Home › Forums › Variable Stars › Magnitude precision on BAA-VSS charts.
- This topic has 16 replies, 5 voices, and was last updated 2 weeks, 1 day ago by Dr Paul Leyland.
10 May 2023 at 8:03 pm #617249
Gary Poyner has just announced on the Alert list that new charts for T CrB at https://britastro.org/vss/xchartcat/t-cr-b_.html
I checked them out and found that they still only have magnitudes to 1 decimal place. Many, many people can measure to at least two decimal places these days. That is why I never use the BAA charts but rely exclusively on their AAVSo equivalents.
Any plans to upgrade (over time, of course, as it will be labour limited) to two decimal places?
I can’t help but feel the BAA-VSS charts should be dragged into the 21st century.
On 111 May 2023 at 4:13 pm #617266
I believe these charts are designed for use by visual observers. There the simplicity of a single decimal place is beneficial to the visual observer.
Andy11 May 2023 at 4:20 pm #617267Paul G. AbelParticipant
Indeed- I find them to be perfectly fine for visual use. I certainly wouldn’t want them with magnitudes listed to 2dp since that kind of precision is not usually possibly visually!11 May 2023 at 8:11 pm #617269
I mentioned it because I am thoroughly sick of being admonished by the VSS database for using non-kosher chart IDs.
Big hint there 😉11 May 2023 at 9:05 pm #617270Gary PoynerParticipant
Why do you think you are being admonished? The sequences for the BAAVSS visual charts have all been entered into the database. When you try to upload a visual observation, it’s checked against the sequence. If there is an error it finds it and doesn’t allow you to enter the observation. The AAVSO DB doesn’t do this. It just goes in – error and all! Our system is far superior.
If you use an AAVSO chart, our DB doesn’t have any sequence information for these charts. They don’t use a lettered sequence of course, and their chart ID is dynamic – and there are thousands of charts. So, our DB sees the chart reference, doesn’t recognise it, then informs you that the chart is unrecognized and that it can’t perform the check for errors. And thats it! The observation still goes into our DB. Most of my observations are made with AAVSO charts, and my data sits happily in the VSS database.
I just don’t understand your concerns!
Gary11 May 2023 at 11:25 pm #617275Paul G. AbelParticipant
I use a lot of AAVSO charts- I tend to put (AAVSO) after the chart sequence but it does generate a warning that the sequence isn’t recognised but as Gary says, the observations still go into the database and you can review it and see it there.
I also like the fact that the BAA VSS database requires both Julian and standard date formats, this greatly reduces the possibility of errors and typos coming into the date or time.
-Paul11 May 2023 at 11:28 pm #617276
My concern is that perfectly good data elicits a warning. I freely accept that the important stuff (magnitudes and their errors, star ids, date-time. filter, explen) goes through after checking. It’s the appearance and untidiness of an essentially useless warning that irritates me.
Perhaps if the chart ID was in a standard format (/^AAVSO X.+$/ for those who recognize Perl-style regexps, the database checking software could avoid issuing a warning.
Paul12 May 2023 at 12:01 am #617277Gary PoynerParticipant
I just don’t see the problem with the DB telling you that your observation hasn’t been checked. It’s an important piece of information to pass on if your DB prides itself in attempting to check the data that is entered into it.
Sorry Paul, but I just don’t get it.
Gary12 May 2023 at 8:31 am #617278
Sorry this is causing you hassle. The point is these ‘warning’ messages are very useful to a large number of our observers. A ‘warning’ simply means ‘can you take a quick look at this to make sure it is expected’. It allows you to proceed with adding the data as only the observer has the knowledge of whether to expect a recognised chart or the other warning messages that are generated. When the upload generates an ‘error’ message then that means something is wrong and it won’t let the upload proceed.
We do have some AAVSO charts in the database. These tend to be older charts before they implemented their latest chart system, or charts created at a specific point in time. When I created the database I had discussions with the AAVSO about getting a copy of their chart data to add to our database. The problem is their charts are not static. A chart ID is not guaranteed to generate the same chart when entered at a later date, as any changes to the AAVSO chart database will result in the same ID giving a slightly different chart.
The chart is particularly important to the visual observers as the BAA database can recalculate magnitudes to the latest sequence. It can actually do that for digital as well as visual observations where sufficient information is provided, though we currently only have it turned on for visual observations.
As a final note, I would point out the AAVSO charts are fantastic and used by many BAA observers. It is just the BAA database cannot use them for more detailed processing as their chart IDs do not uniquely identify the comparison stars and their magnitudes.
Andy12 May 2023 at 9:41 am #617281
Personally I like the AAVSO charts and lists of comparison stars because it’s easy to query via my Python code via the AAVSO API. I combine that with SIMBAD/VIZIER data to get other parameters of the target star and I can then create a good list comparison stars for ensemble photometry. I just live with the chart ID warning when I upload to the BAA database.
Ian.12 May 2023 at 11:22 am #617282
Personally I like the AAVSO charts and lists of comparison stars because it’s easy to query via my Python code via the AAVSO API. I combine that with SIMBAD/VIZIER data to get other parameters of the target star and I can then create a good list comparison stars for ensemble photometry.
That is essentially what I do, though my code is wrotten in Perl rather than in Python.
By and large I download only the V photometry but include B and R as required. B-V, which is provided regardless, give B magnitudes but not, alas, their errors. My ensemble photometry code does The Right Thing with reported errors, which is to add in quadrature.
Out of interest, what SIMBAD/VIZIER data do you use? For my purposes all that is required is the magnitudes and the coordinates, all of which is provided in a single download from AAVSO.12 May 2023 at 11:31 am #617283
The sequences for the BAAVSS visual charts have all been entered into the database. When you try to upload a visual observation, it’s checked against the sequence.
If you use an AAVSO chart, our DB doesn’t have any sequence information for these charts.
Ah, there’s a thing.
In principle the AAVSO sequences could also be added to the BAAVSS database (assumng they are not there already – I don’t know). Those of us doing ensemble photometry generally include the (instrumental,catalogued) values for the (magnitude, error) of those sequence members which are measurable.
In principle, the BAA database could run sanity checks using those sequences too. Either that, or I am missing something.
Further, the AAVSO database could be scraped occasionally (once a year perhaps) to see what comparison stars have changed. What to do after a change should be obvious — pretty much what happens for BAA sequence changes.12 May 2023 at 12:40 pm #617284
Yes, you are missing something.
If we loaded the AAVSO data at a point in time, it would slowly become out of date. This would then generate errors rather than warnings for those charts during observation uploads. When you provide a chart recognised by the BAA database, it then checks the comparison stars match, their magnitudes, and checks the photometry calculation. So adding data that becomes out of date would cause bigger problems than just accepting a warning message.
The whole point of the charts in the BAA database is to allow checks and recalculations. As the AAVSO use numbered comparison stars based on the magnitude, this means star 102 in a chart at one point in time, can be replaced by a different star later. That would corrupt the calculations giving incorrect results. I would not implement a system that I know would give incorrect results under realistic scenarios.
It is much simpler to accept the explanation that you can ignore the chart warning if you don’t expect the chart to be present, as per the user guide for the database.
Andy12 May 2023 at 2:01 pm #617285
Out of interest, what SIMBAD/VIZIER data do you use? For my purposes all that is required is the magnitudes and the coordinates, all of which is provided in a single download from AAVSO.
I use it to get the B-V of the target star. I couldn’t find that in the AAVSO data.
Ian.12 May 2023 at 3:42 pm #617286
I use it to get the B-V of the target star. I couldn’t find that in the AAVSO data.
When I add a new star to my program, I go to https://app.aavso.org/vsp/ and fill in the appropriate fields (Star, FOV, orientation, limiting magnitude, and more) and first get a finder chart, which I print for use at the telescope.
Next the photometry for the sequence in the filters required is downloaded. The B-V values and their errors are provided whether you want them or not, in line with the bottom of the VSP page where we find the words: “V and (B-V) magnitudes are always displayed. Select any other bands you wish displayed below.” A Perl script subsequent mungs the photometry data into a format useful for my current processing pipeline.
I never take a given B-V of the target star as gospel because it can itself vary as the brightness changes. If I want to know a colour index of a VS at a particular epoch I measure it for myself.12 May 2023 at 4:32 pm #617287
When I add a new star to my program…
I call the AAVSO API to get me the VS data and the candidate comparison stars in a requested mag. range and chart width. I use the B-V from SIMBAD to give me a guide to any major differences that there might be in the B-V values of the comparison stars. It’s more of a sanity check – sometime there aren’t enough good choices to throw any out! My code then builds this info into my master variable star csv file which is read by my automated photometry routines (Python and AstroArt8). The API also returns a URI with the chart which I stream down and save as an image file. The BAA and AAVSO upload files are automatically generated.
Ian.12 May 2023 at 11:36 pm #617288
I call the AAVSO API to get me the VS data and the candidate comparison stars in a requested mag. range and chart width. I use the B-V from SIMBAD to give me a guide to any major differences that there might be in the B-V values of the comparison stars. It’s more of a sanity check
So there is a Sanity Clause after all!
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