Observations - 13/10/23

Finally – a clear night! Okay - there was an 18 km/h wind blowing. But I’m quite often sheltered from such. I set up my William Optics 158mm f/7 apochromatic refractor on its Berlebach Planet altazimuth mount in my back garden and started observing at 9pm on a Friday the 13th of October 2023. But no superstition here. The only thing I had to watch for was the cat poo in one corner of the garden. The air temperature was 8˚ Celsius. I stopped this observing session at 11pm. 

I was in the mood for seeking out a faint carbon star. That was because there was no Moon. It’s fair enough to say that not many will be keen to observe this particular carbon: V720 Cas. But you never know!  

So after observing some popular double stars (Polaris, Schedar and Achird) I moved the scope to Cassiopeia as she poses on her throne over my house. Good and high alright, but nowhere near my zenith thankfully. Very near Schedar, there is a nice pair of bright stars, and I settled on one of them - the 3.7 magnitude Zeta Cassiopeiae. 
I then starhopped my way downwards until I arrived at a K7 slightly variable star called V754 Cas that has a rough magnitude of 8.8. This star’s almond brown colour was clearly evident at 40x and 112x. I had never observed this star before. 
I zigzagged my way down to a 9.5 magnitude star called TYC 3655 854 2, and I started looking for my carbon star V720 Cassiopeiae. It’s extraordinary what information we can discover on the website www.aavso.org . V720 Cas is a Mira variable star. It can vary between magnitudes, according to my Guide 9 DVD, from 9.6 to 12.5. So it should be always visible with my scope – except other sources suggest it can become far fainter, even as faint as magnitude +14. 
I have estimated its current magnitude as +12 on www.aavso.org . There is an 11.9 magnitude white star called 3UC287-013871 extremely close to the carbon star. For those interested, V720 Cassiopeiae’s Right Ascension is: 00 hours 45 minutes 07.1 seconds. Its declination is: 53 degrees 26 minutes 48 seconds. 
I could see both stars with my Nagler 5mm (225x) eyepiece. But the carbon star’s good and rich orange hue came through very well at 280x with my William Optics 4mm. I found it to be a real charmer! 
The famous Simbad website gives it a spectral class of C rich, followed by the letter D. I have never come across C rich before. And what the D stands for I don’t know. I have also been unable to find out a rough distance from our Earth to V720 Cas. If anyone could help me out on that one, thank you! I’m sure it’s the case the distance is very great as it is a Mira variable.   
In closing, V720 Cas is the 25th carbon star in Cassiopeia I have observed, and my 115th carbon overall.     

Thank you for reading this report. 
Comments will be very welcome. 

Clear skies from Aubrey. 

      

Hello everyone again.

Subsequently I had seriously good replies to my questions regarding the distance of V720 Cassiopeiae.
I also found out what the letter D stands for on the Simbad website.
Its distance is somewhere in region of 2000 parsecs. That's over 6500 light years!
The letter D refers to Spectral type.
Spectral type is made of 3 parts:
the spectral type, which is made of a temperature class, eventually a luminosity class (roman number) and/or spectral peculiarities;
a quality letter: A=best quality→E=worst quality, ~ =unknown quality
Therefore the "D" is one stage above E.

Clear skies from Aubrey.

Hello Aubrey,

Very many thanks for sharing your observational report with us...and what a goodie it is!

Congratulations on reaching carbon star number 115...that's a great achievement, and your description of its colour made me think what must a carbon star look like if it was our sun.

Lovely post, and clear skies to you.

Darren.

BTW, many thanks for clarifying what a 'D' spectral type means.

Thank you, Darren, for your most kind thoughts!
It's very true to state that carbon stars are exceptionally rare in the heavens above )in our galaxy).
Another extraordinary fact is that carbon stars are considerably cooler that our Sun - somewhere between 2000 and 3000 Kelvin. Whereas Sol is of 5772 Kelvin.
So we would be in trouble if the Earth was orbiting around a carbon star. Our Earth will be an extremely cold planet - and all the other planets for that matter too. These facts make me giggle.
I thank you for raising that particular issue, Darren.

Best regards to everyone from Aubrey.

Hi Aubrey,

That's a good point about the temperature difference...never thought of it like that.

Clear skies,

Darren.