STF450 companion variable?
Posted 21 January 2014 - 05:27 PM
Posted 21 January 2014 - 06:41 PM
My images show the third star almost disappearing in the g' blue-green filter that is close to V, while it is much brighter in the red r' filter. The second star has the same behavior but less so.
I don't know how accurate the Struve values are or if he was skewed by red in the color - but yes the second star seems much fainter than 9.1 in the equivalent V band - and Eichorn's value is 9.65 for the second and 10.71 for the third. My values are even fainter relative to the primary - but they aren't calibrated and they use different filters.
Posted 22 January 2014 - 08:47 AM
Posted 22 January 2014 - 03:26 PM
I will probably do it again but will calibrate the magnitudes with comparison stars.
But there are other more recent published values for the photometric magnitudes of the stars, and they are fainter than the 9.1 value.
Posted 22 December 2014 - 07:35 AM
Guess what - latest WDS entry changed magnitude for B from 9.1 to 9.4mag. Despite being listed in the latest precise measurement WDS file this looks still rather like an estimation and not a measurement due to the lack of a second digit and is probably not the end of the story. Currently I am trying to get the best possible image of STF450 with iTelescope using a V-filter and do then photometry with AAVSO VPhot. So far my result is +7.298/9.726mag with the star disks of A and B somewhat overlapping so I have to reduce exposure time and try again to get this confirmed. But as the mag for A is on spot it does not look this bad for B either.
Posted 26 December 2014 - 08:09 AM
Wilfried, as I'd had a look at Lewis's data on Struve doubles (which I've commented on in the thread on STF 442), I thought I'd see what Lewis offered on your other STF puzzle that re-surfaced recently.
For STF 450, Lewis gives the magnitudes for as 8.5 and 11.0, so a delta-m of 2.5. The delta-m tends to be a better number from old estimates of brightness than the assigned magnitudes, at least when delta-m is not large, and preferably when the separation is not tight. As STF 450 is only moderately close (6") there's less effect of the diminution of brightness of the secondary.
As your most recent data now suggests a delta-m of ~2.4, and as the secondary has turned out to be red, that might sufficiently explain the effect of unexpected visual dimness of the secondary compared to the original 9.1 listed magnitude. A red star at v-mag 9.7 could appear as you've described.
The only observing note I have for STF 450 was with C9.25 some years ago, before you raised questions about it - on a night with an 8-day moon, and at 98x, I did not think the secondary star as dim as your early descriptions suggest, though it was clearly much less bright than the primary. I saw no particular colour in either star. This I agree is not a particularly useful observation except in the particular of not seeing the companion as being dim as 11th mag.
Posted 10 February 2015 - 04:18 AM
Tried to bring the point home that STF450B is somewhat reddish and seems due to this visually fainter than listed in the WDS catalog - but failed. Photometry is a bit shaky with STF450 as the bright primary tends to show a disk large enough to overlap with the secondary even in images down to 1s exposure time. But same conditions for V and B filter should deliver a good indication for B-V color index - with the existing images I got a value 0.6 to 0.7 putting STF450B in the color range of our sun means yellowish.
Nearby reference star UCAC4-570-008469 has +10.855Vmag and +12.317Bmag means B-V color index of 1.462 - now his means really reddish - now this is really confusing for me as I have during several visual observations considered this one as rather equal bright with STF450B.
On the other side STF450A is listed in UCAC4 with +8.539Vmag and +8.369Bmag giving a B-V color index of -0.17 and this is quite blueish - the Vmag value is quite different from WDS with +7.29mag (origin obviously) Tycho II so also here might be something in need of explanation but this should be not such an issue for the B-V color index.
A blueish primary with a yellowish secondary nearby might now seem a reasonable explanation for my visual experience.
Still not fully satisfied I will try again with images with even shorter exposure time to get images with separated star disks for A and B and do then photometry also for A.
Posted 13 February 2015 - 03:19 AM
I think, this is for now my "final" result as I do net expect to get anything "better". Did five 0.2s shots of STF450 with V- and B-filter, stacked each 5 images per filter and got a reasonable good SNR ratio for B with only a slightly touching of the star disks of A and B. Did then photometry for A and B in separate runs with different aperture radius (6 pixels for A and 2 pixels for B) and got the following results:
A: 7.3Vmag and 7.3Bmag giving a B-V color index of zero - indicating a quite blueish star. This result confirms WDS and questions UCAC4
B: 9.7Vmag and 10.5Bmag giving a B-V color index of 0.8 - indicating a tad more reddish than our sun. This result questions the current 9.4mag from WDS (even after correction from 9.1 to 9.4) and I think 9.7 is quite realistic.
"Final" conclusions: WDS mag for STF450B is currently listed still too low but B is not this faint as the visual impression suggests. The reason for the "wrong" visual impression is the color contrast between the blueish primary and the yellow-reddish secondary making the secondary seemingly fainter.
Posted 13 February 2015 - 06:25 AM
Wilfried: seeing your post prompted me to post this:
What follows below is a draft I intended to post in January; but held back in hope of further evaluation in better and moonless nights. These arrived (eventually!) and really nothing to add other than an inconclusive impression that B might indeed show some variability. However my ‘season’ for this part of the sky is over till late summer mornings when I hope to follow up with the pair.
This was observed on Dec. 25, 28, 29, 30, & 31. Less than ideal conditions overall, transparency rated Fairly Good at best and seeing mostly 6/10 – the waxing moon not considered as particularly detrimental/hampering as it encroached from 52º to 14º on the latter 4 nights.
The primary was very obviously blue-white and an orange-yellow (light amber) to B. Seeking naked-eye (as seen with) analogues: Gamma Ori & Epsilon Gem seemed close colour-wise – B looked certainly less ruddy than Mu / Eta Gem. See attached.
The star 110” to the west (C?) is decidedly more ruddy than B; in spite of any contrast hue of B with blue-white A but considered rather less so than Mu/Eta Gem as seen naked-eye.
I would be surprised if star B is brighter than 9.5. Even more surprised (delighted even!) if star “C” is fainter than 10.5 given its continued ready visibility in the 3” finder (x60 & x180) each night, given sky conditions and waxing moon…….
My star “C” is not the closest to A/B with several fainter stars evident in good conditions……
Something on STF 442 to follow.
STF 450.jpg 32.26KB 2 downloads
Posted 14 February 2015 - 01:03 PM
David, you have obviously an excellent eye and equipment for observing colors - your visual observation report corresponds remarkable well with my photometric results to the degree of confirmation.
Posted 16 February 2015 - 07:05 AM
Good to read your response Wilfried.
That naked-eye/eyepiece comparison seems to have some possibilities tho’ it falls down
when trying to match such companions that contrast with an apparent green hue and so forth!
Interestingly, on Dec. 28, the B companion upon initial view showed a pinkish, almost magenta,
hue, for a minute or so before gradually taking on the more orange-yellow cast I settled for overall.
I suspected my looking too soon after the moon was at the root of it……
Posted 16 February 2015 - 08:29 AM
Considering the my result above as "final" was a bit premature - the possibility that STF450B might be variable was quickly ruled out due to the lack of evidence. On the other side there is also no evidence that STF450B is not variable - in the contrary: The WDS records show quite a wide range of magnitudes for B respectively delta_m.
So I will for some time continue with photometry with identical setup in intervals of several weeks - if STF450B is not variable the results should be stable within a reasonable error range. Else we have something to research further
Posted 16 February 2015 - 08:32 PM
Again very useful observations from Dave Gray - and with enough aperture to see colour in the secondary star.
Wilfried, your comment - The WDS records show quite a wide range of magnitudes for B respectively delta_m.
I don't have the complete data set for this one, so are you saying that the delta-m estimates vary greatly, not just the estimated magnitude for the B component? Large variation in delta-m estimates might suggest variability of B as you say (assuming A is stable); large variations in estimated magnitude of B merely suggest uncalibrated photometry.
A further thought. You seem to have estimated star B dimmer than some other observers, based on the difficulty of seeing it. Human vision varies greatly, and some eyes are more sensitive to particular colours than others. The Herschels, William and John, seem to have been more sensitive than most others to red tints, and with perhaps greater sensitivity to the brightness of red stars; their red sensitivity is a point often remarked on. Might it be that your vision is less sensitive to red than the average? so you see the redder stars as less bright? - and perhaps more sensitive to some other part of the spectrum, such as blue?
In my own case, I see red as less saturated than some observers' descriptions; yellow and orange somewhat stronger in some cases; and blue somewhat less saturated. This was already the case decades ago, when I was a lot younger and so not yet having the usual yellowing of the eye lens that happens with age. I don't find red stars dimmer than yellow when the V magnitudes match; rather it's a duller effect. White stars do tend to look brighter at the same V-mag.
Only a speculation about colour sensitivity. Re-reading this thread I was struck by your older observation of star B being difficult with more aperture, and easier with less. I'm not sure how to interpret that. Glare from other nearby stars with more aperture? - possibly, if humidity is high, or with dusty air.
I've not tried STF 450 with small apertures such as 60mm or 80mm, only with 140mm and 235mm, so I've not had a comparison like that. But my notes from the 140mm aperture did not suggest any difficulty with the B star, obvious at only 80x. Hmmm. Time to try it again, if I can get a clear night before the Pleiades wester too far. David Gray in claimed-cloudy Durham County ("near Scotland") seems to be getting more clear nights than I am in supposedly sunny south-east Australia.
Posted 17 February 2015 - 03:23 AM
The latest magnitude measurements of STF450 recorded by the WDS catalog are from 1997: 8.612 in the J- and 8.268 in the K-band. Based on the formula provided by http://brucegary.net...es/method0.html this would give 9.755V-mag. Else there is for B a V-range listed from 9.1 to 11.5 and several times there are values listed from 2.1 to 2.7 in the absence of mag values for A - I interpret these numbers as delta_m.
And regarding color sensitivity - yes, reddish notes appear quite faint to me. Thus I accepted meanwhile that my visual impression needs caution in this regard.
And regarding magnification - as my skies are not black but light grey I often find smaller magnifications delivering a crisper image than larger ones. The moment my personal acuity allows a clear resolution I one step up in magnification for verification - this leads for my eyes under the given conditions quite often to less contrast between background and star disk.
Posted 17 February 2015 - 08:02 AM
The v-magnitudes for star B will vary greatly, as you've noticed - but the V-mags for star A will vary a lot too. Most of them are eye estimates, or photometry of primitive kind, or borrowed numbers for A as a starting point. That's why delta-m is the useful number. We now have what should be a good V-mag for star A - and if the delta-m figures range (as in your example) from 2.1 to 2.7, then with A at 7.3 we have estimates of B from 9.4 to 10.0. The mid-point is 9.7, which matches your recent photometry.
Posted 19 February 2015 - 12:32 AM
Here's some more data to throw into the mix...
I captured this with my C6 SCT, TeleVue 2x barlow, Canon T4i DSLR at ISO1600, raw video, 1fps (1" exposure), 120 frames stacked
First, a stretched image, obviously overexposing the primary (North is nearly straight up, East to the left):
stf450_stretch.jpg 96.46KB 1 downloads
The C component appears to be quite reddish through my DSLR.
And here is the centroid data using AstroImageJ on the unstretched image:
A-B: +2.1 mag
B-C: +0.7 mag
If A is mag 7.3, then my data pins B at about 9.4, and C at about 10.1
Edited by evan9162, 19 February 2015 - 12:33 AM.
Posted 19 February 2015 - 11:09 AM
Darin, thanks for joining - excellent image and clear analysis.
Tricky detail: As your image is made without any filter you have the full range of wavelength covered by your setup. Components A and B have clearly a different spectrum so this should lead necessarily to a delta_m different from the visual range. As your result is ident with the current WDS data this is curiously just another hint that the current WDS data is questionable.
Posted 19 February 2015 - 10:23 PM
Huh. I looked at the WDS data for the "C" component, and it's PA is 177*. It appears that the red star in-line with A and B may not actually be part of the system, just a nearby star.
I also closely examined my image, and found that some of the pixels in the A component were blown out. Reprocessing to eliminate that data clipping showed that B would be about +2.4 mag from A, or right about the mag 9.7 range...
Posted 20 February 2015 - 12:09 AM
The star to the west is not the 'C' star of the WDS listing - this one, brighter than the WDS C star, is V-mag 10.855 (Vizier/Aladin UCAC4); f-mag 10.381. It is not in WDS.
The closer but still wide C star listed by WDS is V-mag 13.944 (same source, UCAC4). It shows nicely on sky survey plates, nearly due south from the AB couple which is a single image on POSS-II (image spread from the bright primary).
The brighter wide component seems most unlikely to be connected with AB. The proper motion for A is much greater and different in form from the p.m. of the red star to the west. Therefore no connection. If it's a red dwarf it would be closer to us than the AB pairing (given that A is a bright 'Sirian' type). AB I'm regarding as a genuine binary, although definite evidence isn't available at present. But the small movement of AB since discovery suggests a binary; if the proper motions were different, over 180 years (1832-2013) they would be expected to result in bigger change than the marginal difference indicated.
The C component has no listed p.m., nor spectrum, so properly evaluating it isn't possible.
Posted 20 February 2015 - 07:03 AM
In view of my comments on my post #34 regarding ‘my’ star “C” and assuming it is indeed as you report: ” is V-mag 10.855” – then I am delighted and surprised to have kept sight of it in the given conditions with my 1961 vintage 3” (uncoated OG) – I would have thought nearer mag 10.0. Also its colour was very apparent in the 16.3” – even on the less favourable dates – for a star close to 11.0 and with the dimmer binoview – and albeit I know I’m very sensitive to ruddy hues.
“…… observed on Dec. 25, 28, 29, 30, & 31. Less than ideal conditions overall, transparency rated Fairly Good at best and seeing mostly 6/10 – the waxing moon not considered as particularly detrimental/hampering as it encroached from 52º to 14º on the latter 4 nights.”
“I would be surprised if star B is brighter than 9.5. Even more surprised (delighted even!) if star “C” is fainter than 10.5 given its continued ready visibility in the 3” finder (x60 & x180) each night, given sky conditions and waxing moon…….”
“My star “C” is not the closest to A/B with several fainter stars evident in good conditions……”
What you say of the true C star: “The closer but still wide C star listed by WDS is V-mag 13.944 (same source, UCAC4).” is consistent with my impressions with the 16.3” D-K. This was constantly caught peripherally in moonlight - binoviewer – and confirmed with monovu. On the best/clearest (moonless) nights there were several similar-distance even fainter stars around A/B.
As to variability of B, all I can offer would be simple visual impressions: looking at similar nearby systems – such as STF444 and SST64 (triple) perhaps some (indirect) inter-comparisons/impressions might prove indicative. That is, say one night STF450B were to appear more elusive than STF 444B – crude but suggestive; and with a number of us looking at a similar time might alert us to something going on……….
Posted 20 February 2015 - 08:43 PM
Dave, not too surprising that your 3-inch OG managed mag 10.8 or so - even "uncoated", though that's a surprise given the 1961 date. Back in the day, a 3-inch was regarded as more of a "real" telescope than the 2.4-inch, and the only 3-inch scopes I met from that era had coated objectives. But, in rural conditions (or near to those) reaching near mag 12.0 is possible with that aperture; certainly ~11.5 even uncoated.
Looking at the notes in the WDS for STF 450, it's identified as a Pleiades star, so about 136 parsecs (~444 ly) from us on the most recent determination. If you work out the scale of the AB separation, 6.2 arcseconds that far away is an immense (projected) separation, over 800 AU. That suggests an orbital period of thousands of years, possibly around 10,000 years (5,000 or so years with different assumptions; more than 10,000 on other assumptions).
My point above, that AB is likely a binary because it shows so little change, takes account of the measured proper motion of the A component - in 180 years it's moved about 4 arcseconds in RA and 7.5 arcseconds in Declination. The very small change in separation over time, with very little angle change, shows that the B star has similar motion. Hence a cpm pair.
Posted 21 February 2015 - 06:44 AM
Sorry Fred I think you misinterpreted – I’ve gone to 12.8 (13.2 suspected once) on several AAVSO charts with the 3” and 11th mag. SNs against somewhat ‘nebulous’ backdrop. It is in the context of moon proximity and slightly hazy skies where my surprise lay. In better conditions I feel I see star “C” much too easily to be near mag 11 – but if it is – delighted!!
Edit Note: In hindsight I have to express some dismay that I looked to be in need of some elementary tutoring in matters telescopic.. .. Such beginner stuff: I went past that level by my definitely uncoated 3”(and eyepieces!) was 10 months in use – the end of 1961 that is. Into late ’62 I had been enlightened by, among others, Sidgwick’s volumes, Norton’s, and Sky & Telescope when its monthly arrival was eagerly anticipated and when it was a joy to read for many years……… Along the way came Aitken’s book, and in 1975(c.) one of the very first copies of the Webb Society’s “Double Stars” – separate sheets held in a plastic channel/spine and still together.
Edited by David Gray, 22 February 2015 - 11:11 AM.
Posted 21 February 2015 - 07:58 PM
Dave, no intention to provide tutoring in matters elementary... :lol:Musing aloud is pretty much all it was....
Observing conditions vary so widely that faintest magnitudes can be wildly different, even before individual eyesight is allowed for.
I should have read your note more carefully ('in the conditions') instead of commenting as if your sky was normally as unhelpful as Wilfried's - his NELM numbers are not good, due to his urban location. Yours, in a village setting, would certainly be better.
Even so, 12.8 with a 3-inch is better than I'd have expected. I have observed from dark sky sites where that's likely to be possible, though I didn't have a 3-inch at the time to check. My 140mm refractor (5.5-inch old-style) certainly shows about 13.2 from my suburban location when there's no moonlight (various UCAC4 magnitudes on wide companions). From the dark-sky sites, when I had a 6-inch Newtonian that was transportable, I found a gain of a full magnitude and a bit more. NELM went from 5.0/5.5 to about 6.5/6.8; telescope limit improved a little less.
The gain in going from 3-inch to 5.5-inch is about 1.3 mags, based on aperture; so 13.2 - 1.3 = 11.9; add a magnitude for rural conditions, = 12.9.
Next time I'll look at the numbers before commenting.
Sidgwick - very useful, and I still value and use the Amateur Astronomer's Handbook. Norton's, my old copy does get occasional use - the tables are a good quick reference. Sky & Telescope I still read, as it has enough of good science summary articles, and the non-beginner's observing articles, to make it worthwhile for me. Internet discussion sites like CN don't replace it; I see them as supplementary, and providing different benefits.
And, coming back to telescopes for doubles - all this reminds me I should be doing more dark-site observing for the closer doubles with dim companions, as part of my checking on neglected doubles. Though I think I'll use more than a 3-inch (and more than a 5.5-inch) for that.
Edited by fred1871, 21 February 2015 - 09:09 PM.
Posted 22 February 2015 - 03:26 AM
Calculated telescope magnitude limit for a 3" scope is (depending on the used formula) somewhat about 12.2mag. This is to take as mean value for good conditions with some spread. 12.8mag would be even with an excellent sky quite extraordinary. My best results with NEML ~4.7 (rural location) and very clean air for such an aperture is about 11.95mag.
Posted 22 February 2015 - 11:11 AM
I think the 1960s 12.8 & 13.2 (suspected) were from a V Ori chart looking at the most recent, in absence of those unfound earlier versions, it suggest that 12.6 & 13.1 (no 12.8/13.2 stars now) applies in reality – subject to locating my annotations on those older ones. Many very good nights over the years did I use that V Ori chart to get beyond 13.0 – but never did with certainty.
NEML: currently a ‘run of the mill’ good night here will be around 6.2 average and a, not that infrequent, very good to excellent one approaching 7.0/7.2.
Not really pushed the 3” in that regard for some years but the 1989 SN in M66 was being reported to max at 12.2 but it was so readily visible to me in the 3”, over a few nights, that I phoned the BAA VS Director to query the matter – suggesting nearer 11.5 and its deep amber hue very apparent in the 16.3” D-K. But I think it remained officially at 12.2 in the reports.
What I can say of the current state of the 3” (air-spaced OG) is that with a certain angle of torchlight there is a very slight milkiness to the flint component: invisible in normal daylight and no halo-effect/hazing apparent with bright objects.
More concerning is in recent years there is a decided brightening of the diffraction rings in the same quadrant on colder nights in winter. If I’m not careful this can masquerade as a faint companion to stars fainter than about mag. 3.5. I suspect the retaining ring may need a slight slackening. Fortunately I can rotate the scope as it is in finder rings on the D-K.
Last night was very clear with the number of stars visible in the Leo Sickle to suggest better than NEML (local) 6.5; and 6-7/10 seeing in the D-K. Earlier 32 & 52 Ori were each two distinct disks in the 3” (x180-220) nothing twixt them difficulty/ease-wise, and both quite charming in the 16.3” (x365 Binovu).
As to my S&T bashing: in kinder moods I simply declare “perhaps I just outgrew it”; so I have moderated my emphasis in my earlier post………and best left at that on here……….
Edited by David Gray, 22 February 2015 - 11:22 AM.