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

Carl Knight
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Joined: 2010-08-27

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.

V0342 Cen color
Sebastian Otero
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Joined: 2010-09-19

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

Additional color photometry
Sebastian Otero
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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

CVs and B-V for data reduction...
Carl Knight
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Joined: 2010-08-27

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.

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484