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T UMa Magnitude Question

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#1 dr.planet

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Posted 29 February 2024 - 12:45 PM

I’m making some star charts based on the Yale Bright Star Catalog, and noticed an oddity around Ursa Major that didn’t match any other charts.  The variable star T UMa, aka HD109729 and HR4800, plotted much brighter than it should.  The Bright Star Catalog has its magnitude listed as 5.5, but all other catalogs have it much dimmer than that, even at its brightest phase of variability.  Does anyone know much about this star, and why it might show up as much brighter in that particular catalog but none of the others?

 

Thanks,

 

    Dave


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#2 lee14

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Posted 29 February 2024 - 01:51 PM

It's possible the magnitude 5.5 entry is simply an error. T UMa typically varies between 6.5 - 13.8. Enter T Uma in the first URL for the actual light curve, the second shows detailed metrics.

 

https://www.aavso.org/LCGv2/

 

https://www.aavso.or...l.top&oid=37107

 

Lee


Edited by lee14, 29 February 2024 - 01:54 PM.

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#3 lee14

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Posted 29 February 2024 - 02:04 PM

I've looked over my personal records for a ten year period, and the estimates ranged from 6.8 to 13.1.

 

Lee


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#4 dr.planet

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Posted 29 February 2024 - 02:19 PM

Thanks all.  Looking into it a little more, some of the stars (~70 or 80) in the Bright Star Catalog including this one are flagged with an "H", meaning "original HR magnitude".  I'm guessing that means T CMa has a magnitude of 5.5 under some previous system that may not correspond to V magnitudes like the rest of the entries.


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#5 Fabricius

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Posted 29 February 2024 - 03:52 PM

The strong variability of T UMa is known since 1856 (discoverer: Hencke) and the magnitude has never been estimated brighter than 6.3 (January 8, 1929).

So it does not make sense to list this star as magnitude 5.5.

Even the mid-19th century Bonner Durchmusterung and the original HR catalogue (Harvard Revised Photometry Catalogue, 1908) listed this star as variable.

T UMa is a red mira star. Only a red filtered photographic plate, late 20th century red sensitive emulsion or modern red sensitive sensor could "produce" a magnitude of 5.5.


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#6 KMA

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Posted 01 March 2024 - 01:07 AM

T UMa may reach maximum

about  June 19  -   2024

 

best for clear sky

KMA


Edited by KMA, 01 March 2024 - 01:12 AM.

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#7 smithrrlyr

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Posted 02 March 2024 - 06:24 PM

In the original, 1930, edition of The Bright Star Catalogue, T UMa is listed as variable, with a range of 5.5 - 12.7. Thus, the 5.5 is there early on. I have not, however, found where the 5.5 originated.  In a 1920 presentation to the AAVSO, Leon Campbell gave 12.8 for the minimum of T UMa, close to the value in the 1930 BSC.  However, he did not give 5.5 for maximum.  He did give 5.2 magnitudes for the typical range in magnitude.  It makes one wonder whether a revised range value could have been confused with the maximum magnitude at some point.  That is just a guess.  I wonder what a circa 1920 AAVSO chart said about its magnitudes? 


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#8 KMA

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Posted 29 March 2024 - 05:56 AM

correction

 

checking  AAVSO  light curve

next maximum of T UMa is predicted

on June 8.

 

best for clear sky

KMA


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#9 Rutilus

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Posted 11 April 2024 - 07:05 AM

I've been imaging T UMa for the past 6 weeks with a 50mm lens, and its been faint. Looking at

the AAVSO data, it must have been at minimum brightness. This morning it appears to have increased a bit,

now around mag.12.5 -13.0, at a guess.  I expect it to increase rapidly during next month a head of a predicted

June maximum. 

Attached Thumbnails

  • T-UMa-11-04-2024.jpg

Edited by Rutilus, 11 April 2024 - 07:06 AM.

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#10 Tapio

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Posted 11 April 2024 - 07:20 AM

correction

checking AAVSO light curve
next maximum of T UMa is predicted
on June 8.

best for clear sky
KMA


What is this prediction based on?

#11 mrm6656

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Posted 11 April 2024 - 08:59 AM

T UMa is a member of the Mira class of variable stars. The Miras are huge red giant stars which pulsate, changing their size along with their temperature  which in turn cause a variation in brightness over several magnitudes. This occurs in a regular cycle like clock-works due to regular variations of the nuclear burning in their interiors. The regularity of the pulsations makes possible predicting their brightness as a function of time based on prior obsevations of the cycle. The cycle will eventually change slowly then end with a star ejecting much of its mass into a planetary nebula and becoming a white dwarf, but the rate of change of the star's pulsation period is very slow on a human time scale.

 

      --- Mike

 

Edit: It's also worth noting that the Mira "class" is not a class of stars in which any given star is permanently a member but is, rather, just one evolutionary stage of many stars of middling mass.


Edited by mrm6656, 11 April 2024 - 09:15 AM.

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#12 lee14

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Posted 11 April 2024 - 10:42 AM

What is this prediction based on?

Good question. The period is 256 days, since it's near minimum at present, the predicted maximum would seem to be in August.

 

Lee


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#13 KMA

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Posted 11 April 2024 - 11:57 PM

T UMa  1231+60  aavso.jpg Here is a snapshot

of aavso  T UMa light curve.

My estimate of maximum is

based on that...

 

best wishes

KMA


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#14 lee14

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Posted 12 April 2024 - 07:20 AM

attachicon.gif T UMa 1231+60 aavso.jpgHere is a snapshot

of aavso  T UMa light curve.

My estimate of maximum is

based on that...

 

best wishes

KMA

Yes, I'm familiar with the light curve, which contradicts a June 8 prediction. The mean time between minima and maxima is over four months. June 8 would be just a little more than two months from the current minimum.

Lee


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#15 KMA

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Posted 12 April 2024 - 12:26 PM

T UMa period is close to 256 days.

Is it from max to max ?

 

best wishes

KMA


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#16 lee14

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Posted 12 April 2024 - 02:35 PM

T UMa period is close to 256 days.

Is it from max to max ?

 

best wishes

KMA

Max to max, minimum to minimum, or any corresponding points on the ascending or descending light curve. Generally it's cited as the time between maxima, but this is a very regular light curve, both in periodicity and shape of the curve itself.

 

Lee


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#17 Rutilus

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Posted 13 April 2024 - 06:20 AM

I have an old DOS based program for predicting the maxima of the LPV stars. I had a go this morning but have totally forgotten how to use it.

I might spend some time over the weekend trying to work it out with my ageing brain cells.

  

On average T UMa takes just over 100 days from minimum to maximum. If the star is coming out of minimum

brightness?, then the next maximum would likely be July/August. I did plug the data into a spreadsheet with a

starting date of JD 2445623 and a period of 256.60 days (GCVS 4th edition, very old data but better than nothing),

the result was a maximum in the middle of July 2024.


Edited by Rutilus, 13 April 2024 - 06:24 AM.

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#18 lee14

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Posted 13 April 2024 - 06:46 AM

This really isn't that complicated. The number of days between minima and maxima for the last several cycles is very close to 130 days. This can be read directly from the light curve,

 

In times past the AAVSO would generate tables of predicted maxima and minima, intended as observation guides, but always with the caveat that the observer should not base their estimates on expectations, but what they actually see.

 

Lee

 

T UMa.jpg

 

 

 

 


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#19 Rutilus

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Posted 13 April 2024 - 08:28 AM

Lee.

I used the curve and bin tools on the AAVSO site and got figures ranging from 95 to 110 days for the light curve posted

above, which is still in line with the old % figure given by the GCVS. Does anybody have a more update % figure from

minimum to maximum for this star?  


Edited by Rutilus, 13 April 2024 - 08:29 AM.

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#20 lee14

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Posted 13 April 2024 - 10:01 AM

Lee.

I used the curve and bin tools on the AAVSO site and got figures ranging from 95 to 110 days for the light curve posted

above, which is still in line with the old % figure given by the GCVS. Does anybody have a more update % figure from

minimum to maximum for this star?  

That range certainly fits the last rise to maximum. From a minimum at ~2460110 to maximum at ~2460215. The first fall to minimum on the chart from there starts at ~2459720 to a maximum at ~2459870, or 150 days. The second ranges from ~2459870 to ~ 2459980, or 110 days, giving a pretty accurate range of variation over time.

 

It is of course, the variation that is of interest, that's why there's an OC curve. If the light curve was perfectly symmetrical and repetitive there'd be little point in monitoring the variability. Also of interest is the way the maxima vary over time, while the minima remain more consistent. The caveat here though, is the much larger number of data points for maxima, and a relative dearth for minima, and the error bar is subsequently higher. Visual observations tend to be more difficult when the variable is near the threshold of visibility, and 14th magnitude can be challenging even for an 8 inch scope.

 

Not that it's in dispute here, but the value of visual observations is not solely in the magnitude estimates, but in determining the period, particularly when T Uma reaches maximum. The large number of data points can pin this down rather well.

 

Lee


Edited by lee14, 13 April 2024 - 10:03 AM.

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#21 Rutilus

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Posted 14 April 2024 - 07:40 AM

Yes Lee, all good stuff which makes variable star observing such a great and interesting subject. 

Seeing that there is a much larger number of data points for maximum in the light curve, I may have a

go at using bisected cords to pin down the date of maximum brightness from the last peak. 

 

Last night was an excellent night for me in my Bortle 8 sky, in spite of moonlight  I was able to get down to

below magnitude 15.0 with a single 30 second exposure with my 80mm f/7 refractor and DSLR.

I was able to get this single exposure  image of T UMa. I also noted that nearby S UMa is getting brighter. 

 

Attached Thumbnails

  • T-UMa-13-04-2023.jpg

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#22 Rutilus

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Posted 24 April 2024 - 03:27 PM

correction

 

checking  AAVSO  light curve

next maximum of T UMa is predicted

on June 8.

 

best for clear sky

KMA

Hi KMA - over the weekend I used bisected cords for a date of the last maximum. If I simply add the period of 256 days

to the date, I get a maximum of 10/11th June 2024. However using the GCVS (% M-m, I went on the GCVS website but

could not find an up-todate figure) data when added to the date (as close as possible to when the star was last at minimum)

the figure I get for maximum is pushed out to the middle of July. Which funny enough is within 24 hours of the date I got on

my spreadsheet (using the GCVS data).

 

Out of interest I plotted the days over and under of observed maximum from the past predicted dates (using mean

graphs of maximums) from the year 1983 (GCVS 4th edition) onto a graph and got the following shown below. 

At the end of the day T UMa will do its own thing, but it will be very interesting to see when the next maximum

is observed. 

Attached Thumbnails

  • T-UMa-graph.JPG

Edited by Rutilus, 24 April 2024 - 03:29 PM.


#23 yuzameh

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Posted 24 April 2024 - 06:24 PM

Hi KMA - over the weekend I used bisected cords for a date of the last maximum. If I simply add the period of 256 days

to the date, I get a maximum of 10/11th June 2024. However using the GCVS (% M-m, I went on the GCVS website but

could not find an up-todate figure) data when added to the date (as close as possible to when the star was last at minimum)

the figure I get for maximum is pushed out to the middle of July. Which funny enough is within 24 hours of the date I got on

my spreadsheet (using the GCVS data).

 

Out of interest I plotted the days over and under of observed maximum from the past predicted dates (using mean

graphs of maximums) from the year 1983 (GCVS 4th edition) onto a graph and got the following shown below. 

At the end of the day T UMa will do its own thing, but it will be very interesting to see when the next maximum

is observed. 

Do that for the past ten or so cycles, take the average period, and the standard deviation of said periods.

 

Add that to the last estimated maximum date and inherent error/range will be around +/- tend days of predicted date (pretty typical for general Mira).

 

Double check with twice mean period added to maximum date of prior cycle, then again for triple check.

 

Examining the BAA photometric database visual observations (see here https://britastro.org/photdb/ and lookup data) the lightcurve profile looks fairly symmetric (shorter period oxygen Mira ones tend to be so) so this should work possibly a bit better than usual.

 

When you figure out how to use the above link you can rubber band zoom into the last twenty or thirty cycles and not a feature not uncommon in Mira variables (well, non-carbon ones).  Often, but not always, a higher than usual minimum is followed by a higher than usual maximum and a lower than usual max by a lower than usual min.  Except of course for when that doesn't happen.  In other words amplitude stays pretty much constant.  In the visual oxygen Mira variables mostly dictated by the amount of metal oxides condensing and vapourising in the atmosphere, the photospheric amplitude, probably best seen in parts of Cousins I or NIR J photometric passbands, is usually only about a mag or two at very best.

 

Fun stuff to think on whilst following your own data over time.


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#24 KMA

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Posted 25 April 2024 - 07:24 AM

Hi Rutilus

 

AAVSO Bulletin 81 (last one from 2018)

lists T UMa maximums at 26 Feb 2018

and again 10 Nov 2018.

Calculating from there

maximum of T UMa will be

23 June 2024.

 

To observe this coming max progressing

it is good to start at least 30days sooner.....        

 

Best wishes  

KMA


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#25 Rutilus

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Posted 25 April 2024 - 09:33 AM

Yuzameh - many thanks for the information. The biggest problem I have at the moment is finding the time and

my brain cells to do the in depth study required with the data.

 

KMA -  Thank you for the dates from 2018. The dates I have from my spreadsheet are longer by 22 days for the 26th Feb

prediction and 21 days longer for the 10th November one.   If I take 21 days off my next prediction date, it comes out

the same as the  23rd June. 

 

Not happy with the big spike in the graph I produced , I double checked things this morning and found that I had

plotted several of the bars in correctly. My apologies here is the corrected one.

Attached Thumbnails

  • T-UMa-graph.JPG

Edited by Rutilus, 25 April 2024 - 09:43 AM.

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