Skip to main content

R Sct photometry question

10 posts / 0 new
Last post
Ed Wiley_WEY
Ed Wiley_WEY's picture
R Sct photometry question

Up until now I have been doing 2-band photometry (V, Ic), so I have not encountered the problem outlined below.

Target is R Sct, which is rather orange (nominal B-V = 1.47)

3 images each of BVRI with very short integration times. So, I stacked.

I picked 60 as the check (B-V = 1.6) as it is similar in color and SNR to R Sct.

Comparisons are 65 (B-V = 0.250) and 71 (B-V = 0.095)

These are the only comparison stars with both Rc and Ic data.

This combination works well for BV (B uncertainty = 0.01, V = 0.014) and VR (Rc = 0.009) but not for Vi or RI filter combinations where the uncertainty in Ic climbs to 0.102.

May I assume that I simply “take the hit” and report the Ic with that uncertainty? Or is it legitimate to try other check/comp combinations in spite of the fact that the two check stars (65, 71) have very different colors from R Sct?

Thanks for any help,

Ed

Eric Dose
Eric Dose's picture
Assuming you're applying

Assuming you're applying proper transforms to take some of the sting out of color-unmatched target, comp, and check stars:

For my own part, I would choose 65 as comp and 71 (or maybe 60) as check. 60 is red enough that it's too likely to be variable for me to prefer as a comp star.

And yes, comp Ic uncertainties will set a low limit on your reported target uncertainties. I'm about to submit CHET reports for some of the >200 red targets I monitor; you might want to consider a CHET report to get better comps etc for this target.

MZK
MZK's picture
Not encountered?

Hi Ed:

Confused? IF VI is what you normally ran and now VI is the pair indicating a problem, why have you not seen it before? Is this the first time you have observed R Sct? If so, it probably means the I mag of this comp is more uncertain? Did you try the others as comps to compare target mag? What were the results? As Eric stated, if you are transforming, any comp selection should work since that procedure is designed to correct for different colors. What did the check star result look like (calculated vs known)?

IMHO, yes, you could report the result and its "not so great" uncertainty if that is what the calculation indicates. You have reported what you measured and the reported error (not tried to hide it with an erroneous 1/snr error) so the user knows that it is less reliable. Of course, trying alternatives to sleuth out what is going on is usually better.

Ken

Ed Wiley_WEY
Ed Wiley_WEY's picture
R Sct Not encountered indeed :)

Hi Ken and Eric:

R Sct is one of the BSM variables that I recently adopted and I am just now obtaining data.

I hit on a good combination I think will work, 65 (check) and 60,71 (check) for Rc and Ic, 60(check), 65,71 (comp) for B and V. 

Ed

MSD1948
MSD1948's picture
R Sct observations.

Hi Ed,

 I also volunteered to for R Sct for the BSM_S Legacy program. 

Are they sending both of us the same data?

Dennis

 

Ed Wiley_WEY
Ed Wiley_WEY's picture
R Sct observations

Hi Dennis,

Probably. I note that our rersults are rather close. I think we are duplicating. We should check. Out of curiosity, what are you using for your comps? I just obtained R ad I data for mine from Tim.

Ed

Added: yes it is your target!

Ed Wiley_WEY
Ed Wiley_WEY's picture
R Sct Duplication

Dennis:

I suspect R Sct is your target. I messaged Michael to clear up the duplication.If this is true, I don't know why I was also receiving those data, hopefully Michael will clear things up. No use duplicating, glad to share my comps ensemble if this is your target.

Ed

MSD1948
MSD1948's picture
My R&I sequences.

Ed,

  For Rc I had 71 check 65 comp.  For Ic I had 65 check 60 comp.

  I noticed in the last couple days the number of stars with Ic mags increased by

a couple. Maybe this was Tim.   I would be interested in seeing your sequences

as I am very new at this.  I volunteered to get more experience.

Dennis

 

nmi
nmi's picture
Hi Ed,

Hi Ed,

I did mistakenly include you in the plan as the adoptor for R Sct. About a week ago I removed you from the plan.  Sorry for the confusion.  I did indicate correctly on the BSM section table that MSD was the adopter and he is receiving images.

Mike

Ed Wiley_WEY
Ed Wiley_WEY's picture
Hi Mike

No problem, Mike. I have worked it out with Dennis.

Ed

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