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Observing double stars using EEVA techniques


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Over the last couple of evenings of clear skies but with an increasingly bright moon, I've taken to observing double stars using the camera/scope/laptop. This is definitely not the same as visual observing; part of my plan is to observe some of the fainter classes (L, T) that are outside the reach of all but the largest visual scopes. For the moment I'm finding it enjoyable and relaxing to choose potentially interesting candidates and watch the image coming in for examples of the different spectral classes.

The first night I simply selected some interesting looking cases from the charts, but last night decided to do a bit of data mining in the Washington Double Star catalogue. My selection criterion was systems with both spectral types listed, and where the spectral types were different from each other in the main class (eg G0 vs F3 was included, but G0 vs G1 wasn't), with the goal of finding some interesting colour contrasts.

For anyone using Jocular here's a data file with 3557 such pairs (just drop it into the catalogues subdirectory of your joculardata directory and it will be available on restart -- the object code in the DSO planner is 'DS').

doubles.csv

In the next post I'll start to include some observations. Feel free to add any others!

Martin

 

 

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Posted (edited)

By the way, I'm sure there are plenty of people who know a lot more about double stars and the WDS discoverer codes than I do, so please do add any relevant info or correct my mistakes.

To kick off with, here's HJ 2668 in Bootes, almost straddling the border with Virgo. This was discovered (by John Herschel?) in 1830 with a separation of 4", and the most recent observation in WDS is from 2015 which found a 10.2" separation. I chose this in part due to the almost equal magnitudes (11.9, 12.1) but without knowing anything about the spectral types (which are not listed in the WDS entry -- this precedes my selection criterion).

image.jpeg.1a5f427fc30c02890e54a4e471e8a2ad.jpeg

Edited by Martin Meredith
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From the same discoverer, and about 0.3 degree due south of HJ 2668, this is HJ 1238 in Virgo, discovered in 1828 with a 10.0" separation. The entry refers to the right-hand pair, with a most-recent (2016) separation of 14.5".

I don't have spectral types listed for these but they must be hotter than the HJ 2668 pair.

Also in the field is a much closer pair which go under the name DOO 56, discovered (as a pair) in 1913 with a separation of 3.1", which had widened slightly to 3.6" by the most recent 2015 measurement. 

image.jpeg.de3f64bca7028d8f12ddaa80b992a305.jpeg

 

Again, I don't have spectral types for these. Possibly I ought to be using shorter exposures -- its all part of the learning experience!

The WDS code for the foursome is 13403+0709

 

 

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Back to Bootes for this evenly-matched pair of 7th magnitude suns, STF 1850, discovered in 1823 by Friedrich Wilhelm Struve. This pair is both brighter (7.1/7.6) and more widely-separated (25.1", similar to its separation the time of discovery) than the earlier ones posted.

These are both A1V class stars (like Sirius), presumably a physically-related pairing. One has a B-V colour index of exactly 0 and the other a shade lower, hence the blueness.

image.jpeg.5d35e9adb76519d704cfe5c59bdc9417.jpeg

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And also from FW Struve, here's STF 1864 in Bootes. This is the naked eye Pi Boötis system consisting of a type B9 mag 4.9 blue star and a type A6 off-white mag 5.8 companion. The discovery date of 1777 presumably precedes Struve(?). The separation has declined from 7" to its current 5.4". It would be nice to see some clear air between the two but seeing on this evening was just under 4".

On this occasion I used much shorter subs, 1s, and mainly in RGB (just a single second of L)

In the WDS the mag 10.6 pale red star at position angle 164 (anticlockwise from 12 o'clock) that can be seen in the shot here at a sep of just over 2 arcmins is considered the 'C' component.

image.jpeg.0a4b0ed2f16cee479b93b0863f928585.jpeg

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Posted (edited)

Very impressive pictures - photographing doubles is quite challenging.

I have been meaning to try some "deep" double star images, using lucky imaging with my C6, but trying to capture some field stars too.

Edited by Ags
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Thanks Ags. I must take a look at your book.

Good luck with your deep images. I tried a couple of doubles that included an L-class companion without a lot of success so far. A different strategy may be needed for these since they mainly emit in the infra-red... My Lodestar picks up some energy in the near-IR. I'm not sure about the ASI 290 that I used for these.

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Posted (edited)

Here's one I'm not sure about. This is a relatively recent discovery from 1998, DEA 84. (BTW, if you're searching for these in the WDS or elsewhere, the discovery codes are all 7 characters and use multiple spaces to make up the count, so there are 2 spaces between DEA and 84)

The primary is an M0 class mag 8.1 star, hence pretty red, and the companion is a mag 14.3 class L2.5 star. The question is: have I captured it? The position angle is 211 degrees and the separation 29.2". There is a faint star at around 210 degrees (where I've placed the DEA 84 label) but it looks to be a little too far out?

[Edit] definitely not caught it! Looking on Aladin there is a label a little further in but one has to look on the PanStarrs/DR1 tab to see a dark red star in that place. No V mag is listed; the 14.3 corresponds to a K-band magnitude....

image.jpeg.a1078ef33a7c5e64bea142df3e94ee1b.jpeg

 

Edited by Martin Meredith
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Martin

Very interested to see how this line of EEVA observing works out. Certainly worth a go in colour and a smaller pixel camera - not for me with the Ultrastar. Short subs definitely give better results when ever I have tried it. Also as is obvious very steady skies work best. The frustration with so called doubles stars is are they true binaries /multiples or just optical?

The Cambridge double star atlas, second edition lists only true binary systems. I do have the Cambridge doubles in excel format and various other lists of true doubles.

You mention L and T doubles - what does the L and T mean?

I use to have an OMC 200 which on a good nights I could track down faint doubles (mag 11, using AV could sometimes get me fainter). 

Have fun with this project,

Mike

 

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Hi Mike

The L and T classes are the cooler extensions to the OBAFGKM sequence added around the turn of the millenium. At that time there was also a still cooler class (provisonally named 'Y') with no members known, but perhaps by now some have been found. Its at this point where the stars and larger planets start to overlap in temperature and chemical element abundance. T for instance contains a strong methane absorption.

I use the 2nd (2011) edition of Kaler's Stars and their spectra, an excellent and nicely technical guide to the stellar sequence.

There is almost no emission at visual wavelengths so we're relying in near-IR capabilities to pick up anything at all. I'm pretty sure I picked up an L class (not part of a double) some years back but I ought to revisit. As I recall it was fainter than 19th mag in the V or B band.

I'll continue to look at using shorter subs. The trick might be to use short subs in L only.

I've added a FWHM calculation to Jocular which so far suggests my seeing (or focus, or tracking... its all confounded) is pretty poor much of the time (worse then 4"). You'll be able to use it with previous captures to see what your seeing is like at some point.

Martin

 

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S 665 in Libra is another near equal pair. HD 133353 on the right is a mag 7.9 type K2 star with a B-V colour index of 1.25, while its companion is mag 8.8 of slighty earlier K0 type and commensurately lower B-V of 1.04. The slight difference in hue is just about visible here.

The position angle (91) and separation (25.1") has barely changed since the discovery of the system back in 1828 -- optical?

An interesting optical/physical debate: https://www.cloudynights.com/topic/495354-most-doubles-in-wds-are-optical/

image.jpeg.e95bd27c0132ed1feb4bb878f891e955.jpeg

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This field in Serpens containing STF 1987, discovered back in 1783, is a case of 2-for-1 as it also contains the fainter pair TOB 255 (disc. 1842).

Luckily for the observer a range of spectral types are on display here. The brightest star is a mag 7.3 A0 type, B-V 0.26 with a blueish tinge, and its close pale yellow companion at 10" sep is type B6, B-V 0.48. 

I don't have spectral info for the TOB 255 pair but I'd guess they're cooler K or M types. Their most recent separation estimate is 15", so not that different from STF 1987 but seemingly more so due to their being dimmer.


image.jpeg.e453c13ed492be03ceb6bcb3f8185dc0.jpeg

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Here's STFA 33 in Hercules, discovered in 1835. The pair are not particularly close (305") but their similar magnitude and contrasting colour make up for that. The blue-ish star is mag 5.9, type A1, while the yellow-orange companion is mag 6.1, type K1.

The system on WDS has 3 further components: the peachy mag 8.5 star at the top is the C component, known as ARN 15, the faint mag 10.4 star between A and B is D, and the mag 11.0 star below the D component is E (I think I've got that all right...).

image.jpeg.b724b2895e798e9ba82f8110594786ab.jpeg

The chosen stretch matters a lot when trying to pull out natural looking star colours. I tend to use small-exponent gamma for luminance since it matches the colour stretch (which is also gamma). But applying the stretch function I often use for faint galaxies shows there's much more going on in this field (including a lovely linear triple asterism):

 image.jpeg.e0ef3f7f0e227666cb47679e900ccf83.jpeg

 

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5 minutes ago, wookie1965 said:

Any SAO numbers for these the only one I can find is Sigma 1850, as I am an avid double star fan I would love to get them in my scope. 

Stelle Doppie seems to find those catalogue numbers, e.g.

https://www.stelledoppie.it/index2.php?iddoppia=132674

https://www.stelledoppie.it/index2.php?iddoppia=61657

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20 hours ago, wookie1965 said:

Any SAO numbers for these the only one I can find is Sigma 1850, as I am an avid double star fan I would love to get them in my scope. 

Try this version. A zero in the SAO column indicates no SAO star found within 0.01 of a degree in both RA and Dec. There are SAO numbers for about half of the 3000 or so in my list; ideally these will correspond to the main DS designations.

doubles.csv

 

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3 hours ago, Martin Meredith said:

Try this version. A zero in the SAO column indicates no SAO star found within 0.01 of a degree in both RA and Dec. There are SAO numbers for about half of the 3000 or so in my list; ideally these will correspond to the main DS designations.

doubles.csv 355.17 kB · 0 downloads

 

Much appreciated thank you.

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