86 replies to this topic

[robin_astro]

As far as the oscillation is concerned, if one judges by the TESS light curve on AE Ursa Majoris wikipedia page, they aren't necessarily identical or very regular.

AE UMa is a double mode pulsator and the two modes at different frequencies interact to produce a beat effect altering the apparent amplitude of the pulse from cycle to cycle. You can see the same effect here in some measurements I made of CC And

 

 

Cheers

Robin

[terrain_inconnu]

You might be interested in some  measurements I made of the the radial velocities of RR Lyrae which shows the relationship between radius and brightness

https://britastro.or...acdefe378f91ae9

 

"Note that many graphics found on the internet incorrectly show the maximum and minimum brightness corresponding to maximum and minimum size of the star. In practise however the brightness is almost identical at maximum and minimum radius and is in fact mainly dependent on the temperature."

 

Various other Delta Scuti stars were also measured to complement some modelling of the Kappa mechanism by Philip Masding

https://arxiv.org/abs/2409.10116

 

Cheers

Robin

 

First of all: this is outstanding, both in terms of execution and insights delivered. The intricacies of pulsating stars have been troubling me for some time now. I always thought that the variation in brightness is driven by the variation in temperature which is driven by the opacity of the contracting/expanding ionized layer (kappa mechanism) and vice versa (i.e. contracting -> hotter -> brighter, expanding -> cooler -> dimmer). Looking at the phase dependency of the parameters in your charts, the relationship is obviously a bit more complicated. It is evident from the phase diagram that the star gets brighter during the final part of the contraction (between phase 0.85 and 0.9), keeps getting brighter during the initial part of the expansion (between phase 0.9 and 1.0) before it reaches its maximum brightness (at phase 1). I am not sure if your data can provide an answer to this (you briefly discuss temperature on a qualitative basis), but how should we think about temperature variation between phase 0.85 and 1 as the star moves from contracting to expanding?

[pvdv]

This seems very interesting - I am digging myself in a deep hole...

Dominic M. Bowman
Amplitude Modulation
of Pulsation Modes in
Delta Scuti Stars
Doctoral Thesis accepted by
University of Central Lancashire, Preston, UK

[Airship]

I had an opportunity to test the new equatorial mode of the Seestar with an S50 this evening. I obtained two sets of test images of M97 using 10 and 20 second subs for 30 minutes each. The eq mode was easy to set up and the tracking quality was excellent. This will be a very useful operating mode for taking photometric images with the Seestar and reduce the challenge of taking data at very high altitudes and long periods of time.

Neat stuff.

[robin_astro]

 I am not sure if your data can provide an answer to this (you briefly discuss temperature on a qualitative basis), but how should we think about temperature variation between phase 0.85 and 1 as the star moves from contracting to expanding?

The temperature changes can be picked up qualitatively in the RR Lyr spectra but the spectral range was chosen primarily for the strength of the lines for the RV measurements so was  not optimum for measuring the Teff. That is probably most easily tracked from photometry (colour B-V) and you will find typical examples of this for Delta Cepheids on line, plotted with phase.

 

As to how the mechanism generates the timing of the temperature changes and what is happening around phase 1, your best bet could be to contact Phil Masding (contact email in the paper) who developed the Kappa process computer model we were testing. One of the outputs of the model will be the temperature of the outer layer.

 

Here is another study of double mode pulsator, delta Cepheid AS Cas, that  I was involved in. (Just contributed some low resolution spectra for spectral classification and an estimate of the temperature range)

https://ui.adsabs.ha.....125B/abstract

(It did include  multiband photometry, though colour changes were not extracted or discussed )

 

Cheers

Robin

[robin_astro]

Phil and I also talk about pulsations and the Kappa model here in this BAA video

https://britastro.or...obin-leadbeater

 

Cheers

Robin

[terrain_inconnu]

The temperature changes can be picked up qualitatively in the RR Lyr spectra but the spectral range was chosen primarily for the strength of the lines for the RV measurements so was  not optimum for measuring the Teff. That is probably most easily tracked from photometry (colour B-V) and you will find typical examples of this for Delta Cepheids on line, plotted with phase.

 

As to how the mechanism generates the timing of the temperature changes and what is happening around phase 1, your best bet could be to contact Phil Masding (contact email in the paper) who developed the Kappa process computer model we were testing. One of the outputs of the model will be the temperature of the outer layer.

 

Here is another study of double mode pulsator, delta Cepheid AS Cas, that  I was involved in. (Just contributed some low resolution spectra for spectral classification and an estimate of the temperature range)

https://ui.adsabs.ha.....125B/abstract

(It did include  multiband photometry, though colour changes were not extracted or discussed )

 

Cheers

Robin

Thank you, lots of directions to explore further. How did you map the expansion velocities (and the derived radii) to phase values? It looks like the maximum velocity coincides with phase 0 which was also used to map maximum brightness. Was this an arbitrary choice or has the synchronicity of expansion velocity and brightness been verified experimentally?

[pvdv]

Thank you, lots of directions to explore further. How did you map the expansion velocities (and the derived radii) to phase values? It looks like the maximum velocity coincides with phase 0 which was also used to map maximum brightness. Was this an arbitrary choice or has the synchronicity of expansion velocity and brightness been verified experimentally?

Have a look around min 25 in the video I believe.

[terrain_inconnu]

Have a look around min 25 in the video I believe.

Pretty much the reason why I asked. The radial velocity chart shown around min 25 states "Phase (relative max brightness)" which is unclear as to what is meant by this (in the arxiv paper a similar statement appears: "the phase referenced relative to the time of maximum brightness"). I would assume that spectroscopic and photometric timestamps have been separately translated to phase numbers (using the same epoch & period and without any shifting), therefore enabling a direct comparison of what happens when. Maybe Robin could clarify if this is indeed the case.

 

[robin_astro]

The phase for both photometry and spectroscopy were calculated from the (heliocentric corrected)  timestamps of the photometry and spectra based on an ephemeris derived either from AAVSO or TESS photometry data (calculated using Peranso) 

 

Any difference in time between photometry and spectroscopy runs was small enough not to be affected by any imprecision/drift in the ephemeris 

 

Cheers

Robin

Edited by robin_astro, 25 March 2025 - 03:39 PM.

[robin_astro]

Phase zero is defined as the time of maximum brightness. The radial velocity measurements used the same reference.

[terrain_inconnu]

The phase for both photometry and spectroscopy were calculated from the (heliocentric corrected)  timestamps of the photometry and spectra based on an ephemeris derived either from AAVSO or TESS photometry data (calculated using Peranso) 

 

Any difference in time between photometry and spectroscopy runs was small enough not to be affected by any imprecision/drift in the ephemeris 

 

Cheers

Robin

 

Thank you for clarifying as I found the wording a bit confusing.

 

The more I look at it, the more interesting this work becomes and the more I learn from it. To this end, I digitally extracted some of the data from this chart in order to create a new chart and highlight the correlation between expansion velocity and brightness which you discuss in the video (after min 30). One can deduct that RR Lyrae's brightness minimum coincides with the maximum rate of contraction while its brightness maximum coincides with the maximum rate of expansion (which is not the same as min and max radius as you already mentioned). On the other hand, for SZ Lyncis (which was also discussed in the video) the brightness rises ahead of velocity and a phase shift between the two is needed to get the best model fit.

 

Assuming that temperature is the main driver of brightness (along smaller contributions from surface effects), it would be interesting to understand how temperature relates to the velocity of expansion/contraction. This is of course a small sample but maybe you have looked at other stars as well (e.g. CC And mentioned above). If so, is there any general statement one can make regarding the link between expansion velocity, brightness, temperature and the underlying mechanism of the pulsations?

 

Edited by terrain_inconnu, 27 March 2025 - 02:38 AM.

[pvdv]

Assuming that temperature is the main driver of brightness (along smaller contributions from surface effects), it would be interesting to understand how temperature relates to the velocity of expansion/contraction. This is of course a small sample but maybe you have looked at other stars as well (e.g. CC And mentioned above). If so, is there any general statement one can make regarding the link between expansion velocity, brightness, temperature and the underlying mechanism of the pulsations?

One thing I gathered from the Bowman's PhD thesis I referenced above is that you can't generalize much...
 

[terrain_inconnu]

One thing I gathered from the Bowman's PhD thesis I referenced above is that you can't generalize much...
 

My thinking is that different type of pulsators could exhibit distinct phase patterns with respect to temperature, brightness, and expansion velocity (e.g. possibly related to the specifics of the involved ionized layers, the inner workings of each star type, its location on the instability strip and so on). However, the underlying mechanism should be able to explain (even if only qualitatively) the different observed behaviours and chain of events.

[robin_astro]

Thank you for clarifying as I found the wording a bit confusing.

 

The more I look at it, the more interesting this work becomes and the more I learn from it. To this end, I digitally extracted some of the data from this chart in order to create a new chart and highlight the correlation between expansion velocity and brightness which you discuss in the video (after min 30). One can deduct that RR Lyrae's brightness minimum coincides with the maximum rate of contraction while its brightness maximum coincides with the maximum rate of expansion (which is not the same as min and max radius as you already mentioned). On the other hand, for SZ Lyncis (which was also discussed in the video) the brightness rises ahead of velocity and a phase shift between the two is needed to get the best model fit.

 

Assuming that temperature is the main driver of brightness (along smaller contributions from surface effects), it would be interesting to understand how temperature relates to the velocity of expansion/contraction. This is of course a small sample but maybe you have looked at other stars as well (e.g. CC And mentioned above). If so, is there any general statement one can make regarding the link between expansion velocity, brightness, temperature and the underlying mechanism of the pulsations?

 

Yes I do have some more observations of other pulsating stars. A couple more are delta Scuti variable Be Lyn and classical delta Cepheid variable SU Cas, shown briefly in the video at 27:40.  These measurements, together with SZ Lyn (and possibly AE UMa though there is not so much data) all show the maximum expansion velocity slightly lagging the maximum brightness by 0.05-0.1 phase. With RR Lyrae however the two are in phase at maximum brightness which I think is confirmed by other measurements in the literature.  My job was to measure the velocities, not work the model so you would need to talk to Phil about the underlying astrophysics  ;-) 

 

Note it looks like there is  an error in the phase scale on Phil's graphs for SZ Lyn shown in the video at 30:20 and in fig 6 in the paper which appears to have been plotted based on phase 0 being at maximum expansion velocity not brightness. I need to check with him on that. All my observations used the standard convention of maximum brightness as the 0 phase reference.  

 

Cheers

Robin

[robin_astro]

 

 

Note it looks like there is  an error in the phase scale on Phil's graphs for SZ Lyn shown in the video at 30:20 and in fig 6 in the paper which appears to have been plotted based on phase 0 being at maximum expansion velocity not brightness. I need to check with him on that. All my observations used the standard convention of maximum brightness as the 0 phase reference.  

 

 

Yes that graph with the model generated curves is plotted with phase zero at maximum expansion velocity which was the convention used for the model at the time rather than the standard convention of phase zero at maximum brightness. The model reproduces the phase shift between expansion velocity and brightness seen in SZ Lyn.

[terrain_inconnu]

Yes that graph with the model generated curves is plotted with phase zero at maximum expansion velocity which was the convention used for the model at the time rather than the standard convention of phase zero at maximum brightness. The model reproduces the phase shift between expansion velocity and brightness seen in SZ Lyn.

A similar phase error seems to appear in the chart for RR Lyrae around 26:45 with respect to the phase of the radius. However none of these (minor) issues take away the great insights delivered by this work and I would be very interested to understand what it takes to perform such measurements (e.g. equipment, techniques, software). There are approaches to perform spectroscopy with the Seestar but I don't think the resolution needed for that level of analysis is there.

[pvdv]

@terrain_inconnu - did you try to get a light curve again?

I shot one yesterday, this time with the Vixen R200SS, CBB filter and 6200MM in bin2x2 and again got a distinct double peak
(just RAW data I have no transformation coefficients for that filter and just relied on Tycho's automatic photometry)
 

 

For any long term frequency analysis, a decent time resolution on the peaks will be needed. Maybe I was a bit optimistic on the Seestar at that magnitude

[robin_astro]

A similar phase error seems to appear in the chart for RR Lyrae around 26:45 with respect to the phase of the radius. However none of these (minor) issues take away the great insights delivered by this work and I would be very interested to understand what it takes to perform such measurements (e.g. equipment, techniques, software). There are approaches to perform spectroscopy with the Seestar but I don't think the resolution needed for that level of analysis is there.

The RR Lyr plots at 26:45 are mine, based on my measurements and are correctly plotted relative to maximum brightness at zero phase. (Unlike the  Delta Scuti variables the expansion velocity and brightness are in phase in RR Lyrae as your replotting of my data showed)  Similarly Phil's plots of model against measured for RR Lyrae at 30:50 are also correct since in the case of RR Lyr, maximum brightness and expansion velocity occur at the same 0 phase

 

It is not possible to do this kind of spectroscopy with the SeeStar or any other telescopes with integrated cameras  as you need to place the high resolution slit or fibre fed spectrograph between the telescope and the camera. It is possible however to do some simple spectroscopy with the Seestar using an objective grating or prism in front of the aperture but for this application the resolution would be too low and because it is a slitless setup there is no fixed reference from which to measure the very small wavelength variations. The aperture of the SeeStar is also too small to collect sufficient light in the time available. (spectroscopy is very photon hungry. As I mention in the video,at the spectral resolution needed, the effective loss of brightness is 11 magnitudes so for RR Lyrae for example this is equivalent to doing photometry on ~mag 19 targets in 10 min exposures to 0.03 magnitude one sigma precision. (I used an 11 inch aperture)

 

Cheers

Robin

Edited by robin_astro, 28 March 2025 - 12:38 PM.

[robin_astro]

 

For any long term frequency analysis, a decent time resolution on the peaks will be needed. Maybe I was a bit optimistic on the Seestar at that magnitude

You don't need good time resolution at the peak to establish the pulsation period and epoch. What you need is as  much accurately time stamped data as possible  scattered over a long time span  (The longer the time span, the more accurate the period.) You can then use a time series analysis program like Peranso

https://www.cbabelgium.com/peranso/

to frequency analyse the data to identify the period(s) and fold the accumulated data into a phase diagram to which the light curve can be fitted.

 

Cheers

Robin

[terrain_inconnu]

@terrain_inconnu - did you try to get a light curve again?
 

Today might be the first clear night after a cloudy week here in Athens though there is still a lot of Saharan dust in the lower atmosphere. Can not recall ever seeing a double peak in TESS or AAVSO light curves for AE Uma.

 

 

The RR Lyr plots at 26:45 are mine, based on my measurements and are correctly plotted relative to maximum brightness at zero phase. (Unlike the  Delta Scuti variables the expansion velocity and brightness are in phase in RR Lyrae as your replotting of my data showed).

I was referring to this chart where the radius seems to be plotted incorrectly as the minimum and maximum radii should coincide with the phases at which the expansion velocity crosses 0.

 

Edited by terrain_inconnu, 28 March 2025 - 12:36 PM.

[robin_astro]

 

 

I was referring to this chart where the radius seems to be plotted incorrectly as the minimum and maximum radii should coincide with the phases at which the expansion velocity crosses 0.

 

rr lyr_.jpg

Ha yes !  Definitely something wrong there with the radius change plot I used for RR Lyr in the presentation.  Mea culpa. Well spotted ! 

At least the plot on the BAA page shows it correctly.

https://britastro.or...acdefe378f91ae9

 

Cheers

Robin

Edited by robin_astro, 28 March 2025 - 01:19 PM.

[robin_astro]

The radius change plots  in the presentation for the other stars look ok too

 

Cheers

Robin

[robin_astro]

Ha yes !  Definitely something wrong there with the radius change plot I used for RR Lyr in the presentation.  Mea culpa. Well spotted ! 

 

If you are interested, I see now where the mistake arose. In the graphic on the BAA page, the direction of the phase scale of the velocity/radius plot on the right is reversed so it mirrors the plot on the left.  When I lifted that plot to use in the presentation I restored the phase scale for the expansion velocity but missed doing that for the radius so in the presentation, the radius plot is mirror imaged about phase 0.  If you "unmirror" it  all is well.

 

Cheers

Robin

[terrain_inconnu]

If you are interested, I see now where the mistake arose. In the graphic on the BAA page, the direction of the phase scale of the velocity/radius plot on the right is reversed so it mirrors the plot on the left.  When I lifted that plot to use in the presentation I restored the phase scale for the expansion velocity but missed doing that for the radius so in the presentation, the radius plot is mirror imaged about phase 0.  If you "unmirror" it  all is well.

 

Cheers

Robin

Oh yes, things like these are so easy to happen. Anyone who has ever combined multiple plots in the same chart should certainly not cast the first stone.