular scope in order to capture the whole field. IF you wanted something closer to 1 x 1 degree, I could choose another scope but all of the alternatives at Siding Spring have much larger apertures - it is likely that some of the stars would saturate their pixels.

What do you think?

Regards: Paul

Paul,

The challenge will be the lack of BVRI filters on T12, but I could change their FITS headers to run a test.  Can you share your images with me?  userid - mgw

Thanks.

Gordon

Gordon,

The weather has been frustratingly bad. Images taken on 18 Nov and 22 Dec have turned out to be affected by high cloud. I have just processed some images from 31 Dec but are yet to measure them. Although not a photometric night, images from 2 Dec may be useable.

The images of NGC 1252 are taken with my new ZWO ASI174MM CMOS camera so I don't know if header is in correct format to upload to VPHOT but will try it out when I get a chance. While only a 12-bit camera it fortunately does not have an ABG so is linear up to its full-well depth of 32ke-. Importantly it uses one of the new Sony chips that has global shuttering so ADU from both longer and shorter exposure times can be used. N.B. the FoV using the ZWO on my 6-inch reflector is 52 x 33 arcmins.

I have measured the BVRI images from 2 Dec images. Attached are the B-V, V-R and V-I plots. Of particular note is that the BSM_Berry value of R for AUID-000-BMC-466 appears erroneous. As you can see from the plot of v-r versus V-R the V-R value of 0.54 given in WEBDA appears to be closer to the correct value. As B-V and V-I plots look consistent my guess is the problem is only with the R value for this star. Noting that only a handful of standards are available at this FoV you and Arne may wish to consider including the following stars: TYC 8498-1035, -0844, -1231 and -1066?

Can send you the images if you want. Promise to become VPHOT capable this year!

Tex

Hi Tex,

There were 237 stars in the 2.2x1.4 degree field of NGC 1252 that had 10 or more observations.  I put very strict limits on the standard deviation of all filters in order to create the uploaded list, resulting in only 37 stars that passed the tests.

TYC 0844-1035 missed the V-band test (with Verr=0.064), even though at V=8.67 it should have been well measured.  The other 3 Tycho stars that you mentioned (0844, 1231, 1066) are 11th magnitude or fainter, and had Verr of about 0.1mag with the BSM systems (which had short exposures to measure the brightest stars in the field without saturation).  They will likely be added when I get the OC61 dataset reduced.

I will be interested in seeing results from your ZWO camera.  I've wanted to buy one of these (either the 174MM you got, or the 1600MM cooled version, as the price can't be beat...as long as they do decent photometry.

Arne

Tex,

Go ahead and send me the fits images and I'll work to upload to VPHOT.  I also need your your telescope gain (e/ADU)) if you have it, plate scale (arc seconds/pixel), linearity limit (again, if you have it), scope latitude/longitude and elevation.

Email me directly at gordonmyers@hotmail.com

Gordon

Arne,

I've resolved the problem with V-R index for AUID 000-BMC-466 (Tyc 8498-1162-1; CD-57 624; NGC 1252 10):

• It's spectral type is listed in SIMBAD as G8.
• The (B-V) of 1.039 and (V-I) of 1.021 appear consistent with this spectral type.
• The R magnitude is 8.594 not 8.954 (I must have transposed the 2 numbers) giving it a V-R of 0.538 consistent with the other photometric indices, spectral type and the measurement of 0.54 given in WEBDA.

Leave it to your experience to select appropriate 11th and 12th magnitude stars to provide further standards in this field. I will now work with Gordon to try my images in VPHOT.

With respect to discussion of ZWO ASI174MM camera, I am happy to send images taken with it and any other information to ascertain its suitability for photometry. Evidently Sony are of the view that CMOS technology will replace CCD within 5 or so years hence my interest in exploring CMOS cameras for photometry. I bought the ZWO ASI174MM soon after its release so mine is the uncooled version. It is only 12-bit which, according to Howell (2000) is the minimum for use for photometry.

My main interest in the camera is that it has global shuttering and no ABG. This means I am able to use the full-well depth of 32ke- and can use both long and short exposures (convert to ADU/sec). I do not plan to buy the cooled version but rather wait until there is a 14- or 16-bit CMOS camera with global shuttering. (currently take regular dark frames throughout an observing session.) ZWO cameras are lightweight, robust and nice to use; they seem to operate without crashing and images can be captured with a variety of 'universal' software (SharpCap, Firecapture, Amcap).

Attached is my linearity check of the ASI174MM.

Tex

Hi Tex,

Glad to hear that you've resolved the problem!

I hope to start working on the OC61 dataset sometime soon, but things always seem to get in the way.  Hopefully those deeper (though smaller field) images will provide a decent extension to the "standards" already in VSP.

I appreciate the information on the ZWO camera.  We need good cheap digital monochrome cameras!

Arne

Gordon,

Sent processed BVRI images to your email address. Please note I have not tried to load these into VPHOT so have no idea as to whether file header is correctly formated.

Tex

Hi Gordon,

In early December I recorded 20 RAW image of NGC 1252 and finally found time to calibrate them and extract the individual color channels using MaxIm V6. The two green channels from each RAW image have been average combined into a single green FITS image. So there are 20 B images, 20 G images and 20 R images which have been uploaded to VPhot and shared with you.

Images were recorded with an Orion ED80T CF and Canon 600D DSLR. The field of view is 2.66 x 1.78 deg which includes 36 standard stars.

I used VPhot to get instrumental magnitudes from each image then used a spreadsheet to determine the following transformation coefficients:

T_vr = -1.143 (0.021)

T_bv = -2.605 (0.026)

T_v = -0.114 (0.009)

I rejected three of the standards (113, 86_1 and 91_1).

It would be great if you could analyse the images and let me what tansformation coefficients you arrive at. Cheers,

Mark

Mark,

I got different values from TG -

Tbv= 2.221 (0.027)
Tb_bv= 0.439 (0.008)
Tv_bv= -0.111 (0.009)
Tvr= 1.340 (0.027)
Tv_vr= -0.210 (0.020)
Tr_vr= -0.464 (0.018)
 

The plots of the data all look very good so these all appear to be good quality images with a good data fit.  I attached all the plots along with the summary table of values and the TA required .ini file (with a .txt extension you should delete before using with TA.)  As to the absolute values, they look larger than expected but I don't really know what is normal for a DSLR.

I can send you all the VPHOT files with the detailed measurements if you want them - let me know your email address.

Hope this helps.

Gordon

Mark, I ZIPed the VPHOT files from my analysis and attached here.

Gordon

Thanks Gordon,

I'll download TG and try to reproduce the results you got. I see you're using V5.11a beta, but V5.10 is the one available from https://www.aavso.org/tg, is there a significant difference between the two versions? Cheers,

Mark

Mark,

You will need to the 5.11a beta version - it supports NGC1252

You can download a copy (TG_V5.11a_beta.pyw) from 

https://1drv.ms/u/s!AuOpcqkoDn_v8U8XigLcmdIiqt1s

Click on "download" 

Gordon

Thanks Gordon,

V5.11a beta installed and I can reproduce your transformation coefficients.

Why is it that only 31 standard stars were used in calculating TC's when the VPhot output files include 36 standards, all of which have SNR above the default value of 20? Cheers,

Mark

Mark,

Good question - my initial look indicates some inconsistency between VPHOT mags and the magnitudes retrieved from VSP on the 5 stars that were dropped by TG.  I'm traveling for a few days but will work to identify the cause of the issue late next week.  The transforms should still be goood, but based on the 31 vs. 36 stars.

Gordon

Thanks Gordon,

there is no rush on resolving this question but it's always good to understand why things are the way they are. Cheers,

Mark

Mark's images of NGC1252 revealed a problem in the V5.11 beta version

A new version TG V5.12 beta is now available

https://1drv.ms/u/s!AuOpcqkoDn_v8VASHDx40IisVUxO

If no new problems are found within the next week I will release this new version.

Thanks to everyone who has run tests!

Gordon

Thanks Gordon,

version 5.12 beta is using all 36 standard stars in my NGC1252 images.

Back in May 2015 I recorded images of M67 using the same telescope and camera so I'll process them in VPhot and TG then see how much the TC's have changed. Cheers,

Mark