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CG Dra, 2021-05-29 09:17:01.000 UTC, V = 16.71 ± 0.091
Difficult to get any good accuracy due to the Moon now.
Nick, I took exposure start from the “JD” field in the FITS, never looked at DATE-OBS. MetroPSF now looks at DATE-OBS as well. I have uploaded the fixed 0.15 here:
http://trafyx.com/wp-content/uploads/2021/05/metropsf-0.15.zip
Thanks for pointing this out.
Max
Thank you, Eric. It can process the whole folder of input images and report in batch, but reports are generated only for objects from the AAVSO VSX database. I’ve never tried it on comets. If you could send me a series of FITS with a comet – three is enough – I could try to see if I can get it reporting.
Thanks, Nick. With those automatic reports one has to be careful, as you might need an ensemble covering a wide range of magnitudes which will raise uncertainties. Perhaps, we need to add an option to fine-tune the range of magnitudes in the ensemble per each target automatically during automatic reporting?
On the timestamps: I’ve just tested a few FITS on my Windows 10 machine and don’t see any issues. Could you please send me the FITS file for testing? Very odd.
Max
Whoops. Forgot to specify encoding for the log file which obviously produces an error on Windows. Please try this fixed version:
http://trafyx.com/wp-content/uploads/2021/05/metropsf-0.15.zip
Happy to announce the latest version of MetroPSF, 0.15. Lots of new stuff:
• Aperture photometry.
This is similar to common aperture photometry algorithms found in other software except that a 2D model of the background is subtracted from the image, so sky annuli are not used.• AAVSO report generation.
MetroPSF can now generate AAVSO-compatible report files.• Automatic reporting on all VSX sources in the image.
MetroPSF can generate reports on all VSX sources found in the image. It cycles through each VSX variable and builds a report file. Although I would not recommend to do automatic reports and submit them blindly (unless you know what exactly you are doing) this is helpful when you need to process multiple FITS files to create a report on a single object or multiple objects with, say, similar magnitudes.• Batch processing of all FITS files in a folder.
Now it is possible to do photometric series, as MetroPSF can process multiple FITS files in a folder at once…• Light curve generation from BAA reports.
…and display a light curve from all the report files generated.• Added ability to remove outliers from the fit – by ensemble limit and maximum separation.
Much more precise photometry, as you can set it up to automatically exclude comparison stars farther than R arcseconds from the target, or that are not fitting well into the comparison ensemble, e.g. limit ensemble to N stars.Convenience changes:
• Reporting number of ensemble stars on the linear regression fit plot.
• Object name in the left panel is now automatically set from VSX catalog for matching sources.
• Display next VSX source.
Can easily cycle through all known variables in your image.• Mouse click now reports time in ISO UTC format along with photometry result.
To copy-paste in forums and discussions.Other changes:
• Increased Astrometry.Net default solve timeout from 120 to 360 s.
• Linear regression fit error is now based on standard deviation.
• MetroPSF now writes a log to metropsf.log.
• Astrometry.net URL and API key setting in the interface.
• PSF fitting algorithm setting.
• FITS crop option.Latest manual: http://trafyx.com/wp-content/uploads/2021/05/metropsf.pdf
MetroPSF program and manual: http://trafyx.com/wp-content/uploads/2021/05/metropsf-0.15.zipMax
Got a good session on May 17th. First observation 06:02, last 09:04 UTC. I wonder, is this a ~ 0.2 mag flickering or irregular modulations or this is actually an eclipse? In case of the latter then why the exit follows by an irregular tail – clumpy accretion disk?
Alas, poor weather at my all locations. Runs cancelled one after another. Was only able to get this today on 0.5 m in New Mexico:
CG Dra, 2021-05-16 07:04:57.000 UTC, V = 16.33 ± 0.11
Many thanks for the article, Jeremy. I’ve scheduled a few instruments in Spain and New Mexico, so hopefully will have some data to chew on.
Grant, many thanks for this suggestion. Simple and effective. I have just implemented this, will appear in version 0.15.
Hi Grant,
Yes, fitting à la DAOPHOT, then deriving differential magnitudes via linear regression fit to an ensemble obtained from a VizieR catalog. You can select the catalog you need. The result shouldn’t be very much different from DAOPHOT, albeit I’m using its implementation in Astropy’s photutils. So, MetroPSF is a convenient GUI to photutils with some add-ons like linear regression fitting, plate solving, source matching, etc.
You click on the source you’d like to measure in the window. Here is a short write-up on functionality, check the Quick Start section here:
http://trafyx.com/wp-content/uploads/2021/04/metropsf-3.pdfNear-saturation are not ignored, but you can choose Gaussian sigma weighting for the ensemble, so PSF fits with high sigmas which generally appear with oversaturated sources, will be assigned less weight in the fit. Would you recommend to introduce “hard cut-off” for oversaturated stars?
Max
P.S. Grant, thinking this over again, an obvious manual solution to avoid oversaturation is to limit source magnitudes in the ensemble, which is possible in MetroPSF already. This can be combined with sigma weighting as well.
Nick, many thanks for the information. With PSF photometry the sky annuli are not used at all, so implementing this approach directly is not possible, unless we introduce a sky annulus setting. But then, if we do this, wouldn’t such uncertainty estimate be fundamentally detached from the photometry algorithm used?
Fortunately, I have found that the iterative PSF photometry algorithm implementation in photutils provides flux uncertainties as output. Here is the link to version 0.14 of the program that reports total error = sqrt(flux_unc^2 + fit_unc^2) instead of relying on an external SNR estimate:
http://trafyx.com/wp-content/uploads/2021/04/metropsf-0.14.zip
I don’t think I have the necessary expertise to develop a new method to estimate uncertainties with PSF fitting photometry. It should be safe to use the flux fit uncertainty provided by the underlying algorithm. I wonder if you agree with this approach and if you could give this version a try.
Maxim
Hi Nick,
Fortunately no additional setting are required – I wanted to keep the program with as little settings as possible to avoid overcomplicating it. Looks like the PSFs are sharper in your image than from the telescopes I typically use, so try setting Lower Bound for Sharpness to 0.2 and redoing photometry. It detects most of the sources in your image this way. If you want to go a little deeper, lower the Star Detection Threshold from 10 to, say, 5 sigmas. This detects pretty much all the sources down to SNR < 1, except for a faint extended source under and to the left of the galaxy.
I will next add a feature to save settings so you wouldn’t have to manually adjust things each time. I think it would be beneficial for user to save their settings once and reuse them.
Please let me know if it works.
Maxim
Nick, do you mind sending me the FITS file with this data? You are likely clicking on sources that didn’t have any photometry fits at all, i.e. appearing without circles surrounding them. This means that the IRAFStarFinder procedure didn’t detect a point source at this location. You should get a full photometry result if you click on a source with circle surrounding it. I initially thought that it could be that some of your sources are below the default 10-sigma detection limit, but I can see that some of the brighter sources weren’t detected as well, so we probably need to introduce another adjustment to the algorithm. Maybe something up with roundness. Would like to play with this FITS data to resolve this.
On the ensemble fit – yes, you are correct, the brightest magnitudes are in the lower left corner. Do you think we should invert the axes?
Nick, I am using SNR = Peak Flux at the centroid / Median Sky Background Level, where Peak Flux is taken from the raw FITS data, and not estimated from the photometric fit, and the sky background is taken over the entire image. Do we need any adjustments here? I wonder how 168 was derived.
Note I was able to improve the uncertainty by limiting the ensemble range to 13-16 mag – see attachment.