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STF450 companion variable?

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#1 WRAK

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Posted 20 February 2012 - 03:12 PM

STF450 (6.2" +7.3/9.1mag) as part of Ally's Braid (Pleiades) should be an easy split with a 120mm refractor (Lord Rating = Easy under somewhat stable seeing) even with heavy light pollution. But depending on seeing conditions I had even trouble to see the +9.1mag companion despite clearly identifying near by stars in the +10mag range.
Tonight I could see the STF450 companion clearly for the first time after several failures but only as rather dim star with may be no more than +11mag when compared for example with the about +10mag stars at the end of Ally's Braid.
This could mean that may be the STF450 companion is a variable star or fading away.
It would be nice if somebody on this forum could recheck this observation. For GoTo users - RA/DE (2000): 03h47m24s/+23°54'52"
Thanks in advance
Wilfried
Vienna/Austria/Europe

#2 Rich (RLTYS)

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Posted 21 February 2012 - 05:58 AM

Wrak, excellent observation. Welcome to the CN Double Star Forum.

Rich (RLTYS)

#3 WRAK

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Posted 25 February 2012 - 02:56 AM

Two nights ago I had again the opportunity to split STF450 - this time with even better seeing. The companion was still a rather dim spot but very stable and was certainly dimmer as the +10mag stars nearby and the +9.1mag accordingly Struve resp. WDS catalogue are certainly no longer valid as far as I can estimate. Has anybody here the equipment for measuring the magnitude of a star?
I will anyway stay on this topic for the near future to see if there is any change in magnitude

#4 Rich (RLTYS)

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Posted 25 February 2012 - 10:44 AM

According to info from the AAVSO STF 450 does not contain any variables.

Rich (RLTYS)

#5 WRAK

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Posted 25 February 2012 - 03:24 PM

Thanks for the effort to check - I think else I would have found a hint in other sources also. What puzzles me is the fact that the STF450 companion seems at least at present much dimmer than the +9.1mag according to the diverse DS catalogues

#6 Rich (RLTYS)

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Posted 26 February 2012 - 06:38 AM

I've seen other doubles where the companion seemed fainter then the stated magnitude, it's not that uncommon.

Rich (RLTYS)

#7 Ed Wiley

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Posted 26 February 2012 - 12:35 PM

I think, but am not sure, that some of the difference might be the spectral class of the star and the reported magnitude derived from different filters. For example, if the delta magnitude reported is derived from a B-filter and you observe in the equivalent of "V", then the delta magnitude may look different, depending on the spectral classes of the two stars. I am not sure how standardized the delta magnitudes are in the WDS.

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#8 VanJan

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Posted 26 February 2012 - 11:11 PM

WRAK,

When your original post appeared, I checked my observing log on this double. None of my notes mentioned anything amiss with the data. Finally had an opportunity to observe this pair again this evening, using a 90mm F/10 achromat at magnifications ranging from 130X to 230X.

I believe Rich's cautionary note above bears somewhat in this case. It is not uncommon for secondary magnitudes to appear fainter than their measured values. Even so, after studying this pair in various portions of the field of view, with both direct and averted vision, both glancing and staring, the pair alone and in comparison to the reddish (another problem in itself) 10th magnitude or so star directly preceding the pair, I have to agree to a degree with you. 9.1 for the secondary is a bit optimistic by a half magnitude or so. At least visually.

Thank you :bow: for posting your detailed observations on this double, and welcome to Cloudy Nights and the double star forum. Looking forward to more reports from you.

Cheers!

#9 WRAK

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Posted 27 February 2012 - 10:30 AM

"not uncommon for secondary magnitudes to appear fainter than their measured values" ist an interesting hint from Rich - I will keep this in mind for future observations.
Thank you very much VanJan for spendig time on observing this pair and checking my impression. You must have dark skies to be able to use magnification up to 230X - I have here heavy light pollution and "loose" <+10mag stars if I go beyond 130X. Anyway I will have a look on this from time to time to see if there are any changes to note

#10 WRAK

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Posted 05 April 2013 - 02:34 AM

This topic still nags me a bit whenever the topic of doubles in or near the Pleiades pops up. Lately I entered the position of STF450 into the AAVSO search utility (http://www.aavso.org...load-apass-data) and got +8.539mag and this is much fainter than the WDS advertised +7.3mag for the primary. I did not get any magnitude data for the secondary but the value for the primary would indicate that my impression that the secondary is fainter than +10mag seems at least plausible.
Wilfried

#11 Ed Wiley

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Posted 05 April 2013 - 06:31 PM

Wilfred: Nothing in the WDS notes mentions A as variable, the magnitude cited is near or the same as reported in the Tycho catalog and the secondary mag might originate in the USNO Pleiades catalog.

Ed

#12 WRAK

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Posted 06 April 2013 - 04:21 AM

Ed, thanks for pointing this out. While I do no longer think this to be a variable star I still doubt the magnitude data somewhat and if in doubt here I think the AAVSO data would be the most reliable so far as these values are averages from several recent observations and also a given error range is listed.
Wilfried

#13 WRAK

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Posted 22 December 2013 - 11:13 AM

Time is running - nearly 2 years ago I posted here my impression that the companion of STF450 is somewhat fainter than advertised. And it seems that I did not get much wiser since as even the UCAC4 catalog fails to show this companion and I did also find no other source with measurements for this star.

Yesterday I missed a chance to get again a look at STF450 because the fog raised in the evening so fast that the clear sky got lost within a few minutes. I intended to do this in a quick session with my 60mm travel refractor because meanwhile I have sampled enough limit observations to be sure that STF450 should be not this difficult to resolve with 60mm if the advertised data is correct.

Hope now for the next chance with a stable clear sky and enough time to setup a larger scope with iris so I can go down to the limit aperture.
Wilfried
PS regarding 60mm scope: May be I will also try it with my C9.25 with the 60mm off axis mask delivering usually stunning crisp images with saturated color hues

#14 WRAK

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Posted 23 December 2013 - 04:14 PM

This evening again a clear sky. This time I acted fast to avoid surprises with fast rising fog. Two scopes 120mm with iris and 60mm refractor. With the 120mm scope I resolved a faint star at 10:30, limit aperture 100mm. Just for fun I tried also the 60mm scope and to my surprise I got also a resolution. So I tried it again with the larger scope with the iris at 60mm - and here also resoltion without troubles. It seems that the glare of Alcyone might pose a problem for larger apertures.
But to be clear - this was no resolution of STF450 but of UCAC4-570-008469 +10.84mag at a position similar to the companion of STF450 but at a distance of ~110" and it seems not very plausible to me that a +9.1mag star should be here in between. Even with a rather small magnification of x100 there should be no problem at all to resolve such a companion at a distance of 5.7".
Wilfried

#15 3c_273

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Posted 23 December 2013 - 04:18 PM

Wilfried, here's my observation of the star:

STF 450: 3:47:24.41 +23:54:52 (J2000). Double. Sp: A2V
Sep: 6.2, PA: 263, Year: 2008 7.29-9.1

Telescope: C-8, Observatory: Little Tycho, Date: 2007 Oct 21, Time: 03:00:00
An ordinary sort of pair in the Pleiades, quite overshadowed by the rest of
the cluster.


Note that the WDS data was added well after the observation was made.

#16 fred1871

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Posted 23 December 2013 - 06:34 PM

Wilfried, the secondary star for STF 450 seems to be absent from the Hipparcos catalog; and the listing in the WDS of its magnitude as '9.1' - a single digit decimal - suggests that it's not a Tycho magnitude, or similar, which would be two-place decimal.

So I think it likely the secondary star is fainter than the WDS listing, and could be mag 10+, perhaps 11. If it were as bright as mag 9.1 it should appear in Hipparcos.

My observation of this pair 5 years ago was with a C9.25, I didn't record anything unexpected about it at the time; but the larger aperture can disguise issues of magnitude in some cases.

Added in Edit: I had overlooked my more recent observation, mentioned here in another thread, at the end of January this year - looked at STF 450 with the 140mm refractor, and could see the close companion already at 80x, though it was more obvious at 114x.
I'll try again soon with that telescope, and with aperture stops to check how it looks at smaller apertures (probably 100mm and 80mm).

#17 WRAK

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Posted 24 December 2013 - 06:57 AM

I have to some degree lost my double star observing routine due to the ongoing foul weather and changing scopes and therefore changing field of views with given eyepieces may add to some confusion - but I think it virtually impossible to have STF450 in view with a magnification of x100 or x180 and not being able to resolve a 5.7" +9.1mag companion while at the same time resolving a 110" +10.81mag star (see the 14' FoV map with the advertised values). Will certainly check this again.
Wilfried

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#18 WRAK

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Posted 25 December 2013 - 11:25 AM

Tried to locate photos of STF450 including UCAC4-570-008469 +10.84mag to have a reference for brightness of the companion I found 2 not this usable images (without UCAC4-570-008469 or with overlapping STF450 components) and one nearly perfect from Chris in his Yahoo Double Star Imaging Group. I took the liberty to copy the center of this photo, make it negative and change the orientation to match my map above. You have to enlarge it 5 times to recognize clearly that the companion of STF450 is only marginally brighter than UCAC4-570-008469.
Further if I apply my pixel count method to this image and compare it with the results I got in my empirical sample for magnitude dependent size of spurious disk I also come to the conclusion that the brightness of the companion is about +10.5mag taking the magnitude of the primary with +7.21mag as reference.
Wilfried

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#19 WRAK

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Posted 25 December 2013 - 01:00 PM

Have found another reference for the faint star UCAC4-570-008469 nearby STF450: USNOA2 1125-01267467 +12.2mag. Would be a hint for even greater faintness of the companion but as I saw this one with my 60mm refractor with calculated TML +11.6mag this seems not very plausible. The producer of my 60mm refractor even advertises only +10.7mag TML thus making even the UCAC4 value of +10.84mag questionable.
Wilfried

#20 fred1871

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Posted 25 December 2013 - 10:05 PM

Wilfried, a couple of thoughts. First, the nearby field star (UCAC4-570-008469, USNOA2 1125-01267467) as mag 12.2 - is that a Blue magnitude? - as the USNO A2 catalog is based on Schmidt plates, red and blue - and if the star is a spectral type late-K or M star, the B-V colour index could be ~1.4, so 12.2 (Blue) becomes 12.2 - 1.4 = 10.8 for V magnitude.

Magnitude limit of the 60mm refractor? - on aperture, 2.0 mags less than a 6-inch, and a conservative mag limit for a 6-inch is 12.9 (quoted in many books). However a 6-inch often enough goes fainter, say to 13.5 - that would suggest 11.5 for 60mm. In really dark conditions I've seen some experienced observers here quote fainter mags than 11.5 seen with 60mm. So your producer of the refractor is being cautious. Better should be possible.

#21 GlennLeDrew

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Posted 26 December 2013 - 02:41 AM

It's worth noting that the completeness limit in the Hipparcos catalog is dependent on galactic latitude. The mission was designed to retain a fairly consistent density on the sky of about 4 stars per square degree. And so the completeness limit is about 9m at the poles (toward CrB and Scl), rising to about 7.5m at the galactic equator. That M45 is at about latitude -20 degrees suggests a completeness nearer to 8m, meaning that the star in question will not have appeared in the HIP input catalog (HIC) unless it's a special program star, some number of which were included to as faint as about 12m.

#22 WRAK

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Posted 26 December 2013 - 06:55 AM

Glenn - thanks, I have often wondered why rather bright stars are not Hipparco listed while rather faint ones are very well, this explains it.

Fred - thanks for the explanation regarding USNO A2 magnitudes. I don't know the spectral type of USNOA2 1125-01267467 (I have the catalog on DVD at home but have at this moment no access to it) but your assumptions seem plausible.

Regarding TML for a 60mm refractor: I know that there are so many factors involved that any given number can only be a mean value with some range for deviations - but I think somewhat slightly above +11mag should be possible.

Meanwhile I checked again the photo of Chris for another reference and found also nearby HD 282973 +9.87magV according to Simbad resp. UCAC4-570-008510 +9.98mag.
To make a direkt comparison I arranged STF450A, STF450B, UCAC4-570-008469 and UCAC4-570-008469 side by side - this shows clearly that STF450B is in between UCAC4-570-008469 +10.84mag and UCAC4-570-008469 +9.98mag and certainly fainter than the latter.
Wilfried

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#23 freestar8n

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Posted 21 January 2014 - 01:50 PM

Hi-

I don't post here much and I don't do much double star work, but WRAK asked about this double in a photometry thread and I thought it might be interesting to look at it. So I took some video with an Edge8 and qhy5l-ii using C, g', and r' filters (Sloan). I did not have much time so I did not do an elaborate calibration or anything - and this is all raw measurement - but I think it tells the story. Basically the third star is very red, with a color index of 1.65 according to one source (described in a later note below).

Here are stacked images with no processing other than aligning and sub-sampling - and dark subtract. These are stacks of 200 frames at 100ms exposure with no quality culling. The star was lower than I wanted and I believe the atmospheric dispersion in the longer filters causes the elongation - it is not a collimation issue.

So here are the images in clear, g', and r' all at the same scale. They are *not* corrected for extinction or response of the camera, but they tell the main story - the third star is very red.

Frank

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#24 freestar8n

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Posted 21 January 2014 - 01:55 PM

Here is a spreadsheet of the measured flux in the stars along with their positions. I did not calibrate the pixel scale so it is based on an assumption of 3.75 micron pixels and 2000mm fl, with sub-sampling by a factor of 4 - which is about 0.1" per pixel in the measured system shown.

I calculate raw magnitudes and then adjust them relative to the g' value for the primary and its color index from below. This is not intended to be exact but it gives the idea of the relative colors of the stars.

Frank

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#25 freestar8n

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Posted 21 January 2014 - 01:58 PM

And here, which somewhat takes the fun out of it, is a Vizier search of the region, which comes up with a database hit of photometry on the Pleiades stars, including STF450. It gives a color index of 1.65 for the fainter star, which is very red.

I don't know how the mags are assigned or adjusted for visual observers or in the double star lists - but this is more information to go by, including captured images. It's a very red star - so it may not match the listed magnitude - depending on how it's measured.

Frank

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