Sunday, August 9, 2020

Double star observations ,July 2020

 In July 2020 I observed 115 double stars.

I did not counted the reobservations.

The summary of those observations is in the tables below.

I added a color code giving an idea about the difficulty of resolving the double stars.

The results are looking  this way : 

- ten observed stars  were so-called ''subarc'' double stars ,highlighted with green

-fourteen observed double stars have a separation between one and two arc seconds = blue

-twelve observed double stars have a separation between two and three arc seconds= yellow

-nineteen observed double stars have a separation between three and ten seconds = orange

- sixty observed  double stars have a separation between ten and 164'' = no color.

The color code and summary:

Promo Queen for July was above any doubt STF 2215 with a separation of 0.44''.

Of course,this double star was not (and can't be) resolved by my 200mm F/6.16 Dobsonian.

But the seeing was good ,really good on the night of July 30.

It was at least 8 on Pickering scale ,maybe even 9 ,at least at moments.

So what I saw at STF 2215 was the smaller Airy disc of the companion overlaped and overpowered by the Airy disc of  the primary ,with at least one third of his diameter seen behind the main star.

The estimated Position Angle was ''West'' which translate in numbers as 270 degrees.

The site ''StelleDoppie'' is showing the accurate PA = 245 degrees.Not only that I'm not ashamed by my PA estimation but ,actually I'm proud of it.Just think to the extreme conditions to see and estimate anything so far bellow the theoretical resolving limit.

This is a sketch of what I saw at STF 2215 on July 30.

This are the parameters of STF 2215 in ''StelleDoppie'' :

You can see  more about STF 2215 here :

Another very interesting double star seen in July was STF 2315 with a separation of 0.6''.

Here the smaller Airy disc of the companion was less overlaped, at least half of it been visible behind the Airy disc of the primary at PA = 115 degrees ,estimated by me as 130 degs.Not very good estimation but not very bad either.

At STF 2315 I was walking very close to the Dawes limit of 0.58'' for my 200mm Newtonian.

We should keep in mind that Dawes limit aply for stars of  6mv and of equal magnitude.

Which is not the case with STF 2315 having a Delta mag = 1.2mv.

This is the  sketch of  STF 2315 in my logbook.

And here is the page of STF 2315 in StelleDoppie :