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DSLR photometry of V342 Cen do I need B-V?

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Carl Knight
Carl Knight's picture
DSLR photometry of V342 Cen do I need B-V?

I am using Iris to do DSLR photometry of V342 Cen.

I have 21 x 30s images of V342 Cen and its comparison stars. I have stacked these in lots of 7 images. I am processing the green channel from each stack. There is general agreement between the resulting green channel images for the instrumental magnitudes of the comparisons and target.

I am using the Reduction Beginners spreadsheet from the Citizen Sky project.

Do I need to provide a B-V value for V342 Cen itself? Entering a value in the spreadsheet there (i.e. I make one up just to see the results) makes a significant difference to the resulting calculated magnitude for V342 Cen itself. If a B-V value is required, where can I obtain one from? VSX does and the photometry table for V342 Cen do not provide one.

I presume as V342 Cen is a classic CV (UG according to VSX) that B-V will vary with orbital period depending upon which components spectra is dominating - Correct?

Cheers.

- Carl.

Sebastian Otero
Sebastian Otero's picture
V0342 Cen color

There are two observations in APASS:

2455611.55385 V= 15.1621 (0.081); 2455611.55436 B= 15.2313 (0.076); B-V= 0.07
2455662.60873 V= 15.8463 (0.068); 2455662.60925 B= 16.1658 (0.059); B-V= 0.32

Best wishes,
Sebastian

Sebastian Otero
Sebastian Otero's picture
Additional color photometry

And this photometry is taken from 1997A&AS..124...55C:

V= 15.47; U-B= -0.61; B-V= 0.14; V-Rc= 0.37; Rc-Ic= 0.32

Carl Knight
Carl Knight's picture
CVs and B-V for data reduction...

Hi Sebastian,

Thanks for the data.

A follow up and more general question(s) (for you or anyone who knows) is:

I expect B-V to be changing as the components orbit. Are the values you have quoted some sort of average or a snapshot? I suspect the latter.

When doing data reduction of CVs is the B-V of the variable even used in the manner intended in the CS Reduction Beginners spreadsheet?

Thanks.

- Carl.

solarbose
solarbose's picture
B-V data of V0388CMA

How do I get B-Vdata of V0388CMa

SFS
B-V: Just measure it!

As I do not use the beginner's spreadsheet, perhaps my answer will not be acceptable to you.  I use the intermediate spreadsheet, which you can download from the software section of the site.  In it, one enters both B and V measurements.  I know as a fact that the B-V catalog value for the target, as entered in the Star Calibration Data area of the spreadsheet, has no effect whatsoever on the calculations.

Furthermore, my understanding is that UGs have strong emission lines when in outubrst, rendering transformation from GB to VB problematical.  That would make the B-V variable.  Thus it is probably better to simply report the G value, using a single comp star (vice an ensemble) and a suitable check star.

The fact that a class of variable stars experiences color changes over their waxing and waning cycles does not always render them unsuitable for DSLR photometry.  Examples of classes that are very DSLR friendly include the Cephied and RR Lyrae families.

CS,

Stephen

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