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WRAK
scholastic sledgehammer


Reged: 02/18/12

Missing HO105?
      #5437592 - 09/24/12 07:47 AM

Last night I had despite the additional light pollution due to half moon and some clouds the opportunity for doing a small session with about 10 double stars in the single digit separation range in the Vul constellation with seeing quality between dancing and speckling diffraction pattern.
Last target was HO105 (HIP 95214, WDS19222+1640) RA 19°22'13" Dec 16°39'45". With 2.9" sep and +8.9/9.9mag a rather easy one compared with for example 1.6" +9.1/10mag STF2488 or 1.6" +9/10.2mag STF2482 in the same session - but I could not split it.
HO105 should be a valid WDS position as 16 observations are mentioned. But the position at the end of a curved line of stars seems to exclude any location problems ...?
If anybody could do a counter check I would appreciate it very much.
Thanks Wilfried


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Missing HO105? new [Re: WRAK]
      #5438359 - 09/24/12 03:56 PM

Correction: Constellation is Sagitta.
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Missing HO105? new [Re: WRAK]
      #5438770 - 09/24/12 08:53 PM

I wish I'd seen your post a few hours earlier, Wilfried - I read it after I came inside from several hours observing. So I could have checked last night. If the weather stays good tonight I'll have a look - as you say, it shouldn't be too hard to see, despite moonlight - unless it's your local light pollution plus moonlight that makes it hard for you to see.

A quick check of the position on the DSS plate shows a bright (9th mag) star there. But the plate won't separate a pair that bright(relative to the ~20th mag limit of the DSS)and close.

The WDS gives modern magnitudes for the pair, so it isn't likely to be another J double photometry problem. And the separation hasn't changed much over 100+ years.


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C_Moon
Pooh-Bah
*****

Reged: 10/23/09

Loc: Beneath the arms of Cassiopeia
Re: Missing HO105? new [Re: fred1871]
      #5438876 - 09/24/12 10:15 PM

Wilfried,

I just observed HO105 now with my 8" Dob. it was somewhat difficult to split due to the faintness of the companion.

I have conflicting info from the s/w Skytools3. The 'object information' dialog lists the companion at 11.2 mag, which seems consistent with my observation. If I hover over the companion after zooming in quite a bit, the companion magnitude is reported as 9.9. Both sources list the primary as mag 8.7.

Seeing here tonight is above average. I went up to a magnifcation of 325x to make the observation. The companion tended to flick in and out, but that may have been due to my not being properly dark adapted as it tended to remain visible more than not towards the end of my observation period.

I am viewing from suburban skies in less than ideal conditions right now due to extraneous lighting from my home and others nearby. I will try again later when lights are off (if I can stay awake).

Edited by C_Moon (09/24/12 10:16 PM)


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Missing HO105? new [Re: C_Moon]
      #5439106 - 09/25/12 02:10 AM

Skytools should be getting its magnitudes from the WDS or some reliable photometry catalog.

The WDS currently lists the magnitudes as 8.91 and 9.94 - double decimals indicate modern photometry, so I'd expect them to be very close to right unless there's been a typo.

The 1996 WDS lists 8.9 and 10.7 (single decimal magnitudes) - the basis for these would require full information on where the secondary magnitude came from. Given the single decimal, it could be based on visual estimates, some of them long ago. The first measure listed is from 1883.

I'll see what I think if tonight stays cloud free - despite too much moonlight for easy observing of fainter doubles.


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C_Moon
Pooh-Bah
*****

Reged: 10/23/09

Loc: Beneath the arms of Cassiopeia
Re: Missing HO105? new [Re: fred1871]
      #5439373 - 09/25/12 09:25 AM

The year listed with the 11.2 mag number is 2001.

I do know that the s/w developer has put a lot of effort in the star catalog, more than just linking to a database. In fact, it's one of the selling points of skytools3, the fact that it uses integrated databases from multiple sources. See explanation here (be sure to see double star specific info at the bottom of the page).

I'll be interested to hear about your observation. Unfortunately, I did not get another chance last night when the lights went out.


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Missing HO105? new [Re: C_Moon]
      #5439735 - 09/25/12 12:49 PM

Begins to get interesting - I was puzzled because I could split in the same session a double with 1.6" sep +9/10.2mag and this is certainly more of a challenge than a double with 2.9" sep and +8.9/9.9mag.
+11.2mag for the companion would explain why I could not see it with my 140mm refractor due to light pollution and splitting it with a 200mm reflector with x325 with some difficulties points also the same direction.
There are some clouds on the sky now but I hope I can have a look myself again this night.
Very interesting is also that Hipparco lists this double with +10.9mag for the companion and Hipparco very often lists the double star components a little bit brighter than WDS.
Wilfried


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Missing HO105? new [Re: WRAK]
      #5440324 - 09/25/12 05:32 PM

Cirrus clouds in combination with the half mood made the observation rather difficult. Seeing test with Eps Lyr rather good - x75 hourglass for both doubles and with x98 clear split. On the way to HO105 I checked STF2488 – 1.6"DS +9.1/10mag: x210 split. Then STF2482 – 1.6"DS +9/10.2mag: no split. Then STF2484 – 2.1"DS +7.9/9.5mag: a bit difficult, x210 split for fractions of seconds. Finally HO105 – 2.9"DS +8.9/9.9mag: Nothing again. Despite the not so perfect conditions I am now quite sure that the companion of HO105 is certainly significantly fainter than +9.9mag. With delta mag of 1 and separation of 2.9" the required aperture for a split should be no more than 40mm.
Wilfried


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Missing HO105? new [Re: WRAK]
      #5444711 - 09/28/12 06:15 AM

Things get even more interesting as Brian Mason (WDS catalogue guard) insists that +9.9mag for the companion is correct because this is a value out of the Tycho catalogue.
As according to my observations +9.9mag is with great probability wrong assuming that 2.9" separation is correct I am somewhat puzzled - with this values an aperture of about 50mm should be sufficient to split this double.
Fred, Paul - it would be great if you could this give another try (may be better with less moon light pollution as now) and maybe somebody else with better equipment as mine in terms of aperture and means of measuring separation, position and estimation of brightness could join us.
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Missing HO105? new [Re: WRAK]
      #5444913 - 09/28/12 10:02 AM

Wilfried, it's on my list to try after the Full Moon - the two nights after I commented turned cloudy here, tonight is raining, but clear weather is supposed to return in the coming week.

My site has moderate, not heavy, light pollution - so I'll try first with the 140mm refractor; if that doesn't show it, I can set up the 235mm SCT, that goes about 1 magnitude deeper.

Interesting that Brian Mason stands by the 9.9 mag listing. After your experience observing this and other pairs for comparison, I was wondering if it was a mistaken entry (meant for another star) and if the old listing - 10.7 - was correct. We'll see (I hope).

If the currently listed magnitudes are correct, then, given the fairly close separation and moderate delta-m, it won't be a pair for the 60-80mm brigade unless they're under very dark skies. Stars near each other are not like stars in a broad field and well separated.


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Missing HO105? new [Re: WRAK]
      #5455741 - 10/04/12 09:13 PM

Wilfried, this one is a puzzle. I've looked at it now with 140mm refractor and 235mm SCT, but have had the problem that the seeing was unsteady.

It's certainly more difficult than the numbers suggest - on the same night I could split pairs that should be similarly difficult, without trouble. The refractor did as well as the larger SCT, the latter being seeing-limited (bigger, and CO).

HO 105 did show as a fuzzy pairing, with occasional glimpses of the secondary as a point within the flared elongated image. It was difficult to evaluate the difference in magnitude between the stars because of the seeing - some moments it looked as if there was about 1 magnitude difference, other moments the secondary seemed fainter.

So, no definitive result as yet. I'll try again, and hope for steadier conditions. But my impression thus far is that the pair is certainly more difficult than I'd expect. I tried various magnifications with both telescopes - 124x, 180x, 235x with the SCT; 100x, 160x, 230x with the refractor.

A month ago, SCJ 25 in Aquila (mags 8.6 and 9.6, at 2.7") was easy in the refractor, the companion showing at 100x. Likewise, STF 2569 in Sagitta (mags 8.4, 9.1 at 2.1") was not difficult - just double at 105x, easy at 167x, again with the refractor (this time using a 2.5x Powermate, which gives a different magnification series from using the telescope "straight"). These were in better seeing conditions. However, same night as HO 105, I could see STF 2651 (mags 8.5, 8.5 at 1.0") as two photocentres in the flared light at 250x and 285x (refractor again), after it looked elongated but not separated at 160x in the flarey, fuzzy seeing. So 'not bright' and close was possible.

HO 105 is past my meridian by the time it gets properly dark here, but is still around 36-37 degrees altitude when I've looked at it.

To be continued ...


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Missing HO105? new [Re: fred1871]
      #5456853 - 10/05/12 04:51 PM

Fred, I hope for a clear night next week as HO105 is with nearly 45° altitude for me still high enough for good seeing so I can try again - but as you observed it seems to be more difficult to split as it should be according to the numbers.
Meanwhile I checked Tycho and found only TYC1600-00055-1 for the primary and Tycho does not list this object as binary - I will have to ask Brían to which Tycho number he refers. The DSS image does not show any hint for a double - one would expect the disk of the star should at least be elongated for a double with delta-m of only 1. Finally last satisfying observation was 2001 - for such an easy target already a long time ago.
I don't see any reason why it should be more difficult to split a 2.9" double +8.9/9.9mag compared with a 1.6" +9.1/10mag as for example STF2488 in the same seeing situation so something is very questionable here


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Missing HO105? new [Re: WRAK]
      #5466318 - 10/12/12 04:08 AM

Yesterday bright sky during the day but clouds in the evening - so I did no longer hope for a clear night but I checked the sky again about 22 pm: clouds were gone, naked eye visibility limit about +3mag, 140mm refractor telescope visibility limit better than +10.7mag (I could see TYC1600-00911-1 +10.72 mag near HO105 easily), transparency not this good but seeing quite good with stable star discs but dancing diffraction rings.
I could again split nearby STF2488 and STF2482 - both fainter and closer doubles as HO105 with similar delta mag. Interestingly I had initially some troubles with nearby 2.1" STF2484 +7.9/9.5mag but I could split this finally also clearly (maybe due to the greater delta mag or some seeing issue for several minutes - but it could be also very well that here also the companion is fainter as listed).
Then again HO105 - not even a hint of a double in form of an elongation or similar, nothing to say of a split. Again: In combination with the other observation results it is impossible that HO105 is a 2.9" +8.9/9.9mag - the secondary is certainly much fainter.
Wilfried


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Missing HO105? new [Re: WRAK]
      #5471635 - 10/15/12 01:57 PM

Brian Mason (WDS) wrote that there may be wavelength dependent uncertainity concerning the magnitude of the secondary. The last measurements were from the AAVSO Photometric All-Sky Survey with two different results: +8.829/9.944mag and +9.342/10.526mag. The latter would better match my observations - and while I could clearly see the +10.5mag stars nearby HO105 it is another task to see a rather close secondary this "faint" (due to light pollution the magnitude limit of my scope is around +11).
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Missing HO105? new [Re: WRAK]
      #5472164 - 10/15/12 07:25 PM

That's very useful information, Wilfried - I agree, the dimmer magnitudes do seem a much better fit for our observations of this double.

Do we have information on what wavelength band/filters were used for obtaining these magnitudes?

I had begun to wonder about this possibility, though it seemed unlikely for such a long-known pair. But recently, making up an observing list for Taurus, I came across some doubles in the WDS with bright magnitudes, but which had no corresponding star marked in atlases I have. Following up, it appears these magnitudes are somewhere in the IR band, so the stars would be extremely dim or even invisible in V-band photometry, and not accessible to visual observers.

The pairs in question had a 'K' code in the WDS notes column, indicating "summary line gives K-band or other infrared (>1 micron) magnitudes".

Not every pair has an indication of the waveband associated with its magnitudes. Most should be V magnitudes, but I suspect some are old 'B' or photographic (blue) magnitudes. And some, at least for secondary stars, might still be old eye-estimates, if Hipparcos/Tycho didn't get data.

Anyway, it looks like a plausible solution to the HO 105 problem.


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Missing HO105? new [Re: fred1871]
      #5472708 - 10/16/12 03:40 AM

There is some explanation concerning filters to find here http://www.aavso.org/apass but this is over my head.
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Missing HO105? new [Re: WRAK]
      #5474452 - 10/17/12 03:23 AM

Thanks, Wilfried, for the web reference - I'd forgotten about the AAVSO photometry megastudy. Astonishing number of stars now in the database. It looks very useful, especially for checking stars a below Tycho's limit.

And with the photometry being in multiple wavebands that's going to be useful too, even though for a lot of purposes V (visual) and B (photographic blue) magnitudes are sufficient.


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Missing HO105? new [Re: WRAK]
      #5475733 - 10/17/12 07:33 PM

Looking at the numbers you've quoted, Wilfried, and given that the spectral type of the 'A' star in HO 105 is B9, the two sets of numbers would refer most likely to the B-magnitudes (brighter for this spectral type)~8.8 and ~9.44, and V-magnitudes (roughly how we see) of ~9.34 and ~10.53.

Taking the latter as accurate, it's little wonder the pair is tougher than expected, especially with only 140mm telescopes, and in your case with extra-high light pollution.

I was observing last night, though a bit late in the evening for HO 105 to be at a good altitude, and again noticed how much harder it is to see a mag 10.5 star very close to a brighter one, than a mag 11.5 by itself. That's with my 140mm refractor.

After trying some very tough doubles for that aperture, in part due to dim companions, I think I'll set up the 235mm SCT for my next night's observing. About a 1-magnitude gain, and that helps a lot.


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Missing HO105? new [Re: fred1871]
      #5476858 - 10/18/12 12:24 PM

Paul reported a split with his 200mm DOB - the required magnification of x325 sounds a bit strange. This aperture would have a refractor equivalent of 133mm meaning we should be able to split it with our 140mm scopes but I go never above x280 because the image then gets rather bad.
Fred, I hope you are lucky with your 235mm reflector and can compare HO105 with STF2488 and STF2482 regarding the faintness of the companions. Its a pity that the advertised data on this double is so uncertain because this would be a good example for adapting the RoT to fainter doubles.
Wilfried


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Missing HO105? new [Re: WRAK]
      #5486044 - 10/23/12 09:04 PM

I tried HO 105 again a few nights ago - it's now getting into a less accessible part of my sky when it first becomes dark, and at lower altitude, so I won't go back to it again this season.

Seeing was only fair-plus, I used the 235mm SCT - a definite fairly uneven little double, I'd estimate the new AAVSO magnitudes, around 9.3 and 10.5, are a good match for what I saw. It was not easy, given mediocre seeing - but clearly two stars visible at medium powers, 196x and 235x. Higher power, 285x, didn't improve the view. Lower power, 125x, only suggested a double without clear resolution.

So I'd say it's another example of older listed magnitudes being misleading. As we've found, this is common with 'J' doubles. I've looked at a number of them now - some appear about as expected from the quoted magnitudes, others are clearly fainter.


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