Affiliation
None
Fri, 12/06/2013 - 14:12
Yes; We've been here before! I resumed monitoring 58521 late Autumn. Playing on a hunch, I settled down to watch the star continually for extended periods during recent sessions. 58521 appears to fluctuate between 9.8 and 10.3 magnitude over an irregular cycle of between 1½ to 3 minutes. The fall is rather abrupt; say 20 seconds. 58521 then regains full brightness at a more leasurly pace...and so on. Perhaps someone would care to have a look. We're talking about the orange star at the centre of M37, for anyone new to this.
Stress this requires watching intently. Settle down in a comfortable position. A binoviewer is reccomended and a power of around x150.
It occurred to me that this could be some form of visual illusion; a product of concentrating over-long at one particular star. With this in mind I selected SAO 58230 – an 8.7 mag star near the centre of M36. And subjected this to the same protracted attention. It didn't appear to alter in the slightest.
Back to SAO 58521! At first, this seemed to have quit fluctuating, but 4½ minutes later, down it went, as if suddenly loosing power...and then slowly recovered to resume cycles of about this duration.
Given the lack of interest elsewhere...what to do? Have decided direct timing must be attempted, not-withstanding the lack of technology. With only a stopwatch; the signals from Frankfurt and my wife to take notes, the aim will be to produce a 30 minute light curve for presentation on the LCG here on the AAVSO web. Please wish me well!
Not really out for this to be nominated “Wilson's Star”; let's emphasize. I do think the object is worthy of a place in The GCVS catalogue and thus attract further attention. Is anybody out there listening? Will this plaintive call be on Forum long enough to be even noticed?
Dragging the original item out of the draw for one last go.
Bill,
I just don't see how a late type 'single' star can vary by this amplitude over such a short time span. What is the physics behind something like this? If it had a disc or accretion stream I wouldn't have a problem.
Gary [pyg]
Yes Gary, this bothers me too! So much so, I’ve never broached the matter with you directly. Have been aware for years now that SAO 58521 appears to vary in a measured way, and I've assumed that it's an overlooked semi regular. Last year, however, it appeared to me, that the star was varying in much shorter order. With the influence of Mike Linnolt it was audited eventually. Consequently I’ve an almost exclusive slot in “Web Obs”! It's really been disconcerting, this season, to notice very short variations indeed. I feel it would've amounted to cowardice, just to say nothing. Let's leave aside theoretical objections, for the moment. What's needed is other observers to either confirm or refute my observations – particularly CCD runs. It's proving difficult to recruit these forces: we all want to get on with our own thing. However, let's live in hope..
HI Bill,
I'm in the process of bringing BSM_NM back on line with updated software. It will take me a few nights to shake the system out before returning to normal survey mode. I'll put SAO 58521 in the queue for a couple of nights of time series to help resolve the issue. The cadence will be about 30 seconds. The angular resolution is not great with BSM, and so several nearby stars of M37 will be included in the aperture, diluting any variation (but 0.5mag variations would be easy to see). I'll let you know what I find.
Arne
Thanks Arne. We have your ear: that feels like real progress. I await the results of the time series monitoring...not without a little apprehension! Will a negative verdict hurt doctor?
Bill.
Hi Bill et al.,
This star may a binary. Its spectrum is composite: A5V+K0III (see VSX for the reference). The spectral type given by SIMBAD is incorrect (as is the citation to its source, which should be to a 1954 paper by Lindblad; the Lindblad type is merely quoted in the source given in SIMBAD. Sheesh!) VSX has the correct spectral type and citation to its source (Upgren, 1966). [Upgren comments that the luminosities might be a bit higher than the spectral types imply.]
There is no resolved cluster star close enough or bright enough to your star to be the source of the composite spectrum, so the star is either a physical binary or the two stars are at different distances but closely aligned on the sky merely by chance. The magnitude difference between the stars cannot be larger than about 2 or only one spectrum would have been seen in that case.
A minor side mystery is that Mt. Wilson observers in the early 20th century did not report the spectrum as composite in their big compilation of spectroscopically determined parallaxes of what they called "M stars". The star was classified by them as M1 (see Adams & co., 1926). However, the Mt. Wilson classification system was not the same as the HD, and their M stars include stars as early as HD type K5.
Cheers,
Thom Gandet (GTN)
Hi Thom,
Thanks for your contribution to this investigation. Your input, exemplifies that meeting of minds we've being trying to provoke for some time. We've been aware of the enigmatic spectral designation for several years, but wasn't conversant with the equivocations with which this is beset. We considered a 13th mag star for a while, that's 11” distant; but this didn't fulfil the part. I'm thinking in terms of an anisometric contact binary, right now. But let's wait to see what Arne's initiatives may throw up.
Bill
I had a 3-hour window while testing a new camera on BSM Berry, so obtained a time series with one-minute cadence on this target. M37 is a nice cluster! Anyway, for the 3-hour window, there is no variation outside of statistical scatter. If I get a chance, I'll do one more time series sometime in the next few nights.
Arne
I was able to use a different set of comparison stars and extend the light curve a half hour; the first night's light curve is attached. Still, no variation outside of statistical scatter. Weather looks like a possible revisit to the field about Christmas.
Arne
Bill, you give 10548CRC as the chartID for this field. Looking at that 30arcmin chart, I do not see any comparison stars marked. What stars are you using for your estimates? You mention stars of magnitude 9.3, 10.0, 10.5, but I cannot identify them.
Arne
Hi Arne,
There were no comparison stars on chart 10548CRC since the chart wasn't the subject of any variable. Therefore I had to appoint two. I chose GSC2410:1293 and GSC2410:316, Identified using “Megastar”. Since the given magnitudes in Megastar are unreliable, John Toone of the BAAVSS helped out here by supplying the Tycho values: 10.0 and 10.5 respectively. I also needed a brighter comparison, at the ready, too. Using chart 10766AJP, I selected GSC241084. John also gave me the Tycho magnitude of this; 9.3. I hope this identifies these three stars for you. I could supply the co-ordinates, as given in Megastar, should you require them. I was less happy employing this latter star, because it involved panning the field of view, though this could be repeated done quite quickly. The most striking features are the fades, anyway.
Bill.
Looking more critically at the two time series results; the latter appears to suggest a rising tendency? From my perspective this is “bright”; though I've sometimes observed 58521 brighter – I'm afraid to admit! When Mike Linnolt took a look at 58521 on April 6th; April 28th and May 16th, his estimates were around 9.8 (steady). John Toon's estimate was about 9.8 too. Not what I was hoping to hear, but at variance with the catalogue figure of 9.19. Leaving aside, for a moment, the whole question of variability; what are we to make of this?
The Comparison stars.
GSC 240:84 (SAO 58560); 05 54 28.08 +32 30 16.2.
GSC 2410:1293 05 52 47.82 +32 32 59.7
GSC 2410:1090* 05 52 07.77 +32 34 18.1
* Had wrongly given 2410:316
[quote=WWJ]
The Comparison stars.
GSC 240:84 (SAO 58560); 05 54 28.08 +32 30 16.2.
GSC 2410:1293 05 52 47.82 +32 32 59.7
GSC 2410:1090* 05 52 07.77 +32 34 18.1
* Had wrongly given 2410:316
[/quote]
Hi Bill,
Whenever you use stars that are NOT plotted as comparison stars using VSP, you need to add enough information in your report so that a researcher can know what stars were used for the estimate. In this case, you should use the GSC name for the "name" of the first and second comparison stars, and then include the magnitudes that you used in the comment field. Without that information, we can't tell whether the estimate matches those from anyone else, or even if the magnitudes you used for the comp stars are correct. This is a very important point for everyone.
Arne
[quote=WWJ]
Looking more critically at the two time series results; the latter appears to suggest a rising tendency? From my perspective this is “bright”; though I've sometimes observed 58521 brighter – I'm afraid to admit! When Mike Linnolt took a look at 58521 on April 6th; April 28th and May 16th, his estimates were around 9.8 (steady). John Toon's estimate was about 9.8 too. Not what I was hoping to hear, but at variance with the catalogue figure of 9.19. Leaving aside, for a moment, the whole question of variability; what are we to make of this?
[/quote]
Only the second time series results should be inspected; this should be considered as a replacement of the first. There does seem to be a small (0.02mag) trend in the time series, but remember that this dataset was taken during the testing of a new camera. Trends are common under those circumstances (no transformation, uncertain knowledge of the extinction, drifting of the field acrosss the CCD, and definitely the influence of clouds at the end of series). They might be real; they are more likely a systematic instrumental effect that would disappear in later visits with better calibration. The important point is that, even if real, they are 25x smaller in magnitude, and 100x different in timescale, than what you are reporting. The spectral type is listed as K0III; K-stars often have small fluctuations with day-to-week timescale. Such 0.02mag irregular variations are uninteresting to most astronomers.
The offset between visual observers and CCD observations (or catalog observations in Tycho and other catalogs) is pretty common. VSX reports a color of (B-V) = 1.6, which is pretty red, and there is often a systematic offset between the two magnitude systems for red objects, especially if the comp stars are much bluer (and I don't know for your choices). In addition, this is a crowded field, so estimates are influenced by nearby neighboring stars that may be blended in your telescope. So if your eyes say that the star is 9.8, and the CCD says that it is 9.2, don't worry - they really are measuring different things.
Arne
Arne,
Thank you for taking all the trouble. What ever's the outcome of this episode, I have, at least, benefited from a one to one tutorial! Namely, how to proceed when reporting stars without available comparisons. Admittedly, things don't look so good for “Wilson's Star” right now, and I'm about to be landed with having bred a turkey!
Bill.
I was able to get another night of time series data, given below. As can be seen, the mean magnitude decreased by about 0.02mag to V=9.16, but there is no evidence of any kind of rapid variability. The one change around day 3.6 was due to my recentering the field (the object was drifting a bit). The increased scatter near the beginning was because the field was slightly out of focus at the start of the night.
Arne
I estimated it again last night, using the exact same comps stars as last April and May. TYC2410-1293-1 (v=9.96) and TYC2410-84-1 (v=9.33) with the Bessell's correction to get v. After so many months away, I had "forgotten" the range of this star, so I consider this a truly unbiased estimate. I got the same magnitude as my last obs, 9.75, and all of my observations average out at 9.80 +/- 0.05 for this star.
This is the typical variation I would expect for my own observations made on a constant star, +/- 0.05 magnitudes. I took a minute or two to carefully make these estimates, and did not notice any drastic short term variations either.
I dont have a good answer as to why another visual observer is seeing it vary by several tenths, and over short time scales as well. However, I always estimated it using a large telescope 50cm aperture, and either 60x or 500x. If a binocular is being used, it might be that the low optical quality and resolution of the instrument is causing a visual "mixing" effect of this star and the close cluster companions. So you might be seeing some scintillation-like effects due to this, maybe like viewing through wavy glass? I would recommend you try estimatig it with a regular telescope, using enough magnification to clearly resolve the star by itself.
Mike LMK