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Fun with slitless spectroscopy and Praesepe

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#1 Organic Astrochemist

Organic Astrochemist

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Posted 24 April 2019 - 11:44 PM

I'm having a lot of fun with my Star Analyzer 100.

Here are some targets that I selected in SkySafari Pro that are all very high probability members of the Beehive cluster (Messier 44)

IMG_3328.jpg

Notice the central concentration.

Here's the core

IMG_3337.jpg

and here is one annotated image I took

praesepe annotated.jpg

The Balmer lines in the A-type and F-type stars clearly stand out. It was easy to identify the G and K type giants. 40 Cnc also stood out because it was as bright as the giants. The spectrum matched a A0V reference.

40 Cnc with A0V.png

I thought it was odd that this A0V was as bright as the giants and that the next closest main sequence star was at least A5V. I had "discovered" a blue straggler. Of course others had discovered this earlier, but it was news to me.

I have processed quite a few spectra, if I have time I'll post some later. This was part of the appeal of slitless spectroscopy, that I could get more spectra in less time.

Here's an outlier, 35 Cnc (G0III, compared to a G0III reference), that lies well outside the 1.2 degree circle.

35 Cnc with G0III.png

 

I wondered why some stars like Epsilon Cancri were so bright when they were labeled in SkySafari as A8V. Well it turns out that the brightest stars that we see in this cluster are giants, blue stragglers and spectroscopic binaries. Epsilon Cancri is a triple A5/A6/F0! I don't think my system is up to parsing these closely matched binaries.

 

Spectroscopy is a lot of fun and I feel like I learn and understand a lot more about what I observe.


Edited by Organic Astrochemist, 24 April 2019 - 11:47 PM.

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#2 TieDyeAstronomer

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Posted 25 April 2019 - 12:31 AM

Nice! I got my first good results with my Star Analyzer 100 + XT8 combination just the other night. It's a ton of fun.

What's causing the blur in your annotated image? It looks chromatic in origin, since it increases towards the red end of the spectrum. What telescope were you using?

Clear Skies!



#3 Organic Astrochemist

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Posted 25 April 2019 - 09:09 AM

Nice! I got my first good results with my Star Analyzer 100 + XT8 combination just the other night. It's a ton of fun.

What's causing the blur in your annotated image? It looks chromatic in origin, since it increases towards the red end of the spectrum. What telescope were you using?

Clear Skies!

What mount do you have for the XT8? Are you using a DSLR?

 

You are correct that I have a ridiculous amount of chromatic aberration. And yet I seem to be able to guess the spectral types of the stars all right. My “telescope” is a cheap 70 mm achromatic guidescope on a camera mount. It looks like this:

B0AE928A-433A-4467-BD3A-1BCE127E7FFE.jpeg

i acquire my images with darks and flats using Sharpcap. I can do 30 s subs at this focal length of 278 mm. Then I stack about 20 images with Nebulosity. Finally I process the spectra with RSpec. I can do this in real time in the field. In this case I have so many spectra that most of them I processed later.

 

At SMSW-2, Dr. David Whelan explained to me the concept of the binary main sequence, which is found above and parallel to the main sequence. Those brighter binaries are some of the main sequence stars I’m able to see with this simple setup. The binaries also have more total mass than comparable single stars and therefore have sunk to the center of the cluster where they are easy for me to view. This paper has a lot of great CMD or HRD and you can see the binary main sequence.

https://arxiv.org/pdf/1804.09378.pdf


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