Hercules doubles, and an OH/IR star

[Ed astro]

Hi all, 

Last week Thursday/ Friday we had clear skies again in the Netherlands. The moon was almost full and it was nearly summer solstice, no good for DSO so I decided to do some double star observing. This time I picked some nice doubles in Hercules to observe with my 6” Skywatcher newton. 

Initially the transparency was excellent but seeing was poor, so I mainly focused on not too difficult to split pairs. First was alfa Herculis aka Rasalgethi. This is one of my favorite double stars in the summer sky. With a separation of 4.6” it was easy to split. The primary has a yellow- orange color, while the secondary seems slightly greenish in contrast. Of course green stars do not occur so this color must be the result of some optical illusion caused by the color and brightness contrast of the pair.

 

Rho Herculis was similar in separation to alfa, both stars were white although the secondary seemed to have a very slightly more bluish color.

About 20 arcmin south of rho Her we find another double known as STT 329. This is a fairly wide pair (about 30”) forming the shortest side of a trapezium- shaped asterism. The primary was yellow white, the secondary was too faint to see any color.

 

Delta Herculis was also an easy split. There is a large difference in brightness between the two stars (mag. 3.1 and 8.3). I did not see any noticeable color contrast in this pair.

 

By the time I was sketching kappa Herculis at around 01:00 clouds started to roll in. Still the sky around Hercules remained relatively clear. Kappa herculis was another beautiful pair with a yellow primary and an orange- yellow secondary.

 

95 Herculis was the last double star I observed that night before clouds blocked my view of the sky around Hercules. This is another beautiful contrasting pair. The components are almost equally bright; the primary is bluish, the secondary is yellowish white. 

 

At 01:30 almost the entire sky was cloudy except for a small area around Aquila. I decided to do a quick sketch of the star R Aquilae, which is one of the few OH/IR stars that is actually visible with small telescopes. OH/IR stars are a particular class of red giant stars that are surrounded by a thick shell of dust and gas expelled from their atmosphere. The “OH” part of the name refers to their unusually strong emission lines of the hydroxyl (OH) molecule at radio frequencies. In fact the OH around those stars acts like a natural “radio laser” (a MASER), amplifying radio waves at very specific frequencies. The “IR” refers to the strong IR emission from the dust around these stars. I have observed a number of OH/IR stars with radio telescopes, but at visible wavelengths most are completely obscured by their own dust clouds. R Aquilae is one of the exceptions that we can actually see, appearing as a 6th magnitude star with a pronounced orange color.

After 01:30 it was completely overcast and I went back inside to warm up and get some sleep.

Eduard

 

[AlcorAlly]

I enjoyed reading this report very much, great sketches too. Thank you for sharing. 

[lunator]

Very nice sketches, Alpha Herc is one of my favourites 😀

[josefk]

Super stuff @Ed astro . These double sessions are pretty relaxing use of the lighter nights aren't they. I love your delicate star renderings and that's interesting stuff re. R Aquilae. Cheers

  

[Emperor!Takahashi!]

My gosh, those are beautiful sketches. Really lovely... I especially love the spikes on the bright stars. It's like I'm seeing it through the eyepiece. Thanks for sharing.

[MZack]

Superb sketches. What technique do you use to create the spike effect?

[Ed astro]

4 hours ago, MZack said:

Superb sketches. What technique do you use to create the spike effect?

I use a very sharp white pencil and a ruler. Quite simple but it takes some practice. 
 

Eduard

[Fraunhoffer]

A lovely report and super sketches. Thank you.

 

[wookie1965]

Brilliant I have copied the doubles and positions to see the difference through my refractor thank you for posting.

[ian61]

Fantastic sketches, thanks for putting them up. I have decided to target the Hercules area this summer and these definitely make me more enthusiastic to do so.