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T UMi like in standstill

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GZN
GZN's picture
T UMi like in standstill

The last month or so , T Umi seems to be in standstill ??¡¡¡  around 11th magnitude.

Regards 

GZN

hhu
hhu's picture
Or maybe a faint maximum?

Or maybe a faint maximum?

sfra
sfra's picture
T UMI standstill

Alfredo,

This behavior does look unusual even for this star!  It's period (and cycle amplitude more recently) has been decreasing since 1979.  Janet Mattei and Grant Foster proposed that this star might have undergone a 'helium flash' (I haven't found the paper or article yet).  Supposely T UMI has had the most dramatic change of any Mira variable.

As Hubert says perhaps this is some sort of faint maximum.  Maybe this is another "stage" of a helium flash?  Wouldn't that be exciting!  It's in a good position to follow for months.

I have observations for this time period that I have not entered in the Database yet. I will start working on today.  Hopefully they will give more data points that are useful.

Frank Schorr (SFRA)

Stan Walker
T UMi standstill

Hi Frank & Alfredo,

The mention of a quick period change interested me.  Both BH Crucis and LX Cygni (I think that's the right star) increased their periods by 20-25% over a couple of decades.  This is dramatically different from R Hydrae, R Aquilae and R Centauri which are usually described as showing helium flash events with a slowly decreasing period - takes a century or two.  I wonder whether it's some type of pulsation mode change.

I plotted the last 12000 days of T UMi which gives 5 blocks of 2400 days.  A quick look shows 8, 9, 10, 11 and 11 maxima in each of these blocks.  So the period change may be complete.  As you state the amplitude has decreased dramatically whereas in the case of BH Crucis it increased slightly along with a 20% or so overall brightening of the star.  BH also changed from a dual maximum object to a single maximum with a pronounced hump. It is the only Mira where B-V colours before and after the period change are available - they show a considerably redder object now.

Even from NZ's far north T UMi is 10 degrees below my horizon.  Very disappointing!

Regards, Stan

pox
pox's picture
reduced pulsation

I think some other pulsating stars have shown similar 'standstills' although not many - but is this because a lot of Miras are unobserved, or not observed at all? RU Cam I seem to remember 'stopped' varying a few years back.

sfra
sfra's picture
T UMI standstill

 

I found the paper I was referring to and a couple more directly related.

Link to Janet Mattei and Grant Foster's paper "Dramatic Period Decrease in T Ursae Minoris":

https://www.researchgate.net/publication/234515590_Dramatic_Period_Decre...

Link to K. Szatmary, L.L. Kiss and Zs. Bebesi's paper "The He-shell flash in action: T Ursae Minoris revisited" which suggests that T UMI will finish its period decrease in 5 to 30 years (the paper is from 2002):

http://arxiv.org/abs/astro-ph/0211284

Link to another related paper by M.R. Templeton, J.A. Mattei, L.A. Willson titled "Secular Evolution in Mira Variable Pulsations":

http://arxiv.org/abs/astro-ph/0504527

Frank Schorr SFRA

hhu
hhu's picture
Maybe it's some kind of hump

Maybe it's some kind of hump like here in T Cep?

 

sfra
sfra's picture
T UMI

Most of the type of 'standstills' (humps) that is typically seen on LPVs such as T CEP, S ORI, RU HER and many other LPVs are typically seen on LPVs that have pretty steady periods.

T UMI has had a decreasing period since around 1979 but it did have a simular 'standstill' of about about 100 days from October 2010 through the end of December 2010 that was followed by a weak maximum.  This 'standstill' certainly can be another extended standstill for this star like the one in 2010.  It will be interesting to see what this star does for the next couple months! 

Frank Schorr SFRA

For more LPVs that show 'standstill' behavior please see:

https://sites.google.com/site/aavsolpvsection/aavso-lpv-program/lpv-humps

GZN
GZN's picture
T UMi like in standstill

Hi all,

Interesting behavior of this star.

Then,  would be the second hump registered on this variable ? Obviously we must pay attention in the next months.

Regards, Alfredo

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