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Grab and Go Spectroscopy

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#26 Organic Astrochemist

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Posted 23 November 2019 - 12:11 PM

Clouds didn't part until after midnight last night so I only got one target, but it was a good one, the planetary nebula IC 418
IC 418 full uncorrected.png
The intensity of the [NII] line at 658.4 nm is pretty big in this planetary nebula. I can't fully resolve this line from Hα at 656.3 nm, but the hump on the right side of the Hα peak probably is the [N II] line.
IC 418 H-alpha.png
The double peaked Hα is due to the structure of the nebula. If you look at images of the nebula, the limbs are much brighter than the center and the two peaks correspond to the two limbs.
IC 418
I was able to resolve quite a few [O III] lines.
IC 418 temperature.png
First, I calculated the ration of [O III] 500.7 nm / [O III] 495.6 nm = 2.84. Richard Walker says the ratio should be ~ 3, but upon further research
nebular lines
I found the calculated value should be 2.88 and that values of 2.8 are well within observations.
Next to calculate the excitation class of this low excitation planetary nebula I used the formula ([O III] 500.7 nm + [O III] 495.6 nm) / Hß 486.1 nm = 2.7 which corresponds to the E1 class, consistent with Walker's value. He says this suggests a temperature for the central star of 35,000K.

 

To calculate the electron temperatures of the nebula, one needs to observe [OIII] at 436.3 nm. I mistook the Balmer line at 434.0 nm for this line. Obviously, the [O III] line at 436.3 nm  is completely beyond the capabilities of this system. I found one reference that suggested an electron temperature of ~9,360 K, this would correspond to a ratio of ([O III] 500.7 nm + [O III] 495.6 nm) / [O III] 436.3 nm ~270. That [OIII] at 436.3 nm is pretty small. 

 

Always lots to learn.


Edited by Organic Astrochemist, 23 November 2019 - 02:19 PM.

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#27 mwr

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Posted 23 November 2019 - 01:14 PM

Really neat that you could resolve the lines that are necessary to calculate the excitation class with the SA-100. Beautiful observational astrophysics! I think the line at 436 nm is rather H gamma and the small bumps at 587 nm and 410 nm are He I and H delta, respectively. 


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#28 Organic Astrochemist

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Posted 23 November 2019 - 02:01 PM

Really neat that you could resolve the lines that are necessary to calculate the excitation class with the SA-100. Beautiful observational astrophysics! I think the line at 436 nm is rather H gamma and the small bumps at 587 nm and 410 nm are He I and H delta, respectively. 

Thanks. Glad to see that someone is paying attention.



#29 mwr

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Posted 24 November 2019 - 07:55 AM

Clouds didn't part until after midnight last night so I only got one target, but it was a good one, the planetary nebula IC 418
 

Small and bright planetary nebula are indeed good objects for the SA-100 and I will put IC 418 on my list (although it is quite low in the sky at my location). Gurzadyan (the"inventor" of the excitation class concept) reports a value of 1.85=(N1+N2)Hß for IC 418 (http://adsabs.harvar...Ap&SS.181...73G). Experimental details were not given, but the data was probably corrected for interstellar extinction.

 

A good resource for finding small and bright planetray nebula, whichI consult quite often is "Planetary Nebula and how to observe them" by Martin Griffiths:

 

https://www.springer...k/9781461417811


Edited by mwr, 24 November 2019 - 01:56 PM.


#30 robin_astro

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Posted 24 November 2019 - 12:01 PM

There is a French group dedicated to discovering new PN candidates and confirming them spectroscopically

http://planetarynebulae.net/EN/

you can see  the spectra here

http://planetarynebu...au_spectres.php

and some discussions on this on the ARAS forum

http://www.spectro-a...wforum.php?f=30

 

Cheers

Robin


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#31 Organic Astrochemist

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Posted 25 November 2019 - 09:37 PM

I've never looked very hard, but double stars as a target for amateur spectroscopists doesn't seem to come up that often.
Double stars are beautiful in their own right, but I have also found them very rewarding for lessons about human vision, optics, astrophysics, stellar classification, stellar evolution, star clusters, galactic structure and now spectroscopy.

74 Psc (also known as Psi1 Psc or STF 88) is a nearby bright pair (V mag 5.273 and 5.455) widely separated (29.2", position angle 160°).

The Washington Double Star Catalog says that the primary is B9.5V and the secondary is A0V and that parallax and proper motion suggest that the pair is gravitationally bound. As main sequence stars, it makes sense that the brighter is bigger and hotter.

However, Simbad says the primary is A1V and the secondary is A0V.

Sky Safari is pretty emphatic that the pair are unrelated, separated by 20 light years.

Enter my grab-and-go spectroscopy rig.

I have the grating so far back that I can't see the zero order spectrum (in this case the pair of stars). Here's a platesolved image to show the relative positions. Fainter secondary is up and the brighter primary is below. Some field stars are labeled (that are over one degree away).
STF 88AB for astrometry solved.jpg

The separation was sufficient for me to get two relatively uncontaminated spectra.
The primary with an A2V reference (because I didn't have an A1V reference):
STF 88A with A2V reference.png
The secondary with an A0V reference:
STF 88B with A0V reference.png
Then both the primary and secondary rectified so that the continuum had a value of 1:
STF 88AB rectified.png
In this spectrum it looks like the Balmer absorptions are greater for the primary than for the secondary. This is consistent with the primary being cooler than the secondary.
To further verify this, I divided the spectrum of the primary by the spectrum of the secondary. All the hydrogen Balmer lines were below 1, showing that the absorptions were greater in the primary than in the secondary. This results because more of the hydrogen atoms in the hotter star have lost their electron and can't absorb. More of the hydrogen atoms in the cooler star still have their electron and can absorb light.
STF 88A divided by STF 88B.png

So this seems consistent with Simbad that the primary is cooler than the secondary. But if the two were a pair of main sequence stars at roughly the same distance then the cooler primary should also be dimmer. Is the primary actually much closer, thus making it brighter? Is the primary evolving off the main sequence and brightening? Are the two physically related?

Interesting questions, but I'm glad the Star Analyzer 100 was able to show me that the brighter star is actually the cooler spectral type.

Edited by Organic Astrochemist, 25 November 2019 - 09:45 PM.


#32 robin_astro

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Posted 26 November 2019 - 11:24 AM

Interesting

 

What is the basis of the 20lyr distance difference in sky safari?  A quick calculation of the distances and uncertainties based the modern parallax measurements suggests that the measured parallaxes are not accurate enough to say whether or not they could be gravitationally bound. (The uncertainties appear large enough to allow them to be) 

 

74 PSc A Hipparcos  275 lyr      error 15  

                Gaia DR2  254                15 (Strangely a much higher error compared with that by Gaia for B)

                Mean         265                10 

 

74 PSc B Gaia          280                  5

 

(As a quick sanity check against Vega (A0v, 25 lyr, Vmag 0)  a similar star at 280 lyr would have a V mag of 5.25 assuming no IS extinction)

 

At this distance, a separation of 29 arcsec would equate to ~2500AU, potentially close enough to be gravitationally bound depending on where they are in their orbit

 

Cheers

Robin


Edited by robin_astro, 26 November 2019 - 11:24 AM.


#33 Organic Astrochemist

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Posted 28 November 2019 - 09:03 PM

Dear Robin,
I don’t know where the information for Sky Safari comes from.

By the way, from where do you get your Gaia distance information? I’ve been using this catalog, but maybe there’s a better way:
http://vizier.u-stra...rce=I/347&-to=3

With respect for the distance between the pair, in addition to the distance of 30” that we see on the sky, I think one also has to consider the 0.2 mag difference between the two. If they had equal luminosity one star should be about 40,000 AU further away and in this case the dimmer star should be MORE luminous.

I used to think that people had a good handle on the absolute magnitude of a star if they knew the spectral type and luminosity class, but maybe that still leaves a lot of uncertainty.

I’m going to continue observing closely matched double stars. I’d like to know what confidence I can have that the Star Analyzer can identify the hotter and cooler companion.

Edited by Organic Astrochemist, 28 November 2019 - 09:04 PM.


#34 robin_astro

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Posted 29 November 2019 - 05:57 AM

Yes there are other dimensions to stellar  classification that can affect the luminosity, for example metallicity, eg

http://www.spectro-a...&start=20#p1703

and circumstellar material which means two spectra of the same spectral type may not have the same spectral energy distribution 

Interstellar extinction  can also affect the apparent brightness.

Having said that, if these two stars are in a common system I would have thought the extinction and  metallicity is likely to be similar. 

 

I first went to SIMBAD and saw that they were giving very similar parallax for both A and B

http://simbad.u-stra...t=SIMBAD search

http://simbad.u-stra...t=SIMBAD search

(SIMBAD also describes A itself as a multiple star system though I have not followed that up)

 

I then noticed that they were using Gaia parallax for B but Hipparcos for A which was surprising so I went to the Gaia archive 

http://gea.esac.esa.int/archive/

and noticed that the Gaia value for A had a rather high uncertainty (actually higher than Hipparcos), which perhaps explains why they quoted Hipparcos for A so it seems the parallax data is not good enough to determine if they are close enough to interract or not. (Perhaps sky safari is using Gaia for both which gives a difference in parallax equivalent to  ~25 lyr but without considering the uncertainties)

 

Cheers

Robin



#35 robin_astro

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Posted 29 November 2019 - 06:13 AM

And just to add to the confusion entering 74Psc into Skiff's catalogue,

http://vizier.u-stra...iz-bin/VizieR-4

reveals some overlap  between the spectral types given for the two stars in the literature.

 

So much is inexact in astronomy that there is room for debate about a lot of it !


Edited by robin_astro, 29 November 2019 - 06:16 AM.


#36 Organic Astrochemist

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Posted 01 December 2019 - 02:22 AM

30 Arietis AB also known as STFA 5, may or may not be a physical system.

 

Stelle Doppie says that it is, but the GAIA data that I looked at seemed to suggest that they might be separated by at least 40,000 AU. Regardless, they don't seem too far apart. 

Because the stars are relatively close to Earth and close to each other differential effects of IS extinction are likely to be quiet small, I think.

 

Here is an image of the spectra. They look quite similar.

30 Ari AB cropped.jpg

 

The primary has been classified as F5V (but also as F4IV and F6III!).

My results are consistent with F5V, but it would be bold to say that I have proved that.

30 Ari A with F5V.png

 

The secondary has been classified as F6V and F7V. My results are also consistent with that.

30 Ari B with F6V.png

 

But what I am interested in testing is how confidently I can compare the two. Here is the comparison of the rectified spectrum. Based on the Balmer lines it is clear to me that the secondary is the cooler star, even though the spectral types are so close. The H-beta and H-delta are deeper in the F5V primary as would be expected because it is hotter and more of the hydrogen atoms have an electron in the higher 2nd energy level, allowing these Balmer absorptions.

 

This is encouraging. I have some other examples I'll post later.

Attached Thumbnails

  • 30 Ari A vs 30 Ari B.png

Edited by Organic Astrochemist, 01 December 2019 - 02:26 AM.


#37 Organic Astrochemist

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Posted 01 December 2019 - 12:20 PM

As Robin has pointed out there is more that goes into spectral classification than just temperature.

I found this a very interesting article, unfortunately I think it is behind a paywall.

Recipe

Basically, by judicious choice of a few spectral lines that have different sensitivities to temperature, surface gravity, metallicity and microturbulence, one could determine many basic stellar parameters.

 

6 Arietis is classified as kA4hA5mA5Va, which means that it is A4 when classified based on Ca II, A5 when classified based on hydrogen and A5 when classified based on metals. Obviously such fine parsing is impossible with a Star Analyzer, but in comparing my spectrum of 6 Ari to standards from A0V to A5V, the small changes in the calcium lines and Balmer lines are evident. Based on the H-zeta line strength and Ca II K line, I would estimate A3V.

Attached Thumbnails

  • 6 Ari with A0V.png
  • 6 Ari with A2V.png
  • 6 Ari with A3V.png
  • 6 Ari with A5V.png


#38 Organic Astrochemist

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Posted 01 December 2019 - 12:29 PM

Here are some more comparisons of nearby wide double stars.

 

Chi Ceti and EZ Ceti are nearby F and G type stars. Because EZ Ceti is two magnitudes fainter the S/N is much worse. In the future I will have to compensate by acquiring many more images for the fainter star. 

 

Later I will also fully explore the possibility of distinguishing luminosity classes with the star analyzer, but I think that Chi Ceti (HD 11171) is better classified as F0V rather than F2III

HD 11171 with F0V.png

HD 11171 with F2III.png

 

The S/N isn't great for EZ Ceti, but still consistent with G3V.

EZ Ceti with G2V.png

 

When I compare the two rectified spectra, no surprise that EZ Ceti is cooler, with shallower Balmer absorptions.

HD 11171 (F0V) vs HD 11131 (G3V).png



#39 Organic Astrochemist

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Posted 01 December 2019 - 12:35 PM

HD 28527 and HD 28568 are another possible close binary pair, widely separated.

 

Simbad classifies HD 28527 as A6IV and I think that based on the Ca II K line at 393.4 nm the spectrum is closer to A7III than A7V.

HD 28527 with A7V.png

HD 28527 with A7III.png

 

HD 28568 is classified as F5V.

HD 28568 with F5V.png

 

Obviously with such a large difference in classification it is obvious which is the hotter star.

HD 28527 A6IV vs HD 28568 F5V.png



#40 Organic Astrochemist

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Posted 08 December 2019 - 02:28 PM

Here's a comparison of Alpha Camelopardalis taken with the Grab-n-Go system and with the Alpy.

With the Alpy 600, the lines across the spectrum are much narrower especially the C III and Hα lines, which are on the red end. 

alpha camelopardalis.png

 

With the Star Analyzer without the wedge prism those lines are greatly wider. So much so that when I took this spectrum I missed the C III line which is unmistakable with the Alpy.

alpha camel.png

 

I'm glad I have both systems. When I don't have time for the Alpy, I can always get a few spectra with the Grab-and-Go system.


Edited by Organic Astrochemist, 08 December 2019 - 03:06 PM.


#41 mwr

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Posted 18 January 2020 - 04:41 PM

 

 

I'm glad I have both systems. When I don't have time for the Alpy, I can always get a few spectra with the Grab-and-Go system.

Inspired by the grab and go concept, I have "upgraded" my MiniTrack system with a SA-100 as objective grating:

 

grab.jpg

 

First light test object was the carbon star W Orionis. 20 frames at 20 sec were obtained during a short clear sky period and were stacked:

 

W_Ori.jpg

 

This spectrum compares well to the spectrum of the carbon star RY Dra from the BAA-database (R=430) which also shows silicon dicarbide (SiC2) bands  (https://britastro.or...ment=&plot=Plot).

Indeed, good to have a system that is installed and set up rapidly for unstable weather conditions.


Edited by mwr, 19 January 2020 - 04:29 AM.



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