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btieman
scholastic sledgehammer
Reged: 07/24/08
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Spectroscopic differences in pulsating variables?
#5276283 - 06/17/12 10:24 PM
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How hard is it to detect spectroscopic differences between min/max of pulsating variables? I'm guessing the longer the period/greater the peak to peak magnitude change the easier? What sort of spectrograph resolution is needed?
Thanks for any info!
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brianb11213
Postmaster
Reged: 02/25/09
Loc: 55.215N 6.554W
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Re: Spectroscopic differences in pulsating variables?
[Re: btieman]
#5276613 - 06/18/12 05:42 AM
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Quote:
How hard is it to detect spectroscopic differences between min/max of pulsating variables? I'm guessing the longer the period/greater the peak to peak magnitude change the easier? What sort of spectrograph resolution is needed?
Which pulsating variables?
I think the only thing you'd be likely to notice changing in the spectrun of a delta Scuti type star is the radial velocity, and for that you're going to need a well calibrated, high resolution spectrograph. Fortunately most of the known Delta Scuti stars are bright.
OTOH some Mira stars have emission lines which are only visible at certain points in the cycle, which can easily be detected with a low resolution objective prism type spectrograph, and no need for calibration.
There's just about every shade in between these extremes.
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nytecam
Postmaster
Reged: 08/20/05
Loc: London UK
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Re: Spectroscopic differences in pulsating variables?
[Re: btieman]
#5277111 - 06/18/12 01:19 PM Attachment (66 downloads)
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Quote:
How hard is it to detect spectroscopic differences between min/max of pulsating variables? I'm guessing the longer the period/greater the peak to peak magnitude change the easier? What sort of spectrograph resolution is needed?
Thanks for any info!
It depends on the variable - I did a complete light cycle awhile back on T Cep at low spectral resolution and the changes are very evident. I'll see if I can find the data and post 
Here's my complete dated sequence of circumpolar T Cep - half of the spectrum to right is in near-infrared and invisible to the eye. The exposure duration [rh column] is a measure of relative variable brightness to ensure similar density spectra eg the star becomes redder/IR as it fades. To the eye the fade is much more pronounced  Did intend making an animated video at the time but little interest shown by amateurs and it got shelved 
Edited by nytecam (06/18/12 02:53 PM)
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btieman
scholastic sledgehammer
Reged: 07/24/08
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Re: Spectroscopic differences in pulsating variables?
[Re: nytecam]
#5278026 - 06/18/12 11:36 PM
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Thanks guys!
I've been mulling over starting to do more spectroscopy. I've never really done much with my scope--a few spectra here and there--but I've worked with scientists who do a lot of both photon and mass spectrometry so I know my way around a little. What I don't have a feel for is what's practical with my equipment. Currently I have an 11" SCT and a StarAnalyser. I'm thinking of steping up to a slit spectrograph.
Some projects of interest include seeing if I can identify asteroid families by spectra and measuring spectral changes in pulsating variables. I like the idea of pulsating variables because I can blend what I can already do well--precision photometry--with something I want to become more profeccient at--spectroscopy. I've got a few crazy ideas I'd like to give a try as well, but I'd to try something more sain first 
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btieman
scholastic sledgehammer
Reged: 07/24/08
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Re: Spectroscopic differences in pulsating variables?
[Re: btieman]
#5278042 - 06/18/12 11:54 PM
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From what I think I understand so far--and overly generalized at that!--many stars pulsate due to expansion, which cools and makes the star less dense, being overcome by gravity which heats and makes the star more dense. The pulsation is this cycle overshooting and self correcting.
The period and intensity changes are related by real matters ability to react. A quick period implies a shallow intensity variation because the star physically can not expand/contract very fast. Longer periods tend towards deeper intensity variations because the star has more time to expand/contract.
So, in general, longer period variables would be more likely to display spectral shifts that are more easily detected. What I'm wondering is how long/deep a pulsation needs to be in order to clearly see a change? I'd love to look at stars that vary fast enough that I can get a single light curve with a clear period so as to make it easier to get multiple spectra at various points in the curve for comparison. Idealy the period would be less than one evenings data gathering--say 6 hours. Again--ideally. Worse case, I'd really like to avoid periods that either so long or alias with daylight/cloudy nights such that it takes many observing sessions to get a complete period. I do have two scopes and two CCDs so I'm not worried about being able to correlate photometric period with spectra.
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NJScope
sage
Reged: 03/08/04
Loc: NJ
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Re: Spectroscopic differences in pulsating variables?
[Re: btieman]
#5279003 - 06/19/12 02:42 PM
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btieman:
As Nytecam suggested it depends on the pulsator but also will depend on what kind of information you are trying to get out of your spectroscopic data. In order to determine global physical parameters such as (L)uminosity, Teff, (R)adius and log g, then you'll need high resolution spectra. Alternatively, since you already have a photometric setup, it is possible to get much of the same information from high precision multi-color light curves. This procedure called the Inverse Photometric Method is described for the RR Lyrae type variable RZ Lyrae. Heady stuff but this might give you a better idea about the possibilities. I haven't found any code for IPM online but there is a application called FAMIAS that runs in Linux and Mac which does have a multi-color light curve routine for mode degree analysis.
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btieman
scholastic sledgehammer
Reged: 07/24/08
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Re: Spectroscopic differences in pulsating variables?
[Re: NJScope]
#5279327 - 06/19/12 05:57 PM
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Thanks Kevin!
I used to write scientific software as my day job and do have a half baked software platform for developing scientific software specific to astronomy up and running. It can currently do live-time frame registration and photometry measurements across a range of apperture settings. I've used it to measure exoplanet light curves in real time--set the software up and it computes a live light curve as data comes in. In the morning, press send and the data is whisked off to the ETD So I'm pretty sure I can handle the software end if need be.
I did think about taking BVRI data as individual channels--a "very low resolution" spectrograph but thought I could avoid the software/data acquisition complexity by acquiring full spectra at once. There should be more info in the full spectra and even a star analyser is orders of magnitude higher resolution than 4 filters! The difference being efficiency...thinking about it, it might be interesting to measure the efficiency difference between a straight V filter and integrating the same portion of the spectrum with the star analyser. The blazed spectrum should be much less efficeint but does anyone know how much so?
As for what I'm looking for? No scientific question I'm looking to answer--at this point I'm mostly looking to test the limits of my instrumentation in an interesting way
Brian
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