Affiliation
None
Sat, 09/27/2014 - 12:04
Whilst monitoring the maximum of XZ Cyg last night, I took time out to check V1357 - the visible component of the x ray source, Cygnus X1. It's down as being 8.72 – 8.93. but appears fainter, to me, at around 9.5. Perhaps someone, out there, interested in variable stars, might care to check it out.
When in this region; “The Cygnus Baseball Diamond”, is worth a visit, too.
Bill Wilson.
This is a bit off topic from your post, Bill, but I sent email to you via this website last week wondering if you wanted to compare any observations of SAO 58521. I wasn't sure if you got it.
Sorry, Paul.
Never received your E-mail. Please try again. I think you'll understand why I'm rather off topic, myself! There's a problem with simultaneous collaboration; namely, the five hour time window. Perhaps, come mid-winter, it'll be dark long enough to accommodate us.
Give you that address again: billwilson@bluebottle.com
I looked at it tonight and got +8.9.
Last evening 27 Sep 14, 2456928.650, it looked to be 8.9V to me. But one observation does not set a trend, so I will look again tonight if I get a chance.
I got +8.9 last night also.
Just took a look at it visually, and its at v=9.35 using the 95 and 89 AAVSO comp stars. This is definitely fainter than the "usual" range!
Mike LMK
Yes!
Several good reasons as to why V1357 Cyg's magnitude might fall outside the given range, periodically. There's the solar wind, and the fact that the orbit with the compact object is known to retrograde. Well worth adding to our visiting list.
Bill Wilson.
Well, the recent observations over the last 2 days show it varying between 9.5 and 8.9, but its only 5 visual observations by 5 different observers. So ,there is the usual suspicion of "inter-observer variation" that needs to be dealt with, to uncover if in fact there is a real variation as such.
From what I have read in the literature, this binary is not eclipsing, so that eliminates that factor as an explanation.
Mike LMK
just checked (2456930.28348 JD) average of 3x12sec exposures was V -mag 8.88.
Visually estimated it at 9.25 a short while ago. Though the number of obsrvations are relatively sparse, there is a definite bimodal split with about half averaging around 8.9 and the other half around 9.3-9.4 This is a bit troubling to see.
LMK
Now, some more recent observations, both visual and CCD have come in. I also looked at all the data on this variable using LCG (attached here). Some issues:
1. Visual data is running several tenths fainter than CCD in general, though some visual and CCD do agree. There is no CCD data prior to 2003 to compare earlier behavior, but this sort of result is not too unexpected given its recent B-V = +0.9, which is getting borderline "red", and thus will tend to pull visual estimates fainter than CCDV ones.
2. The published range of the variable is about 0.2 magnitudes, as Sebastian Otero reported to me after doing a partial literature search. The published mean is pretty much around 8.8-8.9, however, the AID observations over the past 40 years show quite a considerable variation (8.2 - 9.9) in the extremes, with a noticeable change over the long term. In the early times (1970's) the mean visual was around 9.3, this changed to a mean around 8.7 in the 1990's, and now it appears to be back around 9.3 again. One possible reason could be introduction of new sequence in the 1990's, then a correction in the sequence more recently?
3. My personal visual observations over the past week or so show a 0.3 magnitude range, while some CCD show less range. This may be due to better visual coverage over more widespread times?
In conclusion, I believe the "official" range of the variable as shown in the VSX is too narrow, and given that visual observations dominate CCD, maybe the range in VSX should be revised to the visual ones instead?
Still, much more data is needed on the behavior of this object.
Mike LMK
Why am I so interested in this variable? Mainly due to the wide spread between different visual observers and visual/CCDV. My personal visual observations show it has been in a narrow range, averaging magnitude 9.3, but the CCDV observations average around 8.9, with a few visual observations around that brighter range too.
It seems most observers are using the same sequence, the 89 and 95 comps. The comps are not red, the variable is only somewhat red, B-V = +0.90, so I am puzzled why there is a significant offset of 0.3-0.4 magnitudes between different visual observers and visual-CCDV?
Almost every time I look at it, the variables brightness is closer to the 95 comp than the 89 comp. Only one observation I noted it around a brighter 9.05, a mini-"flare-up"?
Mike LMK
What strikes me most here, is the outright lack of interest in this topic, rather than mismatches of estimates. The AAVSO boasts 929 paid up observers in the latest count - 2012-2013. Where is this workforce? You'd expect a matter relating to Cygnus X1 to capture some attention: but this, and indeed, similar items, sink promptly to the bottom of “Active Topics”; usually replaced by matters relating to recalcitrant equipment; or loss of access to specialist data. A vacuum will always be filled in the absence of interest. More visual estimates, backing this topic would certainly throw light, both on divergences of estimates, and the behaviour of the V1357 Cygni system, itself.
[quote=WWJ]
What strikes me most here, is the outright lack of interest in this topic, rather than mismatches of estimates.
[/quote]
Hi Bill, I think this is getting a fair amount of attention, looking at all the recent observaions, both visual and CCD coming in, since your initial announcement on this star. The spread in measurements, especially visual, is troubling.
All I can say is based on my own 10 visual estimates so far, using the same equipment and comp stars, this star has been pretty tightly ranged around v=9.29 (average of 8 estimates) with two noticeable brightenings to v=9.05
More observations are definitely in order here, especially to cover the span of these apparent 0.25 magnitude brightenings!
Mike LMK
Apologies, Mike.
Guess I'm getting a little impatient....The weather's closed down on us, over here, too!
Bill.
Based on the suggestions by Bill and Mike that this star was more variable than the range quoted in VSX, I went ahead and put it on the northern BSM queues starting on 2014-10-06. If you highlight observer HQA, you will see this BVRI data. Three telescopes were used: BSM_HQ, using both an ST-10 and an ST-8 camera; BSM_NM, using an ST-10 camera; and BSM_Hamren, using an ST-8 camera. A selection of comp stars was chosen from the BSM_HQ calibration.
Over the 12-day monitoring period, the star did not vary by more than 0.02mag. The BSM photometry also matches other V-band observers both prior and after the BSM monitoring period. I did leave in a poor dataset on 2014-10-19, because it was taken about the same time as Mike Linnolt was observing. Both the data from 2014-10-19 and 2014-10-20 from BSM_Hamren were compromised by clouds, and so I'd normally delete such datasets, but thought the 2014-10-19 point was useful for now to demonstrate the star was not doing anything unusual. I will remove it in a couple of weeks, when I go back and recalibrate this photometry to improve it a bit more.
I'm taking V1357 Cyg off of the BSM queues. It was fun looking at an old friend (I monitored Cyg X-1 with a near-IR camera at USNO-Flagstaff a decade ago), but I have other old friends to visit.
Arne
[quote=HQA]
I'm taking V1357 Cyg off of the BSM queues.
[/quote]
This may be a bit premature?
[quote=HQA]
Over the 12-day monitoring period, the star did not vary by more than 0.02mag. The BSM photometry also matches other V-band observers both prior and after the BSM monitoring period. I did leave in a poor dataset on 2014-10-19, because it was taken about the same time as Mike Linnolt was observing. Both the data from 2014-10-19 and 2014-10-20 from BSM_Hamren were compromised by clouds, and so I'd normally delete such datasets, but thought the 2014-10-19 point was useful for now to demonstrate the star was not doing anything unusual.
[/quote]
It looks like the range of the HQA CCDV is 0.07 magnitude, not 0.02? This seems fairly consistent with my visual range of around 0.1 magnitude, of the 3/4 of my estimates where the range was averaging around v=9.29, however there are 3 estimates so far showing it about 0.25 magnitude brighter. None of those brighter episodes are closely covered by CCD measurements (with the one exception of the "anomalous" measurement on Oct 19, which is actually 0.2 mag fainter than the rest).
So, it looks like we really need more dense coverage of this star, to see what it is doing during these periods where I have visually seen it about 0.25 mag brighter.
Mike LMK
As an attempt to resolve this question, I revisited the two Hawaii cloudy nights. Out of 12 images taken on each night, I was able to see the target and a handful of stars (so perhaps 2 or 3 magnitudes of extinction) for a single pair of B and V frames for 2014-10-19, and a single set of BVRI frames for 2014-10-20. I carefully selected only a few comparison stars as close to the variable as possible to reduce the effect of the clouds across the frame. I've replaced the 2014-10-20 measures in the AID with these corrected values, and added the BV measures from 2014-10-19. The data are still far inferior to what I normally report, but again, the purpose of this exercise is to look for large scale variability. As you can see from LCG now, no significant brightening occurred on those two nights. I will still be deleting both of these nights in the future.
If you want to look at the actual images for the two nights, they are available at the beginning of the thumbnail sets shown at:
http://images.aavso.org/bsm_hamren/bsm_hamren_141019_images/index1.html
http://images.aavso.org/bsm_hamren/bsm_hamren_141020_images/index1.html
for comparison, here is what the field looks like under clearer conditions:
http://images.aavso.org/bsm_hamren/bsm_hamren_141014_images/index1.html
The 0.02mag value I reported before is the standard deviation from the mean value of the 14 measures prior to 141019. The actual value is 8.916 +/- 0.020, with measures from 3 different sites and 4 different cameras. The extremes are 8.878 to 8.952, or about 0.07mag, but extremes are never reported. I see no evidence of large-scale variation, and have removed this field from the BSM queue.
About a decade ago, we had a really nice group of visual and CCD observers working together on eclipsing binaries. The visual observers would monitor eclipsers with unknown periods (or at least long enough since the epoch was derived that you couldn't trust eclipse timing), and find both the period/ToM and an approximate light curve depth. Then the CCD observers would observe the primary eclipse. If it was total, the rest of the light curve would get filled in so that the light curve could be modeled. The group worked really well together, and was a good example of the synergy possible between the two observational methods.
In the case of V1357 Cyg, individual observers reported large variation (this has happened on other visual stars as well), and reported this on one of the forums. This is certainly the right thing to do - you may have chanced upon a real variation that is important. The problem lies in the follow-up. In my mind, unless you can get another visual observer (or several observers) to monitor at the same time and see the same variation, it is really hard to convince researchers that something is going on (and you shouldn't get upset when they don't jump on the bandwagon). There are too many physical and psychological factors involved in an eyeball estimate. Even for CCD discoveries, most researchers want confirmation. I'm willing to retask Bright Star Monitors to look at some of these cases, since that is their duty - monitoring bright variables. However, it does take some of my personal time to process the data. So in the future, I'll be happy to set up the telescopes, but then ask the requester or a volunteer to extract the photometry and report it to WebObs.
Arne
Well, The "corrected" CCDV from HQA on Oct 19 does show it at its brightest of all the measurments ~8.86, which corresponds to one of the 3 of my bright estimates, 9.05. The Oct 20 CCDV is fainter, but it has a large error bar. My prior brighter estimate on Oct 8 has no CCD counterpart, though. Seems to me there is just too limited/poor amount of data to make any real conclusion, at this point.
I have been visual observing a long time. My typical accuracy is in the 0.05-0.10 mag range, given good sequence. The 0.25 mag brightenings which I have seen on 3 occasions are real. There is no physical or psychological effect I know that could make this star appear, on the one hand, closer to the 95 comp, and then closer to the 89 at another time, using the same equipment and comp stars.
I am not so concerned about the offset between visual and CCDV, on average. Many cases exist like this, due to the differences in response of V filter and human visual, such as color and emission lines, etc. This is a very "hot" Xray emitter!
But the relative visual brightenings of 0.25 cannot be some illusion of mine. One possibility we need to eliminate is the 95, 89 comps being variable.
Mike LMK