Affiliation
Svensk Amator Astronomisk Forening, variabelsektionen (Sweden) (SAAF)
Wed, 09/16/2020 - 08:01
Hi!
I tried measuring V0354 Lyr today, but interestingly enough, I find no comp stars when using VPhot. Or rather, one (1) comp star that was saturated. Could this be correct, or might I do something strange? I'd be happy to share the image with anyone who want to have a look.
Magnus
Magnus:
Where do you think VPhot might find its list of comparison stars?
Is there another place on the AAVSO web site where you can independently find a list (Chart!) of comparison stars for this or any other target?
Give this hint a try. Report what you find so others will know.
Ken
PS: Magnus is taking the VPhot course right now, that's why I answered in this manner!
The VSP is the best place to determine whether or not sequence stars exist for any specific target (chart creating program):
https://www.aavso.org/apps/vsp/
Then, if no sequence (comp) stars are noted you can rquest a sequence:
https://www.aavso.org/request-comparison-stars-variable-star-charts
In this specific case I will go ahead and see if I can create a sequence today without the observer having to make a request.
Good Observing & Ad Astra,
Tim Crawford, Sequence Team
Tim:
You gave him the answer. He would have found it on his own with a hint. He just needed a few minutes.
Ken
V354 Lyr Now Has a 5 comp Sequence.
Ken,
I apologize that I failed to realize you were presenting a learning opportunity to the observer.
Ad Astra,
Tim
Hello!
Thanks! :) Well, I learned something new anyway :) And yeah, I like your way of responding, Ken!
But: I'm still not sure I fully get it. If I draw a 60 arc min chart, or choose to get it as a photometric table, there is more than 5 comp stars. If I choose 45 arc min, there are 5. If you created a sequence, Tim, of 5, where do the others come from....? I guess this is stupid question, but I don't see the process of mechanics behind this.
And: I just now realized that I actually HAVE reported 2 previous measurements of this star. Could that be because I then used a wider field of view? So the 5 you created, Tim, refers to a narrower field? Are there then any standards for this, like "a sequence is within 20 arc mins from the target"? (OK, Ken, I guess I can find those answers somewhere :))
Magnus
Magnus,
A couple of Chart Rules: 60 arc Min Scale (D) charts only show comps as faint as 14.5 V. F scale charts, 18.5 arcmin show comps as faint as 18.5... keep in mind that the observer can manually alter this parameter within the VSP chart options.
Historically, observers CCD equipment had a FOV, ~ of somewhere between 9 arcmin and 25 arcmin, from an F scale to an E scale Chart. In recent years, observers have been using digital equipment with much larger fovs.
With faint targets, which V0354 Lyr basically is, we try to keep the sequence stars as close as possible to the target.
When you increase the size of a target selection fov you have a potential to include comp stars that were created in a smaller fov for a different target(s) and that is what you are picking up with the D scale chart and larger chart sizes; which by the way may be used for any target, if appropriate.
Since you appear to be somewhat of a new observer with the AAVSO, may I suggest that you address any more questions regarding charts directly to me: tcarchcape@yahoo.com
Tim Crawford, Sequence Team
PS-no such thang as a stupid question.... except maybe what time does the 3:00 o'clock parade start ;-)