Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Observations of Close Doubles - Expanded List

  • Please log in to reply
7 replies to this topic

#1 Rustler46

Rustler46

    Viking 1

  • -----
  • topic starter
  • Posts: 751
  • Joined: 10 Feb 2018
  • Loc: Coos Bay, Oregon

Posted 12 February 2019 - 04:16 AM

Like for many amateurs the winter weather in my location on the Oregon coast has been very poor recently. At such times with cloudy nights I enjoy researching resources on the internet or in SkySafari. It is also interesting to examine records of past observations of different celestial targets as recorded in my astronomical observations spreadsheet.

 

This Excel spreadsheet is set up so that the entire 3600+ list of observations can be sorted by any column heading, the most useful being Date or Object. Sorting by the Object column displays all observations of a particular object for all dates. To facilitate examining the 1100+ double star observations I edited each double star observation note to begin with the words "Double star". So when the list was sorted by Observation, all the double stars were grouped together. Then all the double star observations with separations of less than two arc-seconds separation were color coded with the Object cell filled with red. When I then sorted all objects by color, the closest doubles were at the top of the list shown in red. These observations were copied over to a separate Close Doubles sheet, part of the overall spreadsheet. Other sheets in the spreadsheet are: Observations, Instruments, Abbreviations, Sites & Observatories and Drawings.

 

I was interested in examining observations of doubles stars that would be up against the theoretical resolution limit, either the Dawes- or Raleigh-limit for the aperture being used. One problem encountered was correcting the recorded component magnitudes and separations. Often what had been originally recorded in the spreadsheet was from a Sky and Telescope article, Norton's Star Atlas, Burnham’s Celestial Handbook or other old published reference. For the closest doubles the components are often binaries with appreciable change in separation depending on the date of the observation. So for all close doubles I corrected the recorded brightness and separations using Stelle Doppie for the date of observation. In almost all cases this wasn't too hard, using the original observation date and the Stelle Doppie published period and apparent orbit. Also the spreadsheet allowed for comparing the observed separation with the Dawes or Raleigh resolution limits. This was displayed as a computed ratio of observed separation to limit (Dawes or Raleigh). This is shown in the screen shot below with the ratios columns highlighted in color. 

 

 Close Doubles-3.jpg

 

This shows 35 double star observations with the smallest resolution limit ratios. The entire list of sub 2 arc-second separations contains some 85 observations. From these it could be seen that for the larger apertures (10- and 11-inch) there were none that came up against the resolution limit for that aperture. Only for my home-made 8-inch Newtonian and the little AT115EDT refractor were there observations that met or exceeded the limit. I suspect that the seeing wasn't good enough to allow the larger apertures to resolve at the limit. 

 

When I added another sheet to contain the close doubles, I had to re-learn how to do the data sorts (by column headings). Also it was handy to have the column headings remain visible at the top when scrolling down then list. These two embellishments were made using the Data Filter and Windows Freeze Panes menu items. It was important to save the entire spreadsheet before making these changes. That way if the something bad happened that scrambled the data, I could just close the spreadsheet without saving the changes. 

 

The red triangles in the Date column indicate a comment attached to that date, which records observing site and observing conditions like seeing & light pollution. While there could be some errors in my correcting the separations to the date of observation, I hope you enjoy perusing these close double star observations. Any comments or suggestions would be appreciated.


Edited by Rustler46, 12 February 2019 - 09:16 PM.

  • nirvanix likes this

#2 fred1871

fred1871

    Apollo

  • -----
  • Posts: 1377
  • Joined: 22 Mar 2009
  • Loc: Australia

Posted 12 February 2019 - 09:19 PM

Russ, looking at the "Close Double Stars" listing, I can see a variety of issues. Zeta Bootis, for example, has the much reduced separation of a few years ago (0.54") but the description is from 1967 when the observation "easy" was made. Nowadays it's even closer than 0.54", and in a few years will hit periastron which is likely below 0.1".

 

4 Aquarii with a separation of 0.9" is described as seen with 78x, which I doubt was enough power for the eye to see two stars. The oft-quoted 60" apparent separation for the eye seems only to occur in laboratory experiments, or with people of very exceptional eyesight outside the lab - usually, typical eyesight requires somewhere in the 120" to 180", as magnified,to see separation.

 

The dates listed. How about putting these in scientific order - year, month, day, instead of American common-use agricultural form with the month first - very useful for farmers, who know the month (season) is what matters most. Science order preserves the American preference for month before day, so it's not too scary a jump. laugh.gif

 

I could add other items, but enuff for now. I will add that it might be of interest to analyse your data points, assuming there are enough of them that are 'near-limit' observations, to (a) confirm or otherwise the Dawes Limit for near-equal stars, and (b) add to the attempt to work out limits for doubles with significant delta-m : say 2 mags to 4 mags brightness difference. Dawes (a pragmatically derived criterion) doesn't fit for that, Rayleigh is the more useful notion being based on the wave nature of light and the diffraction image with disc and rings.

 

If the full spreadsheet is similar to the short list you've shown us, it's likely of interest mostly for data analysis of particular types of doubles in relation to aperture/magnification/telescope type. CO and its size make a difference with unequal pairs; only a very small difference with equal pairs.

 

That's my impression at the moment, and thoughts on possible usefulness of the listing, perhaps after a tidy-up of those details that have strayed somewhat.



#3 Rustler46

Rustler46

    Viking 1

  • -----
  • topic starter
  • Posts: 751
  • Joined: 10 Feb 2018
  • Loc: Coos Bay, Oregon

Posted 13 February 2019 - 03:15 AM

Russ, looking at the "Close Double Stars" listing, I can see a variety of issues. Zeta Bootis, for example, has the much reduced separation of a few years ago (0.54") but the description is from 1967 when the observation "easy" was made. Nowadays it's even closer than 0.54", and in a few years will hit periastron which is likely below 0.1".

 

4 Aquarii with a separation of 0.9" is described as seen with 78x, which I doubt was enough power for the eye to see two stars. The oft-quoted 60" apparent separation for the eye seems only to occur in laboratory experiments, or with people of very exceptional eyesight outside the lab - usually, typical eyesight requires somewhere in the 120" to 180", as magnified,to see separation.

 

The dates listed. How about putting these in scientific order - year, month, day, instead of American common-use agricultural form with the month first - very useful for farmers, who know the month (season) is what matters most. Science order preserves the American preference for month before day, so it's not too scary a jump. laugh.gif

 

I could add other items, but enuff for now. I will add that it might be of interest to analyse your data points, assuming there are enough of them that are 'near-limit' observations, to (a) confirm or otherwise the Dawes Limit for near-equal stars, and (b) add to the attempt to work out limits for doubles with significant delta-m : say 2 mags to 4 mags brightness difference. Dawes (a pragmatically derived criterion) doesn't fit for that, Rayleigh is the more useful notion being based on the wave nature of light and the diffraction image with disc and rings.

 

If the full spreadsheet is similar to the short list you've shown us, it's likely of interest mostly for data analysis of particular types of doubles in relation to aperture/magnification/telescope type. CO and its size make a difference with unequal pairs; only a very small difference with equal pairs.

 

That's my impression at the moment, and thoughts on possible usefulness of the listing, perhaps after a tidy-up of those details that have strayed somewhat.

Hi Fred,

 

Thanks for your comments and suggestions. I’ll try responding to each point you’ve made:

 

Zeta Bootis was indeed very tight in 1967. On the night of the observation, seeing was described as very good to poor. The description of the image composed of multiple double stars jumping in the field attests to the tenuous, variable state of seeing. My original written record gives the separation as 1.1 arc-seconds. So I had another look at the Stelle Doppie graph of Zeta's orbit. As can be seen the graph has some obvious issues. But I re-measured the separation for the year 2093, which is just 1967.7 + 125.24 years (the double's period). It appears that I made a mistake in measuring its separation in 1967.7 as 0.54 arc-seconds. It now looks to be at least twice that, perhaps 1.2 arc-second, which matches my written record. Do you have access to a record for Zeta's separation in 1967.7? If it was in fact 1.2 arc-second, under good seeing conditions I might have thought it was easy. Anyway if this wider separation for 1967 is correct, then it no longer is as close to the Dawes limit as I had presented. I also have another observation of Zeta Bootis much later in 2003 with a 10-inch reflector. On that occasion there was “no sign of duplicity”, with “two diffraction rings” attesting to excellent seeing. Of course this date is much closer to periastron. 

 

So considering these factors, that 1967 observation can be removed from near the top of the Close Doubles sheet. At least it will move down the list into the area of 2.0-Dawes ratio.

 

As for 4 Aquarii there are a couple of possibilities as to why it was observed at 78X. First I could have exceptional eyesight. smile.gif A more likely cause would be I just neglected to record that magnification had been increased. Such would not be unexpected, since at that time I was still recording observations with ballpoint pen on paper. It was only somewhat later that I began using a voice recorder to enable much more verbose observations that capture progressions in magnification.

 

As for that date format, I agree that YY/MM/DD makes more sense. That is an interesting observation about the American farmer’s view of dates. At first I thought this would be easy to fix. But surprisingly it took a bit of work to get the format adjusted.

 

When I attempted to reformat those cells for a different date format, I discovered that MicroSoft Excel 2011 didn’t appear to offer a year-first format. That would be strange indeed. Then I tried changing the language selection in the date format window to another version of English. Jamaican-English was no help, offering only a 4-digit year-first format. I wanted the year to be just 2 digits to make for a narrow column width. But for Canadian-English the concise date format was offered. So the adjustment has been made. While the farmer in me wants to see month first, the astronomer appreciates seeing the year first.

 

As for analyzing these observations I don’t know if there are enough close-to-limit observations to make it worthwhile. As can be seen in the attached corrected screenshot, there are only two data points for Dawes or better. For 1.2-Dawes there are 5 points, 1.3- to 1.4-Dawes has 5 points, and 1.5- to 1.9-Dawes has 21 data points. And for all of these there are differing delta-magnitudes. But maybe a simple table or graph would be informative, even with few data points. I don’t know if the 85 entries for 2 arc-seconds or less would be of much use. If I were to try analyzing that larger list, the following would of course be useful: 

  • Separation
  • Delta-magnitude
  • Aperture

What would be other useful parameters to include? Would it be useful to include % central obstruction? Any other suggestions – perhaps going to wider separations? I could easily add columns to include additional items. Then I would need to read up on how to initiate the analysis that Excel is capable of doing.

 

Anyway here is the corrected listing of my close double observations, with another entry at 1.8-Dawes ratio (Xi Scorpii, ξ ):

 

 Close Doubles-6.jpg

 

Thanks for your comments, Fred. I always appreciate what you are able to share with us. If you have noted other issues in these observations, I’d like to see what they are, so correction or explanation can be pursued.


Edited by Rustler46, 13 February 2019 - 04:12 AM.


#4 fred1871

fred1871

    Apollo

  • -----
  • Posts: 1377
  • Joined: 22 Mar 2009
  • Loc: Australia

Posted 14 February 2019 - 03:12 AM

Russ, for the moment I'll just provide some data on Zeta Bootis, and thoughts about it. More on other matters later.

 

Zeta Bootis was near its maximum separation back in 1967 when you made notes on it: the separation at the time was around 1.1", maybe just over that. So for a 20cm Newtonian that's not a difficult pair, with near-equal stars. In recent years the separation has been closing down fairly quickly, so in 2003 the separation was 0.70", based on speckle measures in that period. By 2008 that was reduced to 0.60", in 2012 to 0.50", and in 2014 about 0.44".

 

The pair is heading for periastron, which will be an exceedingly close pass of the stars, and the first time (given the 125 year period) that the sequence of closeness can be measured with high accuracy using large telescopes (4-metre class) and speckle interferometry. This should enable an improved orbit to be calculated, as happened with gamma Virginis when it went through periastron last decade, again the first time with modern techniques of measuring, though Gamme Vir doesn't get as close as Zeta Bootis is expected to be.

 

The ephemeris given by USNO in the 6th Orbit Catalogue takes us to a suggested separation of 0.246" for the year 2020.0.  That's based on the best current orbit calculation. Using the numbers for that orbit, software I used gave a minimum separation roughly in 2024, around 0.02". I expect the real numbers to vary somewhat from an ephemeris based on the current orbit calculation.

 

At present, separation is around 0.30".

 

A few months ago, after working through the numbers on Zeta Bootis, and noting a lack of recent published measures, I contacted Brian Mason at USNO suggesting a more concentrated series of measures of Zeta Boo, starting now, and continuing through the periastron period so as to get a much better orbit for this bright binary. His response was positive, and he said he was aware of the matter, and that some preliminary work was underway. Given that, I expect that by the mid-2020s the orbit calculation (and other aspects of this system) will be better known.  

 

Meanwhile, this pair is a disappearing object for smaller scopes and even the medium ones over the next few years. I expect that some folk with larger amateur scopes can show it double this year, and 25cm should still indicate elongation. It will return to 0.30" about 2027 (if the current orbit fits for what will happen), or before or after that if it doesn't. And by the 2030s be more accessible to medium apertures for amateur observers. Back to 1.0" or more? - not in my lifetime.


  • Rustler46 likes this

#5 Rustler46

Rustler46

    Viking 1

  • -----
  • topic starter
  • Posts: 751
  • Joined: 10 Feb 2018
  • Loc: Coos Bay, Oregon

Posted 14 February 2019 - 03:55 AM

Russ, for the moment I'll just provide some data on Zeta Bootis, and thoughts about it. More on other matters later.

 

Zeta Bootis was near its maximum separation back in 1967 when you made notes on it: the separation at the time was around 1.1", maybe just over that. So for a 20cm Newtonian that's not a difficult pair, with near-equal stars. In recent years the separation has been closing down fairly quickly, so in 2003 the separation was 0.70", based on speckle measures in that period. By 2008 that was reduced to 0.60", in 2012 to 0.50", and in 2014 about 0.44".

 

The pair is heading for periastron, which will be an exceedingly close pass of the stars, and the first time (given the 125 year period) that the sequence of closeness can be measured with high accuracy using large telescopes (4-metre class) and speckle interferometry. This should enable an improved orbit to be calculated, as happened with gamma Virginis when it went through periastron last decade, again the first time with modern techniques of measuring, though Gamme Vir doesn't get as close as Zeta Bootis is expected to be.

 

The ephemeris given by USNO in the 6th Orbit Catalogue takes us to a suggested separation of 0.246" for the year 2020.0.  That's based on the best current orbit calculation. Using the numbers for that orbit, software I used gave a minimum separation roughly in 2024, around 0.02". I expect the real numbers to vary somewhat from an ephemeris based on the current orbit calculation.

 

At present, separation is around 0.30".

 

A few months ago, after working through the numbers on Zeta Bootis, and noting a lack of recent published measures, I contacted Brian Mason at USNO suggesting a more concentrated series of measures of Zeta Boo, starting now, and continuing through the periastron period so as to get a much better orbit for this bright binary. His response was positive, and he said he was aware of the matter, and that some preliminary work was underway. Given that, I expect that by the mid-2020s the orbit calculation (and other aspects of this system) will be better known.  

 

Meanwhile, this pair is a disappearing object for smaller scopes and even the medium ones over the next few years. I expect that some folk with larger amateur scopes can show it double this year, and 25cm should still indicate elongation. It will return to 0.30" about 2027 (if the current orbit fits for what will happen), or before or after that if it doesn't. And by the 2030s be more accessible to medium apertures for amateur observers. Back to 1.0" or more? - not in my lifetime.

Hi Fred,

 

Fascinating information you have provided on Zeta Bootis! I'll use 1.1 arc-seconds for my 1967 observation and add that back into the list of close double observations. That will put it at 1.9 ratio with Dawes. 

 

Thanks so much for taking the time to research this pair and respond. Looking forward to anything further you might have regarding this.

 

All the Best, 

Russ


Edited by Rustler46, 14 February 2019 - 03:56 AM.


#6 Nucleophile

Nucleophile

    Messenger

  • *****
  • Posts: 456
  • Joined: 24 May 2013
  • Loc: Austin, TX USA

Posted 14 February 2019 - 07:02 AM

Russ,

 

Revisiting this thread from last year shows how difficult this object has become to observe; I have not had a chance to view it this year.

 

https://www.cloudyni...s-a-tough-test/

 

-Mark M


Edited by Nucleophile, 14 February 2019 - 07:06 AM.

  • Rustler46 likes this

#7 Rustler46

Rustler46

    Viking 1

  • -----
  • topic starter
  • Posts: 751
  • Joined: 10 Feb 2018
  • Loc: Coos Bay, Oregon

Posted 14 February 2019 - 04:22 PM

Russ,

 

Revisiting this thread from last year shows how difficult this object has become to observe; I have not had a chance to view it this year.

 

https://www.cloudyni...s-a-tough-test/

 

-Mark M

Thanks for the reminder, Mark. The discussions on that earlier thread were most informative. This double is quickly retreating into the realm explored only with larger apertures and excellent seeing.

 

Of course it is one thing to be able to detect a close separation. But meaningful accurate measurements of such close pairs will require much larger apertures and special techniques, especially as this one passes periastron. For the rest of us there are plenty of other interesting close pairs to hone our observing skills and test the quality of our optics.


Edited by Rustler46, 14 February 2019 - 04:23 PM.


#8 nirvanix

nirvanix

    Vanguard

  • -----
  • Posts: 2004
  • Joined: 07 Jun 2007
  • Loc: Medicine Hat, AB

Posted 19 February 2019 - 04:28 PM

As per your list I put the splits to eta Gem last night under moderately good seeing. I got A as an orange star and B looked whitish.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics