86 replies to this topic

[terrain_inconnu]

Having done a bit of photometry with a S50 on some variables of all kind, I am wondering whether there are any introductory targets to also do some asteroseismology. Not sure the S50's resolution suffices to actually detect higher modes but if any member here has relevant experience, I would gladly follow any hints.

[Overtime]

asteroseismology? Do you mean astrophotography?

[terrain_inconnu]

asteroseismology? Do you mean astrophotography?

No, I mean asteroseismology.

[Overtime]

You used a few words in your post I never saw before, so I thought it was a typo. My mistake.

[astrogerm]

For asteroseismology you really need a 1-meter aperture telescope and a sophisticated spectrograph. New Mexico State University is involved in a global asteroseismology project called SONG, with several 1-meter scopes strategically located around the globe: http://astronomy.nms...steroseismology.

 

Fore helioseismology (the Sun), there is a GONG project: https://gong.nso.edu/. 

[terrain_inconnu]

For asteroseismology you really need a 1-meter aperture telescope and a sophisticated spectrograph. New Mexico State University is involved in a global asteroseismology project called SONG, with several 1-meter scopes strategically located around the globe: http://astronomy.nms...steroseismology.

 

Fore helioseismology (the Sun), there is a GONG project: https://gong.nso.edu/. 

 

Yes and no. Instead of spectroscopically tracking radial velocity shifts and line profile variations caused by pulsations, asteroseismology is also done by analysing variations in brightness (i.e. photometry). Ideally the two methods are combined. However in order to photometrically resolve higher modes one needs sufficient resolution which is difficult to achieve with ground based telescopes. Hence my quest for a couple of easy targets where amplitudes of excited modes might be large enough to be detected by the S50.

Edited by terrain_inconnu, 16 March 2025 - 12:10 AM.

[pvdv]

Maybe AE Ursae Majoris ? 

On the plus side, within the reach of a Seestar, circumpolar (at least for me), short period, lots of TESS data.
On the minus side, long term project.

https://arxiv.org/pdf/2309.07989

Most other targets/lists I could find are either too faint or have too small photometric variations (imho)

 

[terrain_inconnu]

Maybe AE Ursae Majoris ? 

On the plus side, within the reach of a Seestar, circumpolar (at least for me), short period, lots of TESS data.
On the minus side, long term project.

https://arxiv.org/pdf/2309.07989

Most other targets/lists I could find are either too faint or have too small photometric variations (imho)

 

Thank you. This is an excellent case study, first/second overtone double-mode δ Scuti variables (lots of data, lots of papers). How long would I need to collect data on AE Uma to reach "proof of concept" level?

Edited by terrain_inconnu, 16 March 2025 - 07:57 AM.

[pvdv]

My gut feeling(*) says at least several months, but that's just a gut feeling. The math stuff in the paper is within my reach but the stellar dynamics/seismic modeling are _definitely_ not my area of expertise  

I believe that simply showing "something" is going on would be a win with a seestar. 

(*) they apparently used 116 peaks of AE Uma for their initial frequency analysis, but that was TESS data - I would expect one needs way more with Seestar data if one wants to reach a decent accuracy/confidence level. The seestar data we see on TCrb seems nice and at generally consistent with what one gets with larger scopes but AE Uma is around 1.5 mag fainter. Longer total exposure will introduce noise in the timing of peaks which may severely affect the downstream analysis. 
 

[terrain_inconnu]

My gut feeling(*) says at least several months, but that's just a gut feeling. The math stuff in the paper is within my reach but the stellar dynamics/seismic modeling are _definitely_ not my area of expertise

I believe that simply showing "something" is going on would be a win with a seestar.

(*) they apparently used 116 peaks of AE Uma for their initial frequency analysis, but that was TESS data - I would expect one needs way more with Seestar data if one wants to reach a decent accuracy/confidence level. The seestar data we see on TCrb seems nice and at generally consistent with what one gets with larger scopes but AE Uma is around 1.5 mag fainter. Longer total exposure will introduce noise in the timing of peaks which may severely affect the downstream analysis.

Just an idea born out of ignorance, but maybe the higher cadence of the Seestar (e.g. 10 sec vs 120 sec of TESS) allows to replicate what is already known in a much shorter timespan. I think I will just give it a try and decide how to proceed once I got the first couple of cycles.

[pvdv]

My main concern is that you might not get accurate enough photometry if you don't stack (or average bin the measurements) on a 11.5 mag star. Looking at your nice EH Lib data it seems the noise at mag 10 is significantly higher than at mag 9.5 and we are talking about approx mag of 10.9 to 11.5 here. 

But it doesn't hurt to try and it is ideally placed right now to collect a few cycles. 

[terrain_inconnu]

My main concern is that you might not get accurate enough photometry if you don't stack (or average bin the measurements) on a 11.5 mag star. Looking at your nice EH Lib data it seems the noise at mag 10 is significantly higher than at mag 9.5 and we are talking about approx mag of 10.9 to 11.5 here.

But it doesn't hurt to try and it is ideally placed right now to collect a few cycles.

True. Being under Bortle 9 skies does not help either. But that makes it a challenge, which I like.

[david_od]

I suspect it may be feasible for a few specific targets, at least, considering the following:

Precision multi-band photometry with a DSLR camera
 

 

Specifically, we used a Canon EOS 60D camera that records light in 3 colors simultaneously. The DSLR was integrated into the HATNet survey and collected observations for a month, after which photometry was extracted for 6600 stars in a selected stellar field. We found that the DSLR achieves a best-case median absolute deviation (MAD) of 4.6 mmag per 180 s exposure when the DSLR color channels are combined, and 1000 stars are measured to better than 10 mmag (1%). Also, we achieve 10\,mmag or better photometry in the individual colors. This is good enough to detect transiting hot Jupiters. We performed a candidate search on all stars and found four candidates, one of which is KELT-3b, the only known transiting hot Jupiter in our selected field. We conclude that the Canon 60D is a cheap, lightweight device capable of useful photometry in multiple colors.

 

First photometric properties of Dome C, Antarctica

 

Here we present the first photometric extinction measurements in the visible range performed at Dome C in Antarctica, using PAIX photometer (Photometer AntarctIca eXtinction). It is made with "off the shelf" components, Audine camera at the focus of Blazhko telescope, a Meade M16 diaphragmed down to 15 cm. For an exposure time of 60 s without filter, a 10th V-magnitude star is measured with a precision of 1/100 mag. A first statistics over 16 nights in August 2007 leads to a 0.5 magnitude per air mass extinction, may be due to high altitude cirrus. This rather simple experiment shows that continuous observations can be performed at Dome C, allowing high frequency resolution on pulsation and asteroseismology studies. Light curves of one of RR Lyrae stars: S Ara were established. They show the typical trend of a RRLyrae star. A recent sophisticated photometer, PAIX II, has been installed recently at Dome C during polar summer 2008, with a ST10 XME camera, automatic guiding, auto focusing and Johnson/Bessel UBVRI filter wheels.

 

For a bright enough stars with pulsation modes compatible with both a desirable signal to noise ratio and exposure length to avoid issues with scintillation from seeing, it wouldn't surprise me if at least a some partially decent results could be achieved. This looks interesting enough to at least make some proof of concept testing.
 

Edit to add:

Some techniques discussed here for high precision photometry of asteroids might be of interest as well. For instance, reference stars are chosen per frame, in order to account for absortion variations at different airmasses within each image: Improving Asteroid Photometry by Small Steps.

Also of interest may be this method for photometric measurements:
An optimal extraction algorithm for imaging photometry

Edited by david_od, 17 March 2025 - 09:03 AM.

[terrain_inconnu]

I suspect it may be feasible for a few specific targets, at least, considering the following:

Precision multi-band photometry with a DSLR camera


First photometric properties of Dome C, Antarctica

For a bright enough star with pulsation modes compatible with both a desirable signal to noise ratio and exposure length to avoid issues with scintillation from seeing, it wouldn't surprise me if at least a some partially decent results could be achieved. This looks interesting enough to at least make a few proof of concept testing.
Edit to add:
Some techniques discussed here for high precision photometry of asteroids might be of interest as well. For instance, reference stars are chosen per frame, in order to account for absortion variations at different airmasses within each image: Improving Asteroid Photometry by Small Steps.

Also of interest may be this method for photometric measurements:
An optimal extraction algorithm for imaging photometry

Thank you. That is a lot of encouraging information regarding ground based asteroseismology. I also like the idea of adding asteroids to the mix.

[david_od]

Thank you. That is a lot of encouraging information regarding ground based asteroseismology. I also like the idea of adding asteroids to the mix.

It seems it deserves a look, but I'm reading that the lens used in the HATNet survey with a DSLR is a 11 cm f/1.8 lens.
I think this article is relevant for a more realistic exploration of the topic, given constrains of amateur equipment:
Asteroseismology of red giants from the first four months of Kepler data: Global oscillation parameters for 800 stars

 

Also:
Asteroseismology with Small Telescopes
A 0.5m telescope was used, still more consistent with astrogerm's figure of 1-m class telescopes. The TESS mission uses a ~10cm mirror... but it's in space.

But I just found this:

Twenty-five years of helioseismology research in Uzbekistan

 

In order to carry out long-term international observations of δ Scuti stars and perform asteroseismic analyses of their light-curves Taiwanese astronomers established the TAT (Taiwan Automated Telescope) network (Chou et al., 2006). In 2007 a TAT was installed at Maidanak Observatory in Uzbekistan, and this is shown in Figure 14. Maidanak Observatory is located in the southern part of Uzbekistan, at an altitude of 2,700 m above mean sea level (Ehgamberdiev et al., 2000).

The TAT network has proved to be quite efficient in finding new δ Scuti stars. In 2008 HD 163032 was discovered to be a δ Scuti star, and after four years of observations we were able to precisely determine the mode parameters and their variation with time (Fernández, et al., 2013). We also determined these same parameters for another already-known δ Scuti star, V830 Her (ibid.; see Figure 15). Later we turned our TAT towards one of the targets of the Kepler space mission: NGC6811.
Our main program was to conduct light-curve analyses of known variable stars, and to make follow-up observations for Kepler. At the time we wrote this paper we had obtained light curves of stars in the field of NGC6811 and discovered several new δ Scuti candidates, but were awaiting the arrival of Kepler observations.

[...]

The TAT uses a 9-cm Maksutov-type telescope with f = 25, manufactured by Questar.  The CCD camera is Apogee Alta U6 16-bit 1024 × 1024, and the CCD chip is a Kodak KAF-1101E, with a scale of 2.18 arcsecs per pixel, which gives a field of view of 0.62 ×
0.62 square degrees-

This is more comparable, besides the cooled sensor.
Also, since there are issues to take care of regarding aliasing from the periodicity of observations runs, maybe some good candidate objects should be located closer to your celestial pole, and may need cooperation with other observers at different longitudes.

Edited by david_od, 17 March 2025 - 07:02 PM.

[pvdv]

The key here is "and after four years of observations". A signal is a signal and, if you want to increase SNR, you "stack". What's valid for detected photons is also valid temporally for frequencies. That was the reason for my "long term project" assessment. And that could be (theoretically) worse if one needs long exposures because they reduce the temporal resolution.

And a very good point about potential aliasing. Thanks!

[david_od]

The key here is "and after four years of observations". A signal is a signal and, if you want to increase SNR, you "stack". What's valid for detected photons is also valid temporally for frequencies. That was the reason for my "long term project" assessment. And that could be (theoretically) worse if one needs long exposures because they reduce the temporal resolution.

Oh, definitely, that's a big detail. I was wondering if a program using several simultaneous observations could improve results more rapidly combining them. Since each photometric data point would have a corresponding date and time, it may not be necessary to synchronize the observations, as they should only (I think) give more significant statistical power to those frequencies arising as real oscillation modes in a tool like a Lomb-Scargle periodogram. Probably other analysis tools fare better, but maybe the point stands. (?)

 

From what I remember, I think red giants are "noisy" in radial velocity measurements (please someone correct me if I'm wrong, a quick search wasn't that useful). I was wondering if they are "photometrically noisy" when compared with other types of stars.

[terrain_inconnu]

The key here is "and after four years of observations". A signal is a signal and, if you want to increase SNR, you "stack". What's valid for detected photons is also valid temporally for frequencies. That was the reason for my "long term project" assessment. And that could be (theoretically) worse if one needs long exposures because they reduce the temporal resolution.

And a very good point about potential aliasing. Thanks!

Oh, definitely, that's a big detail. I was wondering if a program using several simultaneous observations could improve results more rapidly combining them. Since each photometric data point would have a corresponding date and time, it may not be necessary to synchronize the observations, as they should only (I think) give more significant statistical power to those frequencies arising as real oscillation modes in a tool like a Lomb-Scargle periodogram. Probably other analysis tools fare better, but maybe the point stands. (?)

 

From what I remember, I think red giants are "noisy" in radial velocity measurements (please someone correct me if I'm wrong, a quick search wasn't that useful). I was wondering if they are "photometrically noisy" when compared with other types of stars.

Just a quick update: got the chance to do the first recoding of AE Uma which proved a bit more difficult than anticipated due to it being close to zenith (a weak point of the alt/az mounted Seestar) and issues with transparency/seeing (lots of rejected frames). Nonetheless, I managed to get two cycles to create a first set of charts (light curve and folded light curve) as shown below. For the folded curve I used the epoch and period as given by the VSX (link).

 

[david_od]

Just a quick update: got the chance to do the first recoding of AE Uma which proved a bit more difficult than anticipated due to it being close to zenith (a weak point of the alt/az mounted Seestar) and issues with transparency/seeing (lots of rejected frames). Nonetheless, I managed to get two cycles to create a first set of charts (light curve and folded light curve) as shown below. For the folded curve I used the epoch and period as given by the VSX (link).

 

AE Uma 1.png

AE Uma 2.png

That's great! Have you tried to observe a field with several tried-and-true stable stars to check for consistency of your results? Also, have you been able to do a sort of "sliding" super-stacking, in which from a long series of measurements you take groups of N, then you drop the first one of the N and add a new point for a new stack, and so on?
At 250mm, I think you would benefit from some of the strategies mentioned in the video about incrementally improving asteroid photometry.

[terrain_inconnu]

That's great! Have you tried to observe a field with several tried-and-true stable stars to check for consistency of your results? Also, have you been able to do a sort of "sliding" super-stacking, in which from a long series of measurements you take groups of N, then you drop the first one of the N and add a new point for a new stack, and so on?
At 250mm, I think you would benefit from some of the strategies mentioned in the video about incrementally improving asteroid photometry.

I recently did M67 as a standard field (for anyone interested in the Landolt fields have a look at this list). I am using ASTAP for photometry and while one can stack in groups of N, there is no rolling option (i.e. remove first, add another etc).

Edited by terrain_inconnu, 21 March 2025 - 02:30 PM.

[pvdv]

I took a shot at it as well (with the TMB 115/805, 533MC and a LPS2 filter because I was at my heavily light polluted location)  the day I suggested it.

Here's a small visualization of the variability I got

https://drive.google...-HKp2aveXp/view

(trying directly from CN gallery)

The animation is just illustrating the concept behind that variability and should not be taken as accurate. Writing a small script was just a way to kill the time while the data was being acquired

Edited by pvdv, 22 March 2025 - 05:29 PM.

[terrain_inconnu]

I took a shot at it as well (with the TMB 115/805, 533MC and a LPS2 filter because I was at my heavily light polluted location)  the day I suggested it.

Here's a small visualization of the variability I got

https://drive.google...-HKp2aveXp/view

(trying directly from CN gallery)

 

The animation is just illustrating the concept behind that variability and should not be taken as accurate. Writing a small script was just a way to kill the time while the data was being acquired

 

For some reason in my recording the modulation of the maximum brightness every other cycle is less pronounced than in yours and other light curves I have seen in the past. Will add a few cycles once the weather clears up to verify.

 

I also really like the idea behind the animation, linking the variation in brightness to the underlying physical processes. However and maybe I am reading the animation wrong but according to the kappa mechanism that drives variability for cepheids, delta scutis etc, pulsating stars actually become brighter while contracting and dimmer as they expand. The relationship between brightness, temperature, and radius can be seen in the following chart:

 

Edited by terrain_inconnu, 23 March 2025 - 12:18 PM.

[pvdv]

That's what I though as well initially, but digging a bit, it is apparently this mechanism which I tried to illustrate

https://en.wikipedia...Kappa–mechanism

Edit: https://library.five...kappa-mechanism

Edit: 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. It may depend on when you look at it. I tried a second observation but was cut off by passing clouds.
 

Edited by pvdv, 23 March 2025 - 01:04 PM.

[robin_astro]

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

Edited by robin_astro, 23 March 2025 - 04:13 PM.

[pvdv]

Thanks! Impressive spectroscopic work there.

As far as the my illustration is concerned, I also initially thought that the star diameter changed but, digging a bit, I stumbled on the Eddington Valve/Kappa Mechanism.
The simple (simplistic?) explanation I found was, schematically, the one in the second link I provided.That led me to try to illustrate the "gas" expansion and increased transparency up to the point gravity brought everything back down. 

I have since found this link https://www.astro.pr.../A403/pulse.pdf that seems interesting.

But, of course, this seems to be a very, very deep rabbit hole!