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predicted dates of max and min or long period variables

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#1 STomkins

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Posted 02 February 2024 - 12:20 PM

Are there up-to-date online resources on the predicted maxima and minima of long-period variable stars? I've found some on BAA's and AAVSO's websites, but they are out-of-date. Any suggestions welcome - thank you!



#2 Tapio

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Posted 02 February 2024 - 12:32 PM

I think you should join AAVSO and their mailing lists.



#3 yuzameh

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Posted 02 February 2024 - 02:16 PM

I think you should join AAVSO and their mailing lists.

Waste of time.

 

All you'll find on there about such things are from a couple of years ago where people were complaining that the AAVSO don't do these anymore, only for the staff to reply that they gave them up because they took too much time and effort.

 

Given that the aavso staff are employed to work for the aavso membership that's something of a sucky attitude.

 

You won't learn much about variable stars on aavso mailing lists, people going on about equipment, charts, etc, yes, but actual variables, nope.



#4 Tapio

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Posted 02 February 2024 - 02:30 PM

I've had different expericence.

Or maybe I don't find 'regular' variables so interesting anymore.

But there are constantly all kind of interesting variable campaigns going where observations are wanted.

Sometimes I almost find these emails overwhelming - there are too much ofthem.



#5 yuzameh

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Posted 02 February 2024 - 02:55 PM

Are there up-to-date online resources on the predicted maxima and minima of long-period variable stars? I've found some on BAA's and AAVSO's websites, but they are out-of-date. Any suggestions welcome - thank you!

One long winded route is to go here

 

http://www.sai.msu.s...-bin/search.htm

 

type in the name of the star or interesting in variable star shorthand (eg R And , X Cam , R Cyg)

 

In a recent update of the GCVS a lot of the old data for epoch and period has been brought to nearer times, although that is often around two decades ago it is better than the past versions at decades and decades old.  Mira variables have varying period length, so any quoted value for that should be thought of as an average.

 

It will give you the "epoch" as a Julian Date (with the preceding 24 missing).

 

For example for R And it says under epoch in the table 53280, which is in full 2453280.

 

Today is JD 2460343 which we'll shorten to 60343.

 

The period it gives is 409.2 days, but you may as well call it 409 as even that is an average and not true for every year.

 

Now, short hand trick :-

 

Take the difference between now (you can still to the 60343 date, everything larger is in the future) and the epoch in the table

 

60343 minus 53280

 

7063 days have elapsed since the measurement of maximum at 53280, you can refer to the latter as the 'base epoch' or 'reference epoch'.  It you know when R And was last at maximum you can convert that date to JD numbers using online JD to date converters (just websearch).

 

Divide 7063 days by the period 409 days and you get 17.3

 

This tells you there have likely been 17 times R And has been at maximum since the 53280 measurement.

 

That means the next maximum will be the 18th time.

 

So, 409 days period multiplied by 18 gives 7362 days.

 

You take that value and add it to the 53280:- 53280+7362

 

That is 60642

 

You take that, put the 24 in front to give 2460642, then you either use your planetarium/charting software and change the JD date to that and see what calendar date that is or you websearch for a converted and enter that number.

 

That leads to, on average, given a date of maximum in 2006 (the 532580 value), and given the average period of 409 days, a calendar date of Nov 27 2024 for the next maxmimum.

 

Now, as Mira are at maximum for about a week or two for visual observers (LONG period variables, no fast changes) you have a prediction of the next maximum being between last couple of weeks of November and first couple of weeks in December.

 

If you think that's too broad, well, Mira variables drift in period, at times randomly, so even the old predictions were best guesses, they are not clockwork, but you get an idea of when to concentrate on maxima.

 

And in many ways that's all they did at AAVSO, although they will have taken more recent lightcurve data from their database and used it to measure the last date of maximum and the ones before those for a few years and then found a recent average period by measuring the time between those maxima and dividing by the number of maxima involved.  The more recent the data the more likely to capture the current region of period drift ranges, but even then you won't get a prediction that will necessarily be good to one week, let alone a day.

 

Have fun, it is far simply than it looks or sounds and is just simple arithmetic.  Used to be a bit trickier but as you can find online JD to calendar date converters nowadays the task is much simpler.



#6 Fabricius

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Posted 02 February 2024 - 03:07 PM

First method (labor-intensive, but best possible result):

AAVSO.org > Pick a star > type a star of your choice, e.g. R Leo > Plot a light curve > point at a recent maximum and click > you will see the date and Julian Date of the maximum > predict the next maximum by adding the known period (R Leo = 312 days).

 

Second method:

Variable Star Index > choose a star, e.g. R Leo. Use the historical epoch of maximum and the catalogued period to calculate future maxima.

 

Third method (easiest):

install the free software Cartes du Ciel.

Start the program > View > Variable stars.

 

LPV-predictions.jpg

 

Fourth method (preferred by me):

do not spoil the fun, point a telescope at the star: it is it faint or bright? Estimate the brightness. Repeat later and and be surprised. See how the brightness has changed. Draw a light curve.


Edited by Fabricius, 02 February 2024 - 03:17 PM.


#7 KMA

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Posted 03 February 2024 - 02:47 AM

There is JD calendar for 2024

on AAVSO website.

KMA



#8 Ed Wiley

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Posted 03 February 2024 - 11:46 AM

Just to clear the air about AAVSO: The entire operation has 8 (eight) official staff members, one of whom is an undergraduate student. All of the rest of the work is done by volunteers working without salary. For example, I teach the 6-week introductory photometry course as a volunteer. Other volunteers teach other courses, gratis. Other volunteer members take care of VPhot. Another writes programs for determining transformation coefficients and another for incorporating the ability to transform data directly in VPhot. The original max-min of LPV was written, I think, by a volunteer. The observing section leaders are all volunteers. The editor of JAAVSO is a volunteer and a professional astronomer to boot. The list goes on...

 

We do this to support AAVSO's mission. Those who do not understand the efforts of we volunteers to support AAVSO and its small paid staff should not recommend anything about AAVSO without understanding more of its actual workings. It's true, AAVSO cannot be everything to everyone's needs, but a bit of understanding is in order.

 

Fabricius: thanks for your post. I'm lazy. I use your #3. But beginners should be aware that the magnitudes are best for V filters and having the Max/Min dates only give those two values and only for that one filter or pair of eyes. But if you click on the name you get lots of information, including a prediction of the current status relative to a simplified light curve. Note that the list is incomplete, there are many more variables, but the selection is excellent for beginners. For well observed LPVs (the kind beginning photometrists should be working on at first), a strategy is to consult the light curve available at AAVSO until they get the hang of what is happening during the period. One strategy is to interpolate and bracket with several different exposures. This brings you to #4 and having the experience to make a good guess and get that SNR over 100. That comes with time.

 

Ed


Edited by Ed Wiley, 03 February 2024 - 12:06 PM.

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