Interstellar Medium and Spectroscopy

Feb 3, 2020
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It seems the definition of the makeup of the Interstellar Medium (ISM) may be a bit variable (or perhaps I'm reading the wrong literature). I have three questions.

1. What is the currently accepted definition of ISM?

2. How might electromagnetic radiation be affected by ISM as it makes its way to our observation posts?

3. How is the impact of ISM (if any) accounted for in the interpretation of spectroscopy results?
 
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rod

Oct 22, 2019
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What is your primary concern here KC Strom?

Sometimes reddening because of dust is known for various stars as viewed from Earth due to their sky position and ISM dust quantity, one example is M42 in Orion like stars in the Trapezium, yet with my telescopes I can see five stars there too in my eyepieces.
 
Feb 3, 2020
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Thanks, Rod.

I'm trying to develop an opinion as to whether there might be "material" of some nature between us and whatever light source we are observing that has the potential to introduce errors in our observations and subsequent interpretations. I'm starting with ISM. and am particularly interested in spectroscopy.
 
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rod

Oct 22, 2019
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KC Strom, the NASA ADS Abstract service has some 300,000 or more papers on the ISM, including spectroscopy, more than I can read :) *introduce errors in our observations and subsequent interpretations*, interesting thinking.

M42 is filled with dust and gas yet I can easily see 5 bright stars in the Trapezium using my 10-inch Newtonian reflector at 90 to 160x views. Spectroscopic studies of starlight from these stars is made too.

Do you feel that these Trapezium stars are not knowable, their distances to them is wrong, and perhaps stellar parallax cannot work to determine accurate stellar distances?

Here is an interesting report on the Trapezium stars in M42. An Improved Hertzsprung-Russell Diagram for the Orion Trapezium Cluster, https://ui.adsabs.harvard.edu/abs/2021ApJ...908...49F/abstract, Feb-2021. "We present a study of the Trapezium cluster in Orion. We analyze flux-calibrated Very Large Telescope/Multi-Unit Spectroscopic Explorer spectra of 361 stars to simultaneously measure the spectral types, reddening, and the optical veiling due to accretion. We find that the extinction law from Cardelli et al. with a total-to-selective extinction value of RV = 5.5 is more suitable for this cluster. "
 
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Feb 3, 2020
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Well, I was hoping not to bias the discussion by inserting too many of my thoughts. However, it seems we base an awful lot of our understanding of the universe on spectroscopic studies - distance, motion, temperature, make up. I just wanted to turn over the rock and see what crawls out.

Rainy day entertainment.
 

rod

Oct 22, 2019
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Well, I was hoping not to bias the discussion by inserting too many of my thoughts. However, it seems we base an awful lot of our understanding of the universe on spectroscopic studies - distance, motion, temperature, make up. I just wanted to turn over the rock and see what crawls out.

Rainy day entertainment.

FYI. KC Strom, I do not consider bias here a problem. I find different groups on the Internet today reject the heliocentric solar system and commonly claim everything in astronomy is false, e.g. stellar parallax and distance measurements, spectroscopic studies of starlight indicating their temperatures, sizes, and surface gravity (e.g. Sirius A and B), etc. I do not see this as bias, just the culture today in social media and Internet thinking. However, just from my personal experience with many hours of telescope observations using my 90-mm refractor and 10-inch Newtonian, I know that something is very wrong with many of these claims about How the Universe Works :) A recent example was a thread on Mars and the opening minutes presented images of Mars claiming NASA fakes the views using CGI and the video images of Mars shown were the truth. Something is very wrong :)
 
Feb 3, 2020
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Agreed, Rod.

There is some pretty unhinged, unsupported and illogical thinking being passed off as reasonable alternatives to currently accepted scientific truths. Science and reality deniers. I assure you I am not in this camp.

That said, there seems to be problem or two with our current understanding of the universe. A universe I seek to understand for my own reasons. I came to this forum a year or so ago assuming I would learn precisely how the universe works. Unfortunately, as I read and read I became increasingly uncomfortable about our collective understanding. However, my goal of understanding remains. Thus I am asking questions.
 
Jun 1, 2020
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Fortunately, science has a pretty strong handle on how light scatters or is absorbed since labs can test all these models. I assume the extensive no. of papers greatly improves all the spectral tweaking.

The greater problem is the spectral extinctions due to our atmosphere. It is militia-dimensional since altitude and particle counts alone greatly effect the spectrums. It’s why a white Sun is often considered to be yellow. 😀

The term is in air mass numbers. AM0, for instance, is the air mass directly above. At very low altitudes, an AM40 is possible. This isn’t linear but exponential.

Particle counts are noted each night at observatories, I think. From ~ 7,000 ft. elev., I once looked through a 8” reflector at a ~G2 star and it appeared to have a yellow tint. I was stunned. But particle counts even at high observatories can be very high. I would enjoy a paper about this.

iPhone
 

rod

Oct 22, 2019
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This post shows an observer and I both viewed the same asteroid (4 Vesta) last night using 10 x 50 binoculars and the same two stars nearby the asteroid in Leo based upon their sky position or angular separation. The issue in this thread is the ISM could be doing something strange like we cannot know the stars true distances from Earth, the stars sizes, surface gravity, or surface temperature because the ISM introduces errors. Without specific example(s) (like using the two stars mentioned in this observation post), not much to go on in this thread concerning what type of error(s) we should be aware of in astronomy.
 
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Feb 3, 2020
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Thank you, Rod.

I appreciate the time you spent answering.

As you mentioned in post #30, there is not a lot to go on. I, of course, don't know what errors to consider.

The second question in post #1 gets to the crux of it. Allow me to restate.

How might electromagnetic radiation be affected by ISM as it makes its way to our observation posts?

As you are well aware the "light" we study has travelled incredible distances through space to make it to our instrumentation. I've been told space is not empty. It seems somewhat plausible to me that the radiation might pass through something along the way with which it interacts, possibly modifying it in some way.

We know light is affected by the contents of our atmosphere. Might similar processes be playing out in deep space with different, unknown elements?

Based upon the limited responses to this thread, I'm guessing conventional wisdom does not consider this an issue. Thus, I'll move on to a new unsupported idea;)
 
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nterplanetary medium (See Wiki)
"Since the interplanetary medium is a plasma, or gas of ions, the interplanetary medium has the characteristics of a plasma, rather than a simple gas. For example, it carries the Sun's magnetic field with it, is highly electrically conductive (resulting in the heliospheric current sheet), forms plasma double layers where it comes into contact with a planetary magnetosphere or at the heliopause, and exhibits filamentation (such as in aurorae)."

Interstellar medium
"The interstellar medium is composed of multiple phases distinguished by whether matter is ionic, atomic, or molecular, and the temperature and density of the matter. The interstellar medium is composed, primarily, of hydrogen, followed by helium with trace amounts of carbon, oxygen, and nitrogen comparatively to hydrogen.[1] The thermal pressures of these phases are in rough equilibrium with one another. Magnetic fields and turbulent motions also provide pressure in the ISM, and are typically more important, dynamically, than the thermal pressure is."

Cat :)
 
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rod

Oct 22, 2019
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Thank you, Rod.

I appreciate the time you spent answering.

As you mentioned in post #30, there is not a lot to go on. I, of course, don't know what errors to consider.

The second question in post #1 gets to the crux of it. Allow me to restate.

How might electromagnetic radiation be affected by ISM as it makes its way to our observation posts?

As you are well aware the "light" we study has travelled incredible distances through space to make it to our instrumentation. I've been told space is not empty. It seems somewhat plausible to me that the radiation might pass through something along the way with which it interacts, possibly modifying it in some way.

We know light is affected by the contents of our atmosphere. Might similar processes be playing out in deep space with different, unknown elements?

Based upon the limited responses to this thread, I'm guessing conventional wisdom does not consider this an issue. Thus, I'll move on to a new unsupported idea;)
KC Strom, you may find this report interesting. ISM dust can cause starlight to be absorbed and reddened. https://astronomy.com/news/2011/10/vista-finds-new-globular-star-clusters-and-sees-right-through-the-heart-of-the-milky-way

Infrared surveys will reveal more too like the report from astronomy magazine. Something about my observations of 4 Vesta last night to consider. "Using 10x50 binoculars, 4 Vesta easy to see near HIP54470 and HIP54319. Retrograde loop in Leo. See slides for details, the two stars near 4 Vesta made easy identification." I used the SIMBAD portal and looked up some specifics on the stars. http://simbad.harvard.edu/simbad/sim-id?Ident=HIP54319&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id, stellar parallax 3.5343 mas, spectral type K5, mv + 6.392. HIP54319 is about 923 LY distance from Earth or 282.94 pc.

Do you think 4 Vesta asteroid distance from Earth last night and the star's distance are altered and in error because of ISM, thus much smaller in size and closer to the Earth?

4 Vesta asteroid about 1.365 au from my binocular view, the stars much farther, HIP54319 more than 900 LY distance.
 
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Jun 1, 2020
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As you are well aware the "light" we study has travelled incredible distances through space to make it to our instrumentation. I've been told space is not empty. It seems somewhat plausible to me that the radiation might pass through something along the way with which it interacts, possibly modifying it in some way.
As I noted above, photons (EM propagations) certainly do interact with the ISM. This is well known. There are astronomers that study this in great detail because adjustments are made to all spectra that need to take the extinctions -- the amount of light per wavelength that was emitted by we don't see -- into account.

There are two basic forms that cause extinctions:
1) Scattering.

There are multiple ways to address scattering and the equations take the wavelength into account. If the photons of a given wavelength encounter a particle that is smaller than the wavelength, then Rayleigh Scattering addresses the scattering involved. Halley, after work form Tyndall, developed the equation that demonstrates that the amount of scattering is a 4th power law. For instance, take blue light (or violet) at 400nm and notice that it will scatter 16x (2^4) more often than deep red at 800nm.

This is why our sky is blue. The no. of photons (flux density) in the blue band from sunlight entering our atmosphere is almost the same number as red photons, but the small air particles including nitrogen, along with pollen, aerosols, etc. cause the blue in sunlight to scatter in various directions. These photons then scatter again from the air above for the same reason, creating a blue sky.

Mie Scattering demonstrates that particles larger than the wavelength of the photons being considered will allow them to scatter primarily forward and back, but not to the side very much. [Einstein helped a co-author on a paper that gives the physics to this, IIRC.] This is why thin clouds can still be bright and why, from above, they are bright white -- the actual color of sunlight. Mie Scattering doesn't favor one color over another, unlike Rayleigh Scattering.

There are other scattering models as well.

2) Absorption. I suspect that the particle densities are taken into consideration. So, a certain percentage of the sky will block starlight. It's very likely that the reduction is well known for any given region of the sky, and is also taken into account since magnitudes are so important.

These extinctions are easiest, perhaps, to see in Bok Globules where the edges of these dark clouds are both dim and red, and for the 2 reasons above.


The particle sizes on Mars (ie CO2) and dust are larger so they don't scatter blue light the same way. But, the sky around the Sun appears blue, oddly enough. This is because the wavelength of red and the particle sizes on Mars are essentially the same, so "Selective Scattering" takes place where the red light scatters as our blue light does in our atmosphere. But the blue light on Mars still passes through but dimmed by absorption.
 
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From post #1:
"2. How might electromagnetic radiation be affected by ISM as it makes its way to our observation posts?"

In addition to my post #12 on ISM and IPM, there is the additional case of voids to be ruled out.
Hole in the Universe by Kulvinder Singh Chadha (All About Space, Issue 115, April 2021) lists the "ingredients of the Universe" as Dark Matter, Gas, Dust, and Stars, as opposed to voids, containing Dark Energy, and Neutrinos.
Voids are stated to have grown from seeds caused by quantum fluctuations from the Big Bang expansion. Smaller voids are believed to have combined to form, for example, the 330 million light years diameter Bootes 'supervoid'. Other voids include the KBC Void, Giant Void, Eridanus Supervoid, Local Void and Southern Local Supervoid.
I am wondering what interactions may be known between EM radiation and dark energy or, for that matter, between EMR and dark matter?
I am aware about the difficulties concerning dark matter (but see Aharonov-Bohm effect) but cannot find anything regarding dark energy.

Cat :)
 
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