Skip to main content

Pointless "Fainter Than(s)"

19 posts / 0 new
Last post
BRJ's picture
Pointless "Fainter Than(s)"

Something I've come to notice when plotting data with the LCG is an up-turn in the number of "fainter than" observations particularly of CV stars that are in fact decidedly brighter than the particular stars ever get at maximum! Multiple such observations (i.e. night after night) by an observer are honestly of no value if there is no hope of ever catching sight of them. It is simply a waste of the observer's time and effort and it escapes me how an individual can think otherwise.

What is further disheartening is the fact that some of these folks should already appreciate and understand this. At the same time, with the ever expanding program of variables followed by AAVSO  it making it ever more difficult to cover them all in a satisfactor manner. Observers should really be trying to formulate their observing programs around the stars that, at least during a portion of their brightness cycles, come within the range of their instruments, not looking at stars that can never be seen with the equipment available to them.

J.Bortle  (BRJ)

SET's picture
Good Point



I agree with John. I stick to eclipsing binaries and LPVs. I know what the limitations are of my scope and eyeball. If I look at an LPV and it happens to be fainter than say 14.5, I'll mark it so on WebObs. However, I don't justy go out and look at very dims stars just so I can tally up observation totals by making lots of dimmer than observations.


By the way, I'm just getting back to more regular visual observing after a terrible last school year that literally made me sick, and then just having my gall bladder removed. So, if you've wondered where the Moderator of the Visual Forum has been, I getting back in the saddle again.

Chris Stephan   SET

lmk's picture
What is maximum?

Even though I generally agree with John's point here regarding making "useless" fainter-thans, something to consider is, can we be sure a variable may not have a new brighter "maximum" in the future?

Take CH Cyg for example, before it brightened to mag 5 that one time, it was considered to have a lower "maximum". Certainly, Miras are pretty much limited to their range by the physics, but many of the other more exotic types can be less predictable.

Even though a rare occurence, we cannot rule out new unexpected behavior of many variables in the future!

Mike LMK

BRJ's picture
Pointless "Fainter Than(s)"

[quote=lmk] Even though a rare occurence, we cannot rule out new unexpected behavior of many variables in the future!

Mike LMK[/quote]


This is true in a general sense and the approach is at least somewhat justified in cases where the object is a recently discovered one. It may also apply to a degree when a particular individual is following a known star with very sparse coverage by others. However, the odds of something strikingly abnormal occurring and being caught in this manner are so vanishingly small that it renders monitoring of this sort of highly questionable value.  

In instances where a star's activity is already being reasonably well monitored by others, often through positive observations, "fainter thans" of far greater brightness than a variable is known to ever attain based on the historical record are honestly pointless.

J.Bortle   (BRJ)


ThomasK's picture
Fainter than

I can only support John's statement.

I have worked a great deal with analyzing Miras, and the first I always do when I analyze a star is to remove the "fainter than"-observations. After that the real anayze begins. Knowing the small significance for fainter than-observations for LPV-stars I very seldom reports such for my own observations. That mean that I usally observe more stars on an evening than I then report.

WWJ's picture
  Re “Fainter


Re “Fainter Than's”.


I can't see that there's a problem here. “Fainter than's” don't appear in the database anyway, and if observers want to waste their time, it's up to them.


There are some significant qualifications to John's prohibition, surely. In the case of V404 Cygni; this should be monitored closely, and the result is a long list of fainter than's: perfectly reasonable! We never know the hour when the accretion disk of the black hole companion might become active, and interested observers want to be in on it!


Jonn will be particularly irritated by my coverage of S And: but this is really a de facto check for possible M31 SN's. OK John? Why shouldn't I get lucky?


Bill Wilson (WWJ)

weo's picture
Fainter-thans DO appear in the database

Bill Wilson wrote that 'Fainter than's don't appear in the database anyway...'

But they do! Fainter-than observations are included in the AAVSO International Database - every observation you submit, positive or fainter-than, is preserved in the database. (You can choose to omit fainter-thans when you are plotting data with VSP, so you may not see them.) In the database record of each observation, the absence or presence of a fainter-than is indicated by a 0 or 1, respectively, in the field before the magnitude value.  When you download a datafile, that 1 is turned into a < symbol, so any fainter-than observations are clearly marked as such.

Good observing,  Elizabeth Waagen

BRJ's picture
Pointless "Fainter Than(s)"


Jonn will be particularly irritated by my coverage of S And: but this is really a de facto check for possible M31 SN's. OK John? Why shouldn't I get lucky?

Bill Wilson (WWJ)



Actually, Bill, nova/supernova search is part and parcel of a separate observing section in the AAVSO, or at least it always was. Reports of individual search campaigns were supposed to be directed to the committee chairman of that section, not entered directly into the AAVSO general database.

J.Bortle   (BRJ)



PYG's picture
Re: Fainter than's

There are many CV's whose coverage is very limited, so the maximum magnitude once in outburst is not known with any certainty.  Even if an outburst occurs at - say - mag 14, there is every chance the next one will be at mag 12 depending on the sub type.  The SDSS and HS stars might fall into this category.  It's a horrible thing to drop a star because you never think that it will become bright enough to be seen in your scope, only for it to have an unexpected superoutburst two mags brighter shortly after you remove it from your programme. I speak from experience here.  Of course there are lots of CV's where the 'extreme' range is known fairly well, and it should be up to the observer to research his/her stars to make sure they are not wasting there own observing time.  

Mira stars are very different of course. If an observer is monitioring a Mira with a maximum of 12.0 for instance with a very small telescope or bins, then surely it's up to the AAVSO to advise that observer that they are probably monitoring the wrong star.  This is what associations do - isn't it?  Advice from HQ is critical in cases like this surely!  Is it possible for an automated process to check 'fainter than's' in the DB and to flag the data and notify the observer if a very obvious error is being made?

Bill mentions V404 Cyg, and this is an excellent example of lots of negative observations finally resulting in a positive observation.  Who would have known how bright V404 Cyg would become before it finally went into outburst in 1989?  My own pre-1989 data might have been thought of as useless until V404 Cyg did it's thing and made a few of us very excited at the time.  I'm certainly glad I persisted with it, despie recording 'fainter than's' for a long time.

Gary (PYG)

Glen chapman
Would not the value of

Would not the value of fainter than measurements be found in the type of object. If we are observing a LPV that has a light curve from say 18th mag to 14th mag with a 3 inch reflector, as someone pointed out, is this not a less than useful datapoint.


Matthew Templeton
Fainter thans can be useful

Fainter-than measures can indeed be useful, and to reiterate what Elizabeth wrote, they are indeed included in the AID and are available to researchers.  Gary Poyner highlighted a special case where a bright fainter than was later found to be useful, but there are some fainter thans that are indeed very useful.  If you're observing R CrB and tell us it's fainter than 4.0, that's not particularly useful; but if you say it's fainter than 10.0, that's very useful.  Likewise for many other classes of variable from LPVs to cataclysmics.  In fact, they've occasionally trumped other positive measures, as for example when an observer can clearly split a close pair and declares that the variable is faint where other observers might report the combined object as a positive detection.

It is not true at all that all fainter-thans are useless.  Many are useful, some are inappropriate, and I don't want to discourage people from making useful observations because a minority of the data are of little use.  If you find a large number of inappropriately bright fainter-thans in a given light curve, please point them out to the AAVSO staff via email, or flag them using Zapper and we can pursue the problem with the observer.

WWJ's picture
  Further to &ldquo;Fainter


Further to “Fainter Than's”


I stand corrected about “fainter thans” not being in the database. Now I'm seeing them everywhere! I've always blithely left that box un-ticked when using the LCG. I can understand, that there might be a congestion problem with FT's in certain places!


Regarding the rather cavalier use of S And. This “variable” is certainly in the database and might as well be put to some practical employment. So I'm using it as a peg for a covert SN check, as I don't want to deal into supernova hunting otherwise. Perhaps we can tolerate the- rather likely - “ fainter than's” turning up in this particular case?




MDAV's picture
Fainter Than's

I would make the argument  that a fainter than for faint stars in the old "Inner Sanctum" range still has some use. The scientific value may be little but useful for planning. 

Here's an example using Matthew's R CrB. During the current decline it sat for a while near 14.5 to 15.0 visually

I currently have two instruments- a 12" Orion Intelliscope and a 12" LX-200. Under routine conditions I can identify the 14.1 comp stars and a 14.6 comp star is my dimmest visual estimate to date. On that date I barely glimpsed the 14.6 comp star using averted vision but R CrB itself was no-where to be seen. I logged it and reported it as a fainter than. I consider these types of fainter thans to be useful in terms of determining whether to bother looking at all. Generally when seeing conditions allowed me to see below 14.1 and I didn't see R CrB I logged it as a fainter than. Knowing my scope performance I did not bother looking further or logging anything if I didn't see down to 14.1 

This carries on to other stars as well in planning. While I try to avoid looking at LCG too close to my observing there are some stars I follow routinely and I will look at others  on my Bulletin list to see if they are worth looking for. Knowing the performance of my instruments if I see fainter than my working limits I take the star off my observing list. Since most of my time is spent on Miras or types that don't normally show sudden rapid increases it makes some sense. 

Obviously this procedure would be pointless on U Sco or a CV that normally sits below my working limits as in John's CV example. But for stars which fade  or brighten across these working limits but do not normally sit at quiescence below them fainter thans have some use.  

BRJ's picture
Fainter Than Observations

I think that at least some of the posters here have missed the thrust of my original post. I am certainly not condemning the reporting of valid "fainter than" estimates of CVs PROVIDING THAT THEY ARE WITHIN THE ACTUAL RANGE OF THE VARIABLE. The situation that I was pointing out was that I see some observers reporting many observations that are one, two, or even more magnitudes brighter than a particular variable ever gets in its active state. A few such estimates from someone are of no importance, but when they begin to amount to a significant portion of a night's large run of estimates I can only conclude that they are being reported simply for the sake of totals. Certainly, they are not of any sort of real value to anyone.

Now I do I report numerous fainter thans of dwarf novae myself, but these are always well within the range that the particular star being reported on exhibits. These sorts of observations indeed have a value in indicating that on a particular date that star can be assumed to not have been in outburst near maximum. Someone who consistently is reporting estimates such as a fainter than 12.5 for a star known to never come above 14.0 , on the other hand, is simply generating valueless numbers with their observing program. This is especially true when the variable is already being monitored through positive observations, or much deeper fainter thans within the star's actual range, by others.

MDAV correctly points out that certain fainter thans can prove useful to other observers as a guide to what variables (particularly slowly varying, non-dwarf novae, types) are currently much too faint to be detected in one's scope and can be just as well avoided until a time when the LCG shows that they are returning to a magnitude range the observer can detect with his equipment. This is a good practice, one I'm currently following in the case of Z UMi and U Aqr, stars which are now several magnitudes beyond my largest scope, but otherwise are normally observed by me.

Proper "fainter than" observations definitely have their place in anyone's program, but reporting pointless estimates on a regular basis, essentially for the sake of generating numbers, is simply a waste of time.

J.Bortle   (BRJ)

lmk's picture
Can one be sure its "pointless" ?

While I do understand where John is coming from, I think we need to be quite careful when we start labelling observations as "pointless". Yes, I can think of some cases where it might be nearly true, such as reporting "fainter thans" several magnitudes brighter than a Mira at maximum. The physics of Miras are pretty well understood, and there is practically zero chance they would suddenly outburst above their maximum.

Yet, can one ever be absolutely sure of anything up in the sky beyond our reach? Maybe some Mira has an unknown companion which is slowly accreting and goes into outburst once? Extremely unlikely, but possible.  As Richard Feynman once said " I have approximate answers and possible beliefs and different degrees of certainty about different things, but I'm not absolutely sure of anything. " !

And, there are many classes of variables which are poorly understood. I can think of several examples of stars which had been within a confined range, then suddenly unexpectedly outburst. DW CNC is a good example. These DQ type stars can be "dangerous" to categorize within a range, and probably most any observations on them may have some value. 

Quite a few other types of unpredictable variables come to mind as well - Novalike, BLLAC, SDOR, YSO, INT, Xray, Blackhole binaries, etc. 

Lets not try to be so sure about telling what people can report. How do we really know what their motives are? Maybe they know something we don't ;)

Mike LMK

BRJ's picture
Addressing the thoughts posed

Addressing the thoughts posed by Mike, I honestly remain totally unconvinced of the value of reporting empty "fainter than" observations. Maybe if there were exceedingly few observers in the AAVSO, such that coverage of even well known and well studied variables was very sparse, one might be able to claim that "fainter than" estimates more than a magnitude, or two, brighter than the historical range of a given star shows could be of some minimal value. However, examination of the observational record proves this idea to be a fiction in nearly all cases. A majority of these empty observations concern well known stars, ones already being monitored by multiple observers on a regular basis. In these cases others are reporting either definite positive observations, if the object is in an active state, or deep negatives well within the known range of the object.

These days the chance observation of some totally unique event going completely unnoticed by any other observer, or institution, except a guy whose program generates a multitude of otherwise valueless "fainter thans" is quite honestly nil. It cannot really be said with a straight face that such an observing practice can justify the reporting of hundreds, perhaps thousands, of "pointless" estimates. 

Admittedly in years long gone by most observers worked basically blind to the latest activities of various stars, at least beyond what they saw from their own observations. In that era it was understandable how an observer could report bright negative estimates as a result of ignorance of a star's current activity. Nowadays, however, one needs only to consult the LCG to see virtually last night's status of a given object. This should be eliminating the generation of pointless observations, not increasing them.

Going out last night, tonite and tomorrow night and each time recording a fainter than 13.5 for Z UMI, which the LCG shows was reported by others to be near magnitude 18 within the last 24 hours, is just a pointless waste of the observer's time and effort. In the long run if he is truly intent on contributing sometime that is meaningful to the AAVSO program and worthy of his time he should be observing variables that are within the range of his instrumentation.

J.Bortle   (BRJ)

MDAV's picture
Pointless Fainter than(s)

LMK made an interesting point on the potential- however small- of an undected companion to a Mira going into outburst. 

Here is a "Makes me wince" example I had from last month. At the annual Calstar event I estimated RS Lyr at mag 11.0  Visually this is a sparsely observed star with only three other visual observations in the previous 200 days but plenty of V observations and a few B ones plus 2 Fainter thans. The other three visual obs are consistent with the photometric data but my obs is brighter than expected by more than a full mag. The two fainter thans are consistent with the other obs but were far enough in advance of mine that they are not definitive. Since I could not tell from my log or my charts what the error was and I could not re-observe I submitted it anyway. I'll assume LMKs example- yippee I've seen a Mira with a previously undeteced companion in outburst. Well- not really. It is not borne out by the V or B photometric data and another observer added an additional visual data point a few days after mine that is consistent with the rest of the data but not mine. Ouch.  

For our purposes here notice that this was a positive observation and not a fainter than. For the moment take out the photometric data and just take the visual. With only 5 total positive visual points and two fainter thans I'm not certain my obs could be marked as an oops-it might be the other guy who had the oops. But add the photometric and the additional visual point and it is clearly mine. Again-for our discussion purposes the Fainter thans did not tell us much but the positive obsrvations did. 




Come on guys, you are all

Come on guys, you are all arguing special cases when you know perfectly well that John is making a valid point.

I am reminded of a comedy routine I performed in front of the old Birch Street HQ about 20 years ago. It was one of those dinner at HQ evenings at an Annual Meeting, and several of us were standing out front. Gemini was rising in the east. I looked up and announced, "U Gem, fainter than 3.5."


Technically, this was a reportable observation. But in reality, it was a joke. So are the observations John is talking about.

hhu's picture
I was just plotting the

I was just plotting the lightcurve of V603 AQL, a NA star, that never gets brighter than magnitude 11. There are a lot of fainter than of magnitude 7 during the last months. Now, that's a big contribution for the variable star science ;-)


Log in to post comments
AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484